Terahertz Imaging, Millimeter-Wave Radar

Army Space and Missile Defense Command Huntsville, Alabama, USA 

Keywords terahertz imaging subwavelength imaging millimeter-wave radar atmospheric effects terahertz sources terahertz detectors. 

In this chapter we begin by discussing these atmospheric limitations, since they permeate the whole technology of MMW, sub-MMW, and THz technology. We then discuss MMW and THz sources, detectors, and systems in separate sections. Finally, we present some results obtained using sensors operating in these bands. These results show the connection between this sensor technology and applications to security. 

Optically-pumped lasers (OPLs) offer very useful power levels at discrete frequencies well into the THz band. Most OPLs comprise some sort of gas cell, which is the active laser medium, that is pumped by a carbon dioxide laser. These devices are inherently inefficient because the 

A family of vacuum-tube MMW sources is based on the propagation of an electron beam through a so-called slow-wave or periodic structure. Radiation propagates on the slow-wave structure at the speed of the electron beam, allowing the beam and radiation field to interact. Devices in this category are the traveling-wave tube (TWT), the backward-wave oscillator (BWO) and the extended interaction oscillator (EIO) klystron. TWTs are characterized by wide bandwidths and intermediate power output. These devices operate well at frequencies up to 100 GHz. BWOs, so called because the radiation within the vacuum tube travels in a direction opposite to that of the electron beam, have very wide bandwidths and low output powers. These sources operate at frequencies up to 1.3 THz and are extensively used in THZ spectroscopic applications [10] [11] [12]. The EIO is a high-power, narrow band tube that has an output power of 1 kW at 95 GHz and about 100 W at 230 GHz. It is available in both oscillator and amplifier, CW and pulsed versions. This source has been extensively used in MMW radar applications with some success [13]. 

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