Metamaterials are assemblies of metallic and/or dielectric materials with properties that are not readily found in naturally existing materials. Hence, metamaterial structures are commonly loaded on/near the patch, embedded in the substrate, loaded/etched from the ground plane or placed as a superstrate layer for enhancing bandwidth and gain, and size miniaturization of conventional patch antennas. The demand for wide bandwidth, high gain, and compact antennas is highly contemplated in recent wireless communication research studies. Despite their lightweight, ease of fabrication, low profile, and simplicity for integration, patch antennas have performance limitations as result of their narrow bandwidth, lower gain, larger size, and lower power handling capacity. To address these problems, metamaterial‐based antennas have gained massive interest. There exist inadequate literatures about review of current state of extensive study reports on metamaterial application for patch antenna performance enhancement. Thus, this paper has reviewed and discussed latest research works on metamaterial applications for performance enhancement of planar patch antennas.

This article presents a planar four-port microstrip line-fed Multiple-Input Multiple-Output (MIMO) antenna operating at 5G millimeter-wave candidate bands of 28 GHz and 38 GHz. A rectangular-shaped patch antenna is designed as a main radiator to obtain a resonance at 28 GHz. Etching of a single-element split-ring resonator (SRR) metamaterial unit cell from the basic patch radiator introduces an additional resonance band at 38 GHz. The suggested MIMO antenna is built on Rogers RT5880 substrate material with a dimension of 14 mm × 14 mm, a thickness of 0.8 mm, and a relative permittivity of 2.2.The measured results show that the antenna achieves bandwidths of 26.6-29 GHz and 37.3-39.3 GHz, whereas greater than 25 dB of port isolation between antenna elements over both bands is obtained without applying any complex decoupling structure. The antenna’s equivalent circuit diagram is presented with the help of lumped elements to characterize its electrical responses. The investigated diversity performance parameters, which result in an envelope correlation coefficient below 0.005, diversity gain of almost 10 dB, and channel capacity loss of less than 0.35 bits/s/Hz, are all found within their conventional limits. The findings show the viability of the design for millimeter-wave 5G applications.

This work presents an integrated planar ve-element antennas system for cognitive radio (CR) applications. The proposed system is composed a ultra-wideband (UWB) antenna for sensing the radio spectrum and four different narrowband (NB) antennas for conducting the communication tasks. The overall antenna system is printed on FR-4 substrate of 50 mm × 50 mm × 1.6 mm dimension. The UWB antenna-coupled at port 5 (P5) is designed for sensing the 3.1 GHz to 10.6 GHz un-licensed UWB band. The rst NB antenna attached to port 1(P1) covers 5 GHz to 11.4 GHz wideband frequency, whereas the paired NB antennas located at port 2 and port 3 (P2 & P3) consists of two similar antennas to achieve MIMO operation and provides 3.05 GHz to 3.75 GHz and 4.9 GHz to 6.1 GHz dual-band operation.The last NB antenna accessible at port 4 (P4) operates in dual-band frequencies of 3.7 GHz to 4.92 GHz and 8.3 GHz to 11.3 GHz. These attained resonant bands cover applications, notably Wi-MAX 3.5 GHz, Upper WLAN, sub 6 GHz 5G, and X-bands in the full UWB spectrum.The minimum isolation among all UWB and NB antennas is 16 dB over the working bands. The MIMO performances of the port 2 and port 3 antenna pairs have been computed considering the envelope correlation coe cient and mean effective gain, and found within their practical limits. The measured results are validated and show a good matching with the simulated ones.The low pro le and planar features of the suggested antenna make it a possible choice to be assimilated within small wireless devices applicable in CR communication.

In this article, a four‐port wideband multiple‐input‐multiple‐output (MIMO) antenna consisting of moon‐shaped slot radiators positioned at the ground plane corners is presented. Slotted square ring metamaterial structures as parasitic element have been loaded on the substrate adjacent to the feed lines to enhance the operating bandwidth and miniaturize the antenna. The proposed MIMO antenna has a measured bandwidth of 3.11 to 6.6 GHz (71.88%) with more than 18 dB isolation between antenna elements. Furthermore, simulated diversity parameters such as envelope correlation coefficient, diversity gain, mean effective gain, and channel capability loss are validated with the measured values and found within the acceptable limits over the operating frequency. The proposed antenna can be applied in 5G below 6 GHz (3.3‐5.0 GHz), WLAN (4.9‐5.725 GHz), and WiFi (5.15‐5.85 GHz) bands.

This work presents an integrated planar five-element antennas system for cognitive radio (CR) applications. The proposed system is composed a ultra-wideband (UWB) antenna for sensing the radio spectrum and four different narrowband (NB) antennas for conducting the communication tasks. The overall antenna system is printed on FR-4 substrate of 50 mm × 50 mm × 1.6 mm dimension. The UWB antenna-coupled at port 5 (P5) is designed for sensing the 3.1 GHz to 10.6 GHz un-licensed UWB band. The first NB antenna attached to port 1(P1) covers 5 GHz to 11.4 GHz wideband frequency, whereas the paired NB antennas located at port 2 and port 3 (P2 & P3) consists of two similar antennas to achieve MIMO operation and provides 3.05 GHz to 3.75 GHz and 4.9 GHz to 6.1 GHz dual-band operation.The last NB antenna accessible at port 4 (P4) operates in dual-band frequencies of 3.7 GHz to 4.92 GHz and 8.3 GHz to 11.3 GHz. These attained resonant bands cover applications, notably Wi-MAX 3.5 GHz, Upper WLAN, sub 6 GHz 5G, and X-bands in the full UWB spectrum.The minimum isolation among all UWB and NB antennas is 16 dB over the working bands. The MIMO performances of the port 2 and port 3 antenna pairs have been computed considering the envelope correlation coefficient and mean effective gain, and found within their practical limits. The measured results are validated and show a good matching with the simulated ones.The low profile and planar features of the suggested antenna make it a possible choice to be assimilated within small wireless devices applicable in CR communication.