Rain-Attenuation Peak Frequency in the Terahertz Band

TL;DR

This paper studies how rain attenuation peak frequency shifts in the terahertz band, revealing a monotonic migration to lower frequencies with increasing rainfall rate, primarily driven by DSD scale.

Contribution

It combines theoretical and empirical models to analyze rain attenuation peak behavior, highlighting the dominant role of DSD scale over other factors.

Findings

Outdoor DSD models show peak frequency shifts lower with increased rainfall.

Peak frequency behavior follows an asymptotic power-law relation.

DSS scale, not drop concentration or temperature, governs peak migration.

Abstract

Rain introduces broadband and frequency-selective attenuation in wideband terahertz (THz) links, making it necessary to identify a compact spectral descriptor that captures how the dominant loss region evolves with rainfall conditions. This article investigates the peak-frequency behavior of rain attenuation by combining Mie-theory calculations with one separable laboratory Gaussian drop-size distribution (DSD) and seven outdoor empirical DSD models whose spectral shapes vary with rainfall rate. The analysis compares total-loss, absorption, and scattering components, examines the roles of characteristic DSD scale and representative drop-size statistics, and evaluates the effect of temperature on the peak location. The results show that, unlike the fixed-shape laboratory case where the peak frequency remains unchanged with rainfall rate, all outdoor empirical DSD models exhibit a monotonic migration of the attenuation peak toward lower frequencies as rainfall rate increases; this behavior is well described by an asymptotic power-law relation and is governed primarily by the rainfall-dependent DSD characteristic scale rather than by total drop concentration or fixed-temperature dielectric dispersion.