Feed Locating and Beamforming in Collocated MIMO Antenna Using Characteristic Mode Theory

In this paper, a procedure for feed placement in a collocated Multiple Input Multiple Output (MIMO) antenna is presented based on characteristic mode theory. The orthogonality of characteristic currents is used to determine optimal feed locations in the presented antenna. First, characteristic mode analysis is done to determine the resonance modes of the antenna; Then the optimal feed locations are determined to excite these orthogonal modes. Moreover, we modify the shape of the radiation pattern of the antenna by changing amplitude excitation of these modes. It is observed that only by changing amplitudes of the antenna modes and their composition at the desired frequency, the shape and the beam width of the antenna pattern is changed.