Wave attenuation through rain with different rainfall rates at millimeter wave (f=77 GHz) and Low-THz (f=300 GHz) frequencies is studied in this paper. Rain has pronounced impacts on electromagnetic wave propagation and one of the well-known effects is attenuation of the transmitted wave. Attenuation at both frequencies and hydrometeor properties (rainfall rate and drop size distribution) are measured simultaneously. The measured drop size distribution is fitted with gamma and Weibull distributions and is also compared to the frequently-used distribution Marshall and Palmer model (MP); Weibull is shown to be a better fit to the measured drop size distributions. Theoretical prediction of attenuation as a function of rainfall rate (up to about 20 mm/hr) is determined using Mie scattering theory, and the fitted gamma and Weibull, and MP distribution models; as well as using the ITU-R recommendation. The calculations are evaluated by comparing them to the experiment. The measured results at 77 GHz best agree with the ITU-R recommendation whereas at 300 GHz, the calculation based on Mie scattering and the Weibull distribution exhibits the best fit to the measured data. The measured data that exceed the theoretical prediction are analyzed and interpreted based on their corresponding observed drop size properties, for the first time.

Experimental measurement results of automotive radar signal attenuation during various intensities of snowfall at the current automotive radar frequency (77 GHz) and low‐terahertz (THz) (100–300 GHz) frequencies are presented and compared in this study. The attenuation is characterised by measuring the ratio of the received power from a reference target through snow precipitation of various intensities and through the same path with no precipitation. Statistical analysis of the attenuation is presented. Higher attenuation is measured at a higher frequency, and also attenuation increases as snowfall rate and liquid water content in snowflakes increases. This study is fundamentally important to investigate the effect of adverse weather conditions on low‐THz radar performance in comparison with the current automotive radars operating in the traditional mm‐wave band. In addition, the effects of low‐THz wave attenuation and scattering due to typical contaminants formed on the radome of automotive radars and reflection from common objects on the road are presented.

Mutual interference in automotive radar is expected to become a major issue owing to the rapid increase in the number of vehicles on the road equipped with radar. The phenomenology of interference in frequency modulated continuous wave radar is presented. Interference is empirically analysed at every signal processing stage in the victim radar by means of experimentally verified simulation modelling. Knowledge of how interference manifests in different domains provides a useful tool to develop algorithms for interference detection, mitigation and/or avoidance. The receiver's filter response is analysed to minimise the interference duration and increase the effectiveness of time‐domain mitigation techniques. A innovative method of interference parameter extraction by using spectrograms is also introduced.

In this paper, signal reduction due to the presence of water content formed on a radome has been studied at low-THz frequencies. The effect of obscurants on signal reduction has been characterized by measuring the ratio of reflected signals from a reference target through the radome, with contaminant and without contaminant. All the measurements have been compared to theoretical models, demonstrating a reasonable agreement. Water is the most common obscurant in outdoor applications and the main cause of performance deterioration in rainy, snowy, and foggy weather. This paper concentrates on the attenuation caused by different forms of distribution of water as a radome contaminant. Both a thin uniform layer of water and randomly distributed water droplets are studied at 150 and 300 GHz. The results show strong signal reduction due to the presence of uniform thickness of water and higher signal reduction with increasing frequency. However, the measured transmissivity through distributed water droplets, which occur in practice due to the surface tension of water, shows lower transmission loss at the shorter wavelength, due to transmission through the distribution of gaps between droplets.

This paper is concerned with modelling of the transmissivity of Low-Terahertz waves through automotive bumper and headlight cover material. This work is part of wider comprehensive studies on the potential for the use higher frequency bands for future automotive sensors. Theoretical models for transmissivity prediction are described, the methodology of experimentation is discussed and experimental results are presented. The theoretical models of reflection and transmission of different base materials which are covered by different layers of paint are based on Fresnel theory, and the phenomena caused by the half wavelength thickness of the medium is analyzed mathematically. The experimental verification of the models in this paper have been undertaken at 300 GHz and 670 GHz, using 77 GHz as a reference frequency.

With the rapid increase in the number of automotive radars on the road, interference becomes unavoidable. This paper analyses the effectiveness of dithering or randomization of FMCW modulation (applying random idle time jitter) on reducing interference. This analysis is undertaken for various interference scenarios and modelling-based results are compared. The results show that the efficiency of interference reduction by employing random idle time jitter strongly depend on the radar waveform parameters and the achievable reduction in interference level is in the range of 0 to 27 dB.