In this manuscript, a four-port MIMO antenna is designed for millimeter wave (mmWave) operation at 24/38 GHz. The proposed MIMO antenna has small footprint of 16.0 mm × 16.0 mm × 0.25 mm (1.28 \({\lambda}_{0}\) × 1.28 \({\lambda}_{0}\) × 0.02 \({\lambda}_{0}\) , where \({\lambda}_{0}\) is wavelength and calculated at lower resonance frequency 24 GHz) using the flexible substrate. The dual-band characteristic is achieved using H-shaped slot in the triangular radiating patch. The orthogonal placement of the patch and defected ground plane using rectangular slot is implemented to achieve the improved isolation > 22 dB across both the operating bands. The antenna demonstrates the gain more than 5.47 dBi and efficiency > 75%. The link margin analysis of the MIMO antenna demonstrates good communication rate of 200 Mbps at a distance of 150 m suitable for mmWave communication. Moreover, the diversity metrics of MIMO antenna are also analyzed to confirm the aspect of its implementation in high-speed communication systems. The envelope correlation coefficient (ECC) of the MIMO antenna is < 0.02, CCL < 0.18, and MEG < −6 dB across the two operating bands at 24/38 GHz. The proposed MIMO antenna is simulated using CST microwave studio and compared with the measured results for practical feasibility. Further, the flexibility performance is also analyzed at different bending radii of Rx = 10, 40, and 70 mm and Ry = 30, 50, and 70 mm, respectively. The reflection coefficient and radiation patterns of the deformed MIMO antenna is minutely altered ensuring the suitable candidate for the wearable application in mmWave frequency spectrum.
