A Comparison of Dual-Polarized, Periodic Arrays of Coincident and Noncoincident Phase Center Radiators

We compare the polarization characteristics of coincident and noncoincident phase center, dual-polarized array antennas. Our analysis generalizes existing work on coincident phase center radiators and examines the dependence of polarization purity on the spatial separation between the two orthogonal sources of an idealized, dual polarized array element. We show that the spatial separation of the sources induces a phi-angle and frequency dependence in the far-field polarization, which vanishes when the sources are coincident. We discuss how attenuators, delay devices and phase shifters can compensate for the spatial separation and angular-dependent properties of the individual source radiation patterns. We also show that over a significant instantaneous bandwidth (20% to 30%) the noncoincident radiator's polarization purity degradation is relatively minor, even at wide scan angles.