UHF satellite array nulls adjacent signals

It is shown how a circularly polarized satellite crosslink antenna provides excellent rejection while maintaining a wide pattern bandwidth. The array treated here uses eight circularly polarized elements placed around the periphery of an existing mission antenna. To obtain a split-beam pattern with satisfactory gain and nulling performance, the array elements are excited in rotating phase of the second mode. The phase of a particular array element in this mode is equal to two times the azimuth angle corresponding to the location of the element. Patterns are computed to investigate the radiation characteristics as functions of frequency, azimuth angle, and element patterns and to explore the effects of small amplitude and phase excitation errors on nulling performance. A figure is included showing the computed patterns at the scale frequencies of 675 and 738 MHz for a radius of 9 in. and a dipole-to-reflector spacing of 6.5 in.