Basic configuration consists of large parabolic dish reflector, smaller hyperboloidal subreflector, and two sets of monopulse feeds located in conjugate focal region on boresight axis of dish

Deerkoski, L. F.

Schmidt, R. F.

English

NASA Technical Reports Server

October 1975
	
B75-10215 
•	 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 10 the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Variable . Beam width Antenna Without Moving Parts 
The problem: 
Variable-beamwidth antennas are used in search 
and tracking operations. In the wide-beamwidth 
mode, the antenna searches for the signal. Once the 
signal is acquired, the antenna is switched to the 
narrow-beamwidth mode for tracking. In conven-
tional arrangements (see NASA Tech Briefs 
B74-10041 and B74-10257), beamwidth is varied 
mechanically. A set of servos moves the reflectors and 
subreflectors in relation to each other to obtain the 
necessary beamwidth. Although effective, the moving 
parts add extra weight to the system. 
The solution: 
A new monopulse antenna system incorporates two 
sets of feeds to vary the beamwidth. Because no 
moving parts are used, this system is lighter than the 
conventional ones. This makes it suitable for 
applications in which weight is a critical factor. 
Figure 1. Antenna Configuration
Figure 2. Two Sets of Feeds 
How it's done: 
The basic antenna configuration is shown in Figure 
1. It consists of a large parabolic dish reflector, a 
smaller hyperboloidal subreflector, and two sets of 
monopulse feeds located in the conjugate focal region 
on the boresight axis of the dish. 
The two sets of feeds are shown in a magnified 
drawing (Figure 2). The inner set, comprising four 
feed elements, is positioned within the effective region 
of the Airy disk at the conjugate focal plane of the 
subreflector. This subsystem, along with the large 
disk 'reflector, provides narrow-beamwidth mono-
pulse, sum-and-difference channel radiation patterns 
that are suitable for tracking-mode operation. The 
second or outer set of monopulse feeds, located 
outside the Airy disk in the region of the first Airy 
ring, widens the beamwidth of the monopulse 
radiation pattern for acquisition-mode operation. 
(continued overleaf) 
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When the antenna operates in the wide-beamwidth Note: 
pattern (the acquisition mode), the difference channel Requests for further information may be directed 
is supplied by the outer set of feeds. The sum channel to: 
pattern is obtained by attenuating and phase shifting Technology Utilization Officer 
the sum channel pattern of the inner feeds. This then Goddard Space Flight Center 
is added to the sum channel pattern of the outer feeds. Code 704.1 
The effect is that the sum channel pattern of the inner Greenbelt, Maryland 20771 
feeds is widened by the interferometer characteristics Reference: T5P75-10215 
of the outer feeds. In the narrow-beamwidth mode 
(the tracking mode), the sum-and-difference channel Patent status: 
radiation patterns are obtained from the inner set of This invention is owned by NASA, and a patent 
feeds.	
- application	 has	 been	 filed.	 Inquiries	 concerning 
The entire operation is accomplished by independ- nonexclusive or exclusive license for its commercial 
ent	 control	 of	 the	 sum-and-difference	 channel development should be addressed to: 
patterns. This control is provided by the monopulse Patent Counsel 
network consisting of a system of hybrid junctions. Goddard Space Flight Center 
The network is connected to the feeds behind the Code 204 
antenna. Since the beamwidth is controlled purely by Greenbelt, Maryland 20771 
diode switching, there are no moving parts.
Source: Leonard F. Deerkoski and 
Richard F. Schmidt 
(GSC-11924)
Categories: 02 (Electronics Systems) 
01 (Electronics - Components 
and Circuitry) 
B75-10215	 03 (Physical Sciences) 


Variable-beamwidth antenna without moving parts

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