  The propagation of millimeter wave (MMW) and sub-terahertz (THz) signals
through plasma sheaths is a critical concern for maintaining communication with
hypersonic vehicles, yet the impact of complex plasma structures on these
high-frequency channels remains insufficiently understood. In this work, we aim
to characterize the transmission properties of MMW and sub-THz waves through
plasma sheaths with various density profiles and ripple structures, addressing
the gap in knowledge regarding the effects of plasma inhomogeneities on signal
propagation. We employ an approach combining Inductively Coupled Plasma (ICP)
data with transfer matrix methods (TMM) to model propagation through both flat
and rippled plasma layers. Our findings reveal that ripple structures in plasma
sheaths significantly affect channel performance, with periodic ripples
reducing cutoff frequency and introducing frequency-selective behavior, while
random ripples cause more unpredictable transmission characteristics. Our
results explore the impact of the arrangement of plasma density layers and the
parameters of ripple structures (period and amplitude) on channel transmission,
group velocity dispersion, and angular dependence of wave propagation. These
results provide crucial insights for the design and optimization of
communication systems for hypersonic vehicles, potentially enabling the
development of adaptive technologies capable of maintaining reliable
communication in complex plasma environments.
