{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,27]],"date-time":"2025-11-27T16:16:14Z","timestamp":1764260174142,"version":"build-2065373602"},"reference-count":21,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2021,6,25]],"date-time":"2021-06-25T00:00:00Z","timestamp":1624579200000},"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","JPMJCR1534","JST Industry-Academia Collaborative R&D"],"award-info":[{"award-number":["JP17942998","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 used a resonant-tunneling-diode (RTD) oscillator as the source of a terahertz-wave radar based on the principle of the swept-source optical coherence tomography (SS-OCT). Unlike similar reports in the terahertz range, we apply the stepwise frequency modulation to a subcarrier obtained by amplitude modulation instead of tuning the terahertz carrier frequency. Additionally, we replace the usual optical interference with electrical mixing and, by using a quadrature mixer, we can discriminate between negative and positive optical path differences, which doubles the measurement range without increasing the measurement time. To measure the distance to multiple targets simultaneously, the terahertz wave is modulated in amplitude at a series of frequencies; the signal returning from the target is detected and homodyne mixed with the original modulation signal. A series of voltages is obtained; by Fourier transformation the distance to each target is retrieved. Experimental results on one and two targets are shown.<\/jats:p>","DOI":"10.3390\/s21134367","type":"journal-article","created":{"date-parts":[[2021,6,25]],"date-time":"2021-06-25T11:07:40Z","timestamp":1624619260000},"page":"4367","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":14,"title":["Discrete Fourier Transform Radar in the Terahertz-Wave Range Based on a Resonant-Tunneling-Diode Oscillator"],"prefix":"10.3390","volume":"21","author":[{"given":"Hiroki","family":"Konno","sequence":"first","affiliation":[{"name":"Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2575-4138","authenticated-orcid":false,"given":"Adrian","family":"Dobroiu","sequence":"additional","affiliation":[{"name":"Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan"}]},{"given":"Safumi","family":"Suzuki","sequence":"additional","affiliation":[{"name":"Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan"}]},{"given":"Masahiro","family":"Asada","sequence":"additional","affiliation":[{"name":"Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan"}]},{"given":"Hiroshi","family":"Ito","sequence":"additional","affiliation":[{"name":"Center for Natural Sciences, Kitasato University, Kanagawa 252-0373, Japan"}]}],"member":"1968","published-online":{"date-parts":[[2021,6,25]]},"reference":[{"key":"ref_1","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_2","doi-asserted-by":"crossref","unstructured":"Caris, M., Stanko, S., Wahlen, A., Sommer, R., Wilcke, J., Pohl, N., Leuther, A., and Tessman, A. (2014, January 8\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_3","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_4","doi-asserted-by":"crossref","unstructured":"Dobroiu, A., Shirakawa, Y., Suzuki, S., Asada, M., and Ito, H. (2020). Subcarrier Frequency-Modulated Continuous-Wave Radar in the Terahertz Range Based on a Resonant-Tunneling-Diode Oscillator. 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