Design and experimental results of a wide-angle coverage 45 GHz multiple-beam antenna for military satellite communications are presented in this paper. The high-gain spot beams with low sidelobe levels and efficient adjacent beam overlap are generated by employing an offset parabolic reflector with overlapping feed clusters. The beam shape can be adapted to cancel either single- or multiple-jammers by varying excitations within the feed cluster corresponding to the beam. Development of antenna components including Potter horn, polarizer, phase-amplitude controller, and beamforming network is discussed. Measured results of the demonstration antenna have shown that sidelobe and crosspolar levels of better than -25 dB are achieved for beams scanned over an eight-degree diameter circular coverage region. The adapted patterns of the antenna agree well with the computations, and null depths of better than 30 dB have been realized over a 4.5% bandwidth. >

Development of a 45 GHz multiple-beam antenna for military satellite communications

A multiband antenna system supporting multiple communication services and multiple beams is presented. Key component of the antenna is the smooth-walled horn that has efficient radiation patterns over three frequency bands that are spread over an octave bandwidth and provides optimal illumination on the reflector at all the frequency bands. Results of the feed horn and the antenna are discussed.

Antenna System Supporting Multiple Frequency Bands and Multiple Beams

The investigation results of multimode feed horns are presented, which provide multi-phase centre radiation performance with the reflector. These feed horns with reflector assembly are suitable for radar systems, where ground moving target indicator (GMTI) mode implementation is desired. The simulations were carried out using Ansoft Corporation's HFSS v8.5 for feed horn, and Ticra's GRASP v7.0 for the reflector.

Multimode feed horn providing multiphase centres with offset reflector antenna

An algorithm to measure in Anechoic Chamber (AC) the antenna Phase Center (PhC) position is presented. It is based on the assumption that the PhC belongs to the geometrical symmetry axis of the antenna under test. In particular, the algorithm is able to account for the possible presence of an unknown misalignment between such axis and the rotation axis of the turntable of the AC, thus extending the two point-approach available in the literature. The method has been validated through measurements on an X-band microstrip radar antenna.

Measurement of the Antenna Phase Center Position in Anechoic Chamber

The phase centre of a feed horn is a theoretical point along the axis of the horn which is the centre of curvature of the phase fronts of the spherical waves. In most feeds, there is a phase centre region rather than a single point because radiation is due to a summation of spherical waves, which seems to emanate from the aperture [1]. Determination of the feed phase centre helps, its location relative to the focal point of the reflector. Different techniques to compute and determine the phase centre location in single and dual reflector geometries are reported in [1-3]. However, when the feed horn has a multimode excitation, the amplitude and phase control of modes provide different constant phase centre locations, which in turn helps to conceptualize a virtual array on the reflector antenna aperture [4].

Performance of multimode (TE 11 +TE 21 ) feed horn for offset reflector antenna providing multiphase centres

Phase center of reflector antenna feeds

A multiple beam satellite system is being currently investigated by the Canadian Department of National Defence for possible applications in future military communications. The EHF Satcom will be operated in the 44/20 GHz links with high gain spot beams designed to provide Canadian coverage from a geosynchronous or a tundra orbit. The authors present the design of the multi-beam receive antenna system and its beam-forming network. Computed results of the antenna electrical performance are also presented. >

K. Rao

Papers

Phase center of reflector antenna feeds

Multiple beam antenna design for the Canadian EHF Satcom