A New Methodology of Antenna Decoupling by Common and Differential Modes Cancellation

Abstract

The mutual coupling effect between antenna elements will degrade the diversity performance of multiinput multi-output (MIMO) systems and deteriorate the antenna efficiency and beamforming performance of antenna arrays. To address this problem, many antenna decoupling techniques, such as decoupling network, defected ground structures, parasitic elements, neutralization line, and decoupling meta-surface, have been proposed in the last decades to reduce the mutual coupling between antenna elements. However, the additional decoupling structure will simultaneously change the reflection coefficients and isolations; thus, multiple iterations have to be performed to achieve a good impedance matching and isolation synchronously, making the decoupling process complicated and time-consuming. In this paper, a simplified antenna decoupling methodology based on the common mode (CM) and differential mode (DM) cancellation is proposed. It is theoretically proved that, the mutual coupling between two antenna elements can be eliminated totally when the corresponding CM and DM impedances are the same. By strategically exploiting the orthogonal field properties of the CM and DM, the CM and DM impedances can be tuned independently without iterations. And the structure for CM and DM impedance matching is exactly the structure for antenna decoupling. Therefore, many new decoupling structures beyond the conventional decoupling schemes can be achieved. The proposed decoupling methodology can be applied to various antennas, such as closely-spaced dipoles, monopoles, inverted-F antennas, patch antennas, and planar-inverted-F antennas, which is a promising candidate for basestation, mobile terminal, and phased array applications.