A new equivalent circuit for admittance inverters and its application for deriving the network equations of ladder and non-ladder narrow band pass RF filters

Design of microwave band pass filters is traditionally based on LC ladder networks. Using the continued fraction expansion for ladder networks, we first explain how the circuit element called inverter arises. We then use a new circuit representation for admittance inverter to obtain the nodal equations for a low pass prototype ladder network. The coupling matrix for non-ladder networks can be easily obtained using the new circuit representation. Finally we point out that the equivalent circuit is useful for determination of coupling matrix elements.