Investigation of isolation enhancement and tune-ability in patch antenna arrays

This paper reports the study of a tunable isolator based on a four-strip resonant structure to reduce the mutual coupling between two patch antennas. Unlike other decoupling structures with a fixed center decoupling frequency, this design provides tunable mutual coupling reduction frequency response and adjustable mutual coupling level by integrating a varactor diode into the strip isolator. This study investigates the effect of the position and capacitance of the varactor diode on mutual coupling. In addition to tune-ability, the tunable four-strip resonator reduces the coupling level at all frequencies around 3.5 GHz by at least 6 dB to less than -28 dB without degrading the impedance bandwidth. Compared to the case with the four-strip resonator structure but without the varactor diode, the isolation is further improved by 2 dB or more. The measured results are consistent with the simulation results.