1 1 United States Department of Commerce

I Al I National Institute of Standards and Technology

NISTIR 90-3939

EMR TEST FACILITIES

EVALUATION OF A

SMALL REVERBERATING CHAMBER

LOCATED AT RADC, GRIFFISS AFB

ROME, NEW YORK

Myron L. Crawford

John M. Ladbury

Bill F. Riddle

Ezra B. Larsen

QC

100

.U56

90-3939

1990
NATIONAL INSTITUTE OF STANDARDS &

TECHNOLOGY

Research Intonation Carla:

Gaithersburg, MD 20899

DATE DUE

Demco, Inc. 38-293
NISTIR 90-3939

EMR TEST FACILITIES

EVALUATION OF A

SMALL REVERBERATING CHAMBER

LOCATED AT RADC, GRIFFISS AFB

ROME, NEW YORK

Myron L. Crawford

John M. Ladbury

Bill F. Riddle

Ezra B. Larsen

Electromagnetic Fields Division

Center for Electronics and Electrical Engineering

National Engineering Laboratory

National Institute of Standards and Technology

Boulder, Colorado 80303-3328

June 1990

Sponsored by

Compatibility and Measurements Division

RADC/RBC

Griffiss AFB, New York 13441

U.S. DEPARTMENT OF COMMERCE, Robert A. Mosbacher, Secretary

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, John W. Lyons, Director

CONTENTS

Page

Abstract - 1

1. Introduction - 2

2. Description of the RADC Small Reverberating Chamber and NIST

Evaluation Systems 3

3. CW Evaluation of the RADC Small Reverberating Chamber 5

3.1 Antenna Coupling Efficiency and VSWR 5

3.2 Chamber Q Factor 6

3.3 Tuner Effectiveness 7

3.4 Test Zone E-Field Uniformity 7

3.5 E-Field Amplitude Calibration 8

3.6 Comparison of Data for the RADC Small Reverberating Chamber

with the NIST Anechoic Chamber 9

4. CW Measurement Uncertainty for the RADC Small Reverberating Chamber 10

4.1 Estimate of Uncertainty for Establishing a CW E-Field

Amplitude in the Chamber 10

4.2 Comments on CW Measurement Uncertainty 10

5. Pulsed RF Evaluation of the RADC Small Reverberating Chamber 11

5.1 Background 11

5.2 Evaluation of Pulsed RF Measurements in the Mode-Tuned

Chamber - 12

5.3 Evaluation of Pulsed RF Measurements in the Mode -Stirred

Chamber - - 13

5.4 Comments on Pulsed RF Measurements 14

6. Summary and Conclusions - - - 14

7. Recommendations - 15

8. Acknowledgments - 16

9. References - 16

iii

LIST OF FIGURES

Figure Page

2.1 Two isometric sketches of the RADC small reverberating

chamber 18

2.2 Cross sectional views of the RADC small reverberating chamber

showing placement of transmitting and receiving antennas,

chamber tuner and isotropic probes for measuring spatial

E-field uniformity 19

2.3 Six photographs of the RADC small reverberating chamber 20

2.4 Photograph of NIST equipment used to evaluate the RADC small

chamber - 21

2.5 Block diagram of instrumentation used in cw evaluation of the

RADC small chamber - 22

2.6 Block diagram of instrumentation used in pulsed rf evaluation

of the RADC small chamber 23

3.1 Measured VSWR of: (a) long wire antennas (0.2 to 18 GHz),

and (b) broadband horn antennas (0.8 to 18 GHz), transmitting

into the RADC small chamber 24

3.2 Measured coupling efficiency of: (a) long wire antennas (0.2

to 18 GHz), and (b) broadband horn antennas (0.8 to 18 GHz),

in the RADC small chamber. Losses determined in (b) are from

cw mode-tuned measurements and from pulsed rf measurements -- 25

3.3 (a) Theoretical and experimental Q of the RADC small chamber,

and (b) ratio of theoretical to experimental Q (0.4 to 18 GHz) 26

3.4 Measured tuner effectiveness in the small chamber using: (a)

long wire antenna (0.2 to 18 GHz), and (b) broadband horn

antenna (0.8 to 18 GHz) 27

3.5a,b Spatial distribution of E-field components in the small

chamber measured with 10 NIST isotropic probes (5 cm dipoles)

,

using long wire antennas for transmitting and receiving:

(a) maximum values, and (b) average values. Net transmitted

power = 1 W 28,29

3.6a,b Spatial distribution of E-field components in the small

chamber measured with 10 NIST isotropic probes (5 cm dipoles)

,

using broadband horn antennas: (a) maximum, and (b) average

values. Net transmitted power = 1 W 30,31

3.7 Average values of E- field components in the small chamber

measured with 10 NIST isotropic probes (5 cm dipoles) , using

long wire antennas: (a) average of the 10 maximum values for

each component, and (b) average of the 10 average values.

Net transmitted power = 1 W 32

v
LIST OF FIGURES (CONTD.)

Figure Page

3.8 Average values of E- field components in the small chamber

measured with 10 NIST isotropic probes (5 cm dipoles) , using

broadband horn antennas: (a) average of the 10 maximum values

for each component, and (b) average of the 10 average values.

Net transmitted power = 1 W - 33

3.9 Maximum and average E-field strengths in the small chamber

measured with: (a) 1 cm dipole probe, and (b) received power

of long wire antenna. Net transmitted power = 0.1 W 34

3.10 Maximum and average E- field strengths in the small chamber

measured with: (a) 1 cm dipole probe, and (b) received power

of broadband horn antenna. Net transmitted power =0.1W 35

3.11 Maximum responses of NIST 1 cm dipole probe to an E-field of

37 dBV/m using: (a) RADC small reverberating chamber, and (b)

NIST anechoic chamber - 36

3.12 Maximum powers received by a broadband (1 to 18 GHz) horn

antenna in an E- field of 37 dBV/m using: (a) RADC small

reverberating chamber, and (b) NIST anechoic chamber 37

3.13 Comparison of: (a) free-space gain of a broadband horn

antenna, with (b) difference in maximum responses of the horn

measured in NIST anechoic chamber minus RADC small

reverberating chamber - 38

5.1a-j Maximum and average values of received rf pulse waveforms in

the mode -tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber;

(a) F = 0.9 GHz - 39

(b) F = 1.3 GHz --- 40

(c) F = 2.0 GHz 41

(d) F = 2.9 GHz 42

(e) F = 4.2 GHz 43

(f) F = 5.65 GHz 44

(g) F = 8.9 GHz 45

(h) F = 12 GHz 46

(i) F = 16 GHz - 47

(j) F = 18 GHz 48

5.2 Graphs of data from figure 5.1 showing the time required for

3 /is rf pulses transmitted into the mode -tuned chamber to rise

to 63 % of the steady state amplitude, using: (a) no absorber,

and (b) 1 piece of 7 . 6 cm x 61 cm x 61 cm rf absorber 49

5.3 Graphs of data from figure 5.1 showing the time required for

3 n s rf pulses transmitted into the mode -tuned chamber to rise

to 90 % of the steady state amplitude, using: (a) no absorber,

and (b) 1 piece of 7 . 6 cm x 61 cm x 61 cm rf absorber 50

vi
LIST OF FIGURES (CONTD.)

Figure Page

5.4a,b Graphs of correction factors for response ammplitude of rf

pulses in the mode -tuned chamber as a function of frequency,

at selected pulse duration, using: (a) no absorber, and (b)

1 piece of 7.6 cm x 61 cm x 61 cm rf absorber 51,52

5.5a-j Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber;

(a) F = 0.9 GHz - 53

(b) F = 1.3 GHz 54

(c) F = 2.0 GHz - 55

(d) F = 2.9 GHz 56

(e) F = 4.2 GHz 57

(f) F = 5.65 GHz - 58

(g) F = 8.9 GHz - - 59

(h) F - 12 GHz 60

(i) F = 16 GHz - 61

(j) F = 18 GHz - 62

5.6 Graphs of data from figure 5.5 showing the time required for

3 /j,s rf pulses transmitted into the mode- stirred chamber to

rise to 63 % of the steady state amplitude, using: (a) no

absorber, and (b) 1 piece of 7 . 6 cm x 61 cm x 61 cm rf

absorber - 63

5.7 Graphs of data from figure 5.5 showing the time required for

3 [i s rf pulses transmitted into the mode -stirred chamber to

rise to 90 % of the steady state amplitude, using: (a) no

absorber, and (b) 1 piece of 7.6 cm x 61 cm x 61 cm rf

absorber - 64

5.8a,b Graphs of correction factors for response amplitude of rf

pulses in the mode -stirred chamber as a function of frequency,

at selected pulse durations, using: (a) no absorber, and (b)

1 piece of 7.6 cm x 61 cm x 61 cm rf absorber 65,66

vii
LIST OF TABLES

Table Page

3.1 Spatial variation of the cw E- field average and maximum

values measured in the RADC small reverberating chamber 67

4.1 Summary of estimated uncertainties for determining the cw

field strength inside the mode -tuned RADC small

reverberating chamber (0.5 to 2.0 GHz) - 68

4.2 Summary of estimated uncertainties for determining the cw

field strength inside the mode-stirred RADC small

reverberating chamber (2 to 18 GHz) - 69

5.1a,b Mode-tuned data obtained from figure 5.1, giving rise times

and correction factors for rf pulses in the RADC small

reverberating chamber - 70,71

5.2a,b Mode-stirred data obtained from figure 5.5 giving rise times

and correction factors for rf pulses in the RADC small

reverberating chamber 72,73

viii
EMR Test Facilities:

Evaluation of a Small Reverberating Chamber

Located at RADC, Griffiss AFB , New York

Myron L. Crawford

J ohn M . Ladbury

Bill F. Riddle

Ezra B. Larsen

Electromagnetic Fields Division

National Institute of Standards and Technology

Boulder, Colorado 80303

This report describes measurement procedures and results from

evaluating a small reverberating chamber located at Rome Air

Development Center (RADC), Rome, New York. The chamber was developed

for measuring and analyzing the electromagnetic

susceptibility/vulnerability (EMS/V) of weapon systems and the radio

frequency (rf) shielding effectiveness of enclosures and materials. A

brief description of the facility is given, including instrumentation

for its evaluation and calibration by the National Institute of

Standards and Technology (NIST) . Work was done earlier at NIST to

evaluate the RADC large reverberating chamber. A follow-on project to

construct and evaluate a small chamber is discussed in this report.

Measurements include: (1) voltage standing wave ratio (VSWR) of the

transmitting and receiving antennas; (2) coupling efficiency of the

chamber; (3) effectiveness of the chamber tuner; (4) E- field uniformity

in the test zone; (5) calibration of test E-fields based on receiving

antenna power measurements and calibrated dipole probe voltage

measurements; (6) responses of standard equipment under test (EUT) to

test fields in the RADC reverberating chamber and the NIST anechoic

chamber; and (7) performance of the reverberating chamber excited by rf

pulses at ten frequencies from 0.9 to 18 GHz, four pulse widths from

0.1 to 3 /is , and for two values of chamber Q. Conclusions are that the

chamber can be used at frequencies down to 500 MHz for cw testing, and

for pulsed rf immunity testing with pulse widths as short as 0.3 /is.

Estimates of measurement uncertainties are given.

Key words : electromagnetic radiated susceptibility/vulnerability

testing ; pulsed rf measurements ; reverberating chamber .

1
1.

Introduction

The use of a reverberating chamber for performing EMS/V measurements is

relatively new. Considerable work has been done to evaluate and document

methods for using this technique [1-3]. Research work has also been done at

the National Institute of Standards and Technology (NIST) to evaluate,

develop, describe, and document the methodology for performing radiated

susceptibility/vulnerability (EMS/V) measurements using a reverberating

chamber. This effort is described in an NIST publication [4] and an IEEE

Proceedings paper [5]. In addition, work was performed to determine the

feasibility of using such a chamber for pulsed rf immunity testing [6,7].

Finally a project for the present sponsor covered the evaluation of a large

reverberating chamber (9.78 m x 5.18 m x 3.69 m)

.

This work is summarized

in an interagency report sent to the sponsor in December 1987 [8]. The

measurements described in that report are similar to those discussed in the

present report, which pertains to a small chamber (1.75 m x 1.41 m x 1.57

m)

,

based on the sponsor's guideline. Both the "large" and "small"

reverberating chambers are now located at Griffiss Air Force Base (AFB) , but

the data for the small chamber were taken by NIST personnel while the

chamber was at its original location at NIST in Boulder, Colorado.

The incentive for performing this work stems from numerous advantages

suggested for the use of a reverberating chamber. These include:

1. Electrical isolation from or to the external environment;

2. Convenience (indoor test facility) compared with an open field test

site

;

3. Ability to generate high level fields over a large test volume with

relatively small power;

4. Broad frequency coverage;

5. Cost effectiveness;

6. Potential use for both radiated susceptibility and emission testing

with minor instrumentation changes;

7. No requirement of physical rotations of the equipment under test

(EUT); and

8. Security.

These advantages are somewhat offset by limitations, which include loss

of polarization and directivity information relative to the EMC/EMI profile

of the EUT, and limited measurement accuracy. However, this technique does

offer a time-efficient, cost-effective way to evaluate the EMS/V performance

of large equipment using an existing shielded enclosure with minor

modifications. The measurement concept utilizes the shielded, high-Q,

multimoded environment to obtain time-averaged field strengths that simulate

"real world" near- field environments. Also, it is sometimes the only

technique by which high exposure fields can be generated safely to perform

EM susceptibility tests required by the Department of Defense for some of

their applications.

These considerations, along with others, motivated RADC to invest in

the research and development of this methodology. They then constructed and

Pi aced into operation two reverberating chamber facilities, one of which is

described in this report.

Measurements described in this report were performed between January

and May, 1989.

2
2. Description of the RADC Small Reverberating Chamber and NIST Evaluation

Systems

The RADC small reverberating chamber is a rectangular shielded

enclosure 1.75 m x 1.41 m x 1.57 m (5.75 ft x 4.625 ft x 5.15 ft) in size,

constructed from sheet aluminum welded together at the edges. Cross

sectional views of the chamber are shown in figure 2.1. It is equipped with

two bulkhead access panels and an access door located at the end of the

chamber. The chamber is also equipped with a tuner shown in figure 2.2

consisting of a rectangular blade about 1 m in cross section. The tuner is

rotated in a step-wise fashion under computer control.

The locations and orientations of the chamber's excitation

(transmitting) and reference (receiving) antennas are shown in figure 2.2.

The antennas are placed so as to be cross polarized or in the corners of the

chamber and oriented toward the corners to ensure that the transmitted

signal couples into all possible modes and to monitor the reference received

signal from all possible modes as efficiently and uniformly as possible.

This must be done without favoring particular modes or transmitting directly

into the chamber's test zone, or coupling the signal directly between the

transmitting and receiving antennas. This is necessary to obtain a

statistically uniform, spatial distribution of the field in the chamber's

test zone. Photographs of six different views of the chamber are shown in

figure 2.3. Captions are given for each photograph describing the

particular view.

Figure 2.4 is a photograph of the NIST equipment used to perform the

chamber evaluations. Figure 2.5 is a block diagram of the NIST system used

for the cw evaluation measurements and figure 2.6 is the block diagram of

the NIST system used for the pulsed rf evaluation measurements of the

chamber. A test field is established inside the chamber by means of an rf

source (cw or pulsed, depending on the tests being performed) connected to

the appropriate transmitting antenna. The term "cw" used here stands for

continuous wave and refers to a single -frequency sinusoidal signal, and the

term "pulsed rf" refers to pulse-modulated cw with characteristics similar

to a pulsed radar signal. Modes excited inside the chamber are stirred by

rotating the tuner, which functions as a field-perturbing device.

The test zone in the chamber is defined as the total volume minus a

minimum separation from the walls and ceiling of approximately 30 cm.

Placement of the equipment under test (EUT) should fall within this volume

except, possibly, relative to the floor. The separation distance between

the EUT and the floor may be less than 30 cm depending upon the intended EUT

configuration relative to the ground plane. Test leads and cables are

routed to appropriate monitors, etc., outside the chamber through shielded

feed-through connectors. Coaxial cables are used for rf signals, and high

resistance lines are used for dc signals. This is done to prevent leakage of

the EM energy to the outside environment or into the instrumentation room.

To minimize impedance mismatching, a 10 -dB attenuator was used whenever

possible between the receiving antenna and the 5 0 -

Q

power sensor or spectrum

analyzer

.

The chamber was evaluated using two different operational approaches

referred to as mode-tuned and mode-stirred [4]. For the mode-tuned tests,

the tuner is stepped in uniform increments and measurements are made at each

tuner position of the net input power supplied to the transmitting antenna,

the receiving antenna power, the field-measuring probe responses and the

3
equipment under test (EUT) response. Corrections are then made for the

changes in the transmitting antenna's input impedance as a function of tuner

position and frequency. The measurement results are then normalized to a

constant net input power value. The number of tuner steps used per

revolution was 200 (increments of 1.8 degree).

For the mode -stirred tests, the tuner was continuously rotated while

sampling the reference antenna received power, the field probe response and

the EUT response at rates much faster than the tuner revolution rate. These

measurements were made using a spectrum analyzer (cw tests) , or transient

digitizer (pulsed rf tests) with diode detectors and "smart" voltmeters

capable of data storage and calculation of statistical functions. Large

data samples (up to 9,999) are obtained for a single tuner revolution.

Tuner revolution rates are adjusted to meet the EUT output monitor, diode

probe response time, and sampling rate requirements of the instrumentation.

Typical rates used were approximately 3 to 6 minutes per revolution. For

mode-stirred tests, the input power was measured only at the beginning of

each measurement cycle. For the cw tests, as shown in figure 2.5, a

calibrated bidirectional coupler was used at the input to the transmitting

antenna to measure the net input power. For the pulsed rf tests, only the

incident signal was measured as shown in figure 2.6. Details of how the

measurement cycles proceed under computer control, and how the data are

recorded, managed, and processed for presentation, are contained in [4,8].

The transmitting and reference receiving antennas used for the cw tests

were long wire antennas (0.2 - 1.0 GHz), and broadband horn antennas (0.8 - 18.0 GHz)

.

For the pulsed rf tests, the mode- tuned approach was used to optimize

absolute measurement accuracy, to obtain complete statistical information

for evaluating the time domain response characteristics of the reference

antenna's received signal, and to determine total energy content in the

received pulse relative to the normalized energy in the transmitted pulse.

The mode-stirred approach was used for relative measurements, with the

digitizing oscilloscope placed in its maximum-hold mode of operation. This

approach is much faster than the mode -tuned approach and results in much

larger data sampling than the mode -tuned approach; however, it does not

provide complete statistical results, since only maximum values are

recorded. The approach used was determined by the final results needed. In

some cases both approaches were used, and the results are given for

comparison. The mode- tuned approach was required for complete statistical

data and total energy ( transmitted-versus-received) analysis. The modestirred approach was used to analyze relative information such as charge and

decay time and to determine test field amplitude correction factors for

input rf pulse widths too short for the chamber to charge up to its steady

state or cw response value. The digitizing oscilloscope used is capable of

measuring signals with rise times of approximately 30 ps , at a sampling rate

of 50 kHz, with sample sizes up to 1024 per scan.

4
3 . CW Evaluation of the RADC Small Reverberating Chamber

How well a shielded enclosure can be made to operate as a reverberating

chamber depends upon a number of considerations. The major requirement is

that the enclosure be large compared to the wavelength of the lowest

frequency intended for use so that sufficient modes, necessary to obtain

statistical spatial field uniformity, exist. Other considerations include

mode density and quality factor [9]. These requirements should be fulfilled

for the RADC chamber described above at frequencies above approximately 500

MHz.

3.1 Antenna Coupling Efficiency and VSWR

The efficiency with which energy can be injected into or coupled out of

the chamber via the transmitting and receiving antennas is determined by:

(a) the VSWR of the antennas (that is, the impedance match between the rf

source and the transmitting antenna or between the receiving antenna and its

output detector) , and (b) the ability of the antennas to couple energy into

or out of the particular modes that exist at the test frequencies of

interest. Rotating the tuner changes the characteristics of the field

inside the chamber, which in turn influences the effective VSWR of the

antennas. Hence the net input power supplied to the chamber's transmitting

antenna and the power accepted by the receiving antenna vary as a function

of tuner position. That is, the impedance match between the rf source and

transmitting antenna, and between the receiving antenna and its termination,

affect the power transfer between the two antennas. This can result in

errors in determining the amplitude of the field inside the enclosure.

Variations, determined statistically, in the VSWR of the two

transmitting antennas used to excite the RADC small chamber are shown in

figure 3.1. The receiving antenna's VSWRs should be similar. The figures

show the maximum, average, and minimum VSWR obtained by rotating the tuner

through a complete revolution at frequencies from 200 MHz to 18 GHz (long

wire antennas) and from 800 MHz to 18 GHz (broadband horn antennas) . Large

variations and high values of VSWR exist, especially at the lower

frequencies. At higher frequencies the variations become less and the VSWR

values are lower, approaching the free -space VSWR of the antennas.

The coupling efficiency of the antennas placed inside the chamber is

defined as the ratio of the net input power delivered to the transmitting

antenna to the power available into a 50 -Q matched impedance at the

terminals of the receiving antenna. These ratios (insertion loss) , referred

to as chamber loss, are given in figure 3.2. The curves show: (a) the

average and minimum losses measured for the mode -tuned approach when using a pair of long wire antennas, and (b) the average and minimum losses using a pair of broadband ridged-waveguide rectangular horn antennas. Impedance

mismatch between the receiving antenna and power detector used to measure

the received power are not accounted for in these measurements. The

magnitude of the error resulting from this is discussed in [4,8] and

included in tables 4.1 and 4.2.

5
3.2 Chamber Quality Factor

The chamber's quality factor (Q) influences the operation of the

chamber in a number of ways. Examples are tuner effectiveness, rf input

power requirements and the accuracy with which test field levels can be

established inside the chamber. Another important factor is the time

required for the chamber to charge up to a steady- state condition after the

input pulsed signal is applied. This influences the chamber's response

characteristics for pulsed rf testing, as will be discussed later.

From resonant cavity theory the chamber's "composite Q" , (^) , can be

determined [9] from the equation

3 V

S<$ /x s r

[’ 1 + 3A t

16 ' >]

( 1 )

3 where V is the volume inside the chamber in m , S is the internal surface

2 1/2

area in m , and 8

= [2 /(uyza)] is the skin depth in m, A is the

wavelength in m, and a, b, and c are the chamber's internal dimensions in m. The chamber's composite Q is determined by averaging the 1/Q values of

all possible modes within a small frequency interval about the frequency of

interest. Equation (1) is considered a maximum or upper bound because it

assumes the chamber losses are due only to finite wall conductivity. In

reality, 'other factors such as rf energy leakage from the chamber, loss in

antenna support structures, and loss in the chamber wall coatings also

contribute to the total losses.

An alternative means of determining the chamber Q is to measure the

insertion loss between a transmitting and receiving antenna pair. If the rf

energy is uniformly distributed throughout the volume of the reverberating

chamber, an empirical value of Q can be obtained [10] from the equation

Q' = 16

••(-at)

(2)

where is the power available at the receiving antenna in W and P^_ is the

net input power delivered to the transmitting antenna in W.

Results obtained using (1) to calculate the composite Q and by using

the chamber loss data shown in figure 3.2 together with (2) to calculate the

experimental Q are shown in figure 3.3. Figure 3.3 (a) gives the

theoretical Q and experimental Q for the RADC small chamber, and figure 3.3

(b) shows the ratio of theoretical to experimental Q. At the higher

frequencies the ratio approaches a value roughly equal to 2. This indicates

that at frequencies where (1) and (2) are valid, there are relatively small

losses other than loss in the chamber walls.

6
3.3

Tuner Effectiveness

A consideration in the operation of a reverberating chamber is the

effectiveness of the tuner to obtain randomness in the distribution of the

test signal inside the chamber. To achieve this the tuner must be

electrically large and be shaped or oriented to distribute energy equally

into all possible chamber modes. A test to determine how well the tuner is

functioning is to measure the ratio of the maximum to minimum power in the

receiving antenna as a function of tuner position. This is done while

maintaining a constant net input power to the transmitting antenna. A large

power ratio indicates that the tuner is effective in redistributing the

scattered fields inside the chamber.

Measurement results for the RADC small chamber are given in figure 3.4.

Figure 3.4 (a) gives the ratio of maximum to minimum received power using

the long wire antennas over the frequency range 0.2 to 18 GHz. Figure 3.4

(b) gives the same type of data using broadband horns over the frequency

range 0.8 to 18 GHz. A number of factors related to the design of the tuner

can influence the magnitude of this ratio. Also, a reduction in this ratio

caused by placing rf absorber and/or an EUT inside the chamber is a measure

of the loading effect. A minimum ratio of 20 dB is recommended to assure

proper operation of the chamber [4]. As seen in figures 3.4 (a) and (b) , a tuner effectiveness greater than 20 dB was achieved for the RADC small

chamber at all frequencies for both types of antennas.

3.4 Test Zone E-Field Uniformity

Tests were made to determine the E- field uniformity in the chamber as

a function of spatial position and frequency, again, using both long-wire

and broadband horn antennas. Ten small NIST isotropic probes [11,12,13]

designed to operate at frequencies up to 2 GHz were placed at various

locations inside the chamber as shown in figure 2.2. Each probe has three

orthogonally oriented dipoles which are aligned with the three axes of the

chamber, namely transverse (Ex), longitudinal (Ey) , and vertical (Ez)

.

Measurements were made of the field strength of each orthogonal component at

the ten locations for each tuner position (200 steps of 1.8 degree for

frequencies 200 - 1000 MHz and 400 steps of 0.9 degree for frequencies 1.0 - 2.0 GHz). These data were normalized for a net input power of 1 W applied

at the input terminals of the transmitting antennas . The maximum and

average values for each field component and the "total magnitude" (root-sumsquared or RSS value of the three components) were then determined from the

complete data sets. The results of these measurements are shown in figures

3.5 and 3.6. The spread in the data shows the amount of spatia^L field

variation inside the chamber at the indicated frequencies. The field

strength in the graphs of figure 3.5 drops significantly at frequencies

below 0.5 GHz. This is due to the decrease in efficiency of the long wire

transmitting antenna used and to the lower number of modes available in the

chamber. The chamber appears to be operating properly at frequencies down

to at least 500 MHz, but with rather large spatial variations at the lower

frequencies. The spatial variations at selected frequencies are summarized

in Table 3.1. The average values, determined statistically from all ten

locations, for the average and maximum E-fields of each component and their

7
composite total are summarized in figures 3.7 and 3.8. The relative

amplitudes of the field components of each figure are approximately the

same. The composite total of the average E- field components in figures 3.7

(b) and 3.8 (b) are approximately 4.8 dB or the ratio of J 3 greater than

the individual components. This indicates that the average component values

are randomly polarized in the chamber. The composite total maximum

amplitudes in figures 3.7 (a) and 3.8 (a), however, are only about 3 dB

greater than the individual components. This indicates that the maximum

components' values are not completely independant of each other. This is

similar to the results obtained in the RADC large reverberating chamber and

in the NIST reverberating chamber and appears to be inherent in the

measurement method. The implication is that if multiple receptors are used

(for example an isotropic probe whose output is a function of all three

orthogonal dipoles) in establishing the test field amplitude inside a

reverberating chamber, the results will be biased either 3 dB for maximum

response data or 4.8 dB for average response data.

A comparison of figures 3.7 and 3.8 indicates slightly higher E- field

amplitudes in the chamber when using broadband transmitting antennas, as

compared with long wire antennas for the same input power. This is because

of the horn's higher efficiency. As mentioned earlier, the E-field

amplitude in the chamber is influenced by the chamber Q. Inserting the 10

probes into the chamber with their lossy transmission lines lowers the

chamber Q and hence the field strength in the chamber compared to the field

strength that would be present without the loading effect of the multi-probe

system.

3.5 E-Field Amplitude Calibration

The field strength in the chamber can be determined in two ways. The

first technique is to measure the power received by the reference antennas,

and then determine the equivalent power density in the enclosure using the

equation [4]

where E is the equivalent electric field in V/m, rj is the average wave

cl 2 impedance of the chamber in Q, is the equivalent power density in W/m ,

in the enclosure, A is the wavelength in m, and is the average measured

received power in W. The average wave impedance is assumed to be

approximately equal to 1207T Q. The validity of (3) has been verified and is

discussed in section 2.3.1 of [4]. The maximum and average electric field

strengths inside the chamber determined from the receiving antenna power

measurements and (3) are shown in figures 3.9 and 3.10. These data were

normalized to 0.1 W net input power to the transmitting antenna.

8
The electric field strength inside the chamber can also be determined

by measuring it with one or more calibrated probes. Data obtained using a

1-cm dipole probe fabricated at NIST are also shown on figures 3.9 and 3.10.

The probe was calibrated in a planar field using a TEM cell [14] at

frequencies up to 500 MHz and in an anechoic chamber at frequencies from 500

MHz to 18 GHz [15]. The assumption is made that the field strength over the

aperture of the probe inside the reverberating chamber will approximate the

planar field used to calibrate the probe. This is reasonable, at least at

frequencies for which the probe is electrically small. Also, the open- space

far-field gain of an electrically small dipole is small (1.76 dB) . Thus,

the probe -measured fields should be equivalent, within approximately 1.76

dB, to the E- fields determined using a receiving antenna. This is true if

the equivalent gains for the probe and receiving antenna, after being placed

inside the chamber, are assumed to be 0 dB. The agreements shown in figures

3.9 and 3.10 are typical of those observed in the data when determining

field strengths inside reverberating chambers.

3.6 Comparison of Data for the RADC Small Reverberating Chamber with the

NIST Anechoic Chamber

Comparisons of the response or EMS/V characteristics of EUT obtained

using an anechoic chamber, with those obtained using a reverberating

chamber, are typically made in terms of maximum (peak) values. The main

reason for this is that the EUT's worst-case performance or susceptibility

is typically the desired quantity. Also, it is very difficult to obtain a

true average response for an EUT from anechoic chamber data. Even

determining the EUT's peak response in an anechoic chamber (depending upon

how well behaved the EUT receiving pattern characteristic is)

requiresconsiderable effort and may involve complete pattern measurements.

The benefit of making the above type of comparison is to obtain a

"correlation factor" between results obtained in the reverberating chamber

and in an anechoic chamber. This should first be done for reference

standard EUTs and then for an EUT which is more typical of operational

equipment. For this effort, two reference EUTs were used. These were: (a)

a 1 cm dipole probe referred to earlier, and (b) a small broadband horn

antenna similar to what is used at frequencies from 0.8 to 18 GHz as the

transmitting and receiving antennas in the chamber. The measurements were

performed in both the RADC small reverberating chamber and in the NIST 4.9 m

x 6.7 mx 8.5 m anechoic chamber in Boulder, CO.

The maximum response values obtained using the 1 cm dipole probe are

given in figure 3.11. The probe response in the anechoic chamber is greater

than its response in the reverberating chamber by an average of about 2 dB

.

This is expected, since it corresponds approximately to the free space gain

of an electrically short dipole. That is, the expected correction factor

between the EUT EMS/V response measurements, in the two facilities, is the

free -space gain of the EUT [4]

.

Measurements of the maximum response of a broadband horn antenna

obtained using the two chambers are shown in figure 3.12. For the anechoic

chamber measurements, the horn was aligned on the boresight (main beam) of

the transmitting antenna to obtain the maximum response. The horn response

is greater in the anechoic chamber than in the reverberating chamber by

9
approximately its free-space gain. This is shown in figure 3.13, which

compares the difference in the horn's maximum response in the two chambers

with the horn's calibrated free-space gain. As expected, the results are in

general agreement.

4. CW Measurement Uncertainty for the RADC Small Reverberating Chamber

4.1 Estimate of Uncertainty for Establishing a CW E-Field Amplitude in the

Chamber

As indicated in section 3, EMS/V test fields can be established in a

reverberating chamber in the following two ways: using a reference receiving

antenna or using a calibrated transfer probe. If a reference receiving

antenna is used, the field strength is determined using eq. (3). If an Efield probe is used, the field strength is determined in terms of the probe

response, after its calibration in a known E-field. Estimates of the

uncertainties in these methods as determined for the RADC small

reverberating chamber are summarized in tables 4.1 and 4.2 for the modetuned and mode-stirred approaches, respectively. These results are similar

to those determined for both the NIST and RADC large reverberating chambers,

details of which are given in [4,8]. General comments given in section 5.1

of [8], explaining the sources of uncertainty, are also applicable to the

RADC small chamber; however, the lower useful frequencies are higher because

of the chamber's smaller size.

4.2 Comments on CW Measurement Uncertainty

Some general comments on interpreting uncertainties of immunity

measurements are given as follows:

(a) If corrections are not made for impedance mismatch of the transmitting

or receiving antenna, absolute amplitude measurements of the test field

strength inside the chamber will be too low. This will cause an error in

determining the EUT response, which will also be too low. For example, the

low frequency data of figures 3.9 and 3.10 for the field determined from the

received power measurements should be corrected (response increased) to

account for the impedance mismatch between the receiving antenna and power

detector

.

(b) The wave impedance, when measuring the maximum response of an EUT,

appears to be higher than 377 ft, especially for frequencies lower than 2

GHz. This means that if a wave impedance of 377 ft is assumed when

determining the maximum amplitude of an exposure field, there will be a

systematic error resulting in too low a calculated E-field value. Since the

actual E- field is higher than the calculated value, this results in too high

an EUT response indication for a specified E- field exposure. If the field

strength is determined by using a calibrated E-field probe, there is still

some uncertainty, since the wave impedance is different in the probe

calibration environment than in the reverberating chamber. An estimate of

this error is included in tables 4.1 and 4.2.

10
(c) The spatial variation of the E-field values in the mode-tuned chamber

decreases with increasing frequency from as great as ± 7 dB at 500 MHz to

less than ± 3 dB at 2 GHz. This variation is expected to continue to

decrease as the frequency increases. However, other variations and

uncertainties were found, using the reference standard EUTs (1 cm dipole and

broadband horn), at high frequencies where the spatial E-field variation is

small. These are due to other sources of error as shown in tables 4.1 and

4.2. One technique to reduce the total error would be to increase the

number of frequencies at which data are taken, or increase the number of

receiving probes used to measure the exposure field, and then average the

data taken.

5. Pulsed Rf Evaluation of the RADC small Reverberating Chamber

5 . 1 Background

Parameters of electromagnetic interference (EMI) signals that can

contribute to upset in electronic equipment include: (a) total energy, (b)

peak amplitude, and (c) transient time characteristics. All these

parameters are modified, relative to free space, for signals transmitted

inside a reverberating chamber. Their characterization inside a reverberating chamber, particularly for pulsed rf fields, provides

information required to determine correction factors as a function of the

input pulse parameters. It also provides insight into the inherent

limitations associated with using this complex environment for pulsed rf

EMS/V testing. Obviously, these factors are influenced by the Q factor of

the chamber, since the time required for the pulsed wave's amplitude to rise

to its steady- state value inside the chamber and to decay to zero after the

input signal is removed, is a function of the chamber's Q. These "charge"

and "decay" times can be reduced by artificially lowering the chamber's Q,

for example, by inserting small amounts of rf absorber. However, this

reduces the accuracy in determining the test field amplitude. Results of

work to evaluate the response characteristics of the chamber when excited by

pulsed rf of various pulse widths and frequencies, and with the chamber

loaded with a small amount of absorber, are contained in this section.

Because of the advantages of using the reverberating- chamber method for

cw EMS/V pre-testing of an EUT, there is considerable interest in using this

technique also for pulsed rf EMS/V testing. Work was performed earlier at

NIST to evaluate the RADC large reverberating chamber response to pulsed rf

excitation [8]. The results of similar work performed for the RADC small

chamber are described in this report.

All the pulsed rf measurements for the small chamber were takeji at 10

different frequencies between 0.9 to 18 GHz. Data taken for the mode -tuned

approach include three pulse widths of 3, 1, and 0.3 /is . The data for the

mode -stirred approach include four pulse widths of 3, 1, 0.3 and 0.1 n s. Broadband ridged-waveguide horn antennas were used for both transmitting and

receiving the rf pulses in the chamber.

11
5.2 Evaluation of Pulsed Rf Measurements in the Mode-Tuned Chamber

The mode-tuned measurement approach was used to determine: (a) the

chamber loss for rf pulse excitation compared with cw excitation, and (b)

the ratio of the received pulse amplitude to the transmitted pulse

amplitude, as a function of time after the input pulse is turned on.

These two parameters were determined for the chamber empty (no absorber) and

with the chamber loaded with 1 piece of 7.6 cm x 61 cm x 61 cm (3" x 24" x

24") rf absorber. The absorber was placed in the center of the chamber on

top of a 15 cm high platform of plastic foam.

Measurements were made with short repetitive rf pulses having pulse

widths of 0.3, 1.0 and 3.0 ^s, to determine the ratio of energy received by

the chamber receiving antenna, to the energy supplied to the transmitting

antenna. The total energy was determined from numerical integration of the

voltage as a function of time. A sample result of the ratio of the input

pulse energy to received pulse energy (loss) is shown on figure 3.2 (b)

.

The chamber losses for cw and rf pulses are equal within 2 dB at all

frequencies. One can conclude from these measurements that even with

significant pulse dispersion as a function of time, as seen by examining

figure 5.1, that the energy associated with the field inside the

reverberating chamber is approximately the same for cw and pulse testing.

Figure 5.1 shows the mode-tuned received pulse measurements for 3 pulse

widths and 2 Q factors. These graphs give an indication of the time

required for the chamber to charge up to its steady state amplitude, and to

decay to zero after the input pulse is turned on and off. The results show

the dependence on frequency and chamber Q. Charge -up time is the time

required for the pulse input signal, radiated from the transmitting antenna,

to complete all significant multiple reflections inside the chamber. Each

graph of power measurement data shows two curves: one for the average value

of received power for all tuner positions (at each instant of time) , and one

for the maximum value of received power (at each instant of time) . Curves

have been added to the maximum curves to give an approximated smooth result.

By examining the curves in figure 5.1 at the selected frequencies and

pulse widths, the approximate charge or decay times can be determined for

the empty (no absorber) chamber and for the chamber loaded with the one

piece of rf absorber. The data extracted from the curves of figure 5.1 are

summarized in table 5.1. Graphs displaying these data are shown in figures

5.2, 5.3, and 5.4. The results of figures 5.2 and 5.3 are given in terms of

the time required for the received signal to rise to 63 % and 90 % of the

steady state amplitude. The steady- state amplitude is achieved if the pulse

duration is sufficient for the chamber to charge up to 100 % of its

amplitude (approximately the cw level) . Curves drawn in are the estimated

results derived from curve fitting to the raw data.

If the transmitted pulse duration is not longer than the charge time of

the chamber, an error will result in establishing a known maximum amplitude

of the test signal in the chamber. An estimate of the correction factor to

apply for this condition can be found by determining the difference (dB) in

the calculated ratio of the received signal amplitude to the transmitted

signal amplitude as a function of time after turning on the transmitted

pulse. Figures 5.4 (a) and (b) give these results for the chamber empty and

12
with 1 piece of absorber. Again, smooth curves derived from an estimated

fit of the raw data are shown. The corrections correspond approximately

with the ratio of the received signal amplitude, as a function of time after

the pulse is turned on, to the steady state amplitude. Graphs shown in

figures 5.4 (a) and (b) are for pulse durations of 1 and 0.3 n s . The

correction factor is significantly lower for the chamber loaded with rf

absorber (lower Q factor). Figures 5.4 (a) and (b) are used to correct for

field- strength reductions in the chamber caused by insufficient time

duration of the transmitted pulses. These correction factors should be

verified further by comparing the measured responses of a well-characterized

EUT to cw fields and to pulsed rf fields of varying pulse widths, using both

anechoic and evaluated (calibrated) reverberating chambers.

5.3 Evaluation of Pulsed RF Measurements in the Mode-Stirred Chamber

Measurements were also made using the mode- stirred approach with the

chamber. Again, as in the mode -tuned approach, two sets of data were taken,

one for the empty chamber ( high Q) and the other for the chamber loaded

with one piece of rf absorber. Measurements were made at the ten different

frequencies from 0.9 to 18 GHz but with four input pulse widths, 0.1, 0.3,

1, and 3 n s • Results of these measurements are given in figures 5.5 to 5.8.

The graphs of figure 5.5 show oscilloscope traces for the selected

frequencies for the 4 input pulse widths. Each graph has two traces. The

upper trace is an envelope of the input pulses applied to the chamber

transmitting antenna; that is, the "painted" envelope derived from all the

input pulses during one complete rotation of the tuner. The signal shown is

the reduced voltage values measured on the side arm of the directional

coupler using a calibrated diode detector connected to one channel of the

digitizing oscilloscope. The lower trace is the time-domain envelope of the

pulses received by the chamber's reference receiving antenna and measured

with a second calibrated diode detector connected to the second channel of

the digitizing oscilloscope. The polarity of this pulse has been reversed

to separate the two traces. The diode detectors have built-in 50 U load

resistors for impedance matching to 50 Q. The spread in the top trace

(input signal) is due to variations in signal amplitude caused by variations

in antenna VSWR (input mismatch) as a function of tuner position. The

magnitude of this variation is frequency dependent, decreasing as the

frequency increases.

The approximate risetimes and correction factors can be determined from

the graphs shown in figure 5.5. These results are summarized in table 5.2.

Figures 5.6 and 5.7 give the time required for the signal to rise to 63 %

and 90 % of the steady state amplitude. Smooth curves were drawn giving the

estimated results derived from a curve fit of the raw data. These data are

similar to the results shown in figures 5.2 and 5.3. Graphs displaying the

correction factors for field- strength reductions caused by insufficient time

duration of the transmitted pulses are shown in figure 5.8. Again these are

similar to figure 5.4, determined for the mode- tuned case.

13
5.4 Comments on Pulsed RF Measurements

Mode -tuned data are generally considered to be more accurate than modestirred data for absolute measurements such as chamber loss and test field

strength. This is because appropriate corrections can be made for impedance

mismatch, cable loss, coupler coupling factors , etc.. The more complete

data acquisition for mode- tuned operation makes it possible to obtain

maximum, average and minimum response values, whereas only the maximum

values can be determined from the mode -stirred measurements. Mode -tuned

measurements are taken for each of the (stopped) tuner positions, and

sampled at each instant of time during the pulse, so that a maximum value

(or minimum or average) can be extracted from the total data taken. Each

pulse is digitized at 512 samples in time, for each of the 200 angular

positions of the tuner during a 360° rotation. Then corrections can be made

to each measurement for cable loss, coupling ratio of the directional

coupler, attenuator calibrations, and diode detector readings according to

previous calibration of power response versus signal frequency and indicated

voltage levels. Mode- stirred data cannot be corrected in the same manner;

hence, representative values only are obtained. However, results derived

from mode- stirred data usually have better definition and are believed to be

more accurate for determining relative parameters, such as charge time and

relative amplitude correction factors. This is because large data sampling

approaching continuous sampling as a function of tuner position is possible,

compared to the limited (200 tuner position) sampling of the mode-tuned

approach. These conclusions are particularly apparent when comparing figures

5 . 4 and 5.8.

It was observed in much of the pulsed rf data that the maximum value of

field strength measured as a function of time after the pulse turn-on,

appears to be slightly greater than the steady-state value. It is

conjectured that this "overshoot" is due to the imperfect (nonins tantaneous) leading edge of the pulse produced by the pin diode switch in

the pulse source. The overall trend, however, is for the shorter pulses to

have a smaller value of peak detected voltage. This is because the on-time

is not sufficient for the EM energy in the reverberating chamber to reach

its steady- state value. Thus, data were taken for a range of pulse

durations to determine the correction factor to be applied when using the

chamber to take EMS/V data for very short radar- type pulses.

6. Summary and Conclusions

(a) Spatial variations of the E- field maximum and average values in the

test volume of the chamber are summarized at selected discrete

frequencies in table 3.1. These data were obtained using the NIST

multiprobe system and the mode -tuned approach with 200 tuner increments

per revolution at frequencies from 0.2 to 1 GHz, and 400 tuner

increments at frequencies from 1 to 2 GHz. The limitation for

determining the spatial E- field variation depends on the increasing

mode density and hence field complexity in the chamber as a function of

increasing frequency. At higher frequencies the sample size becomes

insufficient to determine the maximum value with sufficient accuracy.

The spatial E-field variations should decrease as frequency increases

above 2 GHz to less than the ± 3 dB shown at 2 GHz in the table.

14
(b) The maximum E- field strength established inside the chamber is about 7-

8 dB greater than the average E- field. This is consistent with

previous results obtained for other reverberating chambers such as the

RADC large chamber, the Naval Surface Weapons Center (NSWC) , Dahlgren,

VA, chambers and the NIST reverberating chambers.

(c) Results of reference standard EUT responses determined using the RADC

small reverberating chamber are approximately the same for the same EUT

at the same field levels as using NSWC and NIST reverberating chambers.

(d) The "correlation factor" between free-space (anechoic chamber) and

reverberating chamber results appears to be the free-space (far- field)

gain of the EUT. This implies that susceptibility criteria determined

for an EUT using a reverberating chamber must include an additional

factor proportional to the EUT's open-field estimated gain as a

function of frequency.

(e) Item (d) implies that the directional characteristics of an antenna or

EUT placed inside a reverberating chamber are lost, resulting in an

equivalent gain of unity (0 dB) in this complex highly reflective

environment

.

(f) If a reverberating chamber is used for pulsed rf EMS/V testing, and the

duration of the input pulses to the chamber is shorter than the

chamber's charge time, an error will result in establishing a known

maximum amplitude of the test signal. An estimate of the correction

factors to apply for shorter pulses is given in figures 5.4 and 5.8.

(g) The use of rf absorbing material inside a reverberating chamber

significantly reduces the Q and, hence, charge time of the chamber and

can be used to improve the fidelity of the pulse waveshape of the test

field in the chamber. However, the absorber should not reduce the Q so

much that the reference antenna received power drops more than 6 dB , or

the tuner effectiveness is reduced to less than 20 dB.

7. Recommendations.

(a) The practical lower frequency limit recommended for using the RADC

small reverberating chamber shown in figure 2.1 is approximately 500

MHz.

(b) The mode- tuned approach is recommended for use at frequencies below 2

GHz if absolute levels of the test field are required. The modestirred approach is recommended for use at frequencies above 2 GHz for

absolute measurements or at all frequencies above 500 MHz if only

relative measurements are made.

Based upon antenna VSWR and EUT response data obtained from the

evaluation measurements, the following approaches and number of samples

per tuner(s) revolution are suggested for performing EMS/V testing

requiring absolute determination of test field amplitudes for EUT

response parameters.

15
Frequency Range

0.5-1 GHz

1 - 2 GHz

2 - 4 GHz

4 - 18 GHz

Method

Mode -Tuned

Mode -Tuned

Mode-Stirred

Mode-Stirred

Number of Tuner

Positions or Samples

200

400

> 3000

> 5000

(c) Antennas for transmitting rf energy into the chamber and for measuring

the test E- field amplitude should not be used outside their specified

frequency range. (For example the 0.8 to 18 GHz ridged-horn antennas

should not be used outside their specified band.)

(d) Additional work is needed to verify experimentally the correction

factors shown in tables 5.1 and 5.2 and figures 5.4 and 5.8. This

could be accomplished by comparing the measured responses of a wellcharacterized EUT to cw and pulsed rf fields as a function of

frequency and pulse durations, using both an anechoic chamber and an

evaluated/calibrated reverberating chamber.

8 . Acknowledgments

Work described in this report was sponsored by RADC , Griff iss AFB , NY,

with Charles Blank as project monitor. The authors wish to acknowledge his

assistance in making this project possible. In addition, the authors

express appreciation to Dr. Mark Ma and Dr. Motohisa Kanda for their support

and helpful comments and editorial review.

9. References

[1] Cummings, J.R. Translational electromagnetic environment chamber, a

new method for measuring radiated susceptibility and emissions. Proc

.

IEEE Int. Symp . on EMC; 1975; San Antonio, TX.

[2] Corona, P.; Latmiral , G.; Paolini, E.; Piccioli, L. Performance of a

reverberation enclosure for power measurements in the microwave range.

2nd Symp. Tech Exhibition on EMC; 1977; Montreux, Switzerland.

[3] Bean, J.L.; Hall, R.A. Electromagnetic susceptibility measurements

using a mode-stirred chamber. Proc. IEEE Int. Symp. on EMC; 1978;

Atlanta, GA.

[4] Crawford, M.L.; Koepke , G.H. Design, evaluation and use of a reverberation chamber for performing electromagnetic

susceptibility/vulnerability measurements. Nat. Bur. Stand. (U.S.)

Tech. Note 1092; 1986 April. 148 p.

[5] Ma, M.T.

;

Kanda, M. ; Crawford, M.L.; Larsen, E.B. A review of

electromagnetic compatibility/interference measurement methodologies.

Proc. of IEEE; Vol. 73, No. 3; 1985 March.

16
[ 6 ] Project Progress Report - Final Report FY86 "EMR test facilities - Evaluation of reverberation chamber method for performing EMC

measurements", prepared for RADC/RBCM, Griff iss AFB , NY. by NBS

,

Boulder, CO. Report NO. SR-723-1-87. 1987 January.

[7] Crawford, M.L.; Koepke , G.H. Preliminary evaluation of reverberation

chamber method for pulsed rf immunity testing. IEEE Int . Symp . on

EMC; 1986; San Diego, CA.

[8] Crawford, M.L.; Koepke, G.H.; Ladbury, J.M. EMR test facilities - Evaluation of reverberating chamber located at RADC , Griff iss AFB,

Rome New York. Nat. Bur. Stand. (U.S.) NBSIR 87-3080; 1987 December.

80 p.

[9] Liu, B.H.; Chang, D.C.; Ma, M.T. Eigenmodes and the composite quality

factor of a reverberating chamber. Nat. Bur. Stand. (U.S.) Tech Note

1066; 1983 August.

[10] Corona, P.; Latmiral , G.; Paolini, E. Performance and analysis of

reverberating enclosures with variable geometry. IEEE Trans, on EMC;

EMC- 22. 1980 February.

[11] Larsen, E.B.; Ries, F.X. Design and calibration of the NBS isotropic

electric- field monitor [EFM-5], 0.2 to 1000 MHz. Nat. Bur. Stand.

(U.S.) Tech. Note 1033; 1981 March.

[12] Kanda, M. ; Driver, L.D. An isotropic electric - field probe with tapered

resistive dipoles for broad-band use, 100 kHz to 18 GHz. IEEE Trans,

on MT&T. Vol . MTT-35(2); 1987 February.

[13] Bensema, W.D.; Reeve, G.R.; Koepke, G.H. A multisensor automated EM

field measurement system. Proc . IEEE IMTC/85 Conf ; 1985; Tampa, FL.

[14] Crawford, M.L. Generation of standard EM fields for calibration of

power density meters: 20 kHz to 1000 MHz. Nat. Bur. Stand. (U.S.)

NBSIR 75-804; 1975 January. 40 p.

[15] Bowman, R.R. Calibration techniques for electromagnetic hazard meters:

500 MHz to 20 GHz. Nat. Bur. Stand. (U.S.) NBSIR 75-805; 1976 April.

33 p.

17
BULKHEAD FOR TESTING SHIELDING

EFFECTIVENESS OF MATERIALS

Figure 2.1 Two isometric sketches of the RADC small reverberating chamber.

18
175

BULKHEAD

>

TOP VIEW

*

FEED THROUGH

CONNECTOR

Figure 2.2 Cross sectional views of the RADC small reverberating chamber showing

placement of transmitting and receiving antennas, chamber tuner and

isotropic probes for measuring spatial E-field uniformity.

19
' a ) Front view of the reverberating

chamber with access door in place.

M

(b) Front view of the chamber with

access door removed.

(c) Rear view of the chamber showing ( d)

the tuner motor assembly.

Top view showing the bulkhead for

shielding-effectiveness measurement

.

(e) View inside the chamber showing

probes, long wire antenna, and tuner.

(f ) Side view of the chamber showing

the access bulkhead.

Figure 2.3 Six photographs of the RAJDC small reverberating chamber.

20
21

Figure

2.4

Photograph

of

NIST

equipment

used

to

evaluate

the

RADC

small

chamber.
TUNER

CONTROL

22

Figure

2.5

Block

diagram

of

instrumentation

used

in

cw

evaluation

of

the

RADC

small

chamber

.
ozM

Ph o: a- o W H H O c/3 as

23

Figure

2.6

Block

diagram

of

instrumentation

used

in

pulsed

rf

evaluation

of

the

RADC

small

chamber.
Measured

VSWR

Measured

VSWR

Frequency , GHz

Figure 3.1 Measured VSWR of: (a) long wire antennas (0.2 to 18 GHz), and (b)

broadband horn antennas (0.8 to 18 GHz), transmitting into the RADC

small chamber.

24
Coupling

efficiency

,dB

Coupling

ef

f

iciency

,dB

Figure 3.2 Measured coupling efficiency of: (a) long wire antennas (0.2 to 18

GHz), and (b) broadband horn antennas (0.8 to 18 GHz), in the RADC

small chamber. Losses determined in (b) are from cw mode -tuned

measurements and from pulsed rf measurements.

25
Ratio,

theoretical

to

experimental

Q

Chamber

Frequency, GHz

Figure 3.3 (a) Theoretical and experimental Q of the RADC small chamber,

and (b) ratio of theoretical to experimental Q (0.4 to 18 GHz) . 26
Tuner

effectiveness,

dB

Tuner

effectiveness,

dB

Frequency , GHz ^

Figure 3.4 Measured tuner effectiveness in the small chamber using: (a)

long wire antenna (0.2 to 18 GHz), and (b) broadband horn

antenna (0.8 to 18 GHz)

27
(a)

Maximum

value

Vertical

component

Transverse

component

<n/A9P *PT 9 !3“3 Q1/A9P ‘PT9T1-3

28

Figure

3.5(a)

Spatial

distribution

of

E-field

components

in

the

small

chamber

measured

with

10

NIST

isotropic

probes

(5

cm

dipoles),

using

long

wire

antennas

for

transmitting

and

receiving:

(a)

maximum

values,

and

(b)

average

values.

Net

transmitted

power

— 1

W.
(b)

Average

values

Vertical

component

Transverse

component

m/ ASP ‘PT9T5-3 m/ A8P * PT a TI“3

m/A9P ‘PT^TJ-S m/A9P ‘PT9T1-3

29

Figure

3.5(b)

Spatial

distribution

of

E-field

components

in

the

small

chamber

measured

with

10

NIST

isotropic

probes

(5

cm

dipoles),

using

long

wire

antennas

for

transmitting

and

receiving:

(a)

maximum

values,

and

(b)

average

values.

Net

transmitted

power

- 1

W.
(a)

Maximum

values

Vertical

component

Transverse

component

30

Figure

3.6(a)

Spatial

distribution

of

E-field

components

in

the

small

chamber

measured

with

10

NIST

isotropic

probes

(5

cm

dipoles),

using

broadband

horn

antennas:

(a)

maximum,

and

(b)

average

values.

Net

transmitted
(b)

Average

values

Vertical

component

Transverse

component

31

Figure

3.6(b)

Spatial

distribution

of

E-field

components

in

the

small

chamber

measured

with

10

NIST

isotropic

probes

(5

cm

dipoles),

using

broadband

horn

antennas:

(a)

maximum,

and

(b)

average

values.

Net

transmitted
E-field,

dBV/m

E-field,

dBV/m

(a)

Figure 3.7 Average values of E-field components in the small chamber measured

with 10 NIST isotropic probes (5 cm dipoles), using long wire

antennas: (a) average of the 10 maximum values for each component, and

(b) average of the 10 average values. Net transmitted power - 1 W.

32
-field,

dBV/m

E-field,

dBV/m

w

Figure 3.8

(b)

0.2 0. S 0.6 1 . 1 1 . 4 1 . 7

Frequency, GHz

Average values of E- field components in the small chamber measured

with 10 NIST isotropic probes (5 cm dipoles), using broadband horn

antennas: (a) average of the 10 maximum values for each component, and

(b) average of the 10 average values. Net transmitted power 1 W,

33
ra / ASP *PT 9 TJ”3

34

Figure

3.9

Maximum

and

average

Efield

strengths

in

the

small

chamber

measured

with:

(a)

1

cm

dipole

probe,

and

(b)

received

power

of

long

wire

antenna.

Net

transmitted

power

-

0.1

W.
to w

01 0) * 3 3 * r—t rH * CO CO * > >

*

e OJ 3 00 E CO

to •HX a>

tO > X <

„ OJ

N

X

o

o

C

O

3

er

V-i fju

OJ

J 1 L -1 . . J ,-J J_ J -J JL- J L .1 ID (S in Q in tS

n cn 0J 0J

m/ ASP ‘PI9TJ-3

35

Figure

3.10

Maximum

and

average

Efield

strengths

in

the

small

chamber

measured

with:

(a)

1

cm

dipole

probe,

and

(b)

received

power

of

broadband

horn

antenna.

Net

transmitted

power

-

0.1

W.
(S

OJ

w

N

X

Q

O

c

<U3

O'

0)

J-l

OJ

Am9P ‘ajodip mo j jo asuodsa^

36

Figure

3.11

Maximum

responses

of

NIST

1

era

dipole

probe

to

an

Efield

of

37

dBV/m

using:

(a)

RADC

small

reverberating

chamber,

and

(b)

NIST

anechoic
mgp ‘moq pupqppoiq jo asuodsa'g

c -

•rH V-i 43 « X

C E

C S3

0) X 4J a

c

S3 t»o c

C

3-i ij

O S3 x >-i 4) /~s X

N 3-1 X 43 u J>43 CO J-i «-"

1

r—

<

o H

4-3 CT3 E H wu

TD a

C <

S3 c2 X

-o /—* S3 S3 O

)-i X t»0 . S3 C 3-1 •H 43

, w X

X 3 E

S3 T3 E X

43 \ U

> >

•tH CQ o

43 X> O o

03 r-- X

3-i m o

43 W 4-1 c

3-i O S3

435 H

0 TJ go an h

43 z

4-1 '-V

• X

w

X

sJ £

T3 C C

S3 (0

CNI

c~i

4>

3-i

b£)

•tH

U-*

37
® LH IS \f) E

s

OJ

OJ

N

ace>

e» uC

<Uo

cr

QJ

OJ

Q

OJ

ffp

38

Figure

3.13

Comparison

of:

(a)

free-space

gain

of

a

broadband

horn

antenna,

with

(b)

difference

in

maximum

responses

of

the

horn

measured

in

NIST

anechoic

chamber

minus

RADC

small

reverberating

chamber.
No absorber in chamber. Using 1 piece of absorber.

—i l L l * l -J 0 1 2 3 A 5

Time , us

t-3ms

It i 1-1 1 —

0 0.5 1 1.5 2

Time, ps

r-0 . 3#is

200

1

„ 150

u

&

g 100

0)u

0) ct

Time, fxs

0.5

Time, /js

Figure 5.1(a)

Maximum and average values of received rf pulse waveforms in

the mode -tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 0 . 9 GHz % 39
Received

power,

mW

Received

power,

mW

Received

power,

mW

No absorber in chamber Using 1 piece of absorber.

l lJ I L i i

. j 0 12 3 4 5

Time, ns

r-lps

r-3/iS

r-l^s

r-0 . 3/iS r-0 . 3jxs

Figure 5.1(b)

Maximum and average values of received rf pulse waveforms in

the mode -tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F = 1.3 GHz

40
No absorber In chamber. Using 1 piece of absorber.

r-3/is

0 1 2

Time, /is

J i ^—. 0 1 2

Time, /is

l— J i 0 0.5 1 Time, /is

0 0.5

Time, /is

1

Maximum and average values of received rf pulse waveforms in

the mode -tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 2.0 GHz.

41

Figure 5.1(c)
Received

power,

mW

Received

power,

mW

Received

power,

mW

No absorber in chamber. Using 1 piece of absorber.

r-3 /is

LLLi I i I i I

i . 0 1 2 3 4 5

Time, /is

Time, /is Time, /is

r-0 . 3 /is r—0 . 3 /is

Maximum and average values of received rf pulse waveforms in

the mode-tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 2.9 GHz.

42

Figure 5.1(d)
Received

power,

mW

Received

power,

mW

No absorber in chamber. Using 1 piece of absorber.

r-3fis

—i . J

0 1 2

Time , ps

L I 0 1 2

Time,

r—0 . 3/iS

Mi I ^ in . 0 0.5 1 Time, ns Maximum and average values of received rf pulse waveforms in

the mode- tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F * 4 . 2 GHz.

43

Figure 5.1(e)
Received

power,

mW

Received

power,

mW

Received

power,

mW

No absorber in chamber. Using 1 piece of absorber.

r-3/iS

Time, /is

. . ifT'.rrrr i i 1 — 0 1 2

Time, ps

Jl l. i . i * i i 0 1 2 3 4 5

Time, jis

0 1 Time , ns

2

r-0

3ns

50 1 n 1

Time, n$

r—0 . 3 ns

Maximum and average values of received rf pulse waveforms in

the mode -tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 5.65 GHz.

44

Figure 5.1(f)
No absorber in chamber. Using 1 piece of absorber.

Time, ps

r-3/iS

2 —— 1 t

1—

Time,

r«l/is

* . 1 0 1 2

Time, ns

f-0 .

3

/js

Figure 5.1(g)

Maximum and average values of received rf pulse waveforms in

the mode- tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 8 . 9 GHz.

45
Received

power,

mW

No absorber in chamber. Using 1 piece of absorber.

r-3/iS

Time, ps

0 1 2 3 4 5

Time, ps

Time, /is

r-l/is

Time, ps

1 , _H]

0 0.5 1 Time , ps

UT I — r. 0 0.5 1 Time, /is

Figure 5.1(h)

Maximum and average values of received rf pulse waveforms in

the mode -tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 12 GHz.

46
Received

power,

mW

Received

power,

mW

No absorber in chamber. Using 1 piece of absorber.

r-3^s

Time, ns

r-l^s r-l/is

Time, ns

r-0 . 3*is r-0 . 3 /is

Maximum and average values of received rf pulse waveforms in

the mode -tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 16 GHz.

47

Figure 5 . 1 ( i)
Received

power,

tnW

Received

power,

mW

No absorber in chamber. Using 1 piece of absorber.

_1— 1 —I 1 1 1 **t i T''-'-—a. 0 1 2 3 4 5

Time, ps

T-I^s

0 1 2 3 4 5

Time, ps

r-l/is

0.2 1 1

-1 1

0)l

ex

0 1 Time, ps

2

Time, jxs

Figure 5 . 1 ( j

)

Maximum and average values of received rf pulse waveforms in

the mode-tuned RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 18 GHz.

48
o

CM

f-H I—t o o o o

srl ‘auiTqasya %£^

Frequency

,

GHz

Figure

5.2

Graphs

of

data

from

figure

5.1

showing

the

time

required

for

3

ps

rf

pulses

transmitted

into

the

mode

-tuned

chamber

to

rise

to

63

%

of

the

steady

state

amplitude,

using:

(a)

no

absorber,

and

(b)

1

piece

of

7.6

cm

x

61

cm

x

61

cm

rf

absorber.
o

CM

vO

CN

STi ‘ auiTqasT-tf %Q6

50

Frequency,

GHz

Figure

5.3

Graphs

of

data

from

figure

5.1

showing

the

time

required

for

3

ps

rf

pulses

transmitted

into

the

mode

-tuned

chamber

to

rise

to

90

%

of

the

steady

state

amplitude,

using:

(a)

no

absorber,

and

(b)

1

piece

of

7.6

cm

x

61

cm

x

61

cm

rf

absorber.
gp uoT^oaaao3

51

Figure

5.

A

(a)

Graphs

of

correction

factors

for

response

ammplitude

of

rf

pulses

in

the

mode

-tuned

chamber

as

a

function

of

frequency,

at

selected

pulse

duration,

using:

(a)

no

absorber,

and

(b)

1

piece

of

7.6

cm

x

61

cm

x
N

X

o

O

C

0)cr

a)u

(i-i

gp ‘ao^DEj uoposiaoo

52

Figure

5.4(b)

Graphs

of

correction

factors

for

response

ammplitude

of

rf

pulses

in

the

mode

-tuned

chamber

as

a

function

of

frequency,

at

selected

pulse

duration,

using:

(a)

no

absorber,

and

(b)

1

piece

of

7.6

cm

x

61

cm

x

61

cm

rf

absorber.
F « 0.9 GHz, using 10 dB pad

No absorber in chamber.

r-3/is

Time , pis

Using 1 piece of absorber.

r—3pis

40011

0 2 4 6 8 10

Time, pis

T-l/iS

0 1 2 3 4 5

Time, pis

r-l/is

Time, pis

r—0 .

3

ms

Time, pis

0 1 2 3 4 5

Time, pis

200

r—0 . l^s

ITT 1 1

i

i

4t | i i i

--i—i—J 4

JU.

i

! j 1

r—0 . Ipis

0 1 2 3 4 5

Time, pis

Figure 5.5(a)

Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 0.9 GHz.

53
F - 1.3 GHz,

No absorber In chamber.

using 10 dB pad

Using 1 piece of absorber.

r-3#is

Tine, ms

t-3#is

1

1 TT

_ li

! — j

4 6

Time, ps

i

1

'

j !

t i

; t . |

I I

it !

1 ± i

J

i T t 10

r-l^s

Time, ps

r-l/iS

i i—n

f

I

1 |

1

j

I

!

i —i—i—i

i i i i i •+•4'- 1 1 i

_ — 11 ! 1' 1

2 3

Time, ms

r—0 . 3/iS

Time, ms

r-0 .

fis

r—0 . l/is r-0 . l/is

os£200

i !

i

;

mV

°

0

41

iW

5100

os

ifl

i'l

1 T

200 • i

mV

200

0

0

jlOO

200

-rn

i

— 1 I

i l

!

!

j i -ftk - r --

i\ —— ! i

:

: |

'

J

!

| i lr ! i

i

i

!

i i f

i 1

i t

j

1

if

1

1 i

X

i

1

l

'

|

i

i i i 2 3

Time, ps

2 3

Time, fis Maximum values of received rf pulse waveforms in the modeFigure 5.5(b) stirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F — 1.3 GHz

54
F - 2.0 GHz, using 10 dB pad

Mo absorber in chaaber. Using 1 piece of absorber.

r-3^s t-3ms

Tine, ps Tine, fxs

r-l^s

PS

jj* 200

i n

j h !

4l j

j |

n

1 j J L

j I

j | u mV

0

!

j

! i i TM " j

1 !

% 200

os

Tlw

i m

t \ i j ; j : !

l W ! 400 i !

:

j I i ] + 0 1 2 3 4 5

Tine, m s

r-l/xs

Tine, ps

r-0 . 3/iS

Tine , m s

r-0 . 3fis

Tine, ps

r—0 . lfis r—

0

. Ins

200

o

O

S

40

80

i

i l i i

I

-f -r-T-j

4

\~ i

! 1 1

. . 1 . - .. -

1 . .:

-

i ? .

j 1r 1 . J i

i ~Vi

i I j

«

i

:

i r i

! ! t

i

i j 1

Figure 5.5(c)

2 3 4

Tine , ms Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 2.0 GHz.

55
F - 2 . 9 GHz, using 10 dB pad

No absorber in chamber.

T»3f4S

Using 1 piece of absorber.

r-3/is

r-l/xs

Tine, fis

r-ljis

Time , fis

r—0 . 3jis r-0 . 3/iS

r—

. Ins

Tine, ps

r-0 . 1/iS

Figure 5.5(d) Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 2.9 GHz.

56
Ho absorber In chamber.

r-3/is

F - 4 . 2 GHz, using 10 dB pad

Using 1 piece of absorber.

f-l/lS

1

1 FT

-

i i

1 i

. n i 1 1 H,

1 1 1

200

a

20

AO

200

0 mV

o 20

PC

40

r-3/xs

4 6

Time, ps

r-l/is

i t r

2 3

Time, ns

i

i r" 1

i . rnr

-

! i !

! ! '

i T

n !?!!!!

j

'1 t r

\ m I

*

r

1 JJ j 1

, ...

= i

1

1 i

|

j LZI i t r ;

i i ! 10

1

1

1

1 "f——

1

i i

'

!

1 j * —r--t— i\

«

1 5

\i

j

I M

1+

. j XI

+

1

r-0 . 3/iS t—0 . 3 /iS

u

200

V 0

0

20

40

1 I!

i

\

j

j ±5-.-- u

r-0 . lps

2 3

Time, ps

TT ! i 1

i -

\ \ ~~ T 1 1 i 4.

4

-

i

\

j

1 : 1

1 l

1

*

j ;

J j

I j

j r I

1 i

'

i ft i

i

i

j j

i V: 1

t l • • • 1 1 < 1 t l • i • • i J L

200

0 mV

^ 20

PC

40

u

os

200

,v°

0

20

40

2 3

Time, /is

r—0 . lfis

Time, ps

Figure 5 . 5 (e)

T1 1—,

i i l 4

! H

-4-r —

-

1 ! t

1 !

j 1 i f+ i ill t i

i I -T-*:

-J I

:

i 1

i i 1

i

TH

i — ! J

i i j i

- -I

| j

-r

. -

! i i i i

' \ j

1 ! !

• i i f 4 1r 1 i

i

| i

i

| tHi;

c— j ;

i

:

i

:

fill!

i 2 3 4 5

Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 4.2 GHz.

57
Mo absorber in chamber.

r-3/iS

F - 5.65 GHz, using 10 dB pad

Using 1 piece of absorber.

200

..0

8

20

40

r-3#is

4 6

Time, jus

1

1 m ? i

i !

? : 1 1 '

i 7 !

1 I 1 If!.- j I-

• i I !

: \ i. .. J II }

i

i

tWj

K |14-'! i i !

1 1 i

1 Li i I i

1

1 !i ! I T i 10

r-ljus

mV

200

0

100

200

0 2 3

Time, jus

r—

. 3jus

r-0 . Ijus

200

V 0

8

20

i :

i : t

-t

U

PC

h

r-l^s

2 3

Time, jus

t-O . 3 jus

1

1 —i i

4

-

1

{ -

• i.__J _

i

- i t !

i

1

1 :

+

t

j 11

r

i

j

! L.J

i : t

i ;

1

: _

1

j l !

0 1

1 2 3

Time , jus

r—0 . 1/iS

4 5

i

i

-fc III!

r i i i i

: -1

1L

i j i

i

! r

I l

i 1

i {

i

i i [

1 >1 i j

i if t

i

i

: i

! 4

i

i i

! t

Figure 5.5(f)

2 3 4 5

Time, jus

Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; f - 5.65 GHz.

58
RCVR

F - 8.9 GHz,

No Absorber In chamber.

r*3/is

Tine , ps

using 3 dB pad

Using 1 piece of absorber,

r-3/is

1

i j i 40 Li Jj

J ! 1 0 2 4 6 8 10

Tine , fis

r-l/is

r»0 . 3/xs

Tine, ns

t—0 .

3

fis

r—0 . l/is

Time, ps

API li 1 j ! 0 1 2 3 4 5

Tiae , ps

Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 8.9 GHz

59

Figure 5.5(g)
F - 12 GHz,

No absorber in chamber.

using 3 dB pad

Using 1 piece of absorber.

r-3jis r-3/iS

r-lfis

Time, ps

r-0 . 3/is

i :i

i i

i t !

i

i

1 : j 1

! L_J : ; —

0 12 3 4 5

Time, ps

r—0 . 3/is

Figure 5.5(h) Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 12 GHz.

60
No absorber in chamber Using 1 piece of absorber

16 GHz

r-3ps

1

1

j 1 1

. ; 1' —

! i

i

1 -f-’

. --J

1

1

1

1

1

!

r-3/iS

200

„0

X

20

AO

i

i —i—n

i i • L ..

|

! 4 1 •

! t

1 j \< i i

I

! « I j i i

1

1

1

i • !:

4 l t

1

1

! .

| • +

4

t

1

1 !i i t 1 11 '

i A 6

Tine, ps

10

r-l/is r-l^s

r-0 .

3

fis r—0 . 3^s

200

0 mV

u 20

A0

2 3

Tine, ps

~

i

;

! tX ! -

i r~t-~r -

!

! 3

1 1

i

i 7 ir ! ? 1

i

j

i

i

1 4

4

j !

i

i

i

j j

i

I 1 !

:

i i

! !

r—0 . 1/xs r—0 . 1/is

200

_„0

X

20

A0.

1 2 3

Tine, fis

r,

i

:

j

t 1 i*-- 1 1-

4 r~T~~~ j i! JL

1

i

• ! i

* i 4. •

i p

!

'

! i

i

:

i

i i i

4

i

:

j

i *

t 1

i

Figure 5.5(i) Maximum values of received rf pulse waveforms in the modestirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F - 16 GHz

61
18 GHz

200

0

No absorber in chamber.

r«3/us

1

1

1 —

' h --

!

I n

t

1

“ H

: i I !

li [

1 2 1

200

0 mV

0

g

g

20

40

Using 1 piece of absorber,

r-3jis rr I

’

|

j - ! ! i

! t !L... ! T t

1

I

t j {

1 11

I

; L

i

1 i

j

; 4 6

Time, ;is 10

T-l/JS r-l^s

200

0 mV

u 20

VC

40

|

1 : i

.

j

1

1 ! I

!

1 i ! i i Tt-j j :

;

i

i

i

j ! ; a

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l 5

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0 mV

u 20

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0 mV

0

u 20

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40

2 3

Time, ns

r-0 . l^s

i

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Time, ns Maximum values of received rf pulse waveforms in the modeFigure 5.5(j) stirred RADC small reverberating chamber using no rf

absorber (chamber empty) and 1 piece of absorber; F — 18 GHz.

62
srl ‘auiTqasi^ %£9

63

Figure

5.6

Graphs

of

data

from

figure

5.5

showing

the

time

required

for

3

ns

rf

pulses

transmitted

into

the

mode-stirred

chamber

to

rise

to

63

%

of

the

steady

state

amplitude,

using:

(a)

no

absorber,

and

(b)

1

piece

of

7.6

cm

x

61

cm

x

61

cm

rf

absorber.
Figure

5.7

Graphs

of

data

from

figure

5.5

showing

the

time

required

for

3

/is

rf

pulses

transmitted

into

the

mode-stirred

chamber

to

rise

to

90

%

of

the

steady

state

amplitude,

using:

(a)

no

absorber,

and

(b)

1

piece

of

7

. 6

cm

x

61

cm

x

61

cm

rf

absorber.
Figure

5.8(a)

No

absorber

N

ECoe. o3

0)3

cr

0)p

Ph c 0)

X

•H

M

i—l s

ca 3 o

4) aCA rH

T—1

•3 V£> 3 a)

CX. pi

X 0

44 4) s

Pi p-l o

a)

4-1

w VP>

O • 4-> ra) cd T3 44 3 « O

4-1 fp

*H 0 4) rH c O a 4) 4) s 3 t4 3 cr (X

a>

a> Pi r4 w 44 3o 4-1 £> a O w

0) 3 •o

Pi 0 3

*H cd Pi 4-1 O O -

4-1 3 Pi 3 4) CA 4-1 ,3

Pi Pi O <d O

P) CA O CA ,3

<d <d cd 4-1 Pi O s 4) 3

•1-1 o £s

p> 3 cd o 4=

a> o • Pi • • Pi

Pi •3 40 3 O 4) 3 & O Pi *i4 Pi

Pi CA 0

*H 3 CA

4-1 P» ,3 O w - cd • CA

4) 3 44

CA •0

O Pi ,3 O •H

pi- s 4-1 S

ed cd

O

Pi 4) Pi C3 .3 3 i-4 P) •3 VO

cd

v00

0)u3

60

•H

pH

gp ‘ J.010T3J UOiaoajIJOQ

65
Figure

5.8(b)

1

piece

absorber

gp ‘aoqoej uoT^oarao3

66

Figure

5.8(b)

Graphs

of

correction

factors

for

response

amplitude

of

rf

pulses

in

the

modestirred

chamber

as

a

function

of

frequency,

at

selected

pulse

durations,

using:

(a)

no

absorber,

and

(b)

1

piece

of

7.6

cm

x

61

cm

x

61

cm

rf

absorber.
Table 3.1 Spatial variation of the cw E-field average and maximum

values measured in the RADC small reverberating chamber ,

Frequency

(GHz)

Variation in E-field

500

1000

1500

2000

< ± 7.0

< ± 5.0

< ± 4.0

< ± 3.0

67
Table 4.1. Summary of estimated uncertainties for determining the cw

field strength inside the mode -tuned RADC small

reverberating chamber (0.5 to 2.0 GHz).

Error (dB)

Source of Error 0.5 GHz

Ave . Max

1.0 GHz

Ave . Max

1.5 GHz

Ave . Max

2.0 GHz

Ave . Max

la. Received Power

Cable Loss ±0.05 ±0.05 ± 0.05 ± 0.10

Attenuator Cal

± 0.10 ±0.10 ± 0.10 ±0.10

Antenna Efficiency ±0.05 ± 0.05 ± 0.05 ± 0.10

Pwr. Meter Cal. ±0.20 ±0.20 ± 0.20 ± 0.20

Sub Total ±0.40 ± 0.40 ± 0.40 ± 0.50

Mismatch -3.0 -8.0 -3.0 -8.0 -2.0 -6.0 -2.5 -6.0

lb . E-Field Meas

1-cm dipole probe

2. Sampling

± 1.0

Efficiency

Spatial Field Var.

Limited Sample Size

(see [4])

± 7

±0.2

.0

±0.5

± 5

±0.3

.0

±1.0

± 4

±0.3

.0

±1.2

± 3

±0.3

.0

±1.5

Sub Total ±7.2 ±7.5 ±5.3 ±6.0 ±4.3 ±5.2 ±3.3 ±4.5

3. Wave Impedance

(see [4])

-2.0

+2.0

-2.0

+6.0

-2.0

+2.0

-2.0

+4.5

-2.0

+2.0

-2.0

+3.5

-2.0

+2.0

-2.0

+3.0

E-Field Determined

Bv Receiving Ant.

Total Worst

Case Error

-12.6

+9.6

-17.9

+13.9

-10.7

+7.7

-16.4

+10.9

-8.7

+6.7

-13.6

+9.1

-8.3

+5.8

-13.0

+8.0

RSS Error -8.1

+7.5

-11.5

+9.6

-6.4

+5.7

-10.2

+7.5

-5.2

+4.8

-8.2

+6.3

-4.6

+3.9

-6.4

+5.4

E-Field Determined

Bv DiDole Probe

Total Worst

Case Error

-10.2

+10.2

-10.5

+14.5

-8.3

+8.3

-9.0

+11.5

-7.3

+7.3

-8.2

+9.7

-6.3

+6.3

-7.5

+8.5

RSS Error -7.5

+7.5

-7.8

+9.7

-5.8

+5.8

-6.4

+7.6

-4.9

+4.9

-5.7

+6.4

-4.0

+4.0

-5.0

+5.5

68
Table 4.2. Summary of estimated uncertainties for determining the cw

field strength inside the mode-stirred RADC small

reverberating chamber (2 to 18 GHz).

Error (dE)

Source of Error 2.0 GHz

Ave . Max

.

4.0 GHz

Ave . Max

.

8.0 GHz

Ave . Max

.

12.0 GHz

Ave . Max

.

18.0 GHz

Ave

.

Max. la. Received Power

Cable Loss ± 0.10 ±0.10 ± 0.15 ± 0.15 ± 0.20

Atten. Calibration ± 0.10 ± 0.15 ± 0.15 ± 0.20 ±0.20

Antenna Efficiency ± 0.10 ± 0.15 ± 0.15 ± 0.20 ±0.20

Spec. Analyzer Cal.

Sub Total

±1.00 ±1.50 ±1.50 ±1.50 ±1.50

±1.30 ±1.90 ± 1.95 ± 2.05 ±2.10

Mismatch -2.5 -6.0 -0.9 -2.4 -0.4 -0.8 -1.0 -1.5 -2.0 -2.

lb . E-Field Meas

.

1-cm Dipole Probe ± 1.0 ± 1.5 ± 1.5 ± 2.0 ± 2.0

2. Sampling

Efficiency

Spatial Field Var. ± 3.0 ± 2.0 ± 1.0 ± 0.5 ± 0.5

0.5

Limited Sample Size

(see [4]) ±0.1 ±0.3 ±0.2 ±0.5 ±0.3 ±0.7 ±0.3 ±1.0 ±0.3 ±1.

Sub Total ±3.1 ±3.3 ±2.2 ±2.5 ±1.3 ±1.7 ±0.8 ±1.5

i

±0.8 ±2.1

' |

I 3. Wave Imped ^ 1207r Average < ±2.0,i -2.0 < Maximum < +3.0,

(see [4]) i

' ' t

4. Input Power Var. -1.2 -1.7 i o OO -1.3 -1 .6 -0 .5 -1 .0

E-Field Determined

Bv Receiving Ant.

Total Worst

Case Error

-10.1

+6.4

-14.3

+7.6

-7.8

+6.1

-10.1

+8.9

-7.3

+5.3

-8.1

+6.7

-6.4

+4.9

-7.6*

+6.6

-7.9

+5.9

-9.4

+7.1

RSS Error -4.8

+3.9

-7.5

+4.7

-3.7

+3.5

-4.6

+4.3

-3.5

+3.1

-3.7

+4.0

-3.2

+3.0

-3.6

+3.9

-3.8

+3.0

-4.3

+4.2

E-Field Determined

Bv Dipole Probe

Total Worst

Case Error

-7.3

+6.1

-8.0

+7.3

-6.5

+5.7

-7.3

+7.0

-6.4

+4 .

8

-6.8

+6.2

-5.3

+4 .

8

-6.0

+6.5

-5.8

+4 .

8

-7.0

+7.0

RSS Error -4.0

+3.8

-4.3

+4 .

6

-3.4

+3.3

-3.8

+4.2

-3.2

+2.8

-3.4

+3.8

-3.0

+2.9

-3.2

+3.9

-3.1

+2.9

-3.6

+4.1

69
Table 5.1(a), Mode -tuned data obtained from figure 5.1, giving rise times

and correction factors for rf pulses in the RADC small

reverberating chamber , t - Pulse Width ; CF * Correction Factor

No Absorber 1 Piece Absorber

FreqNominal Rise Time, ns MAX PR CF Rise Time, /is MAX PR CF

GHz r, /as 63% 90% mw dB 63% 90% mw dB

0.9 3 .445 1.139 531 0 .103 .481 167 0

0.9 1 .384 .687 500 0.26 .094 .295 158 0.24

0.9 0.3 .144 .227 320 2.20 .088 .152 171 -0.10

1.3 3 .375 1.075 408 0 .094 .149 104 0

1.3 1 .243 .493 317 1.10 .095 .148 136 -1.17

1.3 0.3 .152 .219 293 1.44 .105 .172 173 -2.21

2.0 3 .635 1.515 212 0 .087 .337 22.4 0

2.0 1 .470 .786 206 0.12 .134 .325 27.3 -0.86

2.0 0.3 .164 .252 67.2 4.99 .085 .144 22.6 -0.04

2.9 3 .495 1.108 116 0 .065 .166 19.3 0

2.9 1 .453 .833 116 0 .076 .244 22.0 -0.57

2.9 0.3 .111 .191 52.7 3.43 .067 .130 20.8 -0.33

4.2 3 .721 1.209 111 0 .161 .264 10.5 0

4.2 1 .421 .689 52.3 3.27 .153 .244 10.2 0.13

4.2 0.3 .144 .208 25.5 6.39 .150 .219 11.1 -0.24

5.65 3 1.111 2.113 52.0 0 .130 .236 4.18 0

5.65 1 .411 .677 31.1 2.23 .135 .286 4.88 -0.67

5.65 0.3 .203 .311 18.7 4.44 .109 .192 5.42 -1.13

8.9 3 .661 1.156 16.8 0 .198 .490 1.39 0

8.9 1 .330 .519 10.8 1.92 .071 .114 0.95 1.65

8.9 0.3 .150 .212 6.24 4.30 .113 .183 1.23 0.53

12 3 .524 1.195 8.70 0 .113 .209 1.17 0

12 1 .482 .815 6.85 1.04 .097 .191 1.36 -0.65

12 0.3 .138 .187 3.74 3.67 .098 .151 0.91 1.09

16 3 .517 1.267 2.67 0 .089 .276 .168 0

16 1 .376 .642 2.03 1.19 .096 .213 .221 -1.19

16 0.3 .180 .242 1.41 2.77 .117 .183 .334 -2.98

18 3 .897 1.630 3.33 0 .216 .392 .146 0

18 1 .633 .860 2.15 1.90 .100 .197 .077 2.78

18 0.3 .200 .269 0.75 6.47 .146 .215 .081 2.56

70
Table

5.1(b).

Mode

-tuned

data

obtained

from

figure

5.1,

giving

rise

times

and

correction

factors

for

rf

pulses

in

the

RADC

small

reverberating

chamber.

T“

Pulse

Width *

CF=

Correction

Factor o <3 On CO o 43 o r-» c- o rH 43 CO 43 CO CO O' 00 SO

tb CQ CM <3 On 43 CO 43 CO NO 43 rH CM o CO CM rH uo o O' in u "0 CM rH <3 CO SO 43 43 CO CM so o1 CMl o§ o1 o1 rHI o rH CM1 CM

co

a> CO co a.

rH # On CM rH 00 rH CM CM On CM CM *3 o O' CM CO rH CO uo 3 o CM rH m O' o rH rH 00 43 sO in >3 CO rH O' 00 uo oo rH

04 O' a> CM CM CM rH CM CO CM rH CM CM rH rH rH rH CM rH rH rH rH CM

CO

CO •H a. Pi coo CO #

a.

<1- CM <3 rH •o co

© 00

O o 00 in

m

O O' CO 00 s£> CO - <3- in s£) rH o m CO 00 o 00 o 00 so in o rH ON rH >3 sO 0> rH rH rH rH rH CM rH rH rH CM o rH o O rH rH rH o rH rH

CO • •H

ei

SO o CM o CO CM >3 ON o 43 SO r- CO n- uo uo O' 00

tb CQ CM rH rH o CM CM

O o rH O' CM rH 00 in rH sO so SO rH o T3 O rH o o m CM rH rH rH rH o rHI o1 o1 o o1 rH O1 rH CM

CO

CO

05

CO #o CO so

m o O'. o in CM o in 00 in >3 >3 SO 43 rH

m

rH on 05CO

•*4

00 O' 00 CO oo rH rH 43 SO O' 43 CM >3 <3 00 rH O' rH O' 3 s£> <3 00 sO SO m 00 NO 00 CM rH CO CM CM CM rH rH CM rH

04

CO cd a.

rH CO #

a.

CO <3 CO

O CO rH rH o CM NO CO 43

m 43 SO CO in rH 3". SO o

v£> 00 <3 in CM rH CO 00 r-» CO O' O' ro r-'. in co O'. O' o o 0)W

CO CM <3 <3 <3 >3

m 43 co NO

O o rH

O rH rH o o o rH

•H ' Qi

CO #

a. O'

mm 00

O CO so

m o rH o r-~ so 43 SO o O' sD CM

CO rH

O o rH in O' so

m oo «3

m so sO CO O' o O' o •* rH o m rH CM rH rH rH CM SO 43 rH CO rH CM CM 43 CM CM CO

CO Os 4> <D CO rH rH rH rH rH CM rH rH rH rH

CO •H rH bS 3

04

CO CO a. #

a. inm

mm rH rH rH >3 C". CO -3 r-«.

m rH

O 00 CO

O sD

<3 CO O' CM rH vO CM rH O'

O

O 00 sO sO co O' rH oo rH co co • <3 CO so 43 r- rH NO m uo 00 rH o o o rH rH rH rH o CM

so a>

CO rH

*H

siN

m UO

cr

X On CO o O' CM so o O' CO o O' CM SO O'

>4 o O rH CM CM 43

m 00 CM NO 00 o rH CM CM 43 UO 00 CM SO 00 rH rH rH rH rH rH

54 54 54 54 54 54 54 54 54 54

a; 0) 0) a; 05 05 0) CD 05 05 X X X X X X X X X X 54 >4 54 54 54 54 54 54 54 54 O 0 O O O O 0 O O o

>4 54 54 54 54 54

u 54 54 54 CO CO CO CO CO CO CO CO CO CO 0> (1) 0) 05 05 05 o> a) 0> 0) X X X X X X X X X X

Xl

XX

XX

X

XX

X

X < < < < < < < < < <

>4 >4 54 54 54 54 54 54 54 54 O o O 0 O 0 O O O 0 <D 0) 05 05 0) 0) <15 05 0) 0) CO (A CO co co CO CO CO CO CO u o cj CJ o cj CJ CJ CJ CJ X X X X X X X X X X 0> o> 05 05 a> 0) 05 05 05 0) < < < < < < < < < < i4 *H “pH •rH *«4 •rH *H •tH *H •H a a 0- a a a a a a a 0 o o o o o 0 0 0 0 I I l I l l l l l l 2 2 2 2 2 2 2 2 2 2 rH rH rH rH rH rH rH rH rH rH

71
Table 5.2(a). Mode-stirred data obtained from figure 5.5 giving rise tiroes

and correction factors for rf pulses in the RADC small

reverberating chamber.

r - Pulse Width ; CF s Correction Factor

Freq

GHz

Nominal

T, MS

No Absorber 1 Piece Absorber

Rise Time, /is MAX VR mVCF

dB

Rise Time, /is MAX

mV

Vr CF

63% 90% 63% 90% dB

0 9 3 .246 .630 447 0 .056 .130 242 0

0 9 1 .173 .453 438 0. 18 .054 .130 239 0 . 11

0 . 9 0 . 3 .144 .261 377 1 . 48 .068 .174 248 - 0 . 21

0 . 9 0 . 1 .045 .064 206 6. 73 .058 .098 189 2. 15

1 . 3 3 .216 .466 328 0 .099 .168 174 0

1 . 3 1 .227 .447 331 - 0 . 08 .121 .186 180 -0 29

1 . 3 0 . 3 .121 .231 254 2. 22 .086 .134 192 -0 86

1 . 3 0 . 1 .055 .095 133 7. 84 .073 .108 160 0 73

2. 0 3 .388 1.157 300 0 .130 .302 86 0

2. 0 1 .432 .837 300 0 .082 .194 76 1 07

2. 0 0 . 3 .171 .267 165 5. 19 .086 .151 75 1 19

2. 0 0 . 1 .069 .151 71 12. 52 .058 .091 64 2 57

2. 9 3 .470 .945 236 0 .073 .130 60 0

2. 9 1 .373 .734 212 0 . 93 .071 .168 68 -1 09

2. 9 0 . 3 .127 .223 123 5 66 .065 .127 64 -0 56

2. 9 0 . 1 .065 .097 74 10. 07 .065 .093 54 0 92

4 2 3 .626 1.437 175 0 .125 .276 32 0

4 2 1 .440 .766 129 2. 65 .119 .250 33 -0 27

4 . 2 0 . 3 .145 .219 66 8. 47 .127 .243 31 0 28

4 2 0 . 1 .065 .097 32 14. 76 .060 .089 16 8 5 60

5 65 3 .591 1.467 96 0 .073 .216 22 0

5 65 1 .291 .676 77 1 . 92 .086 .255 23 -0 39

5 65 0 . 3 .152 .247 50 5. 67 .104 .240 23 -0 39

5 65 0 . 1 .058 .079 23 12. 41 .050 .091 15 5 3 04

8 9 3 .574 1.118 134 0 .078 .142 17 1 0

8 9 1 .345 .669 109 1 . 79 .104 .175 18 8 -0 82

8 9 0 3 .144 .234 62 6. 69 .122 .204 23 -2 57

8 9 0 1 .072 .106 30 13. 00 .064 .118 14 3 1 55

12 3 .540 1.282 98 0 .130 .345 20 0

12 1 .324 .619 82 1 . 55 .127 .291 16 8 1 51

12 0 3 .159 .237 46 6. 57 .110 .228 16 8 1 51

12 0 1 .072 .120 19 .5 14. 02 .063 .090 12 0 4 44

16 3 .514 1.265 77 0 .082 .164 9 7 0

16 1 .384 .794 59 2 31 .166 .324 13 3 -2 74

16 0 3 .201 .277 39 5 91 .088 .183 10 8 -0 93

16 0 1 .108 .144 16 .6 13 33 .063 .090 7 1 2 71

18 3 .475 1.101 48 0 .086 .177 5 9 0

18 1 .306 .647 42 1 16 .101 .175 6 1 -0 29

18 0 .3 .201 .281 27 5 00 .196 .279 6 4 -0 71

18 0 .1 .095 .149 10 .0 13 62 .077 .106 4 6 2 16

72
Table

5.2(b).

Mode-stirred

data

obtained

from

figure

5.5

giving

rise

times

and

correction

factors

for

rf

pulses

in

the

RADC

small

reverberating

chamber

TPulse

Width ;

CF=

Correction

Factor

CO <r CN rs SO rH o CN CO CNn CO p" CN o >3-

n >3 pH

X

Cu CO r- 00

m

O r>- <3- o o m sO rH p-'

n O'

X

O

n >3 O' rH

O X)

X CN o CN co to CO CN o CN o n fO rH <3 CN CN

r—4H rH rH rH rH rH rH

w

0)w

IA =1

rH # •o in rH p- p' O' sO o <3 O' 00 00 rH

m o rH CO

OOX

d o a)m

P-1

X

O

m Os os r"

O CN <r <3- O' o Os O' CO o rH

O o O O' O o rH O O O rH rH rH rH o rH o o o o rH O o rH

CA •H a. oi

rH

tA o #

3.

in in ON

mm 00 CN CN 00

n oo CO 00n

O o «$• CO ro p^ ro *“ <T m so sD vO n P'. o O' n p' n X X n X X X X 0)w O O O O O O o O rH O O o O O o o o o o O

*H

ed

00 CN Os sO pv. r>- O' P". rH

O rHX O'XX o r" rH co rH

Cu cQ >3 CN rH sO <3

XX

n Os

O CN 00 rH

n CN COn

n

O p'. CJ *d

r-1

CN in

m 00

n sO sOnn o o rH

O o o CN rH o o

tA 1 0 « 1 1 1 I

0)ca tA rH 3. 3 # r—<

r—4

p^ co O' r- >3 p^ p" rH st- 'S’ rH p^ co o <3

X

m o o • x CO so CN rH co co p>. 00 p' CO n CN <3 <3 O CN X

tA O' 0)

V) CN CN CN CN CN CN CN CN CN CN rH rH rH rH CN CN CN CN rH CN

a.

H

CO coO tA 3. # <3 rH rH

m CN 'O’ O' rH rH 00

XX

n p" <3- CN

O

X

X co 0) CN r-« CN <3- n -o n o o X 00 00 X CN O CN rH X o x tA rH rH rH rH rH rH rH rH CN CN o o o o rH rH rH rH o rH

•>U CO

00 oo o CO in CN O'

n rH

X rH OS O' p-' o CN rH >3 o

CF CQ r—< o o O'

X O' p'.

n CO rH rH CN o O CN co CO

n p" CN

"d o o1 o o CN rH rH rH CN rH o o» rH rHi o• o1 o rH CSJ1 o1 w

0)

tA 3.

ca # CO •O’ SO SO O' O' ^3- p'- o X 'S’ 00

O

nn rH <3

n rH o m <3 co CO SO sO rH OS <3 CO 00 O' X n in p" o CN r-' 3

Cu o w

•H

<3 >3 00 SO SO SO P'X rH rH rH rH CN CN rH CN ro rH

ca

CsS a.

tA

H #

3.

co r-> CN co o H

n 'S’ <3

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73

NBS»1 14A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NISTIR 90-3939

2. Performing Organ. Report No. 3. Publication Date

June 1990

4. TITLE AND SUBTITLE

EMR Test Facilities : Evaluation of a Small Reverberating

Chamber Located at RADC , Griff iss AFB , Rome, New York .

AUTHOR(S^

ron Crawford, John M. Ladbury, Bill F. Riddle, and Ezra B. Larsen

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s) National Institute of Standards and Technology

DEPARTMENT OF COMMERCE

Boulder, Colorado 80303

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

Compatibility and Measurements Division

RADC/RBC Griffiss AFB, New York 13441

10.

SUPPLEMENTARY NOTES

3 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most sign ificant information. If document includes a significant

This report describes measurement procedures and results from evaluating a small

reverberating chamber located at Rome Air Development Center (RADC), Rome, New

York. The chamber was developed for measuring and analyzing the electromagnetic

susceptibility/vulnerability (EMS/V) of weapon systems and the radio frequency

(rf) shielding effectiveness of enclosures and materials. A brief description of

the facility is given, including instrumentation : for its calibration by the

National Institute of Standards and Technology (NIST) . Work was done earlier at

NIST to evaluate the RADC large reverberating chamber. A follow-on project to

construct and evaluate a small chamber is discussed in this report. Measurements

include: (1) voltage standing wave ratio (VSWR) of the transmitting and

receiving antennas; (2) coupling efficiency of the chamber; (3) effectiveness of

the chamber tuner; (4) E-field uniformity in the test zone; (5) calibration of

test E-fields based on receiving antenna power and calibrated dipole probe

measurements; (6) responses of standard equipment unde-r test (EUT) to test fields

in the RADC reverberating chamber and the NIST anechoic chamber; and (7)

performance of the reverberating chamber excited by rf pulses at ten frequencies

from 0.9 to 18 GHz, four pulse widths from 0.1 to 3 ps , and for two values of

chamber Q. Conclusions are that the chamber can be used at frequencies down to

500 MHz for cw testing, and for pulsed rf immunity testing with pulse widths as

short as 0.3 /js

.

Estimates of measurement uncertainties are given.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

electromagnetic radiated susceptibility/vulnerability testing;

measurements; reverberating chamber

13.

AVAILABILITY

[X] Unlimited

pulsed rf

14. NO. OF

PRINTED PAGES

| | For Official Distribution. Do Not Release to NTIS

f_ J

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

84

15. Price

[jX] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

U.S. GOVERNMENT PRINTING OFFICE: 1990-776-075/25132 USCOMM-DC 6043-P80
'

.