Fabry-Perot Cavity Size Reduction in PRS based MIMO Antennas with Improved Correlation Coefficient Performance for Practical Designs

Abstract

Multiple-Input-Multiple-Output (MIMO) systems are being used extensively in modern communication systems. They address the needs of high data rates and ensure a reliable communication without increasing the transmitted power or using additional frequency spectrum. They are integral part of current 4G/LTE communication standard and will also be an enabling technology for future 5G standard. To provide with their full benefits MIMO systems rely on multiple uncorrelated propagation channels. This correla tion is function of physical channel between transmitter and receiver as well as the radiation pattern of antenna itself. It is difficult to cater for correla tion caused by the antenna itself because of small form factors of practical antennas. In literature, correlation coefficient has been reduced by increas ing port isolation among antenna elements. However, this method does not directly target the radiation patterns of antenna elements which need to be decorrelated. Recently multiple works have reported that this technique does not guarantee correlation coefficient reduction. Hence a method was proposed to deliberately decorrelate radiation patterns of individual antenna element. This was done using a partially reflected surface placed over the MIMO antenna essentially forming a Fabry-Perot cavity. Through this technique ultra-low correlation was achieved. However, the height of designed cavity was λ/4. This height is quite high for design to be used in sub-6GHz frequency range applications. This thesis presents a compact design with reduced cavity height which achieves same ultra-low correlation between an tenna elements. General guidelines have been developed for the design of low-profile cavity for MIMO antennas. Based upon presented guidelines, a partially reflected surface is designed. Working of this surface is validated by decorrelating the fields of two element MIMO patch antenna radiating at 5.36 GHz. During this 95% reduction in correlation coefficient has been achieved with a cavity height of λ/10. Presented design is also fabricated and results are compared with the software-based simulation results. The design can be used for W-LAN applications where compact size is required such as tablet PCs or access points etc.