Abstract: The traditional model-conformation method for microwave filter diagnosis is not suitable for the exact synthesis, so a modified method for the general Chebyshev filter is proposed, i.e., a reasonable restriction has been imposed on the coefficients of the numerator polynomials in both transfer and reflection functions. Afterwards, the coupling matrix of the filter can be evaluated. Thus the tuning direction and magnitude of corresponding physical structures can be determined by comparison with the designed coupling matrix. Finally, two processes of diagnosing and tuning a four-order microstrip square open-loop filter and an eight-order waveguide filter are demonstrated with the help of the modified diagnosis method, and the response of the filter tuned is fine. The return loss and group delay specification are both achieved, and the consumption of the tuning time is also shortened by a half.

Key words: Cauchy method, coupling matrix, computer-aided tuning, filter diagnosis, rational mode