The series fed planar four-port multiple-input-multiple-output (MIMO) antenna design for 28/38 GHz Internet of Things (IoT) and radar applications is presented in this study. Recently, the idea of multiple inputs, multiple outputs (MIMO) antenna systems has been implemented to function at higher frequencies without any restrictions. This study discusses the design of a high gain MIMO antenna for 5G millimetre wave applications. The antenna offers a 440 MHz and 2.56 GHz bandwidth by resonating at 28 and 38 GHz, respectively. The suggested layout is created on an RT Duroid 5880 substrate, measuring 9.53 × 7.85 × 0.8 mm3 in its single-elemental dimension. A 50-Ω microstrip wire supplies the patch antenna with stepped impedance and is wholly grounded. It also features two parasitic slotted components that are electromagnetically connected, as well as an I-shaped slot. Initially constructed as a solitary component, this blueprint was then altered to incorporate four MIMO antenna elements, each measuring a total of 50 × 35 × 0.8 mm3. In order to analyse its performance characteristics and identify the MIMO antenna diversity performance features that qualify the proposed antenna for use in 5G mm-wave and 5G-operated portable devices, a simulated prototype is built and measured.