Tunable Decoupling and Matching Network for Diversity Enhancement of Closely Spaced Antennas

A tunable decoupling and matching network (DMN) for a two-element closely spaced antenna array is presented. The DMN achieves perfect matching for the eigenmodes of the array and thus simultaneously isolates and matches the system ports while keeping the circuit small. Arrays of closely spaced wire and microstrip monopole pairs are used to demonstrate the proposed DMN. It is found that monopoles with different lengths can be used for the design frequency by using this DMN, which increases the design flexibility. This property also enables frequency tuning using the DMN only without having to change the length of the antennas. The proposed DMN uses only one varactor to achieve a tuning range of 18.8% with both return loss and isolation better than 10 dB when the spacing between the antennas is 0.05 λ. When the spacing increases to 0.1 λ, and the antennas are properly matched, the simulated tuning range is more than 60%.