Multiple-stage combline bandpass filter made of /spl lambda//4 transmission line resonators

A new design method is proposed for multiple-stage combline bandpass filter made of transmission line resonators. The Grayzel transformation is used for separating the two adjacent couplings of each resonator and decomposing the filter into a parallel connection of two coupled resonators. After the design is finished, identical resonators are equally spaced with auxiliary capacitors, which is the simplest structure to fabricate.