The Design Method of the Active Negative Group Delay Circuits Based on a Microwave Amplifier and an RL-Series Network

This paper addresses a circuit theory regarding the negative group delay (NGD) principle. The methodology for characterizing this unfamiliar NGD function is described. The basic NGD topology under study is typically an active cell composed of an RF low-noise amplifier (LNA) and an RL-series passive network. It acts as a low-pass NGD topology. The family of the bandpass NGD cell is identified from the low-pass to the bandpass transform. The NGD circuit theory under study is essentially built with the S-parameter approach. The main characteristics of the proposed NGD topology and properties of the NGD level, cut-off frequencies or bandwidth, central frequency, and figure-of-merit are established. The NGD cell is synthesized using the LNA S-parameter model. A method for designing the low- and bandpass NGD cells as a function of the specified NGD values is presented. The NGD cell parameter calculations as functions of the expected NGD level, insertion loss, and reflection coefficient are introduced. Proof-of-concept NGDs are synthesized, designed, simulated, and fabricated to understand and validate the proposed NGD low-pass and bandpass functions. As expected, low-pass and bandpass NGD aspects are obtained. The low-pass NGD circuits present an NGD level of approximately -5 ns over the bandwidth fc = 25 MHz. Next, bandpass NGD circuits were synthesized to operate at approximately 0.5 GHz over the bandwidth Delta f = 50 MHz with an NGD level of approximately -10 ns. The measured results of the low-pass and bandpass NGD are in good agreement with the theoretical prediction obtained with simple lumped circuits. Different applications of the unfamiliar NGD function are described.