Atmospheric and Fog Effects on Ultra-Wide Band Radar Operating at Extremely High Frequencies

Abstract

The wide band at extremely high frequencies (EHF) above 30 GHz is applicable for high resolution directive radars, resolving the lack of free frequency bands within the lower part of the electromagnetic spectrum. Utilization of ultra-wideband signals in this EHF band is of interest, since it covers a relatively large spectrum, which is free of users, resulting in better resolution in both the longitudinal and transverse dimensions. Noting that frequencies in the millimeter band are subjected to high atmospheric attenuation and dispersion effects, a study of the degradation in the accuracy and resolution is presented. The fact that solid-state millimeter and sub-millimeter radiation sources are producing low power, the method of continuous-wave wideband frequency modulation becomes the natural technique for remote sensing and detection. Millimeter wave radars are used as complementary sensors for the detection of small radar cross-section objects under bad weather conditions, when small objects cannot be seen by optical cameras and infrared detectors. Theoretical analysis for the propagation of a wide “chirped” Frequency-Modulated Continuous-Wave (FMCW) radar signal in a dielectric medium is presented. It is shown that the frequency-dependent (complex) refractivity of the atmospheric medium causes distortions in the phase of the reflected signal, introducing noticeable errors in the longitudinal distance estimations, and at some frequencies may also degrade the resolution.

A grid-based indoor radiolocation technique based on spatially coherent path loss model

“…The ratio of the reflected power and refracted power level characterized with refractive index of the obstruction. For instance, metal surfaces behave as a (almost-) perfect reflective medium, while different atmospheric conditions creates significant attenuation for the radio waves [47]. The reflection mechanism can be seen on wave.…”

Dielectric Characterization of Fog in the Terahertz Regime

“…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].…”

“…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]. It was found that apart from the attenuation, the incremental group delay caused by the fog also played a role in the accuracy of the radar as was analyzed theoretically in [5].…”

Constant Envelope Modulation Techniques for Limited Power Millimeter Wave Links

“…Moreover, low power transmissions and reduced receiver sensitivities lead to further degradation in the link performances [11]. These phenomena also apply to radars and remote sensing systems operating in the millimeter and Terahertz frequencies [12].…”

“…Moreover, low power transmissions and reduced receiver sensitivities lead to further degradation in the link performances [11]. These phenomena also apply to radars and remote sensing systems operating in the millimeter and Terahertz frequencies [12].While the bands in the ultra-high frequency (UHF) spectrum are fully used, millimeter waves (the EHF spectrum) are relatively free of users, and broad bands of frequencies can be allocated for wireless communication applications. With the demand for more spectrums for the mobile communication infrastructure, additional bands within the millimeter waves regime are allocated for the future 5G of the cellular networks [13].…”