Interest in the mmWave and sub-THz bands for next-generation communication and radar systems is increasingly growing due to the available electromagnetic spectrum. This has led to an urgent need to develop low-loss and low-fabrication-cost technologies that perform well at these frequencies. The Gap Waveguide (GW) technology is an emerging and viable contender for the development of radio frequency passive components and antenna systems. The GW technology is based on the parallel-plate waveguide principle. According to Maxwell’s equations, ideally, no wave propagates within a structure if the top plate consists of a perfect electric conductor (PEC) while the bottom plate is a perfect magnetic conductor (PMC), and the distance between the plates is less than a quarter wavelength. This PMC structure creates high surface impedance characteristics which provide cutoff to all propagating modes within the airgap. In practice, these magnetic conductors can be created artificially using an Electromagnetic Band Gap (EBG) structure. Based on this simple principle, considerable research and development of novel components with high performance has seen the light in the past decade. The purpose of this paper is to present an overview of current advancements in the design and technical implementations of GW-based antenna systems and components. Practical applications and the industry interest in the developments of the GW technology for mmWave and sub-THz applications have also been scrutinized.

A high equivalent isotropic radiated power (EIRP) active phased array antenna system has been designed and experimentally verified at the 28 GHz band. The phased array employs Gallium Nitride (GaN) based radio frequency front-ends with 31 dBm output power in transmit mode and 3.5 dB noise figure in receive mode. A fully metallic gapwaveguide technology has been employed in order to achieve an efficient heat dissipation per aperture area of the array as well as low-loss array antenna elements that are easily manufactured. The phased array is realized by sub-arraying an 8×8 slot array antenna with horizontal polarization. The presented antenna system is capable of analog beamforming in the range of ±60 degrees in E-plane. The presented high-bandwidth phased array antenna system is a potential candidate for high power and compact size 5G base station antennas for wireless communications requiring high temperature stability at the millimeterwave bands.

A high equivalent isotropic radiated power (EIRP) active phased array antenna is proposed for 5G communication systems at 28 GHz. The numerical design, the measurements of a fabricated prototype and the performance analysis are presented. The antenna design is based on the gapwaveguide technology and consists of 16 × 16 single 45-degree slant-polarized elements. The proposed design employs a low complexity printed circuit board (PCB) structure with only six layers, i.e., a half of existing wideband solutions. The array antenna incorporates up/downconverter integrated circuits (UDCs) and 1 × 4 transceiver beamformer integrated circuits (BFICs). Moreover, a compact and highly efficient transition at the end of each channel of the BFICs has been designed to interconnect the antenna elements with the PCB. The antenna’s frontend loss, which includes the feed line, mismatch, and ohmic losses, is only 1.3 dB. The array covers the scanning range of ±60 degrees in the azimuth plane and ±10◦ in the elevation plane. The S11 < −10 dB frequency bandwidth is from 26.5−29.5 GHz. The maximum EIRP of the antenna is 65.5 dBm at saturation point. The presented design offers a compact, robust and low loss performance solution meeting the high transmission power requirements of 5G applications.