NGD investigation on medusa-shape interconnect structure

This paper explains why the electromagnetic coupling between interconnect main ?-shape and straight I-lines of printed circuit board (PCB) can be source of bandpass (BP) negative group delay (NGD) behavior. The investigation on the NGD effect is established from an innovative microstrip circuit having medusa shape. The medusa topology analytical description is based on the equivalent circuit and S-matrix model. Then, the group delay (GD) response enabling to explain the existence of the BP NGD function is defined. As proofof- concept (POC), the influences of the medusa circuit constituting interconnect line (IL) lengths and interspaces on the BP NGD behavior are illustrated by parametric study. The NGD behavior is explained by the variations of the NGD value and NGD center frequency. More importantly, two NGD medusa prototypes were designed, fabricated, simulated and tested. The BP NGD responses of the two-medusa circuit POCs are validated by a very good agreement between the calculations, simulations and experimentations. The test results confirm that the medusa circuit POCs generate BP NGD responses with NGD level and center frequency of about 1.6 ns and 2.76 GHz respectively.