Digital Non-Foster Impedance Design for Wideband Electrically Small Antennas Beyond the Chu Limit

Although initial results for the digital implementation of non-Foster impedances showed promise for increasing the bandwidth of electrically small antennas beyond the Chu limit, earlier approximate design methods were inadequate to fully describe the complexity of digital impedance circuits. Recently, the input impedance of such digital impedance circuits was discovered to be dependent on the external source impedance of the driving source. Furthermore, this dependence on the driving source impedance was shown to be extraordinarily complicated, even for a purely resistive driving source. Consequently, the digital non-Foster impedance match of an antenna is considerably more complicated, even with a lumped-element antenna model. In this paper, we present a method for designing a stable wideband digital non-Foster circuit to match the impedance of an electrically small dipole antenna. Simulation results confirm the theoretical predictions and efficacy of the design method in producing VSWR bandwidth beyond the Wheeler-Chu limit. An RLC model of a 10 MHz electrically small dipole with Q of 215 and passive-tuned bandwidth of 46.5 kHz is chosen to demonstrate the proposed method. For this antenna with Wheeler-Chu bandwidth limit of 442 kHz and size parameter ka = 0.42 rad, the proposed method results in achieving an impedance bandwidth of 2.3 MHz, or more than five times the Wheeler-Chu limit and 48 times the passive-tuned bandwidth. Lastly, the mid-band noise figure is 12.7 dB when the proposed design is combined with a receiver having 3 dB noise figure. © 2024, Electromagnetics Academy. All rights reserved.