Abstract
Multi-input multi-output (MIMO) antennas operating in the millimeter wave (mmWave) band face challenges related to inter-element interference, limited isolation due to close spacing, and mutual coupling, all of which degrade antenna performance. To address these, this study introduces an advanced technique for enhancing inter-element isolation and minimizing mutual coupling. The proposed approach employs a combination of defective ground structures (DGS) and frequency-selective surfaces (FSS) to achieve effective isolation enhancement. Initially, a mmWave dual-band antenna was designed by incorporating a modified elliptical patch with rotating arms. Subsequently, a six-element dual-band MIMO antenna, measuring 1.97 × 3.39λ2, was developed to operate in the 23.63–32.90 GHz and 36.68–40 GHz bands, covering both ISM and 5G NR bands. The proposed inter-element isolation technique successfully achieves a coupling reduction of 33 dB between the MIMO elements. Furthermore, the designed dual-band MIMO antenna maintains a broadside radiation pattern, with maximum realized gains of 9.12 dBi, 9.19 dBi, 8.80 dBi, and 8.77 dBi at 26 GHz, 28 GHz, 30 GHz, and 38 GHz, respectively. It also demonstrates excellent MIMO diversity performance, including a total active reflection coefficient of9.91 dB. A specific absorption rate (SAR) analysis confirmed that the design complies with safety standards for both 1g and 10g tissue models. Additionally, a communication link scenario for wireless body area network (WBAN) applications was investigated. The combination of high isolation, dual-band functionality, broadside radiation, excellent diversity performance, and acceptable link margin validates the suitability of the proposed MIMO antenna for WBAN communication applications.