A study on negative group delay characteristics of multi-stage F-SIR structure driven by differential-mode

Negative group delay characteristics can be used to signal processing devices such as equalizer for compensation of the group delay of systems, and pulse compression circuit of radar systems. In this paper, to clarify negative group delay characteristics achieved by planar structure, we designed the Folded-Stepped Impedance Resonator (F-SIR) structure on printed circuit board (PCB), which has the symmetrical electric-wall at the guide center driven by differential-mode. Firstly, the group delay characteristics are discussed experimentally and numerical modeling. It was demonstrated that the negative group delay is occurred at anti-resonant frequencies. Secondly, effect of structural parameters (resonator length, distance of gap, number of stage) of F-SIR on negative group delay characteristics is discussed. Finally, multi-stage F-SIR with different resonant frequencies and shorted output line was proposed. The negative group delay of -1.74ns, 10MHz bandwidth and relatively low-insertion loss (-30dB) can be achieved by proposed 3-stage F-SIR structure.