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.

This paper highlights recent developments and challenges on beam steering characteristics of reconfigurable transmitarray antennas. It introduces the operating principle of beam forming/beam steering high gain transmitarray antennas to enable the user to opt for economical and high performance solutions. A transmitarray antenna typically consists of a source antenna and a phase transformation structure. The incident waves generated from the source antenna is tilted using the phase transformation structure in a desired direction to steer the beam. Moreover, the phase transformation structure alters the incident wavefront to a plane wavefront using phase change characteristics. In order to steer a beam to a specific desired angle, it can be divided into two methods. There is a method of applying a transmitarray with a variable transmission phase change or a method of changing the shape of the wavefront of the source antenna. This type of beam forming/beam steering high gain antenna has been mainly studied from the point of view of high efficiency, low profile, and low cost. Several solutions of transmitarray unit cells have been presented in the literature, using PIN diodes, varactors, MEMS switches, and microfluids enable electronics to realize reconfigurable characteristics of transmitarray antennas. This paper analyzes the characteristics of various beam steering high gain reconfigurable transmitarrays (RTA) and highlights the future opportunities and challenges of the structure design for transmitarray antennas. This paper also highlights the challenges and gaps in terahertz and optical frequencies related to future work due to the structure complexity and lack of components’ availability. Moreover, the challenges and limitations related to multi-bit structures and dual-band requirements are presented.

This paper presents a design of a triangular slot-loaded planar rectangular antenna array for wideband millimeter-wave (mm-wave) 5G communication systems. The proposed array realizes an overall size of 35.5 × 14.85 mm². To excite the array elements, a four-way broadband corporate feeding network was designed and analyzed. The proposed array offered a measured impedance bandwidth in two different frequency ranges, i.e., from 23 to 24.6 GHz and from 26 to 45 GHz. The single-antenna element of the array consists of a rectangular patch radiator with a triangular slot. The partial ground plane was used at the bottom side of the substrate to obtain a wide impedance bandwidth. The peak gain in the proposed array is ≈12 dBi with a radiation efficiency of >90%. Furthermore, the array gives a half-power beamwidth (HPBW) of as low as 12.5°. The proposed array has been fabricated and measured, and it has been observed that the measured results are in agreement with the simulated data.