A double-layer waveguide slot array antenna is developed for a 40-GHz-band directional division duplex (DDD) system, which exhibits extremely high utilization efficiency of frequency. To minimize the interference from the surrounding buildings, the Taylor distributions are adopted in both longitudinal and transverse directions over the antenna aperture to suppress the sidelobe levels (SLLs) below -30 dB. A four-corner-fed structure instead of the typical center-feed one is introduced for wideband operation. The perfect magnetic conductor (PMC) terminations are also adopted at the center of feeding waveguides due to the symmetric feed from right-and-left ends. As the predicted antenna performance using HFSS, the antenna gain of more than 31.8 dBi and the reflection of less than -10 dB are estimated over the operating frequency range of 39.5-41.0 GHz. The test antennas are fabricated by diffusion bonding of copper plates. As the measured antenna performance, the antenna gain higher than 30.6 dBi and the reflection lower than -10 dB are achieved over the desired frequency range. The sidelobes are suppressed below -30 dB, and the isolation between two antennas arranged in H-plane is achieved at the level of more than 76 dB.

A wideband circularly polarized planar antenna with hexagonal apertures arrayed over a plate-laminated waveguide slot array is developed in the 60 GHz band. The 2×2-element subarray functioning as the principal component is precisely and efficiently analyzed by the method of moments using numerical eigenmode expansion. This numerical approach is particularly applied to the regions of both the X-shaped cavity and hexagonal radiating aperture for circular polarization. Moreover, the bandwidths of both axial ratio (AR) and impedance matching in the subarray are significantly widened by applying the genetic algorithm in two steps. The bandwidths for both AR <; 3 dB and VSWR <; 1.5 are improved from 4.8% to 14.5% compared with the previous design. Their mechanisms are investigated in detail as well. A 32×32-element array with a uniform illumination is designed and fabricated by the diffusion bonding of thin copper plates. The wideband antenna performance is verified by the experimental evaluation.

This paper investigated the possibility of using an X-band traveling-wave antenna for application in synthetic aperture radar (SAR) on a small-satellite platform. A rectangular slotted parallel-plate antenna panel capable of radiating dual polarization over the same physical aperture was selected for this purpose. The design procedure, which provides for an optimal antenna pattern in a SAR application, is described. A meta-heuristic multiobjective optimization algorithm was applied to synthesize an appropriate far-field pattern, which enhances the quality of the SAR image. Subsequently, the optimization results were used to build a more realistic model of the antenna panel in electromagnetic simulation software. An antenna panel was fabricated, and its electrical characteristics were measured. The fabricated prototype weighed 1310 g and measurements showed nearly 50% aperture efficiency for both circular polarizations [34.6-dBic right-hand circular polarized (RHCP), 34.5-dBic left-hand circular polarized (LHCP), and peak gain at 9.65 GHz], with low side-lobes. A beam shift of 2.1° was observed between the RHCP and LHCP beams at the design center frequency and was later analyzed to be the result of an error in the modeling of the adhesive layer.

A wideband full-metal sidewall-loaded magnetoelectric (ME) dipole array antenna fed by combined ridge-groove gap waveguide is proposed. Three promising full-metal aperture-coupled 2×2-element ME-dipole subarrays are investigated and compared in detail. By introducing sidewalls around the metal pillars and increasing their height to 0.36λ ₀ , the bandwidth of the subarray is substantially enhanced to 33% for S ₁₁ < -15 dB. An eigenmode analysis is performed to explain and validate the broadband property of the proposed subarray with taller pins and sidewalls. The combined ridge gap waveguide and E-plane groove gap waveguide are employed in the feeding layer for a compact array as well as for lower losses and better isolation between the gap waveguides. Wideband ridge-to-groove (RG) and groove-to-ridge (GR) junctions are designed using stepped transformers for bandwidth enhancement. For verification, an 8×8-element sidewall-loaded ME-dipole array is designed and fabricated by computer numerical controlled (CNC) milling technique in the Q-band. The bandwidth for S ₁₁ < -10 dB is widened to 35.9% from 34.5 to 49.4 GHz. From 34.3 GHz to 34.7 GHz and 35.6 GHz to 48.7 GHz, the antenna efficiency is better than 75%, with a bandwidth of 32.5%. The proposed design is attractive for wideband and higher-frequency wireless applications.

An alternating phase fed waveguide array with an oblique arrangement of feed waveguide is proposed. It belongs to single-layer waveguide arrays developed by the authors. Conventional arrays with radiation waveguides arranged perpendicularly to the feed waveguide suffer from accumulated reflection from coupling windows after round-trip propagation at the input port. In the proposed oblique arrangement, the reflections from each coupling window will not accumulate in phase but be diffused away out of phase. First, the design of obliquely arrayed T-junctions is conducted using two-dimensional finite element method (FEM). Then basic operations of the reflection canceling as well as improved voltage standing-wave ratio at the antenna input are confirmed by experiments. Almost the same radiation patterns and gain as the conventional arrays are observed in the measurements

A thinning method based on precoded subarray structures is proposed for planar arrays. It introduces the matrix descriptions, including the subarray structure matrix S and the coefficient vector K, and transforms the thinning of a planar array into the arrangement of predetermined subarrays with specified thinning rates. This process effectively leads to order reduction and achieves fast optimization. We apply the evolutionary algorithm to accomplish the ideal radiation performance iteratively. The dependence of the array performance on S and K is also investigated. For demonstration, the 10×20- and 23×23-element arrays are optimized. By comparing with the traditional thinning methods, it is verified that the proposed method not only provides us with lower sidelobes and narrower beamwidth but also avoids the random element arrangement. In addition, the introduction of precoded subarrays may further reduce production and maintenance costs, especially from engineering implementation and mass production perspectives.