Bandpass NGD Analysis of PCB Folded Li-Shape Trace

An unfamiliar negative group delay (NGD) analysis of folded printed circuit board (PCB) trace constituted by coupled line (CL) is investigated. The PCB trace parameters are identified by defining the modified CL named li-topology, which behaves as a bandpass (BP) NGD function. The main specifications of the BP-NGD function from the S-parameter model are described. The theoretical equations of li-topology parameters are formulated. Then, proofs-of-concept (POC) of folded li-trace with different angles between “l” and “i” transmission line (TL) designed in microstrip technology are presented. Good agreement simulation and measurement results of folded li-POC enable conjecture on the variation of NGD value, NGD center frequency, reflection, and transmission coefficients are discussed. A new behavior characterized by the NGD effect is revealed in the function of the geometrical angle between the “l” and “i” TLs constituting the PCB trace POCs.