Design of a non-Foster actively loaded SRR and application in metamaterial-inspired components

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.