Shielding Effectiveness Measurements Applied to Safety 

Assessment Predictions at Picatinny Arsenal 

by Neal Tesny, Marc Litz, David Conrad, and Lillian Dilks 

ARL-TR-3481 April 2005 

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Army Research Laboratory 

Adelphi, MD 20783-1197 

ARL-TR-3481 April 2005 

Shielding Effectiveness Measurements Applied to Safety 

Assessment Predictions at Picatinny Arsenal 

Neal Tesny, Marc Litz, David Conrad, and Lillian Dilks 

Sensors and Electron Devices Directorate, ARL 

Approved for public release; distribution unlimited.
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Shielding Effectiveness Measurements Applied to Safety Assessment Predictions 

at Picatinny Arsenal

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Neal Tesny, Marc Litz, David Conrad, and Lillian Dilks

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13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

Shielding effectiveness for a screened work area in building 3208 of the Picatinny Arsenal has been measured using techniques 

and processes defined in MIL-STD 188-125-1. The measured frequency ranges go beyond the MIL-STD 10 MHz to 1 GHz, to 

include the frequency range of 1 to 10 GHz. The results of the measurements show that attenuation factors provided in the 

current configuration are sufficient to provide acceptable environmental and safety protection from high-power RF impulse 

sources radiated from within. 

15. SUBJECT TERMS

Shielding effectiveness

16. SECURITY CLASSIFICATION OF:

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Neal Tesny

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iii 

Contents 

List of Figures iv

List of Tables iv

1. Introduction 1

2. Measurement Methodology 1

3. Description of Measurements 2

4. Results 6

5. Time Domain Analysis 15

6. Conclusions 18

Distribution List 20
iv 

List of Figures 

Figure 1. Top view of enclosure showing test point locations. ...................................................... 3 

Figure 2. Electrical schematic for equipment and instrument control. This hardware 

schematically describes the test equipment used during these safety measurements............. 5 

Figure 3. Shielding effectiveness for test point 1, (a) vertical polarization and (b) horizontal 

polarization. ............................................................................................................................ 7 

Figure 4. Shielding effectiveness for test point 2, (a) vertical polarization and (b) horizontal 

polarization. ............................................................................................................................ 8 

Figure 5. Shielding effectiveness for test point 3, (a) vertical polarization and (b) horizontal 

polarization. ............................................................................................................................ 9 

Figure 6. Shielding effectiveness for test point 6, (a) vertical polarization and (b) horizontal 

polarization. .......................................................................................................................... 10 

Figure 7. Shielding effectiveness for test point 7, (a) vertical polarization and (b) horizontal 

polarization. .......................................................................................................................... 11 

Figure 8. Shielding effectiveness for test point 8, (a) vertical polarization and (b) horizontal 

polarization. .......................................................................................................................... 12 

Figure 9. Shielding effectiveness for test point 9, (a) vertical polarization and (b) horizontal 

polarization. .......................................................................................................................... 13 

Figure 10. A 30 dB shielding effect occurs when taping over a 9/16 inch hole in a patch panel.14 

Figure 11. Example of TD reconstruction of impulse from a Gaussian impulse input. .............. 16 

Figure 12. Example of effect on exponential impulse input....................................................... 17 

Figure 13. Comparison of data taken with and without fiber optic link for test point 2, vertical 

polarization. This shows good agreement............................................................................ 18 

List of Tables 

Table 1. Matrix of measurement sets acquired for shielding effectiveness evaluation. ................ 3 

Table 2. Resonant frequencies of a 28’ × 12’ × 8’ box based on full-wave and half-wave 

resonances. .............................................................................................................................. 6 
1 

1. Introduction 

Shielding effectiveness measurements for the 20 MHz to 10 GHz frequency band were made for 

the shielded room that is partially lined with microwave absorber, located in building 3208 of the 

Picatinny Arsenal. The measurements were performed 18 to 20 January 2005. The shielded area 

is constructed from plywood surrounded by a layer of sheet metal on either side of the plywood. 

The room has a double-door and several patch panels. The shielding effectiveness of this type of 

room, as originally installed by the manufacturer, is typically on the order of 60 dB over the 

20 MHz to 1 GHz frequency band. 

Over years of use, the room has been modified for many experiments critical to understanding 

the susceptibility of army materiel. Regular use and modifications will leave a shielded room 

with shielding parameters below those originally specified by the manufacturer. While the 

shielding may be below original manufacturer specification, it is our goal to verify that the 

shielding status is sufficient to provide a safe working environment for personnel operating in the 

building. The measurements described below give a status report of the level of shielding 

provided by the current physical configuration. While attempts will undoubtedly be made in the 

future to improve the shielding effectiveness, we will not make those suggestions in this report, 

as that is not the goal of this effort. 

The measurement techniques followed in this report adhere to standards developed within the 

Department of Defense to evaluate the shielding effectiveness of shielded rooms. A quantitative 

question that arises during this effort pertains to the field strengths that would be necessary to go 

beyond environmental safety limits. The safety office at Army Research Laboratory (ARL) 

follows a policy of as-low-as-reasonably-acceptable. Typical safety levels for peak radio 

frequency (RF) impulses are limited to 1 kV/m at the edge of the facility fenceline. Prediction of 

the fields required to produce these limits would help develop guidelines for future operations of 

high-power RF sources within the shielded room and facility. 

2. Measurement Methodology 

The measurement methodology is based on guidance described in MIL-STD 188-125-1, “Highaltitude Electromagnetic pulse (HEMP) Protection for Ground-based C4I Facilities Performing 

Critical, Time-urgent Missions, Part 1 Fixed Facilities,” 17 July 1998. Although this standard 

was written for a shielding effectiveness threshold of 80 dB over the band measured, the 

methodology is applicable for the measurement focused on safety and environmental hazards 

associated with usage of the bldg 3208 RF shielding levels. 
2 

The MIL-STD calls for the spacing of test frequencies to be logarithmic within each decade with 

a minimum sampling density as follows: 

 10 kHz – 100 kHz: 20 test frequencies 

100 kHz – 1 MHz: 20 test frequencies 

 1 MHz – 10 MHz: 40 test frequencies 

 10 MHz – 100 MHz: 150 test frequencies 

100 MHz – 1 GHz: 150 test frequencies 

The goal of these measurements was focused on safety assessment. Therefore, the envelope of 

frequencies of interest included higher frequencies from those developed for HEMP hardening 

goals. Our final frequency range of interest covered from 300 KHz to 10 GHz. Traveling wave 

tube (TWT) amplifiers were used in performing the attenuation measurements over the 

frequency range from 1 to 10 GHz. 

3. Description of Measurements 

Initial plans called for shielding effectiveness measurements on the enclosure to be made at a 

total of nine test points, eight of them located on the side walls and one point on the ceiling. The 

points are identified in figure 1. However no data was measured for test points four and five 

because no unobstructed position within five feet of the shielded room wall was available for 

access to these points. The frequency bands that were tested ranged from 300 KHz to 10 GHz 

and are shown in table 1 with the corresponding test points. An HP 8753 network analyzer was 

used for all measurements below 3 GHz. The network analyzer was programmed to sample data 

at 401 test frequencies in each of the test bands, i.e., between 300 KHz and 20 MHz, 20 MHz 

and 1 GHz, 1 GHz and 2 GHz, and between 2 GHz and 3 GHz. In the 300 KHz-20 MHz and 

20 MHz-1 GHz bands the frequencies were distributed logarithmically, i.e., log10 of the 

frequencies was uniformly spaced between log10 (20 MHz) and log10 (1 GHz). In the 1 to 2 GHz 

and 2 to 3 GHz bands the frequencies were linearly distributed. Resolution bandwidth was set at 

10 Hz resulting in a sweep time of about 42 seconds. For the measurements in the frequency 

range of 300 KHz to 20 MHz, an AH Systems SAS 562 a powered loop antenna was used to 

receive signals, and a passive tri-loop antenna of approximately 20-inch diameter powered by an 

ENI 2100 power amplifier was used to transmit. For the measurements in the frequency ranges 

of 20 MHz to 1 GHz, 1 GHz to 2 GHz, and 2 GHz to 3 GHz two Bi-logic log-periodic antennas 

were used. The amplifiers used were an Amplifier Research 10W1000 for the 20 MHz to 1 GHz 

range, a Varian VZL-6941K1 TWT for the 1 to 2 GHz range, and a Varian VZS6951K1AD 

TWT for the 2 to 3 GHz range. The data was downloaded from the network analyzer to a laptop 

computer. Both horizontal and vertical polarizations, with respect to E-field, were measured at 

each test point and frequency band, with the exception of the 3 to 4 GHz range which used the 

conical spiral antennas which have circular polarization. 
3 

Figure 1. Top view of enclosure showing test point locations. 

Table 1. Matrix of measurement sets acquired for shielding effectiveness evaluation. 

Measurement Hardward Matrix 

Frequency 

range 

Signal 

connection 

Antenna Analyzer Sampling 1 2 3 4 5 6 7 8 9 

.3-20 MHz Fiber Loop NA 401 pt log √ √ √ √ √ √ √

.02-1 GHz Fiber Bilog NA 401 pt log √ √ √ √ √ √ √

.02-1 GHz Direct link Bilog NA 401 pt log √ √ √ 

1-2 GHz Direct link Bilog NA 401 pt lin √ √ √ √ √ √ √

2-3 GHz Direct link Bilog NA 401 pt lin √ √ √ √ √ √ √

3-4 GHz Direct link Bilog SA 11 pts lin √ √ √ √ 

4-6 GHz Direct link OEW (4-6 GHz) SA 11 pts lin √ √ √ √ 

6-8 GHz Direct link OEW (4-6 GHz) SA 11 pts lin √ √ √ √ 

8-10 GHz Direct link OEW SA 11 pts lin √ √ √ √ 

For the frequency ranges above 3 GHz an HP 8563A, a spectrum analyzer was used to collect 

relative signal levels at discrete frequency points spaced linearly every 100 MHz, with an 

HP8350B sweep oscillator used to generate the signals. For the frequency range from 3 to 

4 GHz, a Varian VZS6951K1AD TWT amplifier was used along with a pair of Emco 3102 

conical spiral antennas. For the frequency range from 4 to 6 GHz, a Hughes 1177H C-band 

TWT amplifier was used along with a pair of WR-187 open-ended waveguides as transmit and 

receive antennas. For the frequency range from 6 to 8 GHz, a TWT amplifier was used along 

with a pair of WR-137 open-ended waveguides. For the frequency range from 8 to 10 GHz, a 

2 1 

4

3 

7 5 6

8 

Doors 

Signal I/O panel 

Signal I/O panel 

9
4 

Hughes 1177H X-band TWT amplifier was used along with a pair of WR-90 open-ended 

waveguides. 

Measurements above 3 GHz were performed only for test points 1, 2, 3, and 6. No 

measurements were performed for test points 7, 8, and 9 between 3 to 10 GHz. Time constraints 

of the test team limited the total number of measurement options. If the information is deemed 

necessary, future testing will be arranged. 

The MIL-STD states that separation between transmit and receive antennas shall be 10 feet 

(± 2 inches) This distance was used for measurements in the frequency bands less than 3 GHz. 

However, above 3 GHz we found that a separation distance of 5 feet could be used to obtain a 

better signal-to-noise ratio while remaining in or near the “far field” and therefore, this 

separation distance was practical for this series of measurements. 

Calibration measurements for both horizontal and vertical polarizations (with reference to the log 

periodic portion of the antennas) were obtained at an antenna separation of 10 feet for the test 

frequency bands 300 KHz to 20 MHz, 20 MHz to 1 GHz, 1 GHz to 2 GHz, and 2 GHz to 3 GHz, 

and at horizontal and vertical polarizations at an antenna separation of 5 feet for the frequency 

bands 3 to 4 GHz, 4 to 6 GHz, 6 to 8 GHz, and 8 to 10 GHz. The conical spiral antennas used in 

the 3 to 4 GHz band are circularly polarized; therefore, a single calibration was performed. The 

measurements were performed in the open area outside of the shielded room in the building. For 

the frequency bands 300 KHz to 20 MHz and 20 MHz to 1 GHz, a fiber optic cable system was 

used to transmit frequency information from the network analyzer to the amplifier. RG-223 

double-shielded RF cables were used to connect the network analyzer to the fiber optic 

transmitter, the fiber optic receiver to the amplifier, the amplifier to the transmit antenna, and the 

receive antenna to the network analyzer. The output signal of the receive antenna was attenuated 

by a single high-power 40 dB attenuator, prior to being fed to the network analyzer. This 

technique prevented overloading the input to the network analyzer. The 40 dB attenuator was 

calibrated separately at the 401 test frequencies corresponding to each of the two bands using the 

network analyzer in order to account for its presence in the receive circuit. 

For the frequency bands above 1 GHz, a direct feed was used in place of the fiber optic link. 

This direct link used the type N bulkhead feed-through in the I/O panel in the front of the 

enclosed room. 

For the frequency bands up to 3 GHz, the network analyzer, receive antenna, fiber optic 

transmitter (which was used up to 1 GHz) and laptop computer were placed inside the shielded 

room for the shielding effectiveness measurements. One end of a fiber optic cable was 

connected to the transmitter. The fiber optic cable passed through a hole in the shielded room 

I/O panel to exit the shielded room so that the other end could be connected to the fiber optic 

receiver. The amplifiers and transmit antenna were also outside the shielded room. For the 

frequency bands above 3 GHz, the spectrum analyzer and receive antennas were placed inside 
5 

the shielded room, and the amplifiers and transmit antennas were placed outside the shielded 

room. 

A diagram of the shielding effectiveness measurement system is shown in figure 2. This shows 

the configuration which uses the fiber optic link. The output of the network analyzer (O) is split 

so that a reference signal (R) can be provided to compare with the signal received by the receive 

antenna (A). For a given frequency and polarization, the difference in intensity between the 

received signal and the reference signal is called A/R. A/R is a measure of the signal loss at that 

frequency due to the path between the transmit antenna and the receive antenna plus additional 

losses and gains due to the various components in the transmitting and receiving circuits 

including cables, the signal splitter, fiber optic equipment, amplifier and antennas. The shielding 

effectiveness at a given frequency is the difference between this value and the value at that 

frequency obtained when the system was calibrated, i.e., when there were no shielded room walls 

between the transmit antenna and receive antenna. This technique is based on the fact that the 

additional system and component losses and gains described above are assumed to be the same 

for the calibration measurement and the shielding effectiveness measurement. 

Figure 2. Electrical schematic for equipment and instrument control. This hardware schematically describes 

the test equipment used during these safety measurements. 

Four measurements were recorded at each test point using the 8753 network analyzer. These 

were 1&2) a noise floor measurement in both vertical and horizontal polarizations and 3&4) a 

shielding measurement in each polarization. Each noise floor measurement was taken with no 

signal being transmitted, thus providing the background noise level needed to determine the 

dynamic range for each point and antenna orientation. The shielding measurements were taken 
6 

with the amplifier on and sending the appropriate signals to the transmit antenna. These signals 

were provided by the network analyzer via the fiber optic cable link. 

For the measurements above 3 GHz, a sweep oscillator connected to a TWT amplifier was used 

to produce signals spaced every 100 MHz in frequency which were transmitted on the exterior of 

the shielded room. The signal levels were then read from an HP8563A spectrum analyzer located 

inside the shielded room. For the frequency range from 3 to 4 GHz, a pair of Emco 3102 conical 

spiral antennas was used as transmit and receive antennas. For frequencies above 4 GHz, 

matching open ended waveguides, within the bands described in table 2, were used as transmit 

and receive antennas. In order to obtain the noise floor, the signal level was obtained from the 

spectrum analyzer when no signal was being transmitted. 

Table 2. Resonant frequencies of a 28’ × 12’ × 8’ 

box based on full-wave and half-wave 

resonances. 

Length (ft) (m) Freq (MHz) 

28 8.48 35.4 

12 3.64 82.5 

8 2.42 123.8 

56 17 17.7 

24 7.27 41.3 

16 4.85 61.9 

4. Results 

Data for each test point and polarization was combined in a large array containing results of all 

measurements. Plots of these arrays for each of the test points for horizontal and vertical 

polarization are shown in figures 3 through 9. The data are plotted along with the dynamic range 

of the measurement system for comparison. Measurements were not made for test points four 

and five because no unobstructed position within five feet of the shielded room wall was 

available for access to these points. The matrix of measurement sets is shown in table 1. 
7 

.

Figure 3. Shielding effectiveness for test point 1, (a) vertical polarization and (b) horizontal 

polarization. 

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-1h

Shielding eff

Dyn Range

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-1v

Shielding eff

Dyn Range

(a) 

(b) 
8 

Figure 4. Shielding effectiveness for test point 2, (a) vertical polarization and (b) horizontal 

polarization. 

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-2h

Shielding eff

Dyn Range

105 106 107 108 109 1010 0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-2v

Shielding eff

Dyn Range

(a) 

(b) 
9 

Figure 5. Shielding effectiveness for test point 3, (a) vertical polarization and (b) horizontal 

polarization. 

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-3h

Shielding eff

Dyn Range

105 106 107 108 109 1010 0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-3v

Shielding eff

Dyn Range

(a) 

(b) 
10 

Figure 6. Shielding effectiveness for test point 6, (a) vertical polarization and (b) horizontal 

polarization. 

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-6h

Shielding eff

Dyn Range

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-6v

Shielding eff

Dyn Range

(a) 

(b) 
11 

Figure 7. Shielding effectiveness for test point 7, (a) vertical polarization and (b) horizontal 

polarization. 

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-7h

Shielding eff

Dyn Range

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-7v

Shielding eff

Dyn Range

(a) 

(b) 
12 

Figure 8. Shielding effectiveness for test point 8, (a) vertical polarization and (b) horizontal 

polarization. 

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-8h

Shielding eff

Dyn Range

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-8v

Shielding eff

Dyn Range

(a) 

(b) 
13 

Figure 9. Shielding effectiveness for test point 9, (a) vertical polarization and (b) horizontal 

polarization. 

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-9h

Shielding eff

Dyn Range

105 106 107 108 109 1010

0

20

40

60

80

100

120

140

freq (Hz)

dB

Shielding effectiveness-9v

Shielding eff

Dyn Range

(a) 

(b) 
14 

Some specific measurements were performed at the request of Picatinny personnel. The patchpanel located between test points 6 and 7 had a small hole (~9/16 inch diameter) in it and had a 

hard signal wire running through it. This hole and wire created a source of leakage. At test point 

6 we measured this leakage and then removed the wire and taped over the hole with copper tape, 

performing the measurements again. The copper taped reduced the signal leakage by at least 

30 dB over the frequency band 2 GHz to 3 GHz, and greater than 10 dB over the range 3 GHz to 

10 GHz. Limits in dynamic range of the TWT source/receiver channel prevented detecting more 

of an improvement between 3 to 10 GHz. The results of shielding effectiveness for both taped 

and untaped patch-panel in the vertical polarization is shown in figure 10. 

2 3 4 5 6 7 8 9 10

x 109

20

30

40

50

60

70

80

90

100

frequency (Hz)

SE (dB)

Tp 6, vert

tp6-untaped

tp6-taped

dyn. range

Figure 10. A 30 dB shielding effect occurs when taping over a 9/16 inch hole in a patch panel. 

At frequencies determined by the physical size of the 28’ × 12’ × 8’ room, the room acts as a 

resonating cavity. If we assume that a single and half wavelength are the most stable modes for 

the cavity oscillation, then the frequencies that might resonate during the measurement process 

are those closest to the resonant values. Table 2 shows the frequencies that would support cavity 

resonances for an empty box the size of the screen room. Of course, the screen room has work 

benches on at least 3 walls and RF absorber on 3 walls. The resonant frequencies calculated 

based on an empty room are idealized, and would not be expected to be precise. They serve only 

as a frequency range within which resonances would be expected to occur. 
15 

The idealized room resonances range from 17 MHz to 123 MHz. It is apparent from the 

shielding effectiveness curves shown for all test point (figures 3 through 9) that this frequency 

range contributes most to the leakage of the shielded room. Every test point measured shows 

some of its lowest shielding effectiveness in this range. 

The HEMP MIL-STD calls for using fiber up to 1 GHz. However since it was desired to 

perform measurements up to 10 GHz and our fiber optic link was limited to 1 GHz, a hard-wire 

connection was used for frequencies between 1 and 3 GHz. In order to compare performance 

between the hard-wire and fiber optic connections and observe any differences in dynamic range 

or coupling, the measurements were performed twice in the 20 MHz to 1 GHz range for test 

points 1, 2, and 3. They were performed once with fiber optic linking the transmit and receive 

components, and another time with a hard-wire connection linking the transmit and receive 

components. In this frequency range there was found to be relatively good correlation between 

the results of each measurement set. The comparison for test point 2 for vertical polarization is 

shown in figure 13 and show results which differ by a few decibels at most. 

5. Time Domain Analysis 

The shielding effectiveness measurement described above provides a scalar value for all 

frequencies measured. These frequency domain (FD) measurements provide the amplitude to 

easily determine the shielding effectiveness, as defined in the MIL-STD. It would be of interest 

to predict the time-domain (TD) pulse shape of a multi-frequency impulse. In order to do this 

correctly, phase delay information is required. The phase was not recorded during this series of 

measurements. This could be performed in the future with a vector network analyzer such as the 

HP 8510C in the future. With this type of instrument, a measurement of phase delay for each 

frequency would also be recorded. With amplitude and phase available, a complete TD 

reconstruction could be performed and the waveshape of an impulse could be predicted. 

The following analysis is less than perfect in that only amplitude data was measured. If we 

assume that the phase delay for all frequencies is zero, we can still calculate a predicted 

waveform outside the shielded room, from a sample input waveform. This prediction will be 

incomplete until such time as phase is measured. However, the calculation can provide insight 

into expected levels of leakage. 

If an impulse is transmitted inside the shielded room, the TD signal received outside the room 

could be estimated by taking the Fourier transform of the transmitted impulse, multiplying it by 

the shielding effectiveness, and then taking the inverse transform to determine the resulting TD 

waveform. The resulting waveform would provide an estimate of the received waveform 

characteristics for insight and understanding. A phase of zero degrees was used when 

reconstructing these waveforms. However, shifting of phase could produce a varying TD signal. 
16 

It is unfortunate that the measurements required by the MIL-STD specify only amplitude and not 

phase. The measurements, which include phase information, can be performed in the future if 

necessary. 

Two example waveforms were used for instructional purposes. First, a Gaussian waveform 

example radiated through the wall at test point 2 would produce the time domain output shown in 

figure 11. Second, an exponential impulse transmitted of the form t*exp(-t) would produce an 

output as shown in figure 12. 

Figure 11. Example of TD reconstruction of impulse from a Gaussian impulse input. 

Input pulse: 

• Gaussian monocycle 

• 500 kV peak 

• 500 pS pulse width 

• 350 pS risetime 

Output pulse: 

• 4.43 kV peak 

• 2280 pS pulse width 

• 2420 pS risetime 

Pulse computation based on 

measured shielding effectiveness

Test point 2 

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

x 10-8

-2000

-1000

0

1000

2000

3000

4000

5000

time (S)

voltage (V)

Output pulse

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

x 10-8

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

x 105

time (S)

voltage (V)

Input pulse
17 

Figure 12. Example of effect on exponential impulse input. 

If we assume a pulsed power source of 2.5 MV pulse into a 450 ohm load, we would calculate 

~14 GW pulse into the load. If we assume a 25% efficiency of the PFN and horn, then the power 

transmitted is ~3.5 GW. The Fris equation for antenna power density radiated allows us to 

calculate the electric field at the wall of the shielded room (~1 m from the antenna). 

2

2 4

t

D

f s

PG E P

π r Z = =

where 

PD = power density (W/m2) 

Pt = power transmitted by source (W) 

G = antenna gain 

r = range from antenna (m) 

Zfs = impedance of free space 

E = electric field (V/m) 

This back-of-the-envelope calculation shows that 500 kV/m would appear at the inside wall of 

the shield room. The electric field appearing outside the screen room, based on the frequencydependent shielding effectiveness measurements performed at test point 2, would suggest 

(see figure 11 and 12) that the electric field outside of the screen room would be ~4.5 kV/m. 

Input pulse: 

• t*exp(-kt) 

• 500 kV peak 

• 500 pS pulse width 

• 117 pS risetime 

Output pulse: 

• 4.43 kV peak 

• 2240 pS pulse width 

• 1900 pS risetime 

Pulse computation based on 

measured shielding effectiveness

Test point 2 

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

x 10-8

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

x 105

time (S)

voltage (V)

Input pulse

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

x 10-8

-1000

0

1000

2000

3000

4000

5000

time (S)

voltage (V)

Output pulse
18 

This provides an example of the radiation levels that may exist. These levels are above those 

that would be permitted at the boundary of government property, but within safety guidelines for 

radar workers. 

108 109

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

tp2v

frequency (Hz)

SE (dB)

with fiber

without fiber

Figure 13. Comparison of data taken with and without fiber optic link for test point 2, vertical 

polarization. This shows good agreement. 

6. Conclusions 

The shielded room shows resonant leakage in the frequency range from 10 MHz to 123 MHz. 

This correlates well with the cavity resonances of the shield room. An 8 MHz signal stands out 

for test point 3. This is the location of the horn array patch panel. 

The areas near both the front and back I/O panels (test points 3 and 6) had the worst shielding 

effectiveness. This was most likely due to the 9/16 inch hole in the I/O panel near test point 6, 

which was not sealed and also contained a hard-wire cable running through a hole in the horn 

array I/O panel at test point 3. 

When operating any high-voltage transmitting equipment inside the shielded room, it is highly 

recommended that all open holes in the I/O panels be sealed tightly with metal plates, with 
19 

fasteners spaced every 1 inch, or as a temporary measure, with metal tape sealed firmly at all 

edges. These techniques are typical in HEMP hardening environments. Any hard wires running 

directly into the shielded room should be removed as well. It was shown that this significantly 

reduces RF leakage as would be expected. 

The area around the door, test point 2, was also shown to have lower shielding effectiveness than 

test point 1. However, it is not clear from the data how much of this degradation was due to 

signal leakage through the I/O panel at test point 3. 

The time domain analysis described in section 5 provides insight and predictions of electric 

fields expected outside of the rf shield room. It is shown that a 500 kV/m impulse radiation 

source would generate approximately 5 kV/m electric fields outside of the shield room. 
20 

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