Exact Design for Commensurate Line Low-pass Filter Using Coupled Stubs

Exact design method for a lowpass filter based on commensurate line elements is proposed, which supports equiripple in-band response and adjustable out-of-band suppression. The filter consists of a section of coupled line, three sections of connecting line, and two open-circuited stubs, all of which have the identical electrical length. The circuit can generate lowpass response with seventh-order filtering function. Each impedance value can be calculated precisely according to given specifications by using proposed design procedure.