Compact and Wideband Flat Negative Group Delay Circuit Investigation

This brief introduces a dual transmission structure with bandpass (BP) negative group delay (NGD) wideband flat behavior. The flat BP-NGD topology is analytically modelled from equivalent circuit composed of transmission line (TL) and stepped-impedance resonator connected by two resistors. As proof of concept (POC), by tuning TL characteristic impedances, the influences of circuit physical variables on NGD flatness are illustrated by parametric study. The flat BP-NGD POC circuit with a size of 48.2 mm $\times 90$ .8 mm ( $0.2\lambda _{g}\times 0.38\lambda _{g}$ ) is designed, fabricated, and measured. A very good agreement is confirmed by simulation and experimentation results of 680 MHz over 290 MHz (42.6%) NGD bandwidth (BW) around 0.7 GHz NGD center frequency. Also, the flat BP-NGD BW reaches 223 MHz (31.8%) over 569 MHz to 792 MHz with ±0.05 ns group-delay fluctuation with insertion and reflection losses better than 14 dB.

I. Introduction

Recently, the negative group delay (NGD) circuits have drawn increasing interest and some applications. A design method of feedforward amplifier for the bandwidth (BW) enhancement was presented [1]. The NGD function was also used to realize a bilateral gain-compensated circuit [2]. By cascading with transmission line (TL), the NGD function enabled to synthesize a frequency independent phase shifter (PS) [3]. The NGD circuits were implemented to realize non-Foster reactive elements [4], [5] which are used to design an arbitrary-angle squint-free beamforming in series-fed antenna arrays [6]. The extension of NGD equalization enables to develop resonance reduction technique [7]. Despite this progressive development of NGD applications, further efforts have to be conducted to overcome the limitations in terms of losses, operation frequency bandwidth (BW) and design complexity.