## 3 Results and Discussion  
The comparison of the complex dielectric permittivity estimation values calculated from the three models described in the earlier sections demonstrated that dielectric soil properties using the Frequency Domain Reflectometry (FDR) sensing method offered significant advantages over traditional methods. However, challenges related to the underground transmission channel were addressed by achieving a self-resonant frequency of 433 MHz. A crucial aspect was the selection of inductance, as at the resonance frequency the inductive reactance of the inductor and the capacitive reactance of the capacitor canceled each other out: they possessed equal magnitudes but opposite signs. This cancellation occurred because, at resonance, the inductive and capacitive components of the circuit were in phase opposition, leading to their effective cancellation. Consequently, the variation in the capacitance of the soil mixture influenced the inductance value at the self-resonant frequency, resulting in changes in output impedance that affected the dielectric permittivity estimation. The main criterion for selecting the inductance was to accommodate a wide range of dielectric permittivities at the self-resonant frequency of 433 MHz. The graphs in Figures 15 and 16 indicate effective gamma detection for a permittivity range of up to 5, particularly when utilizing a varicap to broaden the range for accurate permittivity estimation. The calculated dielectric permittivity of the proposed buried probe enabled effective determination of soil moisture content, with the best performance observed for the model using lossy impedance. Moreover, accurate estimation of dielectric permittivity was noted for shorter electrical lengths. Several key conclusions and limitations of the proposed probe can be outlined:  
* In the region of the measured self-resonance frequency at 433 MHz, even a minor difference in fixture design and calibration can significantly impact the readings, leading to either a large positive inductance or a large negative capacitance. * The effect of residual fixture capacitance is more pronounced with lower-value inductors, while it is often negligible for higher values. * Slight differences in fixture design and calibration can have substantial effects on the calculated dielectric permittivity. * The poor estimation of dielectric permittivity for low values can be attributed to the limited reflection coefficient at the resonance frequency, restricting it to the self-resonance frequency. Maintaining and improving soil resources requires accurate and exact information on soils, especially when tackling major environmental issues, including agricultural abandonment, organic carbon loss, and declining soil health. Numerous methods have been developed for measuring the dielectric permittivity of soil, including the coaxial probe [26; 27; 28], transmission line [29; 30], and parallel plate capacitance [18; 31]. Each method, as summarized in Table 6, has its own limitations and constraints. Key factors such as cost, size, accuracy, and convenience influence the selection  
Figure 27: Dielectric permittivity error vs. estimated dielectric constant. of the most suitable method. Additionally, considerations such as frequency range, material characteristics, and temperature play a significant role in the decision-making process. To minimize production costs, we opted for the parallel plate capacitance method, which is straightforward to construct, using two parallel metal plates. The uniform electric field established between these plates simplifies calculations and analysis. The main advantages of using parallel plate capacitance include its suitability for high-loss materials and the relative ease of measurement. This method is particularly effective at low frequencies, whereas transmission line and coaxial probe methods are better suited for high frequencies and for measuring dielectric permittivity in solids and liquids. The coaxial probe, on the other hand, offers high accuracy for high-loss materials.