Constant-beamwidth antenna development

Broad-band microwave receiving and tracking systems generally require medium to high-gain antennas that have a minimum beamwidth requirement dictated by probability of intercept and acquisition time considerations. This paper discusses a technique whereby the secondary pattern beamwidth variation is decreased or eliminated over portions of the frequency band of these antennas. The antennas consist of a parabolic reflector illuminated by a ridge-loaded horn. A brief analysis, based on empirical antenna equations, is presented along with a description of a pencil-beam antenna and a very broad-band conical-scan tracking antenna that were made possible through the use of this technique.