Offset spherical tri-reflector with shaped subreflectors for wide scan applications

A description is given of the design and analysis of a shaped spherical trireflector which was considered as a candidate for use on a future European data-relaying satellite. The antenna geometry is outlined. The antenna also includes a feed, a feed reflector, and a subreflector. The beam scanning is implemented by moving the feed and the subreflectors about the center of the spherical main reflector. The performance is shown for an antenna equipped with a monopulse tracking system modeled by a combination of TM/sub 01/ and TE/sub 21/ circular waveguide modes. The patterns only change slightly as the antenna is scanned. Typically, the sum beam becomes slightly elliptical. A summary is given of the calculated peak directivity, the scan loss, and the spillover loss for the 3.46 m antenna with no imperfections for the beam on-axis, scanned 10 degrees up and down in natural vertical plane and 10 degrees to the side. The change in spillover loss is included in the scan loss.<>