A wideband high-gain high-efficiency 16 × 16-element slot antenna array is presented for 60-GHz band applications. The antenna is designed based on gap waveguide technology. The most important advantage of using this technology is its ability to decrease complexity and cost of fabrication because there is no requirement of electrical contact between the three layers of the antenna structure. The three layers are a corrugated metal plate with radiating slots, a subarray cavity layer, and a ridge gap waveguide (RGW) feed network layer. The corporate feed network is realized by a texture of pins and guiding ridges in a metal plate. Also, in order to excite the antenna with a standard V-band rectangular waveguide, a transition from RGW to WR-15 is designed. The radiating elements, corrugations, cavity layer, power dividers, and transition are designed and optimized to suppress the reflection coefficient at the input WR-15 port over the desired frequency range from 57 to 66 GHz. Finally, the 16 × 16-element slot antenna array is fabricated by the standard milling technology. The measured results demonstrate about 16% of reflection coefficient bandwidth (|S ₁₁ | <; -10 dB) covering the 56-65.7-GHz frequency range, and the measured gain is larger than 32.5 dBi over the band with more than 70% antenna efficiency.

A wideband 8 ×8-element slot antenna array based on ridge gap waveguide feeding network has been proposed for mmWave applications. The antenna sub-array consists of four radiating slots which are excited by a groove gap cavity layer. Compared with previously published works, the proposed planar antenna array has quite wide impedance bandwidth. The antenna covers a wide band of 50-67.8 GHz with 30% impedance bandwidth (VSWR < 2). Also, the antenna has only 2.5 dB gain variation over the entire bandwidth which implies also good radiation characteristics for the proposed antenna. The maximum measured gain value is about 27.5 dBi with a total efficiency of 80% for the proposed antenna within the band of interest. With this performance, the proposed antenna array is a promising candidate for millimeter-wave communication systems.

This communication presents a wideband aperture-coupled patch antenna array based on ridge gap waveguide feed layer for 60-GHz applications. The novelty of this antenna lies in the combination of relatively new gap waveguide technology along with conventional patch antenna arrays allowing to achieve a wideband patch antenna array with high gain and high radiation efficiency. An 8 × 8-element array antenna is designed, fabricated, and tested. Experimental results show that the bandwidth of VSWR . 2 is up to 15.5% (57.5-67.2 GHz). More than 75% efficiency and higher than 21.5-dBi gain are achieved over the operational bandwidth. The results are valuable for the design and evaluation of wideband planar antenna arrays at millimeter-wave frequencies.

This work presents a high gain D-band slot array antenna with a corporate-fed distribution network designed by the gap waveguide. The gap waveguide technology is employed for overcoming the challenge of appropriate electrical contact related to the mechanical assemblage of the antenna feed network and the radiation layer. The antenna includes 24×16 slots and the basis of the antenna interdigital feeding network includes the ridge and groove gap waveguides. A standard WR-6 waveguide flange at the bottom is used to excite the presented antenna. To understand the fabrication challenges and tolerance issues around 140GHz, an antenna prototype was made by standard CNC milling techniques. The results show that an impedance bandwidth of 5.5% (141.8-149.8 GHz), efficiency higher than 78%, and a peak gain of 33.8 dBi are achieved for the proposed 24×16-element array antenna. According to the results, the presented planar array is a good option for D-band applications and can be used as the building block to develop high efficiency and high gain upper mm-wave antennas.

In this paper, H-plane horn antenna using gap waveguide technology is proposed. The advantage of this tech- nology is its air-filled feature, which improves the impedance matching compared with substrate integrated waveguide horn antennas. Corrugated walls as soft surfaces are used on the outer surfaces of the upper and lower horn plates, which act as barriers around the aperture of the antenna and reduce its back lobe levels. The bandwidth of the antenna for jS11j < 10 dB is 19 to 28 GHz and the gain varies between 8.5 and 12 dBi. The total efficiency is better than 88% in the operation bandwidth. This structure has the capability of easily integrating with other planar microwave components. To such a capability, a coupled resonator filter has been integrated with the antenna to select the desired frequency band and remove the out of band harmonics. For the proof of concept a prototype model is fabricated and tested, where measurement data agree well with the simulation results.

A class of wideband directional couplers suitable for achieving different coupling levels are proposed in this work. The proposed couplers have been implemented using double-layer groove gap waveguide at millimeter-wave frequency range. They are composed of two parallel groove gap waveguide parts placed on top of each other in such a way that the coupling between the two waveguide sections can be achieved via the coupling structures placed in the common wall. Usually, the coupling layer consists of two rows of holes and depending on the number of holes the coupling levels can be controlled. The manifest and applicable property of the proposed directional coupler is that the coupling level can be simply changed using the different coupling layers without changing the top and bottom groove waveguides and transitions. As another significant advantage of the proposed coupler, there is no requirement of good electrical contact among different metallic parts of the structure which considerably simplifies the manufacturing processes and mechanical assembly at millimeter-waves applications. For verification purpose, three sample couplers with coupling levels of 10 dB, 20 dB and 30 dB have been designed, fabricated and measured. To make the device accessible and measurable using standard rectangular waveguides, two types of transitions from groove gap waveguide to standard WR-15 are designed. Simulation and experimental results are in good agreement and show that the proposed couplers have large bandwidth for return loss level of 20 dB, coupling level of 10±1, 20±1 and 30±1 dB, and isolation level of 30, 35 and 40 dB over the desired frequency band of 50 -70 GHz. The proposed directional couplers can be used as good candidates at millimeter-wave frequencies for probing and the design of compact integrated microwave circuits and systems such as antenna array feeding networks.