Influence of the Incidence Angle on the Focusing of Luneburg Lens Partially Covered with Graphene

We consider the plane wave focusing characteristics of a layered cylindrical Luneburg lens equipped with a conformal strip of graphene, in the H-polarization case. The angular width of the strip is arbitrary and its surface impedance is characterized with the aid of the quantum-physics Kubo formalism. We use mathematically accurate full-wave analytical regularization technique, which is based on the analytic inversion of the problem static part. This guarantees the convergence of the resulting numerical algorithm. We compute the focusing ability of microsize lens as a function of the frequency in wide range up to 30 THz. This analysis shows that a graphene strip, placed into the focal area of the Luneburg lens, enhances its focusing ability at a certain resonance frequency proportionally to the quality factor of the plasmon mode of the strip.