A negative group delay tuner with stable insertion loss

A new method is proposed for tunable negative group delay (NGD) circuit in this paper. The tuner is based on a transmission line resonator loaded on a λ/4 stub, and a lumped resistor and two varactors are mounted on it. By properly biasing the two varactors, the susceptance slope parameter and unloaded Q-factor are significantly tuned while the resonant frequency and input admittance are almost unchanged. In the measured results of the tuner prototype designed at 1.0 GHz, when NGD is tuned from 0.2 to 1.9 ns, the stable insertion loss is only changed from 3.4 to 2.5 dB.