###### Abstract
These MIMO systems include Substrate Integrated Waveguide (SIW) based antennas, Empty Substrate Integrated Waveguide (ESIW), Air-gap Filled Antennas (AFAs), Dielectric Resonators (DRA) and planar antenna systems [7; 8; 9; 10; 11; 12; 13; 14; 15]. In [7], triband DRA is proposed for mmwave applications. The triband DRA had stacked radiating elements with semicircular slots etched on each side of top dielectric surface. The resonance bandwidth included 7.34 GHz, 4.04 GHz and 3.30 GHz at resonance frequency of 28, 33 and 38 GHz. A printed dipole four element MIMO antenna is presented in [8]. The total size of the MIMO system is 48 \(\times\) 31 mm\({}^{2}\) with a bandwidth offering of 5 GHz from 26 to 31 GHz. The isolation of the MIMO elements is increased up to 21 dB with the integration of a capacitive loaded loop unit cell. A four-element MIMO antenna in [9] provides resonance bandwidth of 3 GHz with ECC \(<\) 0.0005 among any two radiating elements. Antenna configuration using orthogonal assembly in the mmwave spectrum has thoroughly been investigated in [10; 11; 12; 13]. A dual band mmwave MIMO antenna system for 5G technology is presented in [10]. Additionally, the placement of the antenna elements in an array was constructed in such a way that an acceptable amount of isolation was obtained without the use of conventional decoupling structures or processes. A system made up of four radiating elements and an etched Rogers-5880 substrate having permittivity of 2.2 with a thickness of 0.508 mm was used to illustrate this. An E-shaped patch, an H-shaped slot inside a patch, and a transmission line make up each radiating element. The system has a minimum port isolation of \(-\)28 dB and resonates at two separate mmwave frequencies, namely 28 GHz and 38 GHz with 7.1 dBi at 28 GHz and 7.9 dBi at 38 GHz with average efficiency, and envelope correlation coefficient (ECC) of the system at 70%. A planar 5G MIMO antenna is presented in [11] with total size of \(30\times 30\) mm\({}^{2}\). The four antenna elements in the proposed MIMO antenna are positioned \(90^{\circ}\) apart. Four circle-shaped ring patches make up the transmitting component of each antenna element, and they primarily help the device to operate within the intended frequency range. Additionally, the centre of each antenna element is surrounded by four rings with circles on them, each of which is above the feed line. Minimal mutual coupling is shown by the isolation of more than \(-29\) dB for the working band. Additionally, the suggested MIMO antenna's peak gain and overall efficiency for the working bandwidth are 6.1 dBi and 92%, respectively. Similarly, in [12] the slot monopole antenna systems were presented with a size of 30 \(\times\) 30 mm\({}^{2}\). The antenna was comprised of small five circular arms connected to main circle hence resulting in form of petal flower. The antenna showed a bandwidth of 2 GHz with a central frequency of 28 GHz and peak gain of 5 dBi. In [13] a four element antenna system was presented at 38 GHz with peak gain of 5 dBi and ECC < 0.01. The DRA presented in [14] was designed in a 'plus' shape with radiating elements directly facing each other. Similarly, ESIW and AGF antennas for mmwave have also been reported [15; 16]. In [17], for upcoming 5G cellular applications, a dual-band dual-linear polarisation reflect array design is created. For this reason, a single layer unit cell containing two pairs of miniature fractal patches is made to operate in a dual-polarization mode at two separate frequencies in the Ka-band (27/32 GHz). The complete independence between the intended frequency bands and polarisations is shown by in-depth analysis of unit cell behaviour. Small unit cell sizes, minimal losses, a very simple and thin construction, and an independent optimization of the phase at each frequency and polarisation are all features of the suggested architecture. Two pairs of miniature patches are combined to form the proposed dual-band, dual-polarized reflectarray cell, which is printed on the same substrate layer.