Response calculation of parallel-coupled resonator filters by use of synthesized wave digital network

This paper outlines the concept of combined wave digital/full-wave electromagnetic (EM) approach and its use to synthesize wave digital network of microstrip structure with parallel-coupled line sections. The synthesis procedure is based on equivalent circuit representation by using admittance (J-) inverters and half-wavelength resonators. J-inverter is implemented into wave digital network through its developed model in the form of two-port parallel adaptor. In proposed approach, the full-wave EM tool provides a generalized S-parameter description of coupled-line sections, used to generate their even- and odd-mode characteristic impedances. A parallel-coupled microstrip bandpass filter is designed, fabricated and measured as illustration of combined approach accuracy.