A Preconditioner for Synthesizing Dispersive Bandpass Filters Using Isospectral Flow Method

Synthesizing a bandpass filter with linearly frequency-dependent dispersive couplings using isospectral flow method suffers from plurality of local minimums. A legitimate preconditioner in conjunction with the isospectral flow method is proposed in this paper. The preconditioner can avoid the local minimum issue and lead to fast convergence of the isospectral flow method. A simple but generic strategy to find a preconditioner is proposed in this paper together with its clear physical insight. A forth-order waveguide filter with two strong dispersive couplings is synthesized and manufactured to demonstrate the effectiveness of this method.