A simple procedure for designing wideband interdigital bandpass filters is described. The parameter h is derived in closed form so that the end-coupled lines sections have an electrical symmetry and interior sections have an approximately uniform distribution of characteristic admittances. Microwave filter structures realized as inhomogeneous microstrip-like transmission lines can be analyzed by the method for the homogeneous structures. Using the suggested procedure, a series of octave interdigital bandpass filters in the suspended substrate stripline technique is designed.
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