On low-pass, high-pass, bandpass, and stop-band NGD RF passive circuits

Abstract

The negative group delay (NGD) function is one of the most intriguing phenomena that can be encountered in area of physics. Since the first experiments in the early 1980s, this abnormal phenomenon remains unfamiliar to conventional engineering. Based on physical, analytical, and experimental investigations, it was found that the NGD phenomenon corresponds to the advanced effect of a pulse signal at baseband frequency. This paper introduces the basic understanding of this extraordinary phenomenon. The RF and microwave-circuit theory dedicated to NGD passive circuits based on the S-parameter modeling is established. Two general types of lumped-element-based RF passive topologies, constituted of simple parallel and series mounted impedances, are explored. Low-pass, high-pass, bandpass, and stop-band elementary topologies of passive cells are treated and characterized. The low-pass NGD cells are first-order passive circuits consisting of RL-series mounted in parallel and RC-parallel networks mounted in series. The different steps of the circuit-parameter calculations as functions of the expected NGD level, insertion loss, and reflection coefficient are explained. To validate the theory, proofs-of-concept (POC) of NGD passive circuits were synthesized, designed, and simulated. As predicted in theory, the simulation results confirmed the feasibility of the low-pass, high-pass, bandpass, and stop-band NGD functions. The NGD circuits respected the basic criteria of RF and microwave circuits with reflection coefficients better than −12 dB. Despite the attenuation, the simulated low-pass NGD cell presented an NGD level of about −1 ns and a cutoff frequency equal to 46 MHz. The high-pass NGD cell presented a group-delay frequency response opposite to the low-pass NGD cell. The bandpass NGD cell exhibited an NGD level of about −2 ns at the center frequency of 0.5 GHz, and a bandwidth of about 92 MHz. Furthermore, the counterintuitive time-advance effect, induced by the NGD phenomenon, proven with various arbitrary-waveform baseband signals, was observed. A pulse advancement of about −1 ns was obtained with the considered low-pass passive cell.