A Novel Coupling Matrix Synthesis Technique for Generalized Chebyshev Filters With Resonant Source–Load Connection

This paper reports a novel synthesis method for microwave bandpass filters with resonant source-load connection. In effect, a network realizing N+1 transmission zeros (where N is the number of reflection zeros) is obtained. The method is based on a prototype transversal coupling matrix (N+2, N+2) with source and load connected by a resonant circuit formed by a capacitor in parallel with a frequency-invariant susceptance. To complement the proposed synthesis technique, a method of reconfiguring the transversal coupling matrix as a more practical cross-coupled circuit is outlined. The technique is based on quickly converging gradient optimization with a cost function involving generalized eigenvalues of the transversal coupling matrix and its principal upper and lower submatrices. To illustrate and validate the proposed synthesis procedure, numerical tests have been carried out. Moreover, some aspects of implementation of the resonant connection between source and load were investigated, and experimental verification was performed. A third-order generalized Chebyshev filter with four transmission zeros was designed, fabricated, and tested. The measured results validate the proposed synthesis method.