Wideband Pattern Decorrelation in MIMO Antennas Using Partially Reflective Surfaces

Abstract

Multiple-Input-Multiple-Output (MIMO) antennas are fundamentally employed to enhance the communication experience. Correlation Coefficient (CC) is an important parameter for characterizing the performance of MIMO system. It is the measure of correlation that exists among channels formed in a MIMO system. Low correlation is desirable to take full advantage of MIMO systems. CC is a function of antenna design and prop agation environment. Mostly rich multipath propagation environment is considered for MIMO communication and therefore, CC becomes function of antenna design only. That is why it is an important performance metric for MIMO antenna. Usually calculated using S-parameters of antenna it has been shown lately that S-parameter based CC calculation mostly gives erroneous values. Recently, a new approach was proposed to reduce the correlation coefficient in MIMO antenna by directly dealing with the radiation patterns of the individual antenna elements of MIMO antenna. However, this tech nique can not be used for existing and upcoming practical wideband MIMO antennas used in communication as it is. Although promising, the technique needs to be extended to account for antennas with wider bandwidth. To improve the bandwidth performance of field decorrelation technique, a wideband phase gradient PRS has been proposed. Such PRS has a positive reflection phase gradient and is placed at the top of wideband MIMO antenna. The configuration is referred to as FPC configuration. This arrangement enhances the gain and also helps the beam to tilt in opposite direction that reduces the CC. The approach has been validated using HFSS simulation for a 2-element wideband radiator operating in X band for which there has been 66-88% decrease in CC for 12.5% fractional bandwidth. It corresponds to 78% increase in fractional BW as compared to the previous work. This technique will be helpful in enhancing the performance of 5G MIMO antennas. PRS can be printed on the enclosure of handsets thus enhancing diversity performance without acquiring additional space.