Compact stepped‐impedance lowpass filter with a slot‐back microstrip line

A high-performance stepped-impedance low-pass filter is proposed by using a microstrip line with a longitudinal slot in the ground plane (slot-back microstrip line). The design process is simple and yet effec- tive in improving the performance of the filter structure. Expressions are proposed to obtain the characteristic impedance of a slot-back microstrip line. Because of the high characteristic impedance and slow-wave effect of a slot-back microstrip line, the proposed filter shows a sharper cutoff and a wider stopband with higher attenuation within a smaller circuit area when compared with a conventional stepped-impedance low-pass filter. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1058 -1061, 2008;