In this paper, a systematic research campaign on eighth-mode substrate integrated waveguide (EMSIW) filters is reported. The sizes of these EMSIW resonant cavities are only one-eighth or one-sixteenth of a conventional SIW resonant cavity. Two different coupling topologies, i.e., electric coupling and magnetic coupling, are employed between two EMSIW resonant cavities, which are analyzed theoretically via the response of the structure and the relationship between the cavities. Both coupling topologies enable structural variations that possess advantages and flexibility of the second-order EMSIW bandpass filters (BPFs) designing. By utilizing these basic coupling mechanisms, multilayer board technology, and other practical techniques, a class of triple-order SIW BPFs with the merits of compact size and high selectivity are demonstrated. Specifically, several triple-order EMSIW BPFs composed of pure EMSIW cavities or comprised by combining EMSIW and quarter-mode SIW cavities are simulated, fabricated, and measured for verification.

A W-band large scale substrate-integrated waveguide (SIW) cavity-backed slot array for high-gain applications is presented in this paper. The proposed antenna consists of a compact 16-way power divider and a 32 × 33 slot array. The 16-way power divider at the bottom-layer PCB provides equal-amplitude and alternative-phase excitation for 32 SIWs on the toplayer PCB, each of them supports 33 radiation slots. The loss along with the complexity of the feeding network is reduced by the implement of alternative-phase excitation. To demonstrate the proposed slot array, a 4 × 33 slot array excited by a 2-way power divider is designed firstly. Then, the 4 × 33 slot array is extended to a 32 × 33 slot array by a 16-way power divider. To verify the proposed slot array, the designed array is fabricated and measured. The measured peak gain, radiation and aperture efficiencies are 30.88 dBi, 42% and 22.8% at 93.2 GHz, respectively. The proposed highgain antenna is an excellent candidate for the high frequency millimeterwave (mm-wave) wireless system.

This letter proposes a 140 GHz high efficiency slotted waveguide antenna with a low loss feeding network. The feeding network consists of the feeding slot, the over-mode cavity and the coupling slots, which provides the same-magnitude but alternating-phase excitations for the slotted parallel-plate waveguide array. The alternating-phase excitations are used to implement virtual electric walls for replacing the physical metal walls of the conventional waveguides, which reduces the loss from the metal walls. Hence, the antenna efficiency is improved significantly. Moreover, the implementation challenges of the tiny metal sidewalls of the THz waveguides are avoided. By using the computer numerical control metal-milling technology, an 8 × 8 prototype is designed and fabricated with a relative bandwidth of 10.17%, i.e. from 132 to 146.15 GHz, for demonstrations. Experimental result shows that the radiation and aperture efficiency of the prototype can be as high as 93.4% and 73.2%, respectively. The measured antenna has a maximum radiation gain of 24.59 dBi @ 137.5 GHz, and the cross-polarization level is lower than -32 dB. The proposed antenna provides a promising solution to develop high efficiency upper millimeter-wave and sub-terahertz (THz) applications.

This article reviews the application and technology advancement of gallium (Ga)-based liquid metal (LM) in high-frequency circuits and antennas. It discusses the material properties of common LMs, the fluidic channels used to contain LM and their manufacturing techniques, and the actuation techniques, which are all critical for the design and implementation of LM-based devices. LM’s fluidic and pliable nature, together with its excellent electrical, thermal, and rheological (i.e., fluid flow) properties, provides some unique and innovative solutions to flexible/wearable electronics, reconfigurable circuits, and antennas. This article provides a comprehensive review of a wide range of LM-enabled high-frequency circuits and antennas, including interconnects and transitions, reconfigurable passive circuits (such as resonators, filters, and couplers), switches, phase shifters, reconfigurable antennas, flexible and wearable antennas, and metamaterials (i.e., periodic materials with properties not found in nature). This article presents various design concepts and implementation techniques, highlights key capabilities, and discusses the challenges and opportunities with the use of Ga-based LM materials.

A D-band low-loss mixed-mode filter with high selectivity is proposed and analyzed in this article. The transverse quintuplet/triple topology has been employed in the design with coupled overmode cavities using the TE2N,1,0 modes (N = 2,3,4, ...) and TE2N,1,0-like modes. Two transmission zeros (TZs) are generated in the upper and lower stopbands. The fractional bandwidth (FBW) and positions of the TZs can be flexibly designed by properly selecting the geometries of the proposed overmode cavity, which determines the frequencies of all resonating modes. To improve the frequency selectivity, multiple coupled overmode cavities, which have different spurious responses and TZs distributions, are cascaded for the designed filter. For demonstration purposes, two types of filter architectures are proposed for two D-band mixed-mode bandpass filters, respectively, which shows the design flexibility of the proposed method. The first filter is realized by cascading multiple overmode cavities through waveguide sections, and the second filter is realized by cascading overmode cavities through slots. Experiments are carried out to verify the second filter with TZs. The measured FBW3 ,dB is 17.18% from 128.11 to 152.19 GHz, the minimum insertion loss is around 0.33 dB, and the measured rectangle coefficient (BW40 ,dB/BW3 ,dB) is about 1.38. The measured results agree well with the designed ones, which verifies the proposed method. The proposed filter can be a good candidate for millimeter-wave and terahertz systems.