NTIA Report TR-05-420 

Measurement Procedures for the Radar 

Spectrum Engineering Criteria (RSEC) 

Frank H. Sanders 

Robert L. Hinkle 

Bradley J. Ramsey 

U.S. DEPARTMENT OF COMMERCE 

Carlos M. Gutierrez, Secretary

Michael D. Gallagher, Assistant Secretary 

for Communications and Information 

March 2005

iii

ACKNOWLEDGEMENT AND DISCLAIMER 

Current and former National Telecommunications and Information Administration, Institute for 

Telecommunication Sciences (NTIA/ITS) personnel who performed the majority of the 

measurement results and descriptions presented in this report include Frank Sanders, Bradley 

Ramsey, John Smilley, Robert Matheson, Vincent Lawrence, and John Ewan. Various personnel 

of the NTIA Office of Spectrum Management, especially Robert Hinkle, also worked extensively 

with NTIA/ITS personnel on these measurements, both with the measurement systems in the 

field and as coordinators with other agencies that controlled the measured radars. The body of 

work presented in this report would have been impossible to perform without the dedicated 

efforts of these individuals. 

Certain commercial companies, equipment, instruments, and materials are identified in this 

report to specify adequately the technical aspects of the reported results. In no case does such 

identification imply recommendation or endorsement by NTIA, nor does it imply that the 

material or equipment identified is necessarily the best available for the applications described. 

v

CONTENTS

Page 

ACKNOWLEDGEMENT AND DISCLAIMER .................................................................... i 

EXECUTIVE SUMMARY...................................................................................................... v 

ABSTRACT............................................................................................................................. 1 

1. INTRODUCTION ........................................................................................................... 1 

 1.1 Background ............................................................................................................ 2 

 1.2 Purpose and Structure of this Report ..................................................................... 3 

 1.3 RSEC Compliance and Interference Resolution Policies ...................................... 3 

 1.4 Radar Spectrum Engineering Criteria (RSEC)....................................................... 4 

2. TRANSMITTER OUTPUT POWER DETERMINATION............................................ 5 

 2.1 Introduction ............................................................................................................ 5 

 2.2 Measurements for Radars with Directional Couplers ............................................ 5 

 2.3 Measurements for Advanced Radars...................................................................... 9 

 2.3.1 Advanced radars with directional couplers .............................................. 9 

 2.3.2 Advanced radars lacking directional couplers ......................................... 9 

3. WAVEFORM PARAMETER MEASUREMENTS ....................................................... 11 

 3.1 Introduction ............................................................................................................ 11 

 3.2 Measurement of Pulse Modulation Parameters...................................................... 11 

 3.2.1 Pulse width, rise time and fall time definitions........................................ 11 

 3.2.2 Pulse modulation parameter measurement procedures ............................ 12 

 3.3 Example Measurement Data .................................................................................. 16 

4. PULSE REPETITION RATE.......................................................................................... 20 

 4.1 Introduction ............................................................................................................ 20 

 4.2 Measurements for Conventional Radars ................................................................ 20 

 4.3 Measurements for Advanced Radars...................................................................... 20 

 4.3.1 Non-uniform PRR radiated at a single radar frequency........................... 22 

 4.3.2 Uniform PRR radiated by a frequency-hopping 

 (and mechanically and/or electronically beam-steering) radar ................ 22

 4.3.3 Non-uniform PRR radiated by a frequency-hopping 

 (and mechanically and/or electronically beam-steering) radar ................ 23

 4.4 Example Measurement Data .................................................................................. 23 

5. EMISSION SPECTRA .................................................................................................... 26 

 5.1 Introduction ............................................................................................................ 26 

 5.2 Measurement Point (Hardline vs. Radiated) .......................................................... 26 

 5.3 Measurement Bandwidth for RSEC Measurements............................................... 27 

 5.4 Variation in Measured Spectra as a Function of Measurement Bandwidth........... 30 
vi

 5.5 Determination of Frequency-Stepping Time Interval (Dwell Time) ..................... 31 

 5.5.1 Conventional beam–scanning, fixed–tuned radars................................... 31 

 5.5.2 Complex beam–scanning and frequency–hopping radars........................ 32 

 5.6 Emission Spectrum Measurements and Data Recording ....................................... 33 

 5.6.1 Overview of spectrum measurement procedure....................................... 33 

 5.7 Potential Measurement Problems and Solutions.................................................... 34 

 5.7.1 Possible attenuation mistakes during measurement................................. 34 

 5.7.2 Changes in radar operating mode during a measurement ........................ 35 

 5.7.3 Feed-through and RF front-end overload................................................. 35 

 5.8 Example Emission Spectrum Data......................................................................... 37 

6. ANTENNA PATTERNS................................................................................................. 39 

 6.1 Introduction ............................................................................................................ 39 

 6.2 Measurements of Conventional Antenna Patterns ................................................. 39 

 6.3 Antenna Pattern Measurements for Advanced Radars........................................... 40 

6.4 An Advanced Antenna Pattern Measurement for All Radars ................................ 40 

 6.5 Antenna Pattern Statistics....................................................................................... 40 

7. FREQUENCY TOLERANCE AND TUNABILITY...................................................... 42 

 7.1 Introduction ............................................................................................................ 42 

 7.2 Setup for Measurement of Drift in Operating Frequency ...................................... 42 

 7.3 Measurement of Frequency Drift ........................................................................... 43 

 7.4 Radar Tunability..................................................................................................... 43 

 7.5 Sample Data and Calculations................................................................................ 43 

8. RSEC RADAR RECEIVER PARAMETERS................................................................. 44 

 8.1 Introduction ............................................................................................................ 44 

 8.2 Selectivity............................................................................................................... 44 

 8.2.1 Receiver IF selectivity measurement overview ....................................... 45 

 8.2.2 Swept CW IF selectivity measurement .................................................... 45 

 8.2.3 Receiver selectivity measurement methods for advanced radars............. 48 

 8.3 Receiver Image and Spurious Response ................................................................ 49 

 8.4 Receiver Local Oscillator (LO) Radiation Measurement ...................................... 53 

 8.4.1 LO radiation considerations for advanced radars..................................... 54 

9. REFERENCES ................................................................................................................ 55 

APPENDIX A: DEFINITIONS ............................................................................................. 57 

APPENDIX B: ENSURING ADEQUATE MEASUREMENT SYSTEM INPUT 

ATTENUATION FOR RSEC MEASUREMENTS................................................................ 58 

APPENDIX C: RSEC MEASUREMENT SYSTEM ARCHITECTURE 

AND ALGORITHMS.............................................................................................................. 61 

 
vii

APPENDIX D: RSEC MEASUREMENT SYSTEM CALIBRATION ................................ 80 

APPENDIX E: POSITIONING OF MEASUREMENT SYSTEM FOR RADIATED

MEASUREMENTS ............................................................................................................... 83 

APPENDIX F: VARIATION IN MEASURED PULSE SHAPES ACROSS EXTENDED 

EMISSION SPECTRA .......................................................................................................... 86 

APPENDIX G: VARIATION IN MEASURED SPURIOUS AMPLITUDES AS A FUNCTION 

OF MEASUREMENT BANDWIDTH .................................................................................. 88 

APPENDIX H: RSEC SOFTWARE MODEL ...................................................................... 96 

ix

EXECUTIVE SUMMARY

The National Telecommunications and Information Administration (NTIA) within the 

Department of Commerce serves as the President’s principal advisor on telecommunication 

policy and is responsible for management of the Federal Government’s use of the radio 

frequency spectrum. Through the Technical Subcommittee (TSC) of the Interdepartment Radio 

Advisory Committee (IRAC), Federal agencies develop spectrum standards to ensure effective 

and efficient use of the spectrum. 

Federal radio stations and systems must comply with spectrum standards contained in the NTIA 

Manual of Federal Regulations and Procedures for Federal Radio Frequency Management 

(referred to herein as the NTIA Manual). A radio frequency spectrum standard is a principle, 

rule, or criterion that bounds the spectrum-related parameters and characteristics of a radio 

station or system for the purpose of managing the radio frequency spectrum. Primary radar 

systems operating as radiodetermination stations, radiodetermination-satellite stations, and 

space-based radar systems are subject to compliance with the Radar Spectrum Engineering 

Criteria (RSEC) contained in Chapter 5, Spectrum Standards, of the NTIA Manual. 

The RSEC is intended to ensure an acceptable degree of electromagnetic compatibility among 

radar systems, and between such systems and those of other radio services sharing the frequency 

spectrum. To promote effective and efficient use of the spectrum, the RSEC includes limits on 

transmitter spurious and out-of-band emissions, antenna patterns, receiver selectivity 

characteristics, and radar tunability. 

This report describes suggested methods for measuring characteristics of primary radar systems 

operating in the radiodetermination service for determining compliance with the standards 

contained in the RSEC. Other methods of measuring primary radar characteristics may be used 

if they give technically correct results. This report addresses measurement methods for 

measuring new and advanced radar systems using frequency-modulated and phase-modulated 

pulses; multi-mode radar systems with interleaving pulse modulations and variable pulse 

repetition frequencies; and distributed phased-array antennas with complex beam scanning 

techniques. Examples of RSEC measurements for such radars are presented. 

 

 

MEASUREMENT PROCEDURES FOR THE 

RADAR SPECTRUM ENGINEERING CRITERIA (RSEC) 

Frank H. Sanders1, Robert L. Hinkle2, and Bradley J. Ramsey3

The wide application of radar for various functions makes large demands on the 

electromagnetic spectrum, and requires the application of effective frequency management 

for the equipment and systems involved. Requirements for certain equipment 

characteristics are specified in the NTIA Manual of Regulations and Procedures for Federal 

Radio Frequency Management to ensure an acceptable degree of electromagnetic 

compatibility among radar systems, and between such systems and those of other radio 

services in the frequency spectrum. These standards are called the Radar Spectrum 

Engineering Criteria (RSEC). This report describes techniques for measuring radar 

spectrum-related parameters and characteristics for compliance with the RSEC. 

Measurements for both conventional and advanced radar types are addressed. This report

supersedes NTIA Report 84-157 of August 1984. 

Key words: electromagnetic compatibility; high-power radar; magnetron; radar emission 

mask; radar emission measurements; radar interference; radar spurious

emissions; radar out-of-band emissions; radar unwanted emissions; Radar 

Spectrum Engineering Criteria (RSEC); Radio Spectrum Measurement System 

(RSMS); solid-state transmitter; spectrum occupancy. 

1. INTRODUCTION

This report is intended to assist spectrum managers and engineers in measuring radar emissions 

and using those measurements to verify compliance with the National Telecommunications and 

Information Administration Radar Spectrum Engineering Criteria (RSEC) [1, primarily Chapter 

5]. The RSEC contains spectrum engineering standards applicable to primary radar systems. The 

application of the NTIA RSEC emission mask to emissions of both simple and 

advanced-technology (multi-mode, multiple waveforms, frequency hopping and phased-array) 

radars is described. 

This report updates and expands upon material presented in an earlier NTIA Report [2]. It is 

concerned with measurement techniques for verification of compliance with the RSEC. In 

particular, new measurement techniques are described that are tailored for emissions from 

recently designed types of radar transmitters. Newer types and models of measurement hardware 

are accounted for in this report. 

 

1 The author is with the Institute for Telecommunication Sciences, National Telecommunications 

and Information Administration, U.S. Department of Commerce, 325 Broadway, Boulder, CO 

80305-3328. 

2

 The author is with Alion Science, Annapolis, MD. 

3

 The author is with the RF Metrics Corporation, Westminster, CO. 
2

The measurement procedures described in this report are recommendations; alternative 

measurement procedures that can be documented by measurement personnel to adequately 

quantify the radar characteristics contained in the RSEC are also acceptable. 

In addition, the measurement procedures contained in this report can be used to quantify radar 

characteristics that are required for NTIA certification of spectrum support [1, Chapter 10]. 

These include parameters required for submission in NTIA Forms 33–35 and the similar 

Department of Defense Form 1494. 

1.1 Background

NTIA is responsible for managing the Federal Government's use of the radio spectrum. Part of 

this responsibility is to establish policies concerning spectrum assignment, allocation, and use; 

and to provide the various departments and agencies with guidance to ensure that their conduct 

of telecommunications activities is consistent with these policies [1, Section 8.3]. In discharging 

this responsibility, NTIA: 1) assesses spectrum utilization; 2) identifies existing and/or potential 

compatibility problems among the telecommunication systems that belong to various

departments and agencies; 3) provides recommendations for resolving any compatibility 

conflicts that may exist in the use of the frequency spectrum; and 4) recommends policy and 

engineering changes to promote spectrum efficiency and improve spectrum management 

procedures. 

The Federal Government operates a large number of radar stations. Many of these stations 

produce peak effective isotropic radiated power (EIRP) levels that are among the highest of all 

radio transmitter systems. (Average radar EIRP levels are typically 30 dB less than the peak 

levels.) Even theoretically perfect radar transmitters cannot confine their electromagnetic 

emissions entirely to their assigned operating frequencies, or for that matter even to allocated 

radar spectrum bands, due to the inherent pulse modulation characteristics of these systems. 

Furthermore, practical limitations in radar technology and necessary technical compromises in 

the design of operational radar systems result in higher spurious emission levels than would be 

theoretically predicted for various pulsed waveforms. Even if spurious emissions are suppressed 

by 60 dB or more relative to the peak power at the radar fundamental frequencies, the high peak 

EIRP levels of radar transmitters can cause the out-of-band and spurious emissions of these 

systems to have a significant impact on other spectrum uses. 
3

1.2 Purpose and Structure of this Report 

This report is intended for use by spectrum engineers and managers who must assess the 

emission characteristics of primary radar4 systems. The most practical, efficient, and up-to-date 

techniques for measurement of radar emissions are presented, as developed by NTIA engineers. 

Application of these measurement techniques is described for advanced radars employing 

sophisticated pulse modulation and beam-scanning techniques. Measurement approaches are 

described in the main body of the report. Important definitions are provided in Appendix A. 

Assessment of required amounts of attenuation in measurement system front ends is described in 

Appendix B. Measurement system architecture and algorithms are described in detail in 

Appendix C. Measurement system calibration techniques are described in Appendix D. Methods 

for positioning measurement systems for radiated measurements are presented in Appendix E. A 

limited description of radar spurious emissions and their variation with measurement bandwidth 

are provided in Appendices F and G for the purpose of better understanding the measurement 

procedures. Appendix H is a description and user’s guide for an automated software tool for 

determining the RSEC emission limit mask, including the capability to import measured 

emission characteristic data for comparison with the RSEC emission limit mask. 

1.3 RSEC Compliance and Interference Resolution Policies 

The NTIA manual [1] contains NTIA policies and regulations regarding compliance with 

spectrum standards and interference resolution. The RSEC is intended to ensure an acceptable 

degree of electromagnetic compatibility among primary radar systems, and between such 

systems and those of other radio services sharing the frequency spectrum. RSEC standards are 

concerned with promoting efficient use of the spectrum. However, compliance with these 

standards may not preclude the occurrence of interference. Therefore, compliance with the 

standards does not obviate the need for cooperation in resolving harmful interference problems 

[1, Chapter 5]. 

Taken together, out-of-band emissions and spurious emissions [1, Chapter 5] are called 

unwanted emissions. In principle, unwanted emissions from stations of one radio service shall 

not cause harmful interference to stations of the same or another radio service within the 

recognized service areas of the latter stations whether operated in the same or different frequency 

bands. Providing that appropriate spectrum standards [1, Chapter 5] are met, an existing station 

is recognized as having priority over a new or modified station. Nevertheless, engineering 

solutions to mitigate interference may require the cooperation of all parties involved in the 

application of reasonable and practicable measures to avoid causing or being susceptible to 

harmful interference [1, § 2.3.7]. 

The United States allocates many radio bands to radar services (radiolocation, radionavigation, 

meteorological aids, and other radiodetermination services) on both primary and secondary 

bases. Radar services can have impacts on spectrum engineering outside the allocated radar 

 

4

 “A radiodetermination system based on the comparison of reference signals with radio signals 

reflected from the position to be determined,” [1, Chapter 6] and ITU Radio Regulations. 
4

bands. Some adjacent-band impacts (e.g., RF front end overload) are due to inadequate design of 

receivers in adjacent bands; such impacts cannot be mitigated by improving radar transmitters. 

Other adjacent-band impacts can be due to radar unwanted emission levels, and these can be 

somewhat mitigated by controlling the levels of radar unwanted emissions. 

1.4 Radar Spectrum Engineering Criteria (RSEC) 

This section describes the limits that are placed on U.S. radar unwanted emission levels by the 

NTIA radar spectrum engineering criteria (RSEC) [1]. 

The RSEC applies to all Federal Government primary radar systems. RSEC specifications are 

provided in existing NTIA documentation [1, Section 5.5]. The following list identifies the

technical radar characteristics for which the RSEC specifies limits: 

1) unwanted emission levels relative to the level of the radar fundamental; 

2) emission bandwidth; 

3) antenna pattern characteristics; 

4) frequency tolerance; 

5) frequency tenability; 

6) receiver IF selectivity; 

7) image and spurious rejection. 

Since the initial adoption of the RSEC emission level specification (including spurious emission 

limits) by NTIA in 1973, the RSEC limits have been revised on an ongoing basis. The RSEC is 

updated periodically [1, Chapter 5]. 
5

2. TRANSMITTER OUTPUT POWER DETERMINATION 

The RSEC categorizes radars on the basis of groups (A, B, C, D, and E). Membership in a group 

is determined primarily by radar transmitter peak power, Pp, which is used in RSEC mask 

computations for some radars to determine the ultimate spurious suppression level (X in dB) that 

must be achieved. The radar transmitter peak power (Pp) is defined as the peak power at the radar 

antenna input. In some cases, direct measurement of the radar’s power output may be impossible 

and the specified radar peak transmitter power may have to be taken from radar documentation. 

Direct measurements are desirable whenever possible. The material in this section describes 

methodology for this measurement.

2.1 Introduction 

For purposes of RSEC mask computations, peak power is measured at the nominal maximum

steady-state amplitude of a radar pulse; short-duration peaks within pulses, as may possibly 

occur at some pulse leading edges, should not be used. Because the goal is to measure all 

available transmitter power, it is important to measure the pulse peak power in bandwidths that 

equal or exceed the nominal values presented in Table 1; for multimode radars, using a

combination of modulation types, the measurement bandwidth should be determined by selecting

the radar mode with the widest bandwidth. 

Radiated peak power may be measured directly for radars that can direct their antenna main lobe 

energy directly into a measurement system antenna, such as might be possible on some test 

ranges and for some surface-search radars. A procedure for this approach is given in Section 

2.3.2, below. 

For many operationally deployed radars it may be difficult or impossible to achieve direct 

coupling between a radar antenna main beam and a measurement antenna main beam.5 For those 

systems, peak power should be measured via a hardline connection from within the radar 

transmitter, if possible. If such a connection is unavailable, then transmitter power must be 

assessed via radiated measurements in accordance with Section 2.3.2, below.

2.2 Measurements for Radars with Directional Couplers 

In this context, a conventional radar transmitter is defined as one that sends all of its transmitter 

energy through a directional coupler (accessible to measurement personnel) between the 

transmitter and the antenna, and that does not modulate the pulse frequency during transmission 

 

5 The lower edge of the main beam of an air search radar, for example, is often directed 

more than 1 degree above the horizon. This puts the lower edge of the main beam at a height of

17 m (plus the radar tower height) above the ground at a typical measurement system distance of 

1 km. This height considerably exceeds the likely maximum height of a measurement antenna. 

Furthermore, while main beam gain may be specified in radar documentation, radar antenna 

sidelobe gain levels illuminating the measurement system will not generally be known with 

much accuracy. 
6

(ie., that does not chirp). In this case, all the radar transmitted energy is available at that single 

point and the peak power may be measured at that point. 

The key component for this measurement is a wideband detector. The detector needs to be

wideband, with a fast-response time. It should be operated at a power input level within its 

linear-response region. (For typical detectors, this level will often be between +10 dBm to 

+20 dBm. The maximum permissible detector input level is often about +20 dBm. Detector

manufacturers’ data sheets should be consulted for guidance regarding this parameter.) 

Table 1. Determination of RSEC Measurement Bandwidth (Bm) for Peak Power Measurements. 

Radar Modulation Type RSEC Measurement Bandwidth (Bm): 

Non-FM pulsed and 

phase-coded pulsed 

Bm  (1/t), where t = emitted pulse duration (50% voltage) or 

phase-chip (sub-pulse) duration (50% voltage). 

Example for non-FM pulsed: If emitted pulse duration is 1 μs, 

then Bm  1 MHz. 

Example for phase-coded pulsed: If radar transmits 26-μs 

duration pulses, each pulse consisting of 13 phase-coded chips 

that are each 2-μs in duration, then Bm  500 kHz. 

FM-pulsed (chirped) Bm  (Bc/t)1/2, where Bc = frequency sweep range during each 

pulse and t = emitted pulse duration (50% voltage). 

Example: If radar sweeps (chirps) across frequency range of 

1.3 MHz during each pulse, and if the pulse duration is 55 μs, 

then Bm  154 kHz. 

CW Bm = 1 kHz; See sub-paragraph 4.2 of [1, Chapter 5] for RSEC 

Criteria B, C, and D. 

Example: Bm = 1 kHz. 

FM/CW Bm = 1 kHz; see sub–paragraph 4.2 of [1, Chapter 5] for RSEC 

Criteria B, C, and D. 

Example: Bm = 1 kHz 

Phase-coded CW Bm  (1/t), where t = emitted phase-chip duration (50% voltage). 

Example for phase-coded pulsed: If chip duration is 2μs, then 

Bm  500 kHz. 

Multi-mode radars Calculations should be made for each waveform type as 

described above, and the maximum resulting value of Bm should 

be used. 

Example: A multi-mode radar produces a mixture of pulse 

modulations as used in the above examples for non-FM pulsed 

and FM-pulsed. These values are 1 MHz and 154 kHz, 

respectively. Then Bm  1 MHz 
7

The measurement setup is shown in Figure 1. Although NTIA RSEC documentation [1, Section 

5.5] specifies that power should be measured “at the input to the radar antenna,” the reality is 

that peak power must be measured at a directional coupler in any hardline-coupled scenario. 

Therefore corrections should be applied to the measured parameters to account for the

transmission losses between the measurement point and the antenna input reference point. A 

coaxial cable of appropriate impedance is connected to the input of a wideband detector. 

Figure 1. Radar power measurement configuration for a hardline coupled measurement. 

A variable attenuator (0–70 dB, for example) is inserted at the detector input and is adjusted to 

ensure a linear-response input level to the detector.

6

 Prior to connecting the detector to the radar, 

the attenuator is initially set to a sufficiently high level to protect the wideband detector from 

possible damage. 

Referring to Figure 1, the oscilloscope input impedance needs to be matched to the detector 

output impedance; older detectors often have high-impedance outputs but some newer-model

detectors have relatively low (50 ohm) output impedance. Coupling on the oscilloscope input 

should be set to ‘DC’. The oscilloscope is adjusted to display radar pulse envelopes. The flat-top 

pulse amplitudes (see definition in Appendix A) are recorded.7 The setting of the variable 

attenuator is likewise noted by measurement personnel and is used to correct the amplitude 

displayed on the oscilloscope. 

 

6 For hardline connections to directional couplers, the initial attenuator setting may be derived 

from the radar’s nominal peak power level and the specified insertion loss of the directional 

coupler. 

7 Most oscilloscopes can record data to either an internal disk, an external computer via an IEEE488 (GPIB) bus, or a universal serial bus (USB) external memory unit. Useful results may also 

be achieved by photographing the oscilloscope screen with a film or digital still-frame camera. 
8

This measurement only determines the peak pulse power at the directional coupler. Coupler loss, 

external attenuation values, and losses between the coupler and the antenna input must be taken 

into account to determine the radiated value of Pp. The radar system losses between the 

directional coupler and the antenna usually must be taken from values noted on radar microwave 

components (such as waveguide couplers, filters, etc.). 

The peak power is calculated from a correction for: 1) the attenuation of the directional coupler; 

2) the value of the attenuation between the coupler output and the detector input; 3) the 

conversion of displayed voltage on the oscilloscope display to the power that would have been 

present at the detector input to generate that voltage; and 4) the attenuation of the waveguide 

between the directional coupler and the transmit antenna. The first two factors may be taken 

directly from the attenuator settings, assuming that the attenuation values were previously 

calibrated accurately. 

PP = PPC + LDC + LML − LL + BCF (1) 

where: 

PP = transmitted peak power at antenna input, dBm; 

PPC = measured power at the output of the directional coupler, dBm; 

LDC = loss of the directional coupler, dB; 

LML = loss of the measurement line, dB; 

LL = loss between radar antenna and directional coupler, dB; 

BCF = bandwidth correction factor, dB (if Bdet < Bm; see below). 

The limiting measurement system bandwidth, Bm, should be chosen to exceed the value specified 

in Table 1 for the radar being measured. Many detectors and oscilloscopes may have detector 

bandwidth values, Bdet, that exceed the Bm values of Table 1. But in the event that Bdet is less 

than Bm, it is still possible to estimate the total peak power through a directional coupler

measurement. To do so, the power is measured in the bandwidth Bdet. Then it is corrected by a 

decibel factor of 20 log(Bm/Bdet): 

The conditions for measurement bandwidth correction factor (BCF) for non-FM and phasecoded pulses are: 

t

B

B t

BCF m

m

1

for 120log < 















= (2) 

where: 

Bm = limiting bandwidth of measurement system, MHz; 

t = emitted pulse duration (50% voltage), or phase-chip width for (sub pulse duration 

(50% voltage), microseconds. 
9

The conditions for measurement bandwidth correction factor (BCF) for FM-pulsed (chirped) 

pulses are: 

t

B

B

B t

B

BCF c

m

m

c

<

















= 10log for 2

 (3) 

where: 

Bc = frequency sweep range during each pulse of sub-pulse, MHz; 

Bm = limiting bandwidth of measurement system, MHz; 

t = pulse duration during each pulse of sub-pulse, microseconds. 

For improved accuracy and confidence, this conversion may be checked as follows. Once the 

pulse amplitude has been measured, the detector input is disconnected from the directional 

coupler and is connected to the output of a signal generator (Figure 1). The signal generator 

output is adjusted to the same frequency as the radar and a continuous wave (CW) signal is 

injected into the detector. The level of the input signal is adjusted with signal generator controls 

and/or an external variable attenuator until the detector produces the same detector output level 

as was observed for the pulses. This value may be compared to the value that was inferred from 

the detector manufacturer’s data sheets. They should be close to one another (that is, within 

about a decibel). 

2.3 Measurements for Advanced Radars 

2.3.1 Advanced Radars with Directional Couplers 

In this context, it is assumed that an advanced radar is one that intentionally modulates the 

frequency or the phase of transmitted pulses, but that the radar transmitter still utilizes a 

directional coupler through which all of the transmitted energy passes. In this case, the same 

measurement procedure may be used as described in Section 2.2. As before the limiting detector 

and oscilloscope bandwidth, Bdet, must be verified to meet or exceed the value of Bm in Table 1 

for the radar being measured. 

2.3.2 Advanced Radars Lacking Directional Couplers 

Many advanced radars do not have directional couplers. These include radars with distributed 

arrays of solid state transmitter modules. For these radars, hardline-coupled measurements are 

impossible, and transmitter peak power must be determined either from radar data sheets or from 

radiated measurements. 

As noted in the introduction to this section, radiated measurements are often complicated by lack 

of definitive data on radar antenna gain directed at the location of the measurement system, 

unless the measurement system can be positioned in the main beam of the radar. 
10

The best option in this case is to position the measurement system so that it is directly scanned 

by the radar’s main beam. To ensure that the beams of the radar transmitter and measurement 

system receiver antennas are aligned, the following procedure is used. First, visually align the 

receive antenna approximately with the radar transmitter antenna. Then, if the radar transmitter 

antenna can be manually directed, it should be moved in all its degrees of freedom until a 

maximum response occurs in the measurement system. Alternatively, if the transmitter antenna is 

continuously scanned through space (as is commonly the case), then this initial step is omitted. A 

more detailed description of procedures for positioning measurement systems and aligning 

antenna beams is provided in Appendices C and E. 

The next step is to slowly move the measurement antenna in azimuth and elevation angle until a 

maximized response is achieved. At this point, the beams are aligned. If the polarization of both 

antennas is linear, then the polarization needs to be matched between the two antennas, typically 

by rotating the measurement antenna about its central axis until a maximal response in the 

measurement system is achieved. If the radar emission is circularly polarized, then a circularly 

polarized measurement antenna (with the same polarization sense) should be used. Power is 

measured via a spectrum analyzer (or a detector-oscilloscope combination as shown in Figure 1). 

The bandwidth conditions for the measurement system apply as described above. The measured 

power is corrected to transmitted peak power at the antenna input using the equation: 

Pp = Pr − Gt − Gr + Lp (4) 

where 

Pp = transmitted peak power at the antenna input, dBm; 

Pr = measured power level (corrected for any internal gains and losses), dBm; 

Gt = radar transmitter antenna gain, dBi; 

Gr = measurement system (receiver) antenna gain, dBi; 

LP = propagation loss (free space) between the radar measurement system antennas, dB. 

Note that the rated main beam gain of the transmitter antenna is subtracted from the peak 

effective isotropic radiated power (EIRP) to arrive at the transmitter peak output power. 

For radar transmitters with main beams that cannot be intercepted by the measurement system, 

and which also lack directional couplers, no direct measurement solution exists. In these cases, 

the radar’s specified transmitter peak power must be used, as extracted from radar 

documentation.8

 

8 A radiated measurement of such a radar’s emission will at least provide a lower bound on 

its transmitter peak power. 
11

3. WAVEFORM PARAMETER MEASUREMENTS 

3.1 Introduction 

This section provides guidance for determination of radar waveform parameters used in 

computation of the RSEC emission masks. These include: 

1) pulse and sub-pulse duration (t); 

2) pulse rise and fall times (tr and tf) (referred to subsequently in this document as pulse rise/fall 

time) 9;

3) number of sub-pulses in coded pulses (N); 

4) bandwidth of frequency deviation, (Bc) for FM-pulses (chirped), and (Bd) for FM-CW radars; 

5) compression ratio of FM-pulses (d). 

The pulse parameters need to be measured on only one frequency channel of the radar for each 

type of waveform. For radars utilizing multiple waveforms (e.g., multiple pulse widths or 

chirps), the relevant parameters listed above should be measured for each waveform, but still 

only need to be measured on a single frequency channel for each. 

For some radar designs, the pulse parameters (pulse width (t), pulse rise time (tr), pulse fall time 

(tf) and frequency deviation bandwidth (Bc or Bd), if appropriate) may be measured via a hardline 

connection to a directional coupler. Other radar designs, such as distributed phased array radars, 

do not provide a directional coupler; for these radars, the pulse parameters listed above must be 

measured via radiated energy. 

3.2 Measurement of Pulse Modulation Parameters 

3.2.1 Pulse Width, Rise Time, and Fall Time Definitions 

For the RSEC, pulse width, t, is defined at the 6-dB points (50% voltage points) of radar pulses. 

The rise time, tr, or fall time, tf, is measured between the 10%–90% voltage (-20 to -0.9 dB) 

points on a pulse’s leading or trailing edge, respectively, as shown in Figure 2. For coded pulses, 

tr and tf are the rise and fall times of the sub-pulses. If sub-pulses are not discernable, then tr is 

defined to be 40% of the time required to switch from one phase or chip to the next. 

 

9

 When the fall time, tf, of the radar pulse is less than the rise time, tr, it should be used in place 

of the rise time in applying the RSEC emission mask. 
12

Figure 2. Schematic diagram of RSEC pulse shape parameters. Note that the nominal flat top 

level may have to be estimated as a best-fit on the detected envelope. 

3.2.2 Pulse Modulation Parameter Measurement Procedures 

3.2.2.1 Non-FM (CW) Pulses 

The key component in this measurement is a wideband detector. The detector needs to be 

wideband, with a fast response time characteristic. It should be operated at a power input level 

within its linear-response region. The detector manufacturer’s data sheets should be consulted for 

guidance regarding this parameter. 

Figure 3. Block diagram schematic for measuring waveform parameters using a directional 

coupler. 
13

The setup to measure radar pulse width, rise time and fall time parameters is shown in Figure 3. 

A vector signal analyzer can be substituted in place of the discrete detector and oscilloscope for 

measurements of pulse phase coding and frequency modulation (chirp) characteristics. A coaxial 

cable of appropriate impedance is connected to the input of a wideband (bandwidth exceeding 

(1/tr)) detector. (In the following discussion, tr is used with the assumption that it is smaller than 

tf. But if tf is the smaller of the two quantities, then it should be used in place of tr in the RSEC 

emission mask computations.) A variable attenuator (0–70 dB, for example) is inserted at the 

detector input and is adjusted to ensure a linear-response input level to the detector.

 10

 

Figure 4. Block diagram schematic for measuring radiated waveform. 

Figure 4 shows the setup for making measurements of the radar parameters in the radiated 

waveform. The discrete detector and oscilloscope are used to measure radar pulse envelope 

characteristics. A vector signal analyzer can be substituted in place of the discrete detector and 

oscilloscope for measurements of pulse phase coding and frequency modulation (chirp) 

characteristics. 

The detector output is connected to an oscilloscope. The oscilloscope’s bandwidth should be 

wide enough to ensure that pulse rise/fall time can be measured accurately. Measurement 

personnel should be aware that some oscilloscopes achieve their widest bandwidth performance 

in repetitive sampling modes, but that radar pulses need to be measured in single-shot modes. 

Therefore the oscilloscope bandwidth needs to be known in single-shot mode. For many radar 

pulses, it is desirable that the single-shot bandwidth be at least a few hundred megahertz. 

Impedances should be matched appropriately; most modern oscilloscopes have selectable input 

impedance values. 50 ohms is typically correct. DC coupling should be used on the oscilloscope 

input. The oscilloscope is adjusted to display and record

11

 radar pulse envelopes. 

 

10 For hardline connections to directional couplers, the initial attenuator setting may be derived 

from the radar’s peak power level and the specified insertion loss of the directional coupler. 

11 Most modern oscilloscopes can record data to either an internal disk, an external computer via 

a data link, or a universal serial bus (USB) port connected to an external memory unit. 
14

For the RSEC, radar pulses need to be measured at the 10%, 50%, and 90% voltage points 

(Figure 2). 

A potential impediment to measuring pulse width via radiation is the effect of multipath energy, 

which typically causes distorted pulse envelope shapes. This effect can be minimized by the use 

of a narrow-beam receive parabolic reflector antenna on the measurement system. If multipath 

features (such as a stair-step appearance on the the trailing edge of the pulse) are noted in the 

pulse envelope even when a parabolic antenna is being used, then slight adjustments in the

vertical tilt angle of the antenna should be made, until the multipath features are minimized or 

eliminated. 

Most modern oscilloscopes provide for this type of measurement automatically. For

oscilloscopes that do not have this functionality built in, these points may be determined either 

with manual marker functions; or by performing computations on recorded pulse waveform 

envelopes; or by inserting attenuation (either with combinations of discrete attenuators or 

variable attenuator units) ahead of the detector to adjust the output to the specified levels 

(-0.9 dB, -6 dB, and -20 dB). For the attenuator method, at each of these levels, time markers are 

placed on the measured pulse envelope at a fixed amplitude level. The resulting time intervals 

between the markers at these levels provide the pulse width (delta between the 6-dB points), the 

rise time (delta between the -0.9 dB and -20 dB points on the leading edge), and the fall time 

(delta between the -0.9 dB and -20 dB points on the trailing edge).12 In Section 3.3, Figure 5 

shows such a pulse envelope measurement for a single-frequency weather radar. Figure 6 shows 

a similar measurement for a frequency-hopped radar. 

3.2.2.2 Coded Pulses 

For phase-coded radar pulses (referred to in the RSEC simply as ‘coded’), three pulse parameters 

are required to compute the RSEC emission mask. These are: 

1) ‘chip duration,’ defined as the interval between the 50% voltage points of one chip (intrapulse single phase sub-pulse). This value is used for the variable (t) in the RSEC equations; 

2) chip rise/fall time (tr),13 measured between the 10%–90% points on the rising/falling edges of 

the chips; 

3) total number of chips (N) contained within each phase-coded pulse. 

There are two fundamentally different approaches to these measurements: envelope-detected and 

phase-response. 

 

12 To the extent that detector output is linear, variable attenuation levels might be obviated. Three 

marker functions at appropriate levels could be used to directly read the 10%, 50% and 90% 

voltage points. 

13 When the fall time, tf

, of the radar pulse is less than the rise time, tr, it should be used in place 

of the rise time in applying the RSEC emission mask. 
15

3.2.2.2.1 Envelope-detected Measurement of Coded Pulses 

Measurements of chip duration and rise time/fall time may be performed somewhat similarly to 

the procedures in Section 3.2.2.1. However, measurement of these parameters is complicated 

with a wideband detector because although phase is shifted during each pulse (as a series of 

chips), only the power is observed at the output of a detector. This makes the edges of the chips 

unobservable, in principle. In application envelope artifacts may occur at the phase transitions 

between the chips due to the band limitations of the measurement system, and these artifacts may 

be visible for some types of phase coding. When the transitions are observable, the chip width 

may be measured as the period between amplitude nulls in the transients. Chip rise/fall time may 

be taken to be the same as pulse rise/fall time, or else may be taken to be 40% of the time 

required to switch from one phase or sub-phase to the next. Also, the number of chips may be 

estimated by counting the artifacts within the envelope (e.g., if 12 artifacts occur, then there are 

13 chips in the pulse). Figure 7 shows a wideband detector measurement of a phase coded radar 

pulse.

For radar systems employing continuous phase modulation (CPM) or other phase-shifting 

technologies that eliminate artifacts between chips, it is impossible to determine the number of 

chips, their durations and their rise/fall times by measuring the detected pulse envelope. If phase 

chips are not discernable, then tr is defined to be 40% of the time required to switch from one 

phase or sub-phase to the next. Chip duration and number of chips must be determined from 

radar system documentation. 

3.2.2.2.2 Phase-response Measurement of Coded Pulses 

For phase-coded pulses, the chip duration and rise/fall time may be measured directly only if the 

waveform is sampled without envelope detection. A vector signal analyzer (VSA) can be used 

for this purpose. Current VSA technology does not always allow direct measurement of RF 

energy above about 6 GHz. If radar frequencies are too high for direct measurement with a VSA, 

then a spectrum analyzer may be used to downconvert the RF pulse energy to a lower

14 

frequency that can be fed to a VSA, where chip duration and rise/fall time can be measured 

directly. 

3.2.2.3 FM Pulses 

Measurements of pulse duration (t) and rise/fall time (tr) of FM-pulse radars may be performed 

as described in Section 3.2.2.1. An additional pulse parameter must be measured, the bandwidth 

of the frequency deviation (chirp), (Bc). This parameter can be measured with a modulation 

analyzer if the analyzer can operate at the RF frequency of the radar. Alternatively, this 

parameter can be measured with a vector signal analyzer with an operational setup as shown in 

Figure 4 (or substituted for the discrete detector and oscilloscope shown in Figure 3) and 

described in 3.2.2.2.2. An example measurement of Bc made with a VSA is shown in Figure 8. 

 

14 The spectrum analyzer output is assumed to be accessible at a point prior to the resolution 

bandwidth and detection stages. 
16

The compression ratio of FM-pulse radars is calculated as follows: 

d B t

c = ⋅ . 

3.2.2.4 Phase-coded CW 

Measurements of symbol duration (t) and symbol rise/fall time (tr) may be performed as 

described in Section 3.2.2.2. 

3.2.2.5. FM-CW 

Measurement of the bandwidth of the frequency deviation (Bd) is required. This may be 

performed as described for (Bc) in Section 3.2.2.3 and as shown in the example data of Figure 8. 

3.3 Example Measurement Data 

Figures 5–8 have been taken from three different radars. Note that none of these example radar 

pulses have completely well-defined maximum amplitudes; the amplitude of the pulses is 

estimated as described in Appendix A. 

Figure 5. Diagram of RSEC parameters for a weather radar pulse. 

The radar measured in Figure 5 operates on a single frequency, has a fixed pulse repetition rate 

and no modulation of pulse phase or frequency. The measurement was made using the setup 

shown in Figure 4. 
17

Figure 6. Diagram of RSEC parameters for a short-range search radar pulse. 

The radar measured in Figure 6 hops to sixteen frequencies across 500 MHz of spectrum, but 

with no modulation of pulse phase or frequency. The measurement was made using the setup 

shown in Figure 4. 
18

Figure 7. Diagram of RSEC parameters for a phase-coded pulse with three chips. 

The measurement in Figure 7 is from a radar that performs frequency hopping and electronic 

beam scanning. The pulse was measured with a discrete-component detector connected to the IF 

output of a spectrum analyzer that was in turn tuned to one of the radar frequencies. The 

oscilloscope trigger was set to capture a single-shot trace whenever a sufficiently high pulse 

amplitude occurred. The pulse rise time, fall time, and width are directly measurable, as are the 

chip widths. The chip transition intervals (which are the sum of the chip and rise and fall times) 

are also directly measurable. But the individual chip rise and fall times are not directly 

measurable because they are obscured by the overall pulse envelope. The chip rise and fall times 

could each be estimated as 1/2 of the chip transition interval. Note that the observability of phase 

transitions will vary depending upon details of the phase modulation; phase transitions will not 

be observable in the envelopes of continuous phase modulated (CPM) pulses. For such radar 

pulses, a VSA would be required to measure the phase modulation in time. 
19

Figure 8. Measurement of the frequency deviation in time of a frequency-modulated pulse. 

Figure 8 shows a measurement performed with a vector signal analyzer (VSA) connected to a 

directional coupler of the radar (as shown in Figure 3) in place of the more conventional discrete 

wideband detector and oscilloscope. This measurement could be performed as well on radiated 

pulses. The conventional setup with detector and oscilloscope would be used to measure pulse 

amplitude and 10%, 50%, and 90% levels and corresponding pulse width, rise time, and fall time 

would be measured as shown in either Figure 3 or Figure 4. 
20

4. PULSE REPETITION RATE 

[At the time of this writing, the TSC is considering eliminating the PRR parameter for

determining the X dB limit for the RSEC mask.]

Pulse repetition rate (PRR) is used in computation of the RSEC ultimate suppression level for 

some radars. In some cases, the specified radar pulse parameters may be taken from radar 

documentation, and direct measurement of the radar’s pulse repetition rate may not always be 

necessary. But in the event that a direct measurement is required, the material in this section 

describes the methodology for this measurement.

4.1 Introduction 

For purposes of RSEC computations, PRR is taken as the average number of pulses per second 

emitted by a transmitter. If a hardline connection to a radar directional coupler is available, then 

the PRR measurement is nearly trivial. But if such a connection is not available, then the 

measurement of radiated energy is somewhat more difficult. This section describes both 

approaches to the measurement of PRR. 

4.2 Measurements for Conventional Radars 

In this context, a conventional radar is taken to be a unit that has a directional coupler available. 

The measurement setup is the same as that shown in any of Figures 1, 3, and 4. On an 

oscilloscope the pulse sequence is measured over a period long enough to see repetition in the 

sequence (e.g., for staggered pulse sequences, two or more complete stagger sequences should be 

displayed on the oscilloscope display). If a radar transmits a non-repeating pulse sequence, then a 

sequence of pulses should be recorded on the oscilloscope display. For most radars, this would 

be at least 20 pulses. With the pulses recorded on the oscilloscope display, the PRR is

determined by dividing the number of pulses on the display by the total amount of time on the 

display.

4.3 Measurements for Advanced Radars 

PRR may be most easily measured in the radar transmitter IF section. However, in many cases, 

radar design features (such as inaccessibility of an IF section, lack of an IF section, and multiple 

transmitter modules) or measurement logistics may make measurement of the radiated PRR 

necessary. The technique for basic measurement of the PRR through radiated emissions is as 

follows: 

1) Establish the measurement system at a location with clear line-of-sight to the radar 

antenna, and as close as possible without suffering degradation to the measurement 

system performance (e.g., feed-through) or loss of power from the radar by locating 
21

too far beneath the radar main beam. This is described in more detail in Appendices C

and E. 

2) Use a high-gain antenna (e.g., a 1-meter diameter or larger parabolic) on the 

measurement system to receive pulses from the radar. 

3) Detect the radar pulses in the measurement system using the widest bandwidth 

available. 

4) Set the measurement system oscilloscope to a single-sweep mode, with a relatively 

low trigger threshold. Wait until a series of pulses are recorded. Elevate the trigger 

threshold and wait for another set of pulses to activate the trigger. Continue this 

process until the threshold is so high that no more pulses are recorded. Reduce the 

trigger threshold slightly, and wait for a sequence to be recorded. This is the pulse 

sequence which should be finally recorded, and from which the PRR should be 

calculated. 

If a radar produces a fixed-rate PRR at a single frequency, this procedure is trivial. 

Complications arise in radars with three types of complex PRRs: 

• The PRR is non-uniform. Examples are staggered pulse trains used by air traffic 

control radars and some tactical radars. 

• The radar frequency-hops (and performs mechanical and/or electronic beam-steering) 

between pulses, but at a uniform PRR, resulting in only portions of the pulse train 

being produced at a single measurement frequency. The pulse train is effectively 

fragmented, with pulses apparently missing in the measured train. 

• The radar frequency-hops (and performs mechanical and/or electronic beam-steering) 

between pulses, with a non-uniform (random or staggered) PRR. 

In these cases, there are two problems for RSEC implementation: 

1) How should the RSEC PRR parameter be interpreted for radars with complex (i.e., 

non-periodic) pulse trains? 

2) How can the total pulse train structure be reconstructed, so as to know the total 

number of pulses emitted by the radar per unit time and thus fulfill the requirements 

for RSEC PRR measurement? 

In answer to the first question, the RSEC utilizes PRR for the purpose of determining the average 

power radiated by the radar. Thus, the aggregate number of pulses emitted, on average, per unit 

time, into all space around the radar, and on all radar frequencies, is required for accurate 

RSEC computation. Determination of this value is the purpose of the RSEC PRR measurement. 

(This is why, if the IF section of a radar transmitter is available for hardline connection to a 

measurement system, a measurement at this point would be desirable: all pulses produced by the 

radar would be observable at this point, regardless of the complicating behaviors described 

above.) The second question, how to reconstruct the average PRR from fragmentary received 

pulse sequences, is answered in the next three sub-sections. 
22

4.3.1 Non-uniform PRR Radiated at a Single Radar Frequency

Variation of intervals between pulses is called staggering. Eventually a staggered sequence will 

repeat. Staggering is handled by measuring the radar pulse train for a sufficiently long period of 

time to capture at least one full stagger sequence. The average PRR can be calculated by dividing 

the number of pulses in the stagger sequence by the length of time required to complete the 

stagger sequence. For example, if the stagger sequence consists of eleven pulses emitted in a 

period of 15 ms, then the average PRR is 733

0.015

11

= pulses per second. To determine the 

stagger period, it is necessary to record approximately 20 or more pulses and then measure the 

intervals between the pulses to determine the point where the sequence of intervals repeats—this 

is the stagger period. 

If the pulses are emitted in a random sequence that never repeats, then the PRR must be 

determined by recording a statistically significant number of pulses and then calculating the 

average interval between them. For most radars, a statistically significant number of pulses 

would be 20 or more (because that is how many pulses are usually needed to obtain a good 

response to a target). Most stagger sequences will repeat in 10 pulses or less.

4.3.2 Uniform PRR Radiated by a Frequency-hopping (and Mechanically and/or 

Electronically Beam-steering) Radar

In this case, the measurement system will observe several pulses in a row on a single frequency, 

at uniform intervals, possibly followed by (relatively large) gaps in time during which no pulses 

are observed, or during which pulses are observed at relatively low amplitudes. The gaps are due 

to radar transmissions at frequencies other than the one being monitored and to radar beamsteering to azimuths or elevation angles that are directed away from the measurement system. An 

example of such a measurement is shown in Figure 10. 

With reference to Figure 10, when using a narrow bandwidth measurement system (such as a 

spectrum analyzer), the PRR on a single frequency can be determined by recording the pulse 

train long enough to establish the PRR that occurs when the radar is tuned to the frequency being 

monitored, and when the beam is being directed toward the measurement system. The pulse

sequence on a single frequency may be recorded and the PRR may be accurately calculated for 

that frequency. 

For determination of the total PRR of the radar, however, a wideband detector must be used, as 

depicted in Figure 4. The detector output is directed to an oscilloscope, as shown in that figure, 

and the pulse sequence is captured as described in Section 4.2. An example of this type of 

measurement output is shown in Figure 11. 
23

4.3.3 Non-uniform PRR Radiated by a Frequency-hopping (and Mechanically and/or 

Electronically Beam–steering) Radar 

In this case, the conditions are complicated by the fact that there is no fixed pulse-to-pulse 

interval that can be observed, even when the radar is tuned to the measurement system frequency 

and the radar beam is directed toward the measurement system. For determination of the total 

PRR of the radar, a wideband detector must be used, as depicted in Figure 4. The detector output 

is directed to an oscilloscope, as shown in that figure, and the pulse sequence is captured as

described in Section 4.2. An example of this type of measurement output is shown in Figure 11. 

Although the PRR of the radar in that figure is fixed, a non-uniform PRR would merely show a 

non-uniform spacing between the pulses. The average PRR would be computed from the 

observed data by dividing the total number of pulses in one or more stagger sequences by the 

total time interval within which those pulses were radiated. 

4.4 Example Measurement Data 

0.15

0.20

0.25

0.30

0.35

0.40

0 1 2 3 4 5 6 7 8 9 10

-1 pulse repetition rate = 1096 sec

pulse repetition interval = 0.913 mS

Time (milliseconds)

Amplitude (detected volts)

Figure 9. Example of a fixed-PRR radar pulse sequence. 

The PRR depicted in Figure 9 is from a radar operating on a single frequency. The pulses have 

been detected with a discrete-component detector connected to the video output of a spectrum 

analyzer that was in turn connected to an antenna to measure radiated pulses. The same 

measurement can be performed with the discrete wideband detector and oscilloscope setup of 

Figure 3, or with a discrete wideband detector and oscilloscope connected to an antenna as 

shown in Figure 4. If a radiated measurement is performed, a slight modulation of the pulse 

amplitudes will be observed within the 3 dB points of the radar beam. (For most radars, 10 to 20 

pulses will be observed within that portion of the radar main beam, more than adequate for an 

assessment of the average PRR.) 
24

Figure 10. Pulse repetition measurement on a single channel of a frequency-hopping radar made 

with a spectrum analyzer in a zero-Hertz span mode and positive peak detection. The line is an 

estimated threshold for on-frequency pulses. 

The radar measured in Figure 10 hops through sixteen frequencies that are spread across 

500 MHz of spectrum, for a spacing of (500/(16-1))=33.3 MHz between frequencies. This 

measurement has been performed in a bandwidth of 3 MHz, which is an order of magnitude less 

than the channel spacing. Despite the relative narrowness of the measurement bandwidth 

compared to the channel spacing, the out-of-band emission levels of off-tuned pulses on an 

adjacent channel are high enough to make them visible on the spectrum analyzer display, 

interleaved between the on-tuned pulses (which are indicated with arrows). As a result, the 

apparent spacing between pulses as measured by the spectrum analyzer is half of its true value 

(the apparent spacing being 0.5 ms, whereas the true pulse-to-pulse spacing on a single channel 

of this radar is nominally 1 ms). This artifact can be eliminated by carefully observing that there 

are two classes of pulse amplitude in this measurement. Half the pulses occur at amplitudes 

above a fixed threshold line and half occur below that threshold, and they regularly alternate. 

This pattern can be interpreted by trained personnel as being a set of on-tuned pulses with a 

higher amplitude alternating with off-tuned pulses of lower amplitude. (The same effect can 

occur for radars with multiple beam elevation modes, one high and the other low.) When the 

spacing is measured between the high-amplitude pulses that exceed the critical threshold level, 

the true nominal spacing of 1 ms (actually a measured value of 0.97 ms) on the measurement 

channel is observed. This demonstrates that this technique can provide a valid assessment of the 

pulse-to-pulse spacing on a single channel of the radar, but substantial knowledge on the part of 

measurement personnel is required to correctly interpret this information. 
25

The same radar is measured with a wideband detector in Figure 11. The detector’s frequency 

response range far exceeds the 500 MHz frequency hop range of the radar. Therefore all pulses 

from all 16 radar channels are observed. The envelope of the pulse amplitudes is the beam shape

of the main lobe of the radar antenna, observed as the beam sweeps past the measurement 

location. (Note that there are about 18 pulses within the half-points of the beam, consistent with 

standard radar theory for reliable detections of targets.) The measured PRR is 16,470 pulses per 

second. Compare these data with those of Figure 10, in which pulses from a single channel are 

observed at 1/16 of the nominal rate, along with lower-amplitude responses from adjacent 

channels. 

0

0.04

0.08

0.12

0 0.5 1.0 1.5 2.0

Time (msec)

Amplitude (detected volts)

Figure 11. The pulse repetition rate of the same frequency-hopping radar as that shown in 

Figure 10, but measured with a broadband detector configured as in Figure 4. In this

measurement mode the radar PRR may be accurately measured directly off the graph. 
26

5. EMISSION SPECTRA 

5.1 Introduction 

Limits on unwanted (out-of-band and spurious) radar emissions are critical to spectrum 

efficiency. Radar design factors affecting emission spectrum characteristics include pulse 

shaping, the selection of radar output device, RF output filtering, and antenna frequency 

selectivity (e.g., slotted arrays). These design factors are discussed further in 

Recommendation ITU-R M.1314. Controlling the levels of unwanted emissions is key to 

ensuring compatibility with other systems. This section describes the methodology for measuring 

compliance with RSEC emission spectrum limits. 

Formulas for the computation of RSEC emission mask limits are provided in existing NTIA 

documents [1, Chapter 5]. These can be performed with handheld calculators, if necessary. But 

in order to assist the technical community that must compute RSEC masks for radars, NTIA has 

developed an analytical software tool that calculates the RSEC emission limit mask, and 

alternate emission limit masks. It includes the capability to import measured radar emission 

characteristic data. The analytical tool is available at http://www.ntia.doc.gov/osmhome/. 

Appendix H provides an overview of this analytical tool, including a user’s guide. 

Radar emission spectra present the most difficult challenge in acquiring the data that are needed 

to verify RSEC compliance. Difficulties that must be overcome in acquiring radar emission 

spectra include: 

1) the need to measure emission spectra over a wide dynamic range (90 dB or more); 

2) the need to measure spectra over a wide measurement frequency range (sometimes several 

 gigahertz, plus harmonics); 

3) the need for high sensitivity (usually 10 dB noise figure or less) in the measurement system; 

4) the sometimes challenging task of assessing the proper bandwidth in which to perform the 

 emission spectrum measurement; 

5) proper postioning and operation of a measurement system near a radar, often under difficult 

circumstances. 

A detailed discussion of the measurement system used by NTIA for measuring radar emission 

spectrum characteristics is given in Appendix C. Calibration procedures are described in 

Appendix D. Positioning relative to radar stations for radiated measurements is described in 

Appendix E. The following is a discussion of the procedures used to measure radar emission 

spectra using the NTIA measurement system with some comments on alternative measurement 

procedures. Alternative measurement techniques that give equivalent results may be used. 

5.2 Measurement Point (Hardline vs. Radiated) 

Currently, the RSEC specifies that emission spectra should be measured “at the antenna input” 

[1, Chapter 5]. (At the time of this report’s release, consideration is being given by the Technical 

Subcommittee (TSC) of the Interdepartment Radio Advisory Committee (IRAC) to use radiated 
27

emissions.) Hardline connection points are available in some radars. These are normally 

directional couplers, but they are not generally located at the antenna input. However, some 

modern radars, such as those with distributed phased array antennas, do not have directional 

couplers and cannot be measured at the antenna input. 

Hardline-coupled emission spectrum measurements have some inherent technical drawbacks. 

First, they do not include the effects of frequency selectivity by components after the directional 

coupler including RF filters and the radar antenna. Secondly, directional coupler frequency 

responses usually decrease significantly outside operational bands, whereas RSEC compliance 

measurements (including harmonics) typically need to go well beyond those band edges. Thirdly, 

waveguide modes between the directional coupler and the measurement system input have been 

observed during measurements to result in higher measured levels of unwanted emissions than 

those observed in radiated spectra. 

Radiated emissions determine technical compatibility with other systems. It is therefore desirable 

that RSEC compliance measurements reflect as nearly as possible the emissions that exist in 

space. Due to the drawbacks of using hardline coupling described above, and considering the 

desirability of measuring as nearly as possible the radiation in space, it is recommended that 

RSEC compliance spectrum measurements be performed on radiated emissions, if possible. 

Radiated emission spectrum measurements do present complications due to the following 

factors: rotating radar antennas; radar beam scanning; and radar frequency hopping. Therefore, a 

stepped-frequency measurement procedure, as described in Appendix C, is desirable. Other 

measurement procedures may be used as alternatives to the procedures described in Appendix C. 

But alternative procedures must demonstrably always obtain the maximum peak power emitted 

by the radar at each measured frequency; this is a difficult requirement to satisfy. 

5.3 Measurement Bandwidth for RSEC Measurements 

The appropriate measurement bandwidth is a function of the time waveform characteristics of 

the radar. There are three main types of radar pulsed emissions: non-FM pulsed; phase-coded 

pulsed; and FM-pulsed. Three other radar modulations include: CW; FM/CW; and phase-coded 

CW. The appropriate measurement bandwidths for each waveform type are given in Table 2. The 

criteria of Table 2 should be used for selection of RSEC-compliance spectrum measurement 

bandwidth. 

In addition to performing the above calculations, it is advantageous to confirm the appropriate 

value of measurement bandwidth, Bm, for any given radar system with an empirical observation. 

This observation, called a bandwidth progression measurement, is performed as follows: The 

measurement system receiver is tuned to the fundamental frequency (or the frequency of a 

single channel if the radar frequency-hops), or within the frequency chirp range if the radar 

chirps. The frequency-span range of the measurement system is set to zero hertz. The sweep 

time is set to a value somewhat greater than the radar beam-scanning and frequency-hopping 

interval, so that a maximum-amplitude peak power value is measured for each measurement 

system sweep. The measurement system IF bandwidth is set to the widest available value, and 
28

the received peak power level from the radar in this bandwidth is noted. The measurement

bandwidth is then progressively narrowed, and the peak received power level is recorded as a 

function of the increasingly narrow bandwidths. The end result is a graph or table showing 

measured power as a function of measurement system IF bandwidth. The value of Bm will be 

the widest available bandwidth that gives a peak power reading that is less than or equal to the 

full-peak power reading. 

For example, if the maximum peak power reading occurs at 300 kHz and wider measurement

bandwidths, and a measurement bandwidth of 100 kHz is the next-smaller available bandwidth 

that gives a peak power reading that is less than the maximum peak power reading, then Bm

should be 100 kHz or less. An example is shown in Figure 12. 

Table 2. Determination of RSEC Measurement Bandwidth (Bm) 

Radar Modulation Type RSEC Measurement Bandwidth (Bm): 

Non-FM pulsed and phasecoded pulsed Bm (1/t), where t = emitted pulse duration (50% voltage) or phasechip (sub-pulse) duration (50% voltage). 

Example for non-FM pulsed: If emitted pulse duration is 1 μs, then 

Bm 1 MHz. 

Example for phase-coded pulsed: If radar transmits 26-μs duration 

pulses, each pulse consisting of 13 phase-coded chips that are each 

2μs in duration, then Bm 500 kHz. 

FM-pulsed (chirped) Bm (Bc/t)1/2, where Bc = frequency sweep range during each pulse 

and t = emitted pulse duration (50% voltage). 

Example: If radar sweeps (chirps) across frequency range of 

1.3 MHz during each pulse, and if the pulse duration is 55 μs, then Bm

154 kHz. 

CW Bm = 1 kHz; See sub-paragraph 4.2 of [1, Chapter 5] for RSEC Criteria 

B, C and D. 

 Example: Bm = 1 kHz. 

FM/CW Bm = 1 kHz; See sub-paragraph 4.2 of [1, Chapter 5] for RSEC 

Criteria B, C and D. 

 Example: Bm = 1 kHz 

Phase-coded CW Bm (1/t), where t = emitted phase-chip duration (50% voltage). 

Example for phase-coded pulsed: If chip duration is 2μs, then Bm 

500 kHz. 

Multi-mode radars Calculations should be made for each waveform type as described 

above, and the minimum resulting value of Bm should be used for the 

emission spectrum measurement. 

Example: A multi-mode radar produces a mixture of pulse 

modulations as used in the above examples for non-FM pulsed and 

FM-pulsed. These values are 1 MHz and 154 kHz, respectively. Then 

Bm 154 kHz. 
29

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

0 10 20 30 40

1 kHz

3 kHz

10 kHz

30 kHz

3 MHz 1 MHz 300 kHz 100 kHz

Arbitrary Units

Received Power in Indicated Bandwidth (dBm)

Figure 12. Example of a bandwidth progression measurement for assessment of the proper 

bandwidth in which to measure a radar spectrum for RSEC compliance. Because 100 kHz is the 

widest bandwidth that gives less than a full-power response, it is the ideal bandwidth to use for 

this radar. 

Figure 12 data, collected on the radiated emissions of an operational air search radar, provide an 

example of how to perform a bandwidth progression measurement on a radar emission. The

measurement system was fix-tuned in a zero hertz span to the radar fundamental frequency with 

positive peak detection selected. The spectrum analyzer sweep time was set to slightly more than 

eight rotation periods of the radar transmitter antenna, and the spectrum analyzer’s sweep mode 

was set to ‘single.’ The initial spectrum analyzer IF bandwidth was set to the widest available 

value (3 MHz for this particular analyzer model). After the sweep was commenced, the operator 

waited until the full radar power (in the main antenna beam) had been observed, and then the 

operator switched the bandwidth to the next smaller value in a logarithmic progression (1 MHz) 

and waited until the radar main beam power was measured in that bandwidth. Then the IF 

bandwidth was reduced in the next step of a log progression (to 300 kHz), and the process was 

continued until the radar measured power was observed to clearly roll off at sufficiently narrow 

bandwidths. (The pedestal-like featuress in the trace are sector blanking by the radar transmitter.) 

Figure 12 shows that full radar power was received in 300 kHz but that a slight reduction began 

at 100 kHz. Therefore, based upon the criteria described above, the proper bandwidth for 

measurement of this radar emission spectrum would be 100 kHz or less. A bandwidth of 

300 kHz might even be marginally acceptable, but if the radar spectrum were to be measured in 

1 MHz or wider bandwidths, there would be a risk that the spectrum might appear to not meet 

RSEC mask criteria. Unwanted (out-of-band and spurious) emission levels would appear in their 

proper relationship to measured power at the radar fundamental in spectrum measurement 

bandwidths of 100 kHz or less. But measurement of the extended spectrum in bandwidths less 
30

than 100 kHz would probably be impractical due to the length of time that would be required to 

make the measurement in such narrow bandwidths. 

If multi-mode radars emit specific time waveforms on specific frequencies (e.g., if non-FM 

pulses are emitted at frequency f1 and chirped-pulsed emissions occur at frequency f2), and if the 

calculated measurement bandwidths are different for these two waveforms, then the spectrum 

should be measured in both bandwidths. An example is shown in Figure 13. One fundamental 

frequency (or channel) (left) is unchirped and another channel (right) is chirped. The appropriate 

measurement bandwidths are 100 kHz for the lower-frequency channel (left) and 300 kHz for the 

higher-frequency channel (right). The radar spectrum therefore needs to be measured in both 

bandwidths, as shown in Figure 13. 

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

2700 2750 2800 2850 2900

300 kHz

100 kHz

Frequency (MHz)

Measured Power Level in Specified Bandwidth (dBm)

Figure 13. Emission spectrum measurement performed on a multi-mode chirped radar. 

5.4 Variation in Measured Spectra as a Function of Measurement Bandwidth 

Radar emission levels are bandwidth-limited at their fundamental frequencies. That is, when 

measurement bandwidths equal or exceed the Bm values given in Table 2, the measured peak 

power will be constant no matter how much the measurement bandwidth is increased. 

Conversely, in the radar unwanted (out-of-band and spurious) emission spectrum domain, 

measured levels of unwanted emissions will increase for measurement bandwidths that are wider 

than the Bm values given in Table 2. Consider for example the non-FM pulsed radar emission of 

Table 2, with a critical measurement bandwidth, Bm, of 1 MHz. The peak power measured at its 

fundamental frequency will be constant (or nearly so) for measurement bandwidths greater than 

Bm (1 MHz). However, the measured levels of unwanted emissions will vary as described in 
31

Appendix G. Thus measurements performed in bandwidths inappropriate to Table 2 may result 

in apparent non-compliance with the RSEC, when the radar under test would have in fact been in 

compliance had it been measured in accordance with the Table 2 values of Bm. Emission levels 

can be made to appear arbitrarily high relative to the power at the radar fundamental if 

measurement bandwidths exceed the Table 2 values. This problem is discussed further in 

Appendix G, and is diagrammed graphically in Figure G-7. 

5.5 Determination of Frequency-Stepping Time Interval (Dwell Time) 

As noted in Appendix C, the most practical approach to measurement of radar emission spectra 

is to implement frequency-stepping rather than frequency-sweeping across the spectrum. This 

section describes the procedures for determining the time interval needed to determine peak 

power at each measured frequency (called dwell time) for radar emission spectra that are 

measured with the stepped-frequency approach. 

As described in Appendix C, implementation of the dwell-time stepped-frequency measurement 

approach requires computer control of a spectrum analyzer. Alternative approaches that do not 

require computer control (such as sweeping across the spectrum in a maximum-hold trace mode) 

may be used, but with the caveat that they suffer from significant limitations for the purpose of 

determining compliance of the spectrum with RSEC mask limits. Approaches that do not utilize 

computer controlled frequency stepping of the measurement system tend to be more difficult to 

implement because they are probabilistic instead of deterministic in nature. 

The necessary dwell time is a function of the radar antenna beam-scanning and frequency-tuning 

(fixed-tuned vs. hopping) characteristics. Section 5.5.1 describes the procedure for determining 

dwell time for fixed-tuned radars utilizing conventional beam-scanning techniques. Section 5.5.2 

describes the determination of the dwell time for complex beam-scanning (combined vertical and 

azimuthal beam scanning) and frequency-hopping radars. 

If the radar beam scanning can be stopped for the duration of the emission measurement, then the 

measurement step dwell time can be reduced to about 1 or 2 seconds, and the overall amount of 

time required to complete the measurement will be significantly reduced. 

5.5.1 Conventional Beam-scanning, Fixed-tuned Radars 

In this context, a conventional radar is one that scans a beam only in one dimension (usually 

azimuth); that repeats the scanning in a predictable, periodic manner; and that does not 

frequency-hop. Examples include air search radars with broad vertical beam patterns and 

mechanical azimuth scanning; sector-scanned radars (typically on aircraft); and phased-array 

radars that scan a beam only in azimuth. 

The procedure for determining dwell time is as follows: First, a measurement location is 

identified (see Appendices C and E). Then the measurement system is tuned to the radar 

fundamental frequency and maximum attenuation is invoked in the RF front-end. The measured 
32

level is verified to be less than the saturation level of the measurement system. Attenuation 

(10 dB is suggested) may be inserted and removed from the measurement path to check for 

measurement system linearity. 

The dwell time for each measured frequency needs to be slightly longer than the radar beam 

scanning interval. If the radar rotation interval is already known with certainty (e.g., 6 rpm = 

10 seconds per rotation), then the dwell time may be set immediately, to a slightly longer interval 

(e.g., 11 seconds dwell time for a 10-second antenna rotation time.) 

Alternatively, if the radar antenna rotation rate is not precisely known a priori, the following 

procedure may be used to measure it. The measurement system is tuned to the radar fundamental 

frequency. The frequency span of the measurement system (usually a spectrum analyzer) is set to 

zero hertz, so that the radar beam scanning characteristic is now observed in the time domain on 

the system display. The sweep time of the measurement system is initially set to a few seconds, 

so that the radar beam is seen at least once on the measurement system display. Then the sweep 

time is gradually lengthened and additional sweeps are taken, until the radar main beam appears 

at least twice on the display. When such a display is achieved, a marker function is used to 

determine the time interval between the main beam features; this is the rotation (or sector-scan, if 

appropriate) interval for the radar. The dwell time of the spectrum measurement needs to be set 

at a value slightly longer than this, as mentioned in the paragraph above.

5.5.2 Complex Beam-scanning and Frequency-hopping Radars 

Some classes of radar scan space in elevation as well as azimuth, and may scan both these 

degrees of freedom with some amount of randomness; this is complex beam-scanning. Some 

radars change their tuned frequency on a pulse-to-pulse basis or at fixed or random intervals (i.e., 

they frequency-hop). And some radars combine complex beam scanning with 

frequency-hopping. The procedures for measuring the spectra of complex beam-scanning and 

frequency-hopping radars are nearly identical to those described above. The major difference is 

that the dwell time will need to be lengthened to ensure that a maximum peak level measurement 

will occur at each measurement step in the spectrum. 

Complex beam scanning and frequency-hopping by a radar transmitter have the effect that 

maximum-amplitude pulses may not necessarily be directed toward the measurement system on 

its tuned frequency at predictable intervals, as is the case for conventional radars. Nevertheless, 

the antenna beam and the transmitted frequency will revisit the measurement system location and 

tuned frequency with a high probability within some interval; the problem is to determine that 

interval. 

To do this, the measurement system is tuned to a radar fundamental frequency with the spectrum 

analyzer set to a zero hertz span. The RF front-end attenuation is set to a maximum value. The 

spectrum analyzer sweep time is set to a long interval, on the order of one minute. A single 

sweep is taken. The highest peak is identified, and then a delta marker is used to find the nexthighest peak. The delta marker is used again, to find the next-highest peak after that. The process 

is continued until all peaks with amplitudes within 2 dB of the highest peak have been 
33

catalogued. A pattern normally emerges. This pattern in time intervals between the highest peaks 

indicates the most probable interval that will elapse between radar main beam scans across the 

measurement location on the tuned measurement frequency. Unlike the situation for 

conventional radars described in the previous section, the dwell time for complex radars may 

require two or more antenna rotation periods (e.g., the radar may have a nominal 10-second 

antenna rotation period, but the dwell time required to measure a consistent peak value may be 

20 or 30 seconds). In other words, the necessary time interval may be a random variable with a 

wide variance; in such cases, the dwell time needs to be long enough to assure that a valid peak 

is always measured, and this could turn out to be two or more antenna rotation periods. 

The selected dwell time may be verified as correct by obtaining data in that interval a total of ten 

or twenty times, and noting the peak values returned from each of those individual times. If all 

these peak values are within 2 dB of each other, then the selected dwell time is adequate for the 

RSEC measurement. 

As a matter of efficiency, it has been observed that this dwell time, while necessary for 

measurement of the radar spectrum at fundamental frequencies and within immediately adjacent 

out-of-band spectrum, is longer than what is required for measurement of the spurious spectrum. 

The dwell time required in the spurious domain for complex-beam-scanning and 

frequency-hopping radars is less than that required at the fundamental frequencies. This is partly 

because the antenna does not generate a well-formed beam in the out-of-band and spurious

domains and also because hopping of the fundamental frequency does not affect out-of-band and 

spurious emissions to much extent. 

To determine how much shorter the dwell time can be in the out-of-band and spurious domains, 

measurement personnel should observe the radar’s beam pattern carefully, on a step-by-step 

basis, as the measurement progresses across these domains. Eventually, they will observe that the 

radar peak amplitude is always repeated twice during each step. When this happens, the dwell 

time may be reduced by a factor of two. As the measurement progresses further through the 

spectrum, the phenomenon may occur again. If it does, the dwell time may again be reduced by 

half. This process may be continued as necessary while the measurement progresses, and will 

greatly reduce the overall measurement time without causing any degradation in the results. 

5.6 Emission Spectrum Measurements and Data Recording 

5.6.1 Overview of Spectrum Measurement Procedure 

The radar emission spectrum measurement is performed using the calibration procedure of 

Appendix D and frequency-stepping algorithm described in Appendix C with measurement

bandwidth selected in accord and with Table 2 and dwell time selected as described above. The 

frequency interval from step to step is typically about equal to the measurement bandwidth (e.g., 

if the measurement bandwidth, Bm, is 1 MHz, then the frequency interval between successive 

steps is nominally 1 MHz. (See Appendix C for further discussion of frequency-step interval.) 
34

It is recommended that the measurement be performed in spectrum segments of about 200 

frequency steps (each step corresponding to a single data point in the spectrum) per recorded 

data file. This has been found to strike a reasonable balance between acquisition of a significant 

amount of data per file versus not risking the loss of a large amount of unrecorded data as a

result of possible measurement system failures. 

The first segment of spectrum can conveniently bracket the radar fundamental frequency. The 

next segment begins at the last frequency of the first segment. This sequence of segments 

continues until the radar spectrum is lost in measurement system noise at the high-frequency end. 

Depending upon the radar, such a measurement may extend to as much as a few gigahertz above 

the radar fundamental frequency. Then, the spectrum measurements resume on the low side of 

the fundamental frequency. They continue until the radar emissions are again lost in the 

measurement system noise, this time at the low-frequency end. At this point, the RSEC spectrum 

measurement can proceed to harmonics and possibly sub-harmonics. 

It may also be desirable to measure the emission spectrum in additional bandwidths. Such a set 

of spectra may be found to be useful at a later date, for they will show the progression of 

measured levels as a function of Bm across the spectrum (see Appendix G). 

5.7 Potential Measurement Problems and Solutions 

There are at least four major potential problems that may occur in the course of a spectrum 

measurement. These are: 

1) failure to change attenuation appropriately during measurements; 

2) unanticipated changes in radar operating mode during measurements; 

3) RF energy feed-through (also known as case penetration) into measurement circuitry; 

4) overload of the RF front-end amplifier. 

5.7.1 Possible Attenuation Mistakes During Measurement 

It is often difficult to change attenuation appropriately for every data point. Attenuation errors 

will often appear as vertical cliffs in the spectrum, as shown in Figure 14. In this case, too much 

RF attenuation was removed prematurely, at the point indicated by the arrow, as the 

measurement progressed. Without sufficient attenuation the measurement system front end was 

saturated at a level that was lower than the actual signal level, with the result that the spectrum 

level indicated in the (inaccurately corrected) measurement data is too low at the indicated 

frequency. The measured power levels became accurate again when the radar spectrum power 

dropped below the measurement system saturation level, one division to the right of the arrow on 

the spectrum. This situation illustrates the desirability of having a re-measurement feature in the 

measurement software. Such a feature can be applied to any portions of a radar spectrum that are 

suspected of having been measured with incorrect attenuation. 
35

Figure 14. An example of a spectrum measurement error caused by an incorrect RF attenuation 

setting. 

5.7.2 Changes in Radar Operating Mode During a Measurement 

Radar transmitters sometimes change modes or cease to function while measurements are 

proceeding. Such changes may not be apparent to measurement personnel. Therefore, an 

auxiliary measurement system may be useful during measurements to verify that the radar mode 

is constant. The auxiliary system consists of an omni-directional antenna connected to a second 

spectrum analyzer. The analyzer is fixed-tuned to the radar fundamental frequency. The radar 

beam scanning, frequency-hopping (if any), and peak measured power at that frequency are 

monitored throughout the measurement. Radar mode changes will be indicated by changes in any 

of the observed parameters on the monitor.

5.7.3 Feed-through and RF Front-end Overload 

These are system-linearity problems, and will result in incorrect power measurements. Because 

they are somewhat difficult to detect, it is critical that measurement personnel verify 

repeatedly during the spectrum measurement that the measurement system is behaving 

linearly. Brief descriptions of these problems, diagnostics for their identification, and solutions 

for them are described in this section. 

Feed-through (case penetration) of radar energy directly into measurement system circuitry can 

occur due to the high-energy radar signal coupling directly into measurement system circuitry. 

Resulting measured levels are obviously incorrect in that circumstance. 
36

Front-end overload occurs when the measurement system RF front-end amplifier is saturated by 

the radar fundamental frequency energy. This results in gain-compression of the amplifier. In 

this circumstance the amplifier output is no longer calibrated. Front-end overload typically 

occurs when spectrum levels decrease (roll off) rapidly around the fundamental. To measure 

those lower levels, RF front-end attenuation must be reduced from the value used to measure at 

the fundamental frequency. But in some cases the attenuation must be reduced so much that the 

radar fundamental frequency energy overloads the first amplifier. Although the RF front-end 

tunable bandpass filtering described in Appendix C is specifically intended to mitigate this 

problem, radars with extremely fast spectrum roll-off may nevertheless tend to produce this 

problem. 

Measurement personnel need to perform diagnostics to verify that neither feed-through nor 

front-end overload are occurring, and to mitigate them if they do occur. Both problems are

diagnosed by changing the measurement system RF front-end attenuation by 10 dB to verify 

system linearity. If the measurement system is linear, a 10 dB change in attenuation should result 

in exactly 10 dB of change in the measured power level.15

5.7.3.1 Mitigation of Feed-through and RF Front-end Overload 

If feed-through occurs, additional shielding of the measurement system may be necessary. Such 

shielding may be accomplished by positioning the measurement vehicle behind a building or 

dense foliage, while the measurement antenna is mounted high enough (as on a mast) to see over 

the obstacle(s) toward the radar antenna. 

If front-end overload occurs even though a high-quality, tunable bandpass filter is being used 

ahead of the RF front-end amplifier (as described in Appendix C), then the problem may be 

mitigated by adding a notch filter ahead of the amplifier, with the notch being tuned to the radar 

fundamental frequency. (The measurement system will need to be re-calibrated with the notch in 

place.) The notch is intended to provide the necessary additional frequency-dependent 

attenuation to prevent overload of the amplifier when RF front-end attenuation has to be reduced 

to measure low-level emissions near the fundamental frequency. 

Alternatively, it may be possible to solve the problem by slightly off-tuning the RF front-end 

bandpass filter, so that it is not centered at the measurement frequency. Effectively, this 

attenuates the fundamental by a larger amount than would otherwise be obtained at the frequency 

separation between the radar fundamental and the measured frequency. 

 

15 Or, if automated calibration and attenuation corrections are being made, then the power 

levels obtained with 10 dB attenuation should have the same values as when measured with the 

original attenuation setting. 
37

5.8 Example Emission Spectrum Data 

Example emission spectra are shown in Figures 15, 16, and 17. The data in Figure 15 

demonstrate the need for wide dynamic range in the measurement system as a whole and 

high-performance RF bandpass filtering in the front end. The measurement system noise floor is 

at –90 dBm and the peak measured power level is at almost +30 dBm, for a total dynamic range 

of nearly 120 dB. But while the measurement spans a frequency range of 1500 MHz, most of the 

dynamic range is required in a frequency span of just 150 MHz near the fundamental frequency. 

Without adequate front end preselection, the high power at the fundamental will overload the 

measurement system at all other frequencies. Great care must be taken to avoid attenuation errors 

such as those shown in Figure 14. A measurement system such as that described in Appendix C 

is required to accomplish this sort of measurement. 

Figure 15. Example spectrum of an air search radar. 

Figure 16 illustrates the effect of variations in the measurement bandwidth. The correct 

bandwidths for measurement of this radar are 1 MHz or less, because 1 MHz is the widest

bandwidth that gives less than the full-power response of 3 MHz. Bandwidths wider than 1 MHz 

should not be used because they will result in measured levels of unwanted emissions that are too 

high compared to the power at the fundamental frequency. This is demonstrated by the data 

taken in 3 MHz in Figure 17. In that figure, the curves measured in 3 MHz and 1 MHz both 

attain the same measured maximum power, but the levels of unwanted emissions measured in 

3 MHz are relatively much higher than for the 1 MHz measurement. This is an indication that a 

bandwidth of 3 MHz is too wide for this radar for purposes of assessing RSEC compliance, a fact 

borne out by the result shown in Figure 17. The measurement bandwidths of 1 MHz and 

300 kHz, conversely, show approximately the same relative levels for unwanted emissions, when 

their measured peak power levels at the radar fundamental frequency are normalized. So from 
38

the standpoint of assessing RSEC compliance, the 300 kHz data are as good as the 1 MHz data. 

The only drawback to using 300 kHz or narrower bandwidths is that more data points are 

required to fill in such curves. 

Figure 16. Example bandwidth progression measurement of the fundamental for the radar having 

the measured emission spectra of Figure 17. The ideal measurement bandwidth is 1 MHz. 

Figure 17. Three spectra for a single radar for which the bandwidth progression is shown in 

Figure 16. A bandwidth of 3 MHz obtains the same maximum fundamental frequency power as 

in 1 MHz, but the unwanted emission levels are higher than in 1 MHz. This shows that 3 MHz is 

an incorrect bandwidth for RSEC compliance measurements, but bandwidths of 1 MHz or less

will give correct results. 
39

6. ANTENNA PATTERNS 

The RSEC requires suppression of radar antenna gain outside the main lobe for radars falling 

into the RSEC Criteria Groups C and D. 

6.1 Introduction 

Antenna gain suppression specifications apply to the portion of the antenna pattern that does not 

include the main lobe. They are divided into two categories. For antennas that scan through 360 

degrees of azimuth, the suppression is specified in terms of the median antenna gain as decibels 

relative to the peak of the antenna pattern. The median value of the pattern is the smallest value 

that is greater than or equal to 50% of the measured points. For such radars, the median antenna 

gain in the principal horizontal plane should be –10 dB or less. For other antennas, suppression is 

defined relative to the peak gain of the radar main beam. 

Antenna patterns of operational radar transmitters can not generally be measured in the radar 

main beam, because the main beam energy is usually directed into space in directions 

inaccessible to terrestrial measurement systems. (An example is the beam of a typical air search 

radar, the lower edge of which is ordinarily tilted about a degree above the horizon.) But the 

RSEC is concerned mainly with emissions directed toward terrestrial-based receivers. Hence 

terrestrial-based measurements are adequate for purposes of determining RSEC compliance. This 

section describes procedures for this measurement. 

Radar antenna patterns should be measured from a location that maximizes the signal to noise 

ratio at the measurement system. Guidelines for determining such a location are described in 

Appendices C and E. 

6.2 Measurements of Conventional Antenna Patterns 

The measurement system is fixed-tuned to a radar fundamental frequency in a zero-hertz span. 

The sweep time is set slightly longer than the radar’s beam scanning interval. A single complete 

rotation (or scan) of the radar is recorded. (A stopwatch is useful as an aid to anticipate when to 

trigger the sweep.) The same bandwidth should be used as for the RSEC spectrum measurement 

(Table 2), as this provides maximum dynamic range (signal-to-noise ratio) for the antenna 

pattern measurement. Positive peak detection should be used. Figure 18 shows an example 

pattern. 

If the measurement system has 60 dB or more of instantaneous dynamic range, then the resulting 

antenna pattern should be adequate for purposes of RSEC compliance verification. But if the 

dynamic range is inadequate, then the antenna pattern may have to be measured twice. The first 

time, full attenuation is used. The second time, 20 dB less attenuation is used. The radar will 

saturate on one or more beam peaks. But the lower-amplitude portions of the pattern will emerge 

from the measurement system noise floor. These two measurements may be merged graphically 

or digitally to reveal the complete antenna pattern with the requisite dynamic range.
40

6.3 Antenna Pattern Measurements for Advanced Radars 

The problem for advanced radars is that the electronic scanning and frequency-hopping of the 

beams causes antenna patterns to be measured as discontinuous points rather than smooth 

envelopes. To produce a smooth or nearly smooth envelope, the measurement system should be 

set to measure the radar as described in Appendix E, but the measurement should be repeated ten 

or twenty times. Subsequently, the resulting raw data should be normalized in time and added 

together digitally, to make the final resulting pattern a reasonably smooth envelope.

6.4 An Advanced Antenna Pattern Measurement for All Radars

A problem with all antenna pattern measurements on radars is that multipath-generating 

obstacles in the vicinity of the radar will cause nulls and peaks in any given pattern 

measurement. Variations such as multipath due to vehicles, buildings and other radio-reflective 

objects will also occur. To mostly eliminate these features, perform the following procedures: 

1. Measure the radar antenna pattern several times at one location, and cross-correlate the 

results to eliminate temporal multipath effects at that location; 

2. Then, move the measurement system to another location and repeat the procedure to 

eliminate temporal variation at the second location; 

3. Find the median of the patterns from these first two separate locations; 

4. If desired or necessary, repeat this procedure at a third measurement system location, and 

find the median of the three patterns. 

An example result is shown in Figure 19. This pattern should approach the result that would be

obtained if the radar antenna pattern had been measured in an anechoic chamber. 

6.5 Antenna Pattern Statistics 

Antenna pattern statistical analysis may be performed on the final pattern(s) that result from the 

procedures described above. The analysis will be statistical in nature and will virtually 

necessitate the use of computer-implemented algorithms. Median statistics, such as those 

required by the RSEC, may be easily computed in this manner.
41

Figure 18. Example radar antenna pattern for a surface search radar.

 (a) (b) 

Figure 19. Three antenna patterns. Multipath clutter (a), and median of patterns (b). 
42

7. FREQUENCY TOLERANCE AND TUNABILITY 

7.1 Introduction

The RSEC [1, Chapter 5] specifies a maximum allowable amount of unintentional change in the 

operating frequencies of radar transmitters in Groups B, C, and D. This is called “frequency 

tolerance.” The actual amount of unintentional change in radar transmitter frequency is defined 

as “frequency drift.” RSEC compliance requires that the measured frequency drift is not to 

exceed the frequency tolerance for the radar [1, Chapter 5]. 

Frequency drift, as defined here, is an unintentional change in the average radar transmitter 

frequency, relative to the desired frequency, over a period of time that is long compared to the 

pulse repetition interval. It does not include the effects of transmitter tube frequency pulling, 

intentional frequency modulation, or frequency hopping. For purposes of determining RSEC 

compliance, it is measured in parts per million (ppm) of the desired operating frequency. For 

example, a tolerance of 800 ppm for a radar operating at 2800 MHz would be: 

 

800 10 2800 10 24.2

6 6

⋅ ⋅ ⋅ =

− MHz. 

7.2 Setup for Measurement of Drift in Operating Frequency

This measurement is performed with a spectrum analyzer that is coupled to the radar either 

through a hardline connection (i.e., through the radar’s directional coupler, if one is available) or 

else via a radiated signal. Whichever configuration is used for this measurement, Appendix B 

describes the procedure for setting external RF attenuation prior to the start of the measurement. 

If measurements are to be performed in a radiated mode, then Appendix E should be consulted 

for guidance on the positioning of the measurement system relative to the radar.

With attenuation both outside and inside the spectrum analyzer adjusted as specified in 

Appendix B, the remaining spectrum analyzer settings are configured as follows: 

Table 3. Spectrum Analyzer Parameter Settings for Measurement of Frequency Drift. 

Spectrum analyzer 

parameter 

Value for parameter setting. 

Center frequency Set to any one of the radar’s nominal operating frequencies. 

Frequency span For non-chirped radars, set three to five times wider than the value

of Bm specified for the radar in Table 2. For chirped radars, the 

frequency span is set three to five times wider than the chirp width 

of the radar. 

Detection mode Positive peak. 

IF (resolution) 

bandwidth 

For non-chirped radars, set between 1/10 to 1/3 of the value of Bm

specified for the radar in Table 2. 

Video bandwidth Equal to or greater than the value of the analyzer’s IF (resolution) 

bandwidth. 

Data trace mode Refresh (clear-write) continuously. 
43

For example, suppose a simple pulsed radar has a fundamental frequency of 9500 MHz and a 

pulse width of 50 ns. The nominal necessary bandwidth of the radar is (1/50 ns) = 20 MHz. Then 

the spectrum analyzer center frequency would therefore be tuned to 9500 MHz, with a frequency 

span of 60–100 MHz. The IF (resolution) bandwidth would be set anywhere from 2–7 MHz. 

7.3 Measurement of Frequency Drift 

With the spectrum analyzer configured as described in Table 3, and with the analyzer sweeping 

repetitively across the spectrum range of interest, the radar activity should be observed on the 

analyzer display on the channel that has been selected for the measurement. The spectrum 

analyzer center frequency, reference level, or attenuation level may need to be adjusted slightly 

to center the display on the radar activity on the selected frequency. 

With these adjustments accomplished, the spectrum analyzer data trace mode is put into a 

maximum-hold configuration. Within a few seconds, the peak emission envelope of the radar 

emission on the frequency of interest will fill in a smooth curve. This curve is recorded, either 

electronically or via a photographic image of the instrument display. 

With that operation completed, the trace should be frozen so that no further updates can occur. 

Without changing any spectrum analyzer settings, a second trace is started in an update 

(clear-write) mode, and is then placed into a maximum-hold mode. This second trace will at first 

exactly overlie the first trace. But over an interval of minutes or hours, the envelope may be 

observed to drift relative to the first trace. The frequency change observed over the measurement 

time period is the drift. 

The second trace is recorded to document the drift. Screen cursor functions may be used to most 

easily assess the absolute amount of drift. To determine relative drift in parts per million (ppm), 

divide the absolute drift by the nominal operating frequency (keeping the frequency units the 

same for both the numerator and the denominator in the fraction) and multiply by 106. The 

resulting value is compared to the allowed tolerance listed in the RSEC [1, Chapter 5]. 

7.4 Radar Tunability 

As noted in the RSEC [1, Chapter 5], radar tunability verification is left to the agency that 

controls any given radar. But the technique provided here for observing radar frequency drift can 

also be used to check tunability at any given desired frequency.

7.5 Sample Data and Calculations 

Suppose that a radar operates at 9500 MHz on the first spectrum analyzer trace (taken at the 

beginning of the measurement). After half an hour, the envelope of the second spectrum analyzer 

trace has shifted down in frequency by 11.5 MHz relative to the envelope of the first trace. 

Relative drift is computed as (–11.5/9500)•106 = –1210 ppm.
44

8. RSEC RADAR RECEIVER PARAMETERS 

8.1 Introduction 

RSEC receiver parameter measurements include selectivity, receiver image and spurious 

response, and receiver local oscillator radiation. These parameters are addressed in this section. 

Radar receiver characteristics affect the efficiency with which any given radar system can share 

spectrum with other radars and with non-radar systems. Characterization of receiver parameters 

is thus part of the RSEC. 

8.2 Selectivity

The RSEC specifies characteristics for “overall receiver selectivity” [1, §5.5]. This is meant to 

include all components that might affect the shape of the bandpass of the radar receiver, from the 

antenna to the final display of data output. In many cases, the receiver selectivity of a radar is 

essentially synonymous with the selectivity of the IF section. This is because the RF bandpass 

width is usually at least ten times wider than the IF bandpass and thus has a negligible effect on 

the overall selectivity of the receiver. 

This does not mean that the RF bandpass selectivity is of no concern to spectrum managers. The 

less selective (wider) an RF front end section is, the more vulnerable it is to both unintentional 

and intentional jamming by strong signals that are off-tuned from the radar receiver’s nominal 

operating frequency or frequencies. 

NTIA recognizes that, in the interest of higher spectrum efficiency, it is desirable that every 

radar RF front end should at least be bandpass filtered for the operational band of each radar. 

Even better, from a spectrum efficiency point of view, is for each radar RF front end to be 

relatively narrowly bandpass filtered. If made necessary by frequency hopping modes, such 

bandpass filtering might need to be tunable. This capability can be effected through such 

technology as electronically tunable yttrium-iron-garnet (YIG) filters. 

Lack of RF selectivity is sometimes considered to be an inherent characteristic of 

distributed-array radar transmitter-receiver (T/R) systems, such as arrays of solid state T/R 

modules. But from the standpoint of improved spectrum management practices, inclusion of YIG

(or other technically feasible) filtering is desirable in the T/R modules of distributed-array 

systems, at least in the operational band of each radar. 
45

8.2.1 Receiver IF Selectivity Measurement Overview 

The receiver selectivity is required to be “commensurate with” (taken to mean “approximately 

equal to”) the transmitter bandwidth. In the case of radars belonging to Group B, the term 

“commensurate with or narrower” is used. In the case of radars belonging to Groups C and D, it 

is also required that a change in pulse width be associated with a corresponding change in 

receiver bandwidth. 

Since the receiver response is usually approximately that of the IF section, the procedures 

described here are designed to check the receiver’s IF bandwidth at the 3 dB, 20 dB, 40 dB, and 

60 dB points. 

Receiver selectivity is measured on a test frequency (or frequencies) near the midpoint of the 

radar operating frequency band. If more than one receiver bandwidth is available (either for 

multiple pulse widths or for multiple radar signal processing modes), then all available radar 

receiver bandwidths will be measured. The exact receiver input and output test points are not 

specified and will vary between equipment types. But at a minimum the IF bandpass (or its 

equivalent in digital processors) must be included between the input and output test points. 

In many cases it will be necessary to disable or bypass electronic gain controls that normally 

attenuate returns from objects with large cross sections. In the case of advanced radars, it may be 

necessary to treat the entire radar as a black box for the purpose of bandwidth determination, as 

described below. 

8.2.2 Swept CW IF Selectivity Measurement

If an output is available for the receiver IF section, then its bandwidth can be determined by 

injecting a CW signal and assessing the response at the output as the input signal frequency is 

changed. 

This measurement is nominally performed as shown in Figure 20. The exact configuration used 

will be determined by the radar block diagram and design. Desirable test conditions are for the 

radar to operate in a mode that satisfies the following conditions: 

a) operation with constant gain (AGC fixed); 

b) operation at a constant frequency; 

c) identical amplitude for pulsed and CW signals; 

d) available test points that are accessible, as shown in Figure 20. 
46

Figure 20. Block diagram for receiver IF selectivity measurement. 

The above conditions are usually not met by radars in their normal operational modes. But these 

conditions can often be met by carefully selecting test points (sometimes requiring resoldering of 

circuit cards). The requirements can also often be met in newer radars by changing radar control 

software or using special diagnostic software. Such access to either circuit cards or software will 

require the assistance of specially trained and knowledgeable technicians or radar engineers. 

With regard to the fourth criterion listed above, some radars perform special diagnostics for 

internal and external noise assessment during a portion of the nominal interpulse interval. For 

these radars, a CW signal injection can effectively ruin the internal calibration and ultimately 

halt radar operation; in this case the test signals must be injected as pulses (preferably about ten 

times longer than the radar nominal pulses) rather than as CW energy. 

Regarding sensitivity time control (STC) most radars use this feature or something similar to it to 

compensate for the strongest target returns. Under normal operating conditions, these radars have 

a rapidly changing gain. If the STC is produced at a single point within the radar circuitry, then 

the gain change can be negated by injecting the test signal after that critical point on the block 

diagram. But if the STC is produced in multiple circuits spread throughout the radar receiver, it 

may be necessary to turn off the STC. This may require the assistance of software specialists for 

advanced radar designs. 

Similarly, with regard to maintaining operation on a single frequency during operation, it may be 

necessary to suspend frequency hopping and other diversity modes in the radar’s operation. This 

may be controllable at an operator’s station, or it may require the assistance of software 

specialists for some advanced radar designs. Alternatively, the test signal may be injected 

following the mixer (where the radar operates at a constant frequency). 

Although this measurement is usually best performed by injecting a test signal at the RF input to 

the radar receiver, it may be easier with some radar receivers to inject a test signal at the IF input. 

This is normally acceptable because, as noted above, the overall receiver selectivity of most 

radars is essentially identical to the IF selectivity. 
47

Whichever injection point (RF or IF) is selected for the test signal injection, the following 

procedure is applicable. For injection at the IF, the signal generator is tuned to the frequency of 

the IF amplifier immediately following the first mixer. For RF signal injection the signal 

generator of Figure 20 will be set to one of the radar’s operational frequencies and a coupler 

needs to be available at the RF front end. 

A spectrum analyzer is connected to the IF output, so that as much of the IF selectivity as 

possible is included in the test path. The radar transmitter may be turned on or off, but in either 

case tests should be made to determine that the RF and IF stages are operating normally. (Only 

the IF stages are important if the test signal is injected at the IF.) If automatic gain control (AGC) 

causes receiver gain to change with a test signal, it may be necessary to modulate the test signal 

with a duty cycle similar to the normal PRF and a pulse width about ten times longer than the 

transmitted pulses. As noted above, this expedient is also necessary for advanced radar designs 

that assess noise levels and perform self-calibrations during selected interpulse intervals. The 

spectrum analyzer display will develop to look like Figure 21. With all radar and test 

instrumentation connected together, the test procedure is performed as follows. 

Figure 21. Receiver selectivity measurement as it will develop on a spectrum analyzer screen 

display. 

1) Tune the spectrum analyzer to the IF frequency. Set the analyzer frequency span to about 10-

100 times the nominal radar IF bandwidth. Set the analyzer resolution (IF) bandwidth to about 

0.1 times the nominal radar IF bandwidth and detection is set to peak. System noise through the 

IF amplifier will cause a broad noise peak to appear at the IF frequency. The analyzer frequency 

display should be centered on this peak. 
48

2) Manually adjust the signal generator frequency and amplitude so that the signal appears at the 

center of the spectrum analyzer display with an amplitude about 10 dB higher than the noise. 

Adjust the spectrum analyzer reference level so that the maximum level of the signal response 

touches a horizontal display graticule, which will be called the reference level. Note the signal 

generator amplitude for the reference level. 

3) Increase the signal generator amplitude by 60 dB. Tune the signal generator higher in 

frequency until the amplitude of the signal displayed on the spectrum analyzer equals the 

reference level established in Step (2) above. Increase the spectrum analyzer span if necessary to 

display this frequency. Note the new frequency and use the spectrum analyzer frequency delta 

function to verify the new frequency. Repeat this process by decreasing the frequency of the 

signal generator until the same effect is achieved on the low side of the center frequency, and 

note that frequency as well. The difference between the high and low frequencies is the 

approximate 60 dB bandwidth of the radar. 

4) Repeat Steps (2) and (3) to determine the 40 dB, 20 dB, and 3 dB bandwidths of the radar 

receiver. The only difference is that, each time Step (3) is performed, the signal generator must 

be set to the level relative to the reference that corresponds to the bandwidth that is to be 

assessed (40 dB for the 40 dB bandwidth, etc.). The spectrum analyzer frequency span may need 

to be periodically readjusted to keep the frequency delta values easily measurable and readable. 

8.2.3 Receiver Selectivity Measurement Methods for Advanced Radars 

There are a variety of methods for measuring the receiver selectivity that are closely related to 

the procedure outlined above. A very convenient method is to replace the manually controlled 

signal generator with a tracking generator that is linked to the spectrum analyzer. This method 

has the advantage of enabling the entire bandpass characteristic to be recorded as a single trace 

on the spectrum analyzer. The major disadvantage of this method is that it cannot be used to 

measure many IF amplifiers that are designed to saturate before the 60 dB signal is injected. 

For advanced radars that do not have necessary internal inputs and outputs available, and to 

achieve a more accurate result in general, the test signal may need to be injected at the radar RF. 

This approach will require that radar frequency agility, STC, and AGC all be disabled, or else 

that the test signal be injected as pulses that are synchronized with internal radar trigger pulses. 

For the most advanced radars, in which the entire system must be treated as a black box, the 

following procedure can be used. In this approach, a simulated target (or set of targets) is 

produced at the radar RF front end, and the target frequencies are progressively off-tuned from 

the center frequency at progressively higher amplitudes, those amplitude levels being adjusted to 

make the targets barely visible on the plan position indicator (PPI) for any given amount of 

frequency off-tuning. The radar receiver selectivity is estimated from the combinations of 

measured frequency offsets and corresponding increases in amplitudes that are required to keep 

the targets visible. 
49

1) Radar targets are produced with a signal generator that generates pulses at a nominal radar 

center operating frequency with pulse widths approximately equal to the radar pulse width. The 

output is the radar plan position indicator (PPI) display. For convenience, the simulated targets 

should be generated in synchronicity with the radar trigger pulses so as to produce a ring of 

targets around the center of the PPI as the radar scans progress. 

2) The amplitude of the injected pulses is at first made high enough to clearly identify the pulses 

as targets on the PPI display. Then the amplitude of the pulses is reduced to a level at which the 

target indications reach the threshold. The output level of the pulse generator is noted as a 

reference. 

3) The pulse amplitude is increased by 3 dB relative to the reference level and the frequency of 

the pulse generator is gradually off-tuned, either to higher or lower frequency, until the targets 

again nearly disappear. Then the process is repeated with the signal off-tuned in the opposite 

direction. The total frequency shift is noted as the 3 dB bandwidth of the radar receiver. 

4) The preceding step is repeated for pulses at amplitudes increased by 20 dB, 40 dB, and 60 dB 

relative to the reference level. At each amplitude, the frequency is shifted both upward and 

downward to the limits at which the targets just disappear, the limit at which the corresponding 

total delta frequency shifts are the corresponding bandwidths of the receiver. 

8.3 Receiver Image and Spurious Response 

This test determines the response of the radar receiver to signals of frequencies far removed from 

the nominal radar receiver frequency. These responses are divided into the response of the IF 

image frequency (called the image response) and the rest of the responses (called spurious 

responses). These responses are defined relative to the radar receiver response to a signal at the 

radar receiver tuned frequency. The responses are measured in terms of decibels below the 

desired response, or simply as decibel suppression. This test only applies to the receiver IF and 

RF characteristics; signal processing rejection is not included. 

For radar receivers in RSEC Group B, image responses have no specified limit and all spurious 

responses are to be suppressed at least 50 dB. For radar receivers in Groups C and D, the image 

response shall be suppressed at least 50 dB and all spurious responses are to be suppressed at 

least 60 dB. 

Radar receiver spurious and image responses are measured by injecting a test signal as shown in 

Figure 22. The receiver shall be tested to the lower frequency limits shown in Table 4. The 

receiver will be tested to the upper frequency limits shown in Table 5. 
50

Figure 22. Block diagram for receiver spurious response measurement. 

Table 4. Lower Frequency Limits for Radar Receiver Spurious and Image Response Testing 

Type of connection 

between radar 

transmitter and 

antenna 

Minimum frequency to be tested 

coaxial the lesser of 0.5 F0 or Fbase, where Fbase is the lowest frequency 

used in a frequency multiplying or frequency synthesizing 

method of generating F0

waveguide the greater of 0.5 F0 or 0.9 Fcutoff, where Fcutoff is the waveguide 

cutoff frequency 

Table 5. Upper Frequency Limits for Radar Receiver Spurious and Image Response Testing 

F0, GHz Maximum frequency to be tested 

0 to 2 10 F0 or 10 GHz, whichever is less 

2 to 5 5 F0 or 18 GHz, whichever is less 

5 to 12 4 F0 or 26 GHz, whichever is less 

12 to 40 3 F0 or 40 GHz, whichever is less 

Measurements made in waveguide systems at frequencies above the the normal operating range 

of the waveguide (e.g., harmonics of a signal) are likely to be very difficult and may ultimately 

become impractical for any degree of desired accuracy in the outcome. If such a frequency has 

been reached in the course of testing that it becomes obvious that the coupling loss factors 

through the waveguide components are extremely high, then it may be assumed that spurious 

response is no longer of concern because only a small fraction of incident energy at such 

frequencies would ever be able to reach the radar receiver from the outside world. 
51

The test is performed as follows: A pulsed RF signal is injected into the radar receiver at 

frequencies relatively far away from the radar operating frequency. The selection of a point in 

the signal path to inject the test signal should be made as close to the radar antenna as is 

convenient. 

For advanced radar designs in which no coupler may be available after the antenna, it may be 

necessary to couple directly into a front-end RF amplifier with a coaxial hardline from the test 

instrumentation (as in some types of radars with solid state front end arrays) or else to radiate 

into the radar from a distance. In this case, the reference response to the injected signals must be 

determined relative to the level coupled in at a nominal value of (one of) the radar’s fundamental 

frequencies, F0. 

If the test signal is internally connected, the test point should be chosen so that any bandpass 

filters are in the signal path, but it is critical to avoid damage to the test equipment that could be 

caused by exposure to the radar transmitter output. If an RF filter is used in a signal path shared 

by the transmitted and received signal, then it may be necessary to turn off the transmitter while 

this measurement is in progress. For some advanced radar designs in which such deactivation 

may not be possible, then the option of performing the test via radiated signals, as outlined 

above, may need to be exercised. 

A detector and oscilloscope are connected at the output of the IF section to identify responses 

caused by the input test signal. If possible, the oscilloscope is adjusted so that the test pulse 

appears at a steady point on the scope display; the radar trigger pulse, if available, can be used 

for this purpose. 

The test signal is produced by a signal generator (or a combination of signal generators) which 

covers the required frequency test range. The signal generator is modulated with a pulse of 

duration that is comparable to the nominal pulse width of the radar. The test pulses must be 

synchronized to the radar operation with a delay such that they are placed within the time 

window of maximum receiver sensitivity. For advanced radars that are being assessed via 

radiated pulses, the pulses will have to be transmitted without synchronization but at a high 

enough rate to ensure that some of them always fall within this time window. 

The same trigger pulse is used to synchronize the oscilloscope display to the pulse generation. 

For advanced radars being tested radiatively, the pulses cannot be synchronized and they have to 

be distinguished by using a somewhat different pulse width than the radar generates. Frequencyhopping radars are tested on a single frequency at a time. Chirp radars are tested with a CW 

signal. 

Expected image and spurious response frequencies can be calculated as follows: 

q

p F F

F

LO IF

spurious

( ⋅ ± )

=
52

where p and q are integers (1, 2, 3, ...); FLO is the local oscillator frequency; and FIF is the 

frequency of the first IF. These frequencies should be calculated for all values of p and q up to 10 

or until Fspurious is out of the frequency range of Tables 4 and 5. The receiver should be tested at 

these frequencies with special care when the frequencies are encountered in the next several test 

steps, since spurious responses are possible at these frequencies. Signals at frequencies 

associated with low values of p + q equal to three or less are especially likely to produce 

responses when they fall within the normal operating range of the radar. 

To conduct the test, the following steps are performed: 

1) The radar is tuned to a frequency near the lower edge of the operating band. The pulse 

modulator is adjusted to give a duty cycle of 100% (CW). The signal generator is tuned to the 

radar operating frequency and the signal generator is set to deliver a reference level (nominally 

0 dBm, but other values can be used) to the receiver. Whatever the reference level that is used, 

the signal generator(s) settings must be determined that will generate this level at every 

frequency that is to be tested; approximately twenty frequencies may need to be checked across 

this range to determine the signal generator settings required to achieve this result at each 

frequency. 

2) The signal generator is tuned to the radar operating frequency and the signal is injected. The 

level needs to be high enough to produce an observable effect on the oscilloscope. The pulse 

modulator is adjusted to produce pulses with approximately the same duration and PRF as those 

under test. (But for radiated tests, the pulse width and PRF need to be slightly different from the 

radars’, so that they can be distinguished.) If possible, the pulse modulator is synchronized to the 

pulse trigger of the radar. The signal amplitude is kept below the saturation point of the IF 

amplifier(s). The displayed amplitude of the pulses on the oscilloscope display is noted as a 

reference level. 

3) The signal generator level is increased by 60 dB (for a Group B radar) or 70 dB (for Group C 

and D radars). The signal is tuned above the radar receiver frequency by about ten times the 

bandwidth of the radar receiver. The nominal 60 dB or 70 dB level adjustment will probably 

need to be corrected slightly, using the values determined in Step (1). The oscilloscope is 

monitored constantly for any signals that occur above the reference level. If any such signals are 

observed, the signal generator frequencies that produce such responses are noted as the work 

progresses. 

Steps 1 through 3 are continued until the entire operational frequency range of the radar has been 

tested. 

4) For each frequency on the list generated in Step (3), the suppression is measured. This is 

accomplished by tuning back to each of these frequencies and then adjusting the signal generator 

output level until the level displayed on the oscilloscope is equal to the original reference level. 

The power level required to produce this level is noted at each of these frequencies. The 

difference between the nominal signal generator output level originally used and this new level 

required at each spurious response frequency is the suppression at each of those frequencies. Any 

suppressions smaller than the RSEC requirements should be noted in the test report. 
53

8.4 Receiver Local Oscillator (LO) Radiation Measurement 

[At the time of this report’s writing, the TSC is considering eliminating LO radiation from the 

RSEC.] 

Figure 23 shows the instrumentation required for this measurement. The same receiver input 

point should be selected as for the spurious response measurement (above). The need for a power 

meter will be obviated if the signal generator output is accurately calibrated. 

Figure 23. Block diagram for local oscillator radiation measurement. 

The measurement procedure is as follows. First connect the equipment as shown in Figure 23. 

The spectrum analyzer may be set at a nominal frequency span of 100 MHz with center 

frequency tuned to the radar local oscillator frequency, an IF bandwidth of about 100 kHz 

selected, and a sweep time of about 100 ms selected. 

Next, tune the radar to an operating frequency near the lower edge of the operating frequency 

band and center the spectrum analyzer display at the nominal LO frequency. (The spectrum 

analyzer and cable combination may be calibrated by disconnecting the test cable from the 
54

receiver input and applying a –40 dBm signal at the LO frequency to the receiver end of the 

cable.) 

With the test cable reconnected to the receiver input port, tune the spectrum analyzer to the LO 

frequency and use the calibration derived in the step above to calculate the LO emission referred 

to the receiver input. 

Finally, repeat all the steps above with the radar tuned to the mid-band and the upper edge of the 

operating band. 

8.4.1 LO Radiation Considerations for Advanced Radars 

Local oscillator radiation is probably becoming an anachronistic concern for most modern 

radars, inasmuch as local oscillators are disappearing as a design element in most modern radar 

designs. To the extent that LO’s are still incorporated into radar designs, radiation from these 

elements has not been found to be a significant concern. 
55

9. REFERENCES 

[1] Manual of Regulations and Procedures for Federal Radio Frequency Management, May 

2003, Revisions September 2004, NTIA Office of Spectrum Management, U.S. 

Government Printing Office, Stock No. 903-008-00000-8. 

[2] J.J. Sell, coordinator, “Measurement procedures for the radar spectrum engineering 

criteria,” NTIA Report 84-157, Aug. 1984. 

[3] R.J. Matheson, J.D. Smilley, G.D. Falcon, and V.S. Lawrence, “Output tube emission 

characteristics of operational radars,” NTIA Report 82-92, Jan. 1982. 

[4] William A. Kissick , Ed., “The temporal and spectral characteristics of ultrawideband 

signals,” NTIA Report 01-383, Jan. 2001. 
56
57

APPENDIX A: DEFINITIONS 

For purposes of spectrum management, boundaries within emission spectra are defined by NTIA. 

These are necessary bandwidth, out-of-band emissions, spurious emissions and unwanted 

emissions. They are shown in Table A-1. 

A.1 Spectrum Regions 

Table A-1. Definitions of Spectrum Regions and Related Terms, from Chapter 6 of [1]. 

Term Definition 

Necessary 

bandwidth 

For a given class of emission, the width of the frequency band which is 

just sufficient to ensure the transmission of information at the rate and 

with the quality required under specified conditions. Necessary 

bandwidths for radars as a function of emission type are provided in 

Annex J of [1]. 

Out-of-band 

emissions 

Emission on a frequency or frequencies immediately outside the 

necessary bandwidth which results from the modulation process, but 

excluding spurious emission. 

Spurious emissions Emission on a frequency or frequencies which are outside the necessary 

bandwidth and the level of which may be reduced without affecting the 

corresponding transmission of information. Spurious emissions include 

harmonic emissions, parasitic emissions, intermodulation products and 

frequency conversion products, but exclude out-of-band emissions. 

Unwanted 

emissions 

These consist of spurious emissions and out-of-band emissions. 

For radars, the necessary bandwidth is defined in Annex J of [1]. It is determined at a point that 

is 20 dB below the peak envelope of the spectrum. 

A.2 Frequency Tolerance 

The maximum permissible departure by the center frequency of the frequency band occupied by 

an emission from the assigned frequency or, by the characteristic frequency of an emission from 

the reference frequency. The frequency tolerance is expressed in parts per million (ie., in hertz 

per megahertz). For example, a tolerance of 800 ppm at a frequency of 1000 MHz would be 

800 kHz. 
58

APPENDIX B: ENSURING ADEQUATE MEASUREMENT SYSTEM INPUT 

ATTENUATION FOR RSEC MEASUREMENTS 

Radar transmitters commonly produce peak power levels of +90 dBm or more at the transmitter 

output. Peak EIRP levels radiated into space may be 30 dB higher, on the order of +120 dBm. It 

is important to ensure that the maximum allowable input level to spectrum analyzers and other 

measurement instrumentation is not exceeded by the radar peak output level. 

Maximum allowable input power levels are specified by equipment manufacturers for their 

equipment. The maximum allowable peak level is often higher than the maximum allowable 

average level. For spectrum analyzers, the maximum allowable average level is typically about 

+30 dBm, but the maximum allowable peak level is sometimes not specified by the manufacturer 

for these devices. In that case, the maximum allowable average level should not be exceeded. It 

is usually also important to keep input signal levels within the linear, calibrated response range 

of measurement devices. 

B.1 Hardline Coupling to a Radar Transmitter 

For hardline-coupled measurements, some attenuation will likely be required between the 

directional coupler output and the measurement device input (see Figure 1). Referring to this 

diagram, the minimum decibel amount of attenuation, A, required will be: 

 Aext = Pp − Lc − Ain − Pm

 (B-1) 

where 

Aext = external attenuation (dB) as shown in Figure 1 

Pp = peak power produced by the radar transmitter (dBm) 

Lc = loss through the coupler (dB) 

Ain = attenuation provided internally at the measurement device front end input (dB) 

Pm = maximum input power to measurement instrument after input attenuator (dBm).

For example, if the radar transmitter produces 1 MW (+90 dBm) peak power, if the directional 

coupler output is 20 dB lower than that value, and if the maximum permissible signal allowed at 

the spectrum analyzer input is +10 dBm with 50 dB of internal spectrum analyzer attenuation 

invoked at the front end, then the amount of attenuation that needs to be inserted between the 

coupler output and the spectrum analyzer input is 

(90–20–50–10) = 10 dB. 

In this case, even with 50 dB of RF attenuation invoked in the instrument’s front end, an 

additional 10 dB of external RF attenuation is required between the directional coupler and the 

measurement device input. 
59

B.2 Radiated Coupling to a Radar Transmitter 

All the caveats regarding maximum allowable input power levels and optimal linear response 

and calibration range for measurement instrumentation, as described in section B.1 above, also 

apply to the case of radiative coupling between the measurement system and the radar 

transmitter. Here, the external attenuation, Aext, is inserted between the measurement antenna 

output connector and the measurement device (e.g., spectrum analyzer) input port. The 

difference is that the term for peak power at the measurement system antenna output connector, 

Pr, is [4, Appendix C]: 

 (B-2) 

where 

Pr = peak power at the measurement system antenna output connector (dBm); 

Pp = peak power produced by the radar transmitter (dBm); 

Gt = radar transmitter antenna gain (dBi); 

Gr = measurement system antenna gain (dBi); 

f = measurement frequency (MHz); 

r = distance between radar antenna and measurement antenna (meters). 

The variable Pr takes the place of Pp in Eq. B-1, and the value for the external attenuation, Aext, 

becomes: 

Aext = Pr − Ain − Pm (B-3) 

where all variables are as defined for Eq. B-1. 

For example, suppose a radar transmitter operates at 2800 MHz; that the transmitter produces 

1 MW peak power (+90 dBm); that the transmitter antenna gain is +35 dBi; that the 

measurement system antenna gain is +25 dBi; that the measurement system is positioned 

0.5 miles (0.8 km, or 800 m) from the radar; that the maximum allowable peak power to be 

coupled into the measurement system is +30 dBm; and that 50 dB of RF attenuation is to be 

invoked within the measurement instrument RF front end. Then from Eq. B-2, 

Pr = 90+35+25+27.6–20log(2800)–20log(800) = +50.6 dBm 

And from Eq. B-3, 

Aext = 50–50–30 = –30 dB. 

The negative sign in the answer means that the signal coupled past the measurement instrument 

RF front end will actually be 30 dB below the maximum allowable limit of +30 dBm for this 

situation. No external attenuation is needed in this case. 

P P G G ( f ) (r) r p t r = + + + 27 6. − 20log − 20log
60

On the other hand, if the goal is to limit the peak power level that couples into the measurement 

instrument beyond its own RF front end attenuation to a value of –20 dBm or less, then 

Aext = 50–50–(–20) = 20 dB. 

So in this case 20 dB of external attenuation would need to be inserted between the measurement 

antenna output connector and the input port of the measurement device. 
61

APPENDIX C: RSEC MEASUREMENT SYSTEM ARCHITECTURE AND 

ALGORITHMS 

C.1 Hardware Requirements 

For spectrum measurements and antenna pattern characterization, a general-purpose RSEC 

measurement capability requires that the measurement system hardware have the following 

capabilities: 

1) RF tuning across as much as several gigahertz above and below the radar fundamental. 

The exact amount of tuning capability will depend upon how extensive the radar’s spurious 

emissions are. 

2) Instantaneous measurement dynamic range of about 60 dB. This dynamic range can be 

extended to as much as 120 dB through the use of a measurement algorithm described 

below. Note that approximately 90 dB total dynamic range is required for many RSEC 

spectrum emission compliance measurements. 

3) Measurement system bandwidth as specified in Table 2. 

4) Peak detection. 

5) Low noise figure, usually no higher than 10 dB. 

6) The ability to substantially reject radar fundamental-frequency energy when the system 

is tuned to unwanted emission frequencies. In practice, this amounts to using effective 

bandpass filtering (60-70 dB rejection outside the filter’s bandpass) that tracks the 

measurement system’s tuned frequency. Yttrium-iron-garnet (YIG) filters are a practical 

solution to this problem for frequencies between 0.5 GHz and 26 GHz. 

7) The incorporation of a variable RF attenuator. This attenuator is used to extend the

dynamic range of the measurement system. 

8) A constant-aperture receiving antenna with gain above isotropic on the order of 20–30 

dBi. In practice, a parabolic reflector antenna with a 1-m diameter is usually adequate. This 

antenna gain plays two roles: 

5. it allows the measurement system to observe low-level spurious emissions while 

 tending to reject energy from other radars in the vicinity of the measurement 

system 

6.it tends to reject energy from multipath propagation from the radar. 

9) A mounting arrangement that raises the receiving antenna to a height above ground of 

between 3 m and 10 m is highly desirable. This reduces the amount of multipath energy 

arriving at the antenna, while also providing a clear line-of-sight to the radar transmitter 

antenna in cluttered environments. A rooftop mount or a telescoping mast on a van are 

ideal. 
62

For pulse-characterization measurements, a general-purpose RSEC measurement capability 

requires that measurement system hardware have the following capabilities: 

1) Adequate bandwidth to measure 10%–90% rising edges and falling edges on radar 

pulses, assuming that this parameter needs to be directly characterized by the measurement 

system. Since these intervals may be as short as a few nanoseconds, a bandwidth of as 

much as 1 GHz may be required. This bandwidth should be a single-shot capability in an 

oscilloscope; repetitive sampling techniques that effectively increase a measurement 

system’s bandwidth may not be feasible for some radar pulse sequences. This requirement 

often means that the rising edge measurement will have to be performed on a hardline 

connection to a radar, through a wideband detector and a high-speed oscilloscope.16

2) To measure pulse widths, the measurement system only requires bandwidths as specified 

in Table 1. This measurement may be performed with a wideband detector and an 

oscilloscope connected directly to a hardline coupling on the radar. If such a coupling is not 

available, or if other factors do not allow for hardline-connected measurements, then this 

measurement may also be performed by receiving the radiated pulses with a spectrum 

analyzer and connecting an oscilloscope to the analyzer’s video output or (via a detector) an 

analyzer IF output. 

Figure C-1. Block diagram of the RF front end and associated hardware required for RSEC radar 

emission spectrum compliance measurements.

 

16 Most modern oscilloscopes can record data to either an internal disk, an external

computer via a data link, or a universal serial bus (USB) port connected to an external memory 

unit. 
63

Figure C-2. Block diagram of the RF front end and associated hardware required for RSEC radar 

emission spectrum compliance measurements on high frequency (HF) radars operating below 

about 50 MHz.

C.1.1 Radiofrequency (RF) Front-end Design 

The necessary RF front end hardware and associated equipment required for an RSEC radar 

emission spectrum measurement is shown in Figures C-1 and C-2. The RSEC requirement to 

measure radar spurious emissions as low as 80 dB below the peak measured power at the 

fundamental has significant consequences for the design of the spectrum measurement system. 

The 80 dB limit effectively forces the measurement system to achieve at least 90 dB of dynamic 

range. In many measurement scenarios using a spectrum analyzer the measurement system has 

60 dB or less of total instantaneous dynamic range. The two primary factors that contribute to 

this condition are the available power from the emitter at the receiver and the sensitivity of the 

measurement system. The available power from the radar is fixed and the distance between the 

radar and the measurement system must exceed the far-field boundary, so something must be 

done to extend typical measurement system dynamic range by 30–50 dB or more. This usually 

necessitates the use of a low noise amplifier (LNA) in front of the spectrum analyzer’s input. But 

with the measurement system tuned to a frequency in the radar’s spurious emission spectrum, 

energy from the radar fundamental frequency (perhaps 80-90 dB higher than that being 
64

measured) will overload the LNA, driving down its gain and resulting in an uncalibrated 

measurement. 

The solution is to build an RF front end as shown in the block diagrams in Figures C-1 and C-2. 

In this design, received radar signals first pass through a variable attenuator. During a spectrum 

measurement, the attenuator setting is varied as a function of measurement frequency to keep the 

received signal level within the dynamic range of the rest of the measurement system. The 

maximum value of the attenuator should be equal to the difference between the dynamic range 

required for the RSEC measurement (90 dB) and the maximum instantaneous dynamic range of 

the rest of the measurement system (typically 60 dB). That is, the attenuator should go at least as 

high as 30–50 dB.17

The next stage in the RF front-end is a tunable bandpass filter that tracks the tuned frequency of 

the measurement system. This filter should have 60-70 dB of off-tuned rejection. As this filter 

rejects radar fundamental-frequency energy when the measurement system is tuned to the 

spurious spectrum, it prevents front-end overload of the next measurement stage: the LNA. In 

practice, NTIA/ITS engineers have found that yttrium-iron-garnet (YIG) filters effectively solve 

this measurement problem. 

The LNA is used to provide sufficient sensitivity to measure spurious emissions 90 dB below the 

measured peak power of the radar at the fundamental. LNA noise figure should generally be 

10 dB or less. LNA gain should be just high enough to overdrive the noise figure of the rest of 

the measurement system. For example, if the signal passes from the front-end box through an RF 

line to a spectrum analyzer input, then the following condition should be met by the LNA gain: 

 (C-1) 

where 

GLNA = LNA gain, dB 

NFSA = noise figure of spectrum analyzer, dB 

Lline = line loss between RF front-end and spectrum analyzer, dB 

NFLNA = noise figure of the LNA, dB. 

For example, if the spectrum analyzer noise figure18 is 25 dB, the line loss is 3 dB, and the LNA 

noise figure is 8 dB, then the ideal gain specification for the LNA would be (25 + 3 - 8) = 20 dB. 

 

17 NTIA/ITS measurement systems actually use attenuators that go as high as 70 dB, in 

increments of 10 dB. This provides 110–120 dB dynamic measurement range for these 

measurement systems. A dynamic range of 110 to 120 dB may be required when conducting 

interference coupling mechanism measurements. 

18 Spectrum analyzer noise figure may be determined empirically as follows: With the RF 

input terminated, tune the analyzer to the frequency (or to sweep across the frequency range) 

where noise figure must be determined. Set spectrum analyzer input attenuation to zero. Set the 

IF bandwidth (sometimes called resolution bandwidth) to 1 MHz. Set the video bandwidth to 1 

kHz. Set detection to either average, sample, or peak (the selection doesn’t matter because of the 

GLNA = NF SA + Lline − NF LNA
65

Excessive gain in this stage does not improve system sensitivity or signal-to-noise ratio, but 

reduces system dynamic range; inadequate gain results in system noise figure exceeding that of 

the LNA. 

C.1.2 Additional Hardware 

In addition to the basic hardware already specified for RSEC measurements (spectrum analyzer; 

fast oscilloscope; optional discrete-component detector; RF front-end containing variable 

attenuation, tracking bandpass preselection, and low-noise preamplification; and 1-m parabolic 

reflector antenna with appropriate mount), some additional hardware may be highly desirable. 

NTIA/ITS engineers who perform spectrum measurements often utilize an omni antenna and pair 

it with a second spectrum analyzer as an auxiliary monitoring system. This auxiliary monitors 

the energy from the radar fundamental during the entire time that the spectrum is being 

measured. The purpose is to ensure that radar fundamental power does not vary during the 

measurement.19

C.2 Software Requirements 

NTIA/ITS engineers have found that all measurements associated with the RSEC can be greatly 

augmented in terms of speed, efficiency, reliability, and accuracy through the use of software to 

control measurement equipment and to record data. And for the spectrum measurement portion 

of RSEC testing, software is a virtual necessity. 

Unfortunately, as of the time that this report is being written, no software for RSEC 

measurement control or data recording has ever been commercially produced. NTIA/ITS 

engineers have developed all of the software described here. The software that they have written 

is not proprietary, but currently works with only a limited set of commercially available 

hardware and a custom-built RF front-end box. 

The measurement system software is used to perform the following tasks: 

 1) Perform measurement system calibrations and store the results; 

 

narrowness of the video filter compared to the IF filter). Observe the level of the noise trace. 

Subtract -114 dBm from this level. The result is the noise figure of the spectrum analyzer. 

19 Although radar fundamental power is nominally very stable, it can happen that radar

modes are changed without warning during a measurement, leading to a change in radiated 

power. Furthermore, radars having a nominally fixed center frequency are sometimes switched to 

another frequency without warning during a measurement. And, in cases in which a radar 

antenna has been aimed directly at the measurement system (“boresighted”), the radar antenna 

sometimes drifts in azimuth during the measurement. Without an auxiliary monitoring system to 

watch for these sorts of changes in the radar transmitter’s behavior, much time can be wasted on 

a useless measurement. 
66

2) Perform automated radar emission spectrum measurements, correct results from 

 calibration tables, and store the results; 

3) Store results from manually operated instrumentation during other RSEC measurements, 

 including antenna patterns and pulse parameters.

C.2.1 Stepped Measurement Algorithm 

If there is a single key to the acquisition of radar emission spectra suitable for RSEC compliance 

verification, it is the combination of the RF front-end design (Section 4.2.1 and this appendix) 

and the software implementation of the specialized algorithm described in this section. Without 

this hardware-software combination, a broadband, wide-dynamic range radar spectrum 

measurement is not practical. With this combination, the radar spectrum measurement becomes 

relatively easy, and very practical. 

The software solves two final problems with the radar spectrum measurement: (1) how to obtain 

the peak power from the radar beam every time it scans across the position of the measurement 

system; and (2) how to run the measurement with the proper amount of RF attenuation at each 

measured frequency.20

The key to solving these problems is to not sweep the measurement system’s tuned frequency 

during the measurement. Instead, the measurement system is always tuned to a single frequency 

at a time (that is, is operated with a frequency span of zero hertz). The spectrum analyzer is 

effectively made to operate like a slow-motion oscilloscope, but one with an RF tuner installed. 

This process is called stepping. RSEC spectrum measurements cannot be performed in other than 

a stepped-measurement mode. 

The stepped-spectrum measurement algorithm operates as follows. At each measured frequency, 

the spectrum analyzer is tuned to a zero-hertz frequency span, and the sweep time is set to a 

value slightly longer than the beam-scanning period of the radar. For repetitively scanned radar 

beams, this is trivial: if an air traffic control radar, for example, has a 4.75 second rotation 

period, then the sweep time is set to 5 seconds. For radars with non-repetitive beam scanning 

periods, empirical observations at the measurement location will reveal the amount of time 

required to obtain peak values, as described further in Sections 8 and 9 of this report. Typically, 

no radar requires a sweep time exceeding one minute before the beam again scans across the 

measurement location. 

With the system fixed-tuned to the frequency that is to be measured, the RF attenuation can be 

verified to ensure that its value is appropriate to keep the radar peak power within the dynamic 

range of the measurement system. If it is not, then either the software or the operator adjusts RF 

 

20 The RF attenuation must be adjusted across the measured spectrum, so as to keep the 

received radar signal’s amplitude within the instantaneous dynamic range of the measurement 

system. For example, 70 dB attenuation may be required when tuned to the radar fundamental, 

30 dB may be required when tuned 100 MHz from the fundamental, and 0 dB may be required 

when tuned more than 300 MHz from the fundamental. 
67

attenuation appropriately. In practice, an experienced operator can adjust attenuation with a 

simple keyboard input on a frequency-by-frequency basis, with no delay to the speed of the 

overall measurement. Software adjustments may work by monitoring the radar signal level 

relative to measurement system noise and overload levels. 

Because the spectrum analyzer sweep time (the step interval, or dwell) has been set to exceed the 

beam-scanning interval of the radar, it is ensured that one or more (usually a series of twenty or 

more) maximum-power pulses will be recorded on the spectrum analyzer trace during the dwell 

period. Thus, the measurement system software need only retrieve the peak value from the 

spectrum analyzer trace at each step, correct it for calibration factors, and store it in order to 

complete the measurement of radar peak power at the frequency in question. 

Since each measured frequency takes one radar beam-scan interval, the amount of time required 

for the entire spectrum measurement is just the number of data points multiplied by the scanning 

interval of the radar. But how many points should be measured? There is no reason to measure 

points that are separated in frequency by less than the IF bandwidth of the measurement system, 

nor should the frequency interval between measured points greatly exceed this interval, lest 

significant behavior in the spectrum be missed. Thus, the interval between points should ideally 

be equal to the IF bandwidth of the measurement system. 

For example, an air-search radar with a 10-second rotation period and a 1-μs pulse width should 

ideally be measured with an 11 second dwell interval and a 1 MHz bandwidth, with 1 MHz 

between measured steps. It will require about 40 minutes to measure 200 MHz of this radar 

spectrum. As slow as this process may appear, NTIA/ITS engineers have found no faster or more 

effective method for measuring radar spectra for RSEC compliance. 

While this algorithm might in principle be implemented manually, it would be so tedious as to 

put the entire measurement at risk due to operator fatigue. It has been the experience of 

NTIA/ITS engineers that this algorithm needs to be implemented through software for control of 

the measurement system, automatic calibration corrections, and data recording.

C.2.2 Overall Measurement Algorithm and Flowchart 

The overall procedure for an RSEC measurement is provided here in the form of a flowchart and 

associated notes. This description is intended to provide a coherent overview of the interrelated 

steps and procedures that are individually described in greater detail elsewhere in this report. 

Figure C-3 contains the overall procedure flowchart. 
68

 

Figure C-3. RSEC measurement procedure flowchart. 

The following notes are numbered in correspondence with various steps in the measurement 

process portrayed in Figure C-3. 

(1) Find radar operating frequency or frequencies. The measurement system antenna is 

pointed approximately at the radar. The measurement system RF front end and spectrum 

analyzer (or any instrument used in place of a spectrum analyzer) is adjusted to sweep across the 

frequency range of the operational band of the radar. Measurement system parameters are 

nominally set as shown in Table C-1. 

With the measurement system thus adjusted, spectrum is swept repetitively across the radar 

band, and the peak radar emission spectrum envelope will gradually (but only partially) fill in 

over a period of a few minutes. The peak spectrum envelope will normally fill in sufficiently to 

approximately indicate all the fundamental frequencies that are being radiated by the radar. 
69

After these frequencies have been approximately identified in this manner, and have been noted 

by measurement personnel, then the measurement system is used to determine each of those 

frequencies with more precision. To do this, the measurement system is tuned to each 

approximately identified frequency on an individual basis. At each identified frequency, the 

measurement system is center-tuned to that frequency, and the frequency span range of the 

measurement system is set to 50 MHz. Then the measurement system data trace display mode is 

cleared and a new maximum-hold series of sweeps are undertaken. The result is a more detailed 

spectrum picture of each radar fundamental frequency. The final result of the measurement at 

each fundamental radar frequency is a maximum-hold data trace that shows the fundamental 

frequency with an accuracy of 1 MHz. The resulting set of frequencies is noted for later use in 

the measurement of the radar spectrum. 

Table C-1. Measurement System Parameters for Determination of Radar Fundamental Frequency 

or Frequencies. 

Measurement system parameter Parameter setting 

IF bandwidth 1 MHz 

Video bandwidth Equal to or greater than 1 MHz 

Detection mode Positive peak 

Frequency sweep range Operational band of the radar 

Frequency sweep rate Maximum allowed for the combination of 

measurement bandwidth and frequency sweep range

Trace display mode Maximum hold 

Front end attenuation Sufficient to prevent measurement system overload 

(adjusted empirically) 

(2) Optimize the measurement system antenna configuration. With the measurement system 

tuned to one of the radar fundamental frequencies, and with the measurement system bandwidth 

and detection modes set as described in Table C-1, the frequency sweep range should now be set 

to zero hertz, so that the measurement system is displaying a time-domain picture of the radar 

beam scanning pattern. Then, the measurement system sweep time should be adjusted to an 

amount of time that is substantially longer than a single radar beam-scan interval. For example, if 

the radar beam-scanning interval is 5 seconds, then the measurement system sweep time should 

be set to a value of perhaps 60 seconds. The data display trace mode should be set to refresh 

itself with each trace, rather than the maximum hold mode used earlier. 

With this done, the measurement system antenna pointing angle should be gradually adjusted in 

azimuth, while the maximum received power from the radar is observed at each repetition of the 

radar beam-scan. The process is continued until the azimuth angle that maximizes the measured 

power from the radar is identified; the measurement antenna azimuth is then locked at that 

position. Next, the measurement antenna elevation angle is gradually adjusted in the same 

manner as the azimuth was earlier adjusted, until the optimal elevation pointing angle is 

determined. The measurement antenna pointing angle has been optimized at this point in all 

dimensions, and the antenna should be locked into this position. 
70

Care needs to be taken during this pointing-angle process to ensure that the measurement antenna 

pointing angle is optimized on its main beam, and not on a sidelobe. To be sure of this, it is 

recommended that the measurement antenna pointing angle be varied enough during the 

adjustments to observe the measurement antenna sidelobes on either side of its main beam. 

With the optimal measurement antenna pointing angle fixed, the next step is to determine the 

polarization that optimizes received signal strength from the radar. This is done by measuring the 

radar emission with a variety of polarizations and observing the measured power at each 

polarization. Typical alternative polarizations available to measurement personnel in their 

antennas are: horizontal, vertical, left-hand circular, and right-hand circular. Polarization is 

typically varied by either operating a polarization switch on a measurement antenna feed 

assembly, or else by mechanically changing measurement antenna feeds. The measurement 

polarization setting that maximizes received power from the radar is used for the measurement, 

and should be noted by measurement personnel. 

(3) Check measurement system dynamic range and linearity. This step in the measurement 

process ensures that the measurement system distance from the radar is adequate to achieve a 

large enough dynamic range to check for RSEC compliance, and furthermore that the 

measurement system is not being overloaded by radar emissions. 

In general, the measurement needs to achieve a total dynamic range that is at least 10 dB more 

than the –X dB level of the RSEC spectrum envelope. For example, if the radar needs to meet an 

ultimate suppression level of –80 dB, then the total dynamic range that is needed in the 

measurement will be about 90 dB. 

A problem that is commonly encountered in wide-dynamic range measurements is overload of 

the measurement system due to the high field-strength environment in which the measurement 

system must be operated. Two types of overload may occur. One type may occur because the 

total measurement system RF front end attenuation is inadequate to keep the peak measured 

radar fundamental-frequency energy below the saturation point of the measurement system. The 

other type of overload is due to feed-through of radar energy directly into the measurement 

system amplifiers or detector, bypassing the measurement antenna and front end filtering. Prior 

to commencement of a spectrum measurement, these types of overload should be verified as not 

occurring. 

To perform all of these checks and verifications, the measurement system should first be tuned to 

whichever frequency was previously identified as producing the highest measured emission 

power level. The frequency span of the measurement system is set to zero hertz, with positive 

peak detection and the widest available measurement bandwidth selected. The sweep time should 

be set the same as it was for the adjustment of the antenna pointing angle (i.e., substantially 

longer than a single radar beam scanning interval). In this configuration, the maximum measured 

power from the radar transmitter is being monitored at one of the radar fundamental frequencies 

by the measurement system. 

RF attenuation in the measurement system RF front end should be adjusted to a high enough 

value to keep the maximum measured value from the radar well below the measurement system 
71

saturation level (1-dB compression point). If saturation does occur even when maximum RF 

attenuation is invoked, then the measurement system is too close to the radar and will need to be 

moved further away. 

If the measurement system is not saturated when maximum RF front end attenuation is invoked, 

then the next step is to check for feed-through: that is, radar energy feeding into the measurement 

system without passing through the measurement antenna. This is accomplished by 

disconnecting the measurement antenna and replacing it with a terminator. When this is done, the 

amount of energy feeding into the measurement system past the antenna will be observed on the 

data display trace. With the terminator in place instead of the antenna, the amount of power 

measured on the display should drop many tens of decibels, preferably 60 dB or more. If such a 

drop is not observed, then feed-through may be a serious problem for the measurement system. 

Further use of the approach of disconnecting measurement system components and terminating 

their input ports will allow determination of the location of the feed-through problem in the 

measurement system. 

If feed-through is a problem, then some part of the measurement system needs to be better 

isolated from the incident radar energy. This may be done in more than one way. One approach 

is to improve the shielding of the RF front end and/or the measurement system inside the 

measurement vehicle, depending upon where the radar energy is feeding into the measurement 

system. Implementation of this approach will likely involve a significant amount of time and 

engineering effort. 

Other, more ad hoc approaches may be implemented at field locations. If the feed-through 

problem is occurring in the RF front end, then the front end may be moved inside the shielded 

enclosure of the measurement system vehicle, although this may require a somewhat longer RF 

line connection from the measurement antenna to the front end input, with concomitantly higher 

overall measurement system noise figure. 

If the feed-through problem is occurring within equipment located inside the measurement 

vehicle, then it may be possible to eliminate the feed-through by moving the vehicle to a location 

behind a building or heavy foliage, and to extend the measurement antenna on a mast to a height 

above the building or foliage, while keeping the vehicle shielded behind the obstruction. 

(4) Does measurement system distance from radar need to be changed? If feed-through is 

occurring and none of the measures described above eliminates this problem, then the only 

remaining course of action is to move the measurement system to a larger distance from the 

radar, such that the threshold for feed-through coupling is no longer exceeded. 

If feed-through is not occurring, but the measured power level at the radar fundamental 

frequency exceeds the saturation point of the measurement system when all available front end 

RF attenuation has been invoked, then the measurement system must likewise be moved to a 

larger distance from the radar, until such saturation does not occur. 

If the measurement system is located at such a distance from the radar that the received power 

levels are too low to permit enough dynamic range in the measurement to determine compliance 
72

with the –X dB ultimate suppression level (e.g., if the –X dB level is –80 dB but the maximum 

power being received from the radar will only allow measurement of 70 dB of dynamic range in 

the spectrum), then the measurement system needs to be moved closer to the radar. The decrease 

in distance must be enough to increase the received signal power from the radar enough to 

observe roughly the –X dB level plus an additional 10 dB (e.g., if the –X dB level is –80 dB, 

then the spectrum needs to be measured with at least 90 dB of total dynamic range).

(5) Determine (and record) radar’s scanning interval and pattern. This process is described 

in detail in Sections 5 and 6. An abbreviated description of the process of determining radar scan 

interval, spectrum measurement step time, and antenna pattern is provided here. 

The measurement system is tuned to the radar fundamental frequency (or to one of the

fundamental frequencies, if there is more than one). The frequency range (or span) for sweeping 

is set to zero hertz. IF bandwidth is set to the widest value available, so long as it is less than 

twice the spacing between the selected radar fundamental frequency and an adjacent fundamental 

frequency, (e.g., if the radar has additional fundamental frequencies spaced 10 MHz above and 

below the fundamental, then the bandwidth should be less than 20 MHz). Detection is set to 

positive peak. The measurement system data trace mode is set to acquire a single sweep at a 

time. The sweep time is set to about 60 seconds (or possibly a somewhat longer interval, for 

some very long-range radars, such as space search or strategic early warning systems). 

The radar emission is observed in this mode for a long enough period of time to establish the 

time intervals between maximum-amplitude occurrences of power. For simple radar beamscanning techniques (such as might be encountered with a single-frequency system with a 

mechanically rotated, 360-degree azimuth scanning antenna and no elevation scanning), this 

interval will likely be fixed. For sector-scanned radars, there will be two observed intervals: a 

short, then a long, then a short, then a long, etc. This pattern results from the measurement 

system being off-axis from the center-line azimuth of the radar’s sector scan. The effect will not 

be seen if the measurement system happens to be positioned precisely on the center of the radar’s 

range of sector scan azimuths. 

For more sophisticated radars, the interval between occurrences of the maximum received power 

level may be somewhat irregular. Examples include radars that scan a beam in elevation while 

they are moving the beam in azimuth; radars that employ multiple frequencies, and radars that 

employ fully electronic beam steering techniques. Even for such radars, however, there will 

normally exist a maximum length of time that is allowed to elapse before the radar scans in any 

given direction on any given frequency. This interval can be taken as the radar’s ‘scan interval,’ 

for the purpose of the measurement. 

The scan interval for any radar is determined by observing many occurrences of the maximum 

received power level and noting any repetition that seems to occur in the pattern of these 

occurrences. Some repetition in interval will be observed for virtually any radar. When such an 

interval seems to be observed, the sweep time of the measurement system is set to a value 

slightly longer than that interval. Then, many (ten or more) of those intervals need to be observed 

sequentially with the measurement system. If the radar consistently sends maximum power to the 

measurement system within that interval, then this interval can be taken as the effective scan rate 
73

for the measurement. If, conversely, the radar sometimes does not send maximum power to the 

measurement system within that interval, then the interval needs to be lengthened, and then a 

series of observations should be repeated. This process continues until the observation interval 

that has been selected consistently results in at least one maximum-power event from the radar. 

For the purpose of spectrum measurements, this time interval is the radar’s ‘scan’ interval. 

The scan interval that is determined from these observations is used to set the ‘step’ time for the 

radar spectrum measurement. The step time is the interval that will be used for data points 

collected in the radar emission spectrum. The step time needs to be about ten to twenty percent 

longer than the radar scan interval. For example, if the radar has a scan interval of 4.75 sec, then 

5 sec is a reasonable step interval. Similarly, if the radar has a 10-sec scan interval, then a step 

interval of 11 sec is reasonable. 

When the step interval has been set, at least one data trace should be acquired and recorded 

showing one complete radar scan pattern. This measurement is the effective radar antenna 

pattern as measured at the location of the measurement system. Additional patterns recorded at 

additional locations can be used to eliminate multipath features in the radar antenna pattern 

measurement. 

(6) Determine (and record) radar’s pulse sequencing. This process is described in detail in 

Section 4. No additional description is provided here. With the measurement system configured 

for the previous measurement of antenna pattern, the measurement bandwidth and pulse 

sequencing are measured as described in detail in Section 4. 

(7) Measure (and record) radar pulse width(s) and modulation characteristic(s). This 

process is described in detail in Section 3. With the measurement system configured for the 

previous measurements of antenna pattern and pulse sequencing, the measurement bandwidth is 

set and the pulse sequence measured as described in detail in Section 3. 

(8) Determine (and record) radar’s emission bandwidth. With the radar beam scanning 

interval having been determined (as described in detail in Sections 5 and 6 and summarized in 

Note (6), above), the effective emission bandwidth is determined next. This process of making a 

bandwidth progression measurement is described in detail in Section 5. 

(9) Set measurement system parameters for spectrum measurement, including IF 

bandwidth, video bandwidth, and step interval. The measurement system should now be 

ready to begin the spectrum measurement, and the parameter values to be used for the 

measurement should be known. The IF bandwidth should be set as described in Table 2 (and 

should be consistent with the empirically determined emission bandwidth of the radar as 

described in the bandwidth progression measurement of Section 5). The video bandwidth should 

be set equal to or greater than the IF bandwidth. The step time should be set to the value

determined previously. The detection should be set to positive peak. Initial RF attenuation needs 

to be adjusted to keep the radar energy within the dynamic range of the measurement system at 

the initial frequency of the measurement. 
74

(10) At each frequency step in the measurement, is RF attenuation properly adjusted? It is 

important that the RF attenuation at the front end of the measurement system be consistently 

adjusted from one frequency step to the next to ensure that the received peak power from the 

radar remains within the instantaneous dynamic range of the measurement system. It is also 

important to remain vigilant against the possibility of any sort of direct feed-through of radar 

energy into the measurement system, bypassing the measurement antenna. 

To accomplish these goals, the radar measurement personnel should watch the maximum

received power from the radar relative to both the noise floor and the saturation level of the 

measurement system. This is done by watching the radar maximum level on each data trace from 

each frequency step, and noting how close it is to noise and saturation levels. If, on any given 

step, the radar signal level approaches within 10 dB of either level, then RF attenuation should be 

either reduced (as the noise floor is approached) or increased (as the saturation point is 

approached). A suggested amount of change in RF attenuation per step is 10 dB. Such a routine 

can also be implemented as an automatic feature in measurement control software. 

C.2.3 Data Units, Graphing and Recording 

The RSEC specifies spectrum limits relative to measured peak power at the radar fundamental 

frequency or frequencies. Thus, it is adequate that measured spectrum power levels be recorded 

in decibels relative to an arbitrary power value within the measurement system circuitry. For 

example, NTIA/ITS engineers record spectrum data in units of dBm in 50 ohm circuitry. 

If for some reason the radar emission spectrum needs to be specified in terms of incident field 

strength or EIRP from the transmitter, then the dBm values in the measurement circuitry may be 

converted through the use of gain tables for the measurement antenna. 

For time-domain data, amplitudes may be measured in terms of relative detected voltage (and 

may be converted to dBm if necessary). Time is typically recorded in microseconds for easy 

insertion into the RSEC equations [1, Chapter 5]. 

It is the experience of NTIA/ITS engineers that RSEC spectrum data should be graphed in real 

time, point-by-point, as each dwell interval is completed. This allows examination of the 

measured spectrum for sharp discontinuities that may indicate attenuation errors or unanticipated 

changes in the radar’s transmitter mode. 

All data should be recorded electronically in real time, preferably with accompanying 

hardcopies. Data back-ups are important, as it may prove impossible to revisit a measurement at 

a later date. Pulse characterization data should be captured from an oscilloscope and recorded 

electronically, with appropriate back-up. 
75

C.3 Measurement Hardware and Software (More Detailed Descriptions) 

Block diagrams of the type of measurement system required for RSEC emission spectrum 

measurements are shown in Figures C-1 and C-2. The first element to be considered in the 

system is the receive antenna. The receive antenna should have a broadband frequency response, 

at least as wide as the frequency range to be measured. A high-gain response (as achieved with a 

parabolic reflector) is usually also desirable. The high gain value permits greater dynamic range 

in the measurement; the narrow antenna beamwidth provides discrimination against other signals 

in the area; the narrow beamwidth minimizes problems with multipath propagation from the 

radar under measurement; and spectrum data collected with a parabolic antenna require a 

minimum of post-measurement correction, as discussed in the next paragraph. The antenna feed 

polarization is selected to maximize response to the radar signal. Circular polarization of the feed 

is a good choice for cases in which the radar polarization is not known a priori. The antenna 

polarization may be tested by rotating the feed (if linear polarization is used) or by exchanging 

left and right-hand polarized feeds, if circular polarization is being used. 

Corrections for variable antenna gain as a function of frequency should be considered. Antenna 

gain levels are usually specified relative to that of a theoretically perfect isotropic antenna, in 

units of dBi. The effective aperture of an isotropic antenna decreases as 20log(f), where f is the 

frequency being measured. This means that, if the measurement antenna has a constant effective 

aperture (that is, has an isotropic gain that increases as 20log(f)), no corrections for variable 

antenna gain need be performed. This requirement is met by a theoretically perfect parabolic 

reflector antenna, and is one of the reasons that such an antenna is preferred for a broadband 

radar spectrum measurement. Conversely, to the extent to which the gain of the measurement 

antenna deviates from a 20log(f) curve (including a less-than-ideal parabolic antenna), the 

resulting measurements must be corrected for such deviation. 

The cable connecting the measurement antenna to the measurement system should also be 

considered. A length of low-loss radio frequency (RF) cable (which will vary depending upon 

the circumstances of measurement system geometry at each measurement radar site) connects the 

antenna to the RF front-end of the measurement system. As losses in this piece of line attenuate 

the received radar signal, it is desirable to make this line length as short, and as low-loss, as 

possible.

The RF front-end is one of the most critical parts of the entire measurement system. It performs 

three vital functions. The first is control and extension of measurement system dynamic range 

through the use of variable RF attenuation. The second is bandpass filtering (preselection) to 

prevent overload of amplifiers by high-amplitude signals that are not at the tuned frequency of 

the measurement system. The third is low-noise preamplification to provide the maximum 

sensitivity to emissions that may be as much as 130 dB below the peak measured level at the 

radar fundamental. Each of these sections in the RF front end is considered below. 

The RF attenuator is the first element in the front-end. It provides variable attenuation (e.g. 0–

70dB) in fixed increments (e.g. 10 dB/attenuator step). Use of this attenuator during the 

measurement extends the dynamic range of the measurement system by the maximum amount of 

attenuation available (e.g. 70 dB for a 0–70 dB attenuator). 
76

The key to using the RF front end attenuator with effectiveness in a radar measurement is to tune 

the measurement system in fixed-frequency increments (e.g., 1 MHz), called steps, rather than to 

sweep across the spectrum, as is more conventionally done with manually controlled spectrum 

analyzers. At each fixed-frequency step, the attenuator is adjusted to keep the radar peak power 

within the dynamic range of the other elements in the measurement system (often the front-end 

amplifier and the spectrum analyzer log amplifier are the limiting elements). With the front-end 

RF attenuator properly adjusted at each step, a measurement of the radar power at that frequency 

is performed. In this way, a nominal 60 dB dynamic range for the measurement system is 

extended by as much as 70 dB, to a total resulting dynamic range of 130 dB (or, more 

realistically, 110–120 dB in operational systems). To minimize measurement time, this 

attenuator and the stepped-frequency measurement algorithm that it necessitates can be 

controlled by computer. 

The next element in the front end, the tunable bandpass filter preselector, is necessary if it is 

needed to measure low-power spurious emission levels at frequencies that are adjacent to much 

higher-level fundamental emissions (e.g., 130 dB below fundamental). For example, it may be 

necessary to measure spurious emissions from an air traffic control radar at 2900 MHz that are at 

a level of –120 dBm in the measurement circuitry, while the fundamental emission level is at 

+ 10 dBm and is only 150 MHz away in frequency (at 2750 MHz). The measurement system 

requires an unattenuated low-noise amplifier (LNA) to measure the spurious emission at 

2900 MHz, but the amplifier will be overloaded (and thus gain-compressed) if it is exposed to 

the unattenuated fundamental emission at 2750 MHz. For this reason, attenuation that has 

frequency dependence is required in the front-end at a position before the LNA input. In practice, 

this tunable bandpass filtering is effectively provided by varactor technology (below 500 MHz) 

and by yttrium-iron-garnet (YIG) technology (above 500 MHz). The applicable filters may be 

procured commercially, and should be designed to automatically track the tuned frequency of the 

measurement system. 

The final element in the RF front-end is an LNA. An LNA is installed as the next element in the 

signal path after the preselector. The low-noise input characteristic of the LNA provides high 

sensitivity to low-amplitude spurious radar emissions, and its gain allows for the noise of the rest 

of the measurement system (e.g., a length of transmission line and a spectrum analyzer) to be 

overdriven. This means that the noise figure of the LNA dominates the overall system noise 

figure. 

Considerations for the sensitivity and dynamic range of the measurement system, as well as for 

typical spectrum analyzer noise figures, are the same as those stated in section C.1.1. 

Another option for LNA configuration is one in which LNAs are cascaded. The first LNA is 

placed between two stages within the YIG or varactor bandpass preselector filter. It has a low 

noise figure, but only enough gain to allow for the insertion loss of the second YIG stage. A 

second LNA is placed immediately after the YIG. This option will provide a somewhat lower 

overall system noise figure because the second stage of the YIG is allowed for by the first LNA. 

However, this option may require more advanced design and engineering modifications to the 

preselector filter than an administration may deem practical. 
77

A third option for the measurement system LNA configuration, and one not requiring any

redesign or retrofitting of the front end preselector filter, is to place a lower-gain LNA in the 

front end and a second LNA at the spectrum analyzer signal input. The first LNA is selected to 

have very low noise figure and just enough gain to allow for the RF line loss and the noise figure 

of the spectrum analyzer LNA. The spectrum analyzer LNA, in turn, is selected for a gain 

characteristic that is just adequate to allow for the spectrum analyzer’s noise figure in the 

appropriate frequency range of the radar measurement. This set of two cascaded LNAs may be 

more easily acquired than a single, extremely high-performance LNA. Regardless of the 

configuration of the LNAs, the cascaded gain must be computed at each LNA input to insure that 

the input linear range of each component is not exceeded. 

The remainder of the RF measurement system is expected to be essentially a commercially 

available spectrum analyzer. Any spectrum analyzer which can receive signals over the 

frequency range of interest, and which can be computer-controlled to perform the steppedfrequency algorithm, can be used. As noted above, the high noise figure of currently available 

spectrum analyzers must be allowed for by low-noise preamplification if the measurement is to 

achieve the necessary sensitivity to observe most spurious emissions. 

The measurement system can be controlled via any computer which has a bus interface (GPIB or 

equivalent) that is compatible with the computer controller and interface card(s) being used. In 

terms of memory and speed, modern PC-type computers are quite adequate. The measurement 

algorithm (providing for frequency stepping of the spectrum analyzer and the preselector, and 

control of the front-end variable attenuator) must be implemented through software. Some 

commercially available software may approach fulfillment of this need, but it is likely that the 

measurement organization will need to write at least a portion of their own measurement 

software. While the development of software requires a significant resource expenditure, 

practical experience with such systems has shown such an investment to be worthwhile if radar 

emission measurements are to be performed on a frequent and repeatable basis. 

Data may be recorded on the computer’s hard drive or on a removable disk. Ideally, a data record 

is made for every 100-200 measurement steps, so as to keep the size of data files manageable, 

and to prevent the loss of an excessive amount of data if the measurement system computer or 

other components should fail during the measurement. 

With the radar antenna beam scanning normally, and with the measurement system set up as 

described above, the first data point is collected. A data point consists of a pair of numbers: 

measured power level and the frequency at which the power level was measured. For example, 

the first data point for the above measurement might be −93 dBm at 2000 MHz. The data point is 

collected by monitoring the radar emission at the desired frequency, in a frequency span of 0 Hz, 

for an interval (step time) slightly longer than that of the radar antenna rotation period, or for a 

longer step time for complex radar systems. This time-display of the radar antenna beam rotation 

will be displayed on the spectrum analyzer screen. The highest point on the trace will normally 

represent the received power when the radar beam was aimed in the direction of the

measurement system. That maximum received power value is retrieved (usually by the control 
78

computer, although it could be written down manually), corrected for measurement system gain 

at that frequency, and recorded (usually in a data file on magnetic disk). 

The second measurement point is taken by tuning the measurement system to the next frequency 

to be measured. This frequency is optimally equal to the first measured frequency plus the 

measurement bandwidth (e.g., if the first measurement was at 2000 MHz and the measurement 

bandwidth were 1 MHz, then the second measured frequency would be 2001 MHz). At this 

second frequency, the procedure is repeated: measure the maximum power received during the 

radar beam rotation interval, correct the value for gain factor(s), and record the resulting data 

point. 

This procedure, which consists of stepping (rather than sweeping) across the spectrum, continues 

until all of the desired emission spectrum has been measured. The stepping process consists of a 

series of individual amplitude measurements made at predetermined (fixed-tuned) frequencies 

across a spectrum band of interest. The frequency change between steps is optimally equal to the 

measurement system IF bandwidth. For example, measurements across 200 MHz of spectrum 

might use 200 steps at a 1-MHz step interval and a 1-MHz IF bandwidth. The step interval may 

be set wider in the spurious emission domain to expedite the overall measurement. However, at 

frequencies that are integral multiples (e.g., 2, 3, 4) of the fundamental radar emission, the 

maximum step interval should again be about equal to the measurement system IF bandwidth. 

The measurement system remains tuned to each frequency for a specified measurement interval. 

The interval is called step-time, or dwell. The dwell time for each step is specified by the 

measurement system operator, and is normally slightly longer than the radar beam scanning 

interval. 

Computer control of the measurement system is desirable if this process (step, tune, measure, 

correct for gain, and repeat) is to be performed with efficiency and accuracy. In order to correctly 

measure the peak of the fundamental emission it may be required to use a smaller step interval of 

the order of half or less of the measurement bandwidth over this region. 

The stepped time technique is required to enable the insertion of RF attenuation at the front-end 

of the measurement system as the frequencies approach the center frequency (and any other 

peaks) of the radar spectrum. This ability to add attenuation on a frequency-selective basis makes 

it possible to extend the dynamic range available for the measurement to as much as about 

130 dB, if a 0–70 dB RF attenuator is used with a measurement system having 60 dB of 

instantaneous dynamic range. This is of great benefit in identifying relatively low-power 

spurious emissions. To achieve the same effect with a swept-frequency measurement, a notch 

filter could be inserted at the center frequency of the radar, but there would be no practical way 

to insert a notch filter for all the other high-amplitude peaks that might occur in the spectrum. 

It is important to provide adequate bandpass filtering at the front-end of the measurement 

system, so that strong off-frequency signal components do not affect the measurement of lowpower spurious components. 
79

These measurements may be performed without the radar antenna being rotated, provided that 

the directions of both maximum fundamental emission and any unwanted emission are known.

C.3.1 Clear Channel Advisor for HF Radar Emission Spectrum Measurements 

For HF radars, ionospherically propagated transmissions can travel large distances, and so much 

of the spectrum that is measured by the test antenna will, in general, be exposed to external 

signals. It is therefore important to have a device advising of occupied channels, preferably one 

that can capture this data and give some indication of the signal strength. The spectrum 

measuring system can be used for this, or an independent receiving system. This data can be used 

to reconcile any unwanted emissions that may have been caused by external sources. It should 

also be used to detect a clear channel for the testing within the in-band B−40 and OOB domains. 

C.4 Dynamic Range of the Measurement System 

The measurement system should be able to measure levels of unwanted emissions [1, Chapter 5] 

and as diagrammed in Figure C-4. To obtain a complete picture of the spectrum especially in the 

spurious emissions domain, it is recommended to be able to measure levels of emissions 10 dB 

below the ultimate suppression level [1, Chapter 5]. 

Figure C-4. Diagram of out-of-band and spurious emission suppression levels required by the 

RSEC. It should be noted that Recommendation ITU-R SM.329 recommends under category B 

more stringent limits than those given within Appendix S3 in some cases. This should be taken 

into account when evaluating the required range of measurement and the recommended dynamic 

range of the measurement system. 
80

APPENDIX D: RSEC MEASUREMENT SYSTEM CALIBRATION 

D.1 Calibration Overview 

The measurement system is calibrated by disconnecting the antenna from the rest of the system, 

and attaching a noise diode to the RF line at that point. A 25 dB excess noise ratio (ENR, where 

ENR = (effective temperature, oK, of noise diode/ambient temperature, oK)) diode should be 

more than adequate to perform a satisfactory calibration, assuming that the overall system noise 

figure is less than 20 dB. The technique is standard Y-factor measurement with comparative 

power measurements made across the spectrum, once with the noise diode on and once with the 

noise diode off. 

The noise diode calibration results in a table of noise figure values and gain corrections for the 

entire spectral range to be measured. The gain corrections may be stored in a look-up table, and 

are applied to measured data as those data are collected. The next section describes these 

procedures in more detail. 

The measurement antenna is not normally calibrated in the field. Correction factors for the 

antenna (if any) are applied in post-measurement analysis. 

D.1.1 Gain and Noise Figure Calibration Using a Noise Diode 

Measurement system calibration should be performed prior to every radar emission spectrum 

measurement. As measurements are performed, gain corrections may be added automatically to 

every data point. For measurement system noise figures of 20 dB or less, noise diode Y-factor 

calibration (as described below) may be used. This appendix describes the theory and procedure 

for such calibration. 

Figure D-1. Lumped component diagram of noise diode calibration.

The noise diode calibration of a receiver tuned to a particular frequency may be represented in 

lumped-component terms as shown in Figure D-1. In this diagram, the symbol Σ represents a 

power-summing function that linearly adds any power at the measurement system input to the 

inherent noise power of the system. The symbol g represents the total gain of the measurement 
81

pon = (nf s + enrd

)× gkTB

system. The measurement system noise factor is denoted by nf, and the noise diode has an excess 

noise ratio denoted as enr. (In this appendix, all algebraic quantities denoted by lower-case 

letters, such as “g,” represent linear units. All algebraic quantities denoted by upper case letters, 

such as “G,” represent decibel units.) 

Noise factor is the ratio of noise power from a device, ndevice(W), and thermal noise, 

kTB

ndevice

where k is Boltzmann’s constant (1.38·10−23J/K), T is system temperature in Kelvin, and B is 

bandwidth in hertz. The excess noise ratio is equal to the noise factor minus one, making it the 

fraction of power in excess of kTB. The noise figure of a system is defined as 10 log (noise 

factor). As many noise sources are specified in terms of excess noise ratio, that quantity may be 

used. 

In noise diode calibration, the primary concern is the difference in output signal when the noise 

diode is switched on and off. For the noise diode = on condition, the power, Pon(W), is given by: 

(D-1) 

where nfs is system noise factor and enrd is the noise diode enr. 

When the noise diode is off, the power, Poff(W), is given by: 

poff = nf ( s)× gkTB (D-2) 

The ratio between Pon and Poff is the Y factor: 

y =

pon

poff

















=

nfs + enr ( d )

nfs

 (D-3) 

Y =10log(y) =10log pon

poff

















= Pon − Poff

Hence the measurement system noise factor can be solved as: 

−1

=

y

enr nf d

s

 (D-4) 

The measurement system noise figure is: 

NFs =10log enrd

y −1











 = ENRd −10log( ) y −1 = ENRd −10log 10Y /10 ( −1) (D-5) 

Hence: 

g =

pon − poff

enrd × kTB

 (D-6) 
82

G =10log(pon − poff)−10log enr ( d × kTB)

or 

G =10log 10Pon /10−10Poff /10 ( )− ENRd −10log(kTB)

In noise diode calibrations, the preceding equation is used to calculate measurement system gain 

from measured noise diode values. 

Although the equation for NFs may be used to calculate the measurement system noise figure, 

software may implement an equivalent equation: 

gkTB

p

nf off

s = (D-7) 

NF (p ) (gkTB) P G (kTB) s off off =10log −10log = − −10log

And substituting the expression for gain into the preceding equation yields: 

( )

10/ 10/

10log 10 10 Pon

Poff NFs = Poff + ENRd − − (D-8) 

The gain and noise figure values determined with these equations may be stored in look-up 

tables. The gain values are used to correct the measured data points on a frequency-by-frequency 

basis. 

Excluding the receive antenna, the entire signal path is calibrated with a noise diode source prior 

to a radar spectrum measurement. A noise diode is connected to the input of the first RF line in 

place of the receiving antenna. The connection may be accomplished manually or via an 

automated relay, depending upon the measurement scenario. The noise level in the system is 

measured at a series of points across the frequency range of the system with the noise diode 

turned on. The noise measurement is accomplished with the IF bandwidth set to 1 MHz and the 

video bandwidth set to 1 kHz. The noise diode is then turned off and the system noise is 

measured as before, at the same frequencies. The measurement system computer thus collects a 

set of Pon and Poff values at a series of frequencies across the band to be measured. The values of 

Pon and Poff are used to solve for the gain and noise figure of the measurement system in the 

equations above.
83

APPENDIX E: POSITIONING OF MEASUREMENT SYSTEM FOR RADIATED 

MEASUREMENTS 

E.1 Measurement Environment Conditions 

1 Regarding the measurement distance, the antenna pattern should be measured in the far field 

of the radar antenna. But the spectrum can be measured at distances at least as close as half 

the far field distance, as shown for example in Figure E-1. Variation of the peak received 

signal should be made less than 3 dB when the receiving antenna is moved λD/2H 

horizontally or vertically away from the point where maximum signal is received (H: height 

of the transmitting point, D: measurement distance, λ: transmitting wavelength). 

2 Regarding the measurement site, it is preferable to locate the transmitting and receiving 

antennas in a fairly high position, such as on towers. Note that the height should be 

determined considering the vertical beam width of the radar and measurement antennas, and 

no reflective objects should be between the antennas. 

For the purpose of performing radiated emission measurements on a radar, it is important to 

position the measurement system so that maximum power is coupled from the radar to the 

measurement system. This condition will achieve the highest possible dynamic range in the 

resulting emission spectrum data. 

The question of near field and far field distances inevitably arises for radiated measurements. 

The terms ‘near field’ and ‘far field’ refer to changes in the radiation patterns of antennas as a 

function of distance from such antennas. Antenna patterns gradually approach a limiting case at 

infinite distances, but real-world measurements must be performed at finite distances. Therefore 

criteria have been developed for computation of distances at which radiation patterns are close 

enough to the limiting case to satisfy most engineering and scientific requirements. Two 

common criteria are 2D2/λ and D2/λ. But as noted, these criteria are intended for use in radiation 

pattern measurements, not spectrum measurements. 

For RSEC measurements, the far-field limit may be taken as D2/λ, where D is the radar antenna 

diameter and λ is the wavelength of the radar fundamental frequency. For a 2900-MHz radar 

with a 7-m antenna diameter, for example, the far-field distance will be 475 m. For a 420-MHz 

radar with an antenna diameter of 40 m, the far-field distance will be 2.25 km. 

Pulse shape, modulation, and PRR measurements may be performed within the near field limit. 

Likewise, spectrum measurements may be performed at least as close as half of D2/λ with only 

small differences from a measurement at D2/λ, as shown in Figure E-1. 

Antenna pattern measurements within the near field limit will be incorrect. Thus a distance of 

D

2

/λ or greater is preferred when the measurement system is being positioned for an antenna 

pattern measurement. 
84

Figure E-1. Emission spectrum measurements of a maritime radar made at distances of 105 m 

(D2/λ distance limit) and 65 m, well within that distance. Where the two spectra diverge, the farfield spectrum is lower than the near-field spectrum. 

Because of the shape of typical radar beams, incident power at ground level does not continually 

increase as distance to the radar antenna decreases. Rather, there will usually be a distance at 

which incident power is maximized. Within this distance the power level drops because the 

measurement system is being moved underneath the radar antenna’s highest-amplitude lobes. 

Outside this distance, the effect of 1/r2 geometric drop-off is experienced. The measurement

system should be positioned at this maximum incident power point, unless it is within the near 

field limit of either the radar antenna or the measurement antenna. 

The highest-amplitude location may be determined as follows, assuming that the measurement 

system is vehicularly mounted. A low-gain measurement antenna is mounted on the vehicular 

exterior, preferably on the roof. The antenna is connected to a spectrum analyzer which is tuned 

to the radar fundamental frequency. The spectrum analyzer span is set to zero hertz, the 

resolution bandwidth is set as wide as possible, and positive peak detection is used. The 

spectrum analyzer sweep time is set to a value that exceeds the time it will take to drive the 

vehicle from the radar transmitter to a location a few kilometers away. In practice, this will likely 

be about 300 sec. 
85

The vehicle is initially positioned at the radar transmitter. As the spectrum analyzer sweep is 

triggered (manually), the vehicle begins to drive away from the radar. Every few seconds, the 

radar beam will sweep across the vehicle and the received power value will be observed. The 

received power level will gradually rise as the vehicle moves away from the radar. At some 

point, the received power level will no longer increase, and at longer distances from the radar the 

received power will decrease. The vehicular location where the maximum power was received 

should be noted by the vehicle’s driver; this is the optimum location for the ensuing spectrum 

measurement. 

As rough guidelines, the typical optimal distance from which to perform measurements on air 

search radars and weather radars is between 0.8 km to 1.2 km. Distances on the order of 0.1 km 

(100 meters) or less may be optimal for measurements of emissions from maritime surface 

search radars. 

With the measurement vehicle properly positioned, the measurement system is configured for the 

full RSEC measurement as described in Appendix C. A constant-aperture (parabolic) antenna is 

substituted for the low-gain antenna used in the location survey. The measurement antenna 

should be raised as high as possible on a mast for air search radar measurements. For maritime 

radar measurements, the measurement antenna should be positioned at a height that maximizes 

the coupled power from the radar. 
86

APPENDIX F: VARIATION IN MEASURED PULSE SHAPES ACROSS EXTENDED 

EMISSION SPECTRA 

Since the pulse shape is related to the emission spectrum via the Fourier transform, the pulse 

shape can in principle be observed in complete detail only if the entire emission spectrum is 

convolved within the measurement bandwidth. But in practice, a measurement bandwidth that 

convolves a large number of the highest-amplitude emission lines near the fundamental 

frequency of a spectrum (ie., a bandwidth that equals or exceeds (1/pulse width)) will produce a 

pulse shape that nearly replicates the true pulse shape, as shown in Figure F-1 for a weather 

radar. 

But using the same bandwidth at a frequency within the spurious portion of the emission 

spectrum, the convolved set of emission lines will not produce the pulse shape of Figure F-1a. 

Instead, this sub-set of emission spectrum lines will produce a double pulse shape such as that 

shown in Figures F-1b through F-1d. (These figures are off-tuned measurements made on the 

same radar as Figure F-1a). This phenomenon is referred to vernacularly as “rabbit ears.” The 

spacing between the two spikes will be the same as the nominal pulse width. But between the 

two spikes low-amplitude noise will be observed. Depending upon the spurious frequency, the 

relative amplitudes of the leading-edge spike, trailing-edge spike, and center-pulse noise will 

vary. 

This phenomenon has important implications for the RSEC spectrum measurement. The essential 

significance is that the measurement bandwidth at which the measured peak power remains 

constant varies with frequency. In section 5 a measurement of bandwidth progression shown in 

Figure 12 illustrates the point at which the measured peak power remains constant despite an 

increase in measurement bandwidth. At the fundamental, this point is about 1/t, where t is the 

pulsewidth. In the spurious portions of the spectrum, this bandwidth is much wider, usually 

about 1/tr, where tr is the pulse’s risetime. This variation has important consequences for the 

selection of appropriate bandwidth for the RSEC spectrum measurement, as discussed in 

Section 5 of this report and shown in Figures 16–17 of that section. 
87

 

 (a) (b) 

 

 (c) (d) 

Figure F-1. A weather radar pulse envelope measured at nominal radar center frequency (a), and 

at three other frequencies in the out-of-band and spurious parts of the emission spectrum ((b) 

through (d)). Measurement bandwidth was 8 MHz. The emission lines convolved at the center 

frequency in the measurement bandwidth yield a good approximation of the full-bandwidth pulse 

envelope in the time domain. But the subsets of Fourier lines convolved in the same bandwidth 

at frequencies in the out-of-band spurious portions of the emission spectrum do not yield the 

nominal pulse envelope; instead they tend to produce high-amplitude features in the leading 

edge, trailing edge, or both. (Note however that total pulse duration of off-tuned detected pulses 

is constant, even though much of the structure is low-amplitude and noisy.) 
88

APPENDIX G: VARIATION IN MEASURED SPURIOUS AMPLITUDES AS A 

FUNCTION OF MEASUREMENT BANDWIDTH 

G.1 Introduction 

Pulsed radar transmitters produce broadband spurious emissions at relatively high levels as 

compared to emissions from narrowband communication systems. As documented in [3], radar 

spurious emission levels are typically tens of decibels higher than theoretically predicted sinc2

spectra of pulsed emissions. These emissions in the frequency domain probably correspond to 

short-term transient behavior in the time domain characteristics of the rising and falling edges of 

the radar pulses. 

For spectrum management purposes, radar out-of-band and spurious emissions are limited in the 

U.S. by Government regulations such as the radar spectrum emission criteria (RSEC). RSEC 

spurious emission masks are specified in terms of amplitude suppression relative to the power 

produced at radars’ fundamental frequencies [1] (e.g., suppression might be required to be at 

least 60 dB below the fundamental at frequencies of 100 MHz or more away from the 

fundamental). Mask-compliance limits are computed on the basis of a theoretically perfect 

pulsed emission plus a margin that allows for realistic performance of an economical transmitter 

design. 

Compliance with emission masks is determined through measurements of emission spectra. The 

measured levels of radar unwanted emissions and fundamental-frequency emissions both vary as 

a function of measurement system bandwidth, Bm. But the variation with Bm differs between 

unwanted emissions and the fundamental-frequency emissions. Moreover, the variation of 

unwanted emission levels varies as a function of frequency as well as Bm. This presents a 

problem for radar emission mask-compliance measurements. 

Figure G-1. Schematic representation of the measured power at a radar fundamental frequency 

versus power measured at other frequencies as measurement bandwidth changes. Units are 

arbitrary. 

In a peak-detected power measurement, completely non-coherent (noise-like) emissions should 

vary as 10 log(Bm), while coherent emissions should vary as 20 log(Bm). Since the bandwidth 
89

progression coefficients of 10 and 20 represent limiting cases, radar spurious emissions should 

have a coefficient somewhere between these two values. But no study is known to have been 

undertaken to determine the actual coefficient for radars. An ideal peak-detected measurement is 

shown in Figure G-1. Power measured at the fundamental frequency (far left) first increases at a 

20log rate, but maximizes when measurement bandwidth exceeds the values given in Table 2 of 

this report. But since the power in the rest of the spectrum climbs arbitrarily high as bandwidth 

increases, the difference between power values at the center frequency vs. other frequencies 

(reading between the left and right sides of this diagram) therefore decreases if measurement 

bandwidth is greater than the values of Table 2. 

NTIA/ITS has begun to address this problem by performing emission spectrum measurements on 

a maritime surface search (navigation) radar. The purpose of the measurements has been to 

determine the actual variation of spurious emission levels of a radar relative to the measured 

fundamental level as a function of the measurement bandwidth, Bm. With this value known, 

NTIA will be better able to specify appropriate bandwidths for RSEC-compliance measurements, 

as well as any post-measurement correction factors that might be required. 

G.2 Approach 

A magnetron-based X-band maritime surface search radar was set up with an antenna height of 

approximately 4 m on a mast at a prairie location free of local obstructions. A measurement 

system contained in the RF-shielded enclosure of the NTIA Radio Spectrum Measurement 

System (RSMS) was positioned at a distance of 105 m from the radar. The RSMS received radar 

emissions via a 1-meter diameter parabolic dish antenna with a linear, matched-polarization logperiodic feed. Figure G-2 shows the radar transmitter and the RSMS during the measurement. 

Figure G-2. Maritime radar and measurement system. 
90

The measurement system is shown in block-diagram form in Figure G-3. Following the antenna, 

a variable (0–70 dB) attenuator was adjusted on a frequency-dependent basis to keep the 

received signal level from the radar within the dynamic range of the measurement system. That 

is, the attenuation level was zero when radar emissions were close to measurement system noise, 

but was gradually increased (in 10 dB steps) to as much as 70 dB as the measured frequency 

approached the radar fundamental. The attenuation was gradually decreased at frequencies above 

the radar fundamental, being finally reduced to zero at the upper end of the measured spectrum. 

Figure G-3. Measurement system functional block diagram. 

Following the attenuator, a tunable bandpass filter based on yttrium-iron-garnet (YIG) 

technology isolated the system’s broadband low-noise filter (LNA) from the high-power radar 

fundamental energy as the spectrum measurement progressed. The LNA provided the sensitivity 

required to measure out-of-band and spurious emission levels as much as 100 dB below the 

measured fundamental power level. 

The LNA output was fed into a spectrum analyzer. The critical spectrum analyzer stages are 

shown in Figure G-3, including frequency downconversion; IF filtering; envelope and peak 

detection; analog-to-digital conversion; and final output to a data-recording computer. 

As noted above, the requisite dynamic range of the measurement (about 100 dB) demanded that 

the RF attenuator setting be varied as a function of frequency. Therefore, the measurement 

system could not be operated in a swept-frequency mode. Instead, the measurement system was 

fixed-tuned to a single frequency with a single attenuator setting. A peak-detector circuit was 

operated at the single frequency for a period of time (3 sec) slightly in excess of the radar’s 

antenna rotation period (2.7 sec). This ensured that the radar beam maximum output would be 

sampled at each measured frequency. 
91

With the emission amplitude measured at a single frequency, the measurement system was tuned 

to another frequency, the RF attenuator was adjusted (if necessary) and the measurement process 

was repeated for another 3 sec. This stepped-frequency measurement process was used to acquire 

all data presented in this paper. 

With 100 dB dynamic range available in the measurement, the radar spectrum was measurable 

across 4.2 GHz of spectrum, from 7300 MHz to 11500 MHz. Because the out-of-band and 

spurious emissions are a continuum, lacking discrete carrier frequencies, those emissions could 

be sampled at arbitrary spacings between frequency steps. For this measurement, the step 

interval was set at 6 MHz, for a total of 700 steps (and 701 measured frequencies) across the 

range 7300-11500 MHz. Each spectrum run therefore required about 35 minutes for completion. 

Because the 6 MHz step spacing could result in the omission of the radar fundamental frequency 

from the measured spectrum, a supplemental measurement was made at the radar fundamental 

for each spectrum. This ensured that radar peak power was accurately included in each spectrum 

output. 

The radar can transmit multiple pulse widths, ranging from 80 nsec to 800 nsec. The radar 

spectrum was measured in two pulse modes (80 nsec and 800 nsec) in four IF bandwidths (where 

Bm=300 kHz, 1 MHz, 3 MHz, and 8 MHz). Thus a total of eight spectrum measurements were 

performed. 

G.3 Results 

The measured emission spectra for short-pulse and long-pulse radar modes are shown in Figures 

G-4 and G-5. Measurement system internal noise occurs as a flat floor at frequencies between 

7300-8000 MHz, and as a flat area between 11000-11200 MHz. It is observed that the spurious 

emission levels are changing with a progression that is somewhere between 10 log and 20 log 

bandwidth, depending upon frequency. 

Figure G-6 shows measured power at the radar fundamental frequency (approximately 

9410 MHz) as a function of measurement IF bandwidth. The data in this figure confirm that the 

radar fundamental power follows a 20 log(Bm) rule for values of Bm that are equal to or less than 

(1/pulse width). 

In the short-pulse mode, the 80 nsec pulse width results in a predicted fundamental-frequency 3-

dB emission bandwidth of 12.5 MHz, which is wider than the maximum measurement IF 

bandwidth of 8 MHz. Consequently, the measured power increases as 20 log(Bm) for all points. 

But in the long-pulse mode of 800 nsec pulse width, the 3-dB emission bandwidth is predicted to 

be 1.25 MHz. As a result, the 20 log(Bm) progression breaks down for 3 MHz and 8 MHz Bm

values. 

Figure G-7 quantifies the decibel differences between spectra measured in successive values of 

Bm. These are shown as deviations from a 20 log progression, computed as follows: 
92

( ) 20

log /

−







	









 −

∆ =

x y

x y

B B

P P

where: 

∆ = deviation from 20 log(Bm) progression; 

P[x,y] = log power measured in Bx and By; 

B[x,y] = measurement bandwidth; 

[x,y] are subscripts for successive measurement IF bandwidths (e.g., 3 MHZ and 1 MHz). 

The differences should lie between –10 (corresponding to a noise-like 10 log progression) and 0 

(for the 20 log rule that coherent emissions should follow). Some points lie outside these bounds. 

Deviations outside this range could result from the interaction of spectrum peaks and valleys 

with a particular measurement bandwidth; uncertainty in measured values; or variation in shape 

factors between filters. 

Figure G-4. Maritime radar emission spectrum measured in four bandwidths with transmitter 

operating in short-pulse mode. 

(G-1)
93

Figure G-5. Maritime radar emission spectrum measured in four bandwidths with transmitter 

operating in long-pulse mode. 

Figure G-6. Variation in measured power at the radar fundamental as a function of measurement 

bandwidth and pulse mode. 
94

Some trends are clearly observed in the values for the curves in Figure G–7. The values of the 

deviation curves typically range between –4 and –2, corresponding to variation coefficients 

between 16 and 18. Neglecting the points that exceed zero, the extreme values range between –8 

and 0, corresponding to variation coefficients between 12 and 20, respectively. 

G.4 Summary and Conclusions 

In summary, spurious and out-of-band emissions measured from a maritime navigation radar 

were found to typically vary at a value between 16 log(Bm) and 18 log(Bm). Extreme values 

ranged from a low of 12 log(Bm) to a high of 24 log(Bm). 

These results indicate that the radar spurious emissions did not vary as would be predicted for 

thermal noise (10 log progression). Thus radar spurious emissions should not be characterized as 

“noise-like,” at least for the radar measured in this study. 

Radar emission spectrum measurements that are performed for the purpose of determining the 

suppression of out-of-band and spurious emissions relative to radar fundamental-frequency 

power will show a bandwidth dependent variation. Measurement of spectra in multiple 

bandwidths is recommended until this phenomenon is better understood. 

It may be desirable for future emission masks to accommodate this effect. Such masks might 

include a recommended IF measurement bandwidth, and possibly a method for computing 

correction factors for measurements made in other bandwidths. 

(a) (b) 

Figure G-7a. 8 MHz – 3 MHz smoothed difference, short pulse radar mode. 

Figure G-7b. 3 MHz – 1 MHz smoothed difference, short pulse radar mode. 
95

 (c) (d) 

Figure G-7c. 1 MHz – 300 kHz smoothed difference, short pulse radar mode. 

Figure G-7d. 8 MHz – 3 MHz smoothed difference, long pulse radar mode. 

(e) (f) 

Figure G-7e. 3 MHz – 1 MHz smoothed difference, long pulse radar mode. 

Figure G-7f. 1 MHz – 300 kHz smoothed difference, long pulse radar mode. 
96

APPENDIX H: RADAR SPECTRUM ENGINEERING CRITERIA (RSEC) 

EMISSION MASK SPREADSHEET 

H.1 Introduction 

NTIA has developed an automated model to plot RSEC emission masks as a function of radar 

characteristics. The RSEC Emission Mask spreadsheet will plot the permitted emission limits for 

primary radar stations operating in the radiodetermination service as required [1, § 5.5]. 

Measured emission spectrum data can be imported into the spreadsheet for comparison with the 

RSEC emission limits. The RSEC emission mask spreadsheet is in Microsoft Excel© format. The 

program is available on the following website: http://ntiacsd.ntia.doc.gov/rsec. Comments and 

suggested improvements to the spreadsheet should be sent to Robert Sole at rsole@ntia.doc.gov. 

A user’s guide for the program is given below. 

H.2 System Requirements 

The ITU-R emission mask spreadsheet requires Microsoft Excel 2000© or later version, and 

Microsoft Windows 98© or later operating system. 

H.3 Opening Program 

Start Microsoft Excel. Open the file ITU-R emission mask spreadsheet. When prompted, enable 

the macros. If not prompted to enable macros, then go to the Tools pull down menu, and select 

Macro-Security. In the Security level tab, choose Medium and press OK. Close the spreadsheet 

and re-open it. Upon re-opening the spreadsheet, you should be prompted to enable macros. 

Click on the NEW/Restart button to initialize the spreadsheet. 

H.4 Importing Measured Emission Spectrum Data 

Measured emission spectrum data may be imported into the program. If measured data are being 

used, they should be imported prior to providing the data in Table 1 since the Excel program 

determines some parameters in Table 2 from the measured emission spectra data. The imported 

emission spectrum data files must be in ASCII file format, Easy Plot© file format, or table entry. 

The ASCII file must include the emission spectrum data in two fields: 1) frequency in MHz, 2) 

measured emission spectrum data in absolute power (e.g.; dBW or dBm), or in dB relative to the 

maximum measured signal level. Note: if the data are in absolute power the program will 

normalize the data to dB relative to the maximum measured signal level. 

The procedure for importing measured data into the spreadsheet is as follows. 

A. Click on the Get Data button. 
97

B. An Emission Spectrum Data window will pop up. Click on the Read/Describe Emission 

Spectrum Data button. 

C. An Emission Spectrum Input window will pop up. Click on the Read ASCII File button 

if the emission spectrum data are in an ASCII file. Click on the Read CSV File button if 

the emission spectrum data are in an CSV file. Click on the Read EP File button if the 

emission spectrum data are in an Easy Plot© file. If the spectrum data are not in a file, and 

are available in a Table Entry form, click on Table Entry. 

D. An Open Emission Spectrum Data File window will pop up. Go to the bottom of the 

menu and where it says “Files of type”, use the pull-down menu to select “all files.” Locate 

the file to be imported into the spreadsheet using the Look in pop-down button. Select the 

file to be imported, and click on Open. 

E. Select an emission spectrum file to be loaded into the spreadsheet. Sample emission 

spectrum data are available. See H.13 below for information on sample emission spectrum 

data files. 

F. Click on the OK button, 

G. A window will come on the screen that says Emission Spectrum Data with the ability to 

select fixed frequency or frequency hopping. Select the appropriate radar mode. If you 

select fixed frequency, the window will display the Operating Frequency (FO) based on the 

measured data. If you select the Frequency Hopping Mode, the Lowest Channel Frequency 

(FL) and Highest Channel Frequency (FH) windows will display the selected FL and FH

frequencies based on the measured data. In cases where there are multiple operating 

(fundamental) frequencies, or the radar is a frequency hopping radar, the program may not 

select the appropriate Operating Frequency (FO), or in the case of frequency hopping radar 

the Lowest Channel Frequency (FL) and Highest Channel Frequency (FH) for plotting the 

RSEC emission mask. If the appropriate FO, FL , or FH values were not selected, type in the 

appropriate values. Then click the OK button. Measured data should now be visible on the 

spreadsheet. The Excel program will normalize the power level at the fundamental 

frequency (FO) to 0 dB. Verify that the Fo data in Row 6 of the spreadsheet is in agreement 

with the plotted data. In the case of frequency hopping radars, the value for FO in Row 6 

should be midway between FL and FH. 

H. If desired, the frequency scale of the measured data can be normalized to zero MHz/GHz at 

the radar Fundamental Frequency (FO). Verify that the value for normalized data in Row 6 

is correct. Click on the Normalize to Fo button in Row 34. The measured data will be 

normalized to Fo at zero hertz. 

H.5 Changing Graph Title and X and Y Axes 

Once the measured data have been imported into the spreadsheet, the Titles and the X and Y axes 

ranges on the measured data plot can be changed if necessary. 
98

A. The graph titles, and X and Y axes titles can be changed by clicking on the Set Graphs 

Titles button. Make appropriate changes to the titles, and click on the OK button. 

B. The scale range of the X and Y axes can be changed if necessary by pointing the mouse to 

the X or Y scale on the graph and right click when the Values (X or Y axis) window pop up. 

Then click on Format Axis. A Format Axis window will pop up. Click on the Scale tab, 

and change the axis values as required. Then click on the OK button. The measured data 

should now be in the desired format. 

H.6 Select RSEC Criteria 

Click on the RSEC Criteria button in row 3. A window will appear titled RSEC Criteria which 

provides information on Radar Description and Applicable Criteria. Determine the appropriate 

RSEC Criteria, and click on the RSEC button in Row 3 Column B. A pop-down list for RSEC 

Criteria A, B, C, D, and E will appear. Click on the appropriate criteria. 

If RSEC Criteria D is selected, a window will pop up showing the congested areas for radars 

operating in the 2700-2900 MHz band. If the radar will be operated in a congested area, click on 

the Congested window, Row 8, and insert Y for yes in a congested area. Otherwise insert N for 

not in a congested area. This will change the required slope roll-off from the –40 dB bandwidth 

from 40 dB per decade to 80 dB per decade. 

H.7 Radar Peak Power 

Enter the radar peak power, Pp, in Row 7 of the spreadsheet. The pop-down window to the right 

lets you select appropriate units for specifying peak power. Click on the units then click on the 

pop-down window to change the units. 

H.8 Table 1 – Pulse/Sub-Pulse Characteristics 

Table 1 is provided to input the measured or calculated pulse/sub-pulse characteristics for 

determining the RSEC emission mask limits. The definition of the radar parameters in Table 1 

are provided in the NTIA Manual [1, § 5.5]. Table 2 [1, § 5.5] shows the calculated RSEC 

emission mask parameters and other data needed for determining the RSEC emission mask for 

the radar parameters entered in Table 1 [1, § 5.5].

The Table 1 spread sheet will let you specify up to eight pulse/sub-pulse time waveform 

characteristics for multiple waveform radars. For multiple waveform radars, the RSEC emission 

mask limits are determined from the pulse type (waveform) which results in the maximum 

B(-40 dB) bandwidth. Use the following procedure for providing the pulse/sub-pulse waveform 

information in Table H-1. 
99

A. The column labeled Pulse Type must have a value selected. Place the cursor at the small red 

triangle on the upper right side of the cell for guidance on selecting the proper pulse type. 

There are nine pulse/waveform modulation types to choose from. Type in the appropriate 

number. Once the pulse type is determined, fields in Table 1 that are not applicable to that 

pulse type will have an NA in them. 

B. The column labeled Pulse Width or Sub-Pulse Width (t) must have data entered into it for 

the pulse/sub-pulse width in microseconds. Place the cursor on the small red triangle on the 

upper right side for guidance for determining the pulse width. 

C. The column labeled Pulse Rise/Fall Time (tr) must have data entered into it for the rise/fall 

time in microseconds. If the pulse/sub-pulse fall time (tf) is less than the rise time (tr), tf is to 

be used in place of tr for determining the emission bandwidth calculation. Place the cursor on 

the small red triangle on the upper right side for guidance for determining the pulse rise/fall 

time. 

D. For frequency swept (chirped) pulses, the column labeled Chirp Bandwidth (Bc) must have 

data entered into it for the chirp range in MHz. Place the cursor on the small red triangle on 

the upper right side for guidance for determining the chirp bandwidth. 

E. For CW radars, the column labeled Total Frequency Deviation (Bd) must have data entered 

into it for the frequency deviation range in MHz. Place the cursor on the small red triangle on 

the upper right side for guidance for determining the frequency deviation. 

F. For phase coded pulses, the column labeled Number of Chips per Pulse (N) must have data 

entered into it for the total number of chips per pulse. Place the cursor on the small red 

triangle on the upper right side for guidance for determining the frequency deviation. 

G. The column labeled Pulse Repetition Rate (PRR) must have data entered into it for the 

pulse repetition rate in pulses per second (PPS). Place the cursor on the small red triangle on 

the upper right side for guidance for determining the pulse repetition rate. 

H. For frequency hoping radars, the columns labeled Lowest Channel and Highest Channel 

Frequency (FL and FH) must have data entered into them for the lowest and highest channel 

frequency of a frequency hopping radar deviation in MHz. The data for FL and FH should be 

added to these fields when Pulse Types 3, 4, and 8 are selected in Step A above. Check to 

determine if the data in these fields are correct. Place the cursor on the small red triangle on 

the upper right side for guidance for determining the appropriate values for FL and FH. 

After the radar characteristics data have been completed in Table 1, the calculated parameters 

related to the RSEC Emission Limits Mask for each waveform are shown in Row 1 of Table 2. 
100

H.9 Plotting RSEC Emission Mask 

Review the calculated parameters related to the RSEC Emission Limits Mask data shown in 

Table 2. The RSEC Emission Mask can be plotted on the measured data using the following 

procedure. 

A. The emission mask data that will be plotted over the measured data correspond to the 

Emission Mask Number shown in Column A of Table 2. If the radar mode has multiple pulse 

waveforms, review the B(-40 dB) bandwidths shown in Table 2 for the various pulse 

waveforms. Check the mask number shown in Row 38. If necessary, change the mask 

number in Row 38 to correspond to the Emission Mask number in Column A of Table 2, 

which has the maximum B(-40 dB) bandwidth. Click on the Add/Del button shown in Row 

40. The emission mask will be added in the plot. 

B. To delete the emission mask from the plot, click on the Add/Del button shown in Row 40. 

Check the mask number shown in Row 38. If necessary, change the mask number in Row 38 

to correspond to the Emission Mask number that you want to delete shown in Column A of 

Table 2. 

C. The slope from the B(-40 dB) bandwidth can be changed by clicking on the Set S (slope)

button shown in Row 44. Check the mask number shown in Row 38. If necessary, change the 

mask number in Row 38 to correspond to the Emission Mask number that you want to 

change the slope of shown in Column A of Table 2. 

D. The X dB Floor can be changed by clicking on the X dB Floor button shown in Row 42. A 

specific X dB floor value can be typed in, or the box titled Proposed New X dB Floor can 

be checked. Check the mask number shown in Row 38. If necessary, change the mask 

number in Row 38 to correspond to the Emission Mask number that you want to change in 

Column A of Table 2. 

 

H.10 RSEC Mask Offset 

The RSEC B(-40)dB bandwidth can be offset from the frequency of maximum emission level, 

and can be shifted to center the mask at the measured -40 dB level of the measured data. If there 

is a RSEC mask on the graph, click on the Add/Del Mask button. This will delete the indicated 

mask. To offset the RSEC mask, click on the Mask Shift button and type in the desired 

frequency shift in a positive or negative direction. Then click on the Plot Mask Shift button. 

H.11 Plotting Additional Emission Masks 

Additional emission masks with parameters other than the RSEC Emission Mask can be plotted 

on the measured data. To plot additional emission masks to the data plot, it is necessary to 

provide additional Pulse/Sub pulse characteristics data in another row of Table 1. This can be 

accomplished by clicking on the row in Table 1 that you want copied, and then click the Copy 
101

Row button, rows 22-23. The RSEC Emission Mask data will appear in the corresponding row in 

Table 2. Change the appropriate parameter (e.g.; Slope dB/dec,) in the row of Table 2. Change 

the Mask Number in Row 38 to the appropriate row of Table 2. Click on the Add/Del button 

shown in Row 40. The additional emission mask will be added in the plot. 

H.12 Printing the Spreadsheet 

To print Graph, Table 1, and Table 2, click the appropriate buttons in rows 48, 50, and 52 

respectively. Also, the graphs and Tables can be printed by clicking on the Summary button on 

line 3, and then clicking on the Summary tab at the bottom of the page. (Note: you must click on 

the Summary button on line 3 to import the data prior to clicking on the Summary tab at the 

bottom of the page.) From the Summary page, the spreadsheet can be printed, or copied to a text 

document. 

H.13 Viewing Measurement Data and RSEC Emission Mask Data 

To view the measurement data and RSEC emission mask data, click on the Temp tab at the 

bottom left of the Excel screen. 

H.14 Sample RSEC Spreadsheet Data 

A sample radar emission spectrum is provided below. The radar measured was an Aeronautical 

Radionavigation radar which operates in the 2700-2900 MHz band. Thus the emissions of the 

radar must comply with RSEC-D criteria. RSEC Emission Mask 1 is for a 40 dB per decade rolloff from the –40 dB bandwidth, and RSEC Emission Mask 2 is for an 80 dB per decade roll-off 

from the –40 dB bandwidth for designated congested areas. 

SAMPLE RSEC SPREADSHEET DATA 

Aeronautical Radionavigation Radar 

 RSEC-D 

F0 2844.4 MHz 

Pp 91.500 dBm 

(t) 

Pulse 

Width or

Sub-Pulse

Width 

(u sec) 

(tr) 

Pulse 

Rise/ 

Fall 

time 

(u sec) 

(Bc) 

Chirp 

Band 

width 

(MHz) 

(Bd) 

Frequency

Deviation 

(N) 

Number 

of 

Chips 

(PRR) 

Pulse 

Repetition 

Rate 

(PPS) 

(FL) 

Lowest 

Channel 

Frequency 

(MHz) 

(FH) 

Highest 

Channel 

Frequency 

(MHz) 

1 0.6 0.05NA NA 1 1040NA NA 

2 0.6 0.05NA NA 1 1040NA NA 
102

(Bs) 

Frequency 

Hopping 

Range 

(MHz) 

(Pt) 

Maximum

Spectral

Power 

Density 

(dBm/kHz)

(d)** 

Compresssion Ratio

(no units) 

(PG) 

Processing

Gain 

(Bn(-20))

Necessary

Bandwidth

(MHz) 

B(-40) 

Bandwidth

(MHz) 

(S)* 

Slope 

(dB/dec) 

(X(dB)) 

Floor Level

of 

Mask(dB)

1 0 27.195NA 0.000 10.335 35.796 40 80

2 0.6 27.195NA 0.000 10.335 35.796 80 80

Aeronautical Radionavigation Radar

-120

-100

-80

-60

-40

-20

0

20

2550 2650 2750 2850 2950 3050 3150 3250 3350

Frequency, MHz

Received Power Normalized to Maximum (dB)

Data

Mask 1

Mask 2

Mask 1: , t=0.6, tr=0.05, Bc=NA, d=NA, Bc=NA, N=1, PRR=1040, FL=NA, FH=NA, Bs=0, Pt=27.233, PG=0., Bn(-20)=10.335, B(-

40)=35.796, S=40., X(dB)=80.