A Frequency-Agile Compact Array With a Reconfigurable Decoupling and Matching Network

A new frequency-agile compact antenna array incorporating a reconfigurable decoupling and matching network (DMN) is presented. The array consists of two printed monopole antennas, each loaded with a p-i-n diode. By changing the p-i-n diode states through an inductive biasing line, the array operating frequency can be tuned to the 2.5- or 3.5-GHz band. The array interelement spacing is chosen to be as small as 0.05 λ₀ at 2.5 GHz, which results in a strong mutual coupling between antenna ports. A reconfigurable DMN is proposed to reduce the mutual coupling when the array frequency is switched. Measured results show that the use of the DMN realizes a matched (S₁₁ ≤ -10 dB) and decoupled (S₂₁ ≤ -20 dB) bandwidth of 150 and 160 MHz in the lower and higher bands, respectively. In addition, compared to the strongly coupled array, at least 9% antenna total efficiency improvement is measured over a 125-MHz bandwidth in both the lower and the higher bands. The effect of the ohmic loss in the DMN on the antenna correlation is also investigated.