Multistage dual-plane comb-line filter excited by conductor-backed coplanar waveguide

This paper proposes a novel multi-stage dual-plane comb-line filter having plural attenuation poles just below and above the passband. As this filter has such a structure such that two quarter-wavelength step impedance resonators are placed face-to-face beyond the substrate on each filter block, the mutual coupling between adjacent blocks are small and the optimisation on each block can be done independently. High performance filters up to 4-stages are demonstrated both theoretically and experimentally.