## 1 Introduction  
The new era of communication technology has enabled 5 th Generation (5G)-driven systems that allow for high-speed data rates with enhanced bandwidth and low latencies. Compared to its predecessor, 4 th Generation (4G) systems framework, 5G technology standards offer higher data rates of up to 1 Giga bit/s. Furthermore, 5G systems can be divided into two categories, namely, Sub GHz and mmWave regions, where mmWave is more promising for high-data-rate transmission and to support future cellular devices. The mmWave band of 5G offers a starting frequency of 24 GHz and above, offering much potential. Within the mmWave band, antenna designers have created novel shapes and assemblies. In addition, 28 GHz, 33 GHz and 37 GHz are the bands in mmWave which have drawn antenna designers' attention and have been introduced with these novel shapes and assemblies [1; 2]. MIMO antennas have given a new direction to wireless communication and have become very attractive for 5G applications [3; 4]. A MIMO Antenna offers pattern and spatial diversity characteristics, hence enabling better signal reception and data transmission. Designing a compact 5G MIMO antenna is still a challenging task in the current scenario, since accommodating a higher number of antenna elements together gives rise to coupling effects, which affect antenna performance characteristics. As today's cellular providers attempt to deliver high-quality, low-latency video and multimedia applications for wireless devices, they are limited to a carrier frequency spectrum ranging between 700 MHz and 2.6 GHz [5]. In open literature, a lot of MIMO antennas have been proposed in the mmWave spectrum, targeting different licensed and unlicensed frequencies [6; 7; 8; 9; 10; 11; 12]. In [6], a Substrate-Integrated Waveguide (SIW) antenna is presented, covering a frequency from 57 to 71 GHz for mmWave 5G and short-range radar applications. Although the presented antenna is well-designed, with small size of \(28\times 28\) mm, the compact design is difficult to manufacture due to multilayer assembly and bonding films. Planar antennas are simple and easy to design compared to SIW antenna systems. In [7], a simple planar infinity shell-shape antenna is presented in four-port MIMO configuration; the proposed antenna delivers a bandwidth of 8 GHz, approximately. Similarly, in [8], a nature-inspired four-port MIMO antenna is presented with a bandwidth ranging to 7 GHz with central frequency of 28 GHz. The size of the antenna is 30 \(\times\) 30 mm, and it provides pattern and spatial diversity characteristics. In [9], a tree-shaped four-port MIMO antenna is presented. The antenna provides wideband characteristics of 23-40 GHz while providing peak isolation of 22 dB. The size of the proposed MIMO antenna is 80 \(\times\) 80 mm, which is large enough to be embedded in mmWave circuits. A four-port Dielectric Resonator Antenna (DRA) in [10] provides the bandwidth of 2.23 GHz, ranging from 26.7 to 28.1 GHz. The size of the antenna is 20 \(\times\) 40 mm and antenna isolation has been improved up to a peak value of 22 dB by inserting metamaterial, but introducing metamaterial overall increased the complexity of antenna systems. In [11], an E-Shape H slotted dual-band four-port MIMO antenna is reported. The antenna offers good compact dimensions of 24 \(\times\) 24 mm but the reported bandwidth is too low. In [12], a four-port MIMO antenna system is reported providing bandwidth characteristics of 36.83-40.0 GHz. The antenna is simple in structure but provides low bandwidth. Therefore, this work was intended to design an MIMO antenna that is small in size, covers a wide bandwidth and offers high isolation characteristics throughout the desired resonance bandwidth. The proposed antenna is simple in shape and provides wideband characteristics of almost 15 GHz, with a better isolation value of \(-26\) dB. The isolation level has been improved by inserting a line resonator.