The design of a novel microstrip ultra-wideband (UWB) bandpass filter with quad narrow notched-band functionality is presented. The filter consists of a multi-mode resonator (MMR) constituted from two modified stepped-impedance stubs that generate six resonate modes, five of which are within the UWB passband where the sixth mode is used to extend the upper stopband of the filter. Two transmission zeroes are located at the 3-dB edge of the passband to enhance the filter's selectivity with a skirt factor of 0.955. The MMR is fed through asymmetric interdigital coupled-lines feed to produce controllable notched-band. Additional notched-bands are generated with a parasitic coupled line. The notched-bands are centered exactly to eliminate interference at 5.2 GHz (wireless local area network (WLAN)), 5.8 GHz (WLAN), 6.8 GHz (radio-frequency identification), and 8 GHz (X-band). Good agreement is obtained between simulation and measurement results. The highly compact filter has dimensions of 8.0 × 9.83 mm2.
