Design Engineering of Tri-Band Ulu-Shape NGD Circuit

This paper investigates a negative group delay (NGD) design of Ulu geometrical shape circuit. The NGD basic topology is constituted by a coupled line coupler with two-port terminated by open-ended stub. The S-matrix model of the topology is presented. The design equations allowing to determine the NGD circuit parameters in function of the NGD function specifications, NGD center frequency, NGD values and insertion loss are presented. As proof of concept, a microstrip circuit is designed and fabricated. As expected, the tested results confirm that the circuit behaves as bandpass NGD function. The modeled, simulated and measured results are in good correlation. The POC operates with tri-band NGD behavior with center frequencies around 0.645, 1.285, and 1.87 GHz with NGD values of about −3.5, −2, and −1 ns, respectively.