## 3 Development and Experimentation
### Measurements of Channels 29 and 32  
The initial antenna pattern measurement tests were conducted using a rotary-wing aircraft. Due to the limited flight time of the rotary-wing aircraft, in order to determine the maximum antenna radiation height (for further measurements) the first flight was performed by ascending vertically and measuring the antenna radiation. From the obtained results, it can be seen that the height of the main antenna lobe (maximum radiation) was 235 m above sea level, as shown in Figure 10a.  
At the determined height (235 m), a flight was conducted around the antenna, recording the antenna radiation. The measurement results are presented in Figure 10b.  
The antenna measurement results are difficult to compare to the theoretical because, according to the Kathrein 770 881 antenna description, the results are presented as the vertical radiation pattern's dependence on angle and relative electric field strength (Figure 10c). Meanwhile, the directivity diagram of the Kathrein 770 881 antenna is shown in Figure 10d. Comparing Figure 10b and Figure 10d, it is evident that the directivity diagrams differ. This discrepancy arose because the signal strength was measured in dB at a distance of 200 m from the antenna, whereas the directivity diagram was theoretically obtained at two bays.  
Three-dimensional diagrams of the H-plane for channel 29 at a distance of 200 m from the tower and with a focus on flight accuracy are presented in Figure 11a and Figure 11b, respectively.  
Based on the general specifications for similar Kathrein antennas, the largest dimension is typically around 1.5 m. For example, using the 4G LTE frequency range (700 MHz to 2600 MHz), it is possible to calculate the far field distance for the lowest and highest frequencies using the speed of light constant c in meters per second unit and frequency \(f\) in Hz. For 700 MHz, the wavelength \(\lambda=c/f=3\times 10^{8}/700\times 10^{6}=0.4286\) m and the far field distance is equal to \(R\geqslant 2D^{2}/\lambda=2\times 1.5^{2}/0.42860\approx 10.5\,\)m. Meanwhile, for 2600 MHz \(\lambda=0.1154\,\)m and \(R\geqslant 39\,\)m.  
The far field distance for the Kathrein 770 881 antenna operating in the 4G LTE frequency range is approximately between 10.5 m and 39 m, and our measurements fully covered the area of interest.  
Thus, to measure the antenna pattern using a rotary-wing drone, it was necessary to perform at least two flights:  
* A flight ascending vertically, to measure the radiation extremum along the vertical axis.
* At the determined height, a circular flight around the antenna was performed, with the drone continuously oriented towards the antenna.  
Figure 11: (**a**) A 3D diagram of the H-plane for channel 29 at a distance of 200 m from the tower. (**b**) A 3D diagram of the H-plane for channel 29 at a distance of 200 m from the tower, focusing on flight accuracy.  
Figure 10: (**a**) The maximum signal level was set at an altitude of 235 m. (**b**) A 2D diagram of the H-plane for channel 29 at a distance of 200 m from the tower. (**c**) Vertical radiation pattern. (**d**) Horizontal radiation pattern.  
Measurements of the same antenna were also carried out, using a fixed-wing aircraft flying around the antenna at a fixed radius (330 m) but at different altitudes (in 5 m increments). Due to the high flight speed and long flight duration of the aircraft, it was possible to complete many circles around the antenna and collect a large amount of data at different altitudes, thereby creating a 3D antenna pattern, as shown in Figure 12:  
As seen from the provided examples, when using a fixed-wing aircraft, due to its high flight speed (and high measurement speed), it is not necessary to perform a vertical flight to determine the height of the antenna's radiation maximum. It is sufficient to fly a sufficient number (10-20) of circles around the antenna at different altitudes, thereby obtaining the antenna's 3D pattern, as shown in Figure 13: