This is an interesting question and I hope some good discussions come out of it. Here's my understanding. Metasurfaces consist of subwavelength scatterers/unit cells; a unit cell size of lambda/10 is generally considered subwavelength. Therefore a unit cell spacing of half-wavelength disqualifies a surface/antenna from being called a metasurface. A transmitarray or reflectarray can be considered a metasurface if it meets the subwavelength condition and can achieve some characteristics that are not found in naturally occurring materials (e.g., generalized reflection/refraction).

Mohamed K. Emara Thanks for your reply.

A unit cell size of lambda/10 is generally considered subwavelength, while I noticed there are substantial literatures declaring their structure with unit size of about half wavelength a metasurface. I wonder whether the definition of metasurface becomes more broader.

By the way, do you have any idea what influence will be taken if the unit cell size varies? I am looking forward to reading some related papers.

"A transmitarray or reflectarray can be considered a metasurface if it meets the subwavelength condition and can achieve some characteristics that are not found in naturally occurring materials (e.g., generalized reflection/refraction)."

------------------Does that mean the traditional antenna array can not make a generalized reflection/refraction? According to my limited knowledge， beam steering can be somehow considered as another kind of generalized reflection/refraction.

Many thanks.

Jia Ran Many researchers, myself included, have referred to structures as metasurface even when the scatterers don't meet the stringent subwavelength requirement of