Abstract
A low-profile omnidirectional circularly polarized antenna is proposed by integrating a patch antenna with a loop antenna. Omnidirectional vertically polarized radiation is achieved by modifying the resonant mode within the cavity of the patch antenna, whereas omnidirectional horizontally polarized radiation is realized through the incorporation of composite right/left-handed (CRLH) line segments into the loop antenna. The loop antenna is fed by a microstrip balun, and a common-mode suppression filter is inserted between the loop antenna and the balun to mitigate common-mode interference induced by the excitation of the patch antenna. An unequal Wilkinson power divider, together with transmission lines, is employed to control the power ratio and phase difference between the two antennas, thereby generating circular polarization. Simulated results demonstrate good impedance matching at the center frequency of 2.4 GHz. The axial ratio in the xy-plane remains below 3 dB, with an omnidirectionality of approximately 1 dB. Although the measured results exhibit slight degradation due to environmental effects, they are in good agreement with the simulations, thereby validating the feasibility of the proposed design.
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All data generated or analyzed during this study are included in this published article, including all antenna geometrical parameters, material properties, and measurement results.
References
Shi, J., Wu, X., Qing, X. & Chen, Z. N. An omnidirectional circularly polarized antenna array. IEEE Trans. Antennas Propag. 64(2), 574–581 (2016).
Li, B., Liao, S.-W. & Xue, Q. Omnidirectional circularly polarized antenna combining monopole and loop radiators. IEEE Antennas Wirel. Propag. Lett. 12, 607–610 (2013).
Wu, J. & Sarabandi, K. Compact omnidirectional circularly polarized antenna. IEEE Trans. Antennas Propag. 65(4), 1550–1557 (2017).
Du, C. et al. A compact single-layer high-gain omnidirectional-like circularly polarized array antenna based on complementary source radiation. IEEE Antennas Wirel. Propag. Lett. 22(10), 2547–2551 (2023).
Positano, F., Santamaria, L., Staraj, R. & Lizzi, L. Compact omnidirectional circularly polarized antenna via Alford loop and wire-patch structure combination. IEEE Open J. Antennas Propag. 5(2), 277–285 (2024).
Akmal, M., Alieldin, A. & Eldamak, A. R. A high-power sandwiched omnidirectional circularly polarized antenna for GNSS systems. IEEE Access 11, 31165–31176 (2023).
Liu, X. et al. Horizontally and circularly polarized omnidirectional filtering dielectric resonator antenna. IEEE Trans. Antennas Propag. https://doi.org/10.1109/TAP.2026.3653179 (2026).
Xu, Y., Peng, Z., Wen, S. & Dong, Y. Omnidirectional circularly polarized antenna array with planar configuration. IEEE Trans. Antennas Propag. 70(9), 8602–8607 (2022).
Qin, Y. et al. A compact dual-band omnidirectional circularly polarized filtering antenna for UAV communications. IEEE Trans. Veh. Technol. 72(12), 16742–16747 (2023).
Wu, D., Chen, X., Yang, L., Fu, G. & Shi, X. Compact and low-profile omnidirectional circularly polarized antenna with four coupling arcs for UAV applications. IEEE Antennas Wirel. Propag. Lett. 16, 2919–2922 (2017).
Janpangngern, P., Kuse, R., Phongcharoenpanich, C. & Fukusako, T. Omnidirectional circularly polarized monopole antennas on artificial magnetic conductor ground plane. IEEE Access 12, 74808–74818 (2024).
Ding, Z. et al. A circularly polarized omnidirectional Rydberg atomic sensor using characteristic mode analysis. IEEE Trans. Antennas Propag. 72(12), 9558–9563 (2024).
Huang, G.-L. et al. An omnidirectional monopole antenna with horizontal radiation enhancement for aircraft wireless avionics intra-communications application. IEEE Antennas Wirel. Propag. Lett. 24(10), 3480–3484 (2025).
Park, B.-C. & Lee, J.-H. Omnidirectional circularly polarized antenna utilizing zeroth-order resonance of epsilon negative transmission line. IEEE Trans. Antennas Propag. 59(7), 2717–2721 (2011).
Narbudowicz, A., Bao, X. L. & Ammann, M. J. Dual-band omnidirectional circularly polarized antenna. IEEE Trans. Antennas Propag. 61(1), 77–83 (2013).
Mao, C. X. et al. Compact patch antenna with vertical polarization and omnidirectional radiation characteristics. IEEE Trans. Antennas Propag. 69(2), 1158–1161 (2021).
Iizuka, H. & Hall, P. S. Omnidirectional left-handed loop antenna. In: Proc. IEEE Int. Symp. Antennas Propag. 27–30 (2006).
Borja, A. L., Hall, P. S., Liu, Q. & Iizuka, H. Omnidirectional loop antenna with left handed loading. IEEE Antennas Wirel. Propag. Lett. 6, 495–498 (2007).
Locatelli, A., Capobianco, A. -D., Boscolo, S., Modotto, D., Midrio, M. & De Angelis, C. Low-profile CRLH omnidirectional loop antenna for mobile wireless communications. In: 2012 42nd European Microwave Conference 401–403 (Amsterdam, Netherlands, 2012).
Shen, A. L. et al. Dual-band balun with flexible frequency ratios. Electron. Lett. 50(17), 1213–1214 (2014).
Hsiao, C.-Y., Huang, Y.-C. & Wu, T.-L. An ultra-compact common-mode bandstop filter with modified-T circuits in integrated passive device (IPD) process. IEEE Trans. Microw. Theory Tech. 63(11), 3624–3631 (2015).
Pozar, D. M. Microwave Engineeloop 4th edn. (Wiley, 2012).
Funding
This work was supported by the National Science and Technology Council, R.O.C, under Grant No. 114-2221-E-A49 -110 -.
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J.-H.T. performed the antenna simulations, prepared the figures, and drafted the main manuscript. Y.-J.C. conceived the research idea, developed the antenna architecture, supervised the study, and revised the manuscript. F.-C.C. provided research supervision and funding support, and contributed to manuscript revision. All authors reviewed and approved the final manuscript.
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Tai, JH., Chi, YJ. & Chen, FC. A low-profile omnidirectional circularly polarized antenna using integrated patch and CRLH loop structures. Sci Rep (2026). https://doi.org/10.1038/s41598-026-47310-2
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DOI: https://doi.org/10.1038/s41598-026-47310-2
