Transmission‐type negative group delay networks using coupled line doublet structure

This study presents a novel approach to the design and implementation of transmission‐type negative group delay (NGD) networks based on a coupled line doublet structure. To improve the reflection coefficients, a quarter‐wavelength transmission line is connected between the input and through ports of a coupled line section. For the doublet structure, two coupled line sections are arranged in a symmetrical manner by connecting them back‐to‐back with the help of the quarter‐ wavelength through line. For the experimental demonstration, two planar NGD networks (unmatched and matched doublet NGD networks) are designed, simulated and measured at a centre frequency of 2.14 GHz. From the measurement, a group delay (GD) of −5.66 ns and signal attenuation (SA) of 18.78 dB were obtained in the case of an unmatched NGD network. Similarly, for the matched NGD case, a GD of −6.33 ns, SA of 20.69 dB and input/output return losses >29 dB were obtained at the centre frequency.