## 3 Results and Discussion  
### Measurement Results  
In this subsection, we present the received signal level as a function of distance for measurements in a cornfield (R3 corn stage) at 0.9 GHz and 2.4 GHz under two transmitting and two receiving antenna heights at horizontal and vertical polarization. Figures 5-8 show the received signal level variation with distance for the following scenarios: near-ground (transmitting antenna is placed at a height of \(\lambda/3\) m above ground, \(\text{h}_{\text{TX}}=\lambda/3\) m) and above-ground (transmitting antenna is placed at a height of 0.5 m above ground, \(\text{h}_{\text{TX}}=0.5\) m) installation of a sensor node in the corn field for two heights of the receiving antenna below (\(\text{h}_{\text{Rx}}=2.0\) m above ground) and above (\(\text{h}_{\text{Rx}}=3.4\) m above ground) corn height, at two frequencies of 0.9 GHz and 2.4 GHz for co-polarized horizontal-to-horizontal (H-H) and vertical-to-vertical (V-V) antennas. In all scenarios, the transmitter was positioned in the cornfield and relocated, as illustrated in Figure 3a. In all scenarios under obstructed line-of-sight (O-LoS) conditions, the general trend was that the signal strength was reduced, with distance varying due to constructive and destructive interference. The peak signal strength at a receiving antenna height of 2 m occurred when the distance between the transmitting and receiving antennas was 1 m. At a receiving antenna height of 3.4 m (above the height of the corn), the peak signal strength occurred when the Tx-Rx distance was 5 m (see Figures 5 and 6). Thus, we can see from Figures 5 and 6 that, when the receiving antenna height was below the corn height (\(\text{h}_{\text{Rx}}=2.0\) m), for H-H antennas at 0.9 GHz, the peak values of the received signal were \(-38.7\) dBm (at \(\text{h}_{\text{Tx}}=0.11\) m) and \(-39.1\) dBm (at \(\text{h}_{\text{Tx}}=0.5\) m), while at 2.4 GHz, the peak values of the received signal were \(-53.7\) dBm (at \(\text{h}_{\text{Tx}}=0.04\) m) and \(-48.6\) dBm (at \(\text{h}_{\text{Tx}}=0.5\) m). When comparing the curves shown in Figure 5 for H-H antennas at \(\text{h}_{\text{Tx}}=\lambda/3\) m, it is evident that raising the receiving antenna above the corn (from 2.0 m to 3.4 m) reduced the oscillations in the received signal. This reduction occurred due to the decreased destructive interference at 0.9 GHz. This effect was less noticeable at \(\text{h}_{\text{Tx}}=0.5\) m (Figure 5b), as in the case of co-polarized vertical-to-vertical antennas. At 2.4 GHz, the height of the receiving antenna did not affect the received signal level when the transmitting antenna in the corn field was at a height of \(\lambda/3\) m.  
Figure 5: Received signal level variation with distance at 0.9 GHz for co-polarized H-H and V-V antennas: (**a**) transmitting antenna is placed at a height of \(\lambda/3\) m above ground (\(\text{h}\text{Tx}=0.11\) m); (**b**) transmitting antenna is placed at a height of 0.5 m above ground (\(\text{h}\text{Tx}=0.5\) m). Figures 7 and 8 depict how the transmitting antenna height (sensor node antenna) influenced the received signal level and communication range. We observed that, at 0.9 GHz, H-H antennas, the receiving signal level increased, on average, by 8.7 dB (at h\({}_{\text{Rx}}\) = 2.0, Figure 7a) and 9.6 dB (at h\({}_{\text{Rx}}\) = 3.4, Figure 7b) after increasing the transmitting antenna height from 0.11 m to 0.5 m above ground. This effect was less noticeable at 2.4 GHz (Figure 8), as in the case of co-polarized vertical-to-vertical antennas (Figures 7 and 8).