{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,1]],"date-time":"2026-04-01T18:04:50Z","timestamp":1775066690926,"version":"3.50.1"},"reference-count":20,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2020,10,21]],"date-time":"2020-10-21T00:00:00Z","timestamp":1603238400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Detecting and identifying drones is of great interest due to the proliferation of highly manoeuverable drones with on-board sensors of increasing sensing capabilities. In this paper, we investigate the use of radars for tackling this problem. In particular, we focus on the problem of detecting rotary drones and distinguishing between single-propeller and multi-propeller drones using a micro-Doppler analysis. Two different radars were used, an ultra wideband (UWB) continuous wave (CW) C-band radar and an automotive frequency modulated continuous wave (FMCW) W-band radar, to collect micro-Doppler signatures of the drones. By taking a closer look at HElicopter Rotor Modulation (HERM) lines, the spool and chopping lines are identified for the first time in the context of drones to determine the number of propeller blades. Furthermore, a new multi-frequency analysis method using HERM lines is developed, which allows the detection of propeller rotation rates (spool and chopping frequencies) of single and multi-propeller drones. Therefore, the presented method is a promising technique to aid in the classification of drones.<\/jats:p>","DOI":"10.3390\/s20205940","type":"journal-article","created":{"date-parts":[[2020,10,22]],"date-time":"2020-10-22T20:51:00Z","timestamp":1603399860000},"page":"5940","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":33,"title":["An Investigation of Rotary Drone HERM Line Spectrum under Manoeuvering Conditions"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1294-7093","authenticated-orcid":false,"given":"Peter","family":"Klaer","sequence":"first","affiliation":[{"name":"Defence Research and Development Canada, 3701 Carling Avenue, Ottawa, ON K2K 2Y7, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Andi","family":"Huang","sequence":"additional","affiliation":[{"name":"Defence Research and Development Canada, 3701 Carling Avenue, Ottawa, ON K2K 2Y7, Canada"},{"name":"Department of Systems and Computer Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Pascale","family":"S\u00e9vigny","sequence":"additional","affiliation":[{"name":"Defence Research and Development Canada, 3701 Carling Avenue, Ottawa, ON K2K 2Y7, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0153-6723","authenticated-orcid":false,"given":"Sreeraman","family":"Rajan","sequence":"additional","affiliation":[{"name":"Department of Systems and Computer Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3271-5011","authenticated-orcid":false,"given":"Shashank","family":"Pant","sequence":"additional","affiliation":[{"name":"Aerospace Research Centre, National Research Council Canada, 1200 Montreal Rd., Ottawa, ON K1A 0R6, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Prakash","family":"Patnaik","sequence":"additional","affiliation":[{"name":"Aerospace Research Centre, National Research Council Canada, 1200 Montreal Rd., Ottawa, ON K1A 0R6, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Bhashyam","family":"Balaji","sequence":"additional","affiliation":[{"name":"Defence Research and Development Canada, 3701 Carling Avenue, Ottawa, ON K2K 2Y7, Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,10,21]]},"reference":[{"key":"ref_1","unstructured":"Chen, V.C. (2011). The Micro-Doppler Effect in Radar, Artech House Boston."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Harmanny, R.I.A., de Wit, J.J.M., and Cabic, G.P. (2014, January 8\u201310). Radar Micro-Doppler Feature Extraction Using the Spectrogram and the Cepstrogram. Proceedings of the 11th European Radar Conference, Rome, Italy.","DOI":"10.1109\/EuRAD.2014.6991233"},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Rahman, S., and Robertson, D.A. (2017, January 10\u201312). Millimeter-wave micro-Doppler measurements of small UAVs. Proceedings of the Radar Sensor Technology XXI, Anaheim, CA, USA.","DOI":"10.1117\/12.2261942"},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Rahman, S., and Robertson, D.A. (2018). Radar micro-Doppler signatures of drones and birds at K-band and W-band. Sci. Rep., 8.","DOI":"10.1038\/s41598-018-35880-9"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"911","DOI":"10.1049\/iet-rsn.2018.0020","article-title":"Review of radar classification and RCS characterisation techniques for small UAVs or drones","volume":"12","author":"Patel","year":"2018","journal-title":"IET Radar Sonar Navig."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"138669","DOI":"10.1109\/ACCESS.2019.2942944","article-title":"Machine Learning-Based Drone Detection and Classification: State-of-the-Art in Research","volume":"7","author":"Taha","year":"2019","journal-title":"IEEE Access"},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Bj\u00f6rklund, S. (2018, January 26\u201328). Target Detection and Classification of Small Drones by Boosting on Radar Micro-Doppler. Proceedings of the 2018 15th European Radar Conference (EuRAD), Madrid, Spain.","DOI":"10.23919\/EuRAD.2018.8546569"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Samaras, S., Magoulianitis, V., Dimou, A., Zarpalas, D., and Daras, P. (2019). UAV Classification with Deep Learning Using Surveillance Radar Data. International Conference on Computer Vision Systems, Springer.","DOI":"10.1007\/978-3-030-34995-0_68"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"38","DOI":"10.1109\/LGRS.2016.2624820","article-title":"Drone classification using convolutional neural networks with merged Doppler images","volume":"14","author":"Kim","year":"2016","journal-title":"IEEE Geosci. Remote. Sens. Lett."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1670","DOI":"10.1109\/LGRS.2017.2727824","article-title":"Experimental Analysis of Small Drone Polarimetry Based on Micro-Doppler Signature","volume":"14","author":"Kim","year":"2017","journal-title":"IEEE Geosci. Remote. Sens. Lett."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2","DOI":"10.1109\/TAES.2006.1603402","article-title":"Micro-Doppler Effect in Radar: Phenomenon, Model, and Simulation Study","volume":"42","author":"Chen","year":"2006","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"2949","DOI":"10.1002\/mop.31408","article-title":"Extraction of micro-doppler characteristics of drones using high-resolution time-frequency transforms","volume":"60","author":"Kim","year":"2018","journal-title":"Microw. Opt. Technol. Lett."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"239","DOI":"10.1016\/j.eswa.2019.05.007","article-title":"A UAV classification system based on FMCW radar micro-Doppler signature analysis","volume":"132","author":"Oh","year":"2019","journal-title":"Expert Syst. Appl."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"De Wit, J.J.M., Harmanny, R.I.A., and Molchanov, P. (2014, January 13\u201317). Radar micro-Doppler feature extraction using the Singular Value Decomposition. Proceedings of the 2014 International Radar Conference, Lille, France.","DOI":"10.1109\/RADAR.2014.7060268"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"187","DOI":"10.1109\/LAWP.2018.2885373","article-title":"Numerical Simulation and Experimental Analysis of Small Drone Rotor Blade Polarimetry Based on RCS and Micro-Doppler Signature","volume":"18","author":"Li","year":"2019","journal-title":"IEEE Antennas Wirel. Propag. Lett."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1895","DOI":"10.1109\/JSEN.2017.2785335","article-title":"Automatic measurement of blade length and rotation rate of drone using W-band micro-Doppler radar","volume":"18","author":"Singh","year":"2017","journal-title":"IEEE Sensors J."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Tait, P.D.F. (2013). Radar Automatic Target Recognition (ATR) and Non-Cooperative Target Recognition (NCTR), The Institution of Engineering and Technology. Chapter 3.","DOI":"10.1049\/PBRA033E_ch3"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Huang, A., S\u00e9vigny, P., Balaji, B., and Rajan, S. (2020, January 28\u201330). Fundamental Frequency Estimation of HERM Lines of Drones. Proceedings of the 2020 IEEE International RADAR Conference (virtual), Washington, DC, USA.","DOI":"10.1109\/RADAR42522.2020.9114676"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"257","DOI":"10.1121\/1.396427","article-title":"Measurement of pitch by subharmonic summation","volume":"83","author":"Hermes","year":"1988","journal-title":"J. Acoust. Soc. Am."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"3283","DOI":"10.1242\/jeb.204.19.3283","article-title":"Speeds and wingbeat frequencies of migrating birds compared with calculated benchmarks","volume":"204","author":"Pennycuick","year":"2001","journal-title":"J. Exp. Biol."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/20\/20\/5940\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T10:25:03Z","timestamp":1760178303000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/20\/20\/5940"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,10,21]]},"references-count":20,"journal-issue":{"issue":"20","published-online":{"date-parts":[[2020,10]]}},"alternative-id":["s20205940"],"URL":"https:\/\/doi.org\/10.3390\/s20205940","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,10,21]]}}}