Antenna comprises two parabolic cylinders placed orthogoanlly to each other. One cylinder serves as main reflector, and the other as subreflector. Cylinders have telescoping sections to vary antenna beamwidth. Beamwidth can be adjusted in elevation, azimuth, or both. Design has no restriction as to choice of polarization

Schmidt, R. F.

English

NASA Technical Reports Server

Jaiivary 1975	 B74-10257 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Bidirectional Zoom Antenna 
In a variable-beamwidth (or zoom) antenna, beam-
width can be widened for low-gain operation or 
narrowed for high-gain operation by simple switching. 
In the low-gain mode the wide beamwidth allows the 
antenna to search a large area in one scan. When a 
signal is picked up, the antenna is switched into the 
high-gain mode. The resulting narrow beam increases 
communications efficiency. Two variable-beamwidth 
antennas have already been described in NASA Tech 
Brief B74-10041 (GSC-11760). 
Recently a new bidirectional zoom antenna has 
been developed. It comprises two parabolic cylinders 
placed orthogonal to each other. One cylinder serves 
as main reflector, and the other as subreflector. The 
cylinders have telescoping sections to vary the antenna
beamwidth. The beamwidth can be adjusted in 
elevation, azimuth, or both. The design has no 
restriction as to the choice of polarization. 
As shown in Figure 1, the main reflector is a 
parabolic cylinder with focal axis f1 . Its bottom edge is 
truncated where the dotted line starts. The dotted line 
shows an imaginary continuation of the parabola. The 
subreflector is not truncated and forms a parabolic 
cylinder orthogonal to the main reflector. Its focal 
axis f2, orthogonal to focal axis f1, intersects the top 
edge of the main reflector. Located at the intersection 
is a monopulse multibeam feed aimed at the sub-
reflector. The feed rotates as the beamwidth is 
changed, to maintain the feed position within the Airy 
disk of the system. 
Feed 
-
	 -A
f2 Axis 
 Beam 
	
Main f 	 Moving 
	
Ref lector -..,(
	
-,-"Section 
\.f 
Subreflector 
Note: Beam Arrows are Reversed 
During Reception 
\
Side View
Telescoping	 Main 
Section	 Feed	 Reflector 
I	 -	 I Subreflector 
I	 I 
L----------- J 
Front View 
Figure 1. Antenna Configuration in the High-Gain Mode 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	
information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19740000257 2020-03-17T13:58:32+00:00Z
Feed 
Main Reflector-
/• 
Beam 
Feed	 - Main 
f2 Axis	 - 
Beam 
Beam
S 
Subreflector \
\
\
_____1 r	 _i__--•] 
f1 Axis 
I	 I 
I	 I 
I	 I 
I	 I L----------I 
Figure 2. Antenna Configuration in the Low-Gain Mode 
The main reflector has telescoping sections on its 
right and left sides. The subreflector has a single 
telescoping section to increase or reduce its length. 
The telescoping sections on the main reflector control 
azimuth beamwidth, whereas the telescoping section 
of the subreflector controls elevation beamwidth. The 
sections are moved by rack-and-pinion mechanisms 
driven by servos. 
In Figure 1 all sections are extended to provide the 
high-gain mode. The energy from the feed irradiates 
the subreflector. This energy reflected from the main 
reflector forms a narrow-beam output. 
In the low-gain mode, as illustrated in Figure 2, all 
sections are retracted. Part of the energy from the feed 
misses the subreflector and continues in a straight line 
as spillover. The other part bounces from the sub-
reflector and forms a wide beam. The resulting 
pattern covers a wide area.
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: TSP74-10257 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial 
development should be addressed to: 
Patent Counsel 
Goddard Space Flight Center 
Code 204. 
Greenbelt, Maryland 20771 
Source Richard Schmidt 
Goddard Space Flight Center
(GSC-11862) 
Categories: 01 (Electronics - Components and 
Circuitry) 
02 (Electronics Systems) 
B74-10257
	
03 (Physical Sciences)	
.. .. ...............


Bidirectional zoom antenna

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