A multiple-input-multiple-output (MIMO) antenna with orthogonal circular polarization (CP) is proposed in this paper with an intention to use the antenna in sub-6 GHz 5G applications. The single antenna consists of a radiating slot and feed line. The non-uniform width elliptical ring slot in the ground plane and unequal feed line technique are used to produce CP. The benefit of using ring slot antenna is that this type of antenna can radiate orthogonal CP at the front and back direction, simultaneously. The operating band of single antenna is (3.6-3.8 GHz). The MIMO antenna has 4 single antenna elements where each antenna element is surrounded by the mirrored antenna elements. As a result, MIMO structure provides orthogonal CP. Moreover, this MIMO antenna can also radiate both LHCP and RHCP on the both directions (θ = 0° and 180°) simultaneously. Three interconnected strip lines on the ground plane are designed to connect the individual grounds of the antenna elements. The MIMO antenna provides good isolation and CP gain in the whole band (3.4-3.8 GHz). The envelop correlation coefficient and channel capacity loss are evaluated to judge the MIMO performances and promising result is achieved. To analyze the impacts of user hand, various performance studies are done for the antenna in the vicinity of left hand and right hand phantom model and satisfactory results are achieved. These performances prepare the antenna more attractive to use in 5G cellular applications.

<span>This article represented a heart shape reconfigurable monopole antenna with polarization diversity. The proposed antenna is fed by a 50 Ω microstrip feed line that is printed on a flexible FR-4 (εr=4.4) substrate. The antenna comprises a ring-slot, a cross slot and four positive-intrinsic-negative (PIN) diodes that are soldered on ring slot. Four PIN diodes act as a switch and by controlling these PIN diodes effective current direction is changed hence four various states of polarization are achieved. Four states of polarization such as horizontal linear polarization (H-LP), vertical linear polarization (V-LP), right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) can be switched easily with the help of these PIN diodes and achieved an efficiency of more than 90%. Proposed antenna shows voltage standing wave ratio (VSWR)&lt;2 at all working frequency and -10 dB reflection coefficients (RC) bandwidths (BW) (i.e., S11≤-10 dB) about 32.86% for linear polarization (LP) states while RHCP and LHCP states possess BW of about 31.61% and 31.67% respectively. It also shows axial ratio (AR) BW of 3.41% and 2.44% for RHCP and LHCP, respectively. Besides, the antenna has a well-suited omnidirectional pattern with a positive gain of all working frequency of interest where cross-polarization level is much lower than that of antenna gain.</span>

Design and parametric analysis of a planar array antenna for circular polarization muhammad asad rahman 1 , quazi delwar hossain 1 , md. azad hossain 2 , eisuke nishiyama 3 and ichihiko toyoda 3 A new circularly polarized planar array antenna using linearly polarized microstrip patches is designed and optimized for X-band wireless communication applications. Four square patch elements with feed network are used to design the circularly polarized array antenna. The feed network consists of microstrip lines on the obverse side of the dielectric substrate and slot line on the reverse side of the substrate. Both-sided MIC technology is successfully employed to apply its inherent advantages in the design process of the array structure. The unequal feed line is used to create 908 phase difference between the linearly polarized patches. Therefore, the circular polarization is realized by the combination of linearly polarized patches and unequal feed line. Characteristics of the proposed array are investigated by using two electromagnetic (EM) simulators: advanced design system and EMPro. The 210 dB impedance bandwidth of the antenna is around 5%. The 3 dB axial ratio bandwidth of 1.48% is obtained. The design of the proposed antenna along with parametric study is presented and discussed.

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