Waveguide E-Plane Triple-Insert Filter

A triple planar integrated circuit filter with all-metal inserts and an additional abrupt waveguide step-wall discontinuity is introduced which achieves ultra-broadband high attenuation in the second stopband. The theory is based on field expansion into suitable eigenmodes which allows direct inclusion of both the higher-order mode interaction at all step discontinuities and the finite thickness of the metal inserts. Computer optimized design data for a four-resonator Ka-band proto-type at 27 GHz midband frequency provide a minimum stop-band attenuation of 50 dB between 28 and 42 GHz (80 dB between 30 and 41.6 GHz).