Equivalent Circuit Modeling of a Microstrip UWB Filter

The paper presents the equivalent circuit modeling of an ultra-wideband filter employing stepped impedance resonators on an interdigital coupled line. The stepped impedance half wavelength resonators control the lower cut off frequency and interdigital coupled line controls the upper cut off frequency. The equivalent lumped elements for half wavelength stubs and coupled lines are obtained from transmission line theory. A comparison of transmission characteristics of simulated planar structure and circuit model along with measured results are included. Generalized design equations are also developed for the filter using multivariable regression. The filter can be used in RF front ends of wireless communication systems.