A Single-Layer Dual-Band Dual-Sense Circularly-Polarized Patch Antenna Array with Small Frequency Ratio

A planar dual-band dual-sense circularly polarized (CP) microstrip array is proposed. This array is implemented on a single-layer substrate and easily extended to the design of a larger array. A new antenna element is exploited by symmetrically placing the non-radiative resonators on four side edges of a square patch. A quantitative design method is proposed based on the equivalent circuit model of the antenna element. For given two operating frequencies, the required design parameters of the patch and non-radiative resonators can be calculated. Theoretical magnitude ratio and phase difference responses of two far-field components, as well as axial ratio responses under different parameters, are presented to reveal the characteristics of the antenna element. Full-wave simulation results are found to agree well with the theoretical ones. To further validate the effectiveness, a 2×2-element dual-band dual-sense CP array operating at 2.40 and 2.68 GHz is designed, fabricated and measured, where a small frequency ratio of 1.117 is achieved. The measured realized gains in the low and high bands are 11.7 and 11.8 dBi, respectively, which are approximately equal.