Metasurface-Enabled Superheterodyne Transmitter With Decoupled Harmonic-Free Signal Generation and Precoding

TL;DR

The paper tackles fundamental limitations of conventional metasurface transmitters by introducing a hardware-decoupled metasurface-enabled superheterodyne architecture (MSA) that separates baseband processing from RF beamforming. The core idea is a dual-stage up-conversion with a digital up-conversion (DUC) module for I/Q modulation and a magnitude-phase-decoupled (MPD) metasurface that handles RF mixing and passive precoding, enabling harmonic-free waveform generation and spatially isotropic, arbitrary-order modulations. An analytical framework (unit/array/overall signal models) supports symbol-level isotropy and diversity through passive precoding, while a two-path multi-stream design enables interference cancellation. A 5.8 GHz prototype demonstrates isotropic 256-QAM transmission, Doppler-spoofing waveform generation, and up to 20 Mbps data rate with low distortion, validating the architecture for integrated communication-sensing and security applications in next-generation networks.

Abstract

The evolution of programmable metasurfaces (PM) from passive beamforming to active information transmission marks a paradigm shift for next-generation wireless systems. However, this transition is hindered by fundamental limitations in conventional metasurface transmitter architectures, including restricted modulation orders, symbol-level spatial inconsistency, and significant harmonic interference. These issues stem from the intrinsic coupling between baseband signal processing and radio-frequency beamforming in monolithic designs reliant on simplistic switching mechanisms. This paper proposes a novel metasurface-enabled superheterodyne architecture (MSA) that fundamentally decouples these functionalities. The MSA introduces a dual-stage up-conversion process, comprising a digital up-conversion module for in-phase/quadrature modulation and baseband-to-intermediate frequency conversion, a precoder module for precoding, and a custom-designed magnitude-phase-decoupled metasurface that acts as a reconfigurable reflective mixer array. This decoupling of harmonic-free waveform generation from spatial precoding overcomes the critical drawbacks of existing approaches. Experimental results from a 5.8 GHz proof-of-concept prototype system validate the MSA's superior performance. The system generates spatially isotropic constellations for arbitrary-order QAM modulations, ensures consistent time-frequency signatures for applications like Doppler-spoofing, and achieves data rates up to 20 Mbps within a linear operating region that minimizes nonlinear distortion. The capability of employing spatial diversity and multi-stream interference cancellation has been demonstrated for the first time in a PM-based transmitter.

Figures (16)

• Figure 1: Conceptual illustration and Schematic diagram of MSA. (a) The conceptual illustration proposed MSA backscatter transmitter can independently generate and transmit arbitrary high-order complex signals while performing beamforming, ensuring spatial isotropy of the symbols. (b) The schematic diagram of the proposed MSA transmitter.
• Figure 2: The measured radiation patterns in anechoic chamber under different bias voltage conditions while employing distinct codebook. (a) With beamforming codebook. (b) With random codebook.
• Figure 3: (a) The illustration of arbitrary waveform generation setup utilizing single DUC module. (b) The experimental results of various fundamental waveforms generated by MSA.
• Figure 4: Screenshots of the handheld spectrum analyzer and the received signal spectrum diagrams by the USRP for a 256-QAM single-carrier signal generated by MSA with and without raised-cosine pulse shaping filter
• Figure 5: (a). illustration of two-stream MSA transmitter. (b). Schematic plot of the precoding patterns of two streams after joint phase optimization.