###### Abstract
In addition to purely spectral features that make it possible to see new colors of the spectrum, the subTHz range has other advantages. Despite the significant atmospheric influence on subTHz waves, in some cases, radars and telecommunications have serious advantages over optical means, which are potentially better than subTHz ones, both in terms of capacity and resolution, but are \"blind\" in sunlight or other lighting conditions and completely unsuitable for operation in cloudy conditions. SubTHz waves have advantages for radar and communication applications compared with low-frequency (CM and DM) radio waves [6; 7; 8]. They are, e.g., high precision, i.e., a favorable ratio of the antenna diameter and the beamwidth [9],  
\[\theta\sim\frac{\lambda}{D} \tag{1}\]  
and have high range resolution for a fixed relative bandwidth:  
\[\Delta r\sim\frac{c}{2B} \tag{2}\]  
The HUSIR radar [7] has been designed for geostationary satellite imaging with a 3 cm range resolution. The Space Debris Surveillance Radar with the 0.01 m\({}^{2}\) resolution has a detection range of \(\sim\)1500 km, providing an angular precision of 10 inches. Unfortunately, the HUSIR project was frozen several years ago, but its key components have been already manufactured by Communications & Power Industries, Palo Alto, CA, USA [10]. Similar systems with close parameters can be developed for the Suffa Observatory [11] by the team [12] using the subTHz components presented here and developed in collaboration with the Institute of Applied Physics (IAP RAS) and GYCOM. The main instrument of the Suffa Observatory, the RT-70 antenna, is a Cassegrain structure with a parabolic primary mirror and a hyperbolic secondary mirror. Further calculations have been made for this antenna. However, the USA and Russia, which have been mentioned above, are not the only leaders in R&D of extremely high-power subTHz sources. Some rather effective groups working in Europe [13], Japan [14], and China have already developed several systems that meet the competition. The next section of the article is devoted to the progress achieved mainly by the authors of this paper together and in collaboration with leading international groups. The progress in recent years has been so significant that the factors dominating now among the limitations imposed on the use of subTHz technologies for the development of radio astronomy, radar, and telecommunications, are not technical restrictions, but natural ones, namely, the atmosphere. Certainly, we should make a note of recent achievements of the photonic technologies in those applications too. Remarkable results have been obtained not only for terrestrial applications, but also for space-based ones. Impressive developments of optical technologies [15], including those used in communications [16] and radar applications [17] are quite broad and undoubtedly have significant advantages over longer-wavelength subTHz systems, but their limitations are also known. The applications of subTHz systems presented here are useful additions to optical systems, not only for astronomy, where we have additional spectral windows due to their usage, but for communications and radar applications as well. The third section of this article is devoted to the results of recent studies of the conditions for propagation of the subTHz waves at the most significant and promising sites in northeastern Eurasia conducted by authors during the last decade for the development and installation of new antenna systems for subTHz radioastronomy, radar, and telecommunications. Other, rather exotic, applications proposed for the subTHz range will be only mentioned in this paper, rather than presented in detail, since the authors are not experts in the related field, but are only aware of these research areas.