Figure 2. The amplitudes of electric fields recorded by a sensor in the far-field region, in which the horizontal axis represents k_inρ normalized to k₀ (the free-space wavenumber at 10 GHz), while the vertical axis represents the frequency normalized to ω_p (the angular frequency at 10 GHz).

(a)The metasurface is placed between the target and the sensor. (b)The metasurface is replaced by the FR4-material lens. The region on the left of the blue dashed line corresponds to the propagating modes (PM), while the region on the right of the blue dashed line corresponds to the evanescent modes (EM). These figures demonstrate that as opposed to FR4-material lens, the metasurface is capable of converting the evanescent waves into propagating waves.