THz waves are sandwiched between micro and optical waves with frequencies in the order from 300 GHz up to 10 THz. In this part of the spectrum, technological development remains less advanced compared to optics and microwaves. Electronic devices exhibit cut-off frequencies in the lower THz range, while the energy of THz waves at these frequencies is relatively low, resulting in limited available power and sensitivity. This raises the question of why exploration of this spectral region is worthwhile. Historically, and still predominantly, the primary application has been the development of receivers for astronomical observations in the THz band. The inherent limitations in power and sensitivity characteristic of this spectral region have been mitigated through radiation coupling mechanisms utilizing quasi-optical systems. Recent advancements in silicon technology, coupled with the growing demand for increased bandwidth, have driven the global industry to explore higher frequencies, particularly within the 100–300 GHz spectral range, for sensing and communication applications. The broader bandwidth available at these frequencies enables significantly faster wireless data transmission. Notably, 5G networks already utilize millimeter-wave frequencies, and this trend is expected to continue with the development of 6G. Additionally, radars operating at several hundred gigahertz are being employed for high-resolution object detection across various industrial applications. In this presentation, I will provide an overview of our research activities on quasi-optical antenna systems, initially developed for THz space applications and more recently extended to communication and sensing applications. The discussion will cover the development of highfrequency electromagnetic models used for perfomance optimization, along with a review of multiple prototype implementations spanning in the 100 GHz to 3 THz frequency range. Co-sponsored by: Stracom Speaker(s): Nuria Llombart, Virtual: https://events.vtools.ieee.org/m/481951