Stable band-pass non-Foster circuits

Non-Foster circuits are commonly designed by making active circuits that act like negative capacitors or negative inductors which are then substituted into a desired circuit. The result is usually unstable. It was shown that for linear circuits composed of the ideal elements +R, ±L, ±C, almost all circuit topologies have natural frequencies in the right half plane (RHP) and are a priori unstable. Hence, the standard design approach is misguided. A suitable theory of non-Foster circuits cannot be based on ideal negative capacitors and negative inductors as admissible circuit elements. Two new circuit elements are introduced that provide non-Foster behavior only over a prescribed passband. These elements yield circuits that exhibit desired non-Foster behavior over positive, non-zero bandwidths and, more important, are shown to be provably stable within the framework of linear circuit theory.