A Compact Dual Circularly Polarized Microstrip Patch Array with Interlaced Sequentially Rotated Feed

This communication presents a microstrip patch array, using sequentially rotated feed networks to achieve dual circular polarization in the same band. By interlacing the microstrip patches of adjacent 2 × 2 subarrays, the element spacing is minimized to avoid the challenging grating lobe issue. In this manner, the number of radiating elements is reduced from the conventional 4N to 2N + 2, where N is the number of 2 × 2 subarrays. The array is implemented on a two-layer substrate, with the upper layer hosting the microstrip patch array and the sequentially rotated networks, and the lower layer hosting the power dividers, sharing a common ground plane in the middle. To validate this novel configuration, a prototype is fabricated and measured. It achieves both |S11| < -10 dB and axial ratio < 3 dB bandwidth of 12.5% (4.95-5.61 GHz) for right-hand circular polarization and 14.7% (5.05-5.85 GHz) for left-hand circular polarization. The isolation between the orthogonal circularly polarized ports is about 12 dB in band.