volume | PIER Journals

Abstract

Unmanned aerial FPV systems demand ultra-low latency, high-reliability communication. At high speeds and in cluttered environments, Doppler shifts and rapid multipath changes significantly increase packet error rates (PER). This paper introduces a novel solution: real-time geometry tuning of a circularly polarized helical antenna array to mitigate these effects in ExpressLRS (ELRS) long-range FPV control links. Using full-wave simulations (Ansys HFSS) and blind field trials, we validate system performance. A new analytical framework integrates Doppler-induced frequency offset into the antenna's radiation pattern and PER model. The adaptive array autonomously adjusts coil pitch and diameter based on velocity and attitude, reducing PER by 20% at speeds over 150 mph. It also maintains near-unity VSWR, preventing reflection spikes, and halves RSSI variation, indicating improved link stability. These results demonstrate that tunable helical antennas can effectively mitigate Doppler and multipath impairments in high-mobility UAV environments, informing future antenna designs and supporting the development of AI-integrated, adaptive RF systems for drone racing and autonomous swarms.

1. ExpressLRS Project. Expresslrs --- Open source RC link for radio control, https://www.expresslrs.org/, 2025.
doi:10.34218/ijdmt.5.3.2014.30320140503011

2. Lee, Hakmin, Ye-Bon Kim, and Han Lim Lee, "Reconfigurable antenna for UAV-assisted wide coverage air-to-ground communications," IEEE Access, Vol. 10, 88034-88042, 2022.
doi:10.1109/access.2022.3199700

3. Maih, W., "State of the art in reconfigurable antennas," Proceedings of MAIH, 2024.

4. Balanis, Constantine A., Antenna Theory: Analysis and Design, 4th Ed., John Wiley & Sons, 2016.
doi:10.1002/0471654507.erfme007

5. Antenna-Theory.com. Helical antenna (helix antenna) theory, https://www.antenna-theory.com/antennas/helix.php.

6. DroneTrest, The complete guide to FPV antennas, https://www.dronetrest.com/t/the-complete-guide-to-fpv-antennas/6584, 2018.

7. Taylor, R. and M. White, "Antenna polarization effects in FPV drone communications," Journal of Wireless Engineering, Vol. 10, No. 2, 76-84, 2021.
doi:10.1007/978-1-4615-2758-9_23

8. Wu, Z.-H., W.-Q. Che, B. Fu, P.-Y. Lau, and E. K. N. Yung, "Axial mode elliptical helical antenna with parasitic wire for CP bandwidth enhancement," IET Microwaves, Antennas & Propagation, Vol. 1, No. 4, 943-948, 2007.
doi:10.1049/iet-map:20060239

9. Heading, J., "Abundance of invariant equations and properties for wave propagation in a space of arbitrary dimensions," Journal of Physics A: Mathematical and General, Vol. 17, No. 4, 917, 1984.
doi:10.1088/0305-4470/17/4/032

10. Biowei, Godday, Sulaiman Adeniyi Adekola, Ayibapreye Kevin Benjamin, and Kamoli Akinwale Amusa, "Modelling of electromagnetic wave propagation at free space-human skin interface," Nigerian Journal of Technology, Vol. 43, No. 1, 123-130, 2024.
doi:10.4314/njt.v43i1.14

11. Piao, Shiyuan, Hong Gu, Aina Wang, and Pan Qin, "A domain-adaptive physics-informed neural network for inverse problems of Maxwell's equations in heterogeneous media," IEEE Antennas and Wireless Propagation Letters, Vol. 23, No. 10, 2905-2909, 2024.
doi:10.1109/lawp.2024.3413851

12. Li, Qingsong and Simon Maher, "Deriving an electric wave equation from Weber's electrodynamics," Foundations, Vol. 3, No. 2, 323-334, 2023.
doi:10.3390/foundations3020024

13. Henshaw, William D., "A high-order accurate parallel solver for Maxwell's equations on overlapping grids," SIAM Journal on Scientific Computing, Vol. 28, No. 5, 1730-1765, 2006.
doi:10.1137/050644379

14. Räbinä, Jukka, Sanna Mönkölä, and Tuomo Rossi, "Efficient time integration of Maxwell's equations with generalized finite differences," SIAM Journal on Scientific Computing, Vol. 37, No. 6, B834-B854, 2015.
doi:10.1137/140988759

15. Ansys, Inc., HFSS User Guide: Full-Wave 3D EM Simulation, Ansys, 2023.
doi:10.21236/ada624196

16. Volakis, John Leonidas and John Leonidas Volakis, Antenna Engineering Handbook, Vol. 1755, McGraw-Hill, New York, 2007.
doi:10.21236/ada434995

17. Rao, S. S. S. R., T. V. Ramana, and E. S. Rameswarudu, "Bandwidth and gain enhancement in helical antenna for Ku band and satellite communication applications," International Journal of Research in Engineering and Technology (IJRET), Vol. 5, Special Issue 5, 81-83, 2016.
doi:10.1109/icssit53264.2022.9716525

18. Dinkić, J. L., "Nonuniform helical antennas," School of Electrical Engineering, University of Belgrade, Serbia, 2021.
doi:10.1155/2019/8421809

19. Ojaroudi Parchin, Naser, Haleh Jahanbakhsh Basherlou, Yasir I. A. Al-Yasir, Ahmed M. Abdulkhaleq, and Raed A. Abd-Alhameed, "Reconfigurable antennas: Switching techniques --- A survey," Electronics, Vol. 9, No. 2, 336, 2020.
doi:10.3390/electronics9020336

20. Subbaraj, Sangeetha and Shweta B. Thomas, "Reconfigurable antennas and their practical applications --- A review," Radio Science, Vol. 58, No. 9, 1-13, 2023.
doi:10.1029/2023rs007656

21. Pozar, David M., Microwave Engineering: Theory and Techniques, 4th Ed., John Wiley & Sons, 2021.
doi:10.1109/mwsym.2012.6259373

22. Brown, J. and S. Green, "Adaptive beam steering in UAV communication networks," IEEE Transactions on Aerospace and Electronic Systems, Vol. 58, No. 1, 301-310, 2022.
doi:10.1109/taes.2019.2949384

23. Zeain, Mohammed Yousif, Maisarah Abu, Apriana Toding, Zahriladha Zakaria, Hussein Alsariera, Ihsan Ullah, Ali Abdulateef Abdulbari, Hamizan Yon, Bilal Salman Taha, and Muhammad Inam Abbasi, "Advanced helical antenna design for X-band applications using AI," Progress In Electromagnetics Research C, Vol. 153, 201-211, 2025.
doi:10.2528/pierc25011305

Mr. Ethan Chien

Dr. Jan Steckel