Printed RGW Circularly Polarized Differential Feeding Antenna Array for 5G Communications

In this paper, a differential feeding circularly polarized antenna array implemented with printed ridge gap waveguide technology for millimeter-wave applications is proposed. The differential feeding power divider is designed based on aperture coupling to achieve a stable 180° phase imbalance over 20% operating bandwidth at 30 GHz with sufficient matching level. This power divider is deployed to excite and test the proposed differential feeding antenna. The proposed antenna is formed by a rectangular aperture having a circular-shaped polarizer consisting of patch surrounded by an open-end ring, which is differentially fed. This polarizer is deployed to achieve a circular polarization radiation through a 10 % frequency bandwidth. A high-gain antenna array is implemented by extending the aperture size to have four radiating elements. The antenna array is fabricated, where the experimental results verify a -10 dB impedance bandwidth from 27.7 to 32.4 GHz (15.6%). Moreover, a 3 dB axial ratio bandwidth over 10 % is achieved, which is sufficient enough to cover the operating bandwidth of potential 5G applications at 30 GHz. The fabricated prototype achieves a 3 dB gain of 14 dB, with low cross polarization and a radiation efficiency higher than 84% over the whole operating frequency bandwidth.