{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T04:37:29Z","timestamp":1784695049133,"version":"3.55.0"},"reference-count":33,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2025,5,21]],"date-time":"2025-05-21T00:00:00Z","timestamp":1747785600000},"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>In the context of Doppler radar, studies have examined the changes in the phase shift of the S21 transmission coefficient related to minute movements of the human chest as a response to breathing or heartbeat. Detecting human vital signs remains a challenge, especially when obstacles interfere with the attempt to detect the presence of life. The sensitivity of a measurement system\u2019s perception of vital signs is highly dependent on the monitoring systems and antennas that are used. The current work proposes a computational approach that aims to extract an empirical law of the dependence of the phase shift of the transmission coefficient (S21) on the sensitivity at reception, based upon a set of four parameters. These variables are as follows: (a) the frequency of the continuous wave utilized; (b) the antenna type and its gain\/directivity; (c) the electric field strength distribution on the chest surface (and its average value); and (d) the type of material (dielectric properties) impacted by the incident wave. The investigated frequency range is (1\u201320) GHz, while the simulations are generated using a doublet of dipole or gain-convenient identical Yagi antennas. The chest surface is represented by a planar rectangle that moves along a path of only 3 mm, with a step of 0.3 mm, mimicking respiration movement. The antenna\u2013target system is modeled in the computational space in each new situation considered. The statistics illustrate the multiple regression function, empirically extracted. This enables the subsequent building of a continuous-wave bio-radar Doppler system with controlled and improved sensitivity.<\/jats:p>","DOI":"10.3390\/s25103235","type":"journal-article","created":{"date-parts":[[2025,5,21]],"date-time":"2025-05-21T06:31:27Z","timestamp":1747809087000},"page":"3235","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["A Computational Approach to Increasing the Antenna System\u2019s Sensitivity in a Doppler Radar Designed to Detect Human Vital Signs in the UHF-SHF Frequency Ranges"],"prefix":"10.3390","volume":"25","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0802-2717","authenticated-orcid":false,"given":"David","family":"Vatamanu","sequence":"first","affiliation":[{"name":"Doctoral School of Electrical Engineering, Technical University of Cluj-Napoca, 400020 Cluj-Napoca, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1408-9109","authenticated-orcid":false,"given":"Simona","family":"Miclaus","sequence":"additional","affiliation":[{"name":"Department of Communication, IT and Cyber Defense, \u201cNicolae Balcescu\u201d Land Forces Academy, 550170 Sibiu, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,5,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Kim, H., and Jeong, J. (2020). Non-Contact Measurement of Human Respiration and Heartbeat Using W-band Doppler Radar Sensor. Sensors, 20.","DOI":"10.3390\/s20185209"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Kathuria, N., and Seet, B.-C. (2021). 24 GHz Flexible Antenna for Doppler Radar-Based Human Vital Signs Monitoring. Sensors, 21.","DOI":"10.3390\/s21113737"},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Kathuria, N., and Seet, B.-C. (2020, January 7\u201310). 24 GHz flexible LCP antenna array for radar-based noncontact vital sign monitoring. Proceedings of the Asia-Pacific Signal and Information Processing Association Annual Summit and Conference, Auckland, New Zealand.","DOI":"10.3390\/s21113737"},{"key":"ref_4","first-page":"100106","article-title":"VitRad: A Low-Cost Continuous Wave Doppler Radar System with 3D-Printed Horn Antennas for Human Vital Sign Detection","volume":"11","author":"Jeong","year":"2022","journal-title":"HardwareX"},{"key":"ref_5","first-page":"177","article-title":"Accurate Remote Vital Sign Monitoring with 10 GHz Ultra-Wide Patch Antenna Array","volume":"82","author":"Rabbani","year":"2017","journal-title":"AEU-Int. J. Electron. Commun."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"125","DOI":"10.1016\/j.aeue.2019.01.020","article-title":"Implementation and Experimental Verifications of Microstrip Antennas for Angular Scanning of a Doppler Radar","volume":"101","author":"Karatay","year":"2019","journal-title":"AEU-Int. J. Electron. Commun."},{"key":"ref_7","first-page":"4922","article-title":"Microstrip Patch and Sierpinski Fractal Antennas: Simulations and Experimental Characterization for Vital Signs Detection with Doppler Radar Technique","volume":"13","author":"Vatamanu","year":"2020","journal-title":"Indian J. Sci. Technol."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Mingle, S., Kampouridou, D., and Feresidis, A. (2023). Multi-Layer Beam Scanning Leaky Wave Antenna for Remote Vital Signs Detection at 60 GHz. Sensors, 23.","DOI":"10.3390\/s23084059"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"818","DOI":"10.1002\/mop.30402","article-title":"Frequency Selective Surface Antenna for Remote Vital Sign Monitoring with Ultra-Wide Band Doppler Radar","volume":"59","author":"Rabbani","year":"2017","journal-title":"Microw. Opt. Technol. Lett."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Gouveia, C., Malafaia, D., Vieira, J.N., and Pinho, P. (2018, January 10\u201314). Bio-Radar Performance Evaluation for Different Antenna Designs. Proceedings of the 2018 International Conference on Electromagnetics in Advanced Applications, Cartagena des Indias, Colombia.","DOI":"10.23919\/URSIRSB.2018.8486765"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Mpanda, R.S., Liang, Q., Xu, L., Lin, Q., and Shi, J. (2018, January 21\u201324). Investigation on various antenna design techniques for vital signs monitoring. Proceedings of the Cross Strait Quad-Regional Radio Science and Wireless Technology Conference (CSQRWC), Xuzhou, China.","DOI":"10.1109\/CSQRWC.2018.8455471"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Bo, H., Fu, Q., Xu, L., Lure, F., and Dou, Y. (2016, January 22\u201327). Design and Implementation of a 2.45 GHz RF Sensor for Non-Contacting Monitoring Vital Signs. Proceedings of the 2016 IEEE MTT-S International Microwave Symposium, San Francisco, CA, USA.","DOI":"10.22489\/CinC.2016.319-267"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Das, V., Boothby, A., Hwang, R., Nguyen, T., Lopez, J., and Lie, D.Y.C. (2012, January 15\u201318). Antenna evaluation of a non-contact vital signs sensor for continuous heart and respiration rate monitoring. Proceedings of the 2012 IEEE Topical Conference on Biomedical Wireless Technologies, Networks, and Sensing Systems (BioWireleSS), Santa Clara, CA, USA.","DOI":"10.1109\/BioWireless.2012.6172730"},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"El-Samad, S., Obeid, D., Zaharia, G., Sadek, S., and Zein, G.E. (2017, January 13\u201316). Comparison Between Single and Two-Antenna VNA System Used for Heartbeat Rate Extraction. Proceedings of the 2017 IEEE Asia Pacific Microwave Conference, Kuala Lumpur, Malaysia.","DOI":"10.1109\/SENSET.2017.8125018"},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Shen, T.-M., Kao, T.-Y.J., Huang, T.-Y., Tu, J., Lin, J., and Wu, R.-B. (2013, January 20\u201323). Antenna Design of 60-GHz Micro-Radar System-In-Package for Noncontact Vital Sign Detection. Proceedings of the 2013 IEEE Radio and Wireless Symposium, Austin, TX, USA.","DOI":"10.1109\/LAWP.2013.2239957"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"El-Samad, S., Obeid, D., Zaharia, G., Sadek, S., and Zein, G.E. (2016, January 2\u20136). Feasibility of Heartbeat Detection Behind a Wall Using CW Doppler Radar. Proceedings of the 2016 IEEE Radar Conference, Philadelphia, PA, USA.","DOI":"10.1109\/MECAP.2016.7790091"},{"key":"ref_17","unstructured":"Lan, S., Xu, Y., Chu, H., Qiu, J., He, Z., and Denisov, A. (2015, January 19\u201324). A Novel 24 GHz Microstrip Array Module Design for Bioradars. Proceedings of the 2015 International Symposium on Antennas and Propagation (ISAP), Vancouver, BC, Canada."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"2158","DOI":"10.1109\/TAP.2023.3236764","article-title":"A W-band self-packaged siw-based slot antenna with gain and bandwidth enhancement","volume":"71","author":"Huang","year":"2023","journal-title":"IEEE Trans. Antennas Propag."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"3234","DOI":"10.1109\/TAP.2020.3030999","article-title":"A W-band integrated tapered array antenna with series feed for noncontact vital sign detection","volume":"69","author":"Zhang","year":"2020","journal-title":"IEEE Trans. Antennas Propag."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"7022","DOI":"10.1109\/TAP.2019.2927777","article-title":"Miniaturized circularly polarized Doppler radar for human vital sign detection","volume":"67","author":"He","year":"2019","journal-title":"IEEE Trans. Antennas Propag."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1109\/LSENS.2019.2924695","article-title":"Noncontact vital sensing with a miniaturized 2.4 GHz circularly polarized doppler radar","volume":"3","author":"Gu","year":"2019","journal-title":"IEEE Sens. Lett."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1240","DOI":"10.1109\/ACCESS.2019.2961130","article-title":"A resolution enhancement technique for remote monitoring of the vital signs of multiple subjects using a 24 GHz bandwidth-limited FMCW radar","volume":"8","author":"Lee","year":"2019","journal-title":"IEEE Access"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1393","DOI":"10.1109\/TBCAS.2021.3123830","article-title":"Accurate measurement of human vital signs with linear FMCW radars under proximity stationary clutters","volume":"15","author":"Liu","year":"2021","journal-title":"IEEE Trans. Biomed. Circuits Syst."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1886","DOI":"10.1109\/TMTT.2023.3305075","article-title":"A novel rotary FMCW radar for omnidirectional multiperson localization and vital signs detection","volume":"72","author":"Wang","year":"2023","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"229","DOI":"10.1109\/TBCAS.2023.3257647","article-title":"Comprehensive comparison of continuouswave and linear-frequency-modulated continuous-wave radars for shortrange vital sign monitoring","volume":"17","author":"Antolinos","year":"2023","journal-title":"IEEE Trans. Biomed. Circuits Syst."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"88689","DOI":"10.1109\/ACCESS.2020.2993503","article-title":"A novel realtime human heart rate estimation method for noncontact vital sign radar detection","volume":"8","author":"Ding","year":"2020","journal-title":"IEEE Access"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"8876","DOI":"10.1109\/JSEN.2023.3251978","article-title":"A low frequency portable continuous wave radar system for vital signs monitoring","volume":"23","author":"Ebrahim","year":"2023","journal-title":"IEEE Sens. J."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"16242","DOI":"10.1109\/ACCESS.2022.3148426","article-title":"Multibeam Doppler sensor-based non-contact heartbeat detection using beam diversity","volume":"10","author":"Kitagawa","year":"2022","journal-title":"IEEE Access"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"36888","DOI":"10.1109\/ACCESS.2018.2886825","article-title":"Non-contact detection of vital signs using a UWB radar sensor","volume":"7","author":"Duan","year":"2019","journal-title":"IEEE Access"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"93","DOI":"10.1109\/TMTT.2022.3193408","article-title":"A Wi-Fi frequency band passive biomedical Doppler radar sensor","volume":"71","author":"Tang","year":"2022","journal-title":"IEEE Trans. Microw. Theory Tech."},{"key":"ref_31","unstructured":"Dassault Systems (2025, February 20). CST Studio Suite\u2014Simulia. Available online: https:\/\/www.3ds.com\/products\/simulia\/cst-studio-suite."},{"key":"ref_32","unstructured":"Balanis, C.A. (2016). Antenna Theory: Analysis and Design, John Wiley and Sons."},{"key":"ref_33","unstructured":"ITIS Foundation (2025, March 10). Dielectric Properties of Body Tissues. Available online: https:\/\/itis.swiss\/virtual-population\/tissue-properties\/database\/dielectric-properties."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/25\/10\/3235\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T17:36:26Z","timestamp":1760031386000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/25\/10\/3235"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,5,21]]},"references-count":33,"journal-issue":{"issue":"10","published-online":{"date-parts":[[2025,5]]}},"alternative-id":["s25103235"],"URL":"https:\/\/doi.org\/10.3390\/s25103235","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,5,21]]}}}