Non-Foster circuit embedded within electrically small antenna

Electrically small antennas (ESAs) have high quality factor and low radiation resistance. This implies that ESAs are narrow band and have poor realized gain. In this paper, we present an efficient way to improve the performance of an electrically small antenna by embedding a non-Foster circuit (NFC) inside the antenna structure instead of using matching network at the antenna feed. The antenna with embedded Non-Foster circuit shows remarkable improvement in antenna gain compared to the antenna without the NFC.

I. Introduction

Electrically small antennas (ESAs) are inefficient 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 suffer from many issues including losses, sensitivity, and most important, stability.