  Metasurfaces are ultrathin structures which are constituted by an array of
subwavelength scatterers with designable scattering responses. They have opened
up unprecedented exciting opportunities for extraordinary wave engineering
processes. On the other hand, frequency converters have drawn wide attention
due to their vital applications in telecommunication systems, health care
devices, radio astronomy, military radars and biological sensing systems. Here,
we show that a spurious-free and linear frequency converter metasurface can be
realized by leveraging unique properties of engineered transmissive temporal
supercells. Such a metasurface is formed by time-modulated supercells;
themselves are composed of temporal and static patch resonators and phase
shifters. This represents the first frequency converter metasurface possessing
large frequency conversion ratio with controllable frequency bands and
transmission magnitude. In contrast to conventional nonlinear mixers, the
proposed temporal frequency converter offers a linear response. In addition, by
taking advantage of the proposed surface-interconnector-phaser-surface (SIPS)
architecture, a spurious-free and linear frequency conversion is achievable,
where all undesired mixing products are strongly suppressed. The proposed
metasurface may be digitally controlled and programmed through a field
programmable gate array. This makes the spurious-free and linear frequency
converter metasurface a prominent solution for wireless and satellite
telecommunication systems, as well as invisibility cloaks and radars. This
study opens a way to realize more complicated and enhanced-efficiency
spectrum-changing metasurface.
