Propagation properties of sub-millimeter waves in foggy conditions

Abstract

The propagation of millimeter (MMW) and submillimeter (terahertz, THz) waves in the atmosphere is subject to absorptive and dispersive effects. The resulting attenuation and temporal group delay increase in cloudy and hazy weather. In this work, the effects of water droplets suspended in the air on the propagation of electromagnetic radiation in submillimeter waves are studied theoretically and experimentally. A comparison is made between the link budget in THz frequencies and the expected attenuation for free space optics (FSO) links. Using the modified millimeter-wave propagation model, the frequency-dependent attenuation and group delay are expressed in terms of the complex refractivity of the atmospheric medium. The theory is employed to study the effect of fog and clouds on the accuracy of a frequency-modulated continuous-wave high-resolution radar operating at 330 GHz. In an experiment, the propagation of MMW was studied in a controlled fog chamber for various ranges of visibility, even below 1 m. The resulting attenuation and group delay of submillimeter waves were measured, while the properties of fog (optical visibility distance and water content) were monitored using FSO techniques. Apart from attenuation, the incremental group delay caused by fog also affected the accuracy of the radar. The experimental results were compared with those of an analytical model and were in good agreement even for very low visibility in very foggy conditions. Dispersive effects should be considered in the design of remote sensing radars operating in the MMW and THz regimes.

Atmospheric Effects on OFDM Wireless Links Operating in the Millimeter Wave Regime

“…The model was tested experimentally for various foggy conditions in a controlled environment demonstrating good agreement with measured results [9][10][11].…”

“…The signal phase shift and time delay effects are usually ignored, although they can be significant in extreme conditions [5,6]. Pinhasi et al presented in their previous studies on MMW atmospheric propagation, theoretical and experimental results of absorptive and dispersive propagation effects and their influence on the signal strength and phase dispersion [7][8][9][10][11]. It was found that apart from attenuation, the dispersive effects like group delay should be considered in the design of MMW and THz radar and wireless communication links.…”

Dielectric Characterization of Fog in the Terahertz Regime

“…where ε W and ε W are the real and imaginary parts of the dielectric permittivity of the suspended water (in distinction to the permittivity of the medium, ε (f ) as in (3)), and η (f ) = [2 + ε W (f )] /ε W (f ). The quantities in detail can be found in [2,3,6].…”

“…Models are used to study the effect of clouds and fog on the electromagnetic signal, in particular the attenuation and time delay [4][5][6]. Recently, experimental study in ultra-low visibility artificial fog in a confined space was performed using an artificial fog produced by a "smoke machine" [7].…”

Sensing with Polarized LIDAR in Degraded Visibility Conditions Due to Fog and Low Clouds

“…It was not feasible to conduct well-controlled tests in an open atmosphere, and because experimental work requires a stable and homogenous environment, we therefore measured and characterized LIDAR performances inside an aerosol chamber. Such facilities provide well-defined degraded atmospheric environments, with a wide range of droplet size distributions and visibility ranges [ 6 , 16 , 17 ]; for example, a previous study has successfully been conducted in our fog chamber [ 18 ]. This section also presents the experimental results adjoined with a comparison to the expected radiative transfer calculations results according to our proposed model.…”