Novel ultra-wideband bandpass filter with a notch band using stub-loaded resonator

In this paper, an ultra-wideband (UWB) bandpass filter with a notch band is presented. It consists of a stub-loaded resonator and two feeding lines. The proposed resonator, with a center-loaded short stub and two open stubs, is theoretical analyzed by even- and odd-mode analysis. The first four resonance frequencies can be conveniently adjusted and this enables the convenient design of UWB filters. Meanwhile, a notch-band is generated by the feeding lines. Two defected ground structures (DGSs) are utilized to obtain the required external quality factors. For demonstration, a UWB filter is implemented. Two transmission zeros are generated close to the passband, resulting in high skirt selectivity. Comparisons of the measured and simulated results are presented to verify the theoretical predications.