Field theory CAD of waffle-iron filters

A combined generalized scattering matrix/Galerkin´s method for CAD of waveguide waffle-iron filters is presented. The proposed technique includes the solution of eigenvalue problems for multiridged waveguide sections, the solution of key scattering problems for basic discontinuities and evaluation of total S-matrix of filter. All particular eigenvalue problems and scattering problems are reduced to corresponding systems of electric field integral equations that are solved by Galerkin´s method. High accuracy of evaluated spectrum of multiridged waveguide is obtained due to using of weighted Chebyshev or Gegenbauer polynomials as basis functions taking into account the field asymptotic at the edges. The combined method is verified by available measurements and theoretical and experimental data of references. A number of low-pass waffle-iron filters have been designed for multiband feeders of reflector antennas operating in S, C, X, Ku bands.