The development of fifth-generation (5G) technology is the beginning of a rapid transition in the world of wireless communications. Gbps data rates, minimal latency, and good connectivity are the ultimate aims of 5G. To achieve them, 5G systems employ the mm-Wave frequency band which has a frequency range above 24GHz and so allows for higher bandwidth and gigabit wireless services. Because the size of the antenna elements and their spacings are so small in mm-Wave, massive antenna arrays in the base station may fit into a smaller area while yet providing high gain. However, the problem with the mm-Wave integrated antenna array system is the excessive heat generated per unit volume as there is not enough surface area to dissipate heat. Thermal management of the antenna system is very important as it affects the reliability and lifetime of the electronic components in the system. Both active and passive cooling strategies have been employed with passive cooling being the cost-effective and energy-efficient solution. Heatsink antennas can enhance the cooling capacity by providing dual functionality in terms of both thermal and electromagnetics. Traditionally, most of the works on heatsink antennas are focused at lower frequencies and a few at the mm-Wave frequency range. However, proper mm-wave thermal modeling in active integrated antennas is missing and there isn’t any research on the performance of heatsink antennas in array designs. This thesis work aims in designing and optimizing a heatsink antenna operating at 28 GHz to achieve dual functionality. The second aim of the thesis is to develop an appropriate thermal model for the designed antenna. Following the conduction-based simulations depending on assumed heat transfer coefficients, proper thermal modeling with appropriate beamformer chip characteristics and a CFD-based natural convective simulation setup has been developed without the assumption of a heat transfer coefficient. Optimal heatsink antenna dimensions are chosen based on the electro-thermal performance. Then, the selected antenna has been used in 1D and 2D arrays. Finally, a comparison study has been made with that of the conventional patch antenna. The results obtained have shown that both 1D (1x8) and 2D (4x4) heatsink antenna arrays can achieve a better heat dissipation by lowering the junction temperature of about 10-20 degrees Celsius (for the investigated cases) with higher realized gain and similar side lobe level compared to the respective patch antenna arrays. Furthermore, amplitude tapering of the heatsink antenna array achieved lower sidelobe levels which make this heatsink antenna a low-sidelobe and low-temperature alternative for the patch antenna array.