The status of various efforts in support of the development of computer codes to analyze the radiation patterns of general aviation aircraft and simulate private aircraft is reported. Because of the significant amount of energy scattered by the windshield of private aircraft, a method is being developed to treat high frequency scattering by thin dielectric layers. To treat such aircraft at lower frequencies, i.e., where the aircraft surface area is less than 10 square wavelengths, a moment method code is being modified. The problem of plane (or surface) wave diffraction by the dielectric half plane is constructed and discussed

Burnside, W. D.

Newman, E. H.

Rojas, R. G.

English

NASA Technical Reports Server

ANALYSIS OF AIRBORNE ANTENNA PATTERNS
Roberto G. Rojas
E.H. Newman
W.O. Rurnside
Semi-Annual Technical Report 710964-10
Contract No. NSG 1498 •
September 1982
National Aeronautics and Space Administration
Langley Research Center
Hampton, Virginia 23665
https://ntrs.nasa.gov/search.jsp?R=19830002053 2020-03-21T06:57:32+00:00Z
50272-101
REPORT DOCUMENTATION
PAGE
1. REPORT NO.
4. Title and Subtitle
ANALYSIS OF AIRBORNE ANTENNA PATTERNS
7. Author(s)
Roberto G. Rojas, E.H. Newman, and W.D. Burnside
9. Performing Organization Name and Address
The Ohio State University ElectroScience Laboratory
Department of Electrical Engineering
Columbus, Ohio 43212
12. Sponsoring Organization Name and Address
Naval Aeronautics and Space Administration
Langley Research Center
Hampton, Virginia 23665
3. Recipient's Accession No.
5. Report Date
September 1982
8. Performing Organization Rept. No.
10. Project/Task/Work Unit No.
710964-10
11. Contract(C) or Grant(G) No.
(C)
 NSG 1498
(G)
13. Type o1 Report & Period Covered
Semi-Annual Technical
14.
15. Supplementary Notes
16. Abstract (Limit: 200 words)
This is a summary of the research accomplishments for the reporting
period July, 1981 to January, 1982. The achievements in numerically
modeling the radiation patterns for antennas mounted on private aircraft
are our major objectives.
17. Document Analysis a. Descriptors
b. Identifiers/Open-Ended Terms
Electromagnetic Radiation
High and Low Frequency Solutions
Aircraft Simulations
Thin Dielectric Scattering
Geometrical Theory of Diffraction
Moment Methods
c. COSATI Field/Group
IS. Availability Statement 19. Security Class (This Report)
Unclassified
20. Security Class (This Page)
Unclassified
21. No. of Pages
18
22. Price
(See ANSI-Z39.18) See Instructions on Reverse OPTIONAL FORM 272 (4-77)
(Formerly NTIS-3M
Department of Commerce
TABLE OF CONTENTS
Page
LIST OF FIGURES iv
I. INTRODUCTION 1
II. MOMENT METHOD SIMULATION OF PRIVATE AIRCRAFT - 2
III. DIFFRACTION BY A THIN DIELECTRIC HALF-PLANE 2
IV. CONCLUSIONS , 16
REFERENCES 18
m
LIST OF FIGURES
Figure Page
1 Model for Cessna 150. 3
2 Geometry used for DTD-Moment Method comparison. 6
3 Various terms used in calculating the total 7
UTD field.
4a UTD-MM comparison with electric line source, 8
using geometry shown in Figure 2 with L=2.X,
0=0.05X, (|>s=0.0, ps=l.X.
4b Diffracted surface waves for an electric line 9
source, using geometry shown in Figure 2 with
L=2.X, 0=0.05X, <f>s=0.°, ps=l.X.
4c UTD-MM comparison with electric line 10
-?
source, using geometry shown in Figure 2
i •
with L=2.X, 0=0.05X, ps=2.X5 <J>S=40.°.
4d Diffracted surface waves for an electric Tine 11
source, using geometry shown in Figure 2 with
L=2.X, 0=0.05X, ps=2.X, <j>s=40.°.
4e UTD-MM comparison with electric line .12
source, using geometry shown in Figure 2
with L=2.X, 0=0.05X, <(>s=60.0, ps=2.X.
IV
Figure Page
4f Diffracted surface waves for an electric line 13
source, using geometry shown in Figure 2 with
L=2.X, D=0.05X, ps=2.X, <j>s=60.°.
5a UTD-MM comparison with magnetic line 14
source, using geometry shown in Figure 2
with L=1.A, D=0.1X, ps=2.X, <j>s=60.°.
5b Diffracted surface waves for an magnetic line 15
source, using geometry shown in Figure 2 with
L=1.X, D=0.1X, ps=2.X, <f>s=60.°.
I. INTRODUCTION
This effort is composed of several research topics which are
proceeding in parallel. The major research area is the development of
numerical methods (computer codes) to analyze the radiation patterns for
antennas mounted on general aircraft with specific interest in private
aircraft simulations. We are presently developing a computer code to
analyze private aircraft assuming that the structure is perfectly
conducting and large in terms of the wavelength. Rased on earlier
studies, we found that the windshield of a private aircraft scatters a
significant, amount of energy; however, it can not be approximated as a
perfect conductor [1]. As a result, we have been developing a method to
treat the high frequency scattering by thin dielectric layers [2].
These solutions have been based on a modification of the perfectly
conducting half plane solution
which lacks a rigorous analysis. This has led us
to theoretically analyze the scattering from a thin dielectric layer.
One should note that this is a joint effort between this project and the
Joint Services Program (Contract No. 710816) with the ElectroScience
Laboratory.
In order to treat private aircraft at lower frequencies, i.e.,
where the aircraft surface area is less than 10 square wavelengths, we
have been modifying a moment method code. The moment method compliments
the high frequency solutions already being developed and should provide
excellent results for the lower frequencies. This effort is just
beginning at this time.
1
II. MOMENT METHOD SIMULATION OF PRIVATE AIRCRAFT
We will now briefly describe the effort to compute the patterns of
simple monopoles on small private aircraft. A method of moments
solution will be employed where the aircraft is modeled by an inter-
connection of polygonal .plates, and the monopole is modeled as a thin
wire. The model for a Cessna 150 is shown in Figure 1. It consists of
23 interconnected plates. The wing span of the plane is about 4x at
121 MHz, and 345 surface patch dipole modes are employed. At present we
are in the final stages of code development to compute the radiation
from this aircraft.
III. DIFFRACTION BY A THIN DIELECTRIC HALF-PLANE
The diffraction by a thin dielectric half plane is an important
canonical problem in the study of the diffraction of electromagnetic
waves by penetrable bodies with edges. The excitation for this problem
can be either an electromagnetic plane wave, or a surface wave incident
along the dielectric surface; both types of excitation are considered.
For sufficiently thin dielectric half planes, solutions based on the
Wiener-Hopf technique can be obtained if one approximates the effect of
the thin dielectric slab by an impedance boundary condition. This
analysis begins by bisecting the semi-infinite dielectric half plane by
an electric wall in the first case, and by a magnetic wall in the second
case. The problem of plane (or surface) wave diffraction by the
dielectric half plane is then constructed by appropriately superimposing
Z RXIS VIEW
0 WIRE MODES
345 PLflTE MODES
0 RTTRCH. MODES
TOTR.L MODES
= 1,39
 x •
X RXIS VIEW T .RXIS V I E W
Figure 1. Model for Cessna 150.
the corresponding solutions for the electric and magnetic wall
bisections, respectively. This procedure is expected to yield a
dielectric half plane diffraction coefficient which is far more
accurate than that obtained recently by Anderson for the case when the
incident plane wave electric field is parallel to the edge of the thin
dielectric half plane [3], because the latter analysis employs an
approximate "equivalent" polarization current sheet model for the thin
dielectric half plane. The approximation in [3] 'contains only a part of
the information present in the more general approach being employed in
our work; consequently, it is found that the analysis in [3] yields a
diffraction coefficient which is valid only for an extremely thin
dielectric half plane. Furthermore, the equivalent polarization current
approximation leads to a more complicated Wiener-Hopf analysis when the
magnetic field is parallel to the edge; the latter case has not been
treated by Anderson [3], It is also noted that the Wiener-Hopf factors
for the case treated by Anderson [3] do not appear to be well behaved
for the near edge on plane wave incidence case. In contrast, the
Wiener-Hopf factors being employed in our work are based on Weinstein's
factorization procedure [4] which overcomes the difficulties present in
[3].
At the present time, the diffraction coefficients for the two
dimensional case for both TE and TM plane, cylindrical, and surface wave
excitations of the thin dielectric half-plane have been obtained, and
they are being tested for accuracy as indicated on the next page.
The accuracy of the new diffraction coefficients have been tested
thus far by calculating the radiation patterns for the two-dimensional
geometry shown in Figure 2 using our thin dielectric half-plane
diffraction coefficients, and by comparing these results with those
obtained independently via the moment method.
Since the width of the dielectric strip depicted in Figure 2 is 2X
or IX depending on which source is used, (2A for an electric line
source, IX for a magnetic line source) multiple bounces of the surface .
wave component will have a significant effect for angles of incidence
near grazing, and hence these have to be included in the total solution.
The field contributions pertaining to the various rays shown in Figure 3
have been included in their respective domains of existence; in
particular these contributions result from:
(i) direct fields.
(ii) reflected fields.
(iii) transmitted fields.
(iv) fields diffracted from both edges.
(v) surface waves excited by edge A, diffracted by edge B,
and vice versa,
(vi) surface waves excited by edge A, reflected back by
edge B, and finally diffracted by edge A, and
vice versa.
It is gratifying to note that the field patterns depicted in
Figures 4 and 5 for the electric and magnetic line sources that are
based on our uniform geometrical theory of diffraction (UTD) ray
solutions agree very well with the corresponding moment method solutions
which are based on a totally different but formally exact procedure. It
is noted that for angles of incidence close to broadside on the strip,
the diffracted surface wave does not contribute much to the total
SOURCE
D
e r = 4
Figure 2. Geometry used for UTD-Moment Method comparison
OBSERVATION
POINT
SOURCE
.OBSERVATION
POINT SOURCE
\nf///////f/f7777/////A
(i) direct field
K/////////77//7//1
(1i) reflected field
iSOURCE
\777777/f-f/77///A
.OBSERVATION
POINT
(iii) transmitted field
^SOURCE . OBSERVATION
POINT
:f W///////////////7/M
'"• A B
(iv). edge diffracted fields
.SOURCE
A
.OBSERVATION
POINT
- OBSERVATION
SOURCE POINT
B ; A
(v) edge diffracted surface wave
.SOURCE OBSERVATION
POINT
OBSERVATION.
POINT
^SOURCE
V/////////7TTTA v/////////7777(
A B A B
(v1) reflected surface wave diffracted by edges
of dielectric plate
Figure 3. Various terms used in calculating the total
UTD field.
270 UTD
« • • MM
180
Figure 4a. UTD-MM comparison with electric line source,
using geometry shown in Figure 2 with 1=2.A,
D=0.05\, <|>s=0.0, ps=l.X.
270
Figure 4b. Diffracted surface waves for an electric line
source, using geometry shown in Figure 2 with
L=2.X, 0=0.05A, (t)S=0.°, ps=l.\.
180
Figure 4c. UTD-MM comparison with electric line
source, using geometry shown in Figure 2
with L=2.X, D=0.05A, ps=2.X, <}>s=40.0.
10
270
-20 -10 -0
Figure 4d. Diffracted surface waves for an electric line
source, using geometry shown in Figure 2 with
L=2.X, D=0.05X, p s=2.X, <}>s=40.i. •
11
180
Figure 4e. UTD-MM comparison with electric line
source, using geometry shown in Figure 2
with L=2.X, 0=0.05X, <j>s=60.°, ps=2.X.
12
270
180
Figure 4f. Diffracted surface waves for an electric line
source, using geometry shown in Figure 2 with
L=2.X, D=0.05X, ps=2.X, <|>s=60.0.
13
Figure 5a. UTD-MM comparison with magnetic line
source, using geometry shown in Figure 2
with L=1.X, 0=0.1A, ps=2.X, <{>s=60.0.
14
270
180
Figure 5b. Diffracted surface waves for an magnetic line
source, using geometry shown in Figure 2 with
L=1.X, n=0.1\, ps=2.X, <}>s=60.0.
15
solution and thus, it can be neglected. On the other hand, for angles
of incidence of 60° or larger from normal (broadside) incidence, the
surface wave plays a significant role as expected, and the latter
therefore, has to be included in the total solution.
The case of TE and TM leaky wave excitation of the thin dielectric
half-plane is currently being analyzed. It is expected that this part
of the study will be completed in the near future. In addition, the
extension of the two-dimensional solutions to the three dimensional
problem of plane, cylindrical, conical, and spherical wave excitation of
a thin dielectric half plane is also being investigated as a part of the
future work on this important problem.
The present DTD solution is in a form which suggests an ansatz for
extending the thin dielectric half-plane diffraction coefficient to the
case of a moderately thick dielectric half-plane. This extension and
the extension to the three-dimensional case can be built up from the
two-dimensional solutions.
IV. CONCLUSIONS
The high frequency simulation code used to compute the radiation
patterns for private aircraft using a prolate.spheroid to model the
fuselage is about complete. This code will be ready for simulation
verification during the next reporting period. The low frequency code
development is just getting under way although we expect results which
can be compared with experiment data within the next six months.
16
The theoretical development associated with the thin dielectric
layer scattering is proceeding nicely. Presently, the surface wave
aspects of the solution are being studied.
17
REFERENCES
1. K.W. Burgener and W.D. Burnside, "Analysis of Private Aircraft
Antenna Patterns," Report 710964-2, January 1979, The Ohio State
j
University. ElectroScience Laboratory, Department of Electrical
Engineering; prepared under Grant NSG 1498 for National Aeronautics
and Space Administration, Langley Research Center.
2. K.W. Burgener, "High Frequency Scattering From a Thin Lossless
Dielectric Slab," Report 710964-4, November 1979, The Ohio State
University ElectroScience Laboratory, Department of Electrical
Engineering; prepared under Grant NSG 1498 for National Aeronautics
and Space Administration, Langley Research Center.
3. I. Anderson, "Plane Wave Diffraction by a Thin Dielectric Half
Plane," IEEE Trans. Antennas and Propagation, Vol. AP-27, pp. 584-
589, Sept. 1979.
4. L.A. Weinstein, The Theory of Diffraction and the Factorization
Method, The Golden Press, Boulder, Colorado, 1969.
18


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