Waveguide Filters Based on Capacitive Irises with Additional Attenuation Poles

The new design of directly-coupled band-pass filters insuring inclusion of additional stopband poles is offered. The stopband poles are inserted by means of cutting additional slots in capacitive irises of the filter. The slots are parallel to broad walls of a waveguide. Such method of inclusion of additional poles does not result in increasing dimensions of the filter. Modification of the filter irises results in insignificant change of their K-inverters. They are easily trimed to the desired value. The dimensions of the additional slots determine position and quality factor of the additional stopband poles. They can be situated both in a parasitic transmission band and in a transition region of the fundamental band. The numerical examples for band-pass filters in WR 90 waveguides are given. They show increasing the frequency selectivity and stopband extension. It is reached without a loss increase in the filter transmission band. An example of synthesis of a low-pass filter with a low loss level in a transmission band is also presented.