Loop-type electrically small antenna loaded with non-foster circuit

Although electrically small antennas (ESAs) have gotten an increase attention because of their wide applications in wireless communications, they are not efficient radiators because of their high quality factor (Q). Therefore, matching networks are required to improve their input impedance and radiation characteristics. However, due to gain-bandwidth restrictions, wideband matching cannot be achieved using passive networks. Non-Foster circuits (NFCs), such as negative capacitors, negative inductors, or some of their combinations, are attractive because they can be used in matching ESAs since they violate the gain-bandwidth limitation. Although NFCs are very attractive for microwave and antenna applications, they are active nonlinear circuits and therefore suffer from many issues including losses, difficulty in achieving good performance in the gigahertz frequency range, and most important, stability.