Dual-Band Ultra-Wideband Bandpass Filter

This paper presented a dual-band ultra-wideband (UWB) bandpass filter. The filter is based on a novel UWB bandpass filter structure, proposed by authors recently, which consists of a broadside-coupled microstrip-coplanar waveguide and exhibited its excellent ultra-wideband property. The dual-band operation was implemented by integrating a stub in the broadside-coupled conductors. The resonance of the stub introduces a narrow rejection band in the UWB passband which then results in a dual-band filtering. Such a dual-band UWB bandpass filter is strongly required in practical systems in order to avoid the interference between the UWB radio system and existing radio systems. The rejection band can be easily designed to some specific frequency band(s) by tuning the length of the stub. Simulation, design, fabrication and measurement of dual-band UWB bandpass filters have been carried out mainly following FCC's spectrum mask. The proposed filters demonstrated both excellent ultra-wide bandwidth (from 2.8 GHz to 10.2 GHz) mid rejection performance (> 50 dB at rejection frequencies), as well as good out-band performance better than the requirement of FCC's mask