Distributed Amplifier-based Negative Group Delay Circuit and Its Application

Recent development of reconfigurable negative group delay (NGD) circuits based on distributed amplifiers (DAs) has been reviewed. It is shown that reconfigurable DA-based NGD circuits can be used as tunable non-Foster components, such as negative capacitor/inductor/T-networks. Such NGD circuits also have been used to reduce the squint effect of an antenna array, while steering the main beam direction. The squint-free bandwidth can be increased if one applies more stages in the DA-based design. Furthermore, in this paper, we demonstrate a new method to increase the squint-free bandwidth, which incorporates a tunable squint-free series type antenna array feed line with each element controlled by a two-stage DA-based NGD circuit. The enhanced bandwidth is realized by slightly shifting the center frequency of the NGD circuit at each antenna element, therby increasing the bandwidth of the NGD response. Such schematic has advantages of reduced tuning complexity, compact size, as well as good gain performance.