Wide-band Active Tunable Phase Shifter Using Improved Non-Foster circuit

In this paper, an active phase shifter that features a frequency independent transmission phase response over a wideband frequency ranging from 2 GHz to 4 GHz is designed based on Non-Foster elements. The main objective of this study is to get a phase in transmission slightly tunable around 180° while having low insertion loss and minimum return loss in the considered band. The active phase shifter (PS) topology requires negative capacitances that are obtained by using Negative Impedance Converter (NIC) circuits, which convert load impedance into a negative impedance. However, it is shown that the actual realization of NIC from cross-coupled pair (XCP) with FETs leads to undesired parasitic resistance that has a significant effect on the performance of the phase shifter. Therefore, the negative capacitance used in the PS are built up by cascading two different topologies of XCP circuit that compensates the residual resistance of each other. Moreover, one of the XCP topology is also internally modified to decrease furthermore this resistive part at the implementation level.