  This paper presents an all-electronic approach for loss compensation in
metamaterials. This is achieved by embedding active-transistors based negative
differential resistance (NDR) circuits in each unit cell of the metamaterial
lattice. NDR circuits provide tunable loss compensation over a broad frequency
range limited only by the maximum operating frequency of transistors that is
reaching terahertz values in newer semiconductor processes. Design, simulation
and experimental results of metamaterials composed of split ring resonators
(SRR) with and without loss compensation circuits are presented.
