The PLA’s Pursuit of Terahertz: Facts and Fallacies

Introduction

Successful military operations depend upon freedom of action in the warfighting domains of air, space, ground, sea, and cyberspace. Today, effective command and control and situational awareness depend upon radio communications and sensors. Domination of the electromagnetic spectrum (EMS) enables joint force commanders to gain tactical, operational, and strategic advantage over a potential adversary.[1] EMS is broken down into frequency bands defined by certain physical characteristics, which include radio waves, microwaves, millimeter waves, infrared, visible light, ultraviolet radiation, x-rays, and gamma rays.

Over the past decade, defense establishments around the world have been assessing the feasibility of sensors, radar, and communications operating in the terahertz (THz) portion of the frequency spectrum. The U.S. Department of Defense’s efforts are particularly focused on technological breakthroughs in the microelectronics that would drive THz emitters (DARPA, undated).

The PLA has long believed that modern warfare hinges upon “the fifth domain of the EMS space (第五维电磁空间,di wu wei dianci kongjian),” and that THz is “unquestionably” a key technology to dominate the EMS and gain an edge in military competition. (PLA Daily, April 10). [2] EMS domination is seen as the key to “muting the adversary’s communications, blinding its radars, and paralyzing its networks” to win modern wars. (Civilian Staff WeChat, April 11). Military and civilian resources, both in terms of funding and human capital, have been invested in China’s pursuit of THz technologies as early as the 2005 Xiangshan Science Conference (香山科学会议, Xiangshan Kexue Huiyi), although the exact quality of China’s THz research and development (R&D) remains unclear  (XSSC, November 21; THz Applications WeChat, January 29). The majority of “outputs” of such R&D programs show promise, albeit with seemingly limited military value. Nevertheless, over the past fifteen years or so, China has created a state-led innovation ecosystem to sustain both basic and applied research of THz.

This article first provides a brief introduction to militarily relevant THz technologies and Chinese perspectives on THz. It then identifies key personnel and organizations that China has created to sustain its THz R&D, and finally describes progress made in military applications of THz technology, including communications, radars, and other fields. China-watchers are advised to monitor the advances that the PLA is making in this emerging area of competition in the years to come.

What is THz and How Does the PLA Think About It

THz is a portion of the EMS between the microwave and infrared bands, roughly between 0.1–10 THz, corresponding to wavelengths from 3mm down to 30μm. Thanks to its advantages of good penetrability and low photon energy, THz sensors could feasibly support intelligence, surveillance and reconnaissance (ISR) by detecting personnel behind enemy lines, identifying targets, and supporting terminally guided precision weapons.[3] PLA scholars acknowledge that THz technologies have extensive military applications, and have discussed THz’s possibilities in the following fields: detect and distinguish explosive; assist long-range detection and imaging detection; facilitate battlefield and satellite communications; enhance terminal precision-guided missiles; and facilitate counterterrorism security inspection (PLA Daily, December 22; PLA Daily, May 24). However, THz has been relatively underexplored compared to the rest of the EMS due to technical challenges associated with generating, detecting, and processing signals at these wavelengths.[4]

While acknowledging “gaps” in THz research, Dr. Zeng Yang (曾旸), from the College of Meteorology and Oceanography of the National Defense University of Technology (NUDT/国防科技大学), identified three key military applications: high-speed encrypted communications, high-resolution target detection, and battlefield situational awareness and imaging where THz applications could be useful (PLA Daily, April 10). This echoes an earlier discussion in which PLA analysts explicitly noted that THz technology will play a significant role in “military communications, battlefield reconnaissance, precision guidance, counter-stealth, and electronic countermeasures (ECM)” (PLA Daily, March 31).

Below is a table containing a selected list of key institutions supporting THz research and development in China.

Selected Key Institutions in China’s THz R&D

THz Military Applications and the PLA

Communications

Applied THz technology is often discussed in the context of building a future 6G or even 7G communication network. (Phys.org,

September 8; Fiercewireless, July 14; S&T Daily, May 7) While such discussions remain largely futuristic, Miao Wei (苗圩), former head of the Ministry of Industry and Information Technology (MIIT), said in 2018 that China “has already started looking into 6G development”. Li Shaoqian (李少谦), director of UESTC’s National Key Lab for Communications Counter-Countermeasure Technology (通信抗干扰技术国家级实验室, Tongxin Kang Ganrao Jishu Guojia ji Shiyanshi), has said that “THz communications should be the technology that 6G network is built on,” (Xinhua, March 26).[7] Indeed, Li’s lab was involved in at least one 863 Program project on integrated millimeter wave and THz technology and high-speed baseband signal processing technology research (毫米波和太赫兹总体技术与高速基带信号处理技术研究, Haomibo he Taihezi Zongti Jishu yu Gaosu Jidai Xinhao Chuli Jishu Yanjiu) (UESTC, undated).

Li’s comments echo PLA analysts’ writings about the advantages of THz communications, which include possibilities for high-capacity and highly secure battlefield communications. THz communications can sustain “data transmission that is a hundred times faster than 5G with a latency of microseconds.” (PLA Daily, April 10). Another important consideration is that the decreased angular divergence (that is, the increased directionality) of transmitted signals, owing to the reduced effects of diffraction on THz waves with shorter wavelengths, present a more challenging environment for eavesdroppers compared to the wide-area broadcasts used at lower frequencies.[8]

Although authoritative information is scarce, circumstantial references suggest that Chinese defense scholars have also examined THz technology applications in space. For instance, in 2017, a dedicated subsection on “Telemetry and Control (遥测遥控, Yaoce Yaokong)” of the Third Aerospace Electronic Strategy Forum (航天电子战略研究论坛, Hangtian Dianzi Zhanlve Luntan) organized by the CASC Ninth Academy’s S&T Committee included papers that discussed the use of THz technology in space-based ISR systems, as well as the design of wireless data communications in space.[9] Li Shaoqian’s lab likely also has been involved in exploring the use of THz technologies in space situational awareness, and inter-satellite communications (Renmin Net, October 10). On November 6, UESTC announced on its official website that a 70kg- satellite that bears the university’s name, “UESTC,” also known as Tianyan-05 (天雁05卫星), was successfully launched from China’s Taiyuan Satellite Launch Center (TSLC) in Kelan, Shanxi, to carry out multiple in-orbit testing including using THz communications equipment developed by UESTC (UESTC website, November 6; Sichuan Daily, November 7).

Radar

Theoretically, THz radar can emit tens of thousands of specific frequencies in picosecond and nanosecond pulses at the gigawatt (GW) level. In other words, photons generated by THz radar would have exceptionally short wavelengths of between 0.3 to 3 THz, which can penetrate non-metallic materials, in a similar fashion to x-rays (PLA Daily, April 10). THz radar can also improve multi-target discrimination and recognition by detecting several target sources. While it is generally believed that atmospheric attenuation in the THz band reduces the militarily effective range of the radar, there are nonetheless signals that China is researching the possible applications of THz radar.[10]

In 2011, CAEP’s Terahertz Research Center developed a 140 GHz Inverse SAR (ISAR) capable of real time imaging, and also carried out an imaging test combining THz radar and an unmanned aircraft (IEEE, September 2013). NORINCO’s 209^th Research Institute successfully used a 0.89 THz laser device to detect a “stealth” target in 2012.[11] The same year, China Aerospace Science and Industry Corporation (CASIC) Second Academy’s 23^rd Research Institute—previously involved in developing air defense-related radar and communication systems—reportedly developed China’s first THz synthetic aperture radar (SAR). A flight test was reportedly carried out and the first set of THz video was recorded via SAR. The institute was reported to make improvements in accordance with specific application needs in the future (Xinhua, December 18). Details about the flight test, such as the aircraft altitude, distance to target, picture resolution and size of the target, were not made public.

There is also evidence that Chinese military scholars have looked into the application of THz radar in spacecraft’s early warning and target detection for ballistic missiles, and that they believe it may have a critical role to play in offensive and defensive space systems.[12]

Security Detection

THz electromagnetic waves may be particularly useful for locating, detecting, and characterizing concealed threats, by spectroscopically detecting and identifying concealed materials through their characteristic transmission or reflectivity spectra in the range of 0.5–10 THz. China has made progress in THz’s applications for security detection as well. In February 2020, “all-in-one contactless integrated security check systems” were installed at several metro stations and long-distance bus stations in Shanghai. (Keji Ribao, February 14; Xinhua, February 14) The system was developed by Brainware Terahertz Information Technology Co. (博微太赫兹公司, Bowei Taihezi Gongsi), a subsidiary of CETC’s 38^th  Research Institute Xinhua, March 20).[13]

Conclusion

China and the PLA seek to control the THz portion of the frequency spectrum to gain a military edge. The Chinese civilian and defense academic community appears to be investing significant resources into both basic research of THz technologies and assessing the feasibility of THz technology for military communications, radars, and security detections. Numerous well-coordinated programs have been carried out simultaneously, and the scope of China’s state-sponsored investment in the development of THz technology is impressive. This is intricately linked to China’s perception that dominating the THz spectrum has a potentially decisive role to play in future conflicts. Although key transformational military applications of THz technologies will likely take years to be realized, China’s potential capability to deliver should not be underestimated.

The author thanks Major Carri “ELF” Salas, USAF and Lt Col Mark Stokes, USAF (Ret.) for carefully reading previous drafts of this article and providing valuable feedback.

Dr. Marcus Clay is an analyst with the U.S. Air Force’s China Aerospace Studies Institute (CASI). The views expressed are those of the author, and do not reflect the official policy or position of the U.S. Air Force, Department of Defense, or other agencies of the U.S. Government.

Notes

[1] See: Department of Defense, Electromagnetic Spectrum Superiority Strategy, October 2020.p.2. Accessed at: https://media.defense.gov/2020/Oct/29/2002525927/-1/-1/0/ELECTROMAGNETIC_SPECTRUM_SUPERIORITY_STRATEGY.PDF

[2] Specifically, the quote refers to the “electromagnetic spectrum/domain” in the PLA lexicon, after “land, sea, air and space,” as defined by the Chinese Defense White Paper.

[3] See: Huang Ruixuan, et al, “Design of a Pre-Bunched THz Free Electron Laser,” Particles, 2018,1, 267–278; accessed at: https://www.mdpi.com/2571-712X/1/1/21/htm. For an informative discussion about the military applications of THz, see: Damien Johnson, “Terahertz Technologies and Future Security Environments,” https://othjournal.com/2020/02/28/terahertz-technologies-and-future-security-environments/.

[4] DARPA’s THz Electronics Program reportedly pushed the radiofrequency technology into the trillions of cycles per second, or THz, range, in 2016. This was achieved through two key inventions, namely, the solid-state power amplifier (SSPA), and traveling wave tube amplifier (TWTA), a miniaturized device that relies on a tiny vacuum chamber in which electrons and radio signals interact. See: https://www.darpa.mil/program/thz-electronics, https://www.darpa.mil/news-events/2016-07-12.

[5] In July 2017, this was combined with two other CAS entities – Institute of Remote Sensing and Digital Earth, and Academy of Opto-electronics – to form the Aerospace Information Research Institute (AIR/空天信息创新研究院/“空天院”), https://www.aircas.cas.cn/index_73758.html.

[6] Nian Fushun (年夫顺) and his team in 2018 created the “world’s first integrated THz  test and measurement system” that covers 50 GHz-500 GHz. This has been applied to key national projects including “broad-band mobile communications,” Fengyun satellite, air and space-based communications platforms, radar imaging, and new security body scanners. https://www.qdast.org.cn/art/2017/12/15/art_1186_70976.html

[7] This is the author’s translation of the name of the lab to match the actual meaning of its Chinese name. The official English name for the lab, according to the website of the lab, is National Key Lab of Science and Technology on Communications. See: https://www.ncl.uestc.edu.cn/sysgk1/jgsz.htm.

[8] See: Jianjun Ma et al., “Security and eavesdropping in terahertz wireless links,” Nature, October 15, 2018, https://www.nature.com/articles/s41586-018-0609-x.

[9] See: Mu Jinchao, Sun Zhaoyang, Liu Hao, “THz real-time Sensing and Surveillance Detection Technology for Aerospace Applications (面向空天应用的太赫兹波实时态势感知与监视探测技术),” Compiled Papers of the 3^rd Space Electronic Strategy Forum, 2017. https://gb.oversea.cnki.net/KCMS/detail/detail.aspx?filename=DZZL201712002017&dbcode=CPFD&dbname=CPFD2018.

[10] See: https://www.monch.com/mpg/news/ew-c4i-channel/3881-chinesewhispers.html.

[11] See: Liang Meiyan, Deng Chao, Zhang Cunlin, “THz Radar Imaging Technology (太赫兹雷达成像技术),” Journal of Terahertz Science and Electronic Information Technology, Vol.11, No.2, April 2013. https://webcache.googleusercontent.com/search?q=cache:4dZhYYZ1hjYJ:www.iaeej.com/xxydzgc/ch/reader/download_pdf.aspx%3Ffile_no%3D20130207%26year_id%3D2013%26quarter_id%3D2%26falg%3D1+&cd=1&hl=en&ct=clnk&gl=uk&client=firefox-b-1-d

[12] Wang Xiaohai, “Application and Research Progress of THz Radar Technology in Space Applications (太赫兹雷达技术空间应用与研究进展),” Space Electronic Technology (空间电子技术), Vol. 1, 2015. pp.7-1

[13] Note that this institute is included in the U.S. Department of Commerce’s Entity List. See:https://www.federalregister.gov/documents/2018/08/01/2018-16474/addition-of-certain-entities-and-modification-of-entry-on-the-entity-list.