A satellite tracking system at 78GHz using the over-moded TE21 ground-station antenna pattern

Low power cube-satellites are becoming increasingly popular for earth observations and fast data relay. Their low earth orbit means the available time to download data is only about 10 minutes per fly-by. High frequency (71 to 76 and 81 to 86GHz) radio links have the wide bandwidth required for fast data-transfer and very large antenna gain for a modest diameter (meaning low power can be used) but tracking the fast-moving satellite with a high-gain beam is a problem, requiring a pointing accuracy similar to radio telescopes, but with tracking speed up to 3 degrees a second. This paper outlines a method of automatic servo-tracking of the ground-station antenna to the fast-moving CubeSat (once signal has been acquired) using just the over-moded ground-station linear-polarization TE21 mode to obtain Azimuth/Elevation tracking information from the circular-polarized data signal.