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

A wideband negative group delay (NGD) microwave circuit with group delay flatness and bandwidth enhancement is proposed. The proposed negative group delay circuit (NGDC) is composed of a resistor connected by two transmission lines and a parallel branch consisted of a resistor linking with a stepped‐impedance transmission line and two open stubs. By tuning the characteristic impedance of the transmission lines, the flat‐NGD bandwidth is enhanced. For verification, an NGDC with a size of 0.24 λ g  × 0.34 λ 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 bandwidth of 68.6% over 0.668 to 1.365 GHz. Also, the flat‐NGD bandwidth reaches 46.3% or 0.776 to 1.243 GHz with ±8% group‐delay fluctuation while the insertion loss is less than 18.8 dB and return loss is greater than 21 dB.