NTIA Technical Report TR-10-471

Time-Domain Propagation 

Measurements of the NASA 

Space-Power Facility

Robert T. Johnk

John D. Ewan

Paul M. McKenna

Ronald L. Carey

Nicholas DeMinco

NTIA Technical Report TR-10-471

Time-Domain Propagation 

Measurements of the NASA 

Space-Power Facility

Robert T. Johnk

John D. Ewan

Paul M. McKenna

Ronald L. Carey

Nicholas DeMinco

U.S. DEPARTMENT OF COMMERCE

September 2010

iii

DISCLAIMER

Certain commercial equipment and materials are identified in this report to specify adequately 

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

recommendations or endorsement by the National Telecommunications and Information 

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

for this purpose.
iv
v

CONTENTS

Page

FIGURES....................................................................................................................................... vi

ABBREVIATIONS/ACRONYMS.............................................................................................. viii

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

2 DESCRIPTION OF THE NASA SPACE-POWER FACILITY..................................................2

3 TIME-DOMAIN MEASUREMENT SYSTEM...........................................................................3

4 MEASUREMENT SEQUENCES................................................................................................4

5 TIME-DOMAIN WAVEFORMS ................................................................................................8

6 CHAMBER INSERTION GAIN................................................................................................10

7 EARLY-TIME FOCUSING .......................................................................................................14

8 POWER-DECAY CHARACTERISTICS..................................................................................15

9 ITS/NIST INSERTION GAIN COMPARISONS......................................................................20

10 AXIALLY-SYMMETRIC FINITE-DIFFERENCE TIME-DOMAIN MODEL.....................23

11 CONCLUSIONS.......................................................................................................................28

12 ACKNOWLEDGEMENTS......................................................................................................29

13 REFERENCES .........................................................................................................................30
vi

FIGURES

Figure 1. The SPF vacuum chamber with typical test article. Note the large access doors 

and buttresses in front of and behind the rocket. .......................................................... 2

Figure 2. Measurement system setups. (a) Calibration. (b) Chamber transmission 

measurement. A trigger generator was used for only the horizontal scans. ................. 3

Figure 3. (a) Horizontal and vertical scan planes. (b) Antenna locations....................................... 4

Figure 4. (a) Setup for horizontal scans. (b) Pulse generator inside a shielded box. (c) 

Oscilloscope mounted on receiving cart....................................................................... 5

Figure 5. Test setup for the vertical scan. (a) System deployment. (b) Transmitter....................... 6

Figure 6. The vertical scan test setup with operator at the receiving cart. The transmitter 

is supported by nylon rope from above......................................................................... 7

Figure 7. (a) Conducted generator waveform. (b) Conducted generator amplitude 

spectrum........................................................................................................................ 8

Figure 8. Received oscilloscope waveforms obtained with a discone antenna at (a) 

position 3, vpol . (b) Position 3, hpol. (c) Position 4, vpol. (d) Position 4, hpol. ......... 9

Figure 9. (a) Calculation of S21 from the chamber and reference waveforms. (b) The 

frequency averaging process....................................................................................... 11

Figure 10. Position 10 waveform and amplitude spectrum obtained with discone 

antennas. (a) Position 10, vpol waveform. (b) Associated amplitude spectrum. 

(c) Amplitude spectrum plotted on a log frequency scale (5–200 MHz). (d) 

Frequency-averaged insertion loss (BW=10 MHz). ................................................... 11

Figure 11. Position 4 oscilloscope waveform and amplitude spectrum obtained with logperiodic antennas. (a) Position 4, vpol waveform. (b) Amplitude spectrum. (c) 

Amplitude spectrum.................................................................................................... 12

Figure 12. Frequency-averaged (BW=10 MHz) results obtained over all of the horizontal 

scans for the three antenna types (20 positions). Green (biconical), red 

(discone), and blue (log-periodic)............................................................................... 13

Figure 13. Frequency-averaged (BW=10 MHz) results obtained over all of the vertical 

scans (14 positions) for the three antenna types. Green (biconical), red 

(discone), and blue (log-periodic)............................................................................... 13

Figure 14. Biconical antenna early-time, time-domain signals obtained on the vertical 

scan. (a)_Transmitting antenna at a 90’ () height. (b) Transmitting antenna at a 

100’ (30.5 m) height with the focusing effect annotated in red.................................. 14

Figure 15. Block diagram of the joint time-frequency analysis used to determine power 

decay rates................................................................................................................... 15

Figure 16. (a) Windowed FFT output at a single FFT output bin (300 MHz) plotted at 5 

ns intervals. (b) Frequency-averaged (BW=10MHz) output (blue) and 

corresponding slope estimate (red) obtained at position 1 (log-periodic 

antennas). .................................................................................................................... 16
vii

Figure 17. Frequency-averaged power decay (BW=10 MHz; blue) and LMS estimates 

(red) plotted in 5 MHz increments in the frequency range of 65-105 MHz............... 17

Figure 18. Frequency-averaged power decay (BW=10 MHz; blue) and LMS estimates 

(red) plotted in 5 MHz increments in the frequency range of 785-825 MHz............. 17

Figure 19. Power-decay time results obtained over all of the horizontal scans for three 

antenna types (20 positions). Green (biconical), red (discone), and blue (logperiodic). Decay time calculations (from [3]) are provided, based on skineffect losses only for assumed wall conductivities of σ = 105 (purple), σ = 106

(orange)....................................................................................................................... 18

Figure 20. Power-decay time results obtained over all of the vertical scans for three 

antenna types (14 positions). Green (biconical), red (discone), and blue (logperiodic). Decay time calculations (from [3]) are provided, based on skineffect losses only for assumed wall conductivities of σ = 105 (purple), σ = 106

(orange)....................................................................................................................... 19

Figure 21. ITS chamber insertion gains inferred from measured decay times (biconesgreen, discone-red, lpda-blue) with the assumption ηt= ηr=1. The combined 

NIST VNA results are shown in the black curve (courtesy of John Ladbury of 

NIST). ......................................................................................................................... 21

Figure 22. Two-dimensional, axially-symmetric FDTD model of the SPF, showing the 

pulsed current source and monitor point locations (marked with x’s)........................ 22

Figure 23. (a) FDTD current pulse. (b) Current density amplitude spectrum. ............................. 23

Figure 24. (a) Z-component of the electric field computed at ρ=46’(14.0 m), z = 22’ (6.7 

m) with a current source located at ρ=0’, z = 22’ and σ = 105 (S/m). (b) 

Normalized amplitude spectrum................................................................................. 24

Figure 25. Early-time time waveform for Ez at ρ=22’, z = 20’ showing both the direct 

component and subsequent chamber reflections......................................................... 25

Figure 26. Ez waveforms obtained at six monitor point locations with a wall conductivity 

σ=105 S/m and a source location ρ=0’, z =20’. (a) ρ=20’, z =22’. (b) ρ=20’, z 

=10’. (c) ρ=36’, z =22’. (d) ρ=36’, z =10’. (e) ρ=46’, z =22’. (f) ρ=46’, z =10’........ 26

Figure 27. Ez waveforms obtained at six monitor point locations with a wall conductivity 

σ=106 S/m and a source location ρ=0’, z =20’. (a) ρ=20’, z =22’. (b) ρ=20’, z 

=10’. (c) ρ=36’, z =22’. (d) ρ=36’, z =10’. (e) ρ=46’, z =22’. (f) ρ=46’, z =10’........ 26

Figure 28. JTFA analysis results (blue) for Ez at all of the source/monitor point 

configurations and two conductivities. Theoretical predictions based on wall 

skin-effect losses are plotted in red............................................................................. 27
viii

ABBREVIATIONS/ACRONYMS

dB decibel

DOC Department of Commerce

E3 Electromagnetic Environmental Effects

FDTD Finite Difference Time Domain

ITS Institute for Telecommunication Sciences

LPDA Log-Periodic Dipole Array 

NASA National Aeronautics and Space Administration

NIST National Institute of Standards and Technology

NTIA National Telecommunications and Information Administration

RF Radio Frequency

SPF NASA Space Power Facility located in Sandusky, Ohio
TIME-DOMAIN PROPAGATION MEASUREMENTS OF 

THE NASA SPACE-POWER FACILITY

Robert T. Johnk, John D. Ewan, Paul M. McKenna, Ronald L. Carey, Nicholas DeMinco1

This report describes a recent measurement effort conducted by the Institute for 

Telecommunication Sciences at a chamber located at the NASA Space Power 

Facility (SPF) in Sandusky, Ohio. The report describes the chamber and the

measurement system, and provides some selected time- and frequency-domain 

results. A detailed description of the measurement procedures and post-processing 

is provided. The results obtained indicate that the SPF chamber exhibits robust

reverberant behavior. The flexibility and efficiency of time-domain measurements 

is also demonstrated.

Keywords: antenna; biconical; chamber; decay time; direct pulse; discone; 

electromagnetic; finite-difference time-domain; fast Fourier 

transform; impulse; joint time-frequency analysis; log-periodic; 

oscilloscope; reverberation; ultra wideband.

1 INTRODUCTION

This report describes a recent measurement effort [1] conducted by a team of engineers from the 

Institute for Telecommunication Sciences (NTIA/ITS) at the Space Power Facility (SPF), located 

at the NASA Plumbrook station in Sandusky, Ohio. The SPF houses the world’s largest space 

environment simulation chamber, and is used to test various types of space hardware. In 

addition, we present the results of a simulation using a rotationally-symmetric, finite-difference 

time-domain (FDTD) model of the SPF.

The measurement campaign was carried out using a direct-pulse time-domain transmission 

system. The system measures the time-domain response of the chamber to a short-duration pulse 

that is transmitted and received by a pair of broadband antennas. In this series of tests, three sets 

of antennas were used to perform transmission measurements, covering the frequency range of 

20–1500 MHz. The digitized impulse-response data were post-processed to obtain chamber 

parameters like insertion loss and decay time, which are useful to assess suitability of the SPF for 

electromagnetic environmental effects (E3) testing. This effort was intended to provide baseline 

data for Finite-Difference Time-Domain (FDTD) numerical models of the SPF that were under 

development at ITS. The full-bandwidth data obtained from these measurements were also 

intended to provide a basis for accurate and representative numerical simulations.

The measurements indicate that the chamber exhibits robust reverberant behavior with excellent 

statistical field uniformity throughout the proposed test volume. In addition, the chamber exhibits 

decay rates that are a function of frequency and vary over the range of 15-50 μsec. These long decay 

times result from a combination of large chamber volume and high-conductivity aluminum walls.

 1 The authors are with the Institute for Telecommunication Sciences, National Telecommunications and Information 

Administration, U.S. Department of Commerce, Boulder, CO 80305.
2

2 DESCRIPTION OF THE NASA SPACE-POWER FACILITY

NASA is proposing to perform future E3 testing within the SPF vacuum chamber, which is an 

all-aluminum, hemisphere-on-cylinder vessel 100 feet (30.5 m) in diameter and 122 feet

(37.2 m) high. The E3 testing will be performed at normal atmospheric pressure and temperature, 

with the test article positioned upright near the center of the chamber floor. Figure 1 shows a test 

article being configured for tests inside the chamber. Radio-frequency test equipment will be 

used around the periphery of a space vehicle to conduct system-level radiated susceptibility 

testing. The unique shape, large volume, and high inner-surface reflectivity of the SPF vacuum 

chamber will create a complex electromagnetic field structure inside the chamber. To minimize 

risk to the vehicle under test, it is necessary to thoroughly understand the electromagnetic 

propagation and reverberation characteristics within the chamber volume of the SPF. NASA 

wants to create known electric-field strengths throughout the vacuum chamber, and minimize 

regions of localized high-level radio-frequency electromagnetic field levels. NASA also needs to 

design measurement systems that function optimally within this unique environment.

Figure 1. The SPF vacuum chamber with typical test article. Note the large access doors and 

buttresses in front of and behind the rocket.
3

3 TIME-DOMAIN MEASUREMENT SYSTEM

The time-domain measurement system is shown in Figure 2. It consists of an impulse generator, 

a 12 GHz bandwidth high-speed oscilloscope, two broadband antennas, a trigger generator, and 

precision microwave coaxial cables. This system is similar to one used in an earlier chamber 

evaluation effort [2]. The trigger generator, located outside of the chamber, produces a 1 kHz 

square wave that activates the impulse generator and, at the same instant, initiates an 

oscilloscope sweep. The impulse generator generates a repetitive sequence of 35 V (peak) 

impulses, each with a base width of approximately 1 ns.

The system is first calibrated by providing a direct connection between the transmitting and 

receiving antenna cables (Fig. 2(a)). The generator waveform is attenuated, digitized, and stored 

for subsequent analysis. This step is needed to provide a reference signal to determine chamber 

insertion loss. A 35-dB attenuator is used to provide proper signal conditioning for the 

oscilloscope to prevent distortion or damage to the oscilloscope circuitry. Next, the cables are 

hooked to the transmitting and receiving antennas, and transmission measurements are 

performed within the chamber environment. The impulse generator transmits a series of unipolar 

pulses at a repetition rate of 1 kHz. The transmitted pulses undergo multiple reflections from the 

chamber boundaries, and are received by the oscilloscope then digitized. The system is operated 

in a repetitive mode, and 200 averages are performed on the received waveforms to achieve an

improvement of more than 20 dB in signal-to-noise ratio. Three sets of commercially-available 

transmitting and receiving antennas, with different frequency ranges, were used for the SPF 

evaluation: 1) biconical (20–300 MHz), 2) discone (100–1300 MHz), and 3) log-periodic (300–

7000 MHz).

Figure 2. Measurement system setups. (a) Calibration. (b) Chamber transmission measurement.

A trigger generator was used for only the horizontal scans.
4

4 MEASUREMENT SEQUENCES

Measurement sequences were performed at the locations shown in Figures 3(a) and (b).

Horizontal scans were carried out with the transmitting antennas mounted on dielectric masts and 

carts shown in Figure 4. Each scan was repeated with the three types of antennas. The 

transmitting cart remained at a fixed location for the first two horizontal scans. The transmitting 

antenna cart was parked at the center position for scan 1 with the antenna set at a height of 22'

(6.7 m). The receiving cart was moved to positions 1–10, shown in Figure 3(b). The receiving

antenna was set at a height of 22' (6.7 m) for positions 1–10. Data were also taken with a lower 

receiving antenna height of 10' at positions 2,3,7,9 for the biconical antennas only. The 

transmitting antenna was also vertically polarized throughout the horizontal scans. Data were 

taken with the receiving antenna vertically (vpol) and then horizontally polarized (hpol) at the 22'

(6.7 m) height. The receiving antenna was vertically polarized for all of the 10' (3.05 m) 

measurements. A second horizontal scan was performed with the transmitting antenna cart 

parked at position 7. Data were acquired for all antenna types with the receiver at positions 1–6 

and the antennas vertically polarized at 22' (6.7 m). A limited set was taken at the 10' (3.05 m) 

height with the biconical antennas at the same positions.

A vertical scan was implemented by installing the pulse generator, a battery-powered UPS, and 

transmitting antenna on a plywood platform. The platform was supported by nylon rope to 

minimize spurious reflections. It was raised and lowered by personnel located just outside the top 

of the SPF chamber. The receiving antenna was parked at position 7 and measurements were 

performed with the transmitter parked at 10' (3.05 m) increments for heights of 50'–110' (15.2-

33.5 m) above the chamber floor. 

Figure 3. (a) Horizontal and vertical scan planes. (b) Antenna locations.
5

Figure 4. (a) Setup for horizontal scans. (b) Pulse generator inside a shielded box. (c) 

Oscilloscope mounted on receiving cart.

Figures 5 and 6 depict the vertical scan setup. A fixed transmitting orientation was maintained 

using nylon guy ropes at each scan position. The polarization of the receiving antenna was 

maintained in one configuration in the ascent portion of the scan and then switched during the 
6

descent to achieve polarization diversity. A hard trigger connection was not used for the vertical 

scan because of the physical setup. Instead, the oscilloscope sweep was triggered internally at the 

onset of the received chamber signal.

Figure 5. Test setup for the vertical scan. (a) System deployment. (b) Transmitter.
7

Figure 6. The vertical scan test setup with operator at the receiving cart. The transmitter is 

supported by nylon rope from above.
8

5 TIME-DOMAIN WAVEFORMS

Figure 7(a) depicts a reference waveform obtained from a conducted measurement with 

transmitting and receiving cables connected head-to-head through an attenuator. The resulting 

impulse has a width of approximately 1 ns, and has the amplitude spectrum shown in Figure 

7(b). The useable frequency range for antenna-to-antenna measurements extends from the lowfrequency limit of the antennas used, up to a maximum of approximately 1500 MHz. Figure 8

shows four oscilloscope waveforms obtained at positions 3 and 4 for two polarizations of the 

receiving discone antenna.

There are several striking aspects of these results. First, the temporal extent of the resulting 

waveforms is many tens of microseconds—a result of thousands of reflections from the chamber 

boundaries. The second salient feature is the single-exponential decay envelopes of the 

waveforms. An initial spike is noted for the vertically-polarized (vpol) case, which is caused by 

direct coupling between the antennas. In section 6, we will examine early-time behavior for the 

vertical scan, in which we observe focusing effects.

Perhaps the most interesting aspect is the similarity in waveform amplitudes for the four cases. 

This indicates that the chamber diffuses the propagating waves and provides a nearly equal split 

between the two polarizations. In fact, this trend was seen for all of the antenna types and scan 

positions. The result was unexpected. This diffusion might be caused by the large buttresses that 

support the access doors. More investigation will need to be conducted to understand the reasons 

for this.

Figure 7. (a) Conducted generator waveform. (b) Conducted generator amplitude spectrum.

(a)

(b)
9

Figure 8. Received oscilloscope waveforms obtained with a discone antenna at (a) position 3, 

vpol. (b) position 3, hpol. (c) position 4, vpol. (d) position 4, hpol.

(a) (b)

(c) (d)
10

6 CHAMBER INSERTION GAIN

Insertion gain is computed from the chamber and reference waveforms. A fast Fourier transform 

is applied to each waveform and the frequency-domain results are normalized as shown in Figure 

9(a). The result is the well-known transmission scattering parameter S21 with the reference planes 

located at the transmitting and receiving antenna connector ports. Converting the magnitude of 

S21 to dB obtains the insertion gain.

The transmission data are then electronically stirred [3],[4] by frequency averaging over a 

specified bandwidth, using the process depicted in Figure 9(b). The first step of the process 

consists of squaring the magnitude of the S21 results. This operation produces a scalar power at 

each FFT output bin, which can then be averaged over selected frequency ranges. The bins were 

averaged by entering a rectangular window on a selected FFT bin and averaging its power with 

those of adjacent bins. This is repeated by sliding the window to successive FFT bins and power 

averaging at each position.

An example of this is shown in Figure 9, where a 10 MHz wide sliding window is used. The 

measured time-domain waveform is shown in Figure 10(a), and it consists of an initial directcoupling component, followed by an extended series of reflections from the chamber boundaries.

The Fourier transform of this waveform is shown in Figure 10(b). The resulting amplitude 

spectrum has a “hashy” structure with rapid scintillations, which are caused by multipath. When 

frequency averaging is applied, the rapid variations are removed, generating the smoothed curve 

of Figure 10(d). The figure corresponds to the average chamber insertion gain for this antenna 

configuration. The remaining structure in Figure 10(d), after frequency averaging, is due to 

antenna input mismatch effects. The curve could be further smoothed by applying mismatch 

corrections. However this was not done, since the effects of antenna mismatch errors were

outside the scope of the ITS study.

Of particular interest are several cavity resonance peaks below 10 MHz in Figure 10(c), 

highlighting the large size and volume of this facility. These cavity resonances are quite visible 

below the nominal cutoff frequency of 100 MHz for the discones. Figures 11(a)-(d) show a 

corresponding set of results for a pair of log-periodic antennas. The frequency-averaged insertion 

gain curve of Figure 11(d) is smoother than the result obtained with the discone antennas shown 

above. This is due to a better antenna input impedance match with a reduced source/antenna 

mismatch. The insertion gain curves exhibit a rapid decrease below 300 MHz, which is due to 

the 290 MHz low-frequency cutoff of the log-periodic antennas. The higher cutoff frequency of 

the log-periodic antennas suppress the low-frequency cavity modes, and they are not visible in 

the plots.
11

Figure 9. (a) Calculation of S21 from the chamber and reference waveforms. (b) The frequency 

averaging process.

Figure 10. Position 10 waveform and amplitude spectrum obtained with discone antennas. (a) 

Position 10, vpol waveform. (b) Associated amplitude spectrum. (c) Amplitude spectrum plotted 

on a log frequency scale (5–200 MHz). (d) Frequency-averaged insertion loss (BW=10 MHz).

0 50 100 150 200 -0.1

-0.05

0

0.05

0.1

Discone Pos 10 vpol

time (usec)

signal (V)

0 200 400 600 800 1000 1200 -60

-50

-40

-30

-20

-10

0

Discone Pos 10 vpol

freq (MHz)

|S21|(dB)

101102 -60

-50

-40

-30

-20

-10

0

Discone Pos 10 vpol

freq (MHz)

|S21| (dB)

0 200 400 600 800 1000 1200 -60

-50

-40

-30

-20

-10

0

Discone Pos 10 vpol 10MHz avg

freq (MHz)

|S21| (dB)

(a) (b)

(c) (d)

0 50 100 150 200 -0.1

-0.05

0

0.05

0.1

Discone Pos 10 vpol

time (usec)

signal (V)

0 200 400 600 800 1000 1200 -60

-50

-40

-30

-20

-10

0

Discone Pos 10 vpol

freq (MHz)

|S21|(dB)

101102 -60

-50

-40

-30

-20

-10

0

Discone Pos 10 vpol

freq (MHz)

|S21| (dB)

0 200 400 600 800 1000 1200 -60

-50

-40

-30

-20

-10

0

Discone Pos 10 vpol 10MHz avg

freq (MHz)

|S21| (dB)

(a) (b)

(c) (d)
12

Figure 11. Position 4 oscilloscope waveform and amplitude spectrum obtained with log-periodic 

antennas. (a) Position 4, vpol waveform. (b) Associated amplitude spectrum. (c) Amplitude 

spectrum plotted on a log frequency scale (5–500 MHz). (d) Frequency-averaged insertion loss 

(BW=10 MHz).

If we now plot the averaged results for a number of different antenna configurations, we can 

better describe the statistical field uniformity of the chamber. Figure 12 shows average insertion 

gain plots for 20 antenna configurations and three types of antennas. The resulting curves are 

tightly clustered with a maximum spread of less than 3 dB, indicating good field uniformity over 

the scan plane. 

The same analysis was applied to the vertical scan, and the results are summarized for the three 

antennas in Figure 13. As was mentioned earlier in section 4, the hard trigger configuration of 

Figure 2(b) was not used for the vertical scan. Instead, the sweeps were initiated directly from

the received signal, using the oscilloscope’s internal trigger. Difficulties were encountered with 

this triggering method, due to wireless signals that occurred intermittently inside the SPF. When 

a wireless signal was present, it would cause jitter in the received waveforms and “smear out” 

the averaged waveform. Attempts were made to identify the source of the interference, but with 

no success. NASA engineers speculated that this might be due to wireless networks within the 

SPF building. The chamber itself was not EMI hardened, so signals could penetrate into the 

chamber through gaps in the door, electrical conduits, and the complex vacuum pipe system. The 

frequency-averaged transmission data are shown in Figure 13, where a scalloping is seen 

primarily in the discone and LPDA results. This is attributed to the jitter caused by the wireless 

interference. The values are similar to those obtained in Figure 12.

0 50 100 150 200 -0.03

-0.02

-0.01

0

0.01

0.02

0.03

LPDA Pos 4 vpol

time (usec)

signal (V)

0 500 1000 1500 -60

-50

-40

-30

-20

-10

0

LPDA Pos 4 vpol

freq (MHz)

|S21|(dB)

101

102 -70

-60

-50

-40

-30

-20

-10

0

LPDA Pos 4 vpol

freq (MHz)

|S21| (dB)

0 500 1000 1500 -60

-50

-40

-30

-20

-10

0

LPDA Pos 4 vpol 10MHz avg

freq (MHz)

|S21| (dB)

(a) (b)

(c) (d)

0 50 100 150 200 -0.03

-0.02

-0.01

0

0.01

0.02

0.03

LPDA Pos 4 vpol

time (usec)

signal (V)

0 500 1000 1500 -60

-50

-40

-30

-20

-10

0

LPDA Pos 4 vpol

freq (MHz)

|S21|(dB)

101

102 -70

-60

-50

-40

-30

-20

-10

0

LPDA Pos 4 vpol

freq (MHz)

|S21| (dB)

0 500 1000 1500 -60

-50

-40

-30

-20

-10

0

LPDA Pos 4 vpol 10MHz avg

freq (MHz)

|S21| (dB)

(a) (b)

(c) (d)
13

Figure 12. Frequency-averaged (BW=10 MHz) results obtained over all of the horizontal scans 

for the three antenna types (20 positions): green (biconical), red (discone), and blue (logperiodic).

Figure 13. Frequency-averaged (BW=10 MHz) results obtained over all of the vertical scans (14 

positions) for the three antenna types: green (biconical), red (discone), and blue (log-periodic).

0 500 1000 1500 -60

-50

-40

-30

-20

-10

0

Averaged Results

freq (MHz)

|S21|(dB)
14

7 EARLY-TIME FOCUSING

One of the questions that NASA had at the onset of this effort was whether or not the spherical 

dome of the SPF exhibits focusing effects or caustics. One reason for carrying out a vertical scan 

was to see if any focusing effects did, in fact, occur. The dome of the SPF has a radius of 

curvature of 50'(15.2 m) if we assume it has a spherical shape. From geometric optics of 

spherical reflectors, we should see a focus at one half of the radius of curvature of the dome, or 

approximately 25' (7.6 m) below the top of the dome (97' (29.6 m) above the floor). 

Figure 14 shows two scope waveforms that were obtained in the vertical scan for biconical 

transmitting and receiving antennas with the transmitting antenna oriented for vertical 

polarization and the receiving antenna horizontally polarized. In order to see this effect, we need 

to look at the initial wave front arrival which contains the high-frequency geometric-optics field 

[5], [6]. Figure 14(a) shows the waveform obtained with the transmitter set at a height of 90'. In 

Figure 14(b) the corresponding waveform at the 100' height is shown, and a large spike occurs 

approximately 50 ns after the wave front arrival. We believe this is due to focusing. This is a 

wideband, early-time effect and comprises only a small fraction of the total waveform energy. 

The impact of this effect will depend on the actual E3 testing scenario.

The waveform is plotted over a 0.5 μsec interval, and it shows the early-time response of the 

chamber. The time scales represent a relative, not absolute time since the oscilloscope was 

operated in a free-trigger sweep mode, and the trigger delays were adjusted for display purposes, 

which accounts for the time offset between the waveforms and the scale readings.

Figure 14. Biconical antenna early-time, time-domain signals obtained on the vertical scan. 

(a) Transmitting antenna at a 90' (27.4 m) height. (b) Transmitting antenna at a 100' (30.5 m) 

height with the focusing effect annotated in red.

21 21.05 21.1 21.15 21.2 21.25 21.3 21.35 21.4 21.45 21.5 -0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

S3 DC Pos90 V H

Time (usec)

Received Signal (V)

21 21.05 21.1 21.15 21.2 21.25 21.3 21.35 21.4 21.45 21.5 -0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

S3 DC Pos100 V H

Time (usec)

Received Signal (V)

(a) (b)

21 21.05 21.1 21.15 21.2 21.25 21.3 21.35 21.4 21.45 21.5 -0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

S3 DC Pos90 V H

Time (usec)

Received Signal (V)

21 21.05 21.1 21.15 21.2 21.25 21.3 21.35 21.4 21.45 21.5 -0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

S3 DC Pos100 V H

Time (usec)

Received Signal (V)

(a) (b)
15

8 POWER-DECAY CHARACTERISTICS

The analysis of the chamber time-decay characteristics is implemented using a combination of 

joint time-frequency analysis (JTFA) [7], [8] and frequency averaging. This process is shown in 

Figure 15. The joint-time frequency analysis is implemented by applying a windowed FFT to the 

measured chamber waveform, denoted by ch(t). A sliding window approach is used . This is 

implemented by subdividing the time-domain record into short blocks and then applying an FFT 

to each. A Blackman taper is used with window widths that range from 1–10 μsec. The choice of 

window width is dictated by a combination of desired frequency resolution and signal-to-noise 

ratio. For the results shown here, we used a 10 μsec wide window and performed FFT's at 

successive 5 μsec increments. This process generates a sequence of spectrum amplitude vectors 

that are a function of both the window position τ and frequency fn, which results in a twodimensional array. By selecting a particular FFT output bin (or a group of adjacent bins), we 

compute amplitude spectra for successively larger window positions and infer chamber decay 

rates as a function of frequency. Thus, we can examine amplitude spectrum decay rates over 

selected frequency bands. 

Figure 16(a) shows the output of a 300 MHz FFT bin for a 10-μsec wide Blackman window 

plotted at 5-μsec intervals. The resulting signal decays with irregular variations, which are 

caused by interference between closely-spaced chamber cavity modes. These fluctuations make 

it difficult to estimate the rate of decay. However, if we frequency average the FFT bin outputs 

over a span of 10 MHz, we obtain the smoothed and much-improved result of Figure 16(b). We 

now apply a least-squares (LS) fit to the power-averaged result to obtain a linear estimate of the 

power decay rate, shown by the red line in Fig. 16(b). The slope of this line is used to estimate 

the time it takes the power to decay to 36% (1/e) of its original level. In decibels, this 

corresponds to a change of -4.3 dB. The range over which the LS fit is performed is 40–160 μsec 

in order to ensure that we are on the decaying portion of the signal and well above the system 

noise limit. It is noted that the power decay rate is twice that of the electric and magnetic field 

decay rates.

Figure 15. Block diagram of the joint time-frequency analysis used to determine power decay 

rates.

ch(t) Windowed

FFT

ch(f1,

τ)

ch(fn,τ)

Estimate

Slopes

m1

mn

Power

Average Over

Selected # of

FFT Bins

ch(t) Windowed

FFT

ch(f1,

τ)

ch(fn,τ) n,

τ)

Estimate

Slopes

m1

mn

Power

Average Over

Selected # of

FFT Bins
16

Figure 16. (a) Windowed FFT output at a single FFT output bin (300 MHz) plotted at 5 ns 

intervals. (b) Frequency-averaged (BW=10MHz) output (blue) and corresponding slope estimate 

(red) obtained at position 1 (log-periodic antennas).

Some selected JTFA results are shown in Figures 17 and 18, in which we plot both the frequency 

averaged and resulting LMS slope estimates. Figure 17 shows a set of nine graphs, plotted at 

5 MHz intervals, in the frequency range of 65–105 MHz. Figure 19 shows a corresponding set 

plotted over the range of 785–825 MHz. In both cases, the averaging bandwidth was 10 MHz 

(±5 MHz about each selected frequency). The LMS linear slope predictions are plotted in red, 

and the frequency averaged data are plotted in blue. If one compares the two sets of plots, the 

resulting slopes of the lower frequency set are noticeably steeper. This indicates higher losses at 

the lower frequencies. This also highlights the frequency variability of the chamber losses and 

the power of JTFA analysis.

For each antenna configuration, the power decay rate was computed at 5 MHz intervals. Figure 

19 shows results for all antennas and polarizations for the entire horizontal scan. The results are 

tightly clustered, with spreads that increase with frequency. Below 500 MHz, observed 

variations are typically less than 5 μsec. Above 500 MHz, maximum spreads of approximately 

10 μsec occur. The results for the three antenna types overlap and align quite nicely. This is due 

to a highly reverberant environment that effectively “washes out” the antenna directivity (over 

their operational ranges) [3]. The decay rates also exhibit good uniformity throughout the scans, 

analogous to those of the insertion loss. 

0 20 40 60 80 100 120 140 160 180 200 -40

-30

-20

-10

0

10

20

Time (usec)

Power(dB)

40 60 80 100 120 140 160 -6

-4

-2

0

2

4

6

8

10

12

Frequency MHz

Power (dB)

F Time (usec) reTqimueen(c

uyse

McH) z

(a)

(b)

FrTeTqi

immuee

en(

c

u

(

ys

u

e

Ms

cH)

ezc)
17

Figure 17. Frequency-averaged power decay (BW=10 MHz; blue) and LMS estimates (red) 

plotted in 5 MHz increments in the frequency range of 65–105 MHz.

Figure 18. Frequency-averaged power decay (BW=10 MHz; blue) and LMS estimates (red) 

plotted in 5 MHz increments in the frequency range of 785–825 MHz.

Time (ns)

Power (dB)

Time (ns)

Power (dB)
18

Figure 19. Power-decay time results obtained over all of the horizontal scans for three antenna 

types (20 positions): green (biconical), red (discone), and blue (log-periodic). Decay time 

calculations (from [3]) are provided, based on skin-effect losses only for assumed wall 

conductivities of σ = 105 (purple), σ = 106 (orange).

The decay times exhibit some rather interesting functional behavior. Below frequencies of 100 

MHz, the decay times decrease rapidly, reaching minimum values in the neighborhood of 13 to 

18 μsec. As the frequency is increased above 100 MHz, the decay times increase steadily up to 

about 300 MHz. With the exceptions of several minor dips, the decay rates continue to increase 

up to the highest measured frequency of 1500 MHz.

The 30–300 MHz range is dominated by the antenna loading effects, which is typical for large 

complex cavities [3]. Above 300 MHz, the trend is more complex. Clearly, if wall losses were 

the dominant effect, we would expect to see the decay time decrease with inverse square root of 

the operating frequency. This might be anticipated at higher frequencies, where the antenna 

loading is far less significant. Instead, the decay times continue to increase (at a diminishing rate) 

with frequency, which cannot be explained by wall losses alone. 

It appears that there are additional loss mechanisms. The flattening of the decay rates above 

700 MHz might be due to a combination of aperture leakage and lossy objects. At the time these 

tests were conducted, the SPF chamber was not EMI hardened and wireless signals were 

observed leaking into the closed chamber during some of the measurement sequences, which 

supports the hypothesis of aperture loading in the SPF. Also, the doors are sealed with a rubber 

material that could provide additional RF volumetric losses. Clearly, more analysis and further 

investigation are needed to better understand the power-decay characteristics.
19

Figure 20. Power-decay time results obtained over all of the vertical scans for three antenna 

types (14 positions): green (biconical), red (discone), and blue (log-periodic). Decay time 

calculations (from [3]) are provided, based on skin-effect losses only for assumed wall 

conductivities of σ = 105 (purple), σ = 106 (orange).

Figure 20 shows the corresponding decay results for the vertical scan. All of the measurements 

using the three sets of antennas are included. The resulting decay characteristics show similar 

functional behavior to the horizontal scans. Above 500 MHz, the vertical scan results have 

somewhat lower decay rates and tighter clustering, which is likely due to volumetric loading of 

the human operator inside the chamber for this series of tests. The wireless interference jitter 

described previously had little impact on the power decay results.
20

9 ITS/NIST INSERTION GAIN COMPARISONS

A team of engineers from the National Institute of Standards and Technology (NIST) performed a 

separate series of transmission measurements inside the SPF six months after the completion of the 

ITS effort. They measured transmission gain using a vector network analyzer/optical link 

combination, which directly measures the magnitude and phase of S21. NIST used a similar 

measurement scanning methodology to that previously developed by ITS engineers. In addition, 

NIST engineers applied antenna mismatch corrections to obtain refined estimates of insertion gain.

While the ITS time-domain system can be used to compute S21, it is more precise to use the 

measured power-decay times to infer insertion gain. Hill [3] provides equations that permit the

calculation of insertion gain from the measured power-decay times. There are several reasons for 

using this approach. First, when we acquired the waveforms, we limited the time window of the 

received waveform to 200 μsec, during which, the signal decays to approximately 5% of its 

original amplitude. This results in a truncation error in |S21| of approximately ±0.5 dB. This 

choice was made because longer waveform records would have significantly increased data 

acquisition time. An additional error is caused by amplitude drift in the pulse generator. This 

varied as much as 1 dB during the course of a full-day measurement. Also, no mismatch 

corrections were applied to the insertion data, which contributes additional measurement 

uncertainties. That said, even with these systematic errors, the insertion loss results presented 

here indicate good chamber statistical field uniformity.

The ITS system and associated signal processing, however, provide precise estimates of power 

decay time. First, the computation is based on a single waveform, so it is not subject to either 

amplitude drift or truncation effects.

From Hill [3], we have

| | , (1) 16 2

3 21_

2

avg

t r

S V Q

η η λ

π =

where Q is the chamber quality factor, V is the chamber volume (m3

), λ is the RF source 

wavelength (m), |S21_avg| is the frequency-averaged insertion gain, and ηt and ηr are the 

transmitting and receiving antenna efficiencies respectively.

Also, the power decay time and the chamber quality factor are related by 

Q = 2πfτ , (2)

where f is the RF source frequency in Hz and τ is the power-decay time in seconds. Combining 

(1) and (2) and substituting wavelength for frequency obtains:

(3) 8 | |

2

2

21_ η η τ

π

λ avg t r Vc S =
21

where c = 3.0 x 108 m/sec and τ is the measured power decay time (sec). Equation (3) can now be 

used to calculate insertion gain from the measured power decay times. We used a two-step process 

to compare our results with those of NIST. We took all of the horizontal scan power-decay data 

and averaged the decay times over all of the positions and polarizations. This was done for the 

three antenna types. The result of this process is a frequency-dependent decay time. These results 

were then applied to (3) to obtain insertion gain. Since the transmitting and receiving antenna 

efficiencies have not been characterized for the antennas used, we assume the antennas are lossless

with ηt= ηr=1. This assumption provides an upper limit on the insertion gain.

Figure 21 shows the ITS/NIST insertion gain intercomparisons. The ITS data are plotted for the 

three antenna types. The results for the different antenna types are closely aligned in the 

overlapping frequency ranges, which indicate that mismatch losses have a minimal impact on the 

measured decay times. The NIST VNA data that are shown are derived from a combination of 

antenna types with antenna mismatch corrections applied. The ITS results are offset by 1–2.5 dB 

from those of NIST. The data sets agree fairly well, and the trends are very similar, lending 

confidence to both sets of measurements. Closer agreement might be obtained with additional 

antenna efficiency corrections applied to the ITS data. In a recent paper, Krauthäuser [9] 

performed a series of antenna efficiency measurements in several reverberation chambers using

narrowband, pulsed, time-decay measurements. He found that the antenna efficiencies for a set 

of LPDA antennas varied over the range 0.6≤ η ≤0.75 in the frequency range of 100–1000 MHz. 

The 2.5 dB difference observed above 300 MHz in Figure 21 could be almost eliminated if we 

assume ηt = ηr=0.75. Clearly, more measurements and research are needed to better understand 

the differences in the data sets and to obtain improved correlation. 

Figure 21. ITS chamber insertion gains inferred from measured decay times (bicones-green, 

discone-red, lpda-blue) with the assumption ηt= ηr=1. The combined NIST VNA results are 

shown in the black curve (courtesy of John Ladbury of NIST).

ITS

NIST
22

Figure 22. Two-dimensional, axially-symmetric FDTD model of the SPF, showing the pulsed 

current source and monitor point locations (marked with x’s).

monitor 

points pulsed

current 

source

Conductive

Boundary

σ

ρ

z

x x

x

x

x x

monitor 

points pulsed

current 

source

Conductive

Boundary

σ

ρ

z

x x

x

x

x x
23

10 AXIALLY-SYMMETRIC FINITE-DIFFERENCE TIME-DOMAIN MODEL 

A two-dimensional FDTD model has been developed for the SPF based on axial symmetry. A 

two-dimensional approximation can be made with the following assumptions: 1) we assume that

the chamber is axially symmetric about the vertical center axis of the chamber, and 2) we restrict 

the source current to be on this axis. With these restrictions, Maxwell’s equations can be 

formulated in cylindrical coordinates with two possible sets of transverse field components with 

respect to the z axis: transverse magnetic TMz (Eρ,Hφ,Ez) for an electric current source, or 

transverse electric TEz (Hρ,Eφ,Hz) for a magnetic current source. The ITS model employs a zdirected electric current source located on the chamber axis as is shown in Figure 22. The current 

source is the simple derivative of a Gaussian waveform of unit amplitude shown in Figure 23(a). 

The pulse has significant energy for approximately 5 ns with a resulting amplitude spectrum 

extending beyond 1 GHz shown in Figure 23(b). The Yee cells are spaced at 3.048 cm, with a 

resulting lattice bandwidth of approximately 1 GHz. The wall losses are incorporated into the 

model using a full-wave formulation described in Kunz and Luebbers [10] . Simulations were 

performed for a number of different source/monitor point combinations with wall conductivities

of 105 and 106 S/m. The source and monitor point locations correspond to some of the horizontal 

scan measurement locations

Figure 24(a) shows a computed electric field time-domain waveform with an assumed wall 

conductivity of σ = 105 with a monitor point location of ρ = 46'(14.0 m) and z = 22' (6.7m) and a

source location of ρ=0' and z=20’ (6.1 m). The resulting time-domain waveform exhibits a single 

exponential decay envelope and is similar to the waveforms obtained at other source/monitor 

point locations. 

Figure 23. (a) FDTD current pulse. (b) Current density amplitude spectrum.

0 20 40 60 80 100

Time (ns)

Source Current Density

0

1.0

-1.0

Spectrum Amplitude (dB)

0

40

80

120

-40

0 500 1000 1500

Frequency (MHz)

(a)

(b)

0 20 40 60 80 100

Time (ns)

Source Current Density

0

1.0

-1.0

Spectrum Amplitude (dB)

0

40

80

120

-40

0 500 1000 1500

Frequency (MHz)

0 20 40 60 80 100

Time (ns)

Source Current Density

0

1.0

-1.0

Spectrum Amplitude (dB)

0

40

80

120

-40

0 500 1000 1500

Frequency (MHz)

(a)

(b)
24

Figure 24. (a) Z-component of the electric field computed at ρ=46'(14.0 m), z = 22' (6.7 m) with 

a current source located at ρ=0', z = 22' and σ = 105 (S/m). (b) Normalized amplitude spectrum.

In order to view the FD-TD results in the frequency domain, we take the ratio of the spectrum 

amplitudes of the computed electric-field component and the current source:

, (4) | ( ( )) |

| ( ( )) |

FFT I t

FFT E t SAnormalized =

where SAnormalized is the normalized amplitude spectrum, E(t) is the computed electric-field 

component, I(t) is the source current component, and FFT denotes the fast Fourier transform. 

Applying the waveforms of Figures 24(a) and 23(a) to (4) yields the normalized spectrum of 

Figure 24(b). At frequencies below 25 MHz, we see isolated cavity modes, but above that, the 

modes become more closely spaced due to increasing modal density. Strong modes are predicted 

below 10 MHz—a result that is consistent with the measurements. Figure 25 shows the 

corresponding early-time waveform. The direct arrival is seen at approximately 22 ns, followed 

by an increasing number of chamber reflections. The rate of arrival of chamber reflections 

increases steadily with time and is indistinguishable beyond 300 ns. 

Figure 26 shows 200 μsec long time-domain records of Ez at the six monitor points shown in 

Figure 22. The amplitude does show some decrease as the radius increases, but there is not much 

variation at the two heights. This trend was not seen in the measurements, which might be due to 

the perfect symmetry and lack of diffusers (e.g. door buttresses) in this model. The computed 

waveforms are similar in character, and all of them have a distinctive single-exponential decay 

envelope. There is also a strong resemblance with respect to shape and rates of decay to the 

0

0.2

-0.2

0.1

-0.1

0 50 100 150 200 250 300

Time (ns)

Ez (V/m)

Frequency (MHz)

(a)

0

40

80

-40

-80

Amplitude Spectrum (dB)

10 100 1000

(b)

0

0.2

-0.2

0.1

-0.1

0 50 100 150 200 250 300

Time (ns)

Ez (V/m)

Frequency (MHz)

(a)

0

40

80

-40

-80

Amplitude Spectrum (dB)

10 100 1000

(b)
25

measured full-bandwidth waveforms. Figure 27 shows the electric fields for a wall conductivity 

of σ=106 S/m. Similar trends are seen with respect to the radial and height dependence of the 

waveform amplitudes. Once again, the waveforms have a single-exponential decay envelope. 

The decay rate is several times longer in this case due to the higher wall conductivity.

A JTFA analysis was performed on all of the computed fields and the results are summarized in 

Figure 28 along with theoretical predictions using formulas in [4]. The analysis parameters (e.g. 

window width and taper) which are used here are identical to the ones used previously on the 

measured data in section 8. Both the FD-TD theoretical predictions assume wall losses due to 

skin effect. The results track well at all six positions for both conductivities, indicating that the 

FD-TD model is accurate. In addition, the results validate the JTFA analysis software and 

parameter selection. Since we have not incorporated other loss types (e.g. antenna, aperture, 

volumetric), the JTFA analysis exhibits a functional behavior that is quite different from that of 

the measurements. Additional losses will need to be incorporated into the FD-TD model to 

replicate the measured power-decay characteristics.

Figure 25. Early-time time waveform for Ez at ρ=22', z = 20' showing both the direct component 

and subsequent chamber reflections.

chamber reflections

direct
26

Figure 26. Ez waveforms obtained at six monitor point locations with a wall conductivity σ=105 

S/m and a source location ρ=0', z =20'. (a) ρ=20', z =22'. (b) ρ=20', z =10'. (c) ρ=36', z =22'. (d) 

ρ=36', z =10'. (e) ρ=46', z =22'. (f) ρ=46', z =10'.

Figure 27. Ez waveforms obtained at six monitor point locations with a wall conductivity σ=106 

S/m and a source location ρ=0', z =20'. (a) ρ=20', z =22'. (b) ρ=20', z =10'. (c) ρ=36', z =22'. (d) 

ρ=36', z =10'. (e) ρ=46', z =22'. (f) ρ=46', z =10'. Ez (V/m)

Time (μsec)

(a) (b)

(c) (d)

(e) (f)

Ez (V/m)

Time (μsec)

(a) (b)

(c) (d)

(e) (f)

Time (μsec)

Ez (V/m)

(a) (b)

(c) (d)

(e) (f)

Time (μsec)

Ez (V/m)

(a) (b)

(c) (d)

(e) (f)
27

Figure 28. JTFA analysis results (blue) for Ez at all of the source/monitor point configurations 

and two conductivities. Theoretical predictions based on wall skin-effect losses are plotted in 

red.

0 200 400 600

0

Power Decay Time (

μsec)

800 1000 1200 1400

50

100

Frequency (MHz)

150

200

250

300

σ=10

5 S/m

σ=10

6

S/m

0 200 400 600

0

Power Decay Time (

μsec)

800 1000 1200 1400

50

100

Frequency (MHz)

150

200

250

300

0 200 400 600

0

Power Decay Time (

μsec)

800 1000 1200 1400

50

100

Frequency (MHz)

150

200

250

300

σ=10

5 S/m

σ=10

6

S/m
28

11 CONCLUSIONS

This effort highlights the power and utility of direct-pulse time measurements and joint timefrequency analysis. The measurement system performed well and with high efficiency. The 

results obtained were both repeatable and accurate. 

The measurement effort provided much insight into the electromagnetic environment of the 

NASA SPF chamber. The biggest surprise was the robust diffusion and depolarization that was 

observed, given that there was no paddle present. One possible source are the two large door 

buttresses, which could provide a strong depolarization effect; more research is needed here. 

Another finding was the complex loss mechanisms which are due to a combination of antenna 

loading, conductive wall losses, and possible losses due to aperture/volumetric loading. The 

results indicate that the SPF chamber has the potential to operate as a reverberation chamber over 

a wide frequency range. Further measurements and numerical electromagnetic simulations will 

be required to determine the operational frequency range and the achievable level of 

performance. 
29

12 ACKNOWLEDGEMENTS

The authors want to thank Dr. Kurt Shalkhauser of NASA Glenn Research Center for his 

sponsorship of this effort and for providing this outstanding research opportunity. The authors 

also thank Frank Sanders, Patti Raush, and Jeff Bratcher of ITS for their support of this program. 

The authors would also like to thank Noel Sargent, Cathy Lewis, and Mike Harlacher of the 

NASA Glenn Research Center. In particular, we would like to thank Noel Sargent for his superb 

job of facilitating the vertical scan measurements. The authors also extend thanks to Mike 

Hatfield of the Naval Surface Warfare Center, Dahlgren Division, for sharing his SPF measured 

data and providing excellent insight. We are also indebted to Chriss Hammerschmidt of the ITS 

measurements division for many insights and helpful suggestions. The authors would also like to 

thank Dennis Camell, John Ladbury, and Galen Koepke of NIST for constructive and helpful 

discussions. We are also indebted to Bob Scully of the NASA Johnson Space Center for many 

useful discussions and for getting us involved in this effort.
30

13 REFERENCES

[1] R.T. Johnk, J.D. Ewan, P. M. McKenna, R. L. Carey, N. DeMinco, and K.A. Shalkhauser, 

“Time-domain pulsed measurements of the NASA space power facility,” IEEE 

International Symposium on EMC, 18 to 21 August 2009, pp. 187 to 192.

[2] J.M. Ladbury, R.T. Johnk, and A.R. Ondrejka, “Rapid evaluation of mode-stirred chambers 

using impulsive waveforms,” NIST Technical Note 1381, 1996.

[3] D. A. Hill, “Electronic mode stirring for reverberation chambers,” IEEE Trans. 

Electromagn. Compat., vol. 36, pp. 294–299, 1994.

[4] D. A. Hill, Electromagnetic Fields in Cavities: Deterministic and Statistical Theories, New 

York: IEEE Press, 2009.

[5] M. Kline and I. W. Kay, Electromagnetic Theory and Geometrical Optics, New York: John 

Wiley & Sons, 1962.

[6] L. B. Felsen, “Progressing and oscillatory waves for hybrid synthesis of source excited 

propagation and diffraction, IEEE Trans. Antennas Propagat., vol. AP-32, pp. 775–796, 

1984.

[7] L. Cohen, Joint Time-Frequency Analysis: Theory and Applications, New York, NY, 

Prentice-Hall, 1995.

[8] R.T. Johnk, B. Archambeault, and D. Novotny, “Using joint time-frequency analysis to

enhance time-domain numerical EMC simulations,” Interference Technology, Annual 

Guide, 2003.

[9] H.G. Krauthäuser and M. Herbrig, “Yet another efficiency measurement method in reverb 

chambers,” IEEE International Symposium on EMC, 25 to 30 July 2010, pp. 536 to 540.

[10] K. S. Kunz and R. J. Luebbers, The Finite Difference Time Domain Method for 

Electromagnetics, Boca Raton, Fl: CRC Press, 1993.
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BIBLIOGRAPHIC DATA SHEET

1. PUBLICATION NO.

TR-10-471

2. Government Accession No. 3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Time-Domain Propagation Measurements of the NASA Space -Power Facility

5. Publication Date

September 2010

6. Performing Organization 

Code

7. AUTHOR(S)

R. T. Johnk, J. D. Ewan, P. M. McKenna, R. L. Carey, N. DeMinco

9. Project/Task/Work Unit No.

3108011-300

8. PERFORMING ORGANIZATION NAME AND ADDRESS

Institute for Telecommunication Sciences

National Telecommunications & Information Administration

U.S. Department of Commerce

325 Broadway

Boulder, CO 80305

10. Contract/Grant No.

11. Sponsoring Organization Name and Address

National Telecommunications & Information Administration

Herbert C. Hoover Building

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Washington, DC 20230

12. Type of Report and Period 

Covered

14. SUPPLEMENTARY NOTES

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

significant bibliography or literature survey, mention it here.)

This report describes a recent measurement effort conducted by the Institute for Telecommunication Sciences at a 

chamber located at the NASA Space Power Facility (SPF) in Sandusky, Ohio. The paper describes the chamber and 

the measurement system, and provides some selected time- and frequency-domain results. A detailed description of 

the measurement procedures and post-processing is provided. The results obtained indicate that the SPF chamber 

exhibits robust reverberant behavior. The flexibility and efficiency of time-domain measurements is also 

demonstrated. 

16. Key Words (Alphabetical order, separated by semicolons)

antenna; biconical; chamber; decay time; direct pulse; discone; electromagnetic; finite-difference time-domain; fast 

Fourier transform; impulse; joint time-frequency analysis; log-periodic; oscilloscope; reverberation; ultra wideband.

17. AVAILABILITY STATEMENT

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