Modal S-matrix method for the optimum design of inductively direct-coupled cavity filters

F. Arndt, J. Bornemann, D. Heckmann, C. Piontek, H. Semmerow, H. Schueler
1986 IEE Proceedings H (Microwaves Antennas and Propagation)  
A rigorous field theory method is described for the computer-aided design of a class of rectangular waveguide filters, where the cavities are coupled by irises, £-plane integrated metal inserts, broadside oriented strip obstacles, or multiple quadratic posts. These coupling elements enable low-cost manufacturing, since accurate and inexpensive metal-etching techniques, or materials with standard dimensions may be utilised. The design method is based on field expansion in suitably normalised
more » ... ably normalised eigenmodes which yield directly the modal scattering matrix of two appropriate key building blocks for this kind of filter, the step-wall discontinuity and the N-furcated waveguide section of finite length. The theory includes the finite thickness of the diaphragms, strips or posts as well as the immediate higher-order mode interaction of all discontinuities. The stop-band characteristic of the filter is taken into account in the optimisation process. Optimised data are given for Ku-, E-, W-, and D-band filter examples, whereby it is shown that the theory is also very appropriate for broadband designs. The theory is verified by measured results for a six resonator iris coupled Ku-band filter, with a midband frequency of 15.2 GHz and a seven-resonator metal insert D-band filter, with a midband frequency of 142.5 GHz, snowing measured minimum insertion losses of 0.2 dB and 1.4 dB, respectively. Authorized licensed use limited to: UNIVERSITY OF VICTORIA. Downloaded on December 11, 2008 at 17:27 from IEEE Xplore. Restrictions apply.
doi:10.1049/ip-h-2.1986.0063 fatcat:nr6jsu3utzcbjfa3xtyoz4xfxe