The terahertz frequency range, lying between electronics and optics (300 to 3000 gigahertz frequencies), can be disruptive force in sectors as diverse as from medical imaging, biological research, pharmaceutical monitoring, manufacturing and quality control, and semiconductor testing to communications, and security and defence.
Terahertz wave has strong penetrability, high safety, good directionality, high bandwidth characteristics, can be applied to national defense, military and other civilian areas, and in the military field, expand the terahertz called the fifth battle space. Terahertz can provide revolutionary capabilitites in defense, including Secure Terahertz communications, Chemical and Biological Agent detection and anti-stealth THz ultra wideband radar.
The high bandwidth of THZ radar can also improve target recognition accuracy for missile defence, as the United States Missile Defense Bureau says: “the key problem to missile defense is the successful recognition of the authentic warhead from the balloon decoys and other penetration devices. This is a very difficult issue as it has troubled the defender for 30 years.”
China has claimed to have developed terahertz radar that could unmask stealth fighters like F-35 . THz radar is also counter stealth technology, by emitting tens of thousands of species frequency as well as pico-second and nanosecond pulses at GW level, it can provide information on the composition of targets and thus target identity, not available in other remote sensing methods. Stealth technology in the form of shape stealth, stealth coatings, or plasma stealth are mostly effective only in a specific narrow band and are loose their stealth properties against terahertz.
In recent years, the terahertz radar technology has developed rapidly with breakthroughs in terahertz sources, signal detectors, and other devices, and many terahertz radar systems have been established, mainly for research on high-resolution imaging.
The United States is the first country of the concept of terahertz radar is proposed, and has conducted 0.2, 1.56 and 0.6 THz terahertz THz high resolution radar experiment, verified the feasibility of terahertz radar, laid the foundation for future development.
Demand for new surveillance capabilities for usage in airport screenings and battlefield security check-points has led to the development of terahertz imagers and sensors. There are several advantages of imaging at terahertz frequencies compared to microwave or infrared: the wavelengths in this regime are short enough to provide high resolution with modest apertures, yet long enough to penetrate clothing. Moreover, unlike in infrared, the terahertz frequencies are not affected by dust, fog, and rain.
Several groups around the world are working on the development of terahertz imagers for various applications. One option is to use passive imaging techniques, which were very successful at millimeter-wave frequencies, by scaling in frequencies to terahertz range. However, the background sky is much warmer at terahertz frequencies due to high atmospheric absorption. Since passive imagers detect small differences in temperatures from the radiating object against the sky background, at these frequencies passive imagers do not provide enough scene contrast for short integration times.
On the other hand, in an active imager, the object is illuminated with a terahertz source and the resulting reflected/scattered radiation is detected to make an image. However, the glint from the background clutter in an active terahertz imager makes it hard to provide high fidelity images without a fortunate alignment between the imaging system and the target.
China’s teraherz radar to unmask stealth fighters like F-35
China North Industries Group Corporation tested a device capable of generating terahertz radiation with unprecedented power at a military research facility in Chengdu, Sichuan province, last week, Science and Technology Daily reported on Monday.
The report said the new device could generate stable, continuous radiation at an average level up to 18 watts, and terahertz pulses with peak power close to one megawatt, on par with some military radars. A technical executive at a vendor in China for T-ray devices used in F-35 manufacturing said the reported power levels of the device were “more than a million times higher than the power of the T-ray device used to measure the thickness of coatings on the F-35”.
“The radar-absorbent coatings on the F-35 will look as thin and transparent as stockings if [the Chinese instrument] is as powerful as they claim,” the executive said. Terahertz radiation, or T-rays, can penetrate composite materials to reach underlying metallic layers and is widely used in industrial plants to spot product defects.
But the technology was still bulky and could not be fitted easily on a plane or satellite. “Field deployment may require power output at the kilowatt level. There is still a long way to go before we can monitor stealth fighters or bombers from space,” Qi said.
The new instrument was developed by the China Academy of Engineering Physics in Mianyang, the nation’s largest research institute for the development and production of nuclear weapons. According to the academy’s website, efforts were under way to increase the device’s power output and shrink its size for military applications.
China develops terahertz radar that can image objects behind walls
A report on the English.cri.cn website claims that China has completed research and development of a new radar system, which can penetrate walls and provide scanning imagery of objects inside houses.
According to the report, China Electronic Technology Corporation (CETC) has completed the prototype R&D of China’s first all-solid-state Terahertz imaging radar system. CETC has completed the broadband THz one-dimensional range profile and Inverse Synthetic Aperture Radar (ISAR) imaging experiment.
THz waves carry high frequencies, have short wave lengths, high temporal-frequency spectrum signal to noise ratio and low transmission loss in dense smoke-filled or dusty environments. THz waves can also go through walls and scan objects inside of houses, making it the perfect technology for battlefields and warzones.
In all future urban and anti-terrorist combat settings, ISAR can provide three-dimensional stereoscopic imaging of objects behind walls, detect hidden weapons, militants, tanks, artillery and other equipment behind a thick cloud of smoke.
ISAR is a radar technique that utilizes radar imaging to produce high-quality two dimensional images, which gives it an edge over standard radar techniques. ISAR are used prominently aboard maritime patrol aircraft to identify targets and its images are of a high enough quality to allow for distinguished recognition of various missiles, military aircraft, and civilian aircraft. CETC acquired the first ISAR image with resolution, image side lobes, electrical levels and other indexes that met the expected results.
Terahertz (THz) Radar: A Solution For Degraded Visibility Environments (DVE)
Mustang Technology, now a subsidiary of L3, Inc. has developed a THz imager, the Active Covert Terahertz Imager (ACTI), operating at 300 to 330 gigahertz (GHz). By operating at higher frequencies relative to MMWs, the ACTI can employ higher gain antennas at reasonable SWaP, thereby producing tighter beams and finer resolution. The higher frequencies also offer easy utilization of higher bandwidth components, allowing for finer range resolution. The increase in frequency and corresponding decrease in wavelength also decreases the minimum size required for an object to be detectable. In addition, while the frequency is high for a true radar, the frequency is sufficiently low for the radiation to penetrate obscurants, such as dust storms.
The experimentation using ACTI has proven that it can provide actionable quality images of objects of varying sizes and shapes. The ACTI has further demonstrated a high resolution for its SWaP, including the ability to detect rather small features of the scene that it is imaging, such as a thumbs up sign.
The ACTI demonstrated its ability to utilize or compensate for environmental conditions. At close range, the ACTI has sufficient output power to overcome minor detrimental conditions. For longer ranges, the frequency can be adjusted to decrease the attenuation in humid environments to provide higher quality images, or the frequency can be adjusted to increase attenuation if the signal needs to be hidden from detection.
These capabilities can be applied to other environmental factors as well. For example, dust in the air causes attenuation that is dependent on frequency. The attenuation can be measured, and the ACTI’s frequency can be adjusted to allow improved vision through dust storms and brownout or to utilize these same conditions to aid in masking the signal.
Application of terahertz technology in cooperative detection of space targets
Applications of terahertz technology on the ground may easily suffer from the strong absorption caused by the earth’s atmosphere, especially from water vapor and oxygen; however, the effect of the earth’s atmosphere can be ignored on the air-based or space-based platform, giving a good prospect for terahertz radar in the scene of space targets detection, write Zejian Lu and others from China Academy of Electronics and Information Technology, Beijing, China.
“Detection and tracking of space targets, such as ballistic missiles or space debris, are critical important in space defense system. Generally, tracking of the ballistic missiles can be divided into the boost phase, the ascent phase, the midcourse and the reentry phase. Currently, surveillance and recognition of space targets mainly rely on space-based infrared detectors or ground-based microwave radar equipment. The infrared system can detect the launching of missile at the boot phase and track the target along the ascent phase. However, when the missile enters into the midcourse, the infrared spectrum characteristics would gradually fade.”
“Applications of ground-based radar system in the flight of midcourse can be limited by the light of sight and the attenuation from the earth’s atmosphere. What’s worse, in the midcourse, the missile usually releases a number of interfering targets as baits, which poses a big challenge on reliably identification of the warhead from space debris baits and other target groups. Therefore, high performance radars are urgently needed in order to improve the detection probability and recognition ability in the middle period. Terahertz radar, which can provide more details about the targets because of broader bandwidth, makes a very good candidate for the space target detection.”
Although the terahertz radar can provide better range solution than the microwave radar, the disadvantages are also obvious: the narrow beam of terahertz wave is not suitable for searching the target in wide range. Since the flight distance of space targets usually covers thousands of kilometers and the beam width of terahertz wave is relatively narrow, terahertz radar has to cooperate with traditional microwave radars in order to search the targets in wide area. Zejian Lu and others in their paper, discuss the advantages of terahertz radar over the microwave radar and the application of terahertz radar in the scene of the ballistic missile target detection with cooperation of ground-based radar. details.
Mechanical vibration or rotation of a target, or structure on the target, can cause micro-Doppler effect in the radar echo wave. In detection and tracking of ballistic missile, the micro-Doppler effect is a special signature to discriminate the warhead from other nearby objects such as the booster, the attitude control module, and debris. However, the relative intensity of micro-Doppler effect from traditional microwave radars is usually very weak.
The authors state that the peak value of micro-Doppler effect at 300GHz is almost 30 times than that of 10GHz. This makes sense since the micro-Doppler effect largely depends operating frequency, which, on the other hand, proves that terahertz wave is very sensitive to the microvibration or rotation of the target.