Figure 4

Retrieved constitutive parameters of (a) the shorter and (b) longer dielectric tapers. From these figures, we could achieve negative indices of −6 and −2, respectively. Notice that, the retrieved parameters of the longer taper are not robust due to violation of small-particle approximation; yet, we can still obtain an insight of the taper, for example, the retrieved constitutive parameters of the taper suggest much higher reflectance at the frequencies around 19 and 21.5 GHz due to the opposite signs and distinguished values of permittivity and permeability, respectively, which is consistent with the simulation.