UWB BANDPASS FILTERS USING SHORT-CIRCUITED SHUNT STUBEMBEDDED MULTIPLE-MODE RESONATORS

摘要

An ultra-wideband (UWB) bandpass filter with good outof- band rejection is presented in this work. As a starting part of designing UWB filter, a shunt short-circuited stub is introduced at the center of a half-wavelength resonator and it can generate two transmission zeros near the lower and upper cutoff frequencies. With the use of evenand odd-mode approach, this initial multiple-mode resonator is characterized and designed to build up a bandpass filter with good UWB passband and highly attenuated out-of-band skirt. Next, a coupled-line section with cross-coupling property is formed in this short-circuited stub so as to widen the concerned upper-stopband due to excitation of two more transmission zeros. Finally, a UWB bandpass filter prototype is fabricated to experimentally validate the attractive in-band and out-of-band performances as predicted in theory.