Polarization reconfigurable antennas for space limited multiple input multiple output system

Abstract

Wireless communication undergoes rapid changes in recent years. More and more people are using modern communication services, thus increasing the need for higher capacity in transmission. One of the methods that is able to meet the demands is the use of multiple antennas at both link ends known as Multiple Input Multiple Output (MIMO) system. However, for the space limited MIMO system, it is relatively difficult to accomplish good performance by using conventional antennas. Therefore, to further improve the performance offered by MIMO, Polarization Reconfigurable Antennas (PRAs) can be adopted. The diversity in polarization can be exploited to increase channel capacity. Moreover, the use of PRAs can also provide savings in terms of space and cost by arranging orthogonal polarized together instead of two physically space separation antennas. Here, single and dual port PRAs are proposed. Two techniques are deployed to achieve the PRAs are slits perturbation (switches on the radiating patch) and alteration of the feeding network (switches on the ground plane). Switching mechanism (ideal and PIN diode) is introduced to reconfigure the polarization between left-hand circular polarizations, right-hand circular polarizations, or linear polarization, operating at wireless local area network frequency band (2.4 – 2.5 GHz). Furthermore, by exploiting the odd and even mode of the coplanar waveguide structure, dual ports PRAs are realized with the ability to produce orthogonal linear polarization (LP) and circular polarization (CP) modes simultaneously. Good measured port polarization isolations (S21) of -16.3 dB and -19 dB are obtained at the frequency of 2.45 GHz for configuration A1 (orthogonal LP) and A2 (orthogonal CP), respectively. The proposed PRAs are tested in 2 x 2 MIMO indoor environments to validate their performances by using scalar power correlation method when applied as receiver in both line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios. Channel capacity improvement has been achieved for spatial diversity (92.9% for LOS and 185.9% for NLOS) and polarization diversity (40.7% for LOS and 57.9% for NLOS). The proposed antenna is highly potential to be adopted to enhance the performance of the MIMO system, especially in dealing with multipath environment and space limited applications.