{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,4]],"date-time":"2026-06-04T10:49:19Z","timestamp":1780570159731,"version":"3.54.1"},"reference-count":23,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2025,8,10]],"date-time":"2025-08-10T00:00:00Z","timestamp":1754784000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003069","name":"Instituto Polit\u00e9cnico Nacional","doi-asserted-by":"publisher","award":["20250817"],"award-info":[{"award-number":["20250817"]}],"id":[{"id":"10.13039\/501100003069","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>This work presents the use of a novel impedance coupling technique and electrical length increase by using stub loading placed from the radiator to the ground plane. This method is applied to the design of a small four-element ultrawideband (UWB) MIMO antenna arranged in axial symmetry to achieve a compact array size while obtaining a bandwidth starting from a very low cutoff frequency compared to a conventional radiator operating at the same frequency. The four-element MIMO antenna, with an operational bandwidth of 1.9 GHz to 30 GHz, is based on a wideband monopole with a semicircular geometry, fed by a coplanar structure and an L-shaped half-ground plane section. To increase the electrical length of the structure and achieve a compact antenna design, reactive stub loading is introduced, placing it on the backside of the substrate, located orthogonally between the radiator and the L-shaped ground plane, obtaining a small-sized configuration. The axial symmetry is employed to increase the antennas\u2019 isolation by taking advantage of the orthogonal positioning and making the radiated fields have a low correlation. The antenna array footprint measures 48 mm \u00d7 48 mm, corresponding to 0.3\u03bb0 \u00d7 0.3\u03bb0 at the lower cutoff frequency. The array exhibits a low envelope correlation coefficient (ECC) of around 0.033 at 2 GHz, and less than 0.001 at the rest of the bandwidth; a diversity gain (DG) of approximately 10; a stable total active reflection coefficient (TARC) below \u221210 dB; interport isolation between 20 and 40 dB; and an average gain of 2.8 dBi.<\/jats:p>","DOI":"10.3390\/sym17081285","type":"journal-article","created":{"date-parts":[[2025,8,11]],"date-time":"2025-08-11T08:10:32Z","timestamp":1754899832000},"page":"1285","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Compact Four-Port Axial Symmetry UWB MIMO Antenna Array with Bandwidth Enhancement Using Reactive Stub Loading"],"prefix":"10.3390","volume":"17","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3288-4416","authenticated-orcid":false,"given":"Jos\u00e9 Alfredo","family":"Tirado-M\u00e9ndez","sequence":"first","affiliation":[{"name":"Instituto Polit\u00e9cnico Nacional, SEPI-ESIME Zacatenco, Av. IPN S\/N, Zacatenco, Mexico City 07738, Mexico"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4542-4961","authenticated-orcid":false,"given":"Hildeberto","family":"Jard\u00f3n-Aguilar","sequence":"additional","affiliation":[{"name":"CINVESTAV-IPN, Telecommunications Section, Av. IPN 2508, San Pedro Zacatenco, Mexico City 07360, Mexico"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9569-1171","authenticated-orcid":false,"given":"Roberto","family":"Linares-Miranda","sequence":"additional","affiliation":[{"name":"Instituto Polit\u00e9cnico Nacional, SEPI-ESIME Zacatenco, Av. IPN S\/N, Zacatenco, Mexico City 07738, Mexico"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7584-0675","authenticated-orcid":false,"given":"Ruben","family":"Flores-Leal","sequence":"additional","affiliation":[{"name":"CINVESTAV-IPN, Telecommunications Section, Av. IPN 2508, San Pedro Zacatenco, Mexico City 07360, Mexico"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alberto","family":"Vasquez-Toledo","sequence":"additional","affiliation":[{"name":"Electrical Engineering Department, UAM Iztapalapa, San Rafael Atlixco 186, Mexico City 09340, Mexico"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3731-1315","authenticated-orcid":false,"given":"Ricardo","family":"Gomez-Villanueva","sequence":"additional","affiliation":[{"name":"CINVESTAV-IPN, Telecommunications Section, Av. IPN 2508, San Pedro Zacatenco, Mexico City 07360, Mexico"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4349-0700","authenticated-orcid":false,"given":"Angel","family":"Perez-Miguel","sequence":"additional","affiliation":[{"name":"CINVESTAV-IPN, Telecommunications Section, Av. IPN 2508, San Pedro Zacatenco, Mexico City 07360, Mexico"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,8,10]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"32762","DOI":"10.1109\/ACCESS.2024.3371571","article-title":"Compact Circular-Shaped MIMO Antenna Covers UWB Bandwidth With Four Frequently-Used Band-Notched Characteristics for Multi-Scenario Applications","volume":"12","author":"Zhao","year":"2024","journal-title":"IEEE Access"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"12475","DOI":"10.1109\/JIOT.2023.3333814","article-title":"UWB Connected Ground Transparent 4-Port Flexible MIMO Antenna for IoT Applications","volume":"11","author":"Desai","year":"2024","journal-title":"IEEE Internet Things J."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"211","DOI":"10.2528\/PIERC23051403","article-title":"W-Shaped Eight-Port Wideband MIMO Antenna","volume":"134","author":"Naser","year":"2023","journal-title":"Progress. 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