The rapid advancement of 5G technology has underscored the need for compact, efficient antennas for sub-6 GHz applications, which are crucial for increasingly miniaturized devices. Existing antennas often face challenges related to size, efficiency, and complexity, limiting their practicality in modern communication systems. To address these issues, this study introduces a novel Half-mode Substrate Integrated Waveguide (HMSIW) slot antenna, designed to offer optimal performance and ease of integration. The proposed antenna features a unique hexagonal shape with an octagonal slot on the top layer and a rectangular slot on the bottom layer, fed by a microstrip line. This design facilitates integration and optimizes performance within the sub-6 GHz frequency range. Utilizing CST Studio Suite software, the antenna’s key parameters, including resonance frequency, voltage standing wave ratio (VSWR), bandwidth, radiation pattern, and gain, were thoroughly analyzed. The antenna is designed to resonate at 4.9 GHz, making it ideal for sub-6 GHz 5G applications. It offers a 200 MHz bandwidth at a −10 dB reference line and maintains a VSWR of 2:1. Simulation results confirm that the antenna provides an acceptable radiation pattern and gain, showcasing its potential for effective deployment in contemporary 5G communication systems.