Analysis of Septuple-Band NGD Circuit Using an E-Shaped Defected Microstrip Structure and Two T-Shaped Open Stubs

In this article, a compact distributed septuple-band negative group delay circuit (NGDC) is proposed and analyzed. It is mainly composed of a high–low–high step-impedance microstrip line with an E-shaped groove and two T-shaped open stubs. This NGDC was first simulated and then fabricated by using a conventional printed circuit board (PCB) process with the substrate of RO4350. To investigate the operational mechanism of the NGDC, an equivalent circuit, consisting of nine transmission lines, four series–parallel
LC
resonant circuits, and two T-type series
LC
resonant circuits, has been developed and analyzed. It is found that the theoretical group delay characteristic calculated from the equivalent circuit agrees well both with the simulated data by using ADS as well as HFSS and with the experimental results. The measured seven NGD resonant frequencies occur at 2.03, 2.84, 8.14, 8.74, 13.0, 16.02, and 18.46 GHz, and the corresponding NGD values read −3.65, −3.04, −1.73, −3.23, −1.16, −1.20, and −1.47 ns. The dimensions of the presented passive NGDC are only 25 mm
$\times22$
mm without using any lumped components.