# Using Modeling to Select the Type of Microwave Field Emitter for Dense-Layer Grain Dryers
## 3 Results  
### Studying Microwave Electromagnetic Field Distribution in Horn Antennas  
A mathematical simulation of the microwave electromagnetic field distribution process was performed with the use of CST Microwave Studio software. The following parameters were used for the waveguides during the modeling:  
For the horn antenna: the cross-section of the rectangular waveguide is 45 \(\times\) 90 mm; the length of the rectangular waveguide is 104 mm; a short-circuited partition is installed at the end of the rectangular waveguide; the distance from the short-circuited partition to the magnetron output is 1/2 of the wavelength; the length of the horn is 37 mm; and the dimensions of the horn are 148 \(\times\) 48 mm. For the rectangular and semi-circular waveguides: the cross-section of the rectangular waveguide is 55 \(\times\) 110 mm, and the diameter of the semi-circular waveguide is 110 mm; the length of the waveguides with radiating slots is 400 mm; seven radiating slots with a height equal to the length of the lateral surface and a width of 4 mm are located on the lateral side of the waveguides; the distance between the radiating slots is 1/2 of the wavelength; the position of the short-circuited partition to the magnetron output is 1/2 of the wavelength; and the distance from the output of the magnetron to the axis of the first slit is one wavelength. For all types of radiators, the magnetron output (radiation port) was modeled based on the magnetron's radiating part's dimensions. The outlay of the horn-type waveguide model used in the mathematical simulation process is shown in Figure 6c. The frequency ranged from 2 GHz to 3 GHz with central points of 2.45 and 2.5 GHz selected for mathematical simulations. Owing to these selections, a number of dependences were deduced, presented in Figure 10a,b. Figure 10a,b show, respectively, the graph for the frequency dependence of the standing wave ratio (SWR) and that of the radiation efficiency, for the selected horn-type waveguide. Results of the mathematical simulation show that SWR values fall close to 1.3, for the operating radiation frequency of the magnetron, which is a positive indicator providing evidence of sufficient radiator coherence. Radiation efficiency has a maximum in the radiation frequency range of magnetrons, demonstrating an acceptable level of radiator coherence, as well. In order to evaluate the electromagnetic field spatial distribution, 3D dependencies were calculated. They are presented in Figure 11.  
Results of the 3D mathematical simulations show that there exists a substantial nonuniformity of the electromagnetic field density distribution both along the perimeter of the horn aperture area and in the radiation propagation direction. Therefore, the application of horn-type waveguides ensures rather high values of SWR (1.3) and high radiation efficiency, but the uniformity of the microwave field density distribution must be improved. Earlier performed experimental studies [24] have shown that energy consumption of the grain drying process, in convective-microwave zones, essentially depends on the drying agent parameters and on the method of its supply into the grain drying area. Energy consumption can be minimized when the directions of microwave field propagation into the grain layer and that of the drying agent coincide with each other [24]. In this case, a certain grade of microwave field distribution uniformity and that of drying agent concentration, in the grain layer, has to be ensured. This condition is hard to fulfill for the design option of the convective-microwave zone with horn-type waveguides. That is why an attempt was made to develop a waveguide design capable of complying with the above conditions. Figure 11: The 3D angular pattern and distribution of radiated microwave power for horn-type waveguide: (**a**) 3D angular pattern for microwave electromagnetic field and (**b**) 3D distribution of the radiated microwave field.