Impact of Element Pattern Symmetry on the Effective Degrees of Freedom in Dual-Polarized GNSS Adaptive Antenna Arrays

The effect of element pattern symmetry on the performance of dual-polarized global navigation satellite system adaptive antenna arrays is investigated. To this end, using analytical expressions for the far-fields of circular microstrip antennas, the steady-state beamforming performance of a two-element dual-polarized array with three degrees of freedom (DOFs) is studied through many Monte Carlo simulations. It is shown that in the presence of randomly polarized interferers, regardless of the element pattern symmetry, the dual-polarized array can use all its DOF effectively to suppress up to three interferers and is as effective as a four-element right-handed circularly polarized (RHCP) array. It is, however, shown that if the interferers are RHCP, the dual-polarized array can use its DOF effectively only when the element patterns are asymmetric (unequal in E- and H-planes) and is ineffective in suppressing more than one interferer when the element patterns are symmetric (equal in E- and H-planes). This limitation is important in practice if the interferers are known to be RHCP and the array ground plane is small, since the patterns of microstrip antennas with small ground planes can become nearly symmetric. This finding is verified with a fabricated prototype of a two-element dual-polarized array with a small ground plane.