Fundamentals of Terrestrial Millimeter-Wave and THz Remote Sensing

Abstract

Having long been the realm of molecular chemistry, astronomy, and plasma diagnostics, the upper millimeter-wave band (~100 to 300 GHz) and the THz region above it have recently become the subject of heightened activity in the engineering community because of exciting new technology (e.g., sub-picosecond optoelectronics) and promising new "terrestrial" applications (e.g., counter-terrorism and medical imaging). The most challenging of these applications are arguably those that demand remote sensing at a stand-off of roughly 10 m or more between the target and the sensor system. As in any other spectral region, remote sensing in the THz region brings up the complex issues of sensor modality and architecture, free-space electromagnetic effects and components, transmit and receive electronics, signal processing, and atmospheric propagation. Unlike other spectral regions, there is not much literature that addresses these issues from a conceptual or system-engineering viewpoint. So a key theme of this chapter is to review or derive the essential engineering concepts in a comprehensive fashion, starting with fundamental principles of electromagnetics, quantum mechanics, and signal processing, and building up to trade-off formulations using system-level metrics such as noiseequivalent power and receiver operating characteristics. A secondary theme is to elucidate aspects of the THz region and its incumbent technology that are unique, whether advantageous or disadvantageous, relative to other spectral regions. The end goal is to provide a useful tutorial for graduate students or practicing engineers considering the upper mm-wave or THz regions for system research or development.

Uncooled Detectors Challenges for THz/sub-THz Arrays Imaging

“…In this case, the characteristic angle θ away from the axis of radiation propagation falls down rapidly, e.g., for round lens according to scalar diffraction theory as θ B ≈2.44⋅(l/D max ) [21] forming the so-called Airy disk and determining low spatial resolution of THz/sub-THz systems. Here, β=2⋅θ B is the beam full width,…”

“…The throughput for a plane wave passing a circular aperture of the area A in a solid angle Ω in this case is governed by the antenna theorem A⋅Ω = l 2 [21,23]. The results of NEP calculations without and with account of the power fluctuations connected with radiation at all wavelengths are shown in Fig.…”

Detection of explosives by Terahertz synthetic aperture imaging—focusing and spectral classification

“…While atmosphere attenuation is predominately due to absorption of the THz radiation by water vapor, other attenuation effects such as dust, smoke, fog, and rain could effect the THz transmission. It is thought that rain would increase the effective attenuation due to increased water absorption, while typical micron-scale particles such as dust, pollens, and smoke, would not greatly scatter the THz radiation [6], since the THz wavelength is much longer than typical micron-scale particles.…”

“…(7)) and correlations of all detector pairs are performed using Eq. (6). The interferometric image is reconstructed using Eq.…”

Towards a 120 GHz SiGe LNA for millimeter-wave imaging

“…For imaging receivers, this ratio is most commonly denoted as Noise Equivalent Temperature Difference (NETD). As shown in [4], there are 3 important contributions to the output noise, namely: the quantum noise, the LNA contributed noise and the internal detector noise. Fig.…”