Axial Ratio Improved and Beamforming Enhanced Circularly Polarized Phased Array

In this article, a novel circularly polarized (CP) phased array is proposed with the augmented feature of high-precision beamforming with low axial ratio (AR) and wide AR bandwidth. First, the two-stage sequential rotation feed (SRF) technique is adopted in the CP phased array, broadening the AR bandwidth. Then, the innovative 180 degrees-90 degrees/90 degrees-180 degrees combined SRF network is implemented in the CP phased array, to perform a high-precision beamforming, ensuring low AR and AR bandwidth of scanning beams. Utilizing the proposed SRF topology, output phase differences of the feed network are kept constant over the operating band with an effective improvement of port isolation. Moreover, the coupling transition with filtering responses is applied to reduce the cost and complexity of fabrication. Long blind vias that require the back-drilling process are avoided. Finally, a prototype of the CP phased array for Wi-Fi applications is fabricated. The 180 degrees-90 degrees/90 degrees-180 degrees combined SRF beamforming network is measured separately, with highly stable output phase differences and isolation at output ports of higher than 12.17 dB over the operating band from 2.30 to 2.60 GHz. With the proposed SRF beamforming network, the CP phased array supports a wide-angle scanning of +/- 50 degrees, with high precision of pointing error <= 1 degrees. The AR of beams is lower than 1.31 dB at 2.45 GHz. The AR bandwidth (AR <= 3 dB) of steered beams is 28.6%, from 2.15 to 2.85 GHz.