/ ,: _/

/ / /

J

UNIVERSITY

,.)/<) d S 0

TARGET SIGNATURE MODELING AND

BISTATIC SCATTERING MEASUREMENT STUDIES

W. D. Burnside, T. H. Lee, R. Rojas

[{. J. Marhefka,D. Bensman

The Ohio State University

ElectroScienceLaboratory

Deportmentof ElectricalEngineering

Columbut,Ohio 43212

Semi-Annual Report

721432-1, 721446-1, 721447-1, and 721711-1

('rant No. NAG2-542

Seplember 1988 - February 1989

NASA - Ames Research (.;enter

M()ffett Field, CA 9,1(135

(NASA-CR-185%34) TARGET SIGNATURE MODELING

AND BISTATIC SCATTERIItG MEASUBEMENT STUDIES

Semiannual Report, Sep. 1988 - E'eb. 1989

C0hio State Uniw.] 56 p C SCL 171

G3/32

N89-27870

Unclas

0218050 -
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 obligation

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.
BO27g-lO1

REPORT DOCUMENTATION 1. REPORT NO.

PAGE

4. Title and Subtitle

Target Signature Modeling and Bistatic Scattering

Measurement Studies

2. 3. Recipient's Accession No.

5. Report Date

Sept. 1988- Feb. 1989

_°

7. Author(s) W.D. Burnside, T.H. Lee, R. Rajas s. Performing Org. Xept. No.

R.J. Marhefka, D. Bensman 721432-1, T-21446-1, 721447-1, 721711-1

9. Performing Organisation Name and Address 10. Project/Task/Work Unit No.

The Ohio State University

ElectroScience Laboratory

1320 Kinnear Road

Columbus, OH 43212

12. Sponsoring Organisation Name and Address

University Affairs Branch, NASA - Ames Research Center

M/S 241-25

Moffett Field, CA 94035

11. Contract(C) or Grant(G) No.

(c)

(G) NAG2-542

13. Report Type/Period Covered

Semi-Annual Report

14.

15. Supplementary Notes

16. Abstract (Limit: 200 words)

This is a senti-annual report that sunmaarized the work done on Grant No. NAG2-542 during the

period 1 September 1988 to 28 February 1989. There are four areas of study to be sununarized: 1)

Bistatic scattering measurement studies for a compact range. 2) Target signature modeling for test

and evalution hardware in the loop situations. 3) Aircraft code modification study. 4) SATCOM

antenna studies on aircraft.

17. Document Analysis a. Descriptors

b. Identifiers/Open-Ended Terms

c. COSATI Field/Group

18. Availability Statement

A. Approved for public release;

Distribution is unlimited.

19. Security Class (This Report)

Unclassified

20. Security Class (This Page)

Unclassified

21. No. of Pages

55

22. Price

(See ANSI-Z39.18) See Instructions on ReverJe OPTIONAL FORM 31'3 (4-77

Department of Commerce
Blank Page

ii
Contents

List of Figures v

1 Introduction 1

2 Bistatic Measurement Study 2

2.1 Introduction ........................... 2

2.2 Approach ............................ 3

2.3 Results .............................. 5

2.4 Summary and Conclusions ................... 18

2.5 Acknowledgement ........................ 18

3 Target Signature Study 19

3.1 Introduction ........................... 19

3.2 Scattering Code Overview ................... 19

3.3 Storage Requirements ..................... 21

3.4 Further Work .......................... 23

4

5

Aircraft Code Study 24

4.1 Introduction ........................... 24

4.2 Smoothing Algorithm ..................... 24

4.3 Patch Antenna ......................... 25

4.4 PC Study ............................ 25

SATCOM Antenna Study 26

5.1 Introduction ........................... 26

5.2 Batwing Antenna ........................ 26

5.3 Model Validation ........................ 27

5.4 Further Work .......................... 27

nl

PRECEDiI_G PAGE BLANK NOT FILMED

n(_.,,,L____JNIENI'IONALLr _ILAI_
Bibliography 47

iv
List of Figures

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

2.10

2.11

2.12

2.13

Top view of bistatic scattering measurement in a compact

range. (Transmit and receive compact ranges.) .......

Top view of bistatic scattering measurement in a compact

range. (Transmit compact range and receive horn antenna.)

Bistatic scattering measurement of spheres in OSU compact

range ..............................

Positions of the 6" and 3.25" spheres for the bistatic scattering measurement ........................

Surface plot of the images for the 6" and 3.25" spheres obtained from the bistatic scattered fields ...........

Contour plot of the images for the 6" and 3.25" spheres obtained from the bistatic scattered fields ...........

Surface plot of the images for the 6" and 3.25" spheres obtained from the backscattered fields .............

Contour plot of the images for the 6" and 3.25" spheres obtained from the backscattered fields .............

Positions of the 6", 3.25" and 1" spheres for the bistatic

scattering measurement ....................

Surface plot of the images for the 6", 3.25" and 1" spheres

obtained from the bistatic scattered fields ..........

Contour plot of the images for the 6", 3.25" and 1" spheres

obtained from the bistatic scattered fields ..........

Surface plot of the images for the 6", 3.25" and 1" spheres

obtained from the backscattered fields ............

Contour plot of the images for the 6", 3.25" and 1" spheres

obtained from the backscattered fields ............

4

5

6

8

9

10

11

12

13

14

15

16

17

v
5.10

5.11

5.12

5.13

5.1 Batwing airborne UHF satellite communication antenna of

Dorne and Magolin ....................... 28

5.2 Calculated Batwing right hand circular polarized antenna

pattern at 244 MHz on an 8' ground plane using the NECBSC ............................... 29

5.3 Measured Batwing right hand circular polarized antenna pattern at 244 MHz on an 8' ground plane. (Pattern supplied

by Dome and Margolin.) ................... 30

5.4 Calculated Batwing right hand circular polarized antenna

pattern at 300 MHz on an infinite ground plane using the

NEC-BSC ............................ 31

5.5 Calculated Batwing right hand circular polarized antenna

pattern at 300 MHz on an infinite ground plane using the

ESP code ............................ 32

5.6 Geometry of the model of the P3C aircraft code used in the

NEC-BSC showing the location of the antenna ....... 33

5.7 UTD calculated roll plane pattern for batwing antenna on a

P3C for right hand circular polarization in the roll plane at

300 MHz ............................ 34

5.8 Boeing's measured roll plane pattern for batwing antenna on

a P3C for right hand circular polarization in the roll plane

at 300 MHz .............. : ............ 35

5.9 UTD calculated azimuth plane pattern for batwing antenna

on a P3C for right hand circular polarization in the roll plane

at 300 MHz ........................... 36

Boeing's measured azimuth plane pattern for batwing antenna on a P3C for right hand circular polarization in the

roll plane at 300 MHz ..................... 37

UTD calculated elevation plane pattern for batwing antenna

on a P3C for right hand circular polarization in the roll plane

at 300 MHz ........................... 38

Boeing's measured elevation plane pattern for batwing antenna on a P3C for right hand circular polarization in the

roll plane at 300 MHz ..................... 39

UTD calculated roll plane pattern for batwing antenna on a

P3C for left hand circular polarization in the roll plane at

300 MHz ............................ 40

vi
5.14

5.15

5.16

5.17

5.18

Boeing's measured roll plane pattern for batwing antenna on

a P3C for left hand circular polarization in the roll plane at

300 MHz ............................

UTD calculated azimuth plane pattern for batwing antenna

on a P3C for left hand circular polarization in the roll plane

at 300 MHz ...........................

Boeing's measured azimuth plane pattern for batwing antenna on a P3C for left hand circular polarization in the roll

plane at 300 MHz .......................

UTD calculated elevation plane pattern for batwing antenna

on a P3C for left hand circular polarization in the roll plane

at 300 MHz ...........................

Boeing's measured elevation plane pattern for batwing antenna on a P3C for left hand circular polarization in the roll

plane at 300 MHz .......................

41

42

43

44

45

vii

Chapter 1

Introduction

This is an semi-annual report that summarizes the work done on Grant

No. NAG2-542 during the period 1 September 1988 to 28 February 1989.

There are four areas of study to be summarized:

. Bistatic scattering measurement studies for a compact range. This

work is being conducted by T. H. Lee and W. D. Burnside under Ohio

State University project number 721432.

,

.

Target signature modeling for test and evaluation hardware in the

loop situations. This work is being conducted by R. J. Marhefka

under Ohio State University project number 721446.

Aircraft and missile code modification studies. This work is being

conducted by R. Rojas under Ohio State University project number

721447.

. SATCOM antenna studies on aircraft. This work is being conducted

by R. J. Marhefka and D. Bensman under Ohio State University

project number 721711.

An overview of the research accomplished is described in the separate

chapters below.
Chapter 2

Bistatic Measurement Study

This is a brief review of the portion of the grant pertaining to bistatic

measurement study over the period September 1, 1988 to February

28, 1989. The summary described here is to be presented at the

AMTA meeting in August entitled "Imaging Processing of Bistatic

Scattered Fields Obtained in a Compact Range," by T. H. Lee and

W. D. Burnside.

2.1 Introduction

It is very important in diagnostic radar applications that one can

accurately distinguish various dominant scattering terms associated

with specific features on a target based on its scattering characteristics. Normally, the backscattered fields of the target are collected and

processed to obtain the down-range and cross-range scattering centers [1]. The backscattered fields can be collected either in a far-field

range or in a compact range. On the other hand, bistatic scattering

of a target has been getting a lot of attention recently. Consequently,

the determination of the dominant scattering centers using bistatic

scattered fields of a target is also very important.

In this report, a general image processing technique which utilizes

the bistatic scattered fields collected in a compact range is presented.

The transmitting and receiving antennas can be either two compact

2
ranges or one compact range and a horn antenna. The compact range

reflector can be either focussed or defocussed so that a near field situation can be simulated. The bistatic scattered fields are collected

as a function of frequency and the angle of rotation of the target.

Then, cross-range and down-range images of the target are determined. Experimental results are presented to validate this image

processing technique.

2.2 Approach

Conventional image processing of backscattered fields for a target

uses efficient algorithms such as a Fast Fourier Transform to determine the target image. This requires that the antenna be located a

large distance from the target [2] and that the target be rotated only

through small angles. However, these assumptions are not necessary

in general. For example, it has been shown that one can use defocussed compact range system to simulate a near field illumination of

the target [3]. In order to determine the image of the target from

the collected backscattered fields, a more general image processing

approach has to be implemented [2,3]. The key factor in general image processing is the knowledge of the phase history of the scattering

center associated with a given illumination. The backscattered fields,

which are normally collected as functions of frequency and target angular rotation, are processed by multiplying the received response by

a phase factor which is the complex conjugate of the phase associated

with the path length from the source of illumination to the potential

scattering center and then to the receiver. This data is then summed

to determine the image response. Using this approach, the response

at a true scattering center is more enhanced than those which are not

true scattering centers.

The same processing technique can be used to determine the scattering centers of a target from its bistatic scattered fields. Consider the

bistatic scattering measurement configuration shown in Figures 2.1

and 2.2. The system can be either two compact ranges as shown in

Figure 2.1 or one compact range and one horn antenna (or other an-
PRIMARY

ZONE _ TARGET

ZONE

SECONDARY "

COMPACT RANGE _ ')

Figure 2.1: Top view of bistatic scattering measurement in a compact range.

(Transmit and receive compact ranges.)

tennas) as shown in Figure 2.2. For a target located in the test zone,

the bistatic scattered fields, E°(.f,_,O,_), are collected for a series of

frequencies, f,,, and a series of angles of rotation, 0,_. The image of

the target, I(7.,%) , is determined by

vn----M n--N

i(.y.,,.)= (2.1)

rrt=l rt=l

where

_(%,%,f,,,0,) = 27rf'n(s 1 + s,). (2.2)

c

In Equations 2.1 and 2.2, sl and s2 are the path lengths from the

transmitting antenna to the point (%,%) on the image plane and

from (7-,%) to the receiving antenna, f,,, is the m'th frequency and 0,

is the n'th angle of rotation. It is apparent that if the point, (%,%),

is a scattering center, the bistatic scattered field, E°, should have a

phase factor, e -j2¢, which is the complex conjugate of the phase factor

shown in Equation 2.1. Consequently, the resulting image, I(7,,%),

will peak up at the image location. On the other hand, if (Tffi,Tz)
PRIMARY

COMP A CT RANGE TARGET

ZONE _ IARGET

CENTER OF

TARGET ZONE

Figure 2.2: Top _iew of bistatic scattering measurement in a compact range.

(Transmit compact range and receive horn antenna.)

is not a scattering center, the image will not be as significant. For

each point on the image plane, one can determine the path lengths,

sl and s_ , and use Equation 2.1 to determine the complete image of

the target. The frequency behaviour of the bistatic scattered fields

provides the down range information; whereas,the angle responses

provide the cross range location of the scattering centers.

Since the image processing method given by Equation 2.1 only requires the knowledge of the path lengths, sl and s2, the compact

range reflector can be a defocussed system so that one can simulate a

near field situation. However, one has to determine the ray trajectory

in order to find the point of reflection on the compact range reflector.

2.3 Results

A set of bistatic measurement has been performed at The Ohio State

University ElectroScience Laboratory compact range facility. The

configuration of the measurement is shown in Figure 2.3. Spheres
PRIMARY

COMPACT RANGE SPHERES

STYROFOAM N I I

PLATFORM

--144"----_

F 288"

SECONDARYy

ANTENNA

(7)

i

Figure 2.3: Bistatic scattering measurement of spheres in OSU compact

range.

6
with diameters of 6", 3.25" and 1" were placed on a styrofoam platform which was then positioned at the center of the target zone. The

compact range reflector has a focal distance of 12' and the center of

the target zone is at 24' from the vertex of the reflector with a height

of 60". The second antenna for the bistatic scattering measurement

was located 193" from the center of the target zone in the direction

perpendicular to the axis of the compact range reflector. The height

of this antenna was the same as the center of the target zone. Several

combinations of spheres were used as the target for these measurements. The target was rotated from -30 ° to 30 ° with respect to the

axis of the compact range reflector, and bistatic scattered fields were

collected uniformly across the 2 to 18 GHz frequency band. Since

the compact range has a capability of simultaneously collecting data

from 2 different channels, the backscattered fields were also collected

at the same time. Two image processing results based on these measurements are presented in this section.

The first combination of the spheres used as the target is shown in

Figure 2.4. Note that a 6" sphere is located at X and a 3.25" sphere

at N. The image of this target obtained by processing the bistatic

scattered fields is shown in Figures 2.5 and 2.6. The backscattered

fields can also be processed by using Equation 2.1 by simply assuming

that the two compact range reflectors shown in Figure 2.1 are colocated. The resulting image is shown in Figures 2.7 and 2.8. From

Figure 2.4, the center of the 6" sphere is at 7,=8.485" and %=0.0"

and the center of the 3.25" sphere is at 7,=-4.243" and 7,=-12.728".

However, the scattering centers will not be at these locations because

one has to take the radius of the spheres into account. The images

shown in Figures 2.5 to 2.8 clearly indicate the scattering centers of

this target. One also notices the movement of the sphere scattering

centers from these images. This is because the target was rotated

with respect to the center of the target zone which results in the

movement of the scattering centers in that the sphere reflection point

moves with the angles of incidence. In addition to these scattering

centers, there are other peak responses that appear in these images.

These are secondary scattering centers caused by the creeping waves

associated with each sphere.
TO

ANTENNA

COMPACT

TO

RANGE REFLECTOR

7x

Figure 2.4: Positions of the 6" and 3.25" spheres for the bistatic scattering

measurement.
.,_6 ,°

Figure 2.5: Surface plot of the images for the 6" and 3.25" spheres obtained

from the bistatic scattered fields.

9
0-18. O0 -12. O0 -6. 000 O. 000 8. 000 12. O0 18. 00_

o ,,, I,,, I,,, I,,, I, ,, I , , , .a

0

0

0

o

d0

8-

N d

8

0

! -

oo

7

H

0.004844 o.o_

0.000L09786

O. 00_'03212

O. o00L'os81 l

6" SPHERE

/

0

3.25" SPHERE o oobo_ss_ o.ooA.ss0

G

.°

0

0

-0

8

P

-0

0

0

I

.m

-0

8

!

0

0

0 I

0

!1111111111111111111111 0

LIB. 00 -t2.00 -8.000 0.000 8.000 I2._ 18.0@

X

Figure 2.6: Contour plot of the images for the 6" and 3.25" spheres obtained

from the bistatic scattered fields•

10
Figure 2.7: Surface plot of the images for the 6" and 3.25" spheres obtained

from the backscattered fields.

11
0" ! O. O0 -12. O0 -_. 000 O. 000 lB. 000 12. O0 18. 00..

o , , , I , , , I , , , I , , , I , , , I , , , .=

,_ oo

d

0

0

0--

0

. d.

0 i

0

0

I

0

0

• O. OOH7772

0_3S3

O. 00/"_ 7 SS

6" SPHERE

/

O. 000L0393_.. O0_l149 /

/

0.000L07564

o.o_3tq-oo_s_s2

LIB. 00

O. 00_3784

O(_g O. 0001"0594 3

oo$

0

0

J

3.25" SPHERE

''' I''' i''' I' '' I' ' ' I ' ' '

-12. O0 -6. 000 S. 000 12. O0

P

-0

g

P

0

I

P

-0

g

I

0

0

I

0

O. 000 le.05'

X

Figure 2.8: Contour plot of the images for the 6" and 3.25" spheres obtained

from the backscattered fields.

12
TO

ANTENNA

COMPACT

TO

RANGE REFLECTOR

IMAGE __

__...

Figure 2.9: Positions of the 6", 3.25" and 1" spheres for the bistatic scattering measurement.

The second combination of the spheres used as the target is shown in

Figure 2.9. Note that a 6" sphere is located at V, a 3.25" sphere at J,

and a 1" sphere at L. The resulting images obtained from the bistatic

scattered fields and backscattered fields are shown in Figures 2.10

to 2.13. Again, these images clearly show the scattering centers of the

target and also the secondary scattering centers due to the creeping

waves propagating around the spheres.

13
K

_"

Figure 2.10: Surface plot of the images for the 6", 3.25" and 1" spheres

obtained from the bistatic scattered fields.

14
O" 18. O0

0

0

o

N

oO_

o-

_ooo

0

o-_

0

I

0

0

L 18. ,_0

'5807

-12. O0 -8. 000 O. 000 6. 000 12. O0 18. O_L

, , , I , , , I , , , I , , , I , , , I , , , r ._

H O

O. 030 o

I" SPHERE

/

\

3.25" SPHERE

0.00_2023

O. 0001"07993

H

O. 02452

0.000109436 0.00_2213

H

0.02578

SPHE RE

\

__o. oo&27sg

0

M

O. 0217

0.01

0.00_1790

0.001"18862

1 i I e w ; I I I I I I I I I I I ; I I I I

-12. O0 -6. 000 6. 000 12. O0

0

0

P

-0

8

.o

-0

0

0

!

p

_0

g

I

0

0

O. 000

?,

X

!

0

le. o6)

Figure 2.11: Contour plot of the images for the 6", 3.25" and 1" spheres

obtained from the bistatic scattered fields.

15
Figure 2.12: Surface plot of the images for the 6", 3.25" and 1" spheres

obtained from the backscattered fields.

16
0"18. O0

0

0

o

N

0--

oo- "_ox d

- ! 2. O0 -15. 000 O. 000 6. 000 ! 2. O0 18. 00.

,,, I I,, I,,, I,,, I,,, I , , , .=

o

I

0

o

d

I

0

0

L

_88

i Pt SPHERE

\

_25

O. 1901

/

/

3.25" SPHERE

0.0061746 0.0061709

O. 02423

0.000L06145

H

0.02517

0.00_3400

H

O. 02C

O. 00H9741

ooooLogg2s

!

6" SPHERE

O. 0061891

14

0.01

I I I J I I 1 I I I t I I ! I I ! I I J I I I

,nJ. ';)0 -12. O0 -6. 000 6. 000 12. O0

0

0

0

0

P

-0

8

o

-0

0

0

!

-0

g

!

0

0

O. 000

7

X

!

0

re. o@

Figure 2.13: Contour plot of the images for the 6", 3.25" and 1" spheres

obtained from the backscattered fields.

17
2.4 Summary and Conclusions

An image processing technique using the bistatic scattered fields obtained in a compact range has been presented. Two compact ranges

or one compact range and a horn antenna can be used to perform

the bistatic scattering measurements. The antennas can be either focussed or defocussed. The bistatic scattered fields are then used to

find the image, and consequently, the scattering centers of the target.

The same processing approach can also be used to find the image of

the target from backscattered fields. The processing technique does

not require the target to be at far field of the antennas. Experimental

results have been used to determine the images of various targets via

this processing technique. Very good results have been obtmned and

presented.

2.5 Acknowledgement

Numerical results presented in this report were made possible by a

Grant (Project 355) from The Ohio Supercomputer Center, Columbus, Ohio.

18
Chapter 3

Target Signature Study

This is a brief review of the portion of the grant pertaining to target

signature modeling over the period September 1, 1988 to February

28, 1989.

3.1 Introduction

The objective of this part is to determine and implement an effective method to integrate the use of UTD electromagnetic prediction

codes for simulation of radar cross section into test and evaluation

situations. UTD scattering code predictions can replace costly measurements. The signatures are used in the test loops to evaluate how

effectively radar can follow targets. In this situation, it is necessary

that the data be efficiently obtainable.

3.2 Scattering Code Overview

There is much scattering code development going on in the aircraft

industry. These codes are primarily physical optics codes based on

tiled or patched surfaces. They are used for component analysis and

require large amount of computation times to do the integrations.

Because they are based on physical optics, the specular points are

19
not explicitly defined. In addition, the some of the codes can be

proprietary and/or very expensive.

A physical optics code is being developed by the U. S. Army Missile

Intelligence Agency and Northrop called MISCAT. It is available inexpensively, however, it has the characteristic mentioned above and

in addition has a more basic shape input capability. A new code is

being developed called PGSCAT, which is a patch code for more general model descriptions, but again, it is PO based. Syracuse Research

Corp. has a code that over comes the PO integration by using a scattering center description. There are no higher order terms involved

and it uses basic shape models.

A different class of scattering codes are centered around the BRL

modeling code. The BRL code is a CSG modeller for graphical representation of shapes. ERIM's SKIM code uses the BRL brute force

ray shooting methods to reproduce synthetic aperture radar (SAR)

images. It provides approximations to the fields as projections of the

rays onto pixel planes. The ray shooting technique does find dihedral

and trihedral speculars but it is extremely time consuming. GTRI

has a RCS code similarly centered around the SAR concept. University of Illinois has taken the BRL ray tracing code and added a field

capability to it. The resulting fields lack edge effects and is slow since

it is based on PO and brute force ray tracing.

Another class of scattering codes deal with the near zone fusing problem. NWC has integrated the Ohio State University's NEC-BSC code

into its applications for this purpose.

The suggested approach for test and evaluation purposes, is the use

of a UTD based code such as the RCS - Basic Scattering Code [4].

It explicitly defines the specular, edge, and vertex diffraction points,

as well as some higher order terms. It uses efficient ray tracing techniques based on the chosen geometry models. It does not need integrations since it uses closed form diffraction coefficients. This allows

the flexibility to store the characteristics of the scattering centers of

a target and then add the field information versus angle or frequency

as they are needed. Since test and evaluation hardware in the loop

situations need efficiency and flexibility of operation, this type of approach will be beneficial for large sized targets and the many angles of

2O
approach needed. In addition, it has a bistatic scattering capability

that might be useful in the future.

A study of the various UTD mechanisms that will be most important

for modeling in the test and evaluation situation has been undertaken. Their theoretical characteristics have been studied from the

point of view of obtaining the best way to determine, calculate and

store each term individually. The UTD radar cross section prediction

code, RCS-BSC version 2, has been modified so that its write algorithms for the UTD mechanisms calculated will better accommodate

a volumetric output of the individual fields.

The RCS-BSC version 2 corner diffracted field section as been modified to allow access of an individual corner diffracted field instead of

an edge in order to study which is the best way to store the fields

in the data base. Other field sections will be modified as they are

integrated into the data base.

An algorithm to access and plot the three dimensional field information in the data base has been started. This will allow a visual

presentation of the fields in order to help determine the minimum

sample rate for the different individual types of UTD mechanisms.

3.3 Storage Requirements

In order to better understand the size requirements of the data base

needed for test and evaluation purposes the following simple examples

illustrate the various possible configurations. It is assumed that the

this information is for backscatter at a single frequency at this point.

It is also assumed that a complete volumetric view of the object under

consideration is needed with all polarization information.

For a full up unprocessed scattered field data base:

• Opts -- 1801, dppts = 3601, no. pols. = 4

• Complex number = 8 bytes, step size = 0.1 °

• Storage required = 207 megabytes

21
For a full up processed data base, that is with a median average

representation of the fields:

• Opt_ = 91, _bpt8 = 181, no. pols. = 4

• Complex number = 8 bytes, step size = 2 °

• Storage required = 0.527 megabytes

The median average of the fields is not necessarily desirable, however,

for test and evaluation purposes since the scintillation of the fields is

useful to test radar performance. In addition, the processed data base

can not be used for imaging since the phase information is lost.

For individual dominant terms only, it can be assumed that the sampling rate can be greatly reduce so that:

• Opt8 = 37, _bpt8 = 73, no. pol_. = 4

• Complex number = 8 bytes, step size = 5 °

• Storage required per term = 0.086 megabytes

This implies that approximately 10-20 terms can be used and still

have the storage and more field information content than the processed data base. A few thousand terms can be stored and have the

same information as the full up unprocessed data base. Actually some

of the storage would be needed for several frequencies. This, however,

appears to be the best alternative.

One more possible solution has been investigated. This entails storing scattering centers only and then post processing the fields. The

storage of the scattering centers locations only turns out to be very

complicated since the terms can be shadowed or they can move versus incident and observation direction. In addition, there will be a

trade off between storage and speed of retrieval which will reduce its

desirability for real time test and evaluation purposes.

In summary:

• Full up unprocessed data base requires large amounts of storage.

• Processed data base loses local variations of signals.

• Processed data base can not be used for imaging.

22
• Individual dominant terms can be reconstructed to give the same

information as full up unprocessed data base with less storage.

• Need for multiple frequency information further compounds full

up data storage.

• Individual terms data base will still greatly reduce storage requirements.

• One, two or three dimensional imaging possible.

3.4 Further Work

Test cases, that will represent meaningful situations for test and evaluation purposes, are being determined to validate the algorithms being

developed. Simple scattering shapes will be used such as plate and

cone frustums to test the basic ideas. A model of a QF-100 aircraft

has been suggested by K. Oh and C. L Yu at Pacific Missile Test

Center, since they have measured data on a one fourth scale model.

23
Chapter 4

Aircraft Code Study

This is a brief review of the portion of the grant pertaining to modifications to the aircraft and missile antenna code over the period

September 1, 1988 to February 28, 1989.

4.1 Introduction

The purpose of this effort is to modify the aircraft and missile antenna

code [5] to provide simple models for rectangular microstrip patches

and to add a smoothing algorithm for radiation pattern presentation.

In addition, a study to implement the aircraft code on a personnel

computer will be initiated.

4.2 Smoothing Algorithm

The existing Ohio State University Aircraft code (NEWAIR3) [5] has

been modified so that any spikes in the radiation patterns are removed

by a smoothing algorithm. The input data is as follows:

EX:

LSMOOTH, NAVG, SEN

24
where

LSMOOTH = T, spikes are removed from the output data

F, the output data is not modified

NAVG = # of data points used to compute an average.

It is always even, usually NAVG=4.

SEN = # of standard deviations that is allowed before a

spike is removed. SEN does not have to be an integer.

4.3 Patch Antenna

Another task that is near completion is the addition of a simple model

for a rectangular microstrip patch. The patch is modeled by a pair

of short magnetic monopoles which is accurate when the lowest order

(1,0) mode is excited in the patch. The input data of the NEWAIR3

code (in the SG: command) has been slightly modified to input the

parameters for the rectangular patch.

4.4 PC Study

A study to implement the NEWAIR3 on a personnel computer has

been initiated. Additional memory and software has been obtained

to start the task on an IBM compatible clone. This work will be

continuing during the next phase.

25
Chapter 5

SATCOM Antenna Study

This is a brief review of the portion of the grant pertaining to satellite

communication antenna (SATCOM) modeling over the period from

the start of this part December 1, 1988 to February 28, 1989.

5.1 Introduction

The purpose of this effort is to study the performance of SATCOM

antennas on aircraft. The potential locations of the antenna system

for best pattern and polarization coverage is being assessed on an P3C

aircraft. A circular polarized antenna composed of crossed dipoles is

being considered. The aircraft is being modeled using a computer

code based on the Uniform Geometrical Theory of Diffraction (UTD)

which is the NEC-BSC V3.1 [6].

5.2 Batwing Antenna

The first phase has been to analyze the present candidate UHF SATCOM antenna system and its location on a P3C aircraft using the

NEC-BSC. Naval Air Test Center has provided the antenna system information which is a Dome and Margolin DM 1501341 (Batwing) airborne UHF satellite communication antenna as shown in Figure 5.1.

26
A simple crossed dipole has been used in the code with the corresponding dimensions given in the figure. All the results have been

referenced to a circular polarized isotropic radiator. The calculated

result in Figure 5.2 at 244 MHz can be compared with the measured

result supplied by the manufacturer in Figure 5.3 for the antenna on

a 8 foot ground plane in the principal elevation cut for the antenna.

The results compare very well. In order to test the NEC-BSC's representation of the antenna for a pattern taken along the length of

one of the dipole arms, the pattern at 300 MHz in Figure 5.4 can be

compared with a method of moments result [7] in Figure 5.5. Again

quite good agreement is obtained.

5.3 Model Validation

Naval Air Test Center has supplied extensive model measurements

independently conducted by Boeing on a 1/17 scale model and Lockheed on a 1/10 scale model. The Boeing data is used to validate

the model here. The antenna is located as illustrated in Figure 5.6,

which also shows the computer model used to generate the results.

The calculated results for 300 GHz are compared with measurements

for the roll plane in Figures 5.7 and 5.8, for the azimuth plane in Figures 5.9 and 5.10, and for the elevation plane in Figures 5.11 and 5.12

all for right hand polarization. The cross polarized fields are compare for the roll plane in Figures 5.13 and 5.14, for the azimuth plane

in Figures 5.15 and 5.16, and for the elevation plane in Figures 5.17

and 5.18 all for left hand polarization. Notice that the roll plane

results compare very well. The azimuth and elevation results, however, have about a 10 dB difference near the horizon. This will be

investigated further, but overall the agreement is good.

5.4 Further Work

In the next phase, a study of alternative antenna locations and possibly alternative systems to provide a minimum of 330 ° azimuth, from

27
OUTLINE DIMENSIONS

inches (Centimeters)

t

ioe

l

--T -;_r

_J

E

_, 12"

__° ?MII

i _" I0 SlSI

F I 710

i _1 X'a" I )

--.. _./" ""--""_.__]..-"r--- )-

Figure 5.1: Batwing airborne UHF satellite communication antenna of

Dome and Magolin.

28
Figure 5.2: Calculated Batwing right hand circular polarized antenna pattern at 244 MHz on an 8' ground plane using the NEC-BSC.

29
C P z5 oT"_opk:

n©;

,110

Figure 5.3: Measured Batwing right hand circular polarized antenna pattern at 244 MHz on an 8' ground plane. (Pattern supplied by Dome and

3U

Margolin.)
Figure 5.4: Calculated Batwing right hand circular polarized antenna pattern at 300 MHz on an infinite ground plane using the NEC-BSC.

31
Figure 5.5: Calculated Batwing right hand circular polarized antenna pattern at 300 MHz on an infinite ground plane using the ESP code.

32
I

Figure 5.6: Geometry of the model of the P3C aircraft code used in the

NEC-BSC showing the location of the antenna.

33
Figure 5.7: UTD calculated roll plane pattern for batwing antenna on a

P3C for right hand circular polarization in the roll plane at 300 MHz.

34
ORIGINAL PAGE IS

OF POOR QUALITY

Isotrope . -10.7 dbic

TURNSTILE DIPOLE

m

COII'TAII_r JmGUE *-_0_.

I_¢NUZAII'tR ¢O( k|e( _'

amvl _,Jc_r(io m ol¢0R¢,1

Figure 5.8: Boeing's measured roll plane pattern for batwing antenna on a

P3C for right hand circular polarization in the roll plane at 300 MHz.

35
Figure 5.9: UTD calculated azimuth plane pattern for batwing anI,_nna on

a P3C for right hand circular polarization in the roll plane at 300 MHz.

36
OR_G_N_t. P_E IS

OF POOR QUALITY

Isotrope - -10.7 d'oic

TURN$_t F DIPOLE

Figure 5.10: Boeing's measured azimuth plane pattern for batwing antenna

on a P3C for right hand circular polR.fization in the roll plane at 300 MHz.

37
Figure 5.11: UTD calculated elevation plane pattern for batwing antenna

on a P3C for right hand circular polarization in the roll plane at 300 MHz.

38
ORIGINAL PAGE IS

OF POOR QUALITY

Isotrope . 10.7 _ If

TURNSTILE DIPOLIF

Figure 5.12: Boeing's measured elevation plane pattern for batwing antenna

on a P3C for right hand circular polarization in the roll plane at 300 MHz.

39
Figure 5.13: UTD calculated roll plane pattern for batwing antenna on a

P3C for left hand circular polarization in the roll plane at 300 MHz.

40
ORIGINAL PAGE IS

OF POOR QUALITY

Isotrope - -10.7 db_¢

TURN_;TILE DIPOLE

L

Figure 5.14: Boeing's measured roll plane pattern for batwing antenna on

a P3C for left hand circular polarization in the roll plane at 300 MHz.

41
Figure 5.15: UTD calculated azimuth plane pattern for batwing antenna

on a P3C for left hand circular polarization in the roll plane at 300 MHz.

42
ORIGINAL p ",-""

OF POOR QUALITY

I"

Figure 5.16: Boeing's measured azimuth plane pattern for batwing antenna

on a P3C for left hand circular polarization in the roll plane at 300 MHz.

43
Figure 5.17: UTD calculated elevation plane pattern for batwing antenna

on a P3C for left hand circular polarization in the roll plane at 300 MHz.

44
O_'IGINAL PAGE IS

POOR QUALITY

Figure 5.18: Boeing's measlnred elevation plane pattern for batwing antenna

on a P3C for left hand circular polarization in the roll plane at 300 MHz.

45
zenith to 10 ° above aircraft horizon will be undertaken. The antenna

system must provide performance to maintain the satellite link in areas of high signal fading to multipath effects. This will primarily be

accomplished with the use of the same antenna mentioned above by

exploring alternative locations around the aircraft.

46
Bibliography

[1] D. L. Mensa, High Resolution Radar Imaging. Artech House, Inc,

1981.

[2] D. L. Mensa and K. Vaccaro, "Interpretation of two-dimensional

RCS images," in Proceedings of Antenna Measurement Association Techniques, September 1988.

[3] T. H. Lee and W. D. Burnside, "A near field focus procedure using

compact range data," in Proceedings of Antenna Meanurement

Association Techniques, September 1988.

[4] R. 3. Marhefka, "Radar cross section - basic scattering code, RCS

- BSC (version 2), user's manual," Technical Report 718295, The

Ohio State University ElectroScience Laboratory, Department of

Electrical Engineering, under preparation 1988. Prepared under

Contract No. F33615-86-K-1023 for Wright Patterson Air Force

Base.

[5] W. D. Burnside, J. 3. Kit's, B. Grandchamp, R. G. Rojas, and

P. Law, "Airborne antenna radiation pattern code user's manual," Technical Report 716199-4, The Ohio State University ElectroScience Laboratory, Department of Electrical Engineering, Sep.

1985. Prepared under Grant No. NSG 1498 for National Aeronautics and Space Administration.

[6] R. 3. Marhefka and 3. W. Silvestro, "Near zone - basic scattering code, user's manual with space station applications," Technical Report 718422-13, The Ohio State University ElectroScience

Laboratory, Department of Electrical Engineering, March 1988.

Prepared under Grant No. NSG 1613 for National Aeronautics

and Space Administration.

47
fTjE. H. Newman and R. L. Dilsavor, "A user's manual for the electromagnetic surface patch code: ESP version 1II," Technical Report 716148-19, The Ohio State University ElectroScience Laboratory, Department of Electrical Engineering, May 1987. Prepared

under Grant No. NSG 1613 for National Aeronautics and Space

Administration.

48