Synthesis of Circularly Polarized Cylindrical Microstrip Antennas

A set of new formulations derived from the cavity model (CM) that significantly improve the design of cylindrical single probe-fed circularly polarized rectangular microstrip antennas (CPRMAs) are presented in this article. Comprehensive analysis shows that differentiation of the dominant modes effective loss tangents in the far-field expressions gives rise to new closed-form design equations suitable for electrically thin antennas, extending the applicability and improving the CM accuracy for electrically small and large radii cylinders. Furthermore, a function is proposed to estimate the minimal number of significant terms needed in the far-field infinite series to portray the fields radiated by the antenna accurately. The proposed formulations are also used as part of an iterative CM-based algorithm that fully solves the issue of synthesizing a cylindrical CPRMA for a user-defined input impedance. Several antenna examples are compared to full-wave simulations to demonstrate the algorithm's accuracy. To validate the proposed formulations, a right-hand circularly polarized cylindrical antenna prototype is designed and built to operate at 1.575 GHz over a cylinder with a radius of 25 mm. Comparisons between theoretical and experimental results show excellent agreement.