Metasurface-Enabled Superheterodyne Transmitter for Arbitrary-Order Modulation with Spatially Isotropic Symbol Distribution

Electromagnetically programmable information metasurfaces, as dynamically controllable 2D metamaterials, hold significant promise as low-profile hardware enabling passive wave control and signal generation for backscatter systems. However, current metasurface-based transmitters architecture fundamentally suffer from hardware non-modularization, forcing all transmitter functions onto nonlinear switch-based unit cells, which introduces symbol mapping inconsistency via phase coupling. Moreover, both temporal coding (limited by unit cell diodes) and space-time coding (impaired by symbol anisotropy) exhibit irreducible harmonic interference and entangled control of amplitude, phase, and beam direction. This paper proposes a metasurface-enabled superheterodyne architecture (MSA), comprising a digital up-conversion (DUC) module performing baseband-to-intermediate frequency (IF) conversion, filtering, and digital-to-analog conversion (DAC), and a reconfigurable metasurface featuring programmable unit cells that independently control both the magnitude and phase of the reflection coefficient. Systematically, the architecture leverages a dual-stage up-conversion process, typical of superheterodyne systems, but uniquely employs the metasurface for the final RF conversion stage. Building upon this framework, a proof-of-concept prototype featuring a 5.8 GHz magnitude-phase decoupled (MPD) metasurface (<15 degree phase deviation per state) and a DAC-based DUC module is presented. Extensive validation confirms the metasurface's capability for distortion-free mixing with arbitrary IF signals while maintaining consistent radiation patterns. The prototype successfully implements diverse QAM modulation schemes (4QAM to 256QAM) in mono-static and bi-static configurations, demonstrating symbol isotropy for spatially separated receivers and achieving a data rate of approximately 20 Mbps (at 5 MHz IF)...