This paper presents a gap waveguide based compact monopulse array antenna, which is formed with four unconnected layers, for millimeter-wave tracking applications at W-band (85105 GHz). Recently developed gap waveguide technology removes the need for galvanic contact among metallic layers of waveguide structures, and thereby, makes the proposed antenna suitable for easy and low-cost manufacturing. In this context, a low-loss planar Magic-Tee is designed to be used in a monopulse comparator network consisting of two vertically stacked layers. The gap waveguide planar monopulse comparator network is integrated with a high-efficiency 1616 corporate-fed slot array antenna. The measured results of the comparator network show the amplitude and phase imbalance values to be less than 0.5 dB and 2°, respectively, over the frequency band of interest. The fabricated monopulse array antenna shows relative impedance bandwidths of 21% with input reflection coefficients better than 10 dB for the sum and difference ports. The null in the difference radiation pattern is measured to be 38 dB below the peak of the sum radiation pattern at 94 GHz. The measured gain is about 30 dBi for the same frequency. The low-loss performance of the comparator network and the feed-network of the proposed array, together with the simple and easy manufacturing and mechanical assembly, makes it an excellent candidate for W-band compact direction-finding systems.

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 paper presents an 8×8-element slot array antenna with single-layered corporate-feed based on the ridge gap waveguide technology in the 60-GHz band. As is wellknown, a corporate-feed slot array antenna usually has backed cavities to increase the bandwidth and provide a space for its distribution network, and therefore three layers in total: one layer for radiating slots and two layers for feed network with one layer of back cavities and the other one of power dividers. The antenna in this work is designed by utilizing only two separate metallic layers – a corporate-feed network layer and a radiating slot layer. Compared with the conventional threelayered slot array antennas, the proposed antenna avoids the utilization of the backed-cavity layer so that its complexity and manufacture cost decrease. In order to solve the problem of the narrow bandwidth caused by taking away the backed cavities we utilize double-ridged radiating slots instead of the conventional rectangular ones. A compact transition power divider from standard waveguide WR-15 to the ridge gap waveguide is introduced to excite the proposed array antenna. The 8×8-element slot array antenna has been fabricated by computerized numerical control machining technique. The measured results demonstrate that the -10 dB reflection coefficient has around 17% bandwidth covering 56.5 – 67 GHz frequency range, and the measured gain is better than 26 dBi with more than 70% antenna efficiency over 58 – 66 GHz.

In this communication, a novel dual-polarized highly folded self-grounded Bowtie antenna that is excited through I-shaped slots is proposed for applications in sub-6 GHz 5G multiple-input-multiple-output (MIMO) antenna systems. The antenna consists of two pairs of folded radiation petals whose base is embedded in a double layer of FR-4 substrate with a common ground-plane which is sandwiched between the two substrate layers. The ground-plane is defected with two I-shaped slots located under the radiation elements. Each pair of radiation elements are excited through a microstrip line on the top layer with RF signal that is 180° out of phase with respect to each other. The RF signal is coupled to the pair of feedlines on the top layer through the I-shaped slots from the two microstrip feedlines on the underside of the second substrate. The proposed feed mechanism gets rid of the otherwise bulky balun. The Bowtie antenna is a compact solution with dimensions of 32 $\times $ 32 $\times\,\,33.8$ mm ³ . Measured results have verified that the antenna operates over a frequency range of 3.1–5 GHz and exhibits an average gain and antenna efficiency in the vertical and horizontal polarizations of 7.5 dBi and 82.6%, respectively.

This paper presents the integration of a diplexer with a corporate feed network of a high gain slot array antenna at the Ka-band. A hybrid diplexer-splitter with a novel architecture is proposed to have compatibility for its direct integration with the feed network of the array antenna. A seventh-order hybrid diplexer-splitter is successfully integrated into a corporate feed network of a 16x16 slot array antenna. The proposed integrated diplexer-antenna module consists of three distinct metal layers without the need of electrical contacts between the different layers based on the recently introduced gap waveguide technology. The designed module has two channels of 650-MHz bandwidths each with center frequencies 28.21 and 29.21 GHz. The fabricated prototype provides good radiation and input impedance characteristics. The measured input reflection coefficients for both Tx/Rx ports are better than -13 dB with the measured antenna efficiency better than 60% in the designed passband, which includes the losses in the diplexer.