Ultra-Wideband Millimeter-Wave Planar Array Antenna With an Upside-Down Structure of Printed Ridge Gap Waveguide for Stable Performance and High Antenna Efficiency

In this letter, a wideband millimeter-wave (mmWave) planar array antenna with a printed ridge gap waveguide (PRGW) feeding network is presented. A planar bowtie antenna fed by the PRGW is employed as the array radiation element which combines the bowtie with an upside-down electromagnetic bandgap part by using lamination. Thus, with this new upside-down structure, the proposed array antenna achieves a stable, wideband, and high-antenna-efficiency performance. A prototype of ${8} \times {\rm{8\ }}$ array is fabricated and measured. The measured results show that the proposed array has an impedance matching bandwidth (| S 11| < −10 dB) of 50.3% from 18.6 to 31.1 GHz. The maximum measured gain is 22.1 dBi at 29 GHz, and the total antenna efficiency is above 60% with a bandwidth of 45% from 18.8 to 29.8 GHz.