# Exploring Carbon-Fiber UAV Structures as Communication Antennas for Adaptive Relay Applications
## 4 Discussion  
The experimental assessment of the carbon-fiber antenna integrated into the UAV frame demonstrated close correspondence with theoretical models while also revealing several areas for refinement. In the discussion chapter, return-loss (S\({}_{11}\)) values as low as \(-20\) dB to \(-40\) dB were cited--figures indicative of exemplary matching--yet both simulation and measurement exhibited fewer negative peaks. Such discrepancies, though modest, underscore the importance of aligning reported S\({}_{11}\) values with those observed in practice. Figure 24: Rician distribution. Quantitatively, the theoretical reflection coefficient at 381.45 MHz was \(-\)15.2 dB (VSWR = 1.82), whereas the measured dip reached only \(-\)14.6 dB (VSWR = 1.95). Similarly, at 1.19 GHz, the simulation predicted \(-\)12.8 dB (VSWR = 1.91), but the experiment recorded \(-\)12.1 dB (VSWR = 2.04). These small offsets likely arise from connector tolerances, calibration drift, and the intrinsic material non-uniformity of the carbon-fiber substrate. To recover a few decibels of return loss, one might employ a thin conductive backing--such as copper foil--or refine the feed-line transition to reduce parasitic reflections. A more substantial departure was noted in realized gain. Whereas a conventional \(\lambda\)/4 monopole at 1.2 GHz (L\({}_{\text{monopole}}\simeq\) 6.25 cm) typically achieves approximately 5 dBi, the carbon-fiber element delivered only 0.15-0.19 dBi. Antenna gain directly influences both beamwidth and the antenna's tolerance to misalignment and environmental perturbations. In general, higher-gain elements exhibit narrower half-power beam widths, so even small deviations in orientation or positioning can produce substantial drops in received power. Conversely, our low-gain, quasi-omnidirectional monopole maintains a broad beam--nearly 360\({}^{\circ}\) in azimuth and roughly 40-50\({}^{\circ}\) in elevation for VSWR \(\leq\) 2--making it more forgiving of slight misalignments or UAV attitude changes. For example, the 90\({}^{\circ}\) polarization-mismatch test produced a 15 dB drop in received power, but as a largely omnidirectional radiator, the monopole retained connectivity over a wide angular range. By contrast, a high-gain element would have required precise pointing: a few degrees of pitch or roll could shift the main lobe outside the target receiver's orientation, resulting in rapid link loss. Moreover, narrow beams tend to be more susceptible to multipath-induced nulls since off-axis reflections can constructively or destructively interfere within a limited acceptance angle. In our small-scale fading measurements at 5 m, the Rician K-factor and 5.57 dB indicated a strong line-of-sight component, but a higher-gain antenna with a narrower acceptance angle would have been more affected by occasional transient multipath reflections (seen as an outlier near 50 dB). In summary, the relatively low gain of our carbon-fiber monopole yields a broad beam that is inherently tolerant to UAV motion and environmental fluctuations--a trade-off that sacrifices peak link budget in exchange for reliable connectivity under dynamic conditions. Potential strategies to enhance gain without altering the UAV's overall architecture include the application of a high-conductivity coating, incorporation of parasitic directors or reflectors to shape the near-field, and slight extensions to the underlying metal frame to enlarge the effective ground plane. To contextualize our results, Table 1 compares several representative UAV-mounted antennas from the literature--including directive probes, blade-style designs, and quadcopter frame patches--against our carbon-fiber monopole. By examining material, operating bands, bandwidth, gain, and physical dimensions side by side, one can clearly see the trade-offs between embedded structural antennas and more conventional metallic or PCB solutions.