Electromagnetic scattering by arbitrarily shaped reflectors: Subreflector efficiency
Abstract
A general expression for the electromagnetic scattering by an arbitrary shaped reflector is developed and applied in a computer model of offset hyperboloid reflectors. The computed scattering is shown to be in excellent agreement with scattering measurements made on an offset reflector of projected diameter = 24 cm, at frequencies of 10.35 GHz, 20.7 GHz and 44.5 GHz. Next, using the computer model, the efficiency of the subreflector in a dualreflector antenna is calculated as a function of subreflector diameter and for two values of illumination taper. For subreflectors truncated at the rayoptics boundary the calculated efficiency is 0.83 and 0.91, respectively, for truncation diameter of 7.7 lambda and 30.4 lambda, with 5 dB of illumination taper; these respective efficiencies increase to 0.91 and 0.95 with 12 dB of illumination taper. However, subreflectors of diameter about two wavelengths larger than the rayoptics diameter have very nearly unit efficiency.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 October 1984
 Bibcode:
 1984STIN...8525687D
 Keywords:

 Antennas;
 Coordinates;
 Efficiency;
 Electromagnetic Scattering;
 Subreflectors;
 Antenna Radiation Patterns;
 Mathematical Models;
 Optical Properties;
 Spacecraft Communication;
 Communications and Radar