Simple tuning procedure for coupled-resonator filters

A new method for the initial design of direct-coupled cascaded resonators waveguide filters is proposed. The method is based on tuning the resonant frequency of cascaded resonators separately and is equally valid for the uniform and non-uniform case. The initial values obtained are in many cases a better approximation than equivalent K-inverter resonator prototypes, and the whole design procedure requires significantly less computational effort. Furthermore the method can predict the stopband performance of the filter from the harmonic behaviour of its resonators. Numerical and experimental results in the case of E-plane filters demonstrate the validity.