Fig. 1. (a) Scheme of refractive lens dispersion property with broadband incident wave frequency from f1 to f3. The relative relation of positive dispersion is explained by inverse focal length of F1<F2<F3 for f1>f2>f3. (b) Negative dispersion relation illustration in the proposed broadband metalens for incident wave frequency of f1>f2>f3; its focal length is positively proportional of F1>F2>F3.

Fig. 2. (a) The perspective views of double-layer identical symmetric split-ring resonator metasurfaces sandwiched by the filled dielectric in between. The thickness is marked by t. (b) The cross-section view and its detailed geometry parameters of the proposed complementary SRR metasurface arranged on the x−y plane.

Fig. 3. Transmission performances with different radii of meta-atom for (a) transmission magnitude and (b) phase change distribution along the frequency band, respectively.

Fig. 4. Normalized surface current distributions of unit cell at 11 GHz with different radii of (a) r=4.7  mm, (b) 4.1 mm, and (c) 3.5 mm, respectively. (d)–(f) The corresponding near-field distributions of the unit cell with different SRR radii.

Fig. 5. (a) The simulated transmissive efficiency of the broadband plasmonic metalens ranging from 9 to 12 GHz with a 0.5 GHz step. (b)–(e) are the normalized transmissive plane power patterns for 9 GHz, 10 GHz, 11 GHz, and 12 GHz incident waves, respectively.

Fig. 6. (a)–(d) The focused power patterns on the x–z plane for 9 GHz, 10 GHz, 11 GHz, and 12 GHz incident waves, respectively. Their corresponding focal lengths are marked by horizontal white line. (e)–(h) are the corresponding focused power patterns on the x–y plane for 9 GHz, 10 GHz, 11 GHz, and 12 GHz incident waves, respectively. (i) The detailed focal length distributions along the frequency range from 9 to 12 GHz both for simulations and measurements. The blue line is the fitting for good viewing for its dispersion property.

Fig. 7. (a) The diagram of the experimental setup to measure its broadband focusing including source, sample, and probe. (b) The detailed views of the fabricated broadband metalens on the x–y plane.

Fig. 8. The measured focused power patterns on the x−y plane and its corresponding focal spot size comparisons between simulations and measurements for 9 GHz, 10 GHz, 11 GHz, and 12 GHz incident waves, respectively.

Fig. 9. (a) The measured and simulated focusing efficiency distributions for broadband frequency ranging from 9 to 12 GHz with a 0.5 GHz step. (b) Corresponding spot size and numerical aperture comparisons between simulations and measurements for broadband frequency from 9 to 12 GHz.