Abstract: Unmanned aerial vehicles （UAVs） have been extensively utilized in maritime disaster monitoring and emergency rescue operations. As a critical component of UAV navigation and positioning systems， the Global Navigation Satellite System （GNSS） onboard antenna plays a critical role in ensuring high-precision positioning and stable signal reception in complex maritime environments. Its performance is directly linked to the reliability of UAVs in executing maritime disaster monitoring and emergency rescue missions. However， under extreme natural disaster conditions such as typhoons， existing antennas still exhibit limitations， including narrow beamwidth and unstable circular polarization characteristics， which significantly degrade navigation reliability and pose serious risks to UAV operational safety. To address these challenges， this study proposed a wide-beam circularly polarized omnidirectional antenna. The antenna adopts a three-layer coaxially stacked patch configuration. Symmetrically etched arc-shaped slots were incorporated into the patches to introduce additional reactance components， while uniformly distributed metallized vias （shorting pins） along the patch edges established electrical connections between the radiating patches and ground layer. By integrating capacitive coupling feeding technology， this design optimizes surface current distribution and excites multi-mode resonances， thereby broadening both the axial ratio bandwidth and impedance bandwidth of the antenna. Simulation results demonstrated that the designed antenna achieved an axial ratio bandwidth of 49.11% and an impedance bandwidth of 29.7% over the frequency range of 1.06~1.75 GHz. Furthermore， it maintained stable circularly polarized radiation characteristics across a 176° elevation angle and a full 360° azimuthal coverage， achieving broadband impedance matching and wide-angle circular polarization performance. The antenna exhibited a peak gain exceeding 1.8 dB and cross-polarization discrimination ratio exceeding 15 dB， effectively suppressing multipath interference. For experimental validation， a prototype of the proposed antenna was fabricated and tested. Measured results aligned closely with simulated predictions， confirming the robustness of the design. Additionally， the low-profile and lightweight structure of the antenna is well-suited for integration into compact UAV platforms， addressing the stringent miniaturization requirements of practical applications.