Cassegrain Antenna With Hybrid Beam Steering Scheme for Mobile Satellite Communications

Abstract

A hybrid antenna (HA) with a modified beam steering method is proposed. This antenna has a Cassegrain structure composed of two reflectors and a feeder. The parabolic-shaped main reflector is designed for high gain, while the subreflector is rotational and flat. The feeder is a phased array with arbitrary shaped aperture and 20 element antennas. The HA is capable of two-dimensional beam steering by means of two operations: rotation of the subreflector and phase control of the feed array. The subreflector is small in size and weight, so it can provide rapid beam scanning. Designed to be loaded in vehicles, the HA and can communicate with satellites on the move by tracking the beam control of the feed array. A prototype of the HA is fabricated with aluminum using a machining center operated by computerized numerical control. The prototype is operated at Ka-band for TX and K-band for RX with gains of 47 dBi and 44.4 dBi, respectively, at a steering angle of 0 degrees. The two-dimensional beam steering within +/- 2 degrees with respect to 45 degrees elevation is realized by the subreflector and feed array. All radiation patterns in the beam steering zone meet ITU-R s.465-5 regulations.