# Exploring Carbon-Fiber UAV Structures as Communication Antennas for Adaptive Relay Applications
###### Abstract  
This study investigates the electromagnetic performance of two carbon fiber monopole antennas integrated into a UAV copper frame, with emphasis on design adaptation, impedance matching, and propagation behavior. A comprehensive experimental campaign was conducted to characterize key parameters such as center frequency, bandwidth, gain, VSWR, and S\({}_{11}\). Both antennas exhibited dual-band resonance at approximately 381 MHz and 1.19 GHz, each achieving a 500 MHz bandwidth where VSWR \(\leq\) 2. The modified antenna achieved a minimum reflection coefficient of -14.6 dB and a VSWR of 1.95 at 381.45 MHz, closely aligning with theoretical predictions. Gain deviations between measured (0.15-0.19 dBi) and calculated (0.19 dBi) values remained within 0.04 dB, while received power fluctuations did not exceed 1.3 dB under standard test conditions despite the composite material's finite conductivity. Free-space link-budget tests at 0.5 m and 2 m of separation revealed received-power deviations of 0.9 dB and 1.3 dB, respectively, corroborating the Friis model. Radiation pattern measurements in both azimuth and elevation planes confirmed good directional behavior, with minor side lobe variations, where Antenna A displayed variations between 270\({}^{\circ}\) and 330\({}^{\circ}\) in azimuth, while Antenna B remained more uniform. A 90\({}^{\circ}\) polarization mismatch led to a 15 dBm signal drop, and environmental obstructions caused losses of 9.4 dB, 12.6 dB, and 18.3 dB, respectively, demonstrating the system's sensitivity to alignment and surroundings. Additionally, signal strength changes observed in a Two-Ray propagation setup validated the importance of ground reflection effects. Small-scale fading analysis at 5 m LOS indicated a Rician-distributed envelope with mean attenuation of 53.96 dB, \(\sigma_{\text{dB}}\) = 5.57 dB, and a two-sigma interval spanning 42.82 dB to 65.11 dB; the fitted K-factor confirmed the dominance of the LOS component. The findings confirm that carbon fiber UAV frames can serve as effective directional antenna supports, providing proper alignment and tuning. These results support the future integration of lightweight, structure-embedded antennas in UAV systems, with potential benefits in communication efficiency, stealth, and design simplification. Accepted: 16 June 2025  
1427313 through dynamic environments with potential signal obstructions, such as high buildings, skyscrapers, bridges or tunnels or dense urban areas as places with heavy tree cover. This creates a multipath environment where signals may reflect off various surfaces, leading to increased latency and signal degradation [1]. These factors can cause GPS issues, making it difficult for navigation systems to provide precise positioning in real time. The reduction in GPS accuracy compromises not only location tracking but also the efficiency of autonomous navigation algorithms [2]. Interruptions may occur due to route changes, customer cancellations, or signal interference from static ground-based antennas obstructed by buildings or other obstacles [3; 4; 5]. A reliable communication infrastructure is essential for seamless operation, enabling efficient control and monitoring between ground stations and drones and allowing dynamic rerouting when needed to ensure delivery reliability [6]. Advanced communication protocols and adaptive routing strategies can help mitigate these issues, ensuring minimal downtime and enhanced operational efficiency [7]. Furthermore, addressing these communication challenges is a major problem, particularly in adverse weather conditions, such as strong wind or heavy storms or during unexpected events, which may hinder operational capabilities [8].