Shunt-inductance-coupled waveguide filters with expanded second stopband

A computer-aided design is described for inductive iris and inductive double-strip coupled filters with increased-width resonator sections. The theory includes both the higher-order-mode interaction of all discontinuities and the finite thickness of the irises and inserts. The step-wall discontinuity effect is included in the optimisation process as an additional design parameter. Design examples for midband frequencies of about 11 and 16 GHz are given; the corresponding stop-band attenuation is higher than 50 dB, or 40 dB, up to 18.5 GHz, or 24.5 GHz, respectively.