Wideband Circularly Polarized Substrate Integrated Waveguide Endfire Antenna System With High Gain

A K-band endfire substrate integrated waveguide (SIW) circularly polarized (CP) antenna system on a single-layer printed-circuit board is proposed. A high-gain SIWH-plane horn and a Vivaldi antenna are developed to produce two orthogonal polarizations in the plane of the substrate. They are combined with a low-profile SIW 3-dB coupler to provide identical feeding amplitudes with 900 phase difference. The performance of the CP antenna system is demonstrated over the 23-27-GHz frequency range by comparing simulations and measurements in terms of gain, axial ratio, radiation pattern, and return loss. The results show that the proposed antenna system operates with a wideband 3-dB axial ratio from 24.25 to 26.5 GHz and a high and uniform gain of almost 8 dB. Measured results are found in good agreement with simulations.