Control of inter-resonator coupling using defected ground structure lattice

A novel method to control inter-resonator coupling using the defected ground structure lattice (DGS-L) is proposed. The influence of the geometrical parameters of the lattice on the intensity of the coupling between ring resonators is analysed in detail. It is shown that the inter-resonator coupling can be increased significantly by using DGS-L, which leads to the miniaturisation of wideband bandpass filters designed using standard filter design theory. To illustrate the effect of incorporating the proposed DGS-L, the direct-coupled bandpass filter of the third order has been designed, fabricated and measured. The filter exhibits ~40% wider bandwidth compared with the same filter designed without the use of DGS-L, while its footprint remains unchanged.