# Exploring Carbon-Fiber UAV Structures as Communication Antennas for Adaptive Relay Applications
## 3 Results
### Propagation Models Results  
In the first series of tests in the free space link model, the aim was to verify the classic inverse-square law in the antenna's far-field (Fraunhofer) region by measuring the received power at a fixed transmit level of 10 dBm and a carrier frequency of 1.2 GHz. A stable continuous-wave source fed a calibrated half-wave dipole transmitting antenna, while a matched dipole receiver--mounted on a precision linear track--collected the power readings from 0.5 to 0.5 cm at each measurement at radial distances starting from 2 m out to 8 m. According to the Friis transmission formula, one expects that every time the separation doubles, the received power drops by approximately 6 dB. Figure 17 illustrates the variation of received power (in dBm) as a function of the distance between the transmitting (Tx) and receiving (Rx) antennas, with values ranging from 0 to 8 m. The blue asterisks represent the measured values, while the red curve represents a polynomial fit, which corresponds to the Friis free-space path loss equation, implying that the received power is inversely proportional to the square of the distance. Figure 17 also illustrates the relationship between received power and distance between the transmitting and receiving antennas. The measured values, shown as blue asterisks, follow the expected trend described by the red curve, which models the inverse square law of the Friis transmission equation. As the distance increases, the received power decreases, confirming the theoretical behavior of signal attenuation in free space. While the overall trend aligns well with the model, small deviations are visible--especially between 3 and 6 m--likely due to environmental influences such as multipath propagation, measurement uncertainty, or slight antenna misalignments. Despite these discrepancies, the general consistency between experimental data and theoretical predictions validates the accuracy of the setup and confirms the expected performance of the antenna system across various distances. Figure 16: Radiation pattern in Elevation. The calculated Fresnel and Fraunhofer boundary distances further support the validity of the measured data. For the given antenna setup, both regions converge at approximately 3.38 m, marking the transition point from the reactive near-field to the radiative far-field. Below this threshold, signal behavior is more susceptible to near-field effects, including reactive coupling and complex interference patterns, which may account for the slight anomalies observed in the measurements around 3 to 4 m. Beyond this limit, the measured power closely follows the theoretical free-space model, indicating that the antennas operate within the far-field region where the inverse square law becomes a reliable approximation. This alignment underscores the importance of considering electromagnetic field regions when analyzing antenna performance and confirms that the majority of measurements were conducted under appropriate far-field conditions. Beyond approximately 5 m, the measured power begins to dip slightly below the ideal Friis curve. This extra loss can be attributed to practical, real-world factors: even with absorbers in place, small amounts of multipath or ground-bounce may persist; cable attenuation grows with length; and tiny misalignments become more impactful at lower signal levels. Such effects introduce additional path loss that diverges from the idealized inverse-square prediction. Importantly, these deviations remain modest--in the order of a few decibels--which speaks to the robustness of our matching network, antenna geometry, and alignment procedure. In operational UAV links at longer ranges, engineers would typically add link margin by increasing transmit power, selecting antennas with higher gain, or further fine-tuning the impedance match to ensure reliable communication under these non-ideal conditions.