{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,4]],"date-time":"2026-05-04T18:25:49Z","timestamp":1777919149897,"version":"3.51.4"},"reference-count":30,"publisher":"MDPI AG","issue":"24","license":[{"start":{"date-parts":[[2022,12,14]],"date-time":"2022-12-14T00:00:00Z","timestamp":1670976000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Ministry of Education","award":["NRF2022R1I1A3064460"],"award-info":[{"award-number":["NRF2022R1I1A3064460"]}]},{"name":"Ministry of Education","award":["4199990113966"],"award-info":[{"award-number":["4199990113966"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>In this paper, a compact dual circularly-polarized (CP) planar multiple-input-multiple-output (MIMO) antenna is presented for a sub-6 GHz frequency band. The antenna consists of four identical resonating elements, which are placed in a mirrored-image pattern to obtain polarization diversity. Element 2 is a mirror image of element 1, and elements 3 and 4 are mirror images of elements 1 and 2. Each antenna element comprises an elliptical resonator, a 50-\u2126 microstrip feed line, and a rectangular stub integrated with the feed to increase the surface current path of the antenna, shifting the resonating frequency to the lower side. Additionally, the rectangular stub is lengthened towards the right side (along the +x-axis direction in the antenna element 1), which balances the magnitude and 90\u00b0 phase variance among the horizontal (Ex) and vertical (Ey) fields. The proposed MIMO antenna supports both types of circular polarization, where radiators 1 and 3 radiate right-hand CP (RHCP) rays and radiators 2 and 4 radiate left-hand CP (LHCP) rays. Developing a compact-size MIMO antenna is a challenging task, especially when the antenna elements share the same ground plane and are placed less than half a wavelength apart. The mutual coupling in the proposed antenna is reduced by increasing the spacing between the elements without the use of any extra decoupling structure. Optimal spacing is maintained to achieve compact geometry with less inter-element correlation. The radiators are closely placed with an edge-to-edge spacing of 0.08\u03bb0, where \u03bb0 is the free space wavelength at 3.6 GHz. A peak gain of 5 dBi, efficiency of 90%, an envelope correlation coefficient (ECC) of less than 0.1, and isolation of more than 18 dB are obtained between different ports of the prototype antenna. The overall size of the antenna element is 17 mm \u00d7 17 mm \u00d7 1.6 mm, and the MIMO antenna is 40 mm \u00d7 40 mm \u00d7 1.6 mm.<\/jats:p>","DOI":"10.3390\/s22249827","type":"journal-article","created":{"date-parts":[[2022,12,15]],"date-time":"2022-12-15T03:43:49Z","timestamp":1671075829000},"page":"9827","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":20,"title":["Compact Dual Circularly-Polarized Quad-Element MIMO\/Diversity Antenna for Sub-6 GHz Communication Systems"],"prefix":"10.3390","volume":"22","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6260-6353","authenticated-orcid":false,"given":"Sachin","family":"Kumar","sequence":"first","affiliation":[{"name":"Department of Electronics and Communication Engineering, SRM Institute of Science and Technology, Kattankulathur 603203, India"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5270-0242","authenticated-orcid":false,"given":"Sandeep Kumar","family":"Palaniswamy","sequence":"additional","affiliation":[{"name":"Department of Electronics and Communication Engineering, SRM Institute of Science and Technology, Kattankulathur 603203, India"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hyun Chul","family":"Choi","sequence":"additional","affiliation":[{"name":"School of Electronic and Electrical Engineering, Kyungpook National University, Daegu 41566, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kang Wook","family":"Kim","sequence":"additional","affiliation":[{"name":"School of Electronic and Electrical Engineering, Kyungpook National University, Daegu 41566, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,12,14]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"690","DOI":"10.1109\/LAWP.2011.2161662","article-title":"Performance evaluation of actual multielement antenna systems under transmit antenna selection\/maximal ratio combining","volume":"10","author":"Papamichael","year":"2011","journal-title":"IEEE Antennas Wireless Propag. Lett."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"e23218","DOI":"10.1002\/mmce.23218","article-title":"Design and implementation of a compact tri-band four-port multiple-input-multiple-output antenna","volume":"32","author":"Singh","year":"2022","journal-title":"Int. J. RF Microw. Comput. Aided Eng."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"763","DOI":"10.1007\/s12647-020-00427-9","article-title":"MIMO\/diversity antenna with neutralization line for WLAN applications","volume":"36","author":"Birwal","year":"2021","journal-title":"MAPAN"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"192965","DOI":"10.1109\/ACCESS.2020.3032826","article-title":"A comprehensive survey on \u201cvarious decoupling mechanisms with focus on metamaterial and metasurface principles applicable to SAR and MIMO antenna systems","volume":"8","author":"Alibakhshikenari","year":"2020","journal-title":"IEEE Access"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"035020","DOI":"10.1088\/2058-8585\/ac8e7c","article-title":"Quad-port electromagnetic band gap (EBG)\u2013backed non-isomorphic multiple-input-multiple-output (MIMO) antenna for wearable applications","volume":"7","author":"Govindan","year":"2022","journal-title":"Flex. Print. Electron."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"65","DOI":"10.1017\/S1759078721000106","article-title":"Quad-band multi-polarized antenna with modified electric-inductive-capacitive resonator","volume":"14","author":"Singh","year":"2022","journal-title":"Int. J. Microw. Wireless Technol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"e22170","DOI":"10.1002\/mmce.22170","article-title":"Compact eight-port MIMO\/diversity antenna with band rejection characteristics","volume":"30","author":"Srivastava","year":"2020","journal-title":"Int. J. RF Microw. Comput. Aided Eng."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"5613","DOI":"10.1109\/TVT.2018.2806743","article-title":"An integrated tri-band\/UWB polarization diversity antenna for vehicular networks","volume":"67","author":"Alsath","year":"2018","journal-title":"IEEE Trans. Veh. Technol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"987","DOI":"10.1109\/LAWP.2016.2615884","article-title":"An FSS-based nonplanar quad-element UWB-MIMO antenna system","volume":"16","author":"Bilal","year":"2017","journal-title":"IEEE Antennas Wireless Propag. Lett."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"3504","DOI":"10.1109\/TBME.2022.3171842","article-title":"Electrically small circularly polarized UWB intraocular antenna system for retinal prosthesis","volume":"69","author":"Kaim","year":"2022","journal-title":"IEEE Trans. Biomed. Eng."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"75","DOI":"10.1017\/S1759078719000874","article-title":"A compact four-port UWB MIMO antenna with connected ground and wide axial ratio bandwidth","volume":"12","author":"Kumar","year":"2020","journal-title":"Int. J. Microw. Wireless Technol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"033002","DOI":"10.1088\/1361-6463\/ac2c36","article-title":"A comprehensive survey on \u2018circular polarized antennas\u2019 for existing and emerging wireless communication technologies","volume":"55","author":"Nadeem","year":"2022","journal-title":"J. Phys. D Appl. Phys."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"835","DOI":"10.1017\/S1759078719000461","article-title":"Broadband CPW-fed circularly polarized antenna for IoT-based navigation system","volume":"11","author":"Birwal","year":"2019","journal-title":"Int. J. Microw. Wireless Technol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"739","DOI":"10.1109\/LAWP.2014.2377784","article-title":"Novel printed MIMO antenna with pattern and polarization diversity","volume":"14","author":"Malik","year":"2015","journal-title":"IEEE Antennas Wireless Propag. Lett."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1163","DOI":"10.1109\/LAWP.2016.2626394","article-title":"Three-element MIMO antenna system with pattern and polarization diversity for WLAN applications","volume":"16","author":"Sharma","year":"2017","journal-title":"IEEE Antennas Wireless Propag. Lett."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"290","DOI":"10.1109\/TAP.2015.2496118","article-title":"A broadband dual circularly-polarized square slot antenna","volume":"64","author":"Saini","year":"2016","journal-title":"IEEE Trans. Antennas Propag."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1410","DOI":"10.1109\/TAP.2016.2647705","article-title":"A novel broadband dual circularly-polarized microstrip-fed monopole antenna","volume":"65","author":"Chandu","year":"2017","journal-title":"IEEE Trans. Antennas Propag."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"11241","DOI":"10.1109\/ACCESS.2020.2964902","article-title":"Isolation enhancement of closely packed dual circularly polarized MIMO antenna using hybrid technique","volume":"8","author":"Jamal","year":"2020","journal-title":"IEEE Access"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"11887","DOI":"10.1109\/ACCESS.2020.2966052","article-title":"Enhanced-performance circularly polarized MIMO antenna with polarization\/pattern diversity","volume":"8","author":"Ullah","year":"2020","journal-title":"IEEE Access"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Kumar, S., Lee, G.H., Kim, D.H., Choi, H.C., and Kim, K.W. (2020). Dual circularly polarized planar four-port MIMO antenna with wide axial-ratio bandwidth. Sensors, 20.","DOI":"10.3390\/s20195610"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"90779","DOI":"10.1109\/ACCESS.2020.2993897","article-title":"Planar four-port dual circularly-polarized MIMO antenna for sub-6 GHz band","volume":"8","author":"Saxena","year":"2020","journal-title":"IEEE Access"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"162","DOI":"10.1109\/MAP.2017.2658346","article-title":"Current misuses and future prospects for printed multiple-input, multiple-output antenna systems","volume":"59","author":"Sharawi","year":"2017","journal-title":"IEEE Antennas Propag. Mag."},{"key":"ref_23","unstructured":"(2022, June 01). Available online: https:\/\/www.qualcomm.com\/media\/documents\/files\/5g-spectrum-update-for-mipi-alliance.pdf."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Jamshed, M.A., Ur-Rehman, M., Frnda, J., Althuwayb, A.A., Nauman, A., and Cengiz, K. (2021). Dual band and dual diversity four-element MIMO dipole for 5G handsets. Sensors, 21.","DOI":"10.3390\/s21030767"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2629","DOI":"10.1007\/s13369-021-05720-6","article-title":"Low-interacted multiple antenna systems based on metasurface-inspired isolation approach for MIMO applications","volume":"47","author":"Althuwayb","year":"2022","journal-title":"Arab. J. Sci. Eng."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"5705","DOI":"10.1109\/TAP.2019.2922547","article-title":"Multiband MIMO microwave and millimeter antenna system employing dual-function tapered slot structure","volume":"67","author":"Ikram","year":"2019","journal-title":"IEEE Trans. Antennas Propag."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"3193","DOI":"10.1007\/s00542-018-4189-3","article-title":"Design of 4-element microstrip array of wideband reflector antenna with stable high gain characteristics","volume":"25","author":"Sharma","year":"2019","journal-title":"Microsyst. Technol."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"108601","DOI":"10.1109\/ACCESS.2021.3101441","article-title":"Wideband circularly polarized textile MIMO antenna for wearable applications","volume":"9","author":"Kumar","year":"2021","journal-title":"IEEE Access"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"2048","DOI":"10.1109\/LAWP.2020.3022000","article-title":"A systematic approach for mutual coupling reduction between microstrip antennas using pixelization and binary optimization","volume":"19","author":"Ghadimi","year":"2020","journal-title":"IEEE Antennas Wireless Propag. Lett."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"705","DOI":"10.1049\/el:20030495","article-title":"Exact representation of antenna system diversity performance from input parameter description","volume":"39","author":"Blanch","year":"2003","journal-title":"Electron. Lett."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/22\/24\/9827\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T01:41:12Z","timestamp":1760146872000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/22\/24\/9827"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2022,12,14]]},"references-count":30,"journal-issue":{"issue":"24","published-online":{"date-parts":[[2022,12]]}},"alternative-id":["s22249827"],"URL":"https:\/\/doi.org\/10.3390\/s22249827","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2022,12,14]]}}}