###### Abstract
Substrate integrated waveguide (SIW) antenna for millimeter wave applications offering LHCP and RHCP is given in [13]. The antenna has simple geometry but a large size of 70 mm \(\times\) 63.5 mm \(\times\) 2.2 mm and a narrow ARBW of 0.6 GHz. In [14], a series slot-fed MIMO antenna array with overall size of 28.7 mm \(\times\) 27 mm \(\times\) 25 mm and offering high gain of 11.6 dBi is given. The antenna offers an axial ratio bandwidth of 27.3-29.65 GHz. Although the antenna has compact size, high gain, and wideband axial ratio, the setback is complex geometry. A meta-surface-based antenna for 28 GHz applications is reported in [15]. The antenna has a compact size of 20.4 \(\times\) 20.4 \(\times\) 0.5 and has simplified geometry. The antenna has a high gain of 11 dBi and offers an axial ratio bandwidth of 3.4 GHz. The antenna mechanism is complex due to the loading of meta surface. Aperture couple antenna array for satellite communication is reported in [16]. The antenna offers a wide axial ratio and high peak gain but has large size and complex geometry. In [17], CPW-fed dual band antenna offering LHCP and RCHP is given. The antenna has a compact size of 10 mm \(\times\) 10 mm \(\times\) 0.51 mm but a low gain of 0.51 dBi. Another compact CP antenna is reported in [18]. The antenna has an overall size of 20 mm \(\times\) 20 mm and offers 28.5-32 GHz axial ratio bandwidth. The setback of this reported work is complex geometry and low gain of antenna. A wideband antenna operating at 28 GHz with a bandwidth of 24.2-30.4 GHz is reported in [19]. The antenna is 18.1% axial ratio and has a peak gain of 8.5 dBi. Another work in [20] offers LHCP and RHCP but has complex geometry. The antenna has offers 14.5 dBi and 40% axial ratio bandwidth over K and Ka-band applications. In [22], a novel antenna offering broadband, reconfiguration, and circular polarization is reported. The rotation of the E-shaped patch and its array is utilized to obtain reconfiguration. The reported work offers LHCP and RHCP but has a large geometry of 44.1 mm \(\times\) 78 mm. A millimeter wave antenna operating at 28 GHz is reported in [23] for circular polarization applications. The antenna offers a maximum gain of 21.9 dBi and axial ratio bandwidth of 3 GHz. Although the antenna has high gain and offers wide axial ratio bandwidth, demerit is complex geometry, due to travelling wave feeding approach. From the above discussion and brief literature review, it is clear that there are still research gaps/problems with the design antenna having compact size, simple geometry, low-profile and offers wideband, high gain, and wide axial ratio bandwidth for 5G applications. Therefore, in this paper, an antenna is designed and investigated to meet the requirements of current and future 5G devices operating over a millimeter wave band spectrum of 28 GHz. In this article, a simplified structure, compacted size, low-profile, wideband, high gain, and high radiation efficiency antenna is proposed for millimeter wave applications. The antenna operates at 28 GHz band and is able to operate at LHCP and RHCP. The two-port antenna is designed to obtain the circular polarization in the left and right side. The MIMO antenna element is placed in various places at substrate to examine and study the polarization behavior of the MIMO antenna system. The antenna designing technique and effect of key parameters are given in the next section. In section III, the antenna MIMO configuration is explained by placing the patch element in various orientations. The proposed work is concluded in Section 4, along with references.