Integrated Spherical Ray-Tracing and Spectral Guard-Band Analysis for K/Ka-Band Earth–Space Links

Modern K/Ka-band (18–40 GHz) satellite communication systems, particularly Low Earth Orbit (LEO) and non-geostationary (NGSO) constellations, require accurate elevation-dependent atmospheric propagation modeling to account for narrow beamwidths, stringent link budgets, and extended low-elevation passes where slant-path lengths increase substantially. This work presents an integrated propagation framework that combines ITU-R standardized models with spherical-coordinate ray tracing. The main contributions are the decomposition of total slant-path atmospheric attenuation into constituent physical mechanisms, the quantification of refraction-induced pointing bias (1ε) using Snell’s law in spherical geometry, and the determination of asymmetric frequency guardbands near the 22.235 GHz water-vapor absorption line. The framework is demonstrated using high vertical-resolution numerical integration of ITU-R standard atmospheric profiles for a representative mid-latitude coastal site. Results indicate a pointing bias of approximately 100 mdeg at ε = 10^◦ and a horizontal ray displacement of 8 km at ε = 5^◦. To maintain gaseous-absorption losses below 0.2 dB near 22.235 GHz, frequency offsets of 2.073 GHz (low-side) and 3.923 GHz (high-side) are required, recovering up to 1.8 GHz of usable spectrum compared to conventional symmetric guard-band allocations. By unifying geometric optics with physical-layer attenuation models, this framework provides a practical tool for spectral optimization and link budget analysis in next-generation NGSO systems.