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.