This work introduces a high-gain slot antenna designed for the latest 5G networks, specifically operating at a frequency of 28 GHz. The antenna features a rectangular slot design, and its gain is significantly enhanced using 1x2 and 1x4 antenna arrays, resulting in an approximate increase of 4.2 dBi. The antenna has been fabricated and thoroughly tested, demonstrating operation within the frequency range of 26 GHz to 29.6 GHz with an S11 value of ≤ -10 dB, and achieving a gain of about 5 dBi across this band. The 1x2 and 1x4 antenna arrays have shown a bandwidth with S11 ≤ -10 dB ranging from 25.6 GHz to 29.8 GHz and 26.4 GHz to 29.9 GHz, respectively, attaining gains of 7.4 dBi at 28 GHz and 10.4 dBi at 28 GHz. The simulation and experimental results exhibit consistent patterns, confirming the proposed antenna's suitability for new 5G applications. All simulations were conducted using an EM simulator.