Complement pattern on metamaterial antenna for reducing mutual coupling in MIMO systems

Complement pattern (CP) on multiple antennas in order to reduce the mutual coupling between antenna elements is proposed and investigated. The proposed CP is comprised of meandered transmission lines between antennas on FR4 (epsiv_r=4.6) substrate. The multiple antennas are a printed embedded type based on composite right/left handed (CRLH) metamaterial transmission lines. In order to validate the CP effects, both simulation and measurement results between with-CP and without-CP in metamaterial antennas are used. The CP is presented as an equivalent circuit. Through parametric studies, optimal dimension of CP is determined. Return loss, isolation, radiation patterns of each plane, measured peak gain, and current distributions are provided in this paper. By calculating the envelope correlation coefficient between two antennas, we also demonstrate the effect of CP in metamaterial antenna. Total PCB size is 21.5 times 50 mm² with 1 mm thickness, and antenna space is 21.5 times 10 mm². Resonant frequency with good isolation value is 3.3 GHz. Since metamaterial antenna and CP consist of transmission lines, proposed structures are very useful to apply for the RF devices.