How can the Foster reactance theorem be applied?

Answer 1

circuit components are able to improve the performance of electrically small antennas could actually be realized. A survey of work in progress turned up a large body of theoretical activity directed at promising configurations of FET amplifiers. All investigators identified wide-band stability as the issue of major concern, and some suggested that monolithic fabrication would be needed to ensure it. Stability problems were clearly the reason for the absence of reports on circuit implementations. We found no evidence of even one working model, excepting for an operational-amplifier based circuit whose designers strongly recommend FET techniques over op-amp approaches.

Analyses confirmed that wide band stability was the major issue; circuits designed to provide low-loss reactances at frequencies near 100 mHz required the use of FET devices with positive gain at 25 gHz, and low loss reactive circuit designs were highly susceptible to high frequency oscillation. Substantive progress demanded more information than we could uncover, so we devoted most of our contract effort to achieving a stable non-Foster circuit.