Over the previous few years, the millimetre wave frequency range and sub-THz range have been received a lot of attention as they include unused frequency spectrum resources that are appropriate for providing a lot of applications such as automotive radars, short communication, medical imaging, security, and 5G communications to provide end-user access to Multi-Gbit/s services. On the other hand and because of the restrictions on the communication systems in these ranges such as power, path losses, and attenuation, the present RF antennas can't be used for millimeter and THz applications. The needed antennas should have low-profile, high-gain, acceptable technology, high efficiency and low cost to compensate for these ranges restrictions. Although there are some antenna designs for millimeter and sub THz ranges through the last decay, the antenna designs in these ranges still under investigation and studies to complete the vision of the proposed designs for the aforementioned applications. Thus, they cannot be carried by the optimum response and efficiency for these applications. This thesis aims to introduce a comprehensive study of the main applications that occupy these ranges of frequencies. In addition to introducing efficient antennas for each application with acceptable technology for it.