Ultra-wideband bandpass filter on coplanar waveguide:: Proposal and implementation

In this paper, a novel ultra-wideband (UWB: 3.1 similar to 10.6 GHz) bandpass filter on coplanar waveguide (CPW) is presented, designed and implemented. At first, an open-ended nonuniform or multiple-mode resonator with three distinctive sections is constructed and investigated toward generating the first three resonant modes occurring around the lower-end, center, and higher-end of the UWB band. Then, a CPW interdigital capacitor element with enlarged ground-to-ground distance is characterized to excite two additional resonant poles below and above the UWB's center. As a result, a five-pole UWB bandpass filter with only one full-wavelength is constituted. Its performance is studied on the basis of a simple cascaded transmission-line network, whose parameters are extracted from our self-calibrated method of moments. After the optimized results are confirmed by full-wave simulation over the filter layout, a UWB filter sample is fabricated to demonstrate the actual UWB passband behavior with the 2.8-10.2 GHz bandwidth, where the insertion loss is less than 1.5 dB and variation in group delay is less than 0.33 ns. (C) 2007 Wiley Periodicals, Inc.