A UWB bandpass filter using slotline ring resonator with a notched band

A quadruple-mode UWB bandpass filter is presented. The proposed filter is comprised of a slotline ring resonator, which forms an ultra-wide passband with four resonant modes. Two pairs of defected ground patches are added to improve the desired passband. To achieve a wide upper stopband, a pair of defected ground dumbbell units is introduced. Moreover, a notch band is added around 5.5GHz using a U-shaped slotline to avoid wireless local-area network (WLAN) signals. Finally, a filter is fabricated and tested. Simulated and measured results are in good agreement to exhibit that the proposed UWB BPF has a passband from 3.1GHz to 10.9GHz with a notched band in 5.5GHz, and a wide upper stopband with attenuation level of -12.8 dB up to over 30GHz.