Progress on predicting the patterns of high-frequency antennas on aircraft and shuttles is reported. Patterns are presented for an axial slot antenna on a circular cylinder partially coated with a dielectric layer. Results are shown for Omega signal disturbance by a conducting vertical pole

Burnside, W. D.

Richmond, J. H.

English

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COMPUTER ANALYSIS OF AIRCRAFT AND SHUTTLE ANTENNAS0-
W. D. Burnside
J. H. Richmond $h 7(
The Ohio State University
ElectroScience Laboratory
Department of Electrical Engineering
Columbus, Ohio 43212
SEMIANNUAL STATUS REPORT 2902-16
(15 November 1973 to 15 May 1974)
Grant Number NGL 36-008-138
June 1974
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tC2A rn ABQ g LE ANEOD AS Semiannual 074-266i tatus Rport, 15 Nov. 1973 - 15 jay
1974 (Ohio State Univ.) 12 p HC $4.0g nc
CSCL 17B G3/07 413 02
National Aeronautics and Space Administration
Langley Research Center
Hampton, Va. 23365
https://ntrs.nasa.gov/search.jsp?R=19740018553 2020-03-23T08:40:08+00:00Z
COMPUTER ANALYSIS OF AIRCRAFT AND SHUTTLE ANTENNAS
W. D. Burnside
J. H. Richmond
SEMIANNUAL STATUS REPORT 2902-16
(15 November 1973 to 15 May 1974)
Grant Number NGL 36-008-138
June 1974
National Aeronautics and Space Administration
Langley Research Center
Hampton, Va. 23365
I
ABSTRACT
Progress is reported on predicting the patterns of high-frequency
antennas on aircraft and shuttles. Patterns are presented for an axial
slot antenna on a circular cylinder partially coated with a dielectric
layer. Results are presented for Omega signal disturbance by a con-
ducting vertical pole.
ii
TABLE OF CONTENTS
Page
I. AIRCRAFT AND SHUTTLE ANTENNAS 1
II. DIELECTRIC-FILLED SLOT ANTENNA 3
III. OMEGA SIGNAL DISTURBANCE 7
REFERENCES 8
iii
COMPUTER ANALYSIS OF AIRCRAFT AND SHUTTLE ANTENNAS
I. AIRCRAFT AND SHUTTLE ANTENNAS
During the past six months, the calculated patterns made on the
KC-135 aircraft have been completed and compare very favorably with
measured results taken at NASA Langley. The results of this study will
be presented at the next IEEE Conference[l]. More recently, we have con-
centrated on collecting shuttle data on a model which is similar to the
actual shuttle design. The patterns for various antennas and locations
have been measured at NASA Langley on a scale model. The calculated
patterns are being generated with some of the results illustrated in
Figs. 1 and 2. These results are for antennas located forward of the
CALCULATED
90" ---- MEASURED
1-30 -20 -10 000
RELATIVE POWER (dB)
2700
Fig. 1. Roll plane pattern of a circumferential waveguide
antenna mounted forward of the wings and atop a
scale model shuttle spacecraft.
1
9'0 CALCULATED90 o
---- MEASURED
I80I
1800 \ / 00
-30 -20 10 0
RELATIVE POWER (dB)
2700
Fig. 2. Roll plane pattern of an axial waveguide antenna
mounted forward of the wings and atop a scale
model shuttle spacecraft.
wings, whereas the future results will be for antennas mounted over the
wings. In addition, patterns have been measured and calculated for
antennas mounted on a scale model of the final shuttle design. These
results include the effects of the large booster rockets which are mounted
below the shuttle, and in each case the agreement between the calculated
and measured results is quite good.
The future work in the area of high frequency antenna pattern
analysis involves completing the shuttle study for the antennas mounted
over the wings. In addition, a study will be initiated on the airborne
antennas which might be applied for the microwave landing system. To
date, the polarization used for this system has not been finalized and
has been a topic of much discussion. It is our goal to aid in this
decision by examining the airborne antenna system complexity for each
polarization. The antenna systems generated will be those necessary for
the desired coverage.
2
II. DIELECTRIC-FILLED SLOT ANTENNA
In a previous reporting period, we developed a computer program for
an axial slot antenna radiating through a flush-mounted dielectric window
in a conducting cylinder as in Fig. 3. In the current reporting period,
\ c
RADIUS b
RADIUS
Fig. 3. An axial-slot antenna radiates through a flush-mounted
dielectric window in a conducting circular cylinder.
The principal field components are E and H .
the program was improved to handle larger cylinders and higher dielectric
constants. Figures 4, 5 and 6 illustrate the far-field patterns with
dielectric constants of 2, 3 and 4. The patterns in Figs. 4 and 6 are
reasonably smooth, but in Fig. 5 the pattern breaks up into many lobes
with deep nulls. With a dielectric constant of 3, this undesirable type
of pattern is obtained when the aperture half-angle is b = 13.8, 14.8,
15.8, 16.80, etc. When b differs from one of these critical angles by
more than 0.1 degrees, the pattern becomes smooth again. At each critical
angle, the aperture width is, an integral number of wavelengths for the
lowest-order surface wave.
3
0O-
- - CALCULATED
e = 2Eo
-10 a = 18.7325Xo
b = 19.05 X0
S2a = 1.08*
S24 b = 29.60
Z 2 c = 29.60
-20 x
-30
0 20 40 60 80 100 120 140 160
4 (DEGREES)
Fig. 4. Far-field pattern of TE axial slot radiating through a
flush-mounted dielectric window in a circular cylinder.
The dielectric constant is 2.
4
0z-10
CALCULATED
-20
e = 3 co
xa = 18.7325Xo
b = 19.05 Xo
2o = 1.080
2 0b =29.60
20c = 29.60
-30
0 20 40 60 80 100 120 140 160
#(DEGREES)
Fig. 5. Far-field pattern of TE axial slot radiating through a
flush-mounted dielectric window in a circular cylinder.
The dielectric constant is 3.
5
0S-10
-- CALCULATED
-20
e =4 4o
L- x a = 18.7325Xo
b = 19.05 X0
2 o = 1.080
24 b = 29.60
20c = 29.60
-30
0 20 40 60 80 100 120 140 160
J (DEGREES)
Fig. 6. Far-field pattern of TE axial slot radiating through a
flush-mounted dielectric window in a circular cylinder.
The dielectric constant is 4.
6
This surface-wave resonance phenomenon is less pronounced with a
dielectric constant of 1.2 but is observed when Ob = 14.60. The effect
may be reduced with a lossy dielectric window or by reducing the re-
flections at the edges of the aperture.
In Figs. 4, 5 and 6, the calculations are based on a two-dimensional
model with an infinitely long axial slot in an infinitely-long cylinder.
A case of greater interest is a half-wave axial slot in a long cylinder.
The effects of surface-wave resonance will be smaller for a slot of
finite length.
III. OMEGA SIGNAL DISTURBANCE
The Omega navigation system uses vertically polarized waves with
a frequency of 10 KHz. Experimental measurements show significant phase
variations in the signal in the vicinity of trees, towers and power lines.
There is a possibility, however, that these phase disturbances arise from
local variations in surface impedance rather than the nearby obstacles.
In our initial investigation of this problem, we considered a
vertically polarized plane wave propagating along a horizontal path over
a perfectly conducting flat earth. This wave illuminates a perfectly
conducting vertical pole with a height of 100 feet. The base of the pole
is located at the ground plane and makes contact with it. The radius of
the pole is 0.1 feet.
At 10 KHz, the height of the pole is 0.001. Using image theory,
we may consider the plane wave to have broadside incidence on a 200 foot
pole in free space. The current induced on the pole has essentially a
cosine distribution with maximum current at the base. If the incident
wave has a field strength of one volt per meter, the base current is
0.000267 amperes. The current leads the incident field by 900. In the
extreme near zone the scattered field ES leads the current by 90', and Es
is thus 1800 out of phase with the inci ent field. The total field Ez is
weak in the vicinity of the pole and vanishes at its surface. The pole
does not significantly disturb the phase of the Omega signal in the near
zone or the far zone. (A phase shift of much less than one degree is con-
sidered insignificant.)
For broadside backscatter, the pole has an echo area of 0.67 x 10-16
square wavelengths. As a center-fed dipole antenna, the 200 foot pole has
a terminal impedance Z = 0.0008 - j 110,000 ohms.
In this study we found that the standard thin-wire programs are
inadequate for scattering by a pole as short as 0.001. Therefore, we
developed new programs for thin-wire problems in the Rayleigh region. The
new programs give consistent results when the pole is divided into 4, 6,
8 or 10 segments. New subroutines were developed for near-zone field
analysis, and identical results were obtained with two independent programs.
7
In the next period we plan to investigate Omega signal disturbances
in the vicinity of a tree (modeled as a lossy dielectric pole) and an
overhead power transmission cable.
REFERENCES
1. Burnside, W.D., Marhefka, R.J. and Yu, C.L., "A Study of KC-135
Aircraft Antenna Patterns," presented at 1974 International IEEE/APS
Symposium at Atlanta, Georgia, June 1974.
8


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