Reduction in Out-of-Band Antenna Coupling Using Characteristic Mode Analysis

Out-of-band interference by antenna coupling is frequently encountered and difficult to compensate. In this paper, it is studied for the first time using characteristic mode analysis (CMA). Mutual coupling between two antennas is separated into several fundamental modes, and the contribution of each mode is evaluated through modal mutual admittance (MMA). Some higher order modes, which contribute little to the in-band radiation but much to the out-of-band coupling, are discriminated and controlled by means of inductive loadings. The placement of loadings is suggested by the distribution of eigencurrents and optimum values are obtained by evaluating the MMA. Numerical and experimental results are presented for verification.