Tunable Electromagnetic Band Gap slits for mutual coupling reduction

Novel tunable two-layer Electromagnetic Band - Gap (EBG) slit-patch structures are presented for reducing the electromagnetic coupling between closely spaced CPW-fed monopole antennas. Ultra wideband monopoles are employed in order to demonstrate the tuning range of the slit. The proposed slit is etched in the common ground between the monopoles and a conducting patch is printed on a 55 μm thick polyester dielectric sheet separating it from the slit and the ground. The tuning is achieved by means of a varactor diode placed in the middle of the patch, which is electrically isolated from the ground plane of the antennas since it lies on a different layer. A tunable transmission zero is produced in the S21 leading to a significant reduction of the mutual coupling between the antennas. The tuning range covers the wide operating frequency band of the monopoles. The proposed slit is linear and of sub-wavelength dimensions (~λ/12) and hence it occupies very little space on the ground. Multiple EBG slit-patch structures are considered for more broadband antenna isolation. Simulation results were obtained in 3D electromagnetic simulation software (CST Microwave studio) and are presented.