Compact and Wideband Flat Negative Group Delay Circuit Investigation

This paper introduces a dual transmission structure with bandpass (BP) negative group delay (NGD) wideband flat behavior. The flat BP-NGD topology is analytically modelled from equivalent circuit composed of transmission line (TL) and stepped-impedance resonator connected by two resistors. As proof of concept (POC), by tuning TL characteristic impedances, the influences of circuit physical variables on NGD flatness are illustrated by parametric study. The flat BP-NGD POC circuit with a size of 48.2 mm×90.8 mm (0.2λg 0.38λg) is designed, fabricated, and measured. A very good agreement is confirmed by simulation and experimentation results of 680 MHz over 290 MHz (42.6%) NGD bandwidth (BW) around 0.7 GHz NGD center frequency. Also, the flat BP-NGD BW reaches 223 MHz (31.8%) over 569 MHz to 792 MHz with ±0.05 ns group-delay fluctuation with insertion and reflection losses better than 14 dB.