Design of Ultra-Wideband Bandpass (UWB) Filter with Enhanced Couplings by Using Lumped Capacitors

This paper presents a novel ultra-wideband bandpass (UWB) filter with enhanced input/output couplings by high quality lumped capacitors in place of traditional coupling methods. The filter consists of traditional stub-loaded dual-mode resonator and a pair of lumped capacitors, which symmetrically located at the input/output ports. Different from the technology of parallel-coupled microstrip lines in enhancing the capacitive couplings, this paper uses high quality ceramics trimmer capacitors to realize strong capacitive couplings at the input/output ports. A compact microstrip UWB filter designed by this method is simulated, fabricated and measured. The simulated and measured results are in good agreements, showing validity of the proposed method.