The Design and Investigation of the Low-Pass Filter with High Selectivity and Ultra-Wide Stopband

Abstract

In this work, an ultra-wide stopband low-pass filter (LPF) is proposed using tapered step impedance resonators. The distributed equivalent of the proposed step impedance LPF is extracted, analyzed, and legitimated with simulated and fabricated results. The fabricated prototype has a 3 dB cut-off frequency (fc) of 2.92 GHz and an ultra-wide stop band extended up to 25.7 GHz (8.8fc) with an attenuation level of >20 dB. The transition bandwidth (from 3 to 20 dB) is 0.20 GHz and the roll-off factor is 112 dB/GHz (a reference to 30 dB). The passband insertion loss is 0.32 dB at 1.5 GHz and the normalized circuit size of the filter is 0.055.