Time‐Varying Mosaic Metasurface Architecture Enabling Programmable Multi‐Tone Pseudo‑Doppler Spectral Engineering

ABSTRACT The pseudo‐Doppler effect, an artificial frequency shift produced by time‐varying phase modulation of stationary structures, offers a promising route for electromagnetic (EM) wave manipulation. However, existing time‐modulated metasurfaces are predominantly spatially uniform and single‐channel, limiting pseudo‐Doppler generation to one frequency component per aperture and yielding symmetric harmonic spectra. Here, a time‐varying mosaic metasurface (TVMM) is proposed to realize a programmable multi‐tone pseudo‐Doppler effect. By partitioning the aperture into independently and continuously modulated spatial channels, each assigned a distinct linear phase‐ramp frequency, the TVMM enables simultaneous generation of multiple controllable pseudo‐Doppler components. An X‐band varactor‐loaded prototype is designed, fabricated, and experimentally characterized, exhibiting continuous reflection‐phase tunability approaching 300° over 9.1–10.9 GHz and robust response under oblique incidence. The multi‐tone spectral states are validated using direct spectral analysis and an inverse synthetic aperture radar (ISAR)‐based visualization protocol, in which pseudo‐Doppler frequencies are linearly mapped into spatial displacements. Complex aircraft‐scattering simulations and anechoic‐chamber experiments consistently verify single‐tone, uniform/nonuniform multi‐tone, and dense‐cluster pseudo‐Doppler spectral states. This mosaic time‐varying architecture establishes a general strategy for programmable EM spectral engineering, with potential applications in adaptive sensing, dynamic scattering control, and radar‐signature management.