OICC Press Majlesi Journal of Electrical Engineering 2345-3796 20 2 (June 2026) 2026 06 30 Hexagonal Microstrip MIMO Antenna with Defected Ground Structures for ISM/IoT Application 10.57647/mjee.2026.2002.10 EN Farzaneh Talebi Electrical and Computer Engineering Faculty, Semnan University, Semnan, Iran Pejman Rezaei Electrical and Computer Engineering Faculty, Semnan University, Semnan, Iran https://orcid.org/0000-0002-1266-3229 Sina Kiani Electrical and Computer Engineering Faculty, Semnan University, Semnan, Iran Journal Article 2026 06 30 In this manuscript, an original multiple-input multiple-output (MIMO) array antenna is proposed. The proposed array consists of two mirror-image elements placed adjacently. The proposed MIMO antenna is designed on the Rogers 4003C substrate with dimensions of 54 × 26 × 0.508 mm3. The recommended MIMO antenna exhibits a fractional impedance bandwidth of 13.79% (5.4-6.2 GHz), and achieves an element isolation greater than 22 dB. The proposed MIMO array demonstrates a gain of 5 dB with an efficiency of 95% at 5.8 GHz. Additionally, the MIMO array has a channel capacity loss less of than 0.2 b/s/Hz, an envelope correlation coefficient of ≤ 0.02, a diversity gains of ≥ 9.96 dB, and a mean effective gain ratio between elements of 1 dB. Due to its optimal operating frequency, high efficiency, and compact size, this antenna is an appropriate candidate for ISM/IoT applications.