Reflector collects energy over large region of space and focuses it toward small region where antenna feed is located. When incident energy is in form of plane wave, logical choice for shape of reflecting surface is paraboloid which converts plane wave into spherical wave that converges at a point

Ludwig, A. C.

English

NASA Technical Reports Server

July 1973
	
B73-10291 
•	 NASA TECH BRIEF 
NASA Pasadena Office
	 -4r 
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. 
High-Gain Antenna with Singly-Curved Reflector 
The problem: 
To provide a large, unfurlable, high-gain antenna 
for long-distance spacecraft missions. 
The solution: 
Design a two-reflector system in which the main 
reflector is a segment of a cone. 
How it's done: 
The basic purpose of a reflector is to collect energy 
over a large region of space and focus it towards a 
small region where the antenna feed is located. When 
the incident energy is in the form of a plane wave, 
the logical choice for the shape of the reflecting sur-
face is a paraboloid which converts the plane wave 
into a spherical wave that converges at a point. Para-
boloid reflectors are very desirable from the stand-
point of management of rf energy because a feec 
which couples well with a converging spherical wave 
can be readily constructed; the reflectors are trouble-
some, however, because they have doubly-curved 
surfaces which are difficult to construct within close 
tolerance limits. 
In contrast, singly-curved surfaces are desirable 
from a structural standpoint, but they are not as ef-
ficient as doubly-curved surfaces inasmuch as they 
bring plane waves to focus in only one dimension; at 
best, singly-curved surfaces convert a plane wave into 
a cylindrical (or conical) wave which converges to-
wards a line segment. 
A cone will focus plane waves along a line in the 
form of a conical wave; for a cone with an included 
angle of 900, the focused waves are cylindrical. By
employing a line-source feed, this reflector may be 
used by itself. Alternatively, a subreflector may be 
used to refocus the energy to a point, as illustrated 
in the Gregorian form shown in the diagram; there is 
Z 
a corresponding Cassegrainian form. All surfaces are 
figure-of-revolution about the Z axis, and the contour 
of the secondary reflector is parabolic. Another fea-
ture is that the main reflector aperture illumination 
has a ring-like pattern, i.e., there is a hole in the center. 
This hole extends to slightly less than one-half the 
radius of the main reflector, and the illuminated por-
tion has about 78% of the area of the full aperture. 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000291 2020-03-17T06:55:07+00:00Z
Thus, this type of antenna has a maximum gain 
which is 78% of the maximum gain of a full circular 
aperture of the same diameter. However, in a con-
ventional Cassegrainian or Gregorian system, the 
subreflector blocks an area of perhaps 1-2% of the 
total area; in addition, this area is illuminated by 
roughly 2-4% of the total feed power, so the net 
blockage loss in a conventional system is 3-6%. 
Therefore, the relative potential gain of this design 
is about 80-83% of the standard value. Further, the 
design has the interesting property of reflecting the 
center of the feed pattern to the outer edge of the 
main reflector; this results in improved illumination 
efficiency, which results in overall efficiencies equal 
to conventional paraboloids. However, since the basic 
consideration of this design is structural rather than 
electrical, any comparisons must include structural 
effects. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP 73-10291 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,680,144). Inquiries concerning nonex-
clusive or exclusive license for its commercial devel-
opment should be addressed to: 
NASA Patent Counsel 
Mail Code l 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Arthur C. Ludwig of 
Caltech/JPL
under contract to

NASA Pasadena Office 
(NPO-11361)
. 
. 
B73-10291	 Category 02


High-gain antenna with singly-curved reflector

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