A quad-polarization and frequency reconfigurable square ring slot loaded microstrip patch antenna for WLAN applications

Abstract

In this paper, a novel polarization and frequency reconfigurable microstrip patch antenna which can switch between vertical and horizontal linear polarizations, left hand and right hand circular polarizations at two WLAN frequencies is presented. The orthogonal linear polarizations are achieved by a square microstrip patch antenna fed by two ports on adjacent sides. By introducing corner truncated perturbation on opposite corners of right diagonal of a square patch, orthogonal circular polarizations are achieved. By controlling the bias voltage of two PIN diodes loaded at perturbed corners, a single structure can achieve quad polarization states. Furthermore, by superimposing a square ring slot into the corner truncated square patch and incorporating four PIN diodes into the square ring slot, quad polarization are achieved at dual frequencies. Simulated and measured results indicate that the antenna can achieve quad polarization at two WLAN bands (5.15–5.35 GHz) and (5.75–5.85 GHz). The proposed antenna is simple, has low profile and can be scaled easily for other frequencies.

Introduction

A reconfigurable microstrip antenna (MSA) provides more functionalities than conventional antenna; improves the link quality and capacity which is the most essential part of wireless communication systems. Based on the fundamental parameter of the antenna reconfigured, several single parameter reconfigurable antenna designs have been reported such as frequency reconfigurable [1], pattern reconfigurable [2] and polarization reconfigurable antenna [3]. Recently, several antennas are designed to achieve multiple reconfiguration which enables polarization and pattern reconfiguration [4], frequency and pattern reconfiguration [5], polarization and frequency reconfiguration [6]. These antennas communicate using diverse protocols operating at different frequencies, radiation patterns and polarizations. Frequency and polarization reconfigurable antenna delivers more flexibility and diversity than a single frequency agile or polarization agile antenna. It can offer significant benefits to many wireless communication systems like cognitive radio, software defined radio etc. However, the linkage between frequency and radiation characteristic still present a major challenge in the design.

Many frequency and polarization reconfigurable antennas have been designed and reported in literature [7], [8], [9], [10], [11], [12], [13]. In [7], the antenna consists of a U-slot incorporated into a corner truncated square patch. Frequency diversity characteristic is achieved using a PIN diode in the U-slot and the polarization diversities among linear polarization (LP), right-hand circular polarization (RHCP), and left-hand circular polarization (LHCP) are obtained by switching three PIN diodes placed on the slot and truncating corners of square patch. However, it achieves frequency reconfiguration only for linear polarization. In [8], a novel printed reconfigurable square slot antenna with switchable RHCP and LHCP with dual-band performance is reported. However, additional filters are required to choose each frequency in order to avoid interference. A K band patch antenna with frequency and polarization reconfigurable properties is proposed by Benjamin Rohrdantz et al. [9]. It can switch between two distinct frequency bands, but attains polarization switching only between LHCP and RHCP. Qin et al. [10] realized a frequency and polarization reconfigurable microstrip patch antenna that can radiate horizontal, vertical or slant linear polarizations with a wide independent frequency tuning range for each polarization. However, it cannot generate circular polarization. In our earlier paper [14] a single feed corner truncated square MSA is designed to achieve frequency and polarization reconfiguration. It achieves polarization switching between vertical polarization (VP), RHCP and LHCP at dual frequencies. None of these designs achieve quad polarization reconfigurability. Many quad polarization reconfigurable antennas have been designed [15], [16], [17], but they operate at single frequency. Recently, quad polarization reconfigurable antennas with frequency reconfigurability have been achieved by incorporating the control elements into the feed network [18], [19]. However, orthogonal LP and orthogonal CP operate at different frequency bands. It would be of interest to propose same corner truncated square MSA [14], that can generate horizontal polarization (HP) in addition to VP, RHCP and LHCP at dual frequencies with minimum number of PIN diodes and having simple and compact structure with reduced complexity. In the proposed paper, an attempt is made to design such an antenna by altering the size of square patch antenna proposed in [17], to achieve frequency reconfiguration in addition to quad polarization. The simulations are carried out in Computer Simulation Technology (CST) Microwave Studio [20].