Spacetime crystals engineering sideband-free radiation for high-rate transmission

Spacetime crystals are a class of engineered materials characterized by simultaneous periodic modulation in both spatial and temporal dimensions, enabling concurrent control of frequency and wavevector in harmonic radiation. Existing studies have focused mainly on single-frequency excitation, leaving the manipulation of passband signals within spacetime crystals largely unexplored. Here, we establish a transfer matrix to calculate the band structure of a spacetime crystal antenna and systematically investigate its capability to manage passband signals. We also propose a modulation scheme that achieves approximately sideband-free radiation of loaded signals, thereby furnishing reliable channels for communication systems. Experiments validate that the method emits passband signals without producing undesirable sidebands. Furthermore, we demonstrate successful transmission of signals with a 20 MHz bandwidth under high modulation frequencies, confirming feasibility under practical operating conditions. Our method paves the way for implementing bandwidth-oriented frequency-division techniques in future 6G communication systems and holds strong potential for practical deployment. Engineered spacetime crystals can shape a wave’s frequency and direction simultaneously. This work introduces a spacetime crystal antenna that radiates information-bearing passband signals while suppressing sidebands under high-rate modulation, enabling clear 20-MHz video transmission.