A study of cross polarization effects in reflector antenna arrays

This paper addresses the issue of cross-polarized field components of an array of antennas as compared to that of individual elements of the array. For a single antenna, the co- and cross-polarization components are completely correlated in terms of phase and amplitude in a given direction. The co/cross-pol relations vary as a function of angular position from peak of the beam, which is important when there is pointing error. More specifically, for the reflector antennas, this relation might vary as the antenna points in different directions in azimuth and elevation, due to the changes in gravity profile, wind effects, temperature changes, etc., on the surface and feed/sub/main reflector alignment. In an array environment, these changes will vary among various antennas in the array, and indeed very small mechanical and design variations in the antenna elements (in terms of feed horns, feed/reflector misalignments, surface variations, etc., will contribute to the cross polarization variations. Here we present a study of the effects of the variation of individual antennas on the overall polarization of an array. We first provide a general introduction to the polarization concept and formulation and then provide the results of a statistical study. Ample plots are provided to illustrate the effects. We show that the co/cross polarization ratio for the array is no higher than the worst of the individual elements and indeed is much lower in the majority of cases. This study is useful in the general design of large arrays of small reflector antennas in many instances and specifically for the NASA/JPL Deep Space Network (DSN).