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In this letter a W -band small-size low sidelobe level (SLL) 6 × 16 microwaveguide slot array antenna is proposed based on the silicon micromachining technology. The feeding network within the limited available area consists of several stages of equal T-junctions and TE120-mode-cavity dual-layer power dividers able to build the desired tapering power distribution over a relatively wide bandwidth. The TE120-mode-cavity dual-layer power divider is at the end of the feeding network, which can implement the layer-to-layer transition and the power division simultaneously. Thus, the whole size of the array antenna can be reduced by about 25% compared with the conventional five-stage tree-like feeding network. The overall antenna size is 60 mm × 20 mm × 1.85 mm. The measured maximum gain is 26.1 dBi at 94 GHz, and the corresponding radiation efficiency is 69.2%. The measured SLL in E -plane is below than −18.5 dB within the frequency band from 92 to 96 GHz.

A THz 2-D frequency scanning planar integrated array antenna is developed in this letter. Eight THz leaky-wave antennas are combined with a true-time-delay (TTD) phase-shifting feeding network to steer the beam in two directions by sweeping the frequency. Several H-plane 90° bends with linearly increased length are adopted to achieve the scalable TTD phase shift. The feeding lines are closely spaced to reduce the phase-shifting network occupied area in this progressive phase-shifting scheme. Besides, the E-plane 180° bend is used to construct the double-layer phase-shifting network, maintain the number of multiple scanning sweeps and improve the aperture efficiency. Moreover, in the used microelectromechanical systems (MEMS) fabrication technique, the minimum height of the radiation slot is 0.2 mm, which is too thick and deteriorates the radiating performance. When the double-layer step-profiled radiating slot is used instead of the thick slot, a THz leaky-wave antenna with higher radiation efficiency and better gain flatness can be achieved. Finally, a prototype antenna is fabricated and experimentally validated. The operating frequency range is 325–400 GHz and the beam scanning range is 22.7° × 60° with a maximum radiation gain of 25.28 dBi.

A millimeter-wave near-field-focused (NFF) full 2-D frequency-scanning antenna array is presented in this article. The proposed antenna is achieved by combining an NFF ridged-waveguide slot array with a double-layer folded focused progressive feeding network. The linear ridged-waveguide slot array antenna is designed with a height-modulated ridge to focus on the power in one direction. The folded feeding line with different length is used to generate the desired focused phase and frequency-dependent progressive phase shift in the other direction. In this case, as the working frequency is swept in the considered range, the inherent frequency-dependent behavior of the linear NFF leaky-wave antenna (LWA) allows a single-scanning sweep in one direction, whereas the focused progressive feeding network ensures multiple-scanning sweeps in the other direction. A full 2-D electronic scanning with no coverage blindness in the scanning area is achieved. To the best of our knowledge, the proposed NFF antenna array is the first design to achieve the full 2-D scanning focus in the near-field (NF) region only by sweeping the frequency, which means that the testing information in the NF region can be directly obtained with a certain band of frequency. This type of antenna is a good candidate in NF fast-scanning applications, e.g., electromagnetic imaging/detecting systems.

A W-band decoupling structure sandwiched between a pair of high-gain step-profiled horn array antennas using the silicon micromachining technology is proposed. To suppress the surface wave, 18 choke slots with a depth of one quarter wavelength at 94 GHz are arranged in a triangular-grid array and the isolation can be averagely improved by about 7 dB with a range of 2–20 dB. This decoupling structure and two W-band coplanar array antennas are fashioned and fully integrated together by the silicon micromachining technique. Five 400 μ m thick and one 650 μ m thick silicon wafers are utilized and the total thickness of the antennas is 2.65 mm. Thanks to this technology, light weight, compact size, and high integration of the decoupling structure and array antennas can also be achieved. Additionally, the two array antennas share a common ground plane within a small edge-to-edge spacing of 6.05 mm where TM surface waves exist. Experimental studies validate the performance of the proposed triangular-grid choke slot array.

A wideband air-filled plate array antenna with multistage impedance matching operated in $D$ -band is proposed in this article. To achieve the wide bandwidth, three stages of impedance matching are introduced in the $2\times 2$ subarray, including the step-profiled horn element, the step-profiled power divider cavity with two resonant points, and a modified E-plane bend transition. The integrated step-profiled horn with simple configuration can realize broadband matching. Wideband T-junctions are combined together to form a corporate feeding network. Essential matching pins are introduced to break through the upper bandwidth restriction of the feeding network. In addition, the square aperture shape of the horn element and the air-filled feeding structure contribute to the high radiation efficiency of the proposed array. To satisfy the fabrication tolerance, the MEMS micromachining technology with a high etching precision is utilized. The experimental results show a wide 1 dB down gain bandwidth of 23.54%. The maximum gain is 33.24 dBi and the peak efficiency is 70.91%.

A W-band planar array antenna with high efficiency and wide impedance bandwidth using MEMS micromachining technology is designed and fabricated in this paper. The MEMS fabrication process of selectively etching and gold plating is employed to fabricate the precise structure with the similar property of the hollow waveguide. To satisfy the requirement of maximum thickness, the reduced-height waveguide is applied to design an H-plane equal-amplitude and in-phase power divider with the perturbed and septum structure to enhance its impedance bandwidth. A $\pmb{2}\times \pmb{2}$ -element sub-array is utilized to facilitate the layout of the feeding network in the lower layer. The wide-band-stepped horn is employed as the radiating element. Its simple configuration can guarantee good performance. Finally, an $\mathbf{8}\times \mathbf{8}$ array antenna is fabricated by the MEMS micromachining technology and measured. The total thickness is 2.65 mm, which is less than one free space wavelength. Measurement results indicate that the impedance bandwidth for $\vert \mathbf{S}_{11}\vert is 21.28%. The minimal gain can be up to 23.36 dBi within the whole operating frequency band. Total antenna efficiency is up to 75% covering the range from 86.5 GHz to 104 GHz.