A tri-band microstrip patch antenna, designed for 5G applications, has been developed in this work. The antenna, with dimensions of 6 × 4 × 0.508 mm3, was simulated using CST Microwave Studio 2019. The proposed design used a rectangular patch with a dielectric constant of 2.2 and a dielectric loss tangent of 0.001. The antenna dimensions were optimized using the Design of Experiments (DOE) method. Slotting the patch achieved a minimum return loss of up to -25 dB for each band, with the largest bandwidth of 2.78 GHz. Additionally, the influence of the antenna cutting slot on antenna properties is analyzed to show the trade-off between slot width and reflection coefficient (S11) parameter value.