An ultra-wideband bandpass filter with high return loss and controllable notch band

In this paper, an ultra-wideband (UWB) bandpass filter (BPF) with a high return loss and a notch band is proposed. A high return loss and a notch band can be obtained by controlling characteristics impedance of coupled line and length of the shut stubs, respectively. For the validation, the UWB BPF was designed and measured to obtain 20 dB return loss with a notch band at 5.5 GHz. The results presented indicated that the 20 dB return loss is extended from 2.93 to 5.1 GHz and 6.14 to 11 GHz. The maximum return loss and attenuation at the notch band of 5.6 GHz are 2.3 dB and 16 dB, respectively. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2922-2926, 2016