Stability of non-Foster circuits for broadband impedance matching of electrically small antennas

Non-Foster circuits are promising for numerous microwave and antenna applications because they are not limited by the gain-bandwidth product. However, the stability of these circuits is a key issue for their design. In this paper we introduce a three-step scheme to systematically stabilize a non-Foster circuit (NFC) topology that can be used in numerous applications. To demonstrate the stabilization procedure, a NFC to match electrically small antenna is examined. The circuit is stabilized using conventional controllers. Measurements have been performed and results are showing improvement in the antenna gain up to 14 dB.

I. Introduction

Non-Foster circuit (NFC) components such that negative capacitors, negative inductors, and some of their combination can been implemented using either negative impedance converters (NICs) or negative impedance inverters (NIIs). It is well-known that the so called non-Foster forms [1]–[2] employ active networks of negative inductors and capacitors to bypass the restrictions imposed by the Bode-Fano's gain-bandwidth theory.