Analysis and Design of Intrinsically Dual Circular Polarized Microstrip Antennas Using an Equivalent Circuit Model and Jones Matrix Formulation

Planar dual circular polarization (CP) antennas can be realized with a linearly polarized antenna and a quadrature hybrid, but the hybrid is lossy and undesirable for satellite communications applications where efficiency is paramount. There are surprisingly few hybrid-free, intrinsically dual CP microstrip antenna (MSA) designs in the literature. One reason for this is that it is challenging to obtain high isolation between ports while maintaining low return loss and good polarization quality. To resolve this problem, a method for multicriterion design optimization of dual-CP MSAs is proposed. The method is based on an accurate equivalent circuit model combined with a Jones matrix representation of the antenna response. The model explains the counter-intuitive tradeoff between cross-polarization isolation and impedance mismatch factor. The model also provides an analytical relationship between axial ratio bandwidth and impedance bandwidth, and allows the Wheeler cap method to be generalized to multiport, dual polarization antennas. Based on insights provided by the analysis, an effective matching and decoupling scheme is proposed, leading to an intrinsically dual CP MSA design that is competitive in performance with a dual linear antenna combined with a hybrid. Results are validated by comparison to full wave simulations for practical dual CP antenna examples.