A design methodology for fully canonic NRN filters in coaxial technology

This paper presents a detailed approach to the design and dimensioning of coaxial filters with fully canonic elliptic response. In order get a compact configuration the extracted-pole in-line configuration with non-resonating nodes (NRN) is adopted. First the synthesis of a low-pass prototype is carried out and the generalized coupling coefficients together with the resonant frequencies are computed as outlined in the literature. A suitable de-normalized equivalent circuit is then derived with reference to the specific filter configuration here considered. Finally, the dimensioning of the structure is carried out suitably exploiting full wave simulations for imposing the parameters of the equivalent circuit obtained from the synthesis to the physical structure. The proposed methodology has been validated by the design and fabrication of two high selectivity filters to connect in cascade for realizing a band pass filter easily tunable both in center frequency and bandwidth.