Compact Groove Diamond Antenna in Gap Waveguide Technology With Broadband Circular Polarization at Millimeter Waves

In this article, three compact antennas using the ridge gap waveguide (RGW) technology working in the millimeter-wave band (60 GHz), with a high-purity and broadband circular polarization (CP), are numerically and experimentally analyzed. The structure is fed from the bottom by means of a standard WR-15 waveguide (V-band) to make it compatible with standard measurement systems. It is coupled with a miniaturized step transition to a ridgeline that ends in two arms of different lengths. CP is generated in a simple and effective way, by means of two orthogonal feeder arms that excite a CP in a diamond-shaped slot on top. Simulations and measurements have an excellent agreement reaching a matching bandwidth (S
₁₁
<; -10 dB) from 60.3 to 69.6 GHz (>9 GHz). Applying the axial ratio criterion (AR <; 3 dB) the bandwidth in CP is 14.48%, with respect to the central frequency (60.3-69.6 GHz). The maximum gain is obtained with the most evolved design incorporating a diamond aperture with a horn taper and a circular groove, reaching a value of 11.12 dB at 67.3 GHz.