Compensation networks to improve performance of Non-Foster circuits

Non-Foster circuits (NFC) can be implemented with negative impedance converters (NIC) and/or Inverters (NII). This class of active circuits can violate Foster´s Reactance Theorem, which is applicable to passive lossless circuits, and produce a reactance that has a negative slope with frequency. NFC are usually implemented with active transistor-based circuits. Non-Foster impedance circuit components can be very attractive for microwave and antenna applications since they are not restricted by the gain-bandwidth product. However, there are many issues involved in the design of these circuits, including stability, losses, linearity, and achieving higher operating frequencies into the gigahertz range.