Group delay flatness and bandwidth enhancement of wideband negative group delay microwave circuit

摘要

A wideband negative group delay (NGD) microwave circuit with group delayflatness and bandwidth enhancement is proposed. The proposed negativegroup delay circuit (NGDC) is composed of a resistor connected by two transmissionlines and a parallel branch consisted of a resistor linking with astepped-impedance transmission line and two open stubs. By tuning the characteristicimpedance of the transmission lines, the flat-NGD bandwidth isenhanced. For verification, an NGDC with a size of 0.24λ_g × 0.34λ_g is designed,fabricated, and measured. The measurement shows that an NGD time of−0.5 ns at the center frequency of 1.0 GHz is obtained with the NGD bandwidthof 68.6% over 0.668 to 1.365 GHz. Also, the flat-NGD bandwidth reaches46.3% or 0.776 to 1.243 GHz with ±8% group-delay fluctuation while the insertionloss is less than 18.8 dB and return loss is greater than 21 dB.