with higher data rates can easily be achieved and can be utilized, but we are still faced with the much higher ratio of challenges and limitations such as link losses, multipath effects, small-scale fading as well as short coverage [11]. To fully overcome and alleviate these challenges and limitations, different valuable solutions are available which might handle these issues, such as advanced beam-forming techniques, antennas with high gain and narrow beamwidth, small-cell technology in advanced format, massive MIMO antennas with excellent steerable characteristics of low scanning losses and reconfigurable characteristics [2; 15; 16], and bandwidth enhancement techniques [23; 24; 25; 26; 27; 28]. For mitigating these challenges, antennas with high performance parameters such as antennas with small beam width, small side-lobe level, with characteristics of low scanning losses, are required, which might be able for two- and three-dimensional steering capability at higher levels of frequency scanning. It is a challenging and difficult task to maintain narrow beam width with low scanning levels. For flawless reliable communication, broadband antennas with excellent steerable characteristics, that are small in size, and have narrow beam width and high gain are required at mobile base stations. The key challenges for designers is to maintain a suitable position of the antenna at base station and to maintain stability in the radiation characteristics with other communication components such as Wi Fi, 4G LTE, and LCD; besides these challenges, the back casing composed of metal is an enormous challenge for designers and researchers. Specific absorption losses in terms of the effect of the user's body on antenna performance are required to be inspected. Between each two antenna elements, the mutual coupling should be reduced or isolation between each two elements should be high [29], especially in the case of MIMO antennas. Some other performance parameters such as channel capacity loss (CCL), diversity gain (DG), mean effective gain (MG), and total active reflection coefficient also need to be analyzed [29; 30]. The microstrip antennas are mostly used due to being lower in cost, simple in fabrication, and easy in installation, but they have some limitations such as limited level of gain, narrow in bandwidth, lower efficiency, and low power-handling capability. Various strategies and techniques are used to enhance the bandwidth, such as to create the slots in the radiator of microstrip patch antennas in the ground plane of antennas, as well as impedance matching techniques, increasing the height, and stacking arrangements of patch [2; 3; 15; 16; 17; 18]. For microstrip patch antennas, these are conventional performance enhancement techniques in terms of bandwidth, but they effect some additional performance parameters such as gain, radiation pattern, side-lobe level, and cross-polarization level [25; 31]. Simultaneous use of the coalescence of numerous technologies is needed in the designing of an antenna for enhancement of bandwidth, gain, and efficiency as well as reduction in side-lobe level and achieving a high level of isolation among interelements of a MIMO or array antenna. The above-mentioned techniques are famous conventional techniques for enhancement of performance, especially in bandwidth  
Microstrip antennas are known for their narrow bandwidth, low gain, and low efficiency [31; 32]. By using new technology, researchers are able to increase bandwidth by 70% and gain 30-35 dBi and various structural alterations. There are several methods for increasing bandwidth which have been employed by researchers in the evolution and development of 5G antenna systems for a flawless communication system. The main focus is on the latest key techniques responsible for the improvement in bandwidth, gain, and efficiency, and in the case of MIMO, isolation enhancement is the main target studied in the literature [33].