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National Institute of

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U.S. Department of Commerce

NIST Technical Note 1548

NIST Technical Note 1548

Electromagnetic Airframe Penetration

Measurements of a Beeclicraft Premier lA

Chriss Grosvenor, Dennis Camell, Galen Koepke. and David Novotny

Electromagnetics Division

Electromagnetics and Electrical Engineering Laboratory

National Institute of Standards and Technology

Boulder, CO 80305-3328

Robert T. Joiink

National Telecommunication and Information Agency

Institute for Telecommunications Sciences

Boulder, CO 80305-3328

August 2008

\ ^

U.S. Department of Commerce

Carlos M. Gutierrez, Secretary

National Institute of Standards and Technology

James M. Turner, Deputy Director
Certain commercial entities, equipment, or materials may be identified in this document

in order to describe an experimental procedure or concept adequately. Such

identification is not intended to imply recommendation or endorsement by the National

Institute of Standards and Technology, nor is it intended to imply that the entities,

materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards U.S. Government Printing Office For Sale by the

and Technology Washington: 2008 Superintendent of Documents

Technical Note 1548 U.S. Government Printing Office

Natl. Inst. Stand. Technol. Stop SSOP, Washington, DC 20402-0001

Tech. Note 1 548 Phone: (202) 512-1 800

1 1 pages (August 2008) Fax: (202) 51 2-2250

CODEN: NTNOEF Internet: bookstore.gpo.gov
Contents

1

.

History and Background 1

2. Overview 3

3. Measurement System 5

4. Measurement of Electromagnetic Airframe Penetration 7

5. Reference Measurements 10

6. Airframe Penetration Measurements — Overview 15

6.

1

Extrapolation Results 16

6.2 Main Passenger Cabin Penetration Results 18

6.3 Flight Deck Penetration Results 40

6.4 Rear Cargo Hatch Penetration Results 55

6.5 HIRE Positions for Flight Deck Penetration 68

6.6 Internal Coupling Measurements 73

7. Uncertainty Analysis 81

8. Summary and Conclusions 84

9. References 87

Appendix A. Time-Domain Waveform Analysis 89

Appendix B. Signal and Noise Characteristics 93

Appendix C. TEM and DRG Horn Boresight Gain Characteristics 95

Appendix D. Carbon Fiber Composites 97

D. 1 Dielectric Properties 98

D.2 Shielding Effectiveness 99

Appendix E. Penetration Data for HIRE Frequency Bands 101

Appendix F. Beechcraft Premier I A Measurement Equipment List 105

111
I
Electromagnetic Airframe Penetration

Measurements of a Beechcraft Premier lA

Chriss Grosvenor, Dennis Camell, Galen Koepke, and David Novotny

Electromagnetics Division

National Institute of Standards and Technology

325 Broadway

Boulder, CO 80305

and

Robert T. Johnk

National Telecommunication and Information Agency

Institute for Telecommunication Sciences

325 Broadway

Boulder, CO 80305

The National Institute of Standards and Technology has recently completed shielding

effectiveness/penetration studies on three different aircraft types for the Federal Aviation

Administration. The studies are used to understand the cavity coupling characteristics between

antennas placed in various compartments inside the aircraft and antennas placed at various

angular positions around an aircraft. This document will show how penetration varies as a

function offrequency, antenna type, antenna polarization, and cavity susceptibility. Internal

coupling between two antennas placed in the aircraft at different locations to determine the

quality factor and the time decay offields is also presented. This technical note gives results for

the Beechcraft Premier lA.

Key words: aircraft; cavity coupling; digital signal processing; HIRF; penetration; shielding

effectiveness; synthetic time-domain measurements.

1. History and Background

The Field Parameters and EMC Applications project team of the National Institute of Standards

and Technology (NIST) has recently completed shielding effectiveness studies of three

representative aircraft for the Federal Aviation Administration (FAA). These studies will be

used to provide the FAA with the procedures and data reduction techniques for typical low-level

airframe high intensity radiated fields (HIRF) attenuation/shielding tests. This technical note

addresses aircraft shielding tests conducted on a Beechcraft Premier lA carbon-fiber composite

business jet. The first study was a technical note reporting the results from the FAA's

Bombardier Global 5000 business jet [1], and the final report will be on a Boeing 737-200,

owned and operated by the FAA. The Bombardier Global 5000 represents a typical business jet

and the 737-200 represents a typical commercial aircraft. By measuring all three aircraft and
comparing the results we will have the potential to provide a "design roadmap" for the

optimization of HIRF testing standards for the EMC aircraft manufacturing community.

The FAA currently has specific certification pohcies that address HIRF testing on an aircraft's

electrical and electronic systems. These certification tests have been applied for the past 1

9

years [2]. In the FAA document, the regulatory authorities and industry have defined HIRF

environments, requirements for aircraft HIRF protection, and methods for testing and verifying

the level of HIRF protection. Most of reference [2] discusses HIRF testing for electronic and

electrical subsystems, which this technical note does not address. This technical note

specifically addresses both high- and low-level airframe shielding comphance testing. The HIRF

procedures are found in sections 6.6.2.6 and section 6.6.4 of reference [2].

The basic problem is to evaluate the coupling of an external source into a large, leaky cavity [3-

6]. The cavity could represent the whole aircraft or a cavity (cargo bay, flight deck, etc.),

depending on the expected vulnerability. In a typical HIRF measurement, the measurement

system is calibrated and a reference measurement is taken without the aircraft embedded in the

test setup. The aircraft is then placed into the test setup and various measurements are taken in

susceptible cavities. These attenuation tests are typically conducted using either mechanical

stirring or frequency stirring methods [1-3]. The airframe attenuation is calculated by use of the

following equation,

. _ c 77 _ reference measurement x-.^ atten • cavity measurement

where Aaaen is the airframe attenuation and S.E. is defined as the shielding effectiveness. These

numbers, expressed in decibels, are typically positive so that the more positive the number, the

greater the protection the aircraft provides to electromagnetic fields, and as the number

approaches zero we expect almost no shielding protection. The aircraft HIRF attenuation data

vary as a function of frequency, physical position of the measurement antenna, characteristics of

the aircraft, and configuration of the test site. After a company tests and processes the data, the

information is given to the FAA, which uses it, in conjunction with the subsystem susceptibility

tests, to determine an aircraft's HIRF vulnerability.

The detailed method used to process aircraft HIRF attenuation data is not well documented and

is closely held by the handful of test service providers. Therefore, the interpretation of the data

is not immediately obvious to the certification engineer. This technical note, the Bombardier

technical note [1], and the forthcoming Boeing 737-200 technical note, will consider attenuation

measurements as a ftinction of frequency, antenna position, antenna type, and cavity selection.

Our data-processing methodology will be shown in detail. Using this information, we hope to provide guidelines for both the FAA and test engineers to develop a uniform and transparent test method for data processing and documentation. We know that the confidence levels are expected to be dependent on the number of sample points (measurement geometries) but we

I
should be able to assess the trade-offs between measurement effort (sample number) and risk

(confidence level).

2. Overview

This report summarizes results of a measurement effort conducted by the Field Parameters and

EMC Applications Project team of NIST. This effort consisted of an extensive series of

penetration measurements performed on a Beechcraft Premier lA designed and owned by the

Hawker Beechcraft Corporation. The aircraft was tested at the Hawker Beechcraft facility in Wichita, Kansas during the period from April 16, 2007 to April 20, 2007. The purpose of this

effort is to develop a test methodology that allows us to understand the differences between

various types of aircraft construction.

The effort utilized a NIST-developed measurement system consisting of ultra-wideband

transverse electromagnetic (TEM) horn antennas, 3117 dual-ridged guided (DRG) horn antennas,

a commercially available vector network analyzer (VNA), and interconnecting transmission

media, and an amplifier. Interconnections between transmitting and receiving antennas were

affected using broadband 1 1 GHz and 1 8 GHz precision, analog, electro-optic links in conjunction with a configurable VNA and amplifier for airframe shielding studies up to 18 GHz.

Shielding data were obtained from a direct comparison of two measurements: (1) transmission

measurements between boresighted antennas located outside the aircraft to obtain a reference,

and (2) transmission measurements with one antenna located inside a selected compartment of

the aircraft and a pair of horizontally and vertically polarized antennas for both low-frequencyband and high-frequency-band antennas located outside the aircraft at specified locations.

Shielding data were obtained by comparing processed reference and aircraft transmission data.

This is achieved using an efficient sequence of Fourier and inverse Fourier transformations,

frequency domain convolutions, and filtering combined with time gating and frequency

averaging. Shielding values were obtained by taking the ratio of the gated amplitude spectra of

the aircraft measurement and the gated amplitude spectra of the references. Data smoothing is performed using the frequency-averaging of signal power over a specified bandwidth as described in reference [3],

(2)

Shielding data were obtained with a receiving antenna located in one of three internal

compartments: (1) the main passenger cabin, (2) the flight deck, and (3) the external, rear cargo

hatch. A pair of transmitting antennas were positioned outside the aircraft at a fixed height of

3 m, which is the approximate height of the windows, at a fixed distance of 23 m from the center

of the aircraft. The transmitting antennas were boresighted at the center of the aircraft, and data were obtained for both horizontal and vertical polarizations. We based our tests on HIRE

standard test procedures and previous experience with aircraft shielding measurements. These

standards are concerned with detecting possible leakage into the aircraft. Key areas include the

flight deck, the avionics bay, any windows/doors/joints, and the wing/tail section of the fuselage.
We defined a test setup at various angular positions around the aircraft, around the flight deck of

the aircraft at five positions at a constant distance from the front landing gear of the aircraft, and

internal coupling measurements. In a recent paper [4], questions were raised as to how many

positions need to be measured around an electrically large object to fully characterize the fields

penetrating into the aircraft for a particular high-frequency limit. For this reason, we designed

the test plan as follows: For orbit 1, receiving antennas were placed in the main passenger cabin

and (1) measurements were taken from 0° to 120° every 10°; (2) measurements were taken every

5° fi-om 120° to 150°; and (3) measurements were taken at 160°, 170°, 180°, 190°, 270°, and

330°. For orbits 2 and 3, receiving antennas were placed in the flight deck and in the rear cargo

hatch, and measurements were taken every 10°, which was shown to be sufficient from the first orbit and were taken around the entire aircraft. By traversing around the aircraft we could look

at the symmetry behavior of the carbon-fiber composite structure. After these three orbits, we

concluded with a set of internal couphng measurements to understand the reverberant

environment internal to the aircraft. An aircraft's level of protection, referred to as shielding,

depends on the level of treatment, the compartment, the frequency, the transmitting antenna

polarization, and the angle of illumination.

In this document, we will display penetration values, which are the reciprocal of shielding

values. On the graphs that follow, a penetration near dB means electromagnetic fields can

easily penetrate into that part of the aircraft. Penetration levels for the Premier lA range from

approximately dB to -40 dB. The estimated dynamic range of the measurement system is 50

dB at 4000 MHz and 30 dB at 18,000 MHz. Maximum penetration was observed with the

receiving antenna in the main passenger cabin, while lower values were obtained in the flight

deck and the rear cargo hatch. Penetration in the main passenger cabin was fairly consistent

around the aircraft at values between -10 dB and -15 dB across the frequency band. Minimum

shielding in the main passenger cabin was observed around the tail of the aircraft at a value of

around -20 dB for the antennas in the vertical polarization. Minimum penetration, for the

aircraft, was seen in the rear cargo hatch at positions between 10° and 90°.

This report is divided into five main sections: (1) a description of the measurement system, (2) an overview of the measurement technique, (3) an overview of the signal processing, (4) a summary of results obtained for the three different aircraft compartments and various internal

measurements, and (5) an uncertainty analysis. Six appendices discuss the impact of time gating,

signal and noise, an equipment list, maximum penetration as a ftanction of the HIRF specified

frequency bands, the gain characteristics of the ultra wideband antennas that were used, and a

discussion of the physical properties, fabrication, and electrical properties of carbon-fiber

composite materials.
3. Measurement System

The configuration of the NIST measurement system for these aircraft measurements is shown in Figures 1 and 2. The system consists of: (1) a VNA, (2) two transmitting TEM horn antennas

and two DRG horn antennas configured for horizontal and vertical polarizations, respectively,

(3) a receiving TEM horn antenna and DRG antenna, (4) two coaxial microwave switches to select the polarization of the transmit antennas, and (5) two precision analog electro-optic links

to cover both frequency bands and to provide an interconnection between the transmitting

antennas outside the aircraft and the receiving antenna inside. These links provide a significant

improvement in performance over conventional microwave cables. The optical links result in low transmission losses, low noise, and they do not pick up common-mode noise from

environmental ambient signals. The optical links also provide an improvement in dynamic range

and have better immunity from electromagnetic interference.

The heart of this system is a commercially available four-port VNA that has been configured to acquire complex transmission data (S31 for the TEM antennas and S42 for the DRG antennas, in- phase and quadrature signals). Due to internal hardware limitations, the VNA was limited to a maximum of 16001 frequencies, but we developed software that extends the number of

frequencies to any desired value. If we need more than 16001 points, the software subdivides a given frequency range into a user-selected number of 16001 point sub- bands. The DRG horn

antennas operate from 1 GHz to 1 8 GHz and were configured using two bands resulting in 32002

Optical fiber link to optical receiver

Figure 1. Airframe shielding measurement system (receiving side). The reverberant nature of the airframe permits the reception of horizontal and vertical polarized signals.
Transmitting TEM

horn antennas

Transmitting TEM

iiorn antennas

Channel 1 H-pol Channel 2 V-pol

Figure 2. Transmitting side of the airframe shielding measurement system.

equally spaced measurement points from approximately 0.5 MHz to 18 GHz. The TEM horn

antennas operate from 0.1 GHz to 4 GHz and were configured using one band, resulting in 6401

equally spaced measurement points from approximately 0.5 MHz to 4 GHz. A reduced

frequency spacing is necessary to avoid problems due to aliasing. Prior to connecting the cables

to the antennas, a calibration of all channels was performed to remove systematic transmission

effects due to cabling, switches, and the frequency and phase variations of the optical

transmission link. This procedure calibrates the system to the input of the transmitting and

receiving antennas. Three NIST-developed ultra-wideband TEM horn antennas were used: two

1 .2 m antennas on a tower located outside of the aircraft, either to transmit horizontally and

vertically polarized fields, and a more compact 36 cm TEM horn located in a preselected aircraft

compartment to detect energy coupled into the airframe. For the higher frequency bands three

commercially available DRG antennas were used: two on the same transmitting tower located

outside of the aircraft to transmit horizontally and vertically polarized fields, and a DRG antenna

located in the same preselected aircraft compartment to detect energy coupled into the airframe.

The frequency data were digitized and transferred to a laptop computer for subsequent data

analysis and signal processing.
4. Measurement of Electromagnetic Airframe Penetration

The extraction of airframe penetration characteristics required the two-step measurement

process, shown in Figure 3. In the first step, a reference transmission measurement was

performed by boresighting the transmitting and receiving antennas at a fixed distance. The

reference measurements were performed at a location away from the aircraft in order to minimize reflections from the aircraft. This measurement quantifies the energy incident on the

aircraft, and enables us to calibrate and remove the frequency-dependent effects of the antennas

and interconnecting hardware. In the second step, the receiving antenna was placed in a selected

aircraft compartment, the transmitting antennas were placed at fixed locations, external to the

aircraft, and stepped-irequency transmission data were acquired.

The reference and airframe data were processed using a sequence of filtering, Fourier transforms,

and time gating to obtain the penetration values. The basic process through which the data were

obtained is shown in Figure 4. The raw frequency data were first filtered to maximize signal-tonoise ratio and to minimize effects from the low-frequency cut-off of our electro-optic link.

Next, a tapered frequency-domain window was applied to both sets of data to reduce Gibbs

ringing in subsequent processing. An inverse Fourier transform (IFT) was then applied to the

processed data to obtain time-domain waveforms. Time gates were then applied to isolate the

desired portions of waveforms and remove undesired portions. In the case of the reference, the

time gate was applied to isolate the direct antenna-to-antenna couphng and remove the effects of

Transmitting antennas . J IH Receiving

antennas

Optical fiber

X (variable)

Reference measurement

Transmitting antennas / -j^C y'CJ ~

Figure 3. Two-step airframe shielding measurement procedure used in the

Beechcraft Premier lA evaluation.
Transmission measurement through airframe

Stepped-frequency

aircraft data Background=0

Stepped-frequency

antenna reference Background=0

i

Appropriate filter to emphasize signal

Appropriate filter to emphasize signal

Condition data for FT

and reduce Gibbs ringing

T

Condition data for FT

and reduce Gibbs ringing

Apply time gate(s) to

isolate sample response i

1-

Apply time gate to

isolate sample response

Remove conditioning

ForlFT

Remove conditioning For IFT

Deconvolve airframe spectrum

with

reference spectrum

I

Frequency domain

' Kaiser-Bessel window

<0.02 dB passband ripple >50 dB rejection 0.5 ns on/off transition Frequency domain convolution

Apply distance correction

I

- Frequency domain

antenna correction

Distance correction relative

to antenna-to-antenna reference

Appropriate filter to emphasize signal

Aircraft penetration

Figure 4. Signal processing sequence to obtain airframe penetration.

ground bounce and late-time reflections. Time gating was applied to the airframe data to isolate

either the direct illumination or reverberant fields of the aircraft. Effects from ground bounce were embedded in the waveforms at this distance and therefore cannot be removed by timegating. The time-gated data sets were then transformed back into the frequency domain, and the

penetration (PE), was computed from the deconvolution:

PE = DC 5*42 (gated airframe)

5'42(ga?e<i reference)

(3)

where SAiigated reference) is the antenna-to-antenna coupling with environmental effects gated

out, and S^iigated airframe) is the airframe transmission with gating appUed to minimize noise.
Processed

penetration data

Perform averaging over a selected

bandwidth (BW)

A^

/=]

i

Frequency-averaged

penetration

{PEifi))

Figure 5. The frequency averaging definition.

Since the reference and airframe measurements were typically carried out at different distances, a distance correction {DC) was applied:

/ D DC(J5) = 201og,o Dref (4)

where D is the distance in meters from the aperture of the transmitting antenna to the geometric

center of the aircraft and D,^/ is the distance between the reference antennas. A detailed

description of this procedure is given in reference [3]. Thus, our definition of penetration is based on a comparison of a direct antenna-to-antenna coupling and signal transmission through

the airframe. The penetration, as we define it here, is the reciprocal of shielding (in decibels,

penetration is the negative of shielding). We prefer to display results in terms of penetration

because of a better graphical display and so that we normalize by our reference measurement.

Single aspect penetration characteristics for aircraft exhibit rapid variations with frequency, due

to the large, complex cavity behavior of the aircraft. In order to obtain the volumetric averaged

penetration for a compartment, the processed penetration data are frequency averaged over a

specified bandwidth, by use of the process shown in Figure 5. Averaging the penetration data

reduces the complex cavity variations and highlights systematic coupHng effects. These effects are discussed in detail in references [1-3].
5. Reference Measurements

The test setup for the reference measurements is shown in Figure 6. The transmitting antennas

are shown mounted on one tower with aperture centers located 3 m above the ground. The

receiving antennas were mounted on the other tower. The towers were constructed from PVC

pipes and plywood platforms to produce a low-density support structure with minimal scattering.

The antennas were then boresighted and a distance extrapolation was performed to determine an

optimal reference distance to minimize near-field effects and maximize the period between the

signal and ground bounce. We performed multiple reference measurements with antenna-toantenna separations ranging from 2 m to 35 m. We found that a separation of 6 m was optimal in

terms of accuracy and time separation. Two transmission measurements were performed,

namely, one each for the vertical and horizontal channels. This process required a manual

reorientation of the receiving antenna to be co-polarized with each of the transmitting antennas.

Once the reference data were taken, the receiving antenna was dismounted from the support

tower and placed at selected locations inside the aircraft. The external antenna tower and aircraft are shown in Figure 7. The reference waveforms for the DRG antenna are shown in Figures 8, 9,

and 1 0. The reference waveforms for the TEM horn antenna are shown in Figures 11, 12, and

13. The ungated time-domain reference waveform for the DRG antenna is shown in Figures 8

and 11. The doublet that occurs at 15 ns in Figure 8 and 25 ns in Figure 1 1 correspond to the

direct antenna-to-antenna coupling. The subsequent waveform activity is due to a combination

of internal antenna reflections and environmental scattering due to ground bounce and reflections

from nearby objects. Figures 9 and 12 show the ungated frequency-domain response for the

DRG and TEM horn references, respectively. The antenna-to-antenna coupling response occurs

at 25 ns for these antennas due to the offset of the apertures. The noise-like hash on the

waveform is due to ground bounce and spurious reflections, which were time-gated out of the

reference measurement. After isolating the antenna response for both antennas, we obtained the

gated frequency-domain response of the DRG and TEM horn antennas in Figures 10 and 13,

respectively. These are the waveforms we use as our reference to determine penetration.

10
Figure 6. Reference measurement setup. The transmitting tower is configured and the

receiving antennas will be mounted on top of the second tower.

Figure 7. The transmitting antennas placed on top of a support tower and

boresighted at the center of the aircraft.

11
0.4

0.2 -

3

p.

-auI -0.2 o

2;

-0.4-

-0.6

10

DRG Antenna Response

Ground bounce &

spurious reflections

V '

20 30

Time (ns) 40 50

Figure 8. Ungated time-domain transmission waveform for a DRG antenna

obtained at a separation of 6.0 m and vertical polarization.

10

-10

S -20 H

<u T3I -30 H 60

-40-

-50-

-60

DRG Antenna — No time gate applied

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 9. Ungated frequency-domain amplitude spectrum for a DRG horn antenna

at a separation of 6 m and vertical polarization. Note the hashy behavior due to the

spurious reflections shown in Figure 8.

12

1
DRG Antenna — Time gate applied

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 10. Gated frequency-domain amplitude spectrum corresponding to the

waveform of Figure 9.

0.02

0.01

3

<

O

Z

-0.01 -

-0.02 -

-0.03

TEM Antenna Response

20 40

Time (ns)

Ground bounce &

spurious reflections

60

Figure 1 1 . Ungated time-domain transmission waveform for a TEM horn antenna

obtained at a separation of 6 m and vertical polarization.

13
T3

00

<u •a3

"S

-20

-30

-40

-50

-60

-70

-80

-90 -

-100

TEM Antenna — No time gate applied

500 1000 1500

Frequency (MHz)

2000 2500

Figure 12. Ungated frequency-domain amplitude spectrum for a TEM horn antenna obtained at a

separation of 6 m and vertical polarization. Note the scalloping due to the large ground bounce

reflection shown in Figure 1 1

.

-20

-30

-40

73 -50

-§ -60 c^ -70

-80

-90

-100

TEM Antenna — Time gate applied

n

^

\

^ r^

500 1000 1500

Frequency (MHz)

2000 2500

Figure 13. Gated frequency-domain amplitude spectrum corresponding to the waveform of Figure 12.

14
6. Airframe Penetration Measurements—Overview

We began by measuring the penetration at several extrapolation points on the 45 ° Hne as shown

by the black X's in Figure 14. For penetration measurements, the external transmitting antennas were boresighted at the geometric center of the aircraft and moved to specific clock positions at a

radial distance of 23 m (75 ft) as shown by the blue, dashed line in Figure 14. We applied

antenna gain and distance correction factors to maintain consistency in the results. The receiving

antenna was placed in three compartments of the aircraft: (1) the flight deck, (2) the main cabin,

and (3) the rear cargo hatch. These locations are shown by the red +'s.

300

270 90

240

180

Figure 14. Test master graphic showing internal measurement positions (red +'s),

Extrapolation distances in feet (black X's), measurements around aircraft (blue,

dashed line) at a distance of 23 m (75 ft).

15
6.1 Extrapolation Results

We performed a set of extrapolation measurements from 3.6 m (12 ft) to 30.5 m (100 ft) along

the 45° line to investigate the far- field behavior of the aircraft and to understand how penetration

changes as a function of distance from the aircraft. Distance correction was applied to the data

by use of a reference distance of 6.1 m. These measurements are shown in Figures 15 to 18. The data show a spread of around 10 dB across the frequency spectrum for both the DRG and

TEM horn antennas. We believe this is because, at the closer distances, our antennas see more

of the aircraft, but as we move further from the aircraft the antennas see less of the aircraft and

more of the surrounding environment. In Figure 16, if we remove the 3.6 m data, the 6.1 m

data, and the 9. 1 m data, then the spread in the data is between 2 dB and 3 dB for the DRG horn

antennas. If we remove the 3.6 m and 6.1 m data from Figures 17 and 18, then the TEM horn

extrapolation results show spreads in the data on the order of 2 dB to 5 dB. We note here that the

DRG antennas have higher directivity than that of the TEM horn antennas, which corresponds to the greater spread in penetration data for the TEM horn antenna. These results have been

corrected for both distance and antenna gain. The gains for the DRG horn antenna and the TEM

horn antenna are discussed in Appendix C.

0^

-20

w

a

-40

-60

DRG - Hpol

Extrap

Extrap

Extrap

Extrap

Extrap

Extrap

Extrap

200 MHz

3.6 m (12 ft)

6.1 m(20ft)

9.1 m(30ft)

12.2 m (40 ft) 15.2 m (50 ft) 22.9 m (75 ft) 30.5 m (100 ft)

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 15. Extrapolation measurements for the DRG antenna, horizontal polarization.

16
-20

-40-

-60

DRG - Vpol

Extrap - Extrap - Extrap - Extrap - Extrap - Extrap - Extrap -

200 MHz

3.6 m (12 ft) 6.1m (20 ft) 9.1 m(30ft)

12.2 m (40 ft) 15.2 m (50 ft) 22.9 m (75 ft) 30.5 m (100 ft)

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 16. Extrapolation measurements for the DRG antenna, vertical polarization.

10

10

3 -20

T33

1-30

-40

-50

-60

TEM - Hpol

Extrap - Extrap - Extrap - Extrap - Extrap - Extrap - Extrap -

- 50 MHz

3.6 m (12 ft) 6.1 m(20ft)

9.1 m(30ft)

12.2 m (40 ft) 15.2 m (50 ft) 22.9 m (75 ft) 30.5 m (100 ft)

400 800

Frequency (MHz)

1200 1600

Figure 17. Extrapolation measurements for the TEM antenna, horizontal polarization.

17
-20

(U

-60

-80

TEM - Vpol

Extrap - Extrap - Extrap - Extrap - Extrap - Extrap - Extrap -

- 50 MHz

3.6 m (12 ft)

6.1 m(20ft)

9.1 m(30ft)

12.2 m (40 ft) 15.2 m (50 ft) 22.9 m (75 ft) 30.5 m (100 ft)

400 800

Frequency (MHz)

1200 1600

Figure 18. Extrapolation measurements for the TEM antenna, vertical polarization.

6.2 Main Passenger Cabin Penetration Results

The receiving antenna was located near the geometric center of the main cabin, as shown in

Figure 19. The antennas were placed near the center of the aircraft and were mounted on tripods

to provide support and separation. The antenna position was selected to provide robust

excitation of available cavity modes. The optical fiber was fed through one of the passenger

windows on the left side of the aircraft, which remained partially propped open for the main

cabin and flight deck measurements. We are assuming the effects from this small aperture are minimal. The transmitting antennas were boresighted to the geometric center of the aircraft to avoid assumptions about signal penetration apertures.

Time-domain plots are used as an aid to understand penetration into airframes. We begin by

transforming the measured frequency domain data into the time-domain to look at the signal in

time. Time-domain plots for the DRG antenna in the horizontal polarization are shown in Figure

20 at various angular positions around the aircraft. At an angular position of 0°, we have a moderate, initial sharp impulse response (the direct antenna-to-antenna coupling component),

which decays rapidly within 150 ns. This is indicative of a rapidly decaying reverberant field. Another, much smaller, signal appears at around 400 ns, which we beheve is a signal coming

from the surrounding environment. As we travel around the aircraft we obtain a maximum

18
signal at an angular position of 45 ° decreasing in level until we get to the tail position at 180°. In

typical aircraft, we see very low signal amplitudes toward the tail of the aircraft. For this

aircraft, we see similar levels as we traverse around the aircraft, so we believe that the signal is able to penetrate somewhat equally into the main passenger cabin from all angular positions.

The larger the direct couphng component, the more energy there is that initially gets coupled into

the main passenger cabin and the less energy available in the reverberant field. A more in-depth

discussion of the characteristics of these waveforms is provided in Appendix A. This timedomain analysis provides valuable insight into possible maximum coupling paths. Time-domain

plots for the DRG antenna in the vertical polarization are shown in Figure 21 and time-domain

plots for the TEM horn antennas in both polarizations are shown in Figures 22 and 23. The TEM

horn antennas receive lower signal levels, but there is still time-domain evidence of direct

coupling. Although the TEM horn antennas have low directive gain (broad radiation pattern) the

available penetration from any part of the aircraft allows the antenna to pick up the direct

component.

Frequency-domain plots for various positions around the aircraft are summarized in Figure 24.

The purpose of this plot is to show a snapshot of the variation in penetration level at selected

positions around the aircraft. In a typical aircraft we would expect the signal to drop at the front

and back of the aircraft due to lack of direct signal paths at these positions; however, this aircraft

does not show this behavior. We have also plotted some penetration results at various

symmetrical positions around the aircraft to determine whether there may be leakage points on

one side that are not on the other. This is shown in Figure 25. We would expect a possible

leakage point at the door into the aircraft. In Figure 24, we see that the maximum penetration of

about dB occurs around 900 MHz for the DRG antennas, with the transmitting antenna in the

vertical and horizontal polarizations, at an angle of 30 °, and the receiving antennas in the main

Figure 19. Receiving antenna placement in main passenger cabin.

19
passenger cabin. Minimum penetration of approximately -30 dB occurs at an angle of 180° for

the DRG antenna in the horizontal and vertical polarizations. For TEM horn antennas with

signals below 1 00 MHz, we fmd that the penetration artificially increases, which is an artifact of

the measurement system rapidly losing dynamic range. This reduction in dynamic range is due to combination of increasing airframe shielding performance and reduced antenna efficiency.

Detailed penetration results at each azimuthal position for all antennas and all polarizations are summarized in Figures 26 to 50. The DRG antenna data are frequency averaged over a bandwidth of 200 MHz, and the TEM horn antenna data are frequency averaged over a bandwidth of 50 MHz. We have concluded that these bandwidths work well at suppressing the

"hashy" behavior due to the complex cavity modes while emphasizing the deterministic coupling

effects. Frequency averaging is described in detail in references [1-3]. We see that the highest

penetration occurs at the 30° position for frequencies around 900 MHz. The penetration

increases as we proceed to the tail of the aircraft, with maximum values of around -30 dB. This

directly correlates to the time domain data discussed previously. The horizontally polarized

antennas tend to have higher penetration values than the vertically polarized antennas, which

could be due to the horizontally polarized array of windows around the aircraft. Our purpose in

moving every 10° until we reach the second quadrant and then changing to 5° increments is to investigate the possibility that we may be missing important leakage points by only traversing

every 10° [4]. What we see is that the angular variation in penetration does not change greatly

from position to position, with typical variations less than 5 dB. This can be attributed to a combination of complex cavity behavior and the possible coupling paths into the main passenger

cabin. Due to the large number of coupling apertures, we do not take into account the antenna

pattern effects for either the antennas or the aircraft. If we knew exactly where the fields were

penetrating into the cavity, then these types of corrections would be feasible. These coupling

paths are both vertically and horizontally polarized, and therefore we believe the fields inside the

aircraft are depolarized to a large extent.

The main conclusions for an antenna placed in the main passenger cabin are: (1) main coupling

apertures are the windows on the flight deck, (2) penetration is shghtly lower at the tail of the

aircraft, (3) penetration into the airframe is fairly symmetric and of the same magnitude around

the aircraft , (4) typical penetration values are dB at 30° and -30 dB for the 180° positions, and

(5) the horizontally polarized energy more easily penetrates the airframe than the vertically

polarized energy. We believe this is because of the horizontal "slot apertures" that the array of

windows provides.

20
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26
0° 0-1

-10

T) -20 C

oarrt

<iJ -30

-40

-50

Main Cabin

degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330°

300°

270°

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210'

H

a^i,

180°

30°

60°

90°

120 =

150'

Figure 26. Penetration for all antennas and polarizations for the transmitting tower placed

at the 0° position and the receiving antennas placed in the main cabin.

0-1

-10-

S -30

Oh

-40

-50

Main Cabin

1 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330°

300°

270°

240°

4000 8000 12000 Frequency (MHz)16000 20000

210'

180°

60'

90°

120'

150°

Figure 27. Penetration for all antennas and polarizations for the transmitting tower placed

at the 10° position and the receiving antennas placed in the main cabin.

27
-10

co

•a

330° 30°

300'

270°

240°

Main Cabin

20 degrees

TEM - Hpol

-— DRG - Hpol

TEM - Vpol

DRG - Vpol

210°

180'

150'

-30

-40

-50

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 28. Penetration for all antennas and polarizations for the transmitting tower placed

at the 20° position and the receiving antennas placed in the main cabin.

60°

90°

120°

330°

10

§a

g -30

-40

-50

Main Cabin 30 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

~^ ' \ ^

\

4000 8000 12000

Frequency (MHz)

300°

270°

240°

"H ^

I 16000 20000

210°

180°

60°

90°

120°

150°

Figure 29. Penetration for all antennas and polarizations for the transmitting tower placed

at the 30° position and the receiving antennas placed in the main cabin.

28
-10

S -30

-40

-50

330° 30°

Main Cabin

40 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270°

240°

ZIC^

180'

60°

90°

120'

150°

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 30. Penetration for all antennas and polarizations for the transmitting tower placed

at the 40° position and the receiving antennas placed in the main cabin.

-10-

-30-

-40-

-50

330° 30'

Main Cabin

50 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300'

270°

240°

4000 8000 12000 Frequency (MHz)

~1 '

I 16000 20000

a^

210'

180°

60'

90°

120°

150°

Figure 3 1 . Penetration for all antennas and polarizations for the transmitting tower placed

at the 50° position and the receiving antennas placed in the main cabin.

29
0^

-10

-40

-50

330° 30°

Main Cabin

60 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

300°

270°

240°

~1 '

I 16000 20000

210°

180°

60°

90°

120°

150°

Figure 32. Penetration for all antennas and polarizations for the transmitting tower

placed at the 60 "position and the receiving antennas placed in the main cabin.

0^

-10

-40

-50

330° 30°

Main Cabin 70 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270'

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210° ^^

180°

90°

120°

150'

Figure 33. Penetration for all antennas and polarizations for the transmitting tower

placed at the 70 ° position and the receiving antennas placed in the main cabin.

30
-10-

g -30

CL,

-40-

-50

330' 30°

Main Cabin

80 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270°

240°

210'

180'

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 34. Penetration for all antennas and polarizations for the transmitting tower

placed at the 80 ° position and the receiving antennas placed in the main cabin.

150°

10

s

o

Bl I -30

-40-

-50

330° 30°

Main Cabin 90 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300'

270°

240°

210'

^ ^\

'

\

^

\

^

I 4000 8000 12000 16000 20000

Frequency (MHz)

180 =

60°

90°

120°

150°

Figure 35. Penetration for all antennas and polarizations for the transmitting tower

placed at the 90° position and the receiving antennas placed in the main cabin.

31
-10

-30

-40

-50

330° 30°

Main Cabin

1 00 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270'

240°

210'

180°

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 36. Penetration for all antennas and polarizations for the transmitting tower

placed at the 100 "position and the receiving antennas placed in the niain cabin.

150 =

60°

90'

120°

0° 0^

-10-

T3 -20 CO

rt

<D -30

-40

-50

Main Cabin

1 1 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

-^ '

\ ' \ 4000 8000 12000

Frequency (MHz)

330°

300°

270°

240'

16000 20000

210'

180'

30°

150'

Figure 37. Penetration for all antennas and polarizations for the transmitting tower

placed at the 1 10° position and the receiving antennas placed in the main cabin.

32
0°

10

-30-

-40

-50

Main Cabin

1 20 degrees

TEM - Hpol

DRG - Hpol —TEM - Vpol

DRG - Vpol

330'

300°

270°

240°

I

'

i

'

I

'

I

' I 4000 8000 12000 16000 20000

Frequency (MHz)

210 = 180°

30°

150'

Figure 38. Penetration for all antennas and polarizations for the transmitting tower placed

at the 120 "position and the receiving antennas placed in the main cabin.

0°

-10-

§a

I -30

Oh

-40

-50

Main Cabin

1 25 degrees

TEM - Hpol — DRG - Hpol

TEM - Vpol

DRG - Vpol

330'

300°

270°

240'

210'

4000 8000 12000

Frequency (MHz)

16000 20000

180°

30'

90°

120°

150°

Figure 39. Penetration for all antennas and polarizations for the transmitting tower placed

at the 125 "position and the receiving antennas placed in the main cabin.

33
-10

-30-

-40

-50

330° 30°

Main Cabin

1 30 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300'^

270'

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210°

180°

60 =

90'

120°

150'

Figure 40. Penetration for all antennas and polarizations for the transmitting tower

placed at the 130° position and the receiving antennas placed in the main cabin.

0° 0^

-10-

co

•a

g -30

-40-

-50 4000

Main Cabin

1 35 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

\

^

I ^ 8000 12000

Frequency (MHz)

330°

300°

270°

240°

210°

16000 20000

30"^

60°

180'

90°

120°

150'

Figure 41 . Penetration for all antennas and polarizations for the transmitting tower

placed at the 1 35 ° position and the receiving antennas placed in the main cabin.

34
0°

-10

§

•a

-40

-50

Main Cabin

140 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

330'

300°

270°

240° a-:,

210 = 180°

16000 20000

30°

60'

90°

120'

150°

Figure 42. Penetration for all antennas and polarizations for the transmitting tower placed at the 140° position and the receiving antennas placed in the main cabin.

0°

10

§ -20-

-40

-50

Main Cabin

1 45 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330'

300°

270'

240°

210'

'

\

^

\

'

\

'

\

^

I 4000 8000 12000 16000 20000

Frequency (MHz)

30'

60'

90°

120' a^

150°

180°

Figure 43. Penetration for all antennas and polarizations for the transmitting tower placed at the 145° position and the receiving antennas placed in the main cabin.

35
10

c

oa

-30-

-40-

-50

330° 30°

Main Cabin

150 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

300 =

270°

240°

210°

16000 20000

180°

60'

90"^

120°

150°

Figure 44. Penetration for all antennas and polarizations for the transmitting tower

placed at the 150° position and the receiving antennas placed in the main cabin.

-10

-20 c

o

(Tl

OJ -30

a.

-40

-50

330' 30'

Main Cabin

1 60 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270°

240°

210°

180°

4000 8000 12000

Frequency (MHz)

16000 20000

60°

90°

120°

150°

Figure 45. Penetration for all antennas and polarizations for the transmitting tower placed

at the 1 60 ° position and the receiving antennas placed in the main cabin.

36
0° 0-1

-10-

S -20-

-30

-40

-50

Main Cabin 70 degrees — TEM - Hpol — DRG - Hpol — TEM - Vpol — DRG - Vpol

330'

300°

270°

240°

210'

4000 8000 12000

Frequency (MHz)

16000 20000

180 "^

30°

60°

90°

120'

150°

Figure 46. Penetration for all antennas and polarizations for the transmitting tower placed

at the 170° position and the receiving antennas placed in the main cabin.

0°

-10

B

o

•a2

g -30

-40

-50

Main Cabin

80 degrees — TEM - Hpol — DRG - Hpol — TEM - Vpol

DRG - Vpol

330'

300'

270'

240'

4000 8000 12000

Frequency (MHz)

16000 20000

n

210' ^^

180°

30'

60'

90°

120°

150°

Figure 47. Penetration for all antennas and polarizations for the transmitting tower placed

at the 1 80 ° position and the receiving antennas placed in the main cabin.

37
-10

-40-

-50

330° 30°

Main Cabin

190 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300'

270°

240°

4000 8000 1 2000

Frequency (MHz)

16000 20000

210°

180°

60°

150'

90'

120'

Figure 48. Penetration for all antennas and polarizations for the transmitting tower placed

at the 190° position and the receiving antennas placed in the main cabin.

-10-

o1

I -30

-40

Main Cabin

270 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300

270

240°

330°

210°

180°

30°

60°

90'

120'

150°

-50

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 49. Penetration for all antennas and polarizations for the transmitting tower placed

at the 270° position and the receiving antennas placed in the main cabin.

38
0°

-10

PQ

•a -20 gQaa

(U

(3 -^0

a,

-40-

-50

Main Cabin

330 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

330° 30°

300°

270°

240°

60°

90°

120'

210° 150'

180°

16000 20000

Figure 50. Penetration for all antennas and polarizations for the transmitting tower placed

at the 330 "position and the receiving antennas placed in the main cabin.

39
6.3 Flight Deck Penetration Results

The second penetration study was performed with the receiving antennas placed in the flight

deck between the pilot's and the co-pilot's seat, as shown in Figure 51. The time-domain plots

for the DRG antennas in the horizontal polarization are shown in Figure 52 for various angular

positions around the aircraft. There are direct coupling components visible for almost every

position around the aircraft. Figure 53 shows various penetration positions around the aircraft. Maximum penetration of approximately dB occurs at the nose position for frequencies around

650 MHz, 770 MHz, 1000 MHz, 1525 MHz, and 3100 MHz. ft then drops to -20 dB at frequencies above 2000 MHz. Minimum penetration occurs at the 180° position. For

frequencies below 2000 MHz, horizontal polarization has penetration values around -20 dB, and

for vertical polarization, penetration values are around -25 dB. Penetration values of -40 dB for

the vertical polarization and -30 dB for the horizontal polarization are shown at frequencies

close to 18,000 MHz. Figures 54 to 76 show each individual external position around the

aircraft. Penetration decreases from the front to the back of the aircraft by about 20 dB.

-^^

Figure 51. The receiving DRG and TEM antennas placed between the pilot's and co-pilot's seat.

40
111

II

1

' 1 • 1 'r-'-T^ -'

1

'

1

' 1 1 -

I

'

I

'

I

' I

,il

ri

B

-I

1

' 1'

I

' I' I

I

J

° B S 6 g ° g S § B ° i B B 8 i ° g ; § B

I i B B B g ° g B S B

•irkv ^stmximum airfwir •)> t»n ^t«»f mrlwi ^BtTB»«i «»j

-8

i B B B B ° i B B B

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i Bdtfdd B B B ° B B B B

tf ^ ^ ^

SI

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I ' I

'

I

'

I

'

I

i Bdddd B B B ° B B B B

tf tj ^ ff

I

'

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'

I

' I' I

ill

' I' I' I ' I

' B B a B

) ) 9 9

I

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'

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° B B B B

f t •> 9

° B B B g ° B B § B dddd 4941)''I mi^mdtfnm'-*,

(-

IS

-^ ki^

( ' 1 ' 1 ' 1

' 1

' '

1

' 1' 1' 1

'

II

f

'

I

'

I

' I

'

I

la I

1 B B B B g B B B i i B B B g ° g B B B I i B B B g ° g B B B

(D J3-4—) c

c«c

c , <u M

c

a -o O r: cc Of) Q i^

J3n C

<+::- •^^ C

t/3 1) O

bJj d C

u< rt

<i> *-^ C us

<uE 3

nn t^

.>-< c^ i:a

<+- •o o <U

Ul O

O

OJ

<u D- C/3 C rtC

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T3 a

N (IJ e 03 H o

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o

N

bit o

U- x;

41
(a>)Kv«x lv)w^tw34 Iwi'm"*!

42
-10

I -30

Oh

-40-

-50

Flight Deck

degrees

TEM - Hpol — DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270°

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210'

180°

60'

90°

120'

150°

Figure 54. Penetration for all antennas and polarizations for the transmitting tower placed at the Opposition and the receiving antennas placed in the flight deck.

10

B

Oa

g -30

-40

-50

Flight Deck

1 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270°

240°

60'

90 =

120' cO:^

210' 150°

180°

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 55. Penetration for all antennas and polarizations for the transmitting tower placed at the 10° position and the receiving antennas placed in the flight deck.

43
-10-

Ti -20 aoa(71

(Uc

-^0

Oh

-40-

-50

330° 30°

Flight Deck

20 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270°

240°

4000 ~n ^

\

^

\

^ I 8000 12000 16000 20000

Frequency (MHz)

210°

180°

60°

90°

120°

150 =

Figure 56. Penetration for all antennas and polarizations for the transmitting tower placed at the 20 ° position and the receiving antennas placed in the flight deck.

0°

-10-

-20 coa

<u -10

a,

-40

-50

Flight Deck

40 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

330°

300°

270°

240°

16000 20000

210°

180°

30°

60 =

150 =

90°

120°

Figure 57. Penetration for all antennas and polarizations for the transmitting tower placed at the 40 ° position and the receiving antennas placed in the flight deck.

44
0°

-10

m^ -20-

-30-

-40

-50

Flight Deck

60 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

\ ' \

'

\ 4000 8000 12000

Frequency (MHz)

330'

300'

270°

240°

16000 20000

210°

180°

30°

60°

90°

120'

150 =

Figure 58. Penetration for all antennas and polarizations for the transmitting tower placed at the 60 "position and the receiving antennas placed in the flight deck.

0°

-10

a -20 c

oaKt

u,u

1) -30

cu

-40

-50

Flight Deck

80 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330'

300°

270°

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210'

180°

30°

60°

90'

120'

150°

Figure 59. Penetration for all antennas and polarizations for the transmitting tower placed at the 80 ° position and the receiving antennas placed in the flight deck.

45
0°

-10

§ -30

Oh

-40

-50

Flight Deck

90 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

\

'

\

'

\ 4000 8000 12000

Frequency (MHz)

300'

270°

240°

\

'

I 16000 20000

330 =

210°

180'

30°

60°

90°

120°

150°

Figure 60. Penetration for all antennas and polarizations for the transmitting tower placed at the 90° position and the receiving antennas placed in the flight deck.

0-1

-10

-20 co

•a

(D

<uc

-30

a.

-40

-50

Flight Deck

1 00 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330°

300°

270°

240°

210°

0°

30°

60°

90'

120°

150°

180 "^

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 61. Penetration for all antennas and polarizations for the transmitting tower placed at the 100 "position and the receiving antennas placed in the flight deck.

46
0°

-10

§

•a

-30-

-40

-50

Flight Deck

1 20 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

330'

300°

270°

240°

210°

16000 20000

180'

30°

60°

90°

120"^

150°

Figure 62. Penetration for all antennas and polarizations for the transmitting tower placed at the 120 "position and the receiving antennas placed in the flight deck.

0°

-10

3

-20 c

o

2

§ -30

Oh

-40

-50

Right Deck

140 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

^ '

\

'

\ 4000 8000 12000

Frequency (MHz)

330'

300°

270°

240°

210°

180°

16000 20000

30°

60°

90°

120°

150°

Figure 63. Penetration for all antennas and polarizations for the transmitting tower placed at the 140° position and the receiving antennas placed in the flight deck.

47
-10

g -20 i

a

.S -30 -

-40-

-50

330'^ 30°

Flight Deck

160 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300'

270°

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210°

60°

90°

120'^

150°

180°

Figure 64. Penetration for all antennas and polarizations for the transmitting tower placed at the 160 "position and the receiving antennas placed in the flight deck.

0-n

-10

§a

I -30

-40

-50

330° 30°

Flight Deck

1 80 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300'

270"^

240°

~^ '

I

'

I

'

I

'

I 4000 8000 12000 16000 20000

Frequency (MHz)

^ ^

%

210°

180°

60°

90'

120°

150°

Figure 65. Penetration for all antennas and polarizations for the transmitting tower placed at the 180° position and the receiving antennas placed in the flight deck.

48
0° 0-1

-10

3

-2° c

oa

2

u

g -30

-40-

-50

Flight Deck

200 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330'

300 =

270°

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210°

180'

30°

60'

90°

120°

150°

Figure 66. Penetration for all antennas and polarizations for the transmitting tower placed at the 200 ° position and the receiving antennas placed in the flight deck.

0°

-10

S -20-

S -30

Oh

-40

-50

Flight Deck

220 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

^ '

\

'

\ 4000 8000 12000

Frequency (MHz)

330'

300°

270°

240°

16000 20000

210°

180'

30°

60°

90°

120°

150°

Figure 67. Penetration for all antennas and polarizations for the transmitting tower placed at the 220° position and the receiving antennas placed in the flight deck.

49
0°

c

o

•aS

g -30

-40

-50

Flight Deck

240 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300

270°

240°

^ ^\

'

\

^

\

'

I 4000 8000 12000 16000 20000

Frequency (MHz)

330°

210°

180°

30°

60°

90°

120°

150°

Figure 68. Penetration for all antennas and polarizations for the transmitting tower placed at the 240° position and the receiving antennas placed in the flight deck.

-10

-30-

-40-

-50

330° 30°

Flight Deck

260 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

"H '

\

^

\

4000 8000 12000

Frequency (MHz)

300

270°

240°

60°

90°

120° cO::^

210'

150'

180'

16000 20000

Figure 69. Penetration for all antennas and polarizations for the transmitting tower placed at the 260 "position and the receiving antennas placed in the flight deck.

50
0°

-10

-30-

-40

-50

Flight Deck

270 degrees

TEM - Hpol

DRG - Hpol

DRG - Vpol

330'

300°

270° -*

240

4000 8000 12000

Frequency (MHz)

16000 20000

210°

180°

30°

60°

90°

120 =

150°

Figure 70. Penetration for all antennas and polarizations for the transmitting tower placed at the 270 "position and the receiving antennas placed in the flight deck.

0°

-10

co

•a2

g -30

-40

-50

Flight Deck

280 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330' 30°

300°

270°

240°

60'

90"^

120'

210'

150°

180°

~^ ^

\

'

\

'

\

'

I 4000 8000 12000 16000 20000

Frequency (MHz)

Figure 7 1 . Penetration for all antennas and polarizations for the transmitting tower placed at the 280° position and the receiving antennas placed in the flight deck.

51
-10

-30-

-40-

-50

330° 30°

Flight Deck

300 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300'

270°

240°

4000 8000 12000

Frequency (MHz)

\

^

I 16000 20000

210°

180°

60°

90°

120°

150°

Figure 72. Penetration for all antennas and polarizations for the transmitting tower placed at the 300° position and the receiving antennas placed in the flight deck.

0°

-10

03 -20 c

o

•a

nt

t-, <uc

0) -30

cu

-40

-50

Flight Deck

320 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

I

^

\

^

\ 4000 8000 12000

Frequency (MHz)

300'

270°

240°

16000 20000

330°

210'

30"^

^^^

180°

60°

90'

120°

150°

Figure 73. Penetration for all antennas and polarizations for the transmitting tower placed at the 320° position and the receiving antennas placed in the flight deck.

52
0°

-10

c

oa

I -30

-40-

-50

Flight Deck

340 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330

300°

270^

240°

60°

90°

120'

210'

150°

180°

^ '\

'

\

'

\

'

I 4000 8000 12000 16000 20000

Frequency (MHz)

Figure 74. Penetration for all antennas and polarizations for the transmitting tower placed at the 340 "position and the receiving antennas placed in the flight deck.

0°

-10

I -30

Oh

-40

-50

Flight Deck

350 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

330

300°

270'

240'

16000 20000

210' a^

180°

60°

90°

120'

150°

Figure 75. Penetration for all antennas and polarizations for the transmitting tower placed at the 350 "position and the receiving antennas placed in the flight deck.

53
-10

§a

-30-

-40

-50

330°

Flight Deck

360 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300 =

270°

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210°

180°

60°

90'

120°

150'

Figure 76. Penetration for all antennas and polarizations for the transmitting tower placed at the 360° position and the receiving antennas placed in the flight deck.

54
6.4 Rear Cargo Hatch Penetration Results

A series of penetration measurements was taken with the receiving antennas placed in the rear cargo hatch located at the left rear of the aircraft. The receiving antenna positions for the TEM

horn antenna and DRG antenna are shown in Figure 77. The optical fiber was fed through the

latch hole in the rear cargo compartment.

Figure 78 shows the time-domain plots for the DRG antenna in the horizontal polarization at various positions around the aircraft. Due to the lack of any direct coupling paths from the

outside of the aircraft into the rear cargo hatch, we see no direct antenna-to-antenna coupling in

these plots. However the signal levels are very asymmetric around the aircraft. Large signal

levels are seen from positions 180° to 270°, with minimum signal levels seen at the 40°, 60°, and

90° positions. There appears to be a large shielding object on the inner part of the rear cargo

hatch. Figure 79 shows the penetration plots around the aircraft. High penetration is seen

consistently around the aircraft at a frequency around 860 MHz. The lowest penetration is seen at 40° and 60° with average values of -30 dB (horizontal polarization) and -35 dB (vertical

polarization) for frequencies below 4000 MHz, and average values of -35 dB (horizontal

polarization) and -40 dB (vertical polarization) for frequencies above this. Highest penetration

values are seen at an angle of 270° for both horizontal and vertical polarizations of

approximately -15 dB to -17 dB across the frequency band. We have not seen this type of

pattern in other aircraft. There is a distinct broadband resonance at around 8000 MHz for the

100° to 140° positions. Penetration results at every external angle are shown in Figures 80 to 99.

Optical^

fiber

Figure 77. DRG and TEM antenna placement in the rear cargo hatch.

55
I ' I ' T" = 1—'—I—'—

r

i|[|duiv (i^^lS p-'>Z!|<:u'J"N ^piDiiUury |rudi^|i97r|Rii ^lUijdiuv pu^lS p-'>^FU a

I

' I ' r

ii;|diiiv ['!um<; p.'>7i|iMii

i

3p)ili|(luiv li'iidjs |>07i|rujia)>i A9pnii|(lurv ]V'«diS p9Xi|'^'^''^N A

rS

i^ii;)diiiv I'^^Ib' p>'>'!|i-'UJJON

?pnii[duiv I<;"3|S' p»ff|fiuuii|ij

I—I—I—'—

r

^pnniduiv iL-ifSii,- |i3zi|ruiJor4

co

N

•co

xi

(U j3^

• e1—

(

C^G

c

di

4-^ f5

cfl o si

PiQ C3o

co (1)

;_i

cfl (1) h ^ <uc C

(Ua. C/5 <u

<U

2

c

t: ^^

•c3o

s

(1)

C/3 4-J ^ o t/3

fTl Ci (U c B

'^, Ti H (U o o

TJ (U

(1) OJ g

c/3 H

C3c . o oo

03

(D N

3 JS hO O

Ph Ojpiiiltduiy iru^!^ p.i7i|uiiunfj 3pn|i](Iuiv FC^IS pa^inuio;^ opnindiuv l'""3iS fwn[TMwoN

56
lap) "oii'-jpinj

°/

V / ; 1 ~ ' \ ^ ' § /^- / ^ -- \ /

(9P) iiorinjpu:ij s I 2 ^

13CC

4—* c

cd

(/i flo

^H

r/1 O j:: Oh i:! —

cd

Tl o

-*—

bJ)

(l> ^H e

cd

i= ^

on

cd2^

</3 3O

•n c > c/l <+H c3 O C co C o c3 c 6/) ^ C

rri >

C/1 <u

rt o C ^ o (U td

is J2 <\> ^

(X C/1 C . O

"S

2^

N 3 rt

too (; \u O,

(a|i» uo.|irjpik->d

57
Rear Cargo Hatch

degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330°

300°

270°

240"

8000

Frequency (MHz)

12000 16000 20000

210°

180 =

60°

90°

120°

150'

Figure 80. Penetration for all antennas and polarizations for the transmitting tower placed at the 0° position and the receiving antennas placed in the rear cargo hatch.

0°

Rear Cargo Hatch

20 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330°

300°

270'

240°

210°

"^

\ ^ 8000 12000 16000 20000

Frequency (MHz)

180 =

30°

60°

90'

120°

150°

Figure 8 1 . Penetration for all antennas and polarizations for the transmitting tower placed at the 20° position and the receiving antennas placed in the rear cargo hatch.

58
0°

Rear Cargo Hatch 40 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330°

300°

270°

240'

8000 12000

Frequency (MHz)

16000 20000

210°

180°

30 =

60°

90°

120°

150°

Figure 82. Penetration for all antennas and polarizations for the transmitting tower placed

at the 40° position and the receiving antennas placed in the rear cargo hatch.

0°

Rear Cargo Hatch 60 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

8000 12000

Frequency (MHz)

330°

300°

270'

240'

210°

16000 20000

30°

60°

90'

120'

150°

180°

Figure 83. Penetration for all antennas and polarizations for the transmitting tower placed

at the 60° position and the receiving antennas placed in the rear cargo hatch.

59
-10

1>g -30

-40

-50

330° 30'

Rear Cargo Hatch

80 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

300 =

270°

240'

60°

90°

120°

210°

150°

180°

16000 20000

Figure 84. Penetration for all antennas and polarizations for the transmitting tower placed

at the 80° position and the receiving antennas placed in the rear cargo hatch.

-10

-30

-40

-50

330° 30°

Rear Cargo Hatch 90 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

"1 ^

\

^

\ 4000 8000 12000

Frequency (MHz)

300'

270°

240'

16000 20000

210°

60°

90°

120'

150°

180°

Figure 85. Penetration for all antennas and polarizations for the transmitting tower placed

at the 90° position and the receiving antennas placed in the rear cargo hatch.

60
0°

Rear Cargo Hatch

1 00 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330'

300°

270°

240°

1 ' r 4000 8000 12000 16000 20000

Frequency (MHz)

210°

180°

30°

150°

Figure 86. Penetration for all antennas and polarizations for the transmitting tower placed

at the 100° position and the receiving antennas placed in the rear cargo hatch.

0-1

-10

-40-

-50

330° 30°

Rear Cargo Hatch

1 20 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

~^ ^

\

^

\ 4000 8000 12000

Frequency (MHz)

300 =

270°

240°

16000 20000

210°

180'

150°

Figure 87. Penetration for all antennas and polarizations for the transmitting tower placed

at the 120 "position and the receiving antennas placed in the rear cargo hatch.

61
0°

-10

•a -20 c

o

Bl

u.

(UG

-10

(X,

-40

-50

Rear Cargo Hatch

1 40 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

300'

270°

240 =

16000 20000

330°

210°

180°

30°

60°

90°

120'

150°

Figure 88. Penetration for all antennas and polarizations for the transmitting tower placed

at the 140° position and the receiving antennas placed in the rear cargo hatch.

0°

-10

Ph -30-

-40

-50

Rear Cargo Hatch

1 60 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300'

270°

240°

^ ^\

'

\

'

\

'

I 4000 8000 12000 16000 20000

Frequency (MHz)

330°

210°

180°

30°

60'

90°

120°

150'

Figure 89. Penetration for all antennas and polarizations for the transmitting tower placed at the 160° position and the receiving antennas placed in the rear cargo hatch.

62
0°

-10

-30-

-40

-50

Rear Cargo Hatch

1 80 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330 =

300'

4000 8000 12000

Frequency (MHz)

270°

240°

16000 20000

210°

180 =

30°

60'

90°

120°

150°

Figure 90. Penetration for all antennas and polarizations for the transmitting tower placed

at the 180 "position and the receiving antennas placed in the rear cargo hatch.

-10

a

oa

2

g -30

Oh

-40-

-50

330° 30°

Rear Cargo Hatch 200 degrees

TEM - Hpol -—— DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270'

240°

210°

4000 8000 12000

Frequency (MHz)

16000 20000

60°

90°

120°

150°

180°

Figure 9 1 . Penetration for all antennas and polarizations for the transmitting tower placed at the 200° position and the receiving antennas placed in the rear cargo hatch.

63
0°

10

g -30

Oh

-40

-50

Rear Cargo Hatch 220 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330°

300°

270°

240°

210°

30°

60'

90°

120 =

150°

180°

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 92. Penetration for all antennas and polarizations for the transmitting tower placed at the 220° position and the receiving antennas placed in the rear cargo hatch.

0-1

-10-

§

-30

-40

-50

330° 30°

Rear Cargo Hatch

240 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300

270°

240°

4000 8000 12000

Frequency (MHz)

16000 20000

210° ci^

60 =

90°

120°

150°

180'

Figure 93. Penetration for all antennas and polarizations for the transmitting tower placed at the 240° position and the receiving antennas placed in the rear cargo hatch.

64
0°

10

B

oa

-30-

-40

-50

Rear Cargo Hatch 260 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330'

300°

270°

240°

210° a^

180°

30°

60°

90°

120°

150°

4000 8000 12000 16000 20000

Frequency (MHz)

Figure 94. Penetration for all antennas and polarizations for the transmitting tower placed at the 260° position and the receiving antennas placed in the rear cargo hatch.

0° 0^

-10

coaa

-30

-40

-50

Rear Cargo Hatch 270 degrees

TEM - Hpol

DRG - Hpol ——- TEM - Vpol

DRG - Vpol

330'

300

270° <

240'

210°

~^ ^ \

^

\

^

\

^ I 4000 8000 12000 16000 20000

Frequency (MHz)

180'

30°

60°

90'

120°

150°

Figure 95. Penetration for all antennas and polarizations for the transmitting tower placed at the 270° position and the receiving antennas placed in the rear cargo hatch.

65
10

PQ -20 so

n

(Uc

-30

CL,

-40

-50

330° 30°

Rear Cargo Hatch 280 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

300°

270°

240'

210°

4000 8000 12000

Frequency (MHz)

16000 20000

180'

60'

90°

120°

150'

Figure 96. Penetration for all antennas and polarizations for the transmitting tower placed at the 280° position and the receiving antennas placed in the rear cargo hatch.

-10

I -30

Oh

-40

-50

330' 30°

Rear Cargo Hatch 300 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

^ ^\ ' \ 4000 8000 12000

Frequency (MHz)

300'

270°

240°

210°

16000 20000

60"=

90°

180°

120'

150'

Figure 97. Penetration for all antennas and polarizations for the transmitting tower placed at the 300 ° position and the receiving antennas placed in the rear cargo hatch.

66
0° 0^

-10

-30-

-40-

-50

Rear Cargo Hatch 320 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

330'

300°

270°

240°

210°

16000 20000

ISO"^

30°

60-^

90°

120°

150°

Figure 98. Penetration for all antennas and polarizations for the transmitting tower placed at the 320° position and the receiving antennas placed in the rear cargo hatch.

0°

-10

CQT3 -20 C

O

•3

(Ti O

c

-30

Oh

-40-

-50

Rear Cargo Hatch 340 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

330°

300°

270°

240'

4000 8000 12000 Frequency (MHz)

16000 20000

210°

180 =

60°

90°

120°

150°

Figure 99. Penetration for all antennas and polarizations for the transmitting tower placed at the 340° position and the receiving antennas placed in the rear cargo hatch.

67
6.5 HIRF Positions for Flight Deck Penetration

These tests are standard measurements taken for HIRF evaluation of airframe shielding and

vulnerability as discussed in reference [2]. Five measurements were taken around the flight deck

of the aircraft to investigate shielding vulnerabilities. In our measurements, we offset the

transmitting antenna approximately 15 m from the front wheel of the aircraft. There is no

required offset from the flight deck windows for testing, but there are requirements for angular

positions. These are at 270°, 315°, 0°, 45°, and 90° around the flight deck windows. Figure 100

shows a diagram of these measurement positions and their associated graphs. We see that the

penetration has a maximum value of approximately -5 dB at frequencies below 4000 MHz for

the horizontal and vertical polarizations. The minimum penetration values that occur at the

higher frequencies are between -15 dB and -20 dB. At an angle of 0°, we see three sharp resonances at approximately 1000 MHz, 2000 MHz, and 4000 MHz for the TEM and DRG

antennas in the horizontal polarization. The penetration levels remain similar for each HIRF

position. The separate plots are given in Figures 101 to 105.

68
S 3: -S

^gg81

— S cr

(gp) uo!it;j)3u3(j

(HP) U0HCJ)3U3d

<-~ "o o o o '-' D. c CL a. O S O

0^ U Q:: Q H Q

(ap) uonnj]3U3j

o o o o

D- D- O. D. X X > >

Q ^ O S O

q: Lu OS Q H Q ° X 2 2

(ap) U0I)CJ)3U3d

o o o o

CL O, O. D.

Q"

s 3 tu Oi ^ H Q S 3=

COO

1/5 O

G

CO

1)

X

o

I—

(

(U

t-( 13

OX)

tin

(gpl UO!)BJ)3U3J

69
pa

-10

-20-

-30-

-40-

-50

315

270'

HIRF Flight Deck

270 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

90'

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 101. HIRF Penetration data for all antennas and polarizations for the transmitting tower

placed at the 270"^ position, at a distance of 1 5 m centered on the front landing gear and the

receiving antennas placed in the flight deck.

3

e

o

•a

-10

-20

-30

-40

-50

HIRF Flight Deck

3 1 5 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

315°

270'

45°

90'

^ ^\

^

\ 4000 8000 12000

Frequency (MHz)

16000 20000

Figure 102. HIRF Penetration data for all antennas and polarizations for the transmitting tower

placed at the 315° position, at a distance of 15 m centered on the front landing gear and the

receiving antennas placed in the flight deck.

70
soa

s

-10-

-30

-40

-50

315°

270°

HIRF Flight Deck

degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

90<

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 103. HIRF Penetration data for all antennas and polarizations for the transmitting tower

placed at the 0° position, at a distance of 1 5 m centered on the front landing gear and the receiving

antennas placed in the flight deck.

PQ

-10

-20-

-30-

-40

-50

315

270°

HIRF Flight Deck

45 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

4000 8000 12000

Frequency (MHz)

16000 20000

45°

90°

Figure 104. HIRF Penetration data for all antennas and polarizations for the transmitting tower

placed at the 45° position, at a distance of 15 m centered on the front landing gear and the

receiving antennas placed in the flight deck.

71
-10

coa

0. -30-

-40

-50

315

270'

HIRF Flight Deck

90 degrees

TEM - Hpol

DRG - Hpol

TEM - Vpol

DRG - Vpol

45°

90<

4000 8000 12000 Frequency (MHz)

\ 16000 20000

Figure 105. HIRF Penetration data for all antennas and polarizations for the transmitting tower

placed at the 90° position, at a distance of 1 5 m centered on the front landing gear and the

receiving antennas placed in the flight deck.

72
6.6 Internal Coupling Measurements

Internal coupling measurements can tell us a lot about the propagation environment within the

airframe. They can tell us whether fields are uniform and whether they decay rapidly or more

slowly over time. They can also tell us how well the fields propagate within the airframe and

whether they can easily reach critical components inside the airframe.

NIST conducted several internal coupling measurements with each antenna to determine the

decay time and the quality factor of the internal airframe volume. Because the cabin was

particularly small, the combinations of DRG and TEM antennas were measured separately. We

also had to configure the system differently than for the Bombardier and Boeing 737-200 so that

the network analyzer could be left on the outside of the aircraft, because there was no room for it internally. This new configuration is shown in Figure 106. The individual configurations for the

DRG antennas are shown in Figures 107 to 1 1 1 and for the TEM antennas in Figures 1 12 to 115.

The chosen configurations were meant to physically stir the fields inside the aircraft as much as

possible. The red polygons represent the transmitting and receiving DRG antennas, and the blue

rectangles represent the transmitting and receiving TEM horn antennas.

Optical fiber

If 14 GHz 14 GHz

optical receiver/ optical transmitter/

RF transmitter RF receiver

18 GHz

optical receiver/

RF transmitter

8 GHz

optical transmitter/

RF receiver

Receiving

port

Transmitting

port

Figure 106. Measurement setup for internal configurations.

73
Figure 107. Layout for DRG configuration 1 measurements. One antenna points toward the

front of the flight deck. The second antenna points toward the rear of the aircraft.

L/ Ul_ ^ ^ -^C>,

Figure 108. Layout for DRG configuration 2 measurements. One antenna points toward the

front of the flight deck. The second antenna points into the last righthand seat.

74
Figure 109. Layout for DRG configuration 3 measurements. One antenna points out of the

left window in the flight deck. The second antenna points into the last lefthand seat.

Figure 1 10. Layout for DRG configuration 4 measurements. One antenna points out of the left window in the flight deck. The second antenna points into the middle lefthand seat.

75
2PrTTa

Figure 111. Layout for DRG configuration 5 measurements. One antenna points toward the

first, lefthand window in the passenger cabin. The second antenna points into the middle

lefthand seat.

Figure 112. Layout for TEM configuration 1 measurements. One antenna points out the

righthand window of the flight deck. The second antenna points toward the left rear of the

aircraft.

76
Figure 113. Layout for TEM configuration 2 measurements. One antenna points out the

righthand window of the flight deck. The second antenna points toward the right rear of the

aircraft.

Figure 1 14. Layout for TEM configuration 3 measurements. One antenna points out the

righthand window of the flight deck. The second antenna points toward the right rear seat.

77
We begin by looking at the time decay and quality factor of the airframe for each set of antennas

in each configuration. These are shown in Figures 116 to 119. Time decay is defined as the

period needed for the signal power to decay to its e"' value. The decay over time for the DRG

antennas in Figure 1 16 shows loose clustering behavior from 1 GHz to 16 GHz. The variation in decay over time below 8 GHz is anywhere from two nanoseconds to approximately seven nanoseconds. The variation above 8 GHz is from seven nanoseconds to ten nanoseconds. There

is no discernable pattern behavior as a function of position. The variation in decay over time for

the TEM horn antennas is on the order of a couple of nanoseconds to approximately seven

nanoseconds. The trend shows tighter clustering for the DRG antennas at the lower frequencies

and for the TEM antennas in the higher frequency range. The quality factor is defined as the

radian frequency multiplied by the decay period. The quality factor is much lower for the TEM

horn antennas because of the lower frequency range. Figures 120 and 121 are plots showing the

combined quality factor for both antennas. In Figure 1 20, we show the combined quality factor

for the DRG configuration 5 and the complementary configuration 4 for the TEM horn antennas.

Figure 121 shows both antennas for configuration 1. The two antenna types show good

agreement across their common frequency band from 1 GHz to 2 GHz. The testing community

would like the airframe to approximate a reverberant environment so that certain statistical models can be applied. In a reverberant cavity, we expect the quality factor and time decay to vary little throughout the cavity. Because the quality factor is so low we do not expect a large

number of modes that would support a good reverberant environment. However, further

statistical analysis would have to be completed in order to determine that the cavity itself is not

reverberant.

20 ^

S 16

14

12

10

1^

V

D

V

I

o

n n

V V

TV sV o o ^ ->

n DRG Configuration 1 V DRG Configuration 2

-A- DRG Configuration 3 O DRG Configuration 4

-<>- DRG Configuration 5

-k

^

4 8 Frequency (MHz)

V

n

V

12 16

Figure 1 16. Time decay for DRG antennas in all five internal configurations.

78
200

160

2 120 H u

a

O 80 -

40

^

D D

V V

ir i!!r O O ^ ^

<y

D DRG Configuration 1 V DRG Configuration 2

it DRG Configuration 3 O DRG Configuration 4

<> DRG Configuration 5

8 12 Frequency (MHz)16 20

Figure 1 17. Airframe quality factor (Q) for DRG antennas in all five internal configurations.

40 -n

35 ^>

30-

25 ^]

20

15

10

C)

+ + + TEM Configuration 1 O <> O TEM Configuration 2 nan TEM configuration 3 O O O TEM Configuration 4

t

0.2 0.4 0.6 0.8 Frequency (MHz)

1.2

Figure 1 18. Time decay for TEM horn antennas in aU four internal configurations.

79
20

16-

o 12H

o

6 8

[]

0.2

+

o

+

o

o

+ + + TEM Configuration 1 O O O TEM Configuration 2 D D D TEM Configuration 3 O O O TEM Configuration 4

0.4 0.6 0.8 Frequency (MHz)

1.2

Figure 1 19. Airframe quality factor (Q) for TEM antennas in all four internal configurations.

200

160

o 120 u

& 80

40

0<^

o

o

o

TEM Configuration 4 O O O &

DRG Configuration 5

4000 8000 12000

Frequency (MHz)

~1

16000

Figure 120. Quality factor for both antennas for DRG Configuration 5 and TEM Configuration 4.

80
200 -1

160-

o 120 H u

a

& 80

40

A

A

4000 8000 12000 16000

Frequency (MHz)

Figure 121. Quality factor for both antennas for Configuration 1.

7. Uncertainty Analysis

The sources of uncertainty are based on NISTIR 5019 [7], which provides a natural framework

for the identification of source uncertainties encountered in aircraft shielding along with an

efficient method of accounting for tracking and combining them.

Six sources of measurement uncertainty are considered in our analysis:

Measurement Repeatability

Range Uncertainties/Distance Correction

Time Gating

Drift

Polarization Mismatch

Signal-to-Noise Ratio

These sources of uncertainties (influence factors) were evaluated as follows:

1 . Measurement Repeatability: for a given internal orientation, we took multiple data sets, in which we moved the external antennas to and from the same location.

81
2. Range Uncertainties: We used estimates of variations when positioning the antennas for both

the reference and airframe measurements

3. Time Gating: We determined time-gating uncertainties by varying the gate width and

performing a statistical analysis on the resulting amplitude spectra. See Appendix A for further

discussion.

4. Drift: The uncertainty due to instrumentation drift is small. It was computed by using the data

obtained from system calibration checks done before and after circumnavigating the aircraft. The uncertainty was determined by looking at the difference and dividing that by the average of

the two signals.

5. Polarization Mismatch: Polarization mismatch uncertainties occur when the antennas could be

misaligned for a given polarization. We calculated one uncertainty based on a possible

misalignment of 5°. The other term comes ft^om the possible leakage fi-om one polarization to the other. The cross-polarization of our TEM horn antennas is approximately -20 dB, and for the

DRG antennas it is approximately -15 dB. These two factors both contribute to the polarization

mismatch uncertainty.

6. Signal-to-Noise Ratio: Signal-t- noise uncertainties were calculated for the Global 5000

aircraft. Appendix B of this report summarizes typical signal and noise characteristics.

The impact of these six influence factors on the measured penetration is summarized in Table 1. This table lists the fractional uncertainties [7, 8] resulting from each influence factor. The most

significant error is due to uncertainties in the signal-to-noise ratio. Measurement repeatability

has an influence that is somewhat less than that of the signal-to-noise ratio, but is nevertheless

significant. Time gating is the next largest uncertainty, followed by the range/distance correction

uncertainties, extrapolation uncertainties, polarization mismatch, and drift, respectively.

Polarization mismatch and drift contribute almost nothing to the overall uncertainty.

The combined standard uncertainty was computed using the procedure given in NIST Technical

Note 1297 [9]. The six sources of uncertainties were combined using the root sum-of-squares of

the linear fractional uncertainties averaged over a 200 MHz frequency window. The resulting

uncertainties (in decibels) for penetration are plotted in Figure 122 for the frequency range from

800 MHz to 1500 MHz. The uncertainties were calculated as a function of frequency, and

therefore we have listed an approximate average value in the Table 1. We have broken the

uncertainties into those below 9 GHz and those above 9 GHz, because the noise floor resets itself there due to the internal configuration of both attenuators and mixers in the VNA. We believe

that a reasonable uncertainty bound would be at the 95 % confidence level for the data shown in

Figure 122, remembering that this current uncertainty analysis is based on a limited set of data.

82
Table 1. Typical fractional uncertainties resulting from the six influence factors.

Influence factor

Typical fractional uncertainties

<9GHz >9GHz

Signal-to-noise 1.2 1.6

Repeatability 0.4 0.8

Time gating 0.3 0.6

Range/distancecorrection 0.1 0.4

Extrapolation 0.1 0.4

Polarization mismatch 0.1 0.2

Drift Neg. Neg.

RSS 1.3 2.0

10

PQ•a

c

•a

t;u

o

c

Pi 2-

4000 8000 12000

Frequency (MHz)

16000

Figure 122. Combined standard uncertainty in penetration.

20000

83
8. Summary and Conclusions

The data in this report were collected to provide guidelines for HIRF testing on various aircraft. We have reported on the penetration measurements taken of the Beechcraft Premier lA at the

Hawker Beechcraft Corporation in Wichita, Kansas. We have discussed extrapolation

measurements taken to ensure that the measurements are in the far- field of the transmitting

antenna. We have shown results for measurements taken at various azimuth angles around the

outside of the aircraft with the receiving antenna in the main passenger cabin, the flight deck, and

the rear cargo hatch. We have also performed a series of internal measurements to look at the

reverberant field characteristics within the cavity to determine the viable statistics associated

with the fields.

The main passenger cabin shows the greatest penetration for all three compartments. We

attribute this to the numerous windows. Typical maximum penetration values are -5 dB at 900 MHz; this same frequency shows maximum penetration around the aircraft. Minimum

values of penetration occur at the tail of the aircraft (180°) and are on the order of -30 dB.

Maximum penetration for the flight deck is around -5 dB at an angle of 0° for frequencies

around 650 MHz, 770 MHz, 1000 MHz, 1525 MHz, and 3100 MHz. Minimum penetration occurs at 180° at a value around -40 dB. The rear cargo hatch shows maximum penetration

values of -10 dB from 200° to 270°, while minimum penetration occurs at 0° with a value of

-40 dB. With an antenna in the rear cargo hatch, we see low penetration values on the right side

of the aircraft from a top-down view. Typically horizontal and vertical polarizations penetrate

equally well into the aircraft; however, at the lower frequencies the horizontal polarization has

higher penetration values and occurs toward the tail of the aircraft. We found that symmetry is maintained around the aircraft. HIRF penetration into the flight deck shows approximate values

of -5 dB to -10 dB at lower frequencies and -15 dB at higher frequencies for a radial distance of

15 m from the front landing gear at angles of 270°, 315°, 0° 45° and 90°. The internal coupling

measurements showed that traditional reverberation statistics would not be valid in this cavity,

but good agreement was shown between the two antenna types for quality factor values between

1 GHz and 2 GHz. Finally, we found that major coupling apertures would not be missed if measurements were taken every 10° as opposed to every 5 °. Figure 123 shows results for the

DRG horn antenna in both vertical and horizontal polarizations for various frequencies in each

compartment. Figure 124 shows results for the TEM horn antenna in both vertical and horizontal

polarizations for various frequencies in each compartment. Red circles are for the main cabin,

blue triangles are for the flight deck, and green squares are for the rear cargo hatch. This shows

us that rear cargo hatch penetration is typically lower than that for either the main passenger

cabin or the flight deck at each of these frequencies. We also see that the penetration values are

fairly constant around the aircraft, which we beUeve is due the use of carbon-fiber composite

material. And we see that penetration typically decreases as frequency increases.

84
DRG_Hpol DRG_Vpol

800 MHz

1000 MHz

5000 MHz

10000 MHz

18000 MHz

UOOMH/

''" (DRG-Hpol)

FliyhiDctk B (a i]Rc;irCjrcyHalch

1000 MH/

(DRG-Hpol) • • • Main DL-ck Might Deck

E) S E) Rear Curgu Mulch

140 MKWMH/

(DRG-Hpol) • • • Miiin Deck

nielli Deck EBB Rear Cargo Hurcli

1 0000 MH/

(DRG-Hpol) • • • Muin Deck

niphi Deck S il B RcarCargoHalch

1 8000 MHz

(DRG-Hpol) • • • Main Dock

Mighi Deck

E) B El Rear Curgo Hatch

800 MH/

''" (DRG-Vpol) • • • Mam I>cck

Fl.glii Deck E m SReurCargoHuich

1000 MH/ 'TM (DRG-Vpol) • • • Main Deck

nighl Deck B Isl 19 Reiir Cargo Halch

140 5000 MH/

(DRG-Vpol) • • • Mam Deck

Fllglii Deck

Is) Is] [i) RcurCurgo Hatch

JO 18000 MHz

(DRG-Vpol) • • •Main Deck Flight Deck BBS Rear Cargo Hatch

140 lOOOOMHz

(DRG-Vpol) • • • Main Deck

Flight Deck a D DRor Cargo Hal Figure 123. Graphs for DRG horn antenna in both vertical and horizontal polarizations for various frequencies in each compartment. Red circles (•) are for the main cabin, blue diamonds

() are for the flight deck, and green squares () are for the rear cargo hatch.

85
TEM_Hpol TEM_Vpol

200 MHz

500 MHz

800 MHz

1000 MHz

1300 MHz

200 MHz

(TilM-Hpt^l) • • Muin DccL

Riglii Deck S B Rcur Cargo H;it(.-h

50() MHz

(TEM - Hpol) • • • Mjin Deck

Flishl Deck B H H Rc;ir Curgo Haich

son M Hv (TEM -Hpol) • • • \Um Deck

FIJghi Deck

1) (Sl BRcarCargoHaith

.„. lOOOMHi- (TEM- HpoU • • • M.iin Deck

Flighi Deck S 13 IS Rc^r C^go Haicli

13f)0MH/ (TEM- Vpol) • • • Muln Deck

l-lighi Dock D D Rear Cargo Hal

140 200 MH/

(TEM- Vpol) • • •Main Deck

nighi Deck G B B Rear Curgo Hatch

500 MH/

(TliM- Vpoli • • Main Deck

J^ight Deck a B Rear Cargo Hatch

140 800 MH/

(TEM- Vpol) * # * Main Deck • • • Riglii Deck AAA Rear Cargo Hatch

40 1000 MHi^

(TI-:M- Vpoll • • • Main Deck

I-light Deck B e Rear Cargo Haich

llOOMH/

(TEM-Hpi>l) • • • Main Deck

Fligtii Deck BBS Rc^r Cargo Hal

Figure 1 24. Graphs for TEM horn antenna in both vertical and horizontal polarizations for various

frequencies in each compartment. Red circles (•) are for the main cabin, blue diamonds () are

for the flight deck, and green squares () are for the rear cargo hatch.

86
We thank Howard Jordan from the Hawker Beechcraft Corporation in Wichita, Kansas for

allowing us to measure one of their carbon composite aircraft and we thank David Walen from

the FAA office in Renton, Washington for his sponsorship and financial support for this work.

This was an important measurement effort both to aid in understanding and to help define

standard measurement procedures for HIRF testing.

9. References

[1] C.A. Grosvenor, D. Novotny, D. Camell, G. Koepke, R.T. Johnk, Electromagnetic airframe

penetration measurements for the FAA Bombardier Global 5000, Natl. Inst. Stand. Technol.

Tech. Note 1547 (May 2008).

[2] SAE Aerospace Group, Guide to certification of aircraft in a high intensity radiated field

(HIRF) environment, SAE ARP5583 (January 2003).

[3] C.A. Grosvenor, R.T. Johnk, D.R. Novotny, N. Canales, CM. Weil, J. Veneman. A twophase airframe shielding performance study using ultrawideband measurement systems, Natl.

Inst. Stand. Technol. NISTIR 6622 (January 2003).

[4] P.F. Wilson, D.A. Hill, C.L. HoUoway, On determining the Maximum Emissions From

Electrically Large Sources, 2002 IEEE Trans. Electromagnetic Compatibility, 44(1): 79-86

(February 2002).

[5] R.T. Johnk, B. Archambeault, D. Novotny, Using joint time-frequency analysis to enhance

time-domain numerical emc simulations, 2003 Annual Report Interference Technology (2003).

[6] J.M. Ladbury, T. H. Lehman, G.H. Koepke, Coupling to devices in electrically large cavities or why classical emc evaluation techniques are becoming obsolete, 2002 Intl. Symp. on

Electromagnetic Compatibility, 2: 648-655 (August 2002).

[7] R.C. Wittmann, M.H. Francis, L.A. Muth, R.L. Lewis, Proposed uncertainty analysis for

RCS Measurements, Natl. Inst. Stand. Technol. NISTIR 5019 (January 1994).

[8] J.R. Taylor, An introduction to error analysis, University Science Books, Sausohto, CA.

(1997).

[9] B.N. Taylor, C.E. Kuyatt, Guidelines for evaluafing and expressing the uncertainty of NIST

measurement results, Natl. Inst. Stand. Technol. Tech. Note 1297 (September 1994).'

[10] E.B. Larsen, R.L. Ehret, D.G. Camell, and G.H. Koepke, Calibration of antenna factor at a ground screen field site using an automatic network analyzer, 1989 Intl. Symp. on

Electromagnetic Compatibility, 1: 19-24 (August 1989).

87
[11] http://www.chm.bris.ac.uk/webprojects2002/mjames/chemistry.html. Accessed March 10,

2008.

[12] http://www.geocities.com/vpkelly.geo/blog.html?t=p&pg=l&cnt=5 . Accessed March 10,

2008.

[13] http://en.wikipedia.org/wiki/Graphite-reinforced plastic. Accessed March 10, 2008.

[14] F. Sagnard, A. Berthault, B. Veron, The microwave measurement of the conductivity of a small fiber with an open cavity, IEEE Trans. Instrum. Meas., 49(5): 942-948 (October 2000).

[15] C.A. Johnk, Engineering electromagnetic fields and waves, 2"^^ ed., New York : J. Wiley

and Sons, pg. 168(1988).

[16] M.J. Akhtar, L.E. Feher, M. Thumm, A waveguide-based two-step approach for measuring

complex permittivity yensor of uniaxial composite materials, IEEE Trans. Microwave Theory

Tech., 54(5): 201 1-2022 (May 2006).

[ 1 7] S.P. Rea, D. Wylie, D. Linton, E. Orr, J. McConnell, EMI shielding of woven carbon Fibre

composites, 2004 High Frequency Post-Graduate Student Colloquium, pp. 205-210 (September

2004).

[18] J. Ding, S. Rea, D. Linton, E. Orr, J. McConnell, Mixture properties of carbon fibre

composite materials for electronics shielding in systems packaging, 2006 Electronics System

Integration Technology Conf., 1: 19-25 (September 2006).

[19] C.L. Holloway, M.S. Sarto, M. Johansson, Analyzing carbon-fiber composite materials with

equivalent-layer models, IEEE Trans. Electromag. Compat., 47(4): 833-844 (November 2005).

[20] M. Lin, C.H. Chen, Plane-wave shielding characteristics of anisotropic laminated

composites, IEEE Trans. Electromag. Compat., 35(1): 21-27 (February 1993).

[21] H. Chu, C.H. Chen, Shielding and reflection properties of periodic fiber-matrix composite

structures, IEEE Trans. Electromag. Compat., 38(1): 1-6 (February 1996).

88
Appendix A. Time-Domain Waveform Analysis

The time-domain waveforms can tell us a lot about the penetration into the airframe. Figure 125

shows the time-domain waveform for a DRG antenna transmitting in the horizontal polarization

at an angle of 30° for a receiving antenna located in the main passenger cabin. The figure shows

the linear time-domain response (red trace) and the log-magnitude response (black trace) of the

signal versus time. Using both representations it is easy to define the direct component (green

box), the first-time gate position (blue box), the second time-gate position (magenta box), and

why we either include or exclude certain portions of the signal in our analysis. The first piece of

information we can get is the time-of-flight between the transmitting and receiving antenna.

This is shown by the onset of the direct component. This can give us insight about the distance

between the two antennas. For this measurement we tried to position our transmitting antennas on a 23.5 m circle, with reference to the geometric center, which translates to 75 ft. Taking a close look at the onset of our direct component, as shown in Figure 126, shows us that the time

of flight corresponds to 73.3 ns, and using the conversion that there are 0.983 ft per ns of time of

flight, we conclude that our actual distance was probably 22.0 m (72.1 ft). The direct component

is the antenna-to-antenna response as the signal enters the aircraft. The response is short in duration, and in a log-magnitude format has a rapid decay time. The portion of the signal after

the initial response is due to the reverberant fields that develop from the energy that bounces

around in the cavity due to this initial electromagnetic energy. These have a different decay

characteristic. At 250 ns we apply a stop time gate where we zero the rest of the waveform; this

is shown by the blue box. Notice that we try to apply a stop time gate at a point close to the

noise floor of the signal response, which helps decrease the oscillation in the frequency domain

due to the appHcation of a windowing function. We then want to look at the tiny bit of energy

shown building up and decaying between 250 ns and 550 ns to see whether this energy affects

0.006

0.004

•aa

-ac

-120-

- 0.002

-

-160

-200

-240

-0.002 .2?

-0.004

-0.006

-0.008

200 400

Time (ns)

Figure 125. Time-domain waveforms for a DRG antenna transmitting at angular position 30'

Receiving antenna is in the main passenger cabin.

89
0.006

0.004

0.002

•a3

I

<

.SP -0.002

on

-0.004

-0.006 -

-0.008

Onset of signal

at73.3ns\

50 60 70 80 Time (ns) 90 100

Figure 1 26. Timewaveform for a DRG antenna transmitting at angular position 30 "^ and for the

receiving antenna in the main passenger cabin. Onset of signal occurs at 73.3 ns.

our application of the time gate. Since this energy translates to an event occurring at approximately 250 ft, we believe this event occurs outside the aircraft; but if it is a small buildup

of energy somewhere inside the aircraft, then we want to make sure we include it if it is important in the measurement of this aircraft. Therefore, in the application of our second gate

we include this amount of energy and look at its impact in the frequency domain. This is shown

in Figure 127. The black trace is the penetration without time gating the waveform; in other

words, it is the full time-domain record. The red trace is the penetration for time gating from 10

ns to 250 ns, so that anything that happens outside this period is removed from the record. The

blue trace shows the waveform that includes time-domain information fi^om 10 ns to 550 ns. Since the blue trace obscures the black and red traces, we can say that the extra 300 ns added to the blue trace contains little more information than what was already obtained by the red trace, so we would be safe to stop the time gate at 250 ns and be sure that we are not missing important

information from the time-domain signal.

90
-20 -

-40 m

co5 -60

a

Oh -80

-100 -

-120

Main Cabin

DRG (Hpol)

30 degrees

No Time Gating of Signal

Time Gate applied (10 ns to 250 ns) Time Gate applied (10 ns to 550 ns)

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 127. Frequency-domain waveforms for a DRG antenna transmitting at angular position

of 30°. Receiving antenna is located in the main passenger cabin.

Let us examine the signal at another position. This signal was obtained with the transmitting

antenna located at an angle of 220 ° and the receiving antenna located in the rear cargo hatch.

The time-domain signal is shown in Figure 128. Notice that for this compartment there is no

direct signal path, and the only signal that enters this compartment is of low amplitude and

immediately decays into reverberant fields. Also no pronounced signal amplitude is observed

after 600 ns, where we reach our noise floor, and so the only thing we add to our signal at this

point is noise. This is why we choose to time gate the signal, so that most of the signal is analyzed versus signal plus noise. The frequency-domain signal is shown in Figure 129. The

black curve shows the entire waveform without time-domain gating, and the red curve shows the

signal once a time-gate is applied from 10 ns to 600 ns. This shows that because the signal has

decayed to the noise floor by 600 ns, the noise increases the amplitude of the signal only a little.

91
200 400

Time (ns) 600

0.003

0.002

-0.004

800

Figure 128. Time-domain waveforms for a DRG antenna transmitting at an angular position of 220'

Receiving antenna located in the rear cargo hatch.

-40-

PQ3

co

'Uu

c

D

a- -80-

-120

Rear Cargo Hatch

DRG (Hpol)

220 degrees

No Time Gating of Signal

-|- -|- + Time Gate applied (30 ns to 600 ns)

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 129. Frequency-domain waveforms for a DRG antenna transmitting at an angular position of

220 °. Receiving antenna located in the rear cargo hatch.

92
Appendix B. Signal and Noise Characteristics

Typical signal and noise characteristics are shown in Figures 130 to 132 for the three

compartments: (1) main passenger cabin, (2) flight deck, and (3) rear cargo hatch, at three

different angular positions: (1) 90°, (2) 20°, and (3) 180°, respectively. We have plotted only the

DRG horn antenna in the horizontal polarization for this section. Noise is a function of position

due to the location of ambient RF sources that the aircraft may shield from the internal antennas

as we move around the aircraft. Noise floors tend to be around -60 dB to -80 dB at the lower

frequencies and climb to around -50 dB at the higher frequencies. The rise in noise floor at around 9 GHz is due to the attenuator configuration of the VNA for upper frequencies. The

signal-to-noise ratios for the main passenger cabin vary from 30 dB to 60 dB. In the flight deck,

the signal-to-noise ratio varies from 30 dB to 55 dB, and in the rear cargo hatch, the signal-tonoise ratio varies from 15 dB to 55 dB.

The signal-to-noise characteristics for the TEM horn antennas are a little different, due to the FM frequency bands. For the frequency band from 100 MHz to 1500 MHz, typical signal-tonoise ratios vary from 20 dB at the lower frequencies to 60 dB at the higher frequencies.

0-1

-20

CO

T3

<U

I

a

I -40

05

-60

-80

Main Cabin

90 degrees

DRG-Hpol

Noise floor

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 1 30. Typical signal and noise characteristics for the main passenger cabin. This

particular noise measurement was taken at an angle of 90 °.

93
-20

m3

-op -40

on

-60

-80

Flight Deck

20 degrees

DRG-Hpol

Noise floor

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 131. Typical signal and noise characteristics for the flight deck.

This particular noise measurement was taken at an angle of 20°.

0^

-20

PQ3

T33

? -40

CO

-60-

-80

Rear Cargo Hatch

180 degrees

DRG-Hpol

Noise floor

4000 8000 12000

Frequency (MHz)

16000 20000

Figure 132. Typical signal and noise characteristics for the cargo closet. This particular

noise measurement was taken at an angle of 180°.

94
Appendix C: TEM and DRG Horn Boresight Gain Characteristics

The DRG and TEM horn antennas used in this effort were calibrated before we deployed the

system. This technique can be used to derive antenna gain with specified resistive loads

(typically 50 Q.) at the antenna terminals. An accurate method for doing this is the three-antenna

method. As the name implies, three transmission measurements are made with three

combinations of the three antennas. This procedure is described in detail in reference [10]. This

process yields three equations that can be readily solved for either gain or antenna factor. The

gain characteristics of our DRG horn antennas are shown in Figure 133, the gain characteristics

of our 36 cm TEM horns are shown in Figure 134, and the gain characteristics of our 1.2 m TEM

horns are shown in Figure 135. The gains displayed in these figures include the antenna input

mismatch, which accounts for the reduction of gain at the lower frequencies. The DRG horn

antenna gain, plotted in Figure 133, shows that the low-frequency cutoff of these antennas occurs around 750 MHz. As the frequency is reduced, the input mismatch increases, which accounts for a rapid decrease in antenna gain. Mismatch and gain are not cause and effect but are instead due

to a combination of aperture beam forming, and a better input match accounts for the increasing

gain at the higher frequencies. A maximum gain of approximately 15 dB occurs at 16000 MHz.

The 36 cm antenna results, plotted in Figure 134, shows a maximum gain of approximately 7 dB

realized at 4000 MHz. Results for a NIST 1.2 m horn antenna are plotted in Figure 135. This

horn is longer and has a resistive taper, which improves the low-frequency performance. The

maximum frequency of this antenna is 1500 MHz, due to balun performance limitations, and a maximum gain of 7 dB occurs at this frequency as well.

8000 12000 Frequency (MHz)

16000 20000

Figure 133. Measured boresight antenna gain for a 31 17 DRG horn antenna. The gains plotted

here include the input mismatch effects, which account for the rapid decrease below 750 MHz.

95
1 1 1 1 1 1 _ -t-^

"* ""' *'*** .^?rfrs—

'/

-10 7

c

So

^A .20

GC -30

^0

-50

-51.078_6o

/

-

1 1 1 1 1 1 1

1

500 1000 1500 2000 2500 3000 3500 4000

J. .498. Homl_2^'^

Frequency (MHz)

.4x10-^.

Figure 134. Measured boresight antenna gain for three identical NIST 36 cm TEM horn antennas. The gains plotted here include the input mismatch effects, which account for the rapid decrease

below 100 MHz.

Gam

1 1 1 1 1 1 1

-20

/

-40

1 1 1 1 1 1 1 200 400 600 800 IGOO 1200 1400

Freq Frequency (MHz)

Figure 135. Measured boresight antenna gain for a NIST 1.2 m TEM horn antenna. The gains

plotted here include the input mismatch effects, which account for the rapid decrease below 50

MHz.

96
Appendix D. Carbon Fiber Composites

The use of carbon fiber composites is increasing, due to their high tensile strength, resistance to corrosion, and Hght weight. Carbon fiber parts are used in automobile racing and limitedproduction automobiles, as well as in fairings, motorcycle mudguards, boats, and aircraft. Carbon fiber is being investigated for use in structural engineering in applications such as bridges, concrete structures, and beams, because of its strength and resistance to corrosion.

Carbon fiber is also making its way into many other areas of manufacturing. There is a wide

variation in carbon-fiber composite materials, so this appendix is provided only to add

understanding of how carbon composite materials behave in electromagnetic fields and to understand how they are fabricated. This information is not specific to the tested aircraft because

different manufacturers use different materials and processes.

Carbon fiber has many desirable properties. It is resistant to corrosion and fire; it has high levels

of stress tolerance; and it is chemically inert and unreactive. Carbon fiber has a higher tensile

strength than steel [11]. Carbon fiber has a tensile strength of 3.50, higher that that of steel,

whose tensile strength is only 1.30. It is lighter than steel by a factor of 4.5.

At very high temperatures, around 2500 XI, carbon fiber can be converted to graphite directly,

and therefore has the same chemical structure. The carbon atoms that constitute both carbon

fiber and graphite arrange themselves into honeycomb-like sheets lying on top of each other.

These sheets are, however, less ordered than graphite sheets, and have weak bonds between

layers, and the sheets fold within an individual fiber. Both structures are brittle; however, carbon

fiber is less stable than graphite. Each fiber strand is typically made from thousands of carbon

filaments and these strands are woven together to form the basis of the part. Since only three

carbon atoms are used in interatomic bonding, the fourth atom contributes a free electron to the

matrix, allowing it to act as a conductor even though it is nonmetallic. A spool of carbon strands

is shown in Figure 136 [12].

Carbon fiber composites are materials made from many strands of carbon embedded in some

type of resin. To produce graphite epoxy parts [13], sheets of woven carbon fiber are layered over a mold and oriented to provide optimal strength for the part. Once air is evacuated from the

mold, an epoxy resin is applied and, depending on the part, may be either heated or air-cured.

More information on the process can be found in the references [10-13]. Epoxy resin is used to hold the shape of the part and to give it rigidity in the final product.

97
Figure 136. Spool of carbon fiber strand [12].

Now that we understand the structure of carbon fiber composites, we can begin to explore their

electrical properties and how electromagnetic fields will interact with them. This section

presents measurements of the dielectric constant, the loss tangent, and the conductivity, then the

last section describes their shielding characteristics. By having a good understanding of the

electrical properties, we can begin to understand how the shielding effectiveness (SE) might be

influenced by adopting a metallic, rather than a nonmetallic, structure.

D.l Dielectric Properties

We begin with a microwave measurement of the conductivity of some carbon-fiber inclusions in

various dielectric matrices [14]. These measurements were performed in a Fabry-Perot resonator

at a frequency of 10 GHz. The inclusions were made from Torayca T300 with a stated

conductivity of 5.5 • 10 S/m. The average length of the inclusions was 3.25 mm with a radius of

4 jim. The measured conductivities have an average value of 6.1 • 10"^ S/m ± 15%. The

conductivity of aluminum is around 3.5 • 10^ S/m [15]. So the conductivity measured in this

experiment is about 1000 times less than that of aluminum.

A material's conductivity is directly associated with the imaginary part of the dielectric constant

[16]. In this study, a waveguide transmission method was used to determine the dielectric

constant and effective conductivity (loss tangent) for the electric field both parallel and

perpendicular to the fiber orientation. Several well known materials were measured, along with

four different types of carbon fiber-reinforced polymers. The dielectric properties of the well

known materials are used as a check against the measured properties of the carbon-fiber

composite materials. For the carbon-fiber composites, for the field in the parallel orientation, the

dielectric constant showed values between 1500 and 3500, and in the perpendicular direction, the

dielectric constant showed values between 34 and 55. There is thus a high degree of anisotropy

in these types of materials, and so the orientation of the fibers with respect to the electric field

98
orientation, is critical. The conductivity is also strongly affected by the orientation of the

material with respect to the electric field. The conductivity measured here is an effective

conductivity, because the conductivity of the resin matrix cannot be separated from that of the

carbon fiber. The data show that, for an electric field component parallel to the fiber orientation,

the effective conductivity has values from 30 S/m to 1 10 S/m; and in the perpendicular

orientation we see values from 5 S/m to 13 S/m.

D.2 Shielding Effectiveness

Based on the measurements of conductivity, we can hypothesize that the SE of carbon fiber

composite materials may not have the same values as those for metals. We will discuss the

results from several papers [17-21] and attempt to understand how the SE of carbon-fiber

composite aircraft should compare to that of metallic aircraft. In this technical note, we have

presented the results in terms of penetration, which is just the reciprocal of SE. However, we

will still use SE in this section so that when you refer back to the papers, a mental transition will

not have to be made.

All measurements discussed in the following papers have to do with either single-layer or multilayer carbon-fiber composites in various orientational arrangements. In the layered composites,

a combination of varying angles was used to simulate actual manufactured parts. Numerical

modeHng was used to verify results and to adjust parameters for evaluation. Most of the

modeling is based on an effective-medium mixture theory which assumes that the resin and

carbon fibers are present in fixed percentages of the total matrix. In the first paper, two woven

carbon-fiber composites were measured and a theory developed to explain the SE. The main

contribution to the dielectric constant is assumed to be from the conductivity. The dielectric

constant is used to calculate the reflection and transmission coefficient, which in turn is used to calculate the SE of the layers,

SE=- 20 \og[\T\). (DA)

The theoretical data for a plane wave incident on a sheet of carbon-fiber composite [17, 18] show

that the SE increases exponentially at frequencies above 1 GHz. Measurements for X-band

frequencies have shown that the SE of these carbon fiber composites is not much different from

that of aluminum [17]. Theoretical data for a single layer show SE values of around

66 dB for frequencies from 1 to 18 GHz, and for a multilayer composite the lowest SE value was

86 dB [18]. In another paper [19], equivalent-layer models were developed for a single-ply

carbon-fiber composite to explain the behavior of the reflection coefficient, transmission

coefficient, and SE for a finite-element model. In this paper the SE was plotted for two different

values of conductivity and for composites consisting of two panels or four panels. The data are summarized in Table D. 1 for frequencies less than 1 GHz. The data show that four panels

provide better shielding than two panels and that carbon-fiber composites with higher

conductivity also provide better shielding.

99
Table D.l Modeled conductivity for two-panel and four-panel composites.

(Frequencies less than IGHz.)

Conductivity o (S/m) Two panels Four panels

To 0.032 0.065

1 • lO"* 32 39

The final two papers [20, 21] show the dependency of SE on various parameters such as fiber

orientation, conductivity, number of layers, and angle of incidence. For anisotropic laminated

composites [20], it was shown that the SE is highly dependent on the polarization of the

incoming electric field. For a laminate with a thickness of 4 • lO'^^m, the SE for an electric field

polarized parallel to the anisotropy was 90 dB, whereas, for the electric field polarized

perpendicular to the anisotropy, the SE was 70 dB at a frequency of 1 MHz. The SE for a laminate containing four pUes was about 70 dB at 1 GHz, as opposed to a laminate containing

eight pUes whose SE was about 100 dB at 1 GHz. For an eight-layer laminate whose panel

orientation was [07457907-45°], the SE was approximately 70 dB at 1 MHz, compared to laminate whose panel orientation was [0790°] and had an SE of 80 dB at 1 MHz, and where the

electric field was polarized perpendicular to the fiber orientation of the first panel. Finally, the

last paper shows how various parameters change for a single-ply periodic composite material

[21]. This paper also shows that as the conductivity increases from 10"^ S/m to 10^ S/m, the SE

increases from 60 dB to 120 dB at 1 MHz. Above 10 GHz, the SE does shows no variability as a

function of conductivity. For different fiber diameters, the SE can be changed by a factor of 1.5. As the angle of incidence increases, the SE increases. This model also shows that as the

dielectric constant of the resin changes, the SE remains constant. And finally, for periodic

structures, the reflection and transmission maxima and minima change directly as the ratio of

thickness to wavelength.

These papers have shown us that the shielding effectiveness varies based on a whole array of

parameters, and therefore it would be very difficult to determine whether the penetration for this

particular aircraft was dependent on the carbon fiber structure. We also know that the seams in an aircraft built with carbon-fiber composites are not assembled in the same manner as for an all- metal aircraft, so additional leakage may come from the resulting apertures. We have observed

that the penetration of this carbon-fiber composite aircraft is different from that for the

Bombardier Global 5000 [1]. Based on the above discussion, we can conclude that some of this

difference is due to the carbon-fiber composite structure, and some is due to different leakage

apertures; but overall, the shielding values are comparable to those for a conventional metallic

structure.

100
Appendix E. Penetration Data for HIRF Frequency Bands

The peak and average field strengths in a HIRF environment are defined for specific frequency

bands [2]. The frequency bands that correspond to our measured data are: (1) 200 MHz to 400

MHz, (2) 400 MHz to 700 MHz, (3) 700 MHz to 1000 MHz, (4) 1000 MHz to 2000 MHz, (5)

2000 MHz to 4000 MHz, (6) 4000 MHz to 6000 MHz, (7) 6000 MHz to 8000 MHz, (8) 8000

MHz to 12000 MHz, and (9) 12000 MHz to 18000 MHz. If we determine the maximum

penetration per compartment in these same frequency bands and plot it versus our measured data,

we may find this to be more interesting for the HIRF community. Figures 137 to 139 are plots

for the TEM and DRG antennas, in the vertical and horizontal polarization, at one angular

position for each of the measured compartments. The black dotted line indicates the maximum

penetration for that compartment for a DRG horn antenna in the horizontal polarization for all angular positions.

Figure 137 shows the penetration data as a function of the HIRF environment frequency

bands for the receiving antenna in the main cabin and the transmitting antenna at an angular

position of 0°. This is an angle where there is high electromagnetic penetration into the aircraft. We notice in several frequency bands that the TEM horn antenna in the horizontal polarization is above our maximum penetration line. By using these types of plots it is easy to pick out

troublesome measurements. Penetration into the flight deck at an angle of 300° is shown in

Figure 138. Again the black dotted Hne shows the maximum penetration for all angles as a function of the frequency band. The TEM horn antenna shows more penetration in the lower

frequency bands than does the DRG horn antenna in the horizontal polarization. Finally, Figure

139 shows the penetration for the receiving antenna in the rear cargo hatch, and the transmitting

antenna at an angle of 240°. By looking through the individual frequency bands, we can isolate

high penetration values for any antenna. If we use the maximum penetration for each

compartment, we can then determine the peak and average field levels inside that compartment

from the peak and average field levels outside of the aircraft.

101
-50-

200

0-1

I

'

I 280 320

Frequency (MHz)

400 ~i ' r~

800 900

Frequency (MHz)

-30-

360 500 600

Frequency (MHz)

700

I

'

\ 1400 1600

Frequency (MHz)

\

' \ 4800 5200

Frequency (MHz)

2000 2400 2800 3200

Frequency (MHz)

5600

-^

I

'

i

'

\ ' r~

6000 6400 6800 7200 7600

Frequency (MHz)

"H ' 1

IIOOO 12000

1

'

\ 14000 16000

Frequency (MHz)

"H '\ ^

9000 10000

Frequency (MHz)

18000

Figure 137. Frequency-band exploded view of the penetration for all antennas and

polarizations for the transmitting tower placed at the 0° position and the receiving antenna in

the main cabin.

102
-20-

Flight Deck - 300 degrees TEM - Hpol DRG - Hpol TEM - Vpol DRG - Vpol

1

' T"

280 320

Frequency (MHz)

500 600

Frequency (MHz)

700 ~i

' r~

800 900

Frequency (MHz)

200 240

1000 1200

a -20-

5 -30-

1 ' r

1400 1600

Frequency (MHz)

7

1800 2000 1 ' \

' r

2400 2800 3200

Frequency (MHz)

3600 4a)0

1—'

\

' r

4400 4800 5200

Frequency (MHz)

5600 6000

1

'

\ 14000 16000 Frequency (MHz)

" 1'

\

' I' I

' I 6000 6400 6800 7200 7600 $009) Frequency (MHz) —

I

'

\

'

1 9000 10000 11000

Frequency (MHz)

12000 18000

Figure 138. Frequency-band exploded view of the penetration for all antennas and

polarizations for the transmitting tower placed at the 300° position and the receiving antenna

in the flight deck.

103
-10-

-30-

-40-

Rear Cargo Hatch - 240 degrees TEM - Hpol DRG - Hpol TEM - Vpol DRG - Vpol

280 320

Frequency (MHz)

360 400 n ' T"

500 600

Frequency (MHz)

~1 ' T"

800 900

Frequency (MHz)

200 240

S -20-

1400 1600

Frequency (MHz)

2000 2800 3200

Frequency (MHz)

3600 4000

\

'

\ 4800 5200

Frequency (MHz)

6000

g -30 -

-to-

-50 "^

1

'

\

'

i 6000 6400 6800 7200

Frequency (MHz)

I ' I 14000 16000 Frequency (MHz)

9000 10000 I 1000 Frequency (MHz)

12000

Figure 139. Frequency-band exploded view of the penetration for all antennas and

polarizations for the transmitting tower placed at the 240° position and the receiving antenna

in the rear cargo hatch.

104
Appendix F. Beechcraft Premier lA Measurement Equipment List'

The main equipment used in the evaluation of the Beechcraft Premier lA is hsted below:

Agilent N5230A PNA-L (300 kHz to 18 GHz) with a maximum of 16001

frequencies/trace.

Megaphase Cables (4 m to 5 m)—we used phase stabilized cables to avoid phase drift with temperature variations.

Miteq Optical Fiber Link MDDR/MDDT (1 1 GHz version)—this unit has the ruggedness

and temperature characteristics for field use.

Miteq Optical Fiber Link SCMR/SCMT (18 GHz version)—this unit has the ruggedness

and temperature characteristics for field use.

HP 1 17 13 A Switch Controller and HP 3781 Switches

HP 59306A Relay Actuator

HP E3615A DC Power Supply for relay control

AML 0120L2403 Amplifier for DRG antennas

Harrison 6205 DC Power Supply

Two L2 m TEM Horn Antennas designed and built at the NIST Boulder Laboratories

One 36 cm TEM Horn Antenna designed and built at the NIST Boulder Laboratories

Three 3117 DRG antennas

NIST-developed "RADAR" Labview program used to perform time/frequency

transformations, time gating, and signal processing

NIST-developed "multical" Labview program used to perform multiband VNA

calibrations and to circumvent the 16001 frequency point limitation. This program

permits an arbitrarily large number of frequency points. In practice we typically use as many as 48003 points.

Certain commercial equipment, instruments, or materials are identified in this paper in order to adequately specify

the experimental procedure. Such identification does not imply recommendation or endorsement by the National

Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily

the best available for the purpose.

105

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