An improved bandpass filter using CMRC for ultra-wideband application

An improved ultra-wideband (UWB) microstrip filter with good out-of-band performance is designed and demonstrated. The filter is designed with two multiple-mode resonators (MMR), which are coupled together via a parallel-coupled line. A novel rectangular slit compact microstrip resonant cell (CMRC) is applied to improve the filter performance, which is formed by etching in the central section of the MMR. Combining the CMRC lowpass filter and slow wave characteristic, the improved filter has better out-of-band attenuation characteristic and sharpened rejection skirts outside the UWB passband, and its size is reduced. Good agreement between experimental and simulated results is achieved.