Theory of Coupled Line Coupler-Based Negative Group Delay Microwave Circuit

A fundamental theory of coupled line coupler-based negative group delay (NGD) topology is established in this paper. The microwave circuit under study consists of the isolated- and coupled-accesses connected in a feedback loop through a lossy interconnect line. The NGD topology is built with fully distributed elements. The S-parameter model is formulated in order to derive the NGD optimal values, cutoff frequencies, and bandwidth. Thus, the NGD existence condition as a function of the coupling coefficient and the feedback interconnection attenuation is demonstrated and examined. Hence, the fundamental characteristics of the coupler-based NGD topology are described. In order to verify the feasibility of the theory, NGD prototypes were designed, fabricated, and measured. The implemented one-and two-stage microstrip circuits have NGDs of about -2.3 and -4 ns, respectively, at 1.26 GHz. The reflection coefficients are better than 10 dB and the insertion losses are, respectively, about 2.4 and 4.3 dB. The developed NGD topology, fully constructed with distributed elements without any lumped components, is particularly beneficial in terms of design simplicity. The proposed NGD circuit might find potential application in microwave signal delay correction.