Tunable Double-Layer EBG Structures and Application to Antenna Isolation

A novel electronically tunable two-layer slot-patch one-dimensional electromagnetic band-gap (EBG) structure with significantly simplified biasing network is presented. The proposed structure consists of apertures (slots or slits) etched off a metallic ground, and a varactor-loaded patch printed on a thin dielectric substrate, placed on top of each aperture. The apertures are initially designed using microstrip line excitation and a stop-band is produced in the S
₂₁
response. Tuning of the stop-band is achieved by changing the voltage applied to the varactors which are electrically isolated from the metallic ground, resulting in a simple biasing configuration. As a practical application, the proposed tunable EBG structures are employed in the common ground plane of two closely spaced printed monopole antennas, significantly reducing the mutual coupling between them. Simulation results and measurements of fabricated prototypes are presented.