This letter presents our study on a compact and low-loss E-band bandpass filter (BPF) based on multilayer groove gap waveguide (GGW). Different from other reported planar GGW filters and vertically stacked substrate integrated waveguide (SIW) filters, the proposed filter realizes a cross-coupled quadruplet topology by introducing a pair of unique circular capacitive holes across layers, innovative ridges (capacitive iris), and conventional inductive irises on the same layer, which reduces the insertion loss (IL) while having a smaller size. By tuning the dimensions of the coupling structures and cavities, the filter is optimized to exhibit a superior performance in simulation. The designed filter is fabricated using CNC machining and verified in experiment. The measured results agree with the simulated ones quite well, showing an average IL of 0.45 dB and an 8% relative 3-dB bandwidth at a center frequency of 73.65 GHz. Therefore, the proposed multilayer GGW structure opens a new avenue in designing high-performance filters in millimeter-wave bands.

In this letter, a high-efficiency multibeam circularly polarized (CP) antenna array with the groove gap waveguide (GGW) feeding technology for W-band application is proposed. First, a wideband CP septum antenna element based on GGW structure is proposed. The antenna has a simple structure with high tolerance, and the GGW technology reduces the machine difficulty, making the antenna easier to work in the higher frequency. Next, a 4 × 4 GGW Butler matrix is designed to feed the antenna array. Finally, a high-efficiency W-band four-beam CP endfire antenna array is fabricated and measured. Measured results verify that the antenna has a wider impedance bandwidth of 17.6% from 77.5 to 92.5 GHz for |S ₁₁ | <; -10 dB. The measured AR values of the main lobe range of four beams are almost less than 3 dB. Also, stable radiation patterns are obtained. The maximum gain and radiation efficiency are 15.29 dBic and 89.6%, respectively.

In this letter, a novel 3D multi-beam reconfigurable THz loop antenna capable of steering its main beam in the semi-sphere space (θ ϵ {0°, ±5°, ±10°}; φ ϵ {0°, 30°, 60°, 90°, 120°, 150°}) is presented. The antenna is based on a switchable circular high impedance surface (HIS) using the graphene–metal hybrid approach. The effect of gate voltage on the conductivity of graphene and the switchable reflection characteristic of the graphene-based HIS are combined in the design. Changing the chemical potential of different graphene-based HIS units can effectively adjust the beam direction. The performance of the antenna is analyzed through its reflection coefficients and gain radiation patterns, and simulated results show that the maximum gain can reach 3.23 dBi at 0.5 THz.

A millimeter-wave (mmW) wideband circularly polarized (CP) antenna based on air-filled waveguide is proposed. By introducing two symmetrical ridges in septum antenna, the proposed antenna can obtain a more compact antenna aperture than the septum antenna based on rectangular waveguide (from 0.99 λ × 1.25 λ to 0.66 λ × 0.91 λ). In addition, the high order modes are suppressed to less than -20 dB from 55 to 70 GHz. Then the sharp corner in the AR and Gain plots of septum antenna based on waveguide are eliminated. A simulated operating bandwidth of 16.4% for both |S11| < -10 dB and axial-ratio (AR) < 3 dB within half power beam width (HPBW) is achieved from 56 to 66 GHz. To verify the design, the proposed antenna has been fabricated and measured. The differences between simulations and measurements caused by flange are evaluated. The measured operating bandwidth of 20.9% is achieved from 60 to 74 GHz.

In this article, a compact 94 GHz multibeam antenna array based on the binary phase-controlled concept is proposed. The feeding network is composed of four unconnected layers, and the ridge or groove gap waveguides are adopted as the guided wave structures. A key planar gap waveguide Magic-Tee is designed to obtain 0° and 180° phase states and then integrates with an $8\,\times \,8$ slot antenna array to achieve multibeam operation for the first time. Compared with the traditional phased array and passive beamforming networks (BFNs), the feeding design is simple in construction, consisting of only Magic-Tees and cascaded power dividers without any phase shifters. Benefiting from the gap waveguide technology, the antenna array does not require electrical contact among the metal layers, so it is simple and low cost to manufacture. The $8\times8$ slot antenna array can easily switch among one-beam and three different dual-beam states that point to ±7°, ±17°, and ±38°. The measurement results of 6.6% bandwidth from 91.7 to 98 GHz for both reflection coefficients $< -10$ dB and isolations >25 dB are achieved. The proposed multibeam antenna array would be an attractive candidate for millimeter-wave multiuser communication where it requires multiple beams simultaneously.