Quasi-lumped suspended stripline filters with adjustable transmission zeroes

Based on quasi-lumped resonators in suspended stripline technique, very compact filters are realized. The resonators consist of patch-like capacitive elements and thin inductive strips, coupled electromagnetically to the input lines and adjacent resonators. By properly arranging these resonators, transmission zeroes can be produced and shifted easily to frequencies either below or above the passband. A detailed discussion of this effect is given, and three sample filters are presented. At 8.5 GHz, a four resonator filter has a length of 12 mm only. With a bandwidth of 1.3 GHz, minimum insertion loss is 0.7 dB including connecting lines and transitions to the coaxial test system.