Comprehensive evaluation of a tri-band MIMO antenna with SAR and MIMO performance for 5G devices.

In this work, a compact two-port MIMO antenna has been proposed for 5G millimeter wave applications. The antenna is fabricated on Rogers RT/Duroid 5880 substrate and occupies a footprint of only 12.5 × 4.8 × 0.65 mm³, which is among the smallest dimensions reported in the literature for comparable designs. Even with such tight physical constraints, the antenna is able to provide a gain ranging from 9.3 to 9.7 dBi across three distinct operating bands, namely 26.47-30.85 GHz, 31.29-32.86 GHz, and 35.8-38.48 GHz. The multiband behavior is mainly attributed to the meandered slot-loaded structure, which effectively increases the electrical length without any corresponding increase in the physical dimensions of the antenna. The MIMO performance parameters are also found to be satisfactory. Port isolation of - 20 dB has been achieved, while the envelope correlation coefficient (ECC) is maintained below 0.01. The channel capacity loss is recorded as 0.33 bps/Hz, which confirms that the mutual coupling between the ports is sufficiently low and that stable multi-stream data transmission can be supported. The measured results for S-parameters, gain, radiation patterns, and surface current distributions are in good agreement with the simulated values, thereby validating the design experimentally. SAR analysis has been carried out using a multi-layered human hand phantom model. The obtained SAR values are found to be within the permissible exposure limits for all three operating bands, which is of particular relevance since the antenna is intended for use in handheld and wearable 5G devices. On comparison with recently published works in the literature, the proposed design demonstrates competitive performance in terms of physical size, gain, bandwidth coverage, and electromagnetic safety compliance. Hence, the design can be considered as a suitable candidate for IoT and wearable 5G communication systems.