In this paper, we investigate on the use of non-Foster active elements to increase the operation bandwidth of a split-ring resonator (SRR) for possible application in metamaterial-inspired components. First, we design the circuit topology of the active load required to compensate the intrinsic reactance of the SRR and get a broadband response. Then, we show that the same procedure can be successfully applied to the case of a SRR-based monopole antenna and, in principle, to any metamaterial-inspired device employing SRRs. Finally, integrating an electromagnetic and a circuit simulator, we propose a possible realistic implementation of the active load, based on the employment of commercially available circuit elements. The obtained results (seven times improvement of the impedance bandwidth of the SRR-based monopole antenna) prove that non-Foster active loads can be successfully used to overcome the inherent narrow-band operation of SRR-based passive metamaterials and metamaterial-inspired components. The implementation issues related to circuit element dispersion, parasitic effects, and stability of the active circuit are fully considered in the proposed design.
Barbuto, M., Monti, A., Bilotti, F., Toscano, A. (2013). Design of a non-Foster actively loaded SRR and application in metamaterial-inspired components. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, 61(3), 1219-1227 [10.1109/TAP.2012.2228621].