T-shaped decoupling network for wideband isolation improvement between two strongly coupled antennas

A compact T-shaped network for decreasing the port-to-port coupling between two strongly coupled antennas is investigated. The proposed circuit comprises of a pair of transmission lines followed by the T-shaped lumped element network connected between the two feeds of the antenna. Finally, a simple L-section matching circuit is added to each port to retune the input impedance matching. The proposed network gives a dual-resonant decoupling performance achieving isolation levels of 20 dB across 250 MHz bandwidth at 2.4GHz. The length of the transmission line is designed to introduce a trade-off between the decoupling level and bandwidth. This T-shaped network does not significantly decrease the antenna radiation efficiency. The experimental results coincide with the simulations. The decoupled closely spaced antennas could be used for Multiple-input Multiple-Output (MIMO) applications.