In the recent era, fifth-generation technology (5G) has not been fully implemented in the realm of wireless communication. To have excellent accessible bandwidth feasibility, and in order to achieve the aims of 5G standards, such as higher data rates and ultrahigh-definition video streaming, the millimeter wave (mmWave) band must be employed. Services with minimal latency and many other features are feasible only in the mmWave spectrum. To avoid numerous communication complexities such as high connection losses, short wavelength, and restricted bandwidth, as well as path-loss challenges in the mmWave range, an antenna with wide bandwidth, high gain, narrow steerable beam, high isolation, low side-lobe levels, and multiband features is required to alleviate these difficulties and meet 5G communication standards. To overcome these challenges, specific strategies and techniques should be employed in the traditional antenna designing procedure to excellently improve the performance of the antenna in terms of bandwidth, gain, and efficiency and to reduce the mutual coupling effect between the closely colocated antenna elements in MIMOs and arrays. The researchers reported on a variety of bandwidth and gain improvement approaches. To gain broader coverage, traditional antenna design techniques must be modified. In this study, the latest state-of-the-art work is reviewed, such as the role of the metamaterials (MMTs), parasitic patches, hybrid feeding, EBG structure, impact of the slots with different geometrical shapes in the radiator to achieve the goal of wide bandwidth, boosted gain, reduced side-lobes level, as well as stable radiation properties. Mutual coupling reduction techniques are also briefly reported. The role of reconfigurability is focused on in this study, and at the end, the future challenges in the field of antenna design and possible remedies to such issues are reviewed.

In this communication, a wideband and high-efficiency 8 × 8 antenna array is proposed for W -band. This antenna array is composed of three parts: the magneto-electric (ME) dipole radiating elements, the feeding structure for 2 × 2 subarray, and the feeding network. The proposed high-performance ME-dipole element has side connections on both sides of the two radiating patches, forming a dumbbell-shaped slot in the middle. This novel structure contributes to wide bandwidth, high efficiency, and manufacturing suitability in high frequencies around 100 GHz. Moreover, each 2 × 2 ME-dipole subarray is excited through four aperture-coupled slots right below the ME-dipoles. The main part of the proposed feeding structure is a resonant cavity with a metal bar arranged in the middle to divide the waves, significantly improving the impedance bandwidth (BW) of the subarray. The proposed feeding network exploits novel U-shaped T-junctions with improved low-frequency performance for widened bandwidth. Finally, a cooperate ridge gap waveguide (RGW) feeding network is employed to feed the whole 8 × 8 antenna array through coupling slots right below the cavities. To verify the design, a prototype of the proposed antenna array is fabricated and measured. A measured BW of 28.5% from 81.5 to 108.6 GHz with a maximum gain and radiation efficiency of 26.6 dB and 86.8% are achieved. The proposed antenna array has significant potential in W -band applications such as high data-rate communication, high-gain detection, and high-resolution imaging systems.

In this paper, a novel electromagnetic bandgap (EBG) structure is proposed to manufacture gap waveguides (GWs) at high frequencies. The proposed EBG structure combines parallel shallow grooves and glide-symmetric semicircular holes, located on the upper and lower plate, respectively. Attributed to much-reduced milling depth, an efficient and easier manufacturing process can be realized for the proposed structure. Besides, the layout of the milling grooves can be flexibly adapted, making the proposed EBG structure more easily conformal with GWs. As a validation of the concept, both straight and bent side-by-side GWs exploring the proposed EBG structure are elaborately designed, fabricated and experimentally tested, verifying the features of low loss and high isolation, respectively.

A W-band, high-gain, hybrid slot antenna array based on bulk silicon MEMS technology is proposed in this paper. The high-order-mode cavity is explored to excite the 2 × 2-slot basic unit, so as to reach the low-profile requirement of the bulk silicon MEMS process. To avoid the fragile structure of the large-scale antenna arrays based on the bulk silicon MEMS process, the ridge gap waveguide is employed to build the feed network for a large-scale array. A vertical transition between a rectangular waveguide and a ridge gap waveguide is designed to support the low-loss and low-cost assembling method between the radiation units and the feed network. An 8 × 8-slot hybrid antenna array is simulated and fabricated. The measured results show a relative bandwidth (VSWR < 2) of 8.1% with the first side-lobe level less than −11 dB over the frequency band of 91–97 GHz. A maximum gain of 26.1 dBi with the radiation efficiency of 65.2% is achieved. With high gain and high fabrication efficiency, the proposed hybrid slot antenna array would be valuable for W-band radar applications.

This paper proposes a hexagonal meander-shaped wideband electronically reconfigurable transmitarray (HMRTA) at Ku band for satellite communications and radar applications. The proposed transmitarray offers high gain, low profile, and wideband characteristics with beam-scanning and beam-forming features. The cascaded structure is a low-profile and compact transmitarray. The transmitter (T_x) layer has an angular hexagonal patch with a meandered shape and resonating parasitic patches to enhance the bandwidth. The receiver (R_x) layer comprises a two-part hexagonal receiver patch and a dual ring impedance-matching receiver layer. The current reversal phenomena have executed the 180° phase shift by integrating two diodes in opposite directions. The measured results of a unit cell achieve a minimum insertion loss of 0.86 dB and 0.92 dB for state I and state II. The maximum insertion loss is 2.58 dB from 14.12 GHz to 18.02 GHz and is about 24.83% at 16.5 GHz. The full-wave simulations of a 20 × 20 space-fed reconfigurable transmitarray were performed. Good radiation patterns at all scanning angles of two principal planes are achieved, and the cross-polarization level remains less than −20 dB. The simulated 3 dB gain fluctuation bandwidth of the array is 15.85~18.35 GHz, and the wideband characteristics are verified. The simulation results show that the array can perform beam scanning ±60° in the elevation (y-z) plane and obtain the beam-scanning characteristics for ±60° in the Azimuth (x-z) plane.

This letter presents a wideband, high-efficiency, all-metallic 8×8 Magneto-Electric Dipole (MED) antenna array for fixed-beam Ka-band applications. The design integrates three key features: 1) a novel MED element using mirrored U-shaped structures to achieve a 65.7% element bandwidth; 2) a low-profile, horn-shaped aperture that boosts gain by approximately 1 dB; and 3) a compact H-plane waveguide feeding network with miniaturized T-junctions. A fabricated prototype demonstrates a 36.1% impedance bandwidth, a peak gain of 28.8 dBi, and cross-polarization below -40 dB. The all-metal construction ensures high efficiency, making the array a scalable solution for next-generation Ka-band systems.