Abstract
In recent years, there has been increased interest in the terahertz waveband for application to ultra-high-speed wireless communications and remote sensing systems. However, atmospheric propagation at these wavelengths has a significant effect on the operational stability of systems using the terahertz waveband, so elucidating the effects of rain on propagation is a topic of high interest. We demonstrate various methods for calculating attenuation due to rain and evaluate these methods through comparison with calculated and experimental values. We find that in the 90 - 225 GHz microwave band, values calculated according to Mie scattering theory using the Best and P-S sleet raindrop size distributions best agree with experimental values. At 313 and 355 GHz terahertz-waveband frequencies, values calculated according to Mie scattering theory using the Weibull distribution and a prediction model following ITU-R recommendations best agree with experimental values. We furthermore find that attenuation due to rain increases in proportion to frequency for microwave-band frequencies below approximately 50 GHz, but that there is a peak at around 100 GHz, above which the degree of attenuation remains steady or decreases. Rain-induced attenuation increases in proportion to the rainfall intensity.
Highlights
There is interest in ultra-high-speed wireless communications and remote sensing systems in the terahertz waveband [1] [2]
We applied Mie scattering theory with four types of raindrop size distribution as well as the predictive calculation method recommended by International Telecommunications Union Radiocommunication Sector (ITU-R) for rain attenuation to calculate theoretical values for rain attenuation
2) Raindrop size distribution used in calculations We used several raindrop size distributions for calculating rain attenuation by Mie scattering theory: the M-P, Best, P-S, and Weibull distributions
Summary
There is interest in ultra-high-speed wireless communications and remote sensing systems in the terahertz waveband [1] [2]. In terahertz bands above 300 GHz, in particular, it is easy to predict the effects of atmospheric gases and small-particle clouds, but rain attenuation due to raindrops with particle diameters that are relatively large relative to the wavelength have an especially strong effect and can significantly impact systems that employ atmospheric propagation in these bands. We verify the fitness of these methods by comparing between calculated and measured values for rain attenuation at rainfall intensities of up to 25 mm/hr at frequencies from 96 to 355 GHz. With the goal of applying these results to the wider wavebands used in the field of wireless communications, we evaluate changes in rain attenuation over wider ranges of frequency and rainfall intensity
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