Ultra-wide stopband microstrip lowpass filter using lumped element equivalent circuit

In this paper, a microstrip filter using a modified stepped impedance resonator with high return loss, low insertion loss, and ultra-wide stopband is presented. The frequency response of the filter based on the layout and LC model is presented. The presented LPF consists of stepped impedance resonators to achieve a - 20 dB suppression level from 3.26 GHz up to 30 GHz. Using stepped impedance resonators results in multiple transmission zeros in the stopband. The proposed filter has an insertion loss of 0.1 dB, return loss of 26 dB, and cut-off frequency of 3 GHz. The transition band of the filter (with attenuation levels of - 3 dB and - 20 dB) is 0.26 GHz. The simulated results are close to the measured results, which shows the accuracy of our design.