## 2 Methods and Hardware for Application of subTHz Instruments
### Receivers, Antennas, and the Atmosphere as Critical Factors of subTHz Systems  
The parameters of the presented subTHz generators, amplifiers (see Figure 2), and receivers developed by the team of the coauthors are sufficiently high to ensure the proper  
Figure 1: (**a**) Gyrotron for 250 GHz (330 kW with pulse duration about 100 microseconds, or 250 kW with CW) and (**b**) its output power and efficiency. technical signal/noise ratio when such equipment will be used with new antenna systems for any applications mentioned in the Introduction. However, the above-stated atmosphere issue persists. The main task now is to study the effect of the atmospheric conditions on the subTHz radiation propagating through the atmosphere. To find a solution for the highly efficient channeling of ultra-powerful microwave beams through the atmosphere, we used the techniques and tools developed in astronomy to study the propagation of microwave signals of astrophysical objects through the Earth's atmosphere. Here, we regard the atmosphere as an inhomogeneous dispersing and dissipative medium. The inhomogeneity is presented through one of the generally accepted flat-layered models, within the framework of which the extensive statistics of atmospheric characteristics collected at various locations and altitudes above the sea level have been processed. Speaking about the noticeable progress in the development of large subTHz antenna systems [2,11,30], powerful gyro transmitters (megawatt sources with a line width of 1 Hz and amplifiers with a band of 2 GHz) [12,18], and high-sensitivity quantum level receivers [23,28], we can have a new look at the prospects opening up in applications of the subTHz range, now taking the atmosphere effect into account. In this connection, the choice of the optimal location of the antenna for astronomy, satellite communications, and especially for subTHz radars (due to the two-way passing of radar beams through the atmosphere) is quite critical. A two-band MIAP-2 radiometer [31] was developed to study the atmospheric absorption of electromagnetic waves in the subTHz frequency range by the method of direct subTHz measurement (see Figure 3). The database publicly available on the ZENODO web page [32] is the result of more than ten years of measurements at various geolocations and different altitudes above the sea level, from coastal sites to altitudes of \(\sim\)3 km in the vicinity of the Suffa Plateau and the North Caucasus. It is complemented here by the measurements made in summer 2021 at the Elbrus (5500 m) [33] and Mount Aktashtau (3200 m), which is close to the Suffa Plateau. The direct measurements fulfilled within the framework of the presented research efforts at specifically selected sites showed a radical difference (by an order of magnitude or greater) in the propagation conditions of subTHz beams depending on the location of the antenna and seasonal and other variations, which must be taken into account when considering a choice of the location for antenna systems. At present, extensive satellite and meteorological data are available, from which certain conclusions can be drawn about the prospects of using subTHz instruments without visiting the actual installation site, but based on the data obtained by various methods and  
Figure 2: (**a**) GYRO amplifier for \(\sim\)100 GHz, 3 KW (gyro TWT), and (**b**) its specifications. tools in multiple ranges, in particular, using the optical or even GPS and V-band equipment indicating the water vapor quantity. This handy tool for preliminary estimates was used by us for the initial assessment of test locations and the choice of the directions for the expeditions presented here. However, not only water and vapor absorption, but also other atmospheric components are essential for microwave astrolimate since they have almost no effect on the propagation of beams in the optical or long-wavelength radio bands (e.g., GPS and CM wave radiometers).