MILSTAR reflector antennas with electronic tracking feeds

Current airborne reflector designs for MILSTAR use mechanical techniques for developing a signal to track a satellite. If ionospheric scintillation is present, then slow mechanical tracking is subject to large errors. These errors are avoidable with monopulse tracking. The benefit of monopulse can be realized, without incurring its cost and complexity, by rapid sequential lobing often referred to as pseudo-monopulse or single-channel monopulse. This paper discusses two different feed designs that develop a sum and two difference signals needed for monopulse, and an electronic network to sequentially select and phase reverse the difference signals in combination with the sum, thereby converting the monopulse feed to a pseudo-monopulse system. The first antenna to be discussed is an elliptically shaped offset-fed reflector intended for platforms that require a low-profile antenna. The second antenna is a conventionally-shaped Cassegrain reflector system. In addition to describing the feed approaches, pattern measurements of each antenna are presented over the MILSTAR receive and transmit frequency bandwidths. The antenna designs were funded by the Air Force´s Electronics System Center (ESC) as risk reduction antenna contracts under the MILSTAR Low Cost Terminal Program