Non-Foster Circuit Design for Broadband Matching and Receiver Power Enhancement of Electrically Small Antennas

Abstract

In this paper, we describe the design, fabrication, and measurement results of a non-Foster circuit for improving the wideband matching and receiver power of small antennas. The antennas under consideration are a small monopole antenna and a small inverted F antenna. These antennas experience excessive C and L respectively; which makes it difficult to match their wideband impedance performance. To cancel out the excess C, a negative C non-Foster circuit is designed whereas a negative L non-Foster circuit is designed to cancel out the excess L. An important factor in the design of a non-Foster circuit is the stability, which is obtained by simultaneously considering the open circuit stability condition and transient response. According to the simulation, the optimized non-Foster circuit operates with negative C and L at 100～500 MHz, and it is fabricated with a PCB process and applied to the antennas. The reflection coefficients of the small monopole antenna and the inverted F antenna with non-Foster circuits are less than −10 dB at 150～400 MHz and 220～330 MHz, respectively. In addition, we measured the receiver power using antennas with non-Foster circuits. The small monopole antenna improved by 10.3 dB on average while the small inverted F antenna improved by 7.5 dB, at this frequency band.