## 3 Results
### Dependence of Radiation Efficiency on the Moisture Content in Grain  
The antenna efficiency indicator depends on the relationship between the power supplied to the antenna and that emitted or dissipated inside it. An antenna is supposed to be effective when the major part of the power on its input is emitted into an external space. In antennas with low efficiency, the major part of the power is consumed inside them in the form of power loss or/and gets reflected from them. During the process of modeling, data on the dependence of radiation efficiency and the total radiation efficiency of the waveguides on the moisture content in the grain during processing were obtained (see Figure 7). Figure 7: Dependence of the waveguide’s radiation efficiency on the moisture content in grain: (**a**) radiation efficiency; (**b**) total efficiency. It follows from the obtained graphs (see Figure 7) that the reduction of moisture content in the grain from 26% to 14% leads to a growth in the waveguide's radiation efficiency by 15.1% (from 58.294 dB to 68.729 dB). In this case, not only the value of radiation efficiency but also the shape of its characteristics change with the change in the magnetron radiation frequency. The fundamental magnetron frequency that was selected for modeling (2.45 GHz) is critical for the _Rad Eff_ = _t_(_f_) dependence, since the magnetron is capable of generating oscillations in a rather narrow frequency range of \(\pm\)10% (from 2.426 GHz to 2.475 GHz). That is why an additional reduction in radiation efficiency takes place when the magnetron radiation frequency shifts towards the lower limit of this range. The total radiation efficiency (Figure 7b) also decreases with the growth of the moisture content in the grain (from -11.27 dB to -21.7 dB). This suggests that the growth of the moisture content in the grain subject to processing in the convective-microwave zone results in an increase in microwave energy loss in the waveguide. This situation occurs because the distance of microwave field penetration into the grain layer decreases with its moisture content. The radiation reflected from the grain gets lost in the waveguide. These results have to be considered when matching the waveguides and when defining the algorithm of the convective-microwave unit's operation. Dependence of Microwave Field Distribution in the Active Zone of a Single Magnetron on the Moisture Content in Grain  
During the grain drying process, the grain moves under its own weight within a completely filled convective-microwave zone, passing through different microwave-activated processing areas sequentially. This leads to the grain losing moisture. During the process of grain transport, a situation may occur where grain portions with various moisture contents enter the active zone of the same magnetron. This situation was also simulated. Figure 8 shows the spatial distribution pattern of microwave power dissipated inside grain layers with various moisture content that entered the active zone of a single radiating waveguide. The upper part of the grain layer has a moisture content of \(W\) = 16%, while its bottom portion has a moisture content of \(W\) = 14%. Isopleths for microwave power absorbed by the grain are presented for the outermost grain layer point (152 mm from the waveguide's rear wall and 100 mm from the waveguide's wall nearest to the grain layer). It is evident from Figure 8 that the wetter the grain is, the more microwave energy it absorbs. Despite the fact that grain with different moisture content areas is exposed to the microwave field of the same radiating waveguide, grain fractions with higher moisture content get heated more intensively compared to those containing less moisture. This means that the radiation efficiency in the active zone of a single waveguide will not remain constant during the grain processing. Additionally, it varies depending on the position of the particular radiating waveguide along the vertical axis of the convective-microwave zone.