Design of a non-Foster impedance matching network for electrically small antennas

As an antenna becomes smaller, its input reactance increases to greater than its input resistance, resulting in a significant increase of it radiation quality factor and drastic decrease of its bandwidth. Therefore, there is a need for a matching network at the antenna terminals, which may be devised by negative impedance converters (NIC). In this paper, non-Foster impedance matching networks are designed by the Linvill impedance converters. An expression for the input impedance of NIC is obtained in terms of the hybrid-pi model of the transistor, which is used to compare the performance of several transistors. The input impedance of the NIC and its reflection coefficients are computed to show that the proposed circuits provide wideband performance and exhibit suitable stability conditions.