NTIA Technical Memorandum TM-05-431 

Bandwidth Dependence of 

Emission Spectra of Selected 

Pulsed-CW Radars 

Frank H. Sanders 

U.S. DEPARTMENT OF COMMERCE 

Carlos M. Gutierrez, Secretary 

Michael D. Gallagher, Assistant Secretary 

for Communications and Information 

August 2005

DISCLAIMER 

Certain commercial equipment, instruments, or materials are identified in this report to specify 

the technical aspects of the reported results. In no case does such identification imply 

recommendation or endorsement by the National Telecommunications and Information 

Administration, nor does it imply that the material or equipment identified is necessarily the best 

available for the purpose. 

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CONTENTS

Page 

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

2 APPROACH .................................................................................................................. 3

3 RESULTS AND ANALYSIS ......................................................................................... 4 

4 SUMMARY AND CONCLUSIONS.............................................................................. 12 

5 REFERENCES................................................................................................................ 13

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BANDWIDTH DEPENDENCE OF EMISSION SPECTRA 

OF SELECTED PULSED-CW RADARS 

Frank H. Sanders1

This technical memorandum describes measurements of the radiated emission 

spectra of selected maritime radiolocation radar transmitters in multiple 

bandwidths. The results support published criteria for selection of measurement 

bandwidths for emission spectra of non-FM pulsed-CW radars. This result 

complements the radar spectrum engineering criteria (RSEC) measurement 

procedures described in NTIA Report TR-05-420. 

Key words: radar emission measurement bandwidths; radar emission measurement 

 techniques; radar emissions; radar spectrum engineering criteria (RSEC); 

 spectrum measurements

1 INTRODUCTION 

Radar transmitter out-of-band and spurious emissions (together called unwanted emissions) are 

limited by regulations. Some emission masks (such as the NTIA radar spectrum engineering 

criteria (RSEC)) are specified in terms of amplitude suppression relative to the peak power 

produced at the radars’ fundamental frequencies (e.g., spurious emission suppression must be at 

least 60 dB below the fundamental power). Mask-compliance limits are computed on the basis of 

theoretically perfect emissions plus a margin that allows for realistic transmitter performance. 

Compliance with radar emission masks is determined through measurements. 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. This presents a problem for determining 

radar emission mask-compliance by measurements. 

An ideal peak-detected spectrum measurement result for a non-FM pulsed-CW radar transmitter

is shown in Figure 1. Power measured at the fundamental frequency (far left) varies as 

20 log(Bm), but maximizes when Bm exceeds the values recommended in published literature [1-

2] and reproduced in Table 1. In contrast, the measured power in the rest of the spectrum (the 

unwanted-emission region) climbs arbitrarily high as Bm increases. As a result, the difference 

between power values measured at the fundamental frequency versus other frequencies (reading 

between the left and right sides of Figure 1) decreases if Bm is greater than the values 

recommended in Table 1. 

 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.
Figure 1. Graphical theoretical representation of the measured power at a radar fundamental 

frequency versus power measured at other frequencies as measurement bandwidth changes. The 

modeled radar emission modulation is non-FM pulsed-CW.

This report addresses this issue by describing spectrum measurements on two maritime 

radiolocation (surface search and navigation) radars in the band 2,900-3,100 MHz and three 

maritime surface search radars in the band 8,500-10,500 MHz. The purpose of the measurements 

was to observe the variation of unwanted emission levels of these radars relative to the measured 

fundamental level as a function of Bm, so as to provide a check on the validity of Bm values 

recommended for measurement of emissions from non-FM pulsed-CW radars shown in Table 1. 

Table 1. Published Emission Spectrum Measurement Bandwidth, Bm (from [1-2 ]) 

Radar Modulation Type RSEC Measurement Bandwidth (Bm) 

Non-FM pulsed-CW and 

phase-coded pulsed 

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

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

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

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

CW Bm = 1 kHz

FM/CW Bm = 1 kHz

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

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 measurement. 

2
2 APPROACH 

The pair of 2,900-3,100 MHz maritime radars used in these measurements were provided by the 

government of Japan and were measured jointly by Japan and the United States (NTIA) at the 

Table Mountain radio quiet zone facility north of Boulder, CO. Two of the 8,500-10,500 MHz 

radars were also provided by Japan and were likewise measured jointly at Table Mountain. The 

third 8,500-10,500 MHz radar was the property of NTIA and was measured at Table Mountain 

on a different occasion. The 2,900-3,100 MHz radars were designated S-Band Radars 1 and 2, 

and the 8,500-10,500 MHz radars were designated X-Band Radars 1, 2, and 3, respectively. 

The radars were set up with antenna heights of about 3 m above the ground. The measurement 

antenna was a 1-m parabolic unit mounted about 4 m above the ground. Radiated measurements 

were performed in conformance with published procedures [1-2]. The measurement system

block diagram is shown in Figure 2. The S-Band radars and X-Band Radars 1 and 2 were all 

measured in two bandwidths; X-Band Radar 3 was measured in four bandwidths. Pulse widths of 

these radars are shown in Table 2. 

Figure 2. Block diagram of the radar emission measurement system. The spectrum analyzer 

was an Agilent E-4440A; the RF front end was custom-built by NTIA/ITS. 

Table 2. Emission Characteristics of Radars in this Study 

Radar Designator Pulse width, t

(ns) 

Maximum recommended measurement bandwidth, 1/t 

from [1-2] (MHz)

S-Band Radar 1 60 16.7 

S-Band Radar 2 70 14.3 

X-Band Radar 1 70 14.3 

X-Band Radar 2 60 16.7 

X-Band Radar 3 80 and 800 12.5 and 1.25, respectively

3
3 RESULTS AND ANALYSIS 

The results for S-Band Radars 1 and 2 are shown in Figures 3-6. The results for X-Band Radars 

1 and 2 are shown in Figures 7-10. Because the bandwidths used for the measurements on these 

radars were always equal to or less than (1/pulse width), as specified in Table 1, the resulting 

spectra maintain the same ratios between the power measured at the fundamental frequencies and 

the power measured in the out of band and spurious parts of the spectra. This is demonstrated in 

Figures 4, 6, 8, and 10, where the maximum measured power levels at the radar fundamental 

frequencies are normalized and the emission spectra are observed to overlie each other. 

The measured emission spectra for short-pulse and long-pulse radar modes of X-Band Radar 3 

are shown in Figures 11 and 12. Measurement system internal noise occurs as flat floors at 

frequencies between 7,300-8,000 MHz and 11,000-11,200 MHz. 

Figure 13 shows measured power at the X-Band Radar 3 fundamental frequency (approximately 

9410 MHz) as a function of measurement IF bandwidth. The data in this figure confirm that the 

radar fundamental power varies as 20 log(Bm) for values of Bm that are equal to or less than (1/t),

where t is the radar pulse width. 

Figure 14 shows the spectra of X-Band Radar 3 normalized to the same power level at the 

fundamental frequency in short-pulse (80-ns) mode. In this mode, the 80 ns 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 bandwidths that were used, including 8 MHz. 

Figure15 shows the spectra of X-Band Radar 3 normalized to the same power level at the 

fundamental frequency in long-pulse (800-ns) mode. In this case, the 3-dB emission bandwidth 

is predicted to be 1.25 MHz. The 300-kHz and 1-MHz spectra are identical to each other, 

because these bandwidths (which are less than (1/t)=1.25 MHz) meet the requirements of 

Table 1. But the 20 log(Bm) progression ceases for Bm values of 3 MHz and 8 MHz; 

consequently these spectra show higher levels of unwanted emissions relative to the power 

measured at the fundamental. This effect could cause the radar spectrum to (falsely) appear to 

fail to meet an emission mask limit if it were measured in these bandwidths for that purpose. 

Thus such bandwidths would be incorrect choices for emission mask compliance measurements 

in the long pulse mode, even though they would be acceptable choices for this radar in the short 

pulse mode. 

The data in Figure 14 demonstrate an additional benefit that accrues from using measurement 

bandwidths that match the values of Table 1: the greatest dynamic range occurs in the spectrum

measurements when the bandwidth limits of Table 1 are used. This effect is observed in the 

offsets of the measurement system noise floors of the normalized data traces between 7300-

8000 MHz in that figure. Achieving wide measurement dynamic range is an important 

consideration in emission mask compliance requirements that may specify unwanted emission 

suppression levels of 80 dB relative to the maximum power at the fundamental frequency, and 

which therefore require at least 90 dB of dynamic range in the measurement system. Use of the 

best-matched measurement bandwidth is an easy and effective way to boost dynamic range 

without incurring extra engineering costs on the measurement system. 

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Figure 3. S-Band Radar 1 measured in 1-MHz and 3-MHz bandwidths. 

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Figure 4. S-Band Radar 1 emission spectra with the 1-MHz and 3-MHz data normalized to 0 

dB at the fundamental. Either bandwidth could be used for an emission mask measurement, but 

the 3-MHz data could be collected three times faster than 1-MHz data. 

Figure 5. S-Band Radar 2 measured in 1-MHz and 3-MHz bandwidths. 

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Figure 6. S-Band Radar 2 emission spectra with the 1-MHz and 3 MHz data normalized to 0 

dB at the fundamental. Either bandwidth could be used for an emission mask measurement, but 

the 3-MHz data could be collected three times faster than 1-MHz data. 

Figure 7. X-Band Radar 1 measured in 1-MHz and 8-MHz bandwidths. 

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Figure 8. X-Band Radar 1 emission spectra with the 1-MHz and 8-MHz data normalized to 

0 dB at the fundamental. Either bandwidth could be used for an emission mask measurement, but 

the 8-MHz data could be collected eight times faster than 1-MHz data. 

Figure 9. X-Band Radar 2 measured in 1-MHz and 8-MHz bandwidths. 

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Figure 10. X-Band Radar 2 emission spectra with the 1-MHz and 8-MHz data normalized to 

0 dB at the fundamental. Either bandwidth could be used for an emission mask measurement, but 

the 8-MHz data could be collected eight times faster than 1-MHz data. 

Figure 11. X-Band Radar 3 emission spectrum measured in four bandwidths with transmitter 

operating in short-pulse (80 ns) mode. 

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Figure 12. X-Band Radar 3 emission spectrum measured in four bandwidths with transmitter 

operating in long-pulse (800 ns) mode. 

Figure 13. Measured power at the X-Band Radar 3 fundamental frequency as a function of 

bandwidth and pulse mode. In accordance with Table 1, any of the indicated bandwidths may be 

used to measure emissions in the short-pulse mode, but only bandwidths of about 1 MHz or less 

should be used to measure the long-pulse mode for verification of emission mask compliance. 

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Figure 14. Normalized short-pulse emission spectra of X-Band Radar 3 as measured in 300 kHz, 

1 MHz, 3 MHz, and 8 MHz (from Figure 11), with the fundamental frequency maxima of all 

four spectra set to 0 dB. The normalized spectra are nearly identical within the uncertainty of the 

measurement; any of these bandwidths may be used to correctly measure the radar spectrum. 

Figure 15. Normalized long-pulse emission spectra of X-Band Radar 3 as measured in 

300 kHz, 1 MHz, 3 MHz, and 8 MHz (from Figure 12), with the fundamental frequency maxima

of all four spectra set to 0 dB. 

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4 SUMMARY AND CONCLUSIONS 

In summary, measurements of unwanted (spurious and out-of-band) emissions from five 

different non-FM pulsed-CW maritime radars are shown to yield the same results regardless of 

the value of Bm provided that Bm is less than (1/t), as recommended in Table 1. Time and effort 

can be saved in such measurements without sacrificing the accuracy of results if measurements 

are performed in the widest possible bandwidth that is still less than (1/t). For example, a 

measurement in 8 MHz will take 1/8 as long as a measurement in 1 MHz and will be just as 

accurate, provided that the radar pulse width is less than (1/(8 MHz)) = 125 ns. 

When measurement bandwidths are wider than the values in Table 1 for non-FM pulsed-CW

emissions, it is demonstrated that the measured levels of unwanted emissions are higher relative 

to the fundamental emission level than when they are measured in bandwidths that conform with 

the requirements of Table 1; such bandwidths should not be used for emission mask compliance 

measurements on such radars. 

Maximum measurement dynamic range is demonstrated to occur when the measurement system 

bandwidth equals the bandwidth limits of Table 1. This is an important consideration when 

emission mask compliance requirements are 80 dB lower than the maximum power at the radar 

fundamental, and the measurement system must therefore achieve a dynamic range of at least 

90 dB. Using the best-matched measurement bandwidth maximizes the measurement dynamic 

range without incurring extra engineering costs in the measurement system (such as reducing 

system noise with a higher-performance low-noise amplifier at the RF front end). 

It is noted in passing that 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 that is not entirely 

predictable on theoretical grounds [1]. Therefore, measurement of emission spectra in multiple 

bandwidths, as shown for example in Figures 11 and 12, is recommended until this phenomenon 

is better understood. 

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5 REFERENCES 

[1] F.H. Sanders, R.L. Hinkle, and B.J. Ramsey, “Measurement procedures for the radar 

spectrum engineering criteria (RSEC),” NTIA Report TR-05-420, Mar. 2005. 

[2] ITU-R Recommendation M.1177-3, “Techniques for measurement of unwanted 

emissions of radar systems,” International Telecommunication Union, Radiocommunication 

Sector, 2003. 

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