Compact Circularly Polarized Patch Array Antenna

A circularly polarized (CP) patch array antenna with compact size is proposed in this letter. The proposed radiation element consists of 2 ×2 partly overlapped square patches and one cross-shape slotted substrate integrated waveguide (SIW) cavity with four feeding ports. Stacked structure is adopted for the sake of a compact size and convenient integration with active circuits. Sequential rotating technique is adapted and applied to the radiation element with two-dimensional symmetry to enhance axial-ratio bandwidth performance. The subarray can realize a gain of 11 dBic at 23.6 GHz with the radiation efficiency up to 90%. A prototype array antenna with four subarrays is designed and fabricated to validate the proposed method using low-cost multilayer printed circuit board (PCB) process. Experimental results on reflection coefficient, axial ratio, and gain agree well with simulation results. The prototype array antenna can function well from 23 to 24.2 GHz (5%) with its reflection coefficient under -13 dB and its axial ratio under 3 dB. A maximum gain of 16 dBic can be obtained at 23.3 GHz.