Non-Foster Self-oscillating Single-loop Antenna

A recently proposed concept of a self-oscillating non-Foster antenna array is modified for the case of a single loop. An ordinary loop antenna is split into two smaller half-loops of unequal size, mutually connected via a voltage-inversion negative impedance converter (VNIC). This system effectively operates as a series connection of an ordinary positive-inductance half-loop and a slightly smaller negative-inductance half-loop. Insertion of additional series capacitor introduces instability and the system behaves as broadly tunable self-oscillating antenna. The idea was tested by simulations of a model of small $(\lambda/10)$ loop integrated with a Linvill floating NIC and operating in 50 MHz RF band. Obtained results revealed efficient self-oscillations with a 1:2 tuning bandwidth and the suppression of harmonics better than 20 dB. This antenna might find application in future active metasurfaces.