Tapped-Line Coupled-Transmission-Lines with Applications to Combline and Interdigital Filters

Exact, general, open-wire-line equivalent circuits for tapped-line combline and interdigital arrays are derived using a combination of graph- transformations and induction. A significant feature of the equivalent circuits is that they do not require commensurate length sections. The equivalent circuit for tapped-line interdigital arrays is utilized to develop new design equations for tapped-line interdigital filters. Computed responses for five and twenty percent bandwidth designs show considerably improved VSWR's compared to designs based on previous procedures.