Coupling Matrix Optimization Synthesis for Filters with Constant and Frequency-Variant Couplings

This paper presents a quickly converging optimization technique for synthesis of filters with constant and frequency-variant couplings (FVC). Unlike the works so far appeared in the literature, the proposed technique is not based on the direct optimization of scattering parameters with assigned topology, but it consists of two procedures. Firstly, an FVC coupling matrix with assigned topology is suitably transformed by means of scaling and rotations for obtaining the new coupling matrix with constant couplings. Then, the cost function is constructed as a least squares problem involving both the eigenvalues of the new coupling matrix with constant couplings and that of the transversal coupling matrix. The solution is found via the solvopt optimization method. Two numerical examples with different topologies and specifications are synthesized to show the validation of the method presented in this paper.