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This letter proposes a technique for designing flat lenses using field transformation (FT), as opposed to ray optics (RO) or transformation optics (TO). The lens design consists of 10 layers of graded index dielectric in the radial direction and 5 layers in the longitudinal direction. The central layer in the longitudinal direction primarily contributes to a bulk of the phase transformation, while the other four layers, above and below this middle layer on either side, act as matching layers that help reduce the reflections introduced by the impedance mismatch at the interfaces of the middle layer. The letter compares the performance of the lens, so designed, to those based on the RO and TO techniques. We show that the proposed lens design using FT is broadband, has a better than 1 dB higher gain compared to the RO- and TO-based designs over a wider frequency band, and that its scan capability is superior as well.

Flat-Lens Design Using Field Transformation and Its Comparison With Those Based on Transformation Optics and Ray Optics