The progress in mobile communication and the internet of things facilitates multiple features. The trending technology demands wider bandwidth so that user experiences uninterruptedly. The wider bandwidth and the isolation are two key characteristics of modern device antennas. The design of an ultrawideband (UWB) and four-port MIMO antenna is presented in this study. The semicircular monopole patch is modified by including a guitar shape slot on a radiator and a half-circle slot in the lowered ground plane. The structural transformation affects the current path and enhances impedance matching, resulting in a broader bandwidth. The UWB monopole is replicated to construct a four-port multiple input and multiple output (MIMO) antenna. The separation between the interelement is less than the quarter wavelength. As a decoupling structure, the implicit mutual coupling in the MIMO elements is minimized by parasitic elements on the radiator and defected ground plane (DGS). A novel mesh-like structure embedded in radiating plane and DGS couples the current from an excited antenna and suppresses through the DGS correspondingly and improves the isolation. The overall geometry of the antenna is 45×45×1.6 mm3. The UWB MIMO has a measured impedance bandwidth of 113% between 4.5-16.4 GHz and greater than 20 dB of isolation throughout the bandwidth. Besides the mutual coupling reduction, radiation characteristics and all MIMO diversity parameters are studied. The performance of MIMO diversity characteristics is relatively good, with envelope correlation coefficient0.002, diversity gain.10, mean effective gain<-3 dB, total active reflection coefficient<-10dB, channel capacity loss <0.2 bps/Hz, and multiplexing efficiency<-0.5. The experimental and simulated findings are in line and make the projected design suitable for UWB MIMO applications.

Narrowband antennas fail to radiate short pulses of nano- or picosecond length over the broader band of frequencies. Therefore, Ultrawideband (UWB) technology has gained momentum over the past couple of years as it utilizes a wide range of frequencies, typically between 3.1–10.6 GHz. UWB antennas have been utilized for various applications such as ground-penetrating radars, disaster management through detection of unexploded mines, medical diagnostics, and commercial applications ranging from USB dongles to detection of cracks in highways and bridges. In the first section of the manuscript, UWB technology is detailed with its importance for future wireless communications systems. In the next section various types of UWB antennas and their design methodology are reviewed, and their important characteristics are highlighted. In section four the concept of a UWB notch antenna is presented. Here various methods to obtain the notch, such as slots, parasitic resonators, metamaterials, and filters are discussed in detail. In addition, various types of important notch antenna design with their technical specifications, advantages, and disadvantages are presented. Finally, the need of reconfigurable UWB notch antennas is discussed in the next section. Here various insight to the design of frequency reconfigurable notch antennas is discussed and presented. Overall, this article aims to showcase the beginnings of UWB technology, the reason for the emergence of notching in specific frequency bands, and ultimately the need for reconfiguring UWB antennas along with their usage.

The ever-increasing demand and need for high-speed communication have generated intensive research in the field of fifth-generation (5G) technology. Sub-6 GHz 5G mid-band spectrum is the focus of the researchers due to its meritorious ease of deployment in the current scenario with the already existing infrastructure of the 4G-LTE system. The 5G technology finds applications in enormous fields that require high data rates, low latency, and stable radiation patterns. One of the major sectors that benefit from the outbreak of 5G is the field of flexible electronics. Devices that are compact need an antenna to be flexible, lightweight, conformal, and still have excellent performance characteristics. Flexible antennas used in wireless body area networks (WBANs) need to be highly conformal to be bent according to the different curvatures of the human body at different body parts. The specific absorption rate (SAR) must be at a permissible level for such an antenna to be suited for WBAN applications. This paper gives a comprehensive review of the current state of the art flexible antennas in a sub-6 GHz 5G band. Furthermore, this paper gives a key insight into the materials for a flexible antenna, the parameters considered for the design of a flexible antenna for 5G, the challenges for the design, and the implementation of a flexible antenna for 5G.

A low-profile printed six-port ultrawideband (UWB) antenna with a novel decoupling structure for enhancing port-to-port isolation is analyzed in this paper. Six symmetrical pyramidal form UWB antennas with defective ground structures interspersed with parasitic components served as a unique decoupling structure in the proposed design. The grounded branches and modified rectangular stubs on the ground plane generate closed and open current distribution channels, causing the uniform current flow to be disrupted and the coupling effect to be neutralized. The projected six-port antenna has an electrical dimension of $0.68\times 0.89 \times 0.01\,\,\lambda ^{3}$ ( $\lambda $ is computed using a lower frequency of 2.9 GHz), having a below -10 dB impedance bandwidth of 116% from 2.9 to 11 GHz. Across the impedance bandwidth, the average port-to-port isolation is better than 20 dB. The antenna design has acceptable radiation properties with a peak gain of 8.3 dBi at a frequency of 7.5 GHz. Further, the projected design is also exposed to the time domain characteristics and diversity metrics. Among the different ports, the values of the group delay and fidelity factors are less than 1.5 ns and more than 0.92, correspondingly. The values of the diversity parameters such as ECC < 0.075, DG approximately 10 dB, MEG $ < -3$ dB, TARC $ < -10$ dB, CCL < 0.3 bps/Hz, and ME $ < -2$ dB ensure that the projected design is appropriate for the MIMO applications. The designed antenna is fabricated and measured, and the results are in line with the simulation.

The 5th generation (5G) network was planned to provide a fast, stable, and future-proof mobile communication network to existing society. This research presents a highly compact arc shape structure antenna resonating at 28 GHz for prospective millimeter-wave purposes in the 5G frequency spectrum. The circular monopole antenna is designed with a radius of 1.3 mm. An elliptical slot on the radiating plane aids in achieving an enhanced bandwidth resonating at the frequency of 28 GHz. Including an elliptical slot creates new resonance and helps improve the bandwidth. The antenna has an ultra-compact dimension of 5 × 3 × 1.6 mm³, which corresponds to an electrical length of 0.46λ × 0.28λ × 0.14λ, where λ is free space wavelength at the resonant frequency. The projected antenna has an impedance bandwidth of 15.73 % (25.83–30.24 GHz). The antenna has a good radiation efficiency of 89%, and the average gain is almost 4 dB over the entire impedance bandwidth. The simulated and experimental S11 findings are in good agreement.