Tunable notch characteristics in microstrip ultra-wideband filters

Abstract

Tunable notch characteristics are introduced in microstrip ultra-wideband (UWB) filters. The UWB design concept is based on harmonic characteristics of a half-wavelength 50 ¿ transmission line (at the lowest resonance frequency), which is grounded on both sides. The notch performance is first created by additional capacitive-coupled open stubs. Subsequently, these stubs are replaced by a varactor and bypass capacitors which, in combination with the biasing transmission line, provide transmission zeros in the lower stopband. The basic filter layout exhibits flexibility and compactness. Three different commercial field solvers are used to verify the overall performances of the proposed filters and their tunable notch characteristics.