A powerful tool for the synthesis of prototype filters with arbitrary topology

This paper describes a CAD tool for synthesizing prototype filters with arbitrary topology, with cross-couplings starting also from source and (or) from load; the generalized Chebycheff characteristic is assumed, with asymmetric transmission zeros, both pure imaginary or complex. The proposed method employs the coupling matrix of a generic prototype, obtained through well-established procedures; then the coupling matrix of the desired topology is determined with a procedure based on multiple matrix rotations (similarity transforms) and numerical optimization (the sequence and angles of the rotations are automatically evaluated in the procedure and their knowledge is not a priori required). The novel CAD tool has been tested with some coupling schemes recently proposed, which don´t require diagonal couplings for realizing asymmetric transmission zeros.