Analysis and optimization of ultra-wideband bandpass filters on coplanar waveguide

This paper presents a novel class of ultra-wideband (UWB: 3.1~10.6 GHz) bandpass filters formed on coplanar waveguide. Open-/short-circuited multiple-mode resonators (MMR) are constructed with three distinctive sections and their resonant performances are studied towards allocating the first three resonant modes occurring around the lower-end, center and higher-end of the concerned UWB passband. In parallel, the two parallel-coupled lines with short-/open-circuited ends are characterized to excite two coupling peaks below and above the UWB's center (6.85 GHz). These two UWB filters are then analyzed using a simple cascaded transmission-line network and optimized using the Momentum software, theoretically demonstrating a five-pole UWB passband performance. Predicted results are confirmed in experiment and they show the actual 2.8- to 10.2-GHz UWB passband with the insertion loss <1.5 dB and variation in group delay <0.33 ns.