Compact Single-Layer Wideband CP Antenna Array With Stable Radiation and Filtering Performance Using Patch Resonator and SIW Cavity

In this letter, a new design concept to enhance the bandwidth and out-of-band suppression of the circularly polarized (CP) patch array antenna is proposed without requiring increased size or complicated structure. Based on the similarities in the processing technique and resonant characteristics between the patch resonator and substrate-integrated-waveguide cavity, the two types of resonators are integrated to excite two pairs of orthogonal degenerate modes, which have nearby frequencies and exhibit similar radiation performance. These four radiative modes facilitate significant improvement of both the impedance and gain bandwidths. Meanwhile, two CP axial ratio (AR) poles are produced, thus effectively enhancing the CP bandwidth. Besides, the out-of-band suppression level is enhanced with a radiation null appearing at the upper stopband. To clearly reveal the proposed broadband concept, two array antennas with the scales of 1 × 2 and 2 × 2 are constructed and discussed. Both prototypes demonstrate similar performance improvement. Specifically, the 2 × 2 array achieves an AR bandwidth of 5.94% along with the stable broadside gain of 13.81 dBi to 14.23 dBi. Compared to the traditional patch antenna array, the bandwidth is approximately 3.12 times wider while radiation performance and structural advantages are fully preserved.