Decoupling between ground radiation antennas with ground-coupled loop-type isolator for WLAN applications

A compact and easy to fabricate decoupling method is proposed to yield high isolation for the multiple-input and multiple-output (MIMO) ground radiation antenna (GradiAnt) system. The proposed MIMO antenna system is comprised of two symmetrical, closely spaced, loop-type (GradiAnts) with a ground-coupled loop-type isolator inserted between them. The isolator can be seen as a series resonant circuit which is connected with lumped components to control decoupling. In the proposed MIMO GradiAnt system, a coupling null is induced due to the ground-coupled isolator, which effectively can be used for isolation enhancement between two GradiAnts. Within WLAN band, a minimum 14 dB isolation with a peak value of 42 dB at 2.42 GHz is achieved. In this manuscript, the decoupling principle and controlling mechanisms are first explained, then the antenna performances and tuning mechanisms are discussed in detail. The simulation and the measurement of the MIMO antenna, including the scattering parameters, efficiency, radiation patterns, peak gains and envelope correlation coefficients are conducted to verify the performance of the proposed MIMO system.