Power-Handling Capabilities of Non-Foster Impedance-Matching Networks: Using Gridded Vacuum Tubes and Power Transistors

Non-Foster networks can be used to match the impedances of highly reactive loads to resistive loads over very broad bandwidths. They are used to design ultrawideband, electrically small antennas (ESAs) in which negative impedance converters (NICs) eliminate the very large input reactances of the antennas over wide bandwidths. NICs, however, use active elements that put upper bounds on their power-handling capability. We examine the limitations of the power-handling capabilities of non-Foster impedance-matching networks that use gridded vacuum tubes and compare them with those of the networks using power transistors. Specifically, we examine the requirements for transmitting 5 W of power from a 5.18-m monopole antenna and from an ideal, minimum-quality factor (Q) dipole antenna over the 3-30-MHz band. We describe the situations in which tubes outperform transistors and examine the efficiency levels that can be realistically achieved. The results provide important guidelines for determining the suitability, or lack thereof, of using non-Foster matching networks for ultrawideband transmitting ESAs. Moreover, we offer a method for selecting an active device and the antenna type that can deliver the required power level given the bandwidth and efficiency constraints.