# Designed Circularly Polarized Two-Port Microstrip MIMO Antenna for WLAN Applications
## 1 Introduction
Two ground radiation antennas with polarization diversity performance for WLAN applications in wearable devices have been proposed in [32]. In [33], the authors proposed a circularly polarized MIMO antenna based on an L-shaped dielectric resonator (DR) for WLAN applications. A compact and planar CP-MIMO patch antenna with diversity polarization was described in [34]. The antenna achieved good impedance matching, high isolation, and better gain, but its dimensions are large and the axial ratio (AR) bandwidth was narrow. In [35], the authors show how to use metamaterial to reduce mutual coupling among microstrip patch antennas in a MIMO antenna for WLAN band, which still have limited bandwidth, and the gain is just 4 dB. In [36], the authors designed a four-element compact MIMO antenna for WLAN band with simultaneous pattern and polarization diversities, but there was only 15.4 dB of isolation. In [37], a quad-port MIMO antenna was based on a miniaturized slit-loaded modified slot antenna for the 5 GHz band of WLAN. In [23], the authors proposed a three-element compact MIMO antenna designed with polarization (linear/circular) diversity. For 5.8 GHz WLAN values, [38] designed a CP-MIMO antenna with a power divider, which uses two tuned 90-degree slots. The impact of design on S-parameters and AR was explored in this paper for many features of the MIMO antenna. In [39], for point-to-point communication, a CP-MIMO array antenna in WLAN applications was introduced. In [40], a DR two-port MIMO antenna (DRA) with a circularly polarized radiation was proposed, but having low isolation, the gain was 3.8, and a large dimension. In [41], a compact size and high isolation \(2\times 2\), a MIMO antenna was used for various applications of the ISM band, WLAN, of the lower frequency band of 5G. In [42], a wideband CP two-port MIMO antenna with a compact size was designed for the fifth-generation (5G) region in the sub-six GHz band. A wideband CP-MIMO antenna line patch was proposed among two antenna elements in [43]. A two-port CP-MIMO antenna was designed to have simultaneous patterns and diversity polarization for the WLAN application band [44]. For WiMAX applications, a dual-port MIMO antenna system with circular polarization diversity was investigated [45]. In [46], the MIMO system had a strong pattern and polarization diversity, but it did not have isolation and gain. A DGS structure was used in [47] to improve the inter-port isolation of a super compact \(2\times 2\) MIMO antenna. In this paper, a simple corner square-cut square-patch MIMO-CP antenna is presented for the WLAN application. The design consists of a two-corner square-cut square-shaped patch antenna and a slot in the middle of the ground, which gives low mutual coupling and CP. In this work, first, we designed a single square-cut patch antenna CP for the WLAN application. Then, for the same frequency MIMO-CP antenna with the ground slot, given a similar bandwidth, increase the return loss (S11) value from \(-21\) to \(-38\) dB, shift resonant frequency from 5.53 to 5.6 GHz, reduce mutual coupling, and improve axial ratio. The edge-to-edge distance \(d(0.227\lambda_{0})\) is fixed between two elements for better performance of the MIMO-CP antenna. The analysis of the proposed MIMO-CP antenna was simulated using computer simulation technology (CST) Microwave Studio, and it was fabricated on an FR-4 low-cost dielectric substrate with relative permittivity of 4.4, loss tangent of 0.02, thickness of 1.6 mm, and a total area of 22.5 \(\times\) 50 mm\({}^{2}\). The fabricated MIMO-CP antenna prototype and measurement results are presented in Section 5. The main contributions of this work compared to the recent literature are detailed below:  
A comparative study is carried out to explain the novelty of the proposed MIMO-CP antenna. The comparison clearly shows that the designed antenna gives better performance than the other designs, in terms of size, bandwidth, axial ratio, gain, and isolation.