Receiving mutual impedance of a compact patch antenna array with two elements in a rich multipath environment

The performance of an antenna is changed whenever it is placed within the field of another antenna because of the existence of mutual coupling. The concept of receiving mutual impedance was introduced to characterize the mutual coupling effect in receiving antenna arrays and has been successfully applied in many occasions, such as direction finding, adaptive nulling, and medical imaging. In this paper, the definition of receiving mutual impedance is extended to characterize the mutual impedance coupling effect in two patch antennas operating in a rich multipath environment. In the extended definition, the two antennas are excited by a larger number plane waves coming from different directions. The behaviour of the receiving mutual impedances when the antennas are excited by different number of plane waves is studied and compared with the case of omni-directional antennas. This extends the use of receiving mutual impedance to non-omni-directional antennas for operation in multipath environments and has an implication for receiving antenna array design for multi-antenna systems such as MIMO systems.