Active tunable inductor using non-foster element

A novel approach to design of active tunable inductors is presented. The proposed tunable inductor is a connection of a passive inductor and an active circuit to realize a non-Foster element with variable negative inductance. Tunability is achieved by means of a variable capacitor used as the load of negative impedance converter. The concept verification was done for a tunable inductor circuit implemented on lumped elements in printed circuit board technology. Simulated as well as measured data proved the principle and demonstrated the ability to design small-size stable tunable inductors with wide tuning range and high quality factor.