{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,27]],"date-time":"2025-11-27T16:16:08Z","timestamp":1764260168736,"version":"build-2065373602"},"reference-count":18,"publisher":"MDPI AG","issue":"23","license":[{"start":{"date-parts":[[2020,11,30]],"date-time":"2020-11-30T00:00:00Z","timestamp":1606694400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100002241","name":"Japan Science and Technology Agency","doi-asserted-by":"publisher","award":["JP17942998","CREST JPMJCR1534","JST Industry-Academia Collaborative R&D"],"award-info":[{"award-number":["JP17942998","CREST JPMJCR1534","JST Industry-Academia Collaborative R&D"]}],"id":[{"id":"10.13039\/501100002241","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["16H06292"],"award-info":[{"award-number":["16H06292"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We introduce a new principle for distance measurement in the terahertz-wave range using a resonant-tunneling-diode (RTD) oscillator as a source at 511 GHz and relying on the frequency-modulated continuous-wave (FMCW) radar technique. Unlike the usual FMCW radar, where the sawtooth frequency modulation is applied to the carrier, we propose applying it to a subcarrier obtained by amplitude modulation; this is advantageous when the source cannot be controlled precisely in oscillation frequency, but can easily be modulated in amplitude, as is the case of the RTD oscillator. The detailed principle and a series of proof-of-concept experimental results are presented.<\/jats:p>","DOI":"10.3390\/s20236848","type":"journal-article","created":{"date-parts":[[2020,11,30]],"date-time":"2020-11-30T10:26:12Z","timestamp":1606731972000},"page":"6848","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":15,"title":["Subcarrier Frequency-Modulated Continuous-Wave Radar in the Terahertz Range Based on a Resonant-Tunneling-Diode Oscillator"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2575-4138","authenticated-orcid":false,"given":"Adrian","family":"Dobroiu","sequence":"first","affiliation":[{"name":"Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}]},{"given":"Yusuke","family":"Shirakawa","sequence":"additional","affiliation":[{"name":"Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}]},{"given":"Safumi","family":"Suzuki","sequence":"additional","affiliation":[{"name":"Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}]},{"given":"Masahiro","family":"Asada","sequence":"additional","affiliation":[{"name":"Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}]},{"given":"Hiroshi","family":"Ito","sequence":"additional","affiliation":[{"name":"Center for Natural Sciences, Kitasato University, Sagamihara, Kanagawa 252-0373, Japan"}]}],"member":"1968","published-online":{"date-parts":[[2020,11,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Song, H.-J., and Nagatsuma, T. (2015). Handbook of Terahertz Technologies: Devices and Applications, Pan Stanford Publishing.","DOI":"10.1201\/b18381"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Gr\u00fcner, G. (1998). Terahertz time-domain spectroscopy. Millimeter and Submillimeter Wave Spectroscopy of Solids, Springer.","DOI":"10.1007\/BFb0103417"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"169","DOI":"10.1109\/TTHZ.2011.2159556","article-title":"THz Imaging Radar for Standoff Personnel Screening","volume":"1","author":"Cooper","year":"2011","journal-title":"IEEE Trans. Terahertz Sci. Technol."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Caris, M., Stanko, S., Wahlen, A., Sommer, R., Wilcke, J., Pohl, N., Leuther, A., and Tessman, A. (2014, January 5\u201310). Very high resolution radar at 300 GHz. Proceedings of the 44th European Microwave Conference, Rome, Italy.","DOI":"10.1109\/EuMC.2014.6986807"},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Jaeschke, T., Bredendiek, C., and Pohl, N. (2013, January 2\u20137). A 240 GHz ultra-wideband FMCW radar system with on-chip antennas for high resolution radar imaging. Proceedings of the 2013 IEEE MTT-S International Microwave Symposium Digest, Seattle, WA, USA.","DOI":"10.1109\/MWSYM.2013.6697495"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"5095","DOI":"10.1364\/AO.49.005095","article-title":"Continuous-wave terahertz interferometry with multiwavelength phase unwrapping","volume":"49","author":"Wang","year":"2010","journal-title":"Appl. Opt."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Song, H.-J., and Nagatsuma, T. (2015). Resonant tunneling diodes for terahertz sources. Handbook of Terahertz Technologies: Devices and Applications, Pan Stanford Publishing.","DOI":"10.1201\/b18381"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Izumi, R., Suzuki, S., and Asada, M. (September, January 27). 1.98 THz resonant-tunneling-diode oscillator with reduced conduction loss by thick antenna electrode. Proceedings of the 2017 42nd International Conference on Infrared, Millimeter, Terahertz Waves (IRMMW-THz), Cancun, Mexico.","DOI":"10.1109\/IRMMW-THz.2017.8066877"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"151601","DOI":"10.1063\/1.5051007","article-title":"Large-scale array of resonant-tunneling-diode terahertz oscillators for high output power at 1 THz","volume":"125","author":"Kasagi","year":"2019","journal-title":"J. Appl. Phys."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Tanaka, H., Aoyama, Y., Izumi, R., Suzuki, S., and Asada, M. (2018, January 9\u201313). 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Terahertz Emitters, Receivers, and Applications X, International Society for Optics and Photonics.","DOI":"10.1117\/12.2526709"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Shirakawa, Y., Dobroiu, A., Suzuki, S., Asada, M., and Ito, H. (2019, January 1\u20136). Principle of a Subcarrier Frequency-modulated Continuous-wave Radar in the Terahertz Band Using a Resonant-tunneling-diode Oscillator. Proceedings of the 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Paris, France.","DOI":"10.1109\/IRMMW-THz.2019.8873752"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1080","DOI":"10.1049\/el.2018.5879","article-title":"Low-noise heterodyne detection of terahertz waves at room temperature using zero-biased Fermi-level managed barrier diode","volume":"54","author":"Ito","year":"2018","journal-title":"Electron. 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