Balal Nezah, Pinhasi Gad A, Pinhasi Yosef
Faculty of Engineering, Ariel University, Ariel 40700, Israel.
Sensors (Basel). 2016 May 23;16(5):751. doi: 10.3390/s16050751.
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.
30吉赫兹以上的极高频（EHF）宽带适用于高分辨率定向雷达，解决了电磁频谱较低频段可用频段不足的问题。在该EHF频段使用超宽带信号很有意义，因为它覆盖了相对较大的频谱范围，且没有用户占用，从而在纵向和横向维度上都能实现更好的分辨率。鉴于毫米波频段的频率会受到高大气衰减和色散效应的影响，本文对精度和分辨率的下降情况进行了研究。由于固态毫米波和亚毫米波辐射源功率较低，连续波宽带调频方法成为遥感和探测的自然技术。毫米波雷达用作辅助传感器，在恶劣天气条件下探测雷达散射截面小的目标，此时光学相机和红外探测器无法看到小目标。本文给出了宽带“啁啾”调频连续波（FMCW）雷达信号在介质中传播的理论分析。结果表明，大气介质的频率相关（复数）折射率会导致反射信号相位失真，在纵向距离估计中引入显著误差，并且在某些频率下还可能降低分辨率。
