New Configuration for Ultra-Wideband (UWB) Bandpass Filter with Notch

In this paper, a parallel-coupled line microstrip bandpass filter with an ultra-wideband (UWB) passband and a narrow notched band is presented. The proposed UWB microstrip bandpass filter is constructed of one section of three parallel-coupled line that is a quarter-wavelength long at the center frequency. The filter is designed to have a very wideband passband with a fractional bandwidth of %110 at a center frequency of 6.85 GHz. In order to enhance the filter selectivity, the middle line is extended by a length of quarter-wavelength and shorted to the ground at the end. Therefore, a single transmission zero is generated at each edge of the desired UWB passband which enhances the filter performance. Furthermore, an embedded open circuited stub is implemented to generate a narrow notched band inside the UWB passband for blocking unwanted existing radio signal. The filter design is verified by simulation and experiment where excellent agreement is obtained. The fabricated filter is very compact in size and has very low insertion loss.