In this paper, we present an adaptive uncoupled matching network to compensate any performance degradation of compact Multiple-Input Multiple-Output (MIMO) systems due to antenna mutual coupling effects and channel variations. This method varies the antenna terminal loads per symbolblock, based on a random search algorithm, to find an optimum termination network that maximises the performance metric, such as received power and capacity. It uses the received signals (voltages across the resistances of the terminal loads) to estimate or calculate the performance metric, in order to include the total effects in the optimisation process. By applying the random search algorithm, our method does not require any knowledge of the array parameters such as impedance matrix, or derivatives of the performance metric(s) unlike other optimisation techniques. We demonstrate this scheme by performing simulations to optimise the capacity of a 3 × 3 MIMO considering different propagation scenarios. We observe significant mean capacity improvements (more than 2bits/s/Hz) for all assumed propagation scenarios, when receive array antennas are spaced close as 0.05 and terminated non-identically.
