Device for improving efficiency of parabolic horn antenna system for linearly polarized signal

Schuster, D. M.

English

NASA Technical Reports Server

Sept. 28, 1965 D. M. SCHUSTER 
ANTENNA BEAM-SHAPING APPARATUS 
Fi led Sept. 25. 1961 
I"-- 
ILLUMINATION 
ANGLE 
FIG. I. 
POWER 
FIG. 2. 
L 
" 
h 
Y 
h / 
TOTAL 
Y 
APERTURE SPILLOVER TOTAL ILLUMINATION SPILLOVER - -  - 
ANGLE ANGLE 
- 
(ACCESSION NUMBER) 
b'-- 
(NASA CR OR TMX OR AD NUMBER) 
DANVER M. SCHUSTER 
INVENTOR 
ATTORNEYS. 
https://ntrs.nasa.gov/search.jsp?R=19700025903 2020-03-17T02:02:54+00:00Z
3,209,360 United States Patent OEce Sept. 28, 1965 
1 2 
this embodiment of the invention is intended. Such an 
3,209,360 antenna usually comprises a parabolic-dish reflector 10, 
ANTENNA BEAM-SHAPING APPARATUS supported on a base 12, which is positioned on the ground 
Danver M. Schuster, ABtadena, Calif., ass ipor ,  by mesne 14. A feed horn 16 is positioned approximately at the 
arjsignments, to  the United States o f  America as repre- 
sented by the Administrator of the National Aeronnan- 5 focus of the parabolic antenna. For the purposes of sub- 
tics and Space Administration sequent discussion herein, consider a line which is on the 
Piled Sept. 25,1961, Ser. NO. 140,443 axis between the center of the parabolic dish 16) and the 
2 Claims. (el. 343-781) feed horn 16 as an axis or reference line; and the angle 
made between a plane perpendicular to the axis through 
This invention relates to antennas of the type having 10 the mouth of the feed horn and the reference line is 90°, 
a reflector dish and, more particularly, to improvements and the angle made between the reference line and the tip 
therein. of the antenna dish is an angle Xo. The angle between 
A typical paraboloidal antenna has a waveguide horn X ,  and 90" is known as the ground-illumination angle. 
positioned at the focus for exciting the antenna and also The angle between X,, and 180" is the region in which 
for receiving any signals reflected therefrom. It  is known 15 spillover of the horn power occurs. A significant amount 
that a considerable amount of power is wasted in the re- of received power comes from the ground-illumination 
gion outside of the paraboloidal-dish-illumination angle. angle over which the ground radiates thermal noise power 
This may be termed spillover power. A significant into the horn, to cause noise signals which interfere with 
amount of power (at least eight to ten percent of the the desired signals reflected from the antenna dish. 
total) falls within the region known as the ground-illu- 20 Considering FIGURE 2, there is shown a plot of the 
mination angle. The ground-illumination angle is the re- distribution of the power radiated or  received by the type 
gion included between a plane passing through the mouth of antenna shown in FIGURE 1 versus the angle made 
of the horn perpendicular to the antenna axis and a line with the reference plane. The power-distribution curve 
which connects the center of the horn mouth to the edge 20 indicates a maximum power on the axis, or the zero- 
of the paraboloidal dish. Since ground-temperature radi- 25 degree line, and then tapers off on either side of this line. 
ation is usually the largest oontributor to the antenna The actual useful power is the power included between 
temperature of a receiving antenna, it is important to re- +Xo and -Xo, which is known as the aperture illumina- 
duce the amount of spillover power in the ground-illumi- tion. The regions between +Xo and +90° and -Xo 
nation region. and -90" indicate the ground-illumination power. The 
An object of this invention is the provision of structure 30 power shown between +Xo and +18O0 and -Xo and 
for reducling the percentage of power received by a wave- -180" is the total spillover power. By employing struc- 
guide horn from the ground-illumination region. ture as shown by this invention, the amount of the total 
Another object of this invention is the provision of a spillover power is reduced substantially to the extent 
simple and improved structure whereby the efficiency of shown by the dotted lines 22, 22'. Effectively, the power 
a paraboloidal-type antenna is increased either for receiv- 35 radiated in the total spillover angle, and to a large extent 
ing or transmitting. within the ground-illumination angle, is attenuated con- 
These and other objects of the invention may be siderably. This, of course, results in the thermal noise 
achieved in an arrangement whereby a conductive ground power being reduced considerably, whereby the antenna 
plane is positioned around the mouth of the wave-guide for temperature is reduced. The antenna efficiency is im- 
preventing the N-plane component of the undesired power 40 proved because the power formerly wasted in spillover is 
from being radiated into the ground-illumination region. now utilized in aperture illumination. 
The ground plane is also tilted at an angle in order to Referring now to FIGURE 3 and to FIGURE 4, in 
effectuate cancellation of the E-plane wave-pattern por- accordance with this invention, there is provided a largc, 
tion of the undesired radiation. flat ground plane 30 around the mouth of the horn 16. 
In an application for patent by Danver M. Schuster 45 This gronnd plane may be made of any suitable conduc- 
and David L. Nixon for Antenna Beam-Shaping Appa- tive metal. This ground plane 30 effectively comprises 
ratus, filted September 25, 1961, Serial No. 140,509, three panels, two side panels 3QA, 30B, which are tilted 
which is assigned to a common assignee, there is shown at some angle a with respect to a center panel 30C, which 
and described a beam-shaping arrangement suitable for is effectively in the plane of the mouth of the horn 16. 
use with both linearly and circularly polarized waves. 50 The use of a large, flat ground plane which is not bent 
This invention is suitable for use with linearly polarized at some angle a eliminates unwanted side and back radia- 
waves. tion for the H-plane pattern, but not for the E-plane pat- 
The novel features that are considered characteristic tern. In the N-plane, the E-vector for the wide angle and 
of this invention are set forth with particularity in the the diffracted fields is everywhere parallel to the ground 
appended claims. The invention itself, both as to its 55 plane. One of the boundary conditions of electromag- 
organization and method of operation, as well as addi- netic theory requires that a tangential E-field go to zero 
tional objects and advantages thereof, will best be under- at a conducting surface. Thus, when the diffracted field 
stood from the following description when read in con- is reflected from the ground plane, it reverses phase, so 
nection with the accompanying drawings, in which: that the total E-field is zero at the surface of reflection. 
FIGURE 1 shows, for the purpose of illustration, an At a small distance farther away, the diffracted and wide- 
antenna of the general type with which this invention is angle fields will be out of phase and cancel. 
employed; Tilting the ground plane in the direction of the E-plane, 
FIGURE 2 is a graph showing, for comparative pur- as is done with panels 30A and 303, produces a shield- 
poses, the energy distribution for the antenna of the type ing effect, as far as the E-radiation pattern is concerned. 
shown in FIGURE 1, without this invention and with 65 The length L of the ground plane must be sufficient to 
this invention; reduce diffraction around the end of the ground plane. 
FIGURE 3 is a plan view of an embodiment of the This has been found to be on the order of three wave- 
invention; and lengths at the frequency at which the antenna is operated. 
FIGURE 4 is a side view of the invention. The length L can also show a resonance effect for medium 
Reference is now made to FIGURE 1, which is a 70 to small ground planes. The angle of tilt, 90"-a, should 
schematic view of the general type of antenna for which be chosen to be about equal to the edge-illumination 
3,209,360 
3 4 
angle, Xo, of the dish. The width across the flat surface ates from said horn and does not reach said reflector dish, 
should be at least two to three times the wavelength at said improvement comprising means for attenuating said 
the frequency at which the antenna is operated. A width unwanted energy including a ground plane adapted to be 
across the flat surface of four wavelengths was utjilized in mounted at the mouth of said horn, said ground plane 
a test model. 5 having a center portion extending in the plane of the 
This invention provjdes an improvement in the beam mouth of said horn and two side portions bent in the sanle 
pattern, as represented by the dotted lines 22, 22' in FIG- direction at an angle away from said center portion in 
URE 3. This device is only suitable for use with linearly the direction of the E-plane, each said side portions hav- 
polarized signals. Effectively, it constitutes a large, fiat ing a length on the order of three wavelengths of said 
ground plane for the 5%-plane and a tilted ground plane 10 energy, a width on the order of two to four times the 
in  the E-plane. wavelength of said energy, the angle at which said side 
There has accordingly been described and shown here- portions are bent away from said center portion being 
in a novel and useful arrangement for attenuating the substantially equal to the edge-illumination angle of said 
power radiated from a dish-type antenna which causes dish. 
deleterious effects whereby the operation of the antenna 15 
is considerably improved. 
I claim: 
1. The improvement for an antenna of the type hav- 
ing a reflector dish and a wave-guide horn for radiating 
energy at said reflector dish and for receiving energy 20 
therefrom, and wherein there is unwanted energy which 
radiates from said horn and does not reach said reflector 
dish, said improvement comprising ground-plane means 
adapted to be mounted about the mouth of said horn for 
eliminating side and back radiation for the H-plane com- 23 
ponent of said unwanted energy, said ground-plane means 
also being bent in the direction of the E-plane for elimi- 
nating the E-plane oomponent of the side radiation of said 
unwanted enerzv. 
References Cited by the Examiner 
UNITED STATES PATENTS 
1/42 Peterson ----------- 343-912 X 
5/42 Icing -------------- 343-783 X 
5/49 Clapp ------------- 343-914 X 
4/52 Williinson ------------ 343-786 
11/52 Van Atta ------------ 343-786 
4/53 Dorne --------------- 343-708 
7/57 Alford ------------- 343-742 X 
2/58 Chu et al. ---------- 343-781 X 
6/58 McClellan ------------ 3 4 3 7 8 1  
FOREIGN PATENTS 
5/59 France. 
2. The impryvement for an antenna of the type having 30 
a reflector dish and a wave-guide horn for radiating en- ELI LIEBERMAN, Actiizg Primary Examiner. 
ergy at said reflector dish and for receiving energy there- HERMAN K. SAALBACH, Examiner. 
from, and wherein there is unwanted energy which radi- 


Antenna beam-shaping apparatus Patent

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