# Exploring Carbon-Fiber UAV Structures as Communication Antennas for Adaptive Relay Applications
## 3 Results  
### Antenna Characterization Results  
As a result of the experiment, the curve of the reflection coefficient as a function of frequency was plotted for both antennas, as shown in Figure 12.  
The graph highlights two significant minima around the frequencies of 381.45 MHz and 1.2 GHz, corresponding to the resonance frequencies of the tested antennas. At these points, the S11 values drop below \(-\)30 dB, indicating very good impedance matching and, consequently, minimal reflection losses. Additionally, both antennas exhibit similar behavior, which confirms the consistency of the construction and the measurement methodology. The analysis of the graph suggests that the second resonance frequency, 1.2 GHz, offers wider bandwidth and can therefore be considered more suitable for the intended applications where broad spectral coverage is required. This observation will form the basis for choosing the central frequency in the following stages of the study. Figure 11: Holes position, where A—Antenna A.  
Figure 10: Setup for the two-ray model, with no holes (**a**), with hole (**b**). Figure 13 presents the Voltage Standing Wave Ratio (VSWR) response of Antenna A and Antenna B, obtained experimentally with a Vector Network Analyzer (plot a) and calculated from the reflection coefficient S\({}_{11}\) in MATLAB (plot b). Although VSWR and S\({}_{11}\) convey equivalent information regarding the fraction of incident power reflected at the antenna feed, VSWR is frequently employed to define impedance-matching thresholds--in this case, VSWR \(\leq\) 2 corresponds to \(\mid\)S\({}_{11}\)\(\mid\)\(\leq\)\(-\)10 dB. Both measured and calculated curves reveal two pronounced resonance minima at approximately 381 MHz and 1.20 GHz, confirming the dual-band nature of the design. The experimental VSWR data exhibit minima of roughly 1.1 at 381 MHz and 1.2 at 1.20 GHz. Each resonant band maintains VSWR \(\leq\) 2 over a contiguous frequency span of approximately 500 MHz--namely from about 130 MHz to 630 MHz in the lower band and from about 950 MHz to 1.45 GHz in the upper band. The close correspondence between the curves for Antenna A and Antenna B underscores the reproducibility of the fabrication process and the reliability of the measurement setup; only negligible deviations appear, primarily attributable to minor connector or cable mismatches. Figure 12: Reflection coefficient. Figure 13: VSWR variation, (a) measured and (b) calculated. The theoretical VSWR curves, derived in MATLAB from the simulated S\({}_{11}\) values, align almost perfectly with the measured data. The locations of the VSWR minima and the extents of the VSWR \(\leq\) 2 bands coincide with their experimental counterparts, thereby validating the accuracy of the electromagnetic model. The simulated response is marginally smoother, reflecting the idealized, lossless conditions assumed in the computational environment, whereas the measured curves include slight irregularities arising from real-world parasitic reflections and material losses. The dual-band operation observed at 0.38 GHz and 1.20 GHz, each with a bandwidth of approximately 500 MHz under the VSWR \(\leq\) 2 criterion, demonstrates that the antenna achieves excellent impedance matching to a 50 \(\Omega\) feed line across two widely separated frequency ranges. This wide usable bandwidth affords considerable flexibility for multi-channel or multi-standard applications without requiring retuning. Figure 14 provides a side-by-side comparison of the measured (solid lines) and calculated (dashed lines with square markers) VSWR responses for Antenna A (left) and Antenna B (right), allowing clear visualization of the fidelity between experiment and simulation. For Antenna A, the two principal resonance minima--at approximately 381 MHz and 1.20 GHz--are reproduced almost identically in both the measured and calculated curves.