On the Performance of the Zoned Fishnet Metamaterial Lens With Positive and Negative Reference Phase

In this letter, several converging fishnet metalenses are designed using both the zoning and reference phase techniques. They are engineered with a focal length of 1.5λ
₀
at the design frequency of 55 GHz (λ
₀
= 5.45 mm) at which the fishnet metamaterial has an effective refractive index of n
_lens
= ~0.68. Three metalenses are analyzed-with positive, negative, and without reference phase-in order to compare their performance. The focal properties are evaluated both numerically and experimentally, demonstrating a good agreement between them. The best performance is achieved for the zoned metalens with positive reference phase, with an experimental power enhancement at the focal length of 6.2 dB, better axial resolution (0.65λ
₀
), and reduced lateral lobes compared to the other designs.