## 3 Results and Discussion
### Measurement Results
Comparing the curves in Figure 8, we can see that at 2.4 GHz, the received signal levels for transmitting antenna heights of 0.04 m and 0.5 m were nearly equal at a receiving antenna height of 2.0 m.  
Figure 6: Received signal level variation with distance at 2.4 GHz for co-polarized H-H and V-V antennas: (**a**) transmitting antenna is placed at a height of \(\lambda/3\) m above ground (h\({}_{\text{Tx}}\) = 0.04 m); (**b**) transmitting antenna is placed at a height of 0.5 m above ground (h\({}_{\text{Tx}}\) = 0.5 m). Figure 7: Received signal level variation with distance at 0.9 GHz for co-polarized H-H and V-V antennas: (**a**) receiving antenna height below the corn height (h\({}_{\text{Rx}}\) = 2.0 m); (**b**) receiving antenna height above the corn height (h\({}_{\text{Rx}}\) = 3.4 m). The results show that higher receiving levels were measured for co-polarized H-H antennas than for co-polarized V-V antennas for all scenarios in O-LoS conditions. The difference in the received signal level for vertical and horizontal polarization was due to the density of vegetation, its structure (leaves and stalks), and the water content [41], but predominantly (mainly) because in the corn field, the biomass was concentrated in the vertically oriented stalks planted in rows, as described in Section 2.1. For horizontally polarized waves, the electric field was perpendicular to the corn stalks. For vertically polarized waves, the electric field was parallel to the corn stalks, coupling strongly. By comparing the curves of Figure 5, we observe that at 0.9 GHz co-polarized H-H antennas, the receiving signal level increased, on average, by 12.5 dB (at h\({}_{\text{Tx}}\) = 0.11 m, h\({}_{\text{Rx}}\) = 2.0, Figure 5a), 11.6 dB (at h\({}_{\text{Tx}}\) = 0.11 m, h\({}_{\text{Rx}}\) = 3.4, Figure 5a), and 16 dB (at h\({}_{\text{Tx}}\) = 0.5 m, h\({}_{\text{Rx}}\) = 2.0 and h\({}_{\text{Rx}}\) = 3.4, Figure 5b) in the same cases of co-polarized V-V antennas. From the results, we can conclude that at 0.9 GHz, the antenna polarization has an essential impact on the received signal level in the wireless sensor networks deployed in an agricultural environment for IoT-based smart agriculture. From the obtained results (Figures 5-8) summarized in Tables 2 and 3, we can examine how the height of the transmitting and receiving antennas impacted the coverage area of a wireless sensor network for IoT-based smart agriculture. We assume that, for a reliable data connection between the sensor node (transmitter) and the gateway (receiver), the minimum received level should be \(-\)106 dBm (there would not be successful data transmission if the level fell below this threshold). Our analysis revealed that increasing the height of the receiving antenna above the corn height, from 2.0 m to 3.4 m, expanded the coverage area. Thus, at 0.9 GHz, for H-H antennas, with h\({}_{\text{Tx}}\) = 0.11 m (h\({}_{\text{Tx}}\) = \(\lambda\)/3 m) and an Rx antenna height of 3.4 m, the distance range was 105 m, whereas at an Rx antenna height of 2.0 m, it was 90 m. At 2.4 GHz, for H-H antennas, with h\({}_{\text{Tx}}\) = 0.04 m (h\({}_{\text{Tx}}\) = \(\lambda\)/3 m) and an Rx antenna height of 3.4 m, the communication distance range was 45 m, whereas at an Rx height of 2.0 m, it was 40 m. Also, we observed a more significant increase in the communication distance between the Tx-Rx antennas by increasing the transmitting antenna height from h\({}_{\text{Tx}}\) = \(\lambda\)/3 (0.11 m at 0.9 GHz and 0.04 m at 2.4 GHz) to 0.5 m above ground level. Consequently, we can conclude that connectivity in a wireless sensor network for agriculture applications in a corn field is more sensitive to the sensor antenna's height from the ground than to the gateway antenna's height from the ground. Figure 8: Received signal level variation with distance at 2.4 GHz for co-polarized H-H and V-V antennas: (**a**) receiving antenna height below the corn height (h\({}_{\text{Rx}}\) = 2.0 m); (**b**) receiving antenna height above the corn height (h\({}_{\text{Rx}}\) = 3.4 m).