Circularly Polarized Substrate Integrated Waveguide Antenna With Wide Axial-Ratio Beamwidth

A circularly polarized (CP) substrate integrated waveguide (SIW) antenna is presented. First, our study demonstrates that wide axial-ratio beamwidth can be achieved by exciting a square slot with four pins. Second, gap rings are employed around the pins to control the resonant frequency of the antenna. After the variation of thee diameters of gap rings, the frequency of best impedance match corresponds to that of the widest axial-ratio beamwidth. Finally, a CP antenna is designed and fabricated. Experimental results are found in good agreement with simulations in terms of radiation patterns, gain, axial ratio, and reflection coefficient. In particular, the 3-dB axial-ratio beamwidth at the center frequency of 7.98 GHz is extended to 150°.