## 2 Methods and Hardware for Application of subTHz Instruments
### Prospects for Gyrotrons on the Sufffa Antenna for Radar and Telecommunication Applications  
The use of the above-mentioned transmitters, receivers, and antennas under the estimated atmospheric limitations will be assessed. The new instruments allow obtaining data transmission rates for communication and the range and resolution of radars. The content of a radar depends on many factors: the design, signal processing device, operation conditions, etc. Leaving out these conditions, we can estimate the range only roughly, let alone the fact that the basic radar equation itself is approximate, and different test objects under radar surveillance can yield noticeably different results. Nevertheless, an approximate set of some values will allow a rough estimation of the performance of the system being developed from the following Formula (3) [9]. We can derive the value of the range:  
\[r_{\text{max}}=\sqrt[4]{\frac{\gamma E\eta S^{2}\sigma}{2\pi N_{0}q_{\text{min }}^{2}\lambda^{2}}} \tag{3}\]  
where:  
\(\gamma\) is the coefficient of nonoptimality of the receiving device;  
\(E\) is the energy of the probing signal;  
\(E=\tau\)\(P\)\(\cdot\)\(T\) is the average power, where \(\tau\) is the absorption of the atmosphere, \(P\) is the transmitter power, and \(T\) is the signal duration (signal accumulation time);  
\(\eta\) is the efficiency of the transmitting antenna;  
\(S\) is the effective area of the antenna (here, it is assumed that the reception and transmission are carried out by one antenna);  
\(S=K\)\(S_{A}\);  
\(K\) is the rate of antenna aperture area utilization;  
Figure 4: A typical picture [23] of atmospheric propagation in the first four subTHz transparency windows (3, 2, 1.3, and 0.8 mm) can be used for open-air terrestrial applications. The transparency windows are separated by intense absorption lines. The peaks are due to absorption lines for oxygen (two leftmost) and water (three following). \(S_{A}\) is the geometric area of the aperture for the antennas used,  
\[S_{A}=\pi\bigg{(}\frac{b}{2}\bigg{)}^{2}; \tag{4}\]  
\(b\) is the diameter of the antenna;  
\(\sigma\) is the effective scattering area of the object, which depends on the shape, orientation, size, and reflective properties of the test object and the wavelength; when probing extended objects, one should take into account the area of reflections determined by the radiation pattern of the radiating antenna;  
\(N_{0}=\) kT\({}_{e}n\) is the spectral intensity of white noise;  
\(k=1.38\times 10^{-23}\)J/K is the Boltzmann constant;  
\(T_{e}\) is the effective ambient noise temperature;  
\(n\) is the noise factor of the receiver;  
\(q_{\rm min}^{2}\) is the minimum signal-to-noise ratio (minimum in terms of the power at the output of the linear part of the receiver); and  
\(\lambda\) is the wavelength. Specific numerical values of the parameters of receivers, antennas, transmitters, and atmospheric attenuation used for simulations are presented below. To estimate the first-approximation maximum range (\(r\)), radar parameters can be conveniently set as typical, that is, shared by most radars, varying the above-specified parameters of receivers, transmitters, and antennas. It is also convenient to take the generally accepted dimensions of a test object being a metal ball with a diameter of 1 m and \(\sigma\) = 0.8. The calculations for \(\lambda\) = 3 mm made by using Equation (3) without taking into account the influence of the atmosphere give promising results for up to 2500 km. It is more than the thickness of the atmosphere (<100 km). The range of radar without the atmosphere should be much better for 1.3 and 0.8 mm. However, the atmosphere is taken into account in the formula as the additional attenuator \(\tau\) along the signal path, the latter being single for a communication channel and double for radar. When a signal is emitted, the atmosphere reduces the effective power of the transmitter. When a signal is received, it reduces both the level of the received signal and adds its own Nyquist noise and other noises to the SNR.