A study on the lens effects on the terahertz signals propagating in reentry plasma sheaths at different speeds

The “communication blackout” caused by the plasma sheath of hypersonic vehicles is a major challenge in the aerospace field, where the sheath's “lens effect” leads to spatial distortion and energy dissipation of electromagnetic waves. This paper analyzes the transmission mechanism of terahertz waves in non-uniform flow fields by combining fluid dynamics with the fourth-order Runge–Kutta ray tracing algorithm. The results reveal the dynamic spatial evolution of the lens effect: the plasma sheath does not act as a single lens but rather exhibits region-dependent focusing and defocusing effects on the signal. The research clarifies the narrowing effect of flight velocity on the transmission window and identifies a window with a stable linear deflection response. Inspired by these observations, this paper proposes an active “adaptive combined gradient lens pre-angle compensation” scheme. This scheme introduces a dynamically tunable lens array, transforming the deteriorating flow field into part of the antenna system, allowing the “antenna–lens array–sheath” to be reconfigured into a lens antenna structure. This architecture enables pre-deflection of the signal, achieving parallel collimation of the outgoing signal. This approach achieves directional energy concentration of terahertz signals, reduces geometric attenuation, and proposes a strategy for high-speed and reliable relay communication in aerodynamic environments.