Synthesis of Microwave Filters with Dispersive Coupling Using Isospectral Flow Method

In this paper, an iterative method is introduced to synthesize microwave filters with linearly frequency-dependent dispersive coupling elements. By employing a legitimate orthogonal transformation and scaling process, the dispersive coupling matrix can be represented by a frequency-independent coupling matrix with extra cross couplings for reflecting the dispersion. By applying the isospectral constrained optimization, the synthesized coupling matrix can be guaranteed to be in the desired coupling topology. The proposed method exhibits fast convergence and does not suffer much from the multiple local minimums as compared to other brute-force optimization methods.