Use of generalized coupling coefficients in the design of extracted-poles waveguide filters with non-resonating nodes

In this paper the use of generalized coupled coefficients for designing waveguide filters with non-resonating nodes (NRNs) is presented. These coefficients have been introduced in the literature for reducing the difficulties associated to the design of filters using NRNs. The waveguide filters here considered present transmission zeros produced by shunt-connected, short circuited H-plane stubs. An equivalent circuit, including the effects of connecting junctions is first defined for the whole filter; then, using a previously developed procedure, a low-pass prototype with the same topology is synthesized and the generalized coupling coefficients are computed. Using these coefficients, the prototype can be easily de-normalized and the relevant geometric dimensions of the filter analytically evaluated. This procedure allows a relatively accurate dimensioning of the filter without resorting to numerical optimization which is very time consuming when performed in electromagnetic environment. A 4th-order filter with two transmission zeros has been designed following the proposed approach; the computed performances confirm the validity of the proposed method.