The Ohio State University 

I 

ANALYSIS OF AIRBORNE ANTENNA SYSTEMS 

USING GEOMETRICAL THEORY OF DIFFRACTION 

AND MOMENT METHOD COMPUTER CODES 

Richard G. Hartenstein, Jr. 

The Ohio State University 

ElectroScience Laboratory 

Department of Electrical Engineering 

Columbus, Ohio 43212 

Technical Report No. 716199-6 

Grant No. NSG 1498 

August 1985 

Nat i onal Aeronaut i cs and Space Admi ni st rat i on 

Langley Research Center 

Hampton , Vi rgi ni a 23665 

(HASA-CR-181248) AXALYSIS OF AIBBCBHE N87-27869 

ABTbYLA SPSlEtS USING GECHE2FlCAt 'IHECEY OF 

(Chi0 State Univ,) 76 F Auail: ElIS HC 

ACS/M€ A01 CSCL 20N 63/32 0093170 

C~ZP~~AZIICK iim~KEEW EETECE CCEECITEE ccms Unclas 
NOTICES 

When Government drawings, specifications, or other data are 

used for any purpose other than in connection with a definitely 

related Government procurement operation , the United States 

Government thereby incurs no responsibility nor any ob1 igation 

whatsoever, and the fact that the Government may have formulated, 

furnished, or in any way supplied the said drawings, specifications, 

or other data, is not to be regarded by implication or otherwise as 

in any manner licensing the holder or any other person or corporation, 

or conveying any rights or permission to manufacture, use, or sell 

any patented invention that may in any way be related thereto. 
REPORT DOCUMENTATION ,a- REPOW NOPAGE 

-. 

~ ~- 

2. B. Rocipent's Acccrsion No. 

Augw 1985 

L 

k hHormiry 0l.aniration Rmpt. No. 

----- 71 61 99-6- 

10. P&Ut/TaSk/WOr(r Unit NO. 

-_____ 

11. contract(C) or CrantG) No. 

(G) NSG 1498 

(GI 

__ __.-.--- 

13. Type of Rap~l( L Period Covered 

Tec hn i ca 1 

14. 

Computer codes have been developed to analyze antennas on aircrafts and 

in the presence of scatterers. The purpose of this study is to use these 

codes to develop accurate computer models of various aircraft and antenna 

systems. 

relay pod antenna, and traffic advisory antenna system installed on a Bell 

Long Ranger helicopter. Computer results are compared to measured ones with 

good agreement. These codes can be used in the design stage of an antenna 

system to determine the npt4m.m antenna lcc?ticz ~.nd SZVE v~:"~,ble ~SIII~ ana 

cost 1 y fl i ght -hours. 

The antenna systems analyzed are a P-3B L-Band antenna, an A-7E UHF 

C. COSATI FimldlGroup -- - ___ 1. Avr~llabllity Statmmont 21. No of Pales 

22. 

69 

Price 

Iln-sifiedUncl ass i f i ed 

10. Socurity CImsr (This Paw) 

(See A,?39.18) Sw fnitrwtiona on R .ii - OPTIONAL FORM 272 (4-77) 

(formerly NTIS-35) 

Dmpartmcnt of Commerca ii 

t 
TABLE OF CONTENTS 

LIST OF TABLES 

LIST OF FIGURES 

CHAPTER 

I INTRODUCTION 

I1 SUMMARY OF COMPUTER CODES 

A. INTRODUCTION 

B. AIRBORNE ANTENNA CODE 

C. BASIC SCATTERING CODE 

D. ELECTROMAGNETIC SURFACE PATCH CODE 

I11 P-3B L-BAND ANTENNA ANALYSIS 

IV A-7E UHF RELAY POD ANALYSIS 

V TRAFFIC ALERT AND COLLISION AVOIDANCE SYSTEM ANALYSIS 

VI SUMMARY AND CONCLUSIONS 

PAGE 

iv 

V 

1 

3 

3 

4 

8 

13 

16 

34 

48 

67 

REFERENCES 69 

iii 
LIST OF TABLES 

TABLE 

I CODES AND BASIC CAPABILITIES 

iv 

PAGE 

3 
LIST OF FIGURES 

FIGURE 

2.1 Various GTD terms calculated in the Airborne Antenna Code. 

2.2 Various GTD terms calculated in the Basic Scattering Code. 

2.3 Current modes calcualted in the Electromagnetic Surface 

Patch Code. 

3.1 P-36 line drawing. 

3.2 P-36 L-band antenna location. 

3.3 Measured P-38 azimuth L-band antenna radi ation pattern. 

3.4 P-36 computer model. 

3.5 P-36 azimuth L-band antenna radiation pattern. 

3.6 Monopole/beacon simulation geometry. 

3.7 ESP code input file for monopole/beacon simulation. 

3.8 ESP code output file for monopole/beacon simulation. 

3.9 P-36 azimuth L-band antenna radi at i on pattern . 3.10 Airborne antenna code input file for P-36 L-band antenna 

simul ati on . 3.11 P-3B elevation L-band antenna radiation pattern. 

3.12 P-36 elevation L-band antenna radiation pattern. 

4.1 A-7E line drawing. 

4.2 UHF relay pod. 

4.3 Measured A-7E UHF relay pod azimuth antenna radiation 

pattern. 

PAGE 

6 

10 

15 

17 

18 

19 

20 

21 

23 

24 

25 

27 

29 

32 

33 

35 

36 

37 

V 
FIGURE PAGE 

4.4 Antenna geometry for ESP code. 38 

4.5 ESP input file. 39 

4.6 Partial listing of ESP results. 41 

4.7 Airborne antenna code input file. 43 

4.8 Azimuth antenna radiation pattern of the monopole on the 

ellipsoid with the three rear monopole present. 44 

4.9 Computer model of A-7E UHF relay pod. 45 

4.10 Airborne antenna input file for goemetry of Figure 4.9. 46 

4.11 A-7E UHF relay pod azimuth antenna radiation pattern. 47 

5.1 AOA array geometry and location. 49 

5.2 AOA antenna performance hovering just above the ground. 51 

5.3 AOA performance of antenna on a groundplane. 52 

5.4 AOA antenna mounted near rotating cylinders. 53 

5.5 AOA performance of antenna near rotating cylinders. 54 

5.6 ESP input file for AOA antenna simulation. 56 

5.7 AOA antenna simulation geometry. 57 

5.8 Calculated AOA transfer function using the ESP code. 58 

5.9 

5.10 AOA antenna/cylinder geometry. 

Calculated AOA transfer function using the BSC. 59 

60 

5.11 Calculated AOA performance in the presence of cylinders. 61 

5.12 AOA antenna/rotor blade geometry. 63 

5.13 AOA antenna/blade BSC input file. 64 

5.14 Calculated AOA antenna performance in the presence of 

shaft and blades. 65 

5.15 Calculated AOA antenna performance 15 degrees above th? 

ai rcraft horizon . 66 

vi 
CHAPTER I 

INTRODUCTION 

The success of an airborne avionics system is critically dependent 

on its antenna system. The antenna system provides the vital link from 

the aircraft to the ground station or another aircraft. The antenna 

performance is affected by the aircraft structure, and its radiation 

pattern will depend on the antenna location. Many times an antenna will 

be arbitrarily placed on an aircraft only to find that after many costly 

hours of flight time that the antenna coverage is inadequate. 

Computer codes have been developed to analyze antennas on an 

aircraft or in the presence of scatterers. 

performance of an airborne antenna can be modelled during the 

development stage of the system, thus saving costly flight time. 

codes can also be used to help determine the causes of a problem in the 

radiation coverage of an existing system. 

Using these codes, the 

The 

The purpose of this study is to use these codes to develop accurate 

computer models of various aircraft. 

airborne antenna radiation patterns which are then compared to measured 

results. 

Antenna Code, the Basic Scattering Code and the Electromagnetic Surface 

Patch Code. These codes are described in Chapter 11. 

The codes are used to analyze 

Three codes are used throughout this study; the Airborne 

1 
An L-band antenna installed on a P-3B aircraft is analyzed in 

Chapter 111. 

analyzed in Chapter IV. 

Bell Long Ranger helicopter is analyzed in Chapter V. 

VI contains a summary and conclusions. 

A UHF relay pod antenna mounted on an A-7E aircraft is 

A traffic advisory antenna system installed on 

Finally, Chapter 

2 
CHAPTER I1 

SUMMARY OF COMPUTER CODES 

A. INTRODUCTION 

This chapter briefly describes the three computer codes used to 

generate the theoretical results of this study. The basi c capabi 1 i ti es 

of each code are summarized in Table I. The Airborne Antenna Code and 

TABLE I 

CODES AND BASIC CAPABILITIES 

CODE 

AIRBORNE 

ANTENNA 

CODE 

BASIC 

SCATTERING 

CODE 

CAPABILITIES 

Near- or far-field patterns of antennas 

mounted on a aircraft or similar structure. 

Used for slots, stubs or arrays mounted on 

an aircraft fuselage or convex surface. 

Far-field patterns of antennas in the presence 

of conducting scattering structures. Used, 

for example, for antennas on a ship, truck, 

aircraft, etc. The antennas can not be 

mounted on a curved surface which 

complements the Ai rborne Antenna Code. 

ELECTROMAGNETIC Far-field or scattering patterns of antennas 

SURFACE PATCH in the presence of wires and/or plates. Can 

CODE be used to determine mutual coupling effects. 

It is limited to structures that are small in 

terms of the wavelength. It complements the 

two previous codes in that they require 

electrically large structures. 

3 
Basic Scatteri ng Code were devel oped using the Uniform -Geometrical 

Theory of Diffaction. 

a moment method solution. Each code is described in some detail in the 

The Electromagnetic Surface Patch Code implements 

following sections. 

B. AIRBORNE ANTENNA CODE 

The Airborne Antenna )de is a Fortran compu ,er code devel oped 

to determine the radiation patterns of antennas mounted on a perfectly 

conducting composite ellipsoid in the presence of a set of finite, 

perfectly conducting flat plates. The analysis of the antenna radiation 

patterns is based on the Uniform Geometrical Theory of Diffraction (UTD) 

[1,2,3]. 

an ellipsoid and adding flat plates to simulate the wings, vertical 

stabilizer, and any other scattering structure that may be present. 

flat plates can be attached to the fuselage and/or to each other. 

This code is applied to aircraft by modelling the fuselage as 

The 

The Ai rborne Antenna Code can calculate arbitrary conical azimuthal 

and great-ci rcle elevation patterns. 

monopoles , up to a quarter-wave1 ength long, and arbi t rari ly oriented 

slot antennas. Mutual coupling effects, for example, between two 

monopoles can be accomplished with the help of a moment method solution. 

Image theory can be applied to model the monopoles as dipoles and to 

calculate the re1 ati ve current di stri bution. The re1 ati ve currents are 

then input into the Airborne Antenna Code as two sources. The radiation 

pattern from the second source is superimposed on the pattern of the 

primary source for the final pattern. 

The code can analyze radial 

4 
The Airborne Antenna Code calculates and superimposes a number of 

different fields for each given geometry. 

first-order and second-order fields. The fi rst-order fields are the 

source, reflected, and di ff racted terms ; whereas, the second-order 

f iel ds are the ref1 ected/refl ected, di f f racted/ref 1 ected, 

reflected/diffracted and diffracted/di ffracted ones. 

terms are illustrated in Figure 2.1. Any higher-order terms caused by 

additional interactions are assumed to be insignificant compared to the 

dominants ones and are not included in this code. The code calculates 

only the first-order terms unless the user specifies that the 

second-order terms are to be included. 

The total field is made up of 

These various 

Because UTD is a high frequency solution, only the most basic 

structural features of the aircraft need to be modeled. 

techniques are used to determine the field incident on and reflected by 

the various structures. 

are summed with the geometrical optics field at an observation point. 

To determine the field at a given observation point, a ray path must be 

determined. This path can be the direct source radiation, reflection 

from a plate, diffraction from an edge, or via a second-order mechanism 

trajectory. 

diffraction. 

structures. 

code proceeds to the next scatterer or observation point. If the path 

is not shadowed, the field is computed and added to the total field. 

Ray optical 

The diffracted fields are found using UTD and 

Each path is determined using the laws of reflection and 

It is then determined if the path is shadowed by any 

If the path is shadowed, the field is not computed, and the 

5 
SOURCE FIELD REFLECTED FIELD 

DIFFRACTED FIELD REFLECTED -REFLECTED 

FIELD 

Figure 2.1. Various GTD terms calculated in the Airborne Antenna Code. 

6 
REFLECTED - DIFFRACTED 

FIELD 

DIFFRACTED - REFLECTED 

FIELD 

DIFFRACTED -DIFFRACTED 

FIELD 

Figure 2.1. (continued). 

7 
This approach of shadowing rays might lead to various 

discontinuities in the resulting pattern, but the UTD solution is 

discontinuities. The UTD diffraction 

the discontinuities to produce a continuous 

designed to avoid these 

coef f i ci ent s smoot h out 

field. If discontinuit 

hi gher-order terms need 

es still exist, it usually ind cates that 

to be included . Because of the nature of the UTD analysis, there are limitations 

associated with the Airborne Antenna Code. 

at least a wavelength long. The radii of the ellipsoid should be at 

least a wavelength long, and each antenna should be at least a 

Each plate should have edges 

wavelength from any plate edge. 

reduced to a quarter wavelength for engineering purposes. 

In many cases, this limit can be 

The Airborne Antenna Code is user-oriented in that the user can run 

the code without knowing all the details of its operation. 

need only be familiar with the input, output, capabilities and 

limitations of the code so that he can properly interpret its results. 

More information on the use of the code can be found in reference [4]. 

The user 

C. BASIC SCATTERING CODE 

The Basic Scattering Code (BSC) is a Fortran IV computer code 

developed for the electromagnetic analysis of the radiation from 

antennas in the presence of complex structures. 

capability to predict far- and near-field radiation patterns as well as 

The code has the 

8 
coupling between antennas in the presence of scattering structures. 

addition, it can be used to determine potential radiation hazards. 

scattering structures are simulated by piecing together perfectly 

conducting flat plates, f i n i t e e l l i p t i c cylinders and finite thin 

diel ect ri c sl abs . The BSC can model a wide variety of antennas. A source can be 

In 

The 

specified as an electric or magnetic type. 

three different current distributions can be simulated. They are the 

uniform, sinusoidal, and standard TEOl mode (cavity back slot) current 

distributions. An aperture width can be specified or set equal to zero 

in the case of a dipole antenna. 

far-field of the antenna, the antenna can be represented by its pattern 

factor to SAVC cnrnpiitpr time; 

its array factor. 

the same manner that was described for the Airborne Antenna Code. 

For a given source type, 

If all scattering centers are in the 

S.im!'!zr!y, 2~ zpp=v -.I C~R be reprerented !y 

The BSC can account for mutual coupling effects in 

Like the Airborne Antenna Code, the analysis used is based nn the 

Uniform Geometrical Theory of Diffraction. Therefore, the solution is 

constructed in a similar manner. A ray path is determined by the laws 

of reflection and diffraction, and if no structure blocks the ray path, 

then the field is computed at the observation point. 

contai ns source, ref 1 ected, di ff racted , ref 1 ected/ref 1 ected, 

reflected/diffracted, and di ffracted/reflected terms. 

terms include interactions between two plates, between two cy1 i nders, 

and between a plate and cylinder. The various terms are illustrated in 

Figure 2.2. 

The total field 

The second-order 

9 
< so URCE % 1RCE 

SOURCE FIELD 

PLATE REFLECTED AND 

PLATE DIFFRACTED 

SOURCE 

SOURCE 

CY LlNDER REFLECTED AND 

CYLINDER DIFFRACTED 

CYLINDER END 

CAP REFLECTED 

Figure 2.2. Various GTD terms calculated in the Basic Scattering Code. 

10 
SOURCE 0 

CYLINDER END CAP 

RIM DIFFRACTED 

DOUBLY PLATE REFLECTED 

0 0 

\ 

SOURCE 

PLATE REFLECTED / PLATE DIFFRACTED / 

PLC\TE DIFFRACTED PLATE REFLECTED 

Figure 2.2. (continued). 

11 
PLATE REFLECTED / CY LlNDER CYLINDER REFLECTED/ 

REFLECTED AND PLATE PLATE REFLECTED 

REFLECTED / CYLINDER DIFFRACTED 

CYLINDER REFLECTED / 

PLATE DIFFRACTED 

PLATE DIFFRACTED / 

CYLINDER REFLECTED 

Figure 2.2. (continued). 

12 
Because this code is also derived from the UTD, its limitation are 

similar to those of the Airborne Antenna Code. 

edges at least a wavelength long. The length, and major and minor radii 

of each cylinder should be at least a wavelength. 

should be a wavelength from all edges. 

the source should be a wavelength from the slab and the incident field 

should not strike the slab too close to grazing. 

Each plate should have 

Each antenna element 

If a dielectric slab is used, 

The BSC is designed to be user-oriented. A user can run the code 

with a minimum amount of knowledge of how the code operates. However, 

the user should have a basic understanding of the input, output, 

capabilities, and limitations so he can properly define the input and 

interpret the results. Details on the use and operations of the BSC can 

4- +ha II---I rei - rp- .a 

luullu 111 ~IIc U~CI 3 L~J and Curie LOJ mdnuais. 

D. ELECTROMAGNETIC SURFACE PATCH CODE 

The Electromagnetic Surface Patch (ESP) Code is a Fortran IV 

computer code which applies a moment method solution to thin wires and 

rectangular plates. The purpose of the code is to model antennas with 

thin wires and any supporting structure or scatterer with flat plates 

and/or thin wires. 

attached to plates. 

or loaded by complex impedances. The code computes the currents induced 

on each wire and plate, the antennas input impedance and admittance, and 

its efficiency. 

Wires can be attached to plates, and plates can be 

The wires can be fed by arbitrary complex voltages 

The ESP code can compute the far-field antenna 

13 
radi ation patterns, both theta and phi pol ari zations. 

problem, the code can compute either the backscattered or bistatic 

scattered patterns for theta, phi and cross polarizations. The code 

produces either great -ci rcl e elevation or conical azimuthal patterns . Finally, the code can plot the wire/plate geometry as well as the 

calculated patterns. 

For a scattering 

To find the currents, each wire is divided into segments. Two 

adjacent wire segments make up a wire dipole mode. Similarly, each 

plate is divided into smaller rectangular segments. The rectangular 

segments are paired with adjacent rectangular segments to form surface 

patch dipole modes. 

2.3. The limitations associated with this code are mainly placed on the 

size of these segments. The length of each wire segment and the length 

and width of each plate segment should be limited to a quarter 

wavelength. 

should be at least a tenth of a wavelength from the edge of the plate. 

These two current modes are illustrated in Figure 

Also, any attachment point between a wire and a plate 

The ESP code is also a user-oriented code. The user need only 

define the wire and plate geometries, type of computation desired, and a 

few various other parameters to execute the program. Information on the 

use of the ESP code can be found in the user's manual C71. 

14 
9 

J -S 

t 

A 6 

iz 

0 A 

I3 

Figure 2.3. Current modes calcualted in the Electromagnetic Surface 

Patch Code. 

15 
CHAPTER I11 

P-3B L-BAND ANTENNA ANALYSIS 

In 

to simu 

four-tu 

this chapter the Airborne Antenna and the ESP Codes are app 

aircraft as illustrated in Figure 3.2. An omnidirec 

pattern in the azimuth plane is desired for this app 

as Figure 3.3 shows, the radiation pattern is fairly 

i ed 

ate a P-3B antenna problem. 

boprop anti -submarine ai rcraft equipped with numerous avi on c 

The P-3B, shown in Figure 3.1, is a 

systems. Among these is an L-band antenna located on the belly of the 

i onal radi at i on 

i cation . However, 

omni di recti onal 

except for the rear quadrant where the gain is reduced by 4-6 dB. The 

measured data shown in Figure 3.3 was taken in flight at the Naval Air 

Test Center (Patuxent River, Maryland). 

Using the Airborne Antenna Code, the L-band antenna was modelled as 

a quarter-wave monopole attached to an ellipsoid with 17 plates added to 

simulate the wings, horizontal stabi 1 i zers, and engine housings . Figure 

3.4 shows a diagram of the computer model. The results of this 

simulation are shown in Figure 3.5 with the measured results. The 

calculated radiation pattern is fairly omnidirectional with some 

constructive interference from the wings. 

pattern, the calculated pattern agrees very well in the front quadrant; 

Compared to the measured 

16 
Figure 3.1. P-3B line drawing. 

17 
L-BAND 

ANTENNA 

Figure 3.2.. P-3B L-band antenna location. 

18 
NOSE 

DB PLOT 

nnx WIND io w 

~OL: vmitrn 

SCRLE: IOW/DIV 

FREO= 1.070 CHZ 

LEFT 

HING RIGHT 

UlNF 

Figure 3.3. Measured P-3B azimuth L-band antenna radiation pattern. 

19 
U 

*\ANTENNA 

Figure 3.4. P-3B computer model . 

20 
LEFT 

WING 

NOSE 

OB PLOT 

IAX GRIN8 10 08 

SCALE: lOOB/DIV 

fREO= 1.070 GHZ 

roL: VERTIC~ 

TAIL 

Figure 3.5. P-3B azimuth L-band antenna radiation oattern. 

Calculated (using single souice) - 

- Measured 

RIGHT 

WING 

21 
however in the side quadrants, the patterns differ by as much as 2-3 dB 

and in the rear quadrant by as much as 6 dB. 

Closer examination of the P-3B belly shows a marker beacon located 

only 11 

ESP code 

problem, 

reradi at 

model 1 ed 

analyzes 

nches (less than one wavelength) behind the antenna. Here, the 

was used to model the antenna and beacon as a mutual coupling 

as if currents were being induced on the beacon and 

ng. 

as a dipole in free-space. Since the Airborne Antenna Code 

only radial monopoles or slot antennas, the beacon was modelled 

Using image theory in the ESP code, the monopole was 

as a shorted dipole in the ESP code. The source dipole was placed in 

front of the shorted dipole as shown in Figure 3.6. 

ESP code input file for this geometry is shown in Figure 3.7. 

3.8 shows the ESP code output file. 

complex current of -0.179-jO.155 on the shorted dipole compared to 

0.970-jO.242 on the source dipole. 

and mode 2 as indicated in the boxes on page 26. Mode 5 is the center 

mode of the shorted dipole and mode 2 is the center mode of the source 

dipole. 

A listing of the 

Figure 

The ESP code calculated a relative 

These value are taken from mode 5 

The current of mode 5 relative to mode 2 was then input into the 

Airborne Antenna Code as a second source, and the results were 

superimposed on the single source pattern . to the measured results in Figure 3.9. 

agreement throughout the pattern except in the rear quadrant where the 

difference was reduced to 1-3 dB. 

did well to simulate the coupling effect of the beacon, but not as well 

These results are compared 

This comparison shows very good 

It also shows that the computer model 

22 
Q SHORTED DIPOLE 

Q SOURCE DIPOLE 

Z RXIS VIEW 

X RXIS VIEW 

G WIRE MODES 

0 PLRTE MODES 

0 RTTFlCH. MODES 

G TOTFlL MODES 

H SCRLE = 0.37 

SOURCE 

DIPOLE 

SHORTED 

DIPOLE 

Y RXIS VIEW 

Figure 3.6. Monopole/beacon simulation geometry. 

23 
12 11 10 4 10 18 11 

0 0 1 000 

1 0 1 9000 

0 0 1 000 9000 000 

0 0 1 000 

1070.0 -1 0000025 

00 

00 

8 10 0 1 

0 00 0 00 -.O688 LDIEOaE 

0 00 0 00 0.0344 

0 00 0 00 0 00 

0 00 0 00 0,0344 

0 00 0 00 0.0688 

-.27% 0.0 -00688 LBEParJ 

-.2794 0.0 0,0344 

-.27% 0.0 0 00 

-,2794 0.0 0 .(I344 

-.27% 0.0 0 .O6 88 

1 2 

2 3 

3 4 

4 5 

6 7 

7 8 

8 9 

9 10 

3 0 (l.O,OOO) (ooo,ooo) 

Figure 3.7. ESP code input file for monopole/beacon simulation. 

24 
ER42.(MEIZ) = 1070.000 

wpNE(M) = 0.280 

WIRE RADIUS(#) = 0,0002500 

mTP= 10 

INTD= 18 

INT= 4 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

0 .ooooE+oo 

0 .oooowoo 

0 .oooowoo 

0.0000w00 

0.0000w00 

-0.27 94BOO 

-0.2794NOO 

-0.2794BOO 

-0.2794FitOO 

-0.2794EitOO 

0 .ooooFrl-oo 

0 .oooowoo 

0.0000w00 

0 .ooooEitoo 

0 .oooomoo 

0.0000m00 

0 .oooomoo 

0 .ooooEitoo 

0 .ooooEitoo 

o.oooowo 

-0.688OoO1 

-0.3440~-01 

0 .oooowo 

0.3440 E-01 

0.6880001 

-0,688OE01 

-0.3440 001 

0.0000~0 

0.3440 BO1 

0.6880001 

1 1 2 3 1 2 

2 2 3 4 2 3 

3 3 4 5 3 4 

4 6 7 8 5 6 

5 7 8 9 6 7 

6 8 9 10 7 8 

Figure 3.8. ESP code output file for monopole/beacon simulation. 

25 
2 

3 

4 

5 

7 

8 

9 

10 

0.34400001 

0.34400001 

0.34400001 

0.34400001 

0.34400001 

0.34400001 

0.34400001 

0.344OOEiOl 

0.10OOEtO1 0.0OOOWO -Is BY PI'. A OF SEGFENT 3 

1 0.755 0.0092660 -20 . 0.008728 -0.003112 

2 

3 0.7 55 0.0092660 -20 . 0.008728 -0.003 112 

4 0 017 4 0.0021398 -U9. -0.001616 -0.001403 

6 0.17 4 0,0021398 -U9. -0.001616 -0.001403 

1 - .ooo 0.01227 26 0.011894 -0.003026 f 

15 0,237 0.0029130 -13 9 . -0.002203 -0.0019O6 1, 

CHJWNTIW EDRRJN 1 GEC&E!IRY I= 7.69 SECICNE 

Figure 3.8. (continued). 

26 
LEFT 

UING 

OB PLOT 

nnx WING IO w 

SCALE: 1008/0IV 

fRLO= 1.070 CHZ 

?OL: VEnTIfRL 

RIGHT 

HING 

TAIL 

Figure 3.9. P-3B azimuth L-band antenna radiation pattern. 

Calculated (including 2nd source) - 

- Measured 

27 
at modelling the physical blockage. 

or by any object near a source, is a problem which could be further 

The blockage caused by the beacon, t 

investigated. The problem is that when the beacon was modelled by a 

plate in the Airborne Antenna Code, the code could not model any 

coupling effects. Also, the plate was too close to the source so the 

code calculated a large null in the rear quadrant. The beacon was 

therefore modelled as a shorted dipole so that the coupling effect could 

be included in the Ai rborne Antenna Code as a monopol e. The Ai rborne 

Antenna Code input file for this simulation is shown in Figure 3.10. 

The input file for the single source problem was the same except for the 

SP: and the second SG: and EX: commands. 

The elevation pattern for the P-3B L-band antenna was available, 

so it was also calculated. Results are presented in Figures 3.11 and 

3.12. Figure 3.11 shows the calculated single source results compared 

to the measured results and shows good agreement off the nose and a 

difference of 1-3 dB off the tail. The second source was included for 

Figure 3.12 which shows even better agreement . In the case of the P-3B L-band antenna, the Airborne Antenna Code 

and the ESP code proved to be valuable tools for simulating the antenna 

performance. In both azimuth and elevation patterns, agreement between 

measured and calculated results was very good. 

28 
m: INmcEEs 

3 

E: 

71 .Or71 00,548 e0 plU6 e0 

F 

om ,o e ,o e 

FC: TRu"E NaSE & TAlL 

FI F 

524 00 r-548 e 

EQ: EREQmcY 

lJoO70,loO 

S: S(XTR(EGEXH3'IRY 

00,o eo 

1 

oe,oe 

0 e rO e ,O e 12 076 13 

1erO. 

E: PORrwING 

4 IT 

34. ,-56 0 ,-4. 

0 e r-598 e ,-103 e 

0 ,-598. r-198. 

34. ,-56 e ,-215. 

E: ST~OARDWIIE 

4 IT 

34 r56 1-215 e 

0 r5 98 e ,498 - 

0 e ,598 p-103 

34 e 156 e ,-4 

E: PoKPTAn~ 

4 IT 

0 l ,-37 l ,524 l 

-14 e r-246 e ,506 l 

-14 e ,-246 l ,453 l 

0 e 1-37 e ,383 e 

E: STARBGIRD TAIL WIN 

4 rT 

0 e ,37 e r383 0 

-14 e ,246 e ,453 e 

-14 0,246 e ,506 e 

0.,37.,524. 

4 IT 

68*,16e,l72e 

76. ,16 J72e 

7 6 e ,-16 ,17 2 

68. ,-16 e ,172. 

F-3B PUSEUY;E GEDM3'IRY AT S!ClWICN 352 

EG: DOPRERBIMKPI;E 

Figure 3.10. Airborne antenna code input file for P-3B L-band antenna 

simul at i on l 

29 
Figure 3.10. (continued). 

30 
Figure 3.10. (continued). 

31 
NOSE 

09 PLOT 

nnx GAINS IO 06 

SCALE: toDB/OIV 

FBEOm 1.070 GHZ 

POL: VERTICAL 

Figure 3.11. P-3B elevation L-band antenna radiation pattern. 

- Calcualted (using single source) 

- Measured 

TAIL 

32 
NOSE 

OB PLOT 

MX tmw, io m 

ruL: VERTICAL 

SCALE: IODWDIV 

FREP= 1.070 CHZ 

Figure 3.12. P-3B elevation L-band antenna radiation pattern. 

Cal cul ated (i ncl udi ng second source) - 

- Measured 

TAIL 

33 
CHAPTER IV 

A-7E UHF RELAY POD ANALYSIS 

In this chapter a UHF relay pod installed on an A-7E is analyzed 

using the Airborne Antenna and ESP Codes. The A-7E is a subsonic 

single-seat tactical fighter as shown in Figure 4.1. 

15 foot equipment pod mounted on the outer port underwing pylon. 

The relay pod is a 

The 

pod is equipped with various receiver/transmitters and four UHF blade 

antennas. The pod and antenna locations are illustrated in Figure 4.2. 

An omnidirectional radiation pattern in the azimuth plane is desired for 

each antenna. 

Figlr1.e 4.3 shows the measured radiation pattern which has blockage and 

nulls throughout the pattern. 

at the Naval Air Test Center (Patuxent River, Maryland). 

The forward-most antenna is analyzed in this chapter. 

The measured results were taken in flight 

In the analysis of the A-7E UHF relay pod, the ESP code was first 

used to determine the currents induced on each antenna on the pod. The 

four antennas were modelled as half-wavelength dipoles in free-space, as 

shown in Figure 4.4, using the ESP input file shown in Figure 4.5. The 

forward-most antenna was excited with a unit amplitude source, and the 

three rear antennas were loaded with 50 ohms to simulate their 

connections to 50-ohm cables. A partial listing of the ESP code results 

34 
UHF R -LL nn Llll POD 

ELAY 

POD 

Figure 4.1. A-7E line drawing. 

35 
AFT-FWD 

Figure 4.2. UHF relay pod. 

36 
OB PLOT 

HOSE 

LEFT 

HING 

wax WIN: IO ~ll 

SCRLE: lOW/DIV 

FREO= O.SY6 CHZ 

POL: VERTICRL 

RIGHT 

MlNG 

Figure 4.3. Measured A-7E UHF relay pod azimuth antenna radiation 

pattern. 

37 
LOADED 

DIPOLES 

e SOURCE D1 POLE 

Z QXIS VIEW 

12 WIRE MODES 

0 PLRTE MODES 

0 RTTQCH. MODES 

12 TOTRL MODES 

1-1 SCFfLE = 0.89 A 

X RXIS VIEW 

SOURCE 

DIPOLE 

LOADED 

DIPOLES 

f 8 

Y FlXIS VIEW 

Figure 4.4. Antenna geometry for ESP code. 1 

38 
0 2 11 10 4 10 18 11 

0 0 1 0.0 

1 0 1 95.0 

0 0 1 0.0 OD0 0.0 

0 0 1 OD0 

346.1 -1 0.0005 

00 

00 

162001 

0.0 0.0 -0.2166 

0.0 0.0 -0.1083 

0.0 0.0 M.0000 

0.0 0.0 M.1083 

0.0 OD0 Me2166 

-1.2573 0.0 -0.2l66 

-1,2573 0.0 -0,1083 

-1.2573 0.0 M.0000 

-1.2573 0.0 M.1083 

-1.2573 0.0 M.2166 

-1.7653 0.0 -0.1083 

-1.7653 0.0 M.0000 

-1,7653 0.0 M.1083 

-1.7653 0.0 M.2166 

-2.2733 0.0 -0,2166 

-2.2733 0.0 tO.0000 

-2.2733 0.0 M.1083 

-2.2733 0.0 M.2166 

12 

23 

34 

45 

67 

78 

89 

9 10 

11 12 

12 13 

13 14 

14 15 

16 17 

17 18 

18 19 

19 20 

3 0 (1.0,O.O) (0.0,O.O) 

-1,7653 0.0 -0.2166 

-2,2733 0.0 -0,1083 

ITEST m0-E 

IMONOKlLE 49.5 INCHES 

1BEHIND TEST KNORXE 

ImORXE 69,5 INCHES 

IBEEIIND TEST MXORXE 

Figure 4.5. ESP input file. 

39 
is given in Figure 4.6. 

are indicated in the boxes on page 42. Modes 2, 5, 8 and 11 are the 

center modes of each dipole. The currents of modes 5, 8, and 11, 

relative to the current of mode 2 are input into the Airborne Antenna 

Code as addi t i onal sources . 

The relative currents induced on each dipole 

In the Airborne Antenna Code, the ellipsoid is used to model the 

pod, rather than the aircraft fuselage. 

any additional plates to determine the effects of the three rear 

antennas. 

shown in Figure 4.7, 

The code was first run without 

The Airborne Antenna Code input file for this geometry is 

and the calculated radiation pattern is shown in 

Figure 4.8. These results show minimal interference compared to the 

measured pattern. 

Eight plates were added to the ellipsoid to simulate the side of 

the aircraft, the wing, the horizontal stabilizer, and the pod mount. 

This geometry is illustrated in Figure 4.9, using the input file shown 

in Figure 4.10. 

0.6227 wavelengths which may be pushing the accuracy of the code, but 

the calculated pattern shown in Figure 4.11 does very well to show the 

lobing and blockage caused by the side of the aircraft. 

It should be noted that the diameter of the pod was 

This is a case where the Airborne Antenna Code could have been used 

in the early stages of development to show the interference caused by 

the aircraft. 

predict a fairly complicated radiation pattern, and even though the 

diameter of the ellipsoid was less than a wavelength, the code provided 

reasonably good results . 

The Airborne Antenna Code used a simple input geometry to 

40 
lNPUT DATA 

FREQ.(MHZ) - 346.100 

WAVE(M) - 0.867 

WIRE RM)IUS(M) - 0.0005000 

WIRE CONDUCTIVITY -1 e00 KGWS/M 

GEOMETRY FOR ME 0 RATES 

20 POINTS OF( ME WIRE 

1 x (1) 

1 O.OOOOE+OO 

2 O.OOOOE+OO 

3 O.OOOOE+OO 

4 O,OOOOE+OO 

5 O.OOOOE+OO 

6 -0.1257E+Ol 

7 -0.1257E+Ol 

8 -0.1257E+Ol 

9 -0.lZ57E+Ol 

10 -O.l2!57E+Ol 

11 -0.1765E+Ol 

1 2 -O.l765E+01 

13 -0.1765E+Ol 

14 -0.1765E+Ol 

15 -Om1765E+O1 

16 -0.2273E+01 

17 -0.2273E+01 

18 -0.2273E+01 

19 -0.2273E+01 

20 -0.2273E+Ol 

Y (I1 

O.OOOOE+OO 

O.OOOOEtO0 

0. OOOOEtOO 

0 .OOOOEtOO 

0 .OOOOEtOO 

0 .OOOOE+OO 

o.ooooEtoo 

0 .OOOOE+OO 

O.OOOOE+OO 

0 .OOOOE+OO 

O.OOOOE+OO 

0.0 OOOE+OO 

0 .OOOOE+OO 

0 .OOOOE+OO 

O.OOOOE+OO 

O.OOOOE+OO 

0. onnr?E+nQ 

O.OOOOE+M) 

0 .OOOOE+OO 

O.OOOOE+OO 

2 (11 

-0.21 66EtOO 

-0.1 083E+OO 

O.OOOOE+OO 

0.1 083E+OO 

0.21 66E+OO 

-0.2166E+OO 

-0.1 083E+OO 

0.1083E+OO 

0.2166E+00 

-0.21 66E+OO 

-0.1 083E+00 

0 .OOOOE+OO 

0.1 083E+00 

0.21 66E+OO 

-0.21 66E+00 

42 * 1 c!83E+0!? 

O.OOOOE+OO 

0.1 083E+OO 

0.21 66E+OO 

O.OOOOE+OO 

MODES ON THE WIRE STRUCTURE 

MAXlWM NUMBER OF MODFS AT WE !??!!E = 2 

NUMBER OF WIRE MODES = 12 

MINIWM NUMBER OF MODES ATONE mtm - 1 

I Il(1) 12(1) 13(1) 

1 1 2 3 

2 2 3 4 

3 3 4 5 

4 6 7 8 

5 7 8 9 

6 8 9 10 

7 11 12 13 

8 12 13 14 

9 13 14 15 

10 16 17 18 

11 17 18 19 

12 18 19 20 

JA( I 1 

1 

2 

3 

5 

6 

7 

9 

10 

11 

13 

14 

15 

JB(1) 

2 

3 

4 

6 

7 

8 

10 

11 

12 

14 

15 

16 

Figure 4.6. Partial listing of ESP results. 

41 
16 SEGMNTS (H THE WIRE 

J IA(J) IB(J1 D(J)(M) 

1 1 2 0.10830E+OO 

2 2 3 0.1 0830E+00 

3 3 4 0.10830E+00 

4 4 5 O.l0830E+OO 

5 6 7 0.1 0830E+OO 

6 7 8 0.1083OE+OO 

7 8 9 O.l0830E+OO 

8 9 10 O.l0830E+OO 

9 11 12 0.10830E+00 

10 12 13 0.10830E+00 

11 13 14 0.10830E+00 

12 14 15 O.l083OE+OO 

13 16 17 0.1 0830E+00 

14 17 1 8 0.1 0830E+00 

15 18 19 0.1083OE+OO 

16 19 20 0.1 0830E+00 

LISTING OF LOADS AND GENERATORS 

O.lOOOE+Ol O.OOOOE+OO VOLTS BY PT. A OF SEGMENT 3 

0.5000E+02 0.0000E+OO OHMS BY PT. A OF SEGMENT 7 

0.5000E+02 0.0000E+OO OHMS BY PT. A OF SEMNT 11 

0.5000E+02 O.OOOOE+OO OHMS BY PT. A OF SEGENT 15 

NWR = NUMBER OF WIRE MODES = 12 

NPLTM = NUMBER OF PLATE K)DES = 0 

NAT = NUMBER OF ATTACHFENT MODES = 0 

ANTENNA MODAL CURRENTS 

MODE EL MAG ABS MAG PHASE 111 COMPLEX I11 

1 0.765 0.0084501 -31. 0.00721 1 -0.004406 

2 1 .ooo 0.01 10438 -27. 0.009883 -0.004928 f 

3 0.765 0.008450 1 -31. 0.00721 1 -0.004406 

4 0.067 0.0007370 - 58. 0.000386 0.000628 L 

L 

5 0.091 o .ooi 0077 55. 0.000578 0.000825 1 

6 .067 

7 0.040 0.0004422 -168. -0.000433 -0.000090 

-0.000088 

0.0004422 -168. -0.000433 -0.000090 

0.000332 -0.000176 

0.0003757 -28. 0.0003 32 -0.000176 

8 0,055 0.0006058 -172. -0.000599 

9 0.040 

10 0.034 0.0003757 -28. 

12 0.034 

rt 1 0.047 0.00051 47 -31. 0.000440 -0.000268 -] 

INPUT ADMITTANCE(MH0S) 0.009883 J -0.004928 

INPUT IMF€DANCE(OHMS) - 81.034 J 40.406 

EFFICIENCY(F'ERC€NT) - 99.167 

Figure 4.6. (continued). 

42 
UN: UNm IN mcBEsI 

3 

PI;: FODGEXXE'IRY 

10.6,10.6A800 ,132.0 

T 

0. ,O . ,O . FQ: FREQUENCY 

1 ,O e346111 00 

SG: SWmGEXBE'IRY . 0.0,o.o 

1 

O0,O. 

0. YO 10 ,8 .53,3 

i.,O. 

BO: BINARYOIITAIT 

T 

ED: AZIM~P~PAT~~WN 

90 ,O r87 

0,360 rl 

T,O .e 

SP:SUPERIMEIXSE SCXJRCES 

Tr1.0 ,O 00 

M:EXEClJTE 

SG: 2NDSaJRm 

0 00 ,-49 05 

1 

O.,O. 

0 ,O PO r8 053 13 

0 0091 r82 00 

EX: EXECUTE 

9[;: 3RDsaJm 

O.O,69o5 

1 

0. ,O . 0 10 ,O. r8 .53,3 

OoO55,-145 00 

EX: E)(EaJTE 

SG: 41HsuJRa 

0 00 ,-89 05 

1 

o.,o. 

0 10 ,O r8 053 13 n naq a n u our1 ,-r.u 

EX: EXECUTE 

Figure 4.7. Airborne antenna code input file. 

43 
OB PLOT 

NOSE 

~. - raii VERTICAL 

RIGHT 

WING 

Figure 4.8. Azimuth antenna radiation pattern of the monopole on the 

ellipsoid with the three rear monopole present. 

44 
Fi gu re 

t 

UHF RELAY 

POD 

UHF RELAY 

POD 

4.9. Computer model of A-7E UHF relay pod. 

45 
UN:IN INCEES 

3 

FG:POD GEOMETRY 

10.6r10.6r48.0 ,132.0 

T 

0 . PO . 10 . FQ:FREQUENCY 

lr0.3461rloO 

SG:SOURCE GEOMETRY 

0 00 rO 00 

1 

0.10. 

0 10 10 r8 053r3 

ItrO. 

=:POD MOUNT 

4 rF 

-10 07 rO 05 r13 03 

-29.6 10 r-14 06 

-29.6 10 r-79.2 

-10 e7 rO 05 r-79.2 

PG :WING 

4 rF 

-17 04 r105 04 r-86 00 

-17 04,105 04 r-143 -8 

-36.8 r-135.6 r-92.8 

-36.8r-135.6r77.2 

PG:SIDE OF A/C 

4 rF 

-48 08 r-13 5 -0 r-26 5 -0 

-48.8 r-135.0 r255.0 

-49.8 ,-140 00 r255.0 

-49 08 r-140 00 r-265 00 

PG: 

4rF 

-48.8 r-135.0,-265.0 

-48.8 r-135.0 r255.0 

-37 08 r-13 2 .Or255 0 

-37 08 r-132.0 r-265.0 

PG: 

4 rF 

-37.8r-132oOr-265oO 

-37 08 r-132.0 r255.0 

0 -0 r-129 -0 r255 00 

0 -0,-129 -0 p-265 00 

PG: 

4rF 

0.0 1-129.0 r-265.0 

0 00,-129 00 r255 00 

12 00 r-13 0 00 r255 00 

12 00 ,-13 0 00 r-265 00 

PG: 

4rF 

12.0 r-13O.Or-265.0 

12.0 ,-130.0r255.0 

16 *0~-132oOt255.0 

16 00 r-13 2 00 r-26 5 00 

=:TAIL WING 

4 rF 

-7 2 r-13 5 6 r-17 5 0 

-7 02 ,-135 06 r-257 05 

-17 -4 r-17 00 r-280 -0 

-17 04 r-17 00 r-265.0 

B0:BINARY OUTPUT 

T 

PD:AZ IMUTH PLANE PATTERN 

90 10 r86. 

0,360 rl 

TrO 00 

SP:SUPERIMPOSE OTHER SOURCES 

TI1 00 rO -0 

EX: EXECUTE 

SG:HI SOURCE 

0 00 r-49 05 

1 

O.rO. 

0 PO rO ,8 053 r3 

0 0091 f82 00 

EX : EXECUTE 

SG:MID SOURCE 

0.01-69.5 

1 

0.10. 

0 10 10 18.53 r3 

0.055p-145.0 

EX:EXECUTE 

SG:LO SOURCE 

0 00 r-89 05 

1 

0.10. 

0 10 10 r8 .53,3 

0 0047 r-4 00 

EX : EXECUTE 

Figure 4.10. Airborne antenna input file for goemetry of Figure 4.9. 

46 
LEFT 

WING 

NOSE 

OB PLOT 

mx UIIWI io m 

roLr VERTICAL 

ScaLE: lQ#/OIV FREb O.sY6 GHZ 

TAIL 

Figure 4.11. A-7E UHF relay pod azimuth antenna radiation pattern. 

Calculated - 

- Measured 

RIGHT 

WING 

47 
CHAPTER V 

TRAFFIC ALERT AND COLLISION AVOIDANCE SYSTEM ANALYSIS 

The Basic Scattering Code (BSC) is used in this chapter to analyze 

the Traffic Alert and Collision Avoidance System.(TCAS) as installed on 

a Bell Long Ranger helicopter. The Long Ranger helicopter is a 

turbi ne-powered general -purpose seven-seat 1 i ght he1 i copter . TCAS is a 

traffic advisory system which informs the pilot of the angle-of-arrival 

(AOA) of an incoming signal, and therefore, the bearing in azimuth of 

another aircraft in the vicinity. The system utilizes a four-element 

array of quarter-wave monopoles, each positioned on the corners of a 

quarter-wavelength squale as shown in Figure 5.l(a). 

located on a flat area above the cockpit, in front of the rotor shaft as 

shown in Figure 5.l(b). 

through a network of hybrids. This network has two outputs; a sum and 

delta output. The output of the sum channel is the four input signals 

added in phase. The output of the delta channel is a sum of the four 

inputs with different phase shifts added to three of the inputs. The 

sum and delta output are, respectively given algebraically by 

The array is 

The outputs from each antenna are processed 

c=A+B+C+D 

and 

A = (D-B) + j(C-A) 

48 
FOREWARD 

ELEMENT D $ -i/ELEMENT A 

0 

PORT - x 

I 

SIDE 4 

STAR BOA R D 

SIDE 

to 

ELEMENT C 1 

ELEMENT 6 

AFT 

(0) ARRAY GEOMETRY 

FIBERGLASS 

EXHAUST 

I-. .._.I.. 

nun MIVICNNA 

HYDRAULIC 

RESERVOIR m 

0 6 10 2OM. 

(b) ARRAY LOCATION 

Figure 5.1. AOA array geometry and location. 

49 
where A, B, C and D represent the complex voltage levels of the four AOA 

antennas. The angle-of-arrival is then given by 

eA = 4A - $1 - 6 (5.3) 

where eA is the angle-of-arrival , 

is the phase of the delta channel and 6 is a constant offset angle 

determined through cal i bration . 

is the phase of the sum channel , @A 

Measured data has been taken on the TCAS antenna by the Lincoln 

Laboratory of the Massachusetts Institute of Technology. A signal was 

radiated toward the aircraft as it hovered just above the ground. 

the aircraft slowly rotated, the actual bearing of the transmitter and 

As 

the TCAS output heading were recorded. Results are shown in Figure 5.2. 

Measurements of the AOA antenna system were also taken in an 

anechoic chamber. The four monopoles were mounted on an aluminum 

circular ground plane, 4 feet in diameter, and rotated in the presence 

of a test signal. 

for this test condition is called the AOA transfer function. This 

transfer function, shown in Figure 5.3, indicates the phase difference 

between the sum and delta channels versus the incident bearing angle. 

The plot of the output phase versus actual bearing 

Three metal cylinders were placed near the antenna to simulate the 

rotor shaft. 

Figure 5.4, and the results of this configuration are shown in Figure 

5.5. 

The cylinders were mounted on a turntable as shown in 

TO simulate the problem on the computer, the ESP code was first 

used ot determine any coupling effects. As a backscatter the 

monopoles were modelled as dipoles in free-space, and the 

calculated the currents induced on each dipole as the ang 

50 

problem, 

ESP code 

e-of -arr Val 
180 

BO Q 

W 

P 

Q 

Y 

B 

a 

rn~ 

a 

a 

w 

E 

! 

3 

CD 

-90 

I 9' 

-180 

-180 -90 0 

MEAN = 40' 

SIGMA = 20' 

s., 

..I m -. 

BO 

~ 

* 180 

(LEFT) (NOSE) (RIGHT) 

ACTUAL BEARING (DEG.) 

Figure 5.2. AOA antenna performance hovering just above the ground. 

51 
I 

?’ 

O 

W 

n 

E 

k 

d 

a 

. 

w 

W 

v) 

Y 

a 

B 

s 

2 

0 

90 * 

0 

-00 

- 180 0 90 iao -180 -00 

(LEFT) (NOSE) (RIGHT) 

ACTUAL BEARING 

Figure 5.3. AOA performance of antenna on a groundplane. 

52 
POLAM. CPFTER 6HAFl 

AND TWO 1. DIAM. 

SlDE MS 4 MONOeOLTS 

/ TURNTABLE 

4 FT. DUM. 

QROIIM) PLANEFigure 5.4. AOA antenna mounted near rotating cylinders. 

53 
0" ELEVATION 

'SHADED BAND DENOTES 

VARIATION IN OUTPUT AS 

ROTOR MOVES 

-90 0 90 180 

ACTUAL BEARING (DEW 

Fi gure 5.5. AOA performance of antenna near rotating cy1 i nders . 

54 
of the incident field varied. The ESP input file and the geometry are 

shown in Figures 5.6 and 5.7, respectively. The calculated currents 

were then added using Equations (5.1) and (5.2) to determine the AOA 

transfer function. The results are shown in Figure 5.8 with an offset 

of 5.38 degrees included in the results. The results show very little 

i nterference from coup1 i ng . The BSC was also used to calculate the transfer function using the 

same geometry in Figure 5.7. 

calculated individually and the four fields were used in Equations (5.1) 

and (5.2) to produce a sum and delta output. The phase of these two 

fields were compared, and the difference is the transfer function shown 

in Figure 5.9. These results also show very little interference and are 

ticar ly luttiliicai to Figure 5.8. inis suggests that the smaii amount of 

fluctuation is because the geometry looks symmetrical from eight aspect 

angle. The offset here was 45 degrees, which will be constant in the 

following BSC applications. 

The field patterns of each dipole was 

1.. :Ae- VI . 

-. inree cyiinaers were added to the model as shown in Figure 5.10. 

The BSC calculated the fields for the geometry shown and with the 

cylinders rotated about the center cylinder's axis to simulate the 

anechoic chamber results. 

shown and with the cylinders rotated counter-clockwise 45, 90 and 135 

degrees. 

variation as the rotor shaft turns. This figure now shows the 

interference experienced in the anechoic chamber. 

Four calculations were made; the geometry 

The results are overlayed in Figure 5.11 to simulate the phase 

55 
12 11 0 0 4 10 18 11 

0 0 1 0.0 

0 0 1 0.0 

0 0 1 0.0 0.0 0.0 

1 0 1.0 90.0 

1090.0 -1 0.00025 

00 

00 

16 20 0 4 

0.0344 0 -0344 -.0688 

0 -0344 0.0344 -.0344 

0.0344 0.0344 0.0 

0 -03 44 0 -0344 + .03 44 

0 -03 44 0 -03 44 + -0688 

-.0344 0.0344 -.0688 

-.0344 0.0344 -.0344 

-.0344 0 -0344 +.0344 

-.0344 0.0344 +.0688 

-.0344 -.0344 -.0688 

-.0344 -.0344 -.0344 

-.0344 -.0344 0.0 

-.0344 -.0344 +.0344 

-.0344 -.0344 +.0688 

0 -0344 -.0344 -.0688 

0.0344 -.0344 -.0344 

0.0344 -.0344 0.0 

0.0344 -.0344 +.0344 

0.0344 -.0344 +.0688 

12 

23 

34 

45 

67 

78 

89 

9 10 

11 12 

12 13 

I3 14 

14 15 

16 17 

17 18 

18 19 

19 20 

3 0 (0.0,O.O) (50.0,O.Ol 

7 0 (0.0,O.O) (50.0,O.O) 

11 0 (0.0,O.O) (50.0,O.O) 

15 0 (0.0,O.O) (50.0,O.O) 

-00344 0.0344 0.0 

IM=NOECO;E A 

IMCNOFOLE B 

Ib'KNOmE C 

1b'KNOECO;E D 

Figure 5.6. ESP input file for AOA antenna simulation. 

56 
8 

< 

8 

b 

Z RXIS VIEW 

12 WIRE MODES 

0 PLFlTE MODES 

0 FITTRCH. MODES 

12 TOTRL MODES 

SCRLE = 0.20 ), I-----+ 

RXIS VIEW Y RXIS VIEW 

Figure 5.7. AOA antenna simulation geometry. 

57 
c) 

z 

M 

a 

a 

m 

W 

0 

W 

w 

a 

/ 

/ 

0 90 180 

ACTURL BERRING (DEGI 

Figure 5.8. Calculated AOA transfer function using the ESP code. 

58 
-180 B -90 0 90 180 

ACTUAL BEARING IDEGI 

Figure 5.9. Calculated AOA transfer function using the BSC. 

59 
00. THREE CYLINDERS 

4 MONOPOLE ARRAY 0. 

am 

Z-AXIS 

VIEW 

THREE 

CYLINDERS 

X-AXIS 

VIEW 

Y-AXIS 

VIEW 

Fi gure 5.10. AOA antenna/cyl i nder geometry . 

60 
A 

0 

w 

0 

L 

c( 

a 

a 

m 

W 

ta 

Figure 5.11. Calculated AOA performance in the presence of cylinders. 

61 
Since the spacing of the cylinders was small compared to the 

wavelength, the three cylinders were replaced with a plate and rotor 

blades were added to the computer model to determine their effects. 

geometry is shown in Figure 5.12 using the BSC input file in Figure 

5.13. The calculations were taken with the rotor shaft and blades 

rotated every 30 degrees. The results are overlayed in Figure 5.14. 

The 

Finally, the AOA performance was calculated at an elevation angle 

of 15 degrees above the horizon, so the signal would pass through the 

blades. The fields were calculated using the geometry shown in Figure 

5.12 and with the rotor shaft and blades rotated every 30 degrees. The 

results are overlayed in Figure 5.15, and are similar to the previous 

ones . 

The BSC provided a fairly accurate model of the AOA antenna system. 

It showed that without any scatterers, the system should be accurate 

within about 3 degrees (plus an offset). The model also showed that in 

the presence of scatterers, an undesireable amount of error is 

introduced. Finally, the model did well to simulated the results taken 

on the ai rcraft and in the anechoic chamber. 

62 
/BLADES 

I I r/ 

1 

2 -AXIS VIEW 

7 BLADES 37' \ 

I 

X-AXIS VIEW 

Figure 5.12. AOA antenna/rotor blade geometry. 

40" k 

Y -AX IS 'VI EW 

63 
a: 

Qil: TQS KIUR DIKLE ARRAY 

a: 

m: mmCY tG€m 

1.090 

PD: AZIMJ~ mmm 

0 . 10 . 190 . 10 

TF90 -0 

0,360 ,l 

us: SaJRa urn 

0 

UN: GEDWTRY 

3 

SG: DIPQLE A 

1.35,1.3510.0 

0. rO . 190 . 10 . -21 05 10 

1.10. 

a: 

Qil: RCXCM'E ROR SHAFT & BLADES 

a: 

RT: 

-40 . ,O ,O . 0. 10 . 190 . 1150 00 

E: PLm 

4 10 

3 00 10 00 1-3 9 

-3 00 10 00 1-3 9 . -3 00 10 00 1+3 9 . 3 00 10 00 r+3 9 . E: BLADES 

6 10 

6 00 1222.0 138 

4.010.0138. 

6 00 1-222.0 ,380 

6.,-222.138. 

-4.0 10 00 138. 

-6.p222.38. 

LP: LINE FRm 

T 

IQ: EXEKU'JE 

NS: 

KT: ORDGINALO%UX;IN 

0 . 10 . 10 . 0 . 10 . f90 . rO . -1 035 11 035 rO 00 

0.10 . 190 . 10 . -21.510. 

1.10. 

2Q: E)(ECUTE 

NS: 

9G: DIPaLEC 

9G: DIHZEB 

-1 03 5 11 03 5 10 

0 . 10 . 190 . ,o. -21 05 10 

1.10. 

IQ: EXEKUTE 

NS: 

SG: DIHZED 

-1.35r1.35,O. 

0 . 10 . 190 . 10 . -2r.510. 

1.10. 

IQ: EXE(LITE 

EN: END 

Figure 5.13. AOA antenna/blade BSC input file. 

64 
CL 

0 

W 

E! 

0 

z 

U 

a 

a 

m 

W 

0 

W + 

J 

3 

u 

J 

u 

a 

a 

0 

I I 

I 0 90 1; 0 

ACTUAL BERRING (DEGl 

Figure 5.14. Calculated AOA antenna performance in the presence of 

shaft and blades. 

65 
A 

0 

w 

E 

0 

2 

m 

a 

a 

m 

W 

0 

w 

IJ 

3 

u 

-I 

u 

a 

a 

180 

ACTUAL BEARING IDEGI 

Figure 5.15. Calculated AOA antenna performance 15 degrees above the 

ai rcraft horizon . 

66 
CHAPTER VI 

SUMMARY AND CONCLUSIONS 

The purpose of this study was to develop accurate computer models 

of various aircraft and antenna systems. 

utilized; the Airborne Antenna Code, the Basic Scattering Code, and the 

Electromagnetic Surface Patch Code. 

Three computer codes were 

An L-band antenna installed on a P-3B aircraft was analyzed using 

the Airborne Antenna Code. The aircraft fuselage was modelled as an 

ellipsoid with plates added to model the wings, horizontal stabilizers 

and engine housings. The ESP code was also used in the model to 

determine the current induced on a marker beacon located behind the 

antenna. 

second source. 

results. 

This current was input into the Airborne Antenna Code as a 

Results showed very good agreement with measured 

A UHF relay pod on an A-7E aircraft was also analyzed using the 

Airborne Antenna Code. 

and the wing, pod mount, horizontal stabilizer and the side of the 

aircraft were modelled by plates. The ESP code was again used because 

three other antennas were located on the pod. The currents induced on 

the three antennas were calculated using the ESP code and input into the 

This time the pod was modelled as an ellipsoid 

67 
Airborne Atnenna Code. 

wavelength which may be pushing the accuracy of the code, but the 

calcualted results did well to show the lobing and blockage caused by 

the side of the aircraft. 

The diameter of the ellipsoid was less than a 

Finally, a traffic advisory system installed on a Bell Long Ranger 

he1 i copter was analyzed using the Basic Scatteri ng Code. Cy1 i nders were 

used to model the rotor shaft which was located behind a four-element 

array of momopole antennas. Later, the cylinders were replaced by a 

plate and additional plates were added to simulate the rotor blades. 

The array was connected to a hybrid network which determined the 

angle-of-arrival of an incoming signal. 

the angle-of-arrival, and the results were compared to measured results. 

The BSC provided a fairly accurate model of the AOA antenna system and 

did well to shown the error introduced by the rotor shaft and blades. 

The BSC was used to calculate 

The Ai rborne Antenna Code, Basic Scattering Code and 

Electromagnetic Surface Patch Code provide powerful tools for 

predicting the performance of airborne antenna systems. 

be very useful in the design stage of an antennas system to determine 

the optimum antenna location. 

could be saved by first using these codes. 

These codes can 

Valuable time and costly flight-hours 

68 
REFERENCES 

113 R.G. Kouyoumjian and P.H. Pathak, "A Uniform Geometrical Theory of 

Diffraction for an Edge in a Perfectly-Conducting Surface," Proc. 

IEEE, Vol . 62, pp. 1448-1461, November 1974, 

[e] R.G. Kouyoumjian, P.H. Pathak and W.D. Burnside, "A Uniform GTD 

for the Diffraction by Edges, Vertices and Convex Surfaces,' 

Theoretical Methods for Determi ni ng the Interaction of 

Electromagnetic Waves with Structures, Edited by J.K. Skwi rynski , Si jthoff, and Nordhoff, Netherlands, 1978. 

[3] P.H. Pathak, N. Wang, W.D. Burnside and R.G. Kouyoumjian, "A 

Uniform GTD Solution for the Radiation from Sources on a Convex 

Surface," IEEE Trans. on Antenna and Propagation, Vol . AP-29, No. 

4, pp. 609-622, July 1981. 

[4] Hsin-Hsien Chung and W.D. Burnside, "General 3D Airborne Antenna 

Radiation Pattern Code User's Manual ," Technical Report 711679-10, 

The Ohio State University ElectroScience Laboratory, Department of 

Electrical Engi neeri ng, prepared under Contract No. 

F30602-79-C-0068 for Rome Air Development Center, July 1982. 

C51 R.J. Marhefka and W.D. Burnside, "Numerical Electromagnetic 

Code-Basic Scattering Code (Version 2), Part I: User's Manual", 

Technical Report 712242-14, The Ohio State University , Elect roSci ence Laboratory, Department of Elect ri cal Engi neeri ng , prepared under Contract N00123-79-C-1469 for Naval Regional 

Cont racti ng Off i ce, December 1982. 

C6l R.J. Marhefka, "Numerical Electromagnetic Code-Basic Scattering 

Code (Version 2), Part 11: Code Manual," Technical Report 

712242-15, The Ohio State university, ElectroScience Laboratory, 

Department of Electrical Engineeri ng , prepared under contract 

N00123-79-C-1469 for Naval Regi onal Contract i ng Off i ce, December 

1982 . C71 E.H. Newman, "A User's Manual for: Electromagnetic Surface Patch 

Code (ESP)" Technical Report 713402-1, The Ohio State University, 

ElectroScience Laboratory, Department of Electrical Engineering, 

prepared under Grant No . DAAG-29-81-K-0020 for U.S. Army Research 

Office, July 1981. 

69