Bandwidth Limits for Lossless, Reciprocal PEC-backed Arrays of Arbitrary Polarization

A bandwidth limit was recently developed for antenna arrays backed by a PEC ground plane, under pure TE or TM polarization . In this paper, we extend this result to account for simultaneous excitation of both TE and TM modes, yielding a more general bandwidth limit for lossless and reciprocal PEC-backed arrays (LRPBA) under arbitrary polarization. For a linearly polarized LRPBA, the result is a simple expression for the maximum realizable impedance bandwidth as a function of scan angle. For a circularly polarized LRPBA, there appears to be a fundamental trade-off between polarization purity and impedance bandwidth. Overall, the maximum possible impedance bandwidth of a LRPBA at broadside is twice that of the same array whose polarization is held constant over frequency.