Wideband Chebyshev Bandpass Filter With Extended Upper Stopband Using Shunt Short-Ended Slotline Stubs

Abstract

A wideband bandpass filter (BPF) with in-band Chebyshev equal-ripple responses and extended upper stopband is proposed, which is composed of composite microstrip, slotline, and coplanar waveguide (CPW) structure. According to the odd-mode and even-mode equivalent circuits, there are four in-band transmission poles constructing the ultrabroad bandwidth can be directly deduced. In addition, there are two sets of lowpass filter (LPF) embedding in the CPW connecting line to greatly widen the upper stopband without increasing circuit size. In order not to affect original passband Chebyshev equal-ripple responses, the LPFs are synthesized using the low-pass prototype network. Furthermore, there are two finite frequency transmission zeros (TZs) which generated by cross-coupling effects located at lower and upper side of passband to effectively improve the shirt selectivity. Finally, for experimental verification, the proposed BPF prototype is manufactured and tested. Experimental results are consistent with predicted theoretical responses, which verify the validity and feasibility of proposed approach.