In this work, four low-loss compact waveguide phase shifters with self-compensating characteristics are proposed, studied, and demonstrated over the entire G-band (140-220 GHz) for the first time. The full-band phase shifting is achieved by combining opposite properties of the reference line and the main line. In addition, the proposed phase shifters can be easily fabricated by using a split-block machining technology in both E- and H-plane-cut configurations, therefore making them attractive for simultaneously combined E-plane and H-plane waveguide circuits and systems. Compared with the state-of-art techniques, the proposed phase shifters present competitive advantages in terms of bandwidth performance, phase shift range, low loss, simplicity and compactness as well as fabrication flexibility. Four prototypes with 45° and 90° phase shifts, covering the whole G- band with both E-plane-cut and H-plane-cut configurations were fabricated and measured. Measured results confirm the anticipated performances and their potential applications for THz waveguide circuits and systems. To validate its feasibility, a 90° phase shifter was integrated with a multiport interferometric circuit as an application example. Compared with other reported works, the performance of the multiport circuit is significantly enhanced in terms of return loss, insertion loss, isolation, and phase error, which makes the phase shifter a very practical component for THz systems, in particular broadband multiport interferometric transceiver systems. 

Compact 140-220 GHz E/H Waveguide Phase Shifter and Its Application to Terahertz Multiport Circuits

This paper introduces a comparator network for monopulse radars at the millimeter wave Ka band (26-29GHz). The network design is based on four Magic T’s connected in an assembly through various bend junctions and lines. The network is implemented using gap waveguide technology where each Magic T consists of a hybrid coupler loaded with a 90° phase shifter at the output ports. The full comparator network achieves 15 dB isolation between the output ports. Less than 10° phase imbalance is achieved with 11% bandwidth. Compared time domain and frequency domain simulations show very good agreement in these results which validates the network performance. 

Ridge Gap Waveguide Monopulse Comparator for Millimeter Wave Direction Finding Systems

This paper presents a wideband sub-terahertz (sub-THz) inline transition from microstrip line (MSL) to rectangular waveguide (RWG). The transition employs the bow-tie antenna to achieve a compact inline transition and wideband impedance matching with the RWG, resulting in bigger bandwidths than the transitions using dipoles. In order to overcome the substrate width limitations of conventional probes, the perfect magnetic conductor (PMC) packaging concept is used in this paper, resulting in a better integration ability with large-sized monolithic microwave integrated circuits (MMICs). Two back-to-back transition prototypes related to different angles of the bow-tie antenna have been fabricated to evaluate the transition performances in the sub-THz band. The tested large-sized substrates have a large width of 10.826 mm and a length of 10.8 mm, the length of the MSL is 9.28 mm. According to the experimental results, in the 110-170 GHz band, prototype I has a reflection coefficient of less than -11 dB and an insertion loss of 1.79-2.6 dB, while prototype II has a reflection coefficient of less than -8.5 dB and an insertion loss of 1.52-2.5 dB. 

Sub-THz Inline Transition from Microstrip Line to Waveguide for Large-sized MMICs

A low-cost millimeter-wave wideband filtenna integrating filtering and radiation performance for next-generation millimeter-wave (mmWave) Internet of Things (IoT) devices is proposed in this article. The filtering performance is achieved by utilizing the intrinsic high-pass property of a microstrip-fed magneto-electric dipole (ME-dipole) and filtering feeding mechanism. Several shorted parasitic patches are settled around the E-dipole to enhance the radiation performance within the operating band and develop suppression levels at both the lower and upper bands. A stepped cross-shaped microstrip-line structure is added in the center of the radiating aperture to generate two resonances, so that the in-band impedance performance and the selectivity can be improved. Measurement results indicate that the proposed filtenna achieves a wide operating bandwidth of 30.26% (22.8-31.4 GHz), a peak gain of 8.21 dBi and an out-of-band gain suppression better than 23 dB. Furthermore, a 2×2 filtenna subarray is constructed with some shorted parasitic patches being shared, and then, a 4×4 circularly-polarized (CP) sequential rotated (SR) array is also delicately designed using the 2×2 filtenna subarray. Remarkable operating bandwidths and appropriate out-of-band suppression performance with simplistic structures are all confirmed well through experiments. The outstanding performance of the proposed filtenna and its arrays makes them potential candidates for the B5G/6G mmWave communications. 

Low-Cost Wideband Millimeter-Wave Filtenna and Its Arrays for Miniaturized IoT Devices

This review delves into the crucial role of gap waveguide (GW) technology in advancing millimeter-wave (mm-wave) communication systems, specifically focusing on the exploration of beamforming components and antennas for advanced applications. With an emphasis on achieving high-data-rate and low-latency services, GW technology becomes instrumental in the development of cost-effective mm-wave solutions. The paper investigates practical applications, highlighting various components essential for beamforming antenna systems, including mm-wave antennas with diverse polarizations, power combining and dividing components like directional couplers, and beamforming feeding networks. These components collectively contribute to the comprehensive integration of a beamforming antenna system within the mm-wave frequency band. As the mobile communication landscape evolves, GW technology emerges as a key enabler for meeting the growing demands of consumers and technology in advanced applications, as detailed in this comprehensive review of GW solutions. 

pdf/exploring-gap-waveguide-solutions-a-review-of-millimeter-3rgncoi3wj.pdf

Exploring Gap Waveguide Solutions: A Review of Millimeter-Wave Beamforming Components and Antennas for Advanced Applications

In this letter, a filtering antenna array is designed and operates at Ka-band based on the gap waveguide (GWG) technology. The filtering function is achieved by using the GWG filtering feeding network, incorporated with ridge gap waveguide and groove gap waveguide (GGW). The GGW cavity is cascaded vertically to excite the microstrip patches. Finally, 8 × 8 filtering antenna array prototype is fabricated and measured with WR-28 waveguide flange. The filtering antenna array is fed by the WR-28 with a transition from GWG to WR-28 waveguide. Due to low loss characteristic of the GWG filtering feeding network, the measured antenna gain is more than 25 dBi with –25 dB cross polarization. Its working frequency is centered at 35.25 GHz with 4.3% impedance fractional bandwidth. There is a good agreement between measurements and simulations.

Ka-Band Filtering Antenna Array Based on Gap Waveguide Technology

With the fast development of next-generation wireless communication and radar sensing, the millimeter-wave frequency band is becoming more and more important due to its rich spectrum, wide bandwidth, and ability to support the miniaturization of antennas and circuits <xref ref-type="bibr" rid="ref1">[1]</xref>, <xref ref-type="bibr" rid="ref2">[2]</xref>, <xref ref-type="bibr" rid="ref3">[3]</xref>, <xref ref-type="bibr" rid="ref4">[4]</xref>. High-performance, low-loss, and low-cost millimeter-wave circuits and modules are the key elements for wireless front-end systems. For planar transmission lines, such as microstrip lines and coplanar waveguides, they are very easy to integrate with other circuits for low-cost and low-profile physical designs. However, the high insertion loss and radiation loss from planar transmission lines limit their applications at the millimeter-waveband. As for rectangular and cylindrical waveguides, their main application is in the areas of low loss and high power handling, but their 3D structure is difficult to integrate with other planar passive and active circuits. The substrate-integrated waveguide (SIW) is a better way to merge the advantages of planar transmission lines and rectangular waveguides, but it still suffers from dielectric losses at the millimeter-wave frequency range.

Gap Waveguide Technology: An Overview of Millimeter-Wave Circuits Based on Gap Waveguide Technology Using Different Fabrication Technologies

On the base of gap waveguide (GWG), a transition is designed between microstrip line (MSL) and waveguide at W-band in this paper. The proposed MSL to waveguide transition consists of MSL, groove GWG, ridge GWG and WR-10 waveguide. The electromagnetic waves propagate from MSL to substrate integrated waveguide (SIW), then the energy transfer from SIW to groove GWG by two metallic pins to coupled electromagnetic waves. Then, the groove GWG is connected to the ridge GWG. Finally, the ridge GWG probe is applied for WR-10 waveguide transition. For the groove GWG and ridge GWG, ball-grid-array (BGA) play a significant role of improving performance, and limit the energy transmission over the path we have designed. The simulated results show the operating frequencies of the proposed transition are from 85.5 to 104 GHz. The proposed transition has advantages of light weight and low profile, and has potential applications in antenna in package.

W-Band Light Weight and Low Profile Transition from Microstrip to Waveguide Based on Gap Waveguide Technology

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Ka-Band Filtering Antenna Array Based on Gap Waveguide Technology

Gap Waveguide Technology: An Overview of Millimeter-Wave Circuits Based on Gap Waveguide Technology Using Different Fabrication Technologies

W-Band Light Weight and Low Profile Transition from Microstrip to Waveguide Based on Gap Waveguide Technology