Directivity optimization of a reflector antenna with cluster feeds  A closedform solution
Abstract
The directivity of a reflector antenna deteriorates as the feed moves away from the focal point for beam scanning. This deterioration can be substantially reduced if a cluster feed instead of single feed is used to control a beam. A closedform solution is presented for the cluster excitation to achieve the optimum directivity. For an offset 108 lambda parabolic reflector scanning 10 beamwidths, the optimum directivity achieved by a 19element (sevenelement) cluster is 12 dB (8 dB) higher than that of a single element. Comparison of the optimumdirectivity design and the popular conjugate field matching design is made. When the cluster spacing d is greater than 1 lambda, it is found that the optimum directivity is higher than that of conjugate field matching (CFM) scheme by an insignificant amount, although the excitations of two designs can be quite different. For d less than 0.5 lambda, the optimum design may exhibit the supergain phenomenon, namely extremely high directivities achieved by an oscillatory cluster excitation.
 Publication:

IEEE Transactions on Antennas and Propagation
 Pub Date:
 November 1985
 DOI:
 10.1109/TAP.1985.1143516
 Bibcode:
 1985ITAP...33.1163L
 Keywords:

 Antenna Design;
 Antenna Feeds;
 Directional Antennas;
 Directivity;
 Reflectors;
 Antenna Arrays;
 Antenna Radiation Patterns;
 Matrices (Mathematics);
 Polarization (Waves);
 Communications and Radar