Backward-wave slab with electrically tunable index of refraction

In this paper we demonstrate the electrical tunability of a free-space-matched backward-wave slab, composed of three-dimensionally arranged and periodically loaded transmission lines. The host transmission-line network is composed of microstrip lines, whereas the loading is achieved with lumped capacitors and inductors. As the capacitors can be easily replaced by electrically tunable varactors, we study the tunability of the slab, i.e., the tunability of the effective refractive index, and the effect of this tuning on the impedance of the slab.