A compact stepped impedance 7th order microstrip filter

This paper presents a miniaturized step impedance low pass filter based on slow wave microstrip transmission lines. The miniaturized filter operating at 2.45 GHz is designed and implemented on a double-layer PCB substrate with metallic vias embedded in the lower substrate layer to provide the slow-wave effect. Based on this concept, a 41% size miniaturization is achieved as compared to conventional microstrip filter prototype. The measured filter performance present a return loss of better than 20 dB and an insertion loss of 0.25 dB in the pass band.