In this paper, a Fabry-Perot cavity (FPC) antenna with a partially reflective surface (PRS) consisting of two dielectric slabs with identical thickness and permittivity to increase the gain with wide bandwidth is presented. The PRS is placed in front of a broadband U-shaped microstrip patch antenna to create an air-filled cavity between the PRS and the ground plane of the antenna structure. The configuration of the two dielectric slabs aims to create a positive phase gradient of the reflection coefficient, which strongly controls the gain bandwidth performance. The proposed PRS was first designed and analyzed using a transmission line model and then verified by a full-wave simulation. The measurement results show that the proposed FPC antenna achieves a gain improvement of up to 5 dB compared to the antenna without PRS, with a 3-dB gain bandwidth of 11.5% and a broadside peak gain of 9.88 dBi. In addition, the measured impedance bandwidth is approximately 18.8% and ranges from 4.95–6 GHz, which covers the required frequency band for vehicle-to-everything (V2X) applications.

Pure metallic reflectarray antennas have good power efficiency and low fabrication cost, which were limited to single band operation. A dual-band reflectarray antenna is developed for two directional beams by two feeds. The reflecting elements are metal waveguides, and have novel properties of both resonant and non-resonant modes at the two frequency bands. The low and high frequency bands can be easily separated by the cutoff frequency of waveguide modes. The phase changing mechanisms via ray optics and fundamental waveguide modes, respectively provide simple formulations for elemental structure design of directional beams. Radiation characteristics of the linear and circular polarizations are cross-examined with good performance by full-wave simulations using HFSS, FEKO and CST at 28 and 60 GHz bands for 5G front-haul network applications.