Design of a Broadband Flexible Monopole Antenna for Open Sea Communication

For the requirements of frequency modulation (FM) broadcasting communication in open-sea areas (resonant frequency 98 MHz), ground-based station signals are difficult to cover, and the large size of rigid buoy antennas limits the number that vessels can carry. To address this issue, this paper designs a flexible buoy antenna, which achieves a volume compression ratio of 88% in the folded state. The antenna is a vertical monopole type, with a center frequency of 98 MHz and dimensions of 879 mm × 120 mm. Simulation results show that S11 remains below −10 dB across 90–105 MHz, reaching a minimum of −30 dB. Measurement results demonstrate that within the 88–107 MHz band, S11 is below −10 dB, with the minimum value increasing in magnitude to −24 dB. The measured center frequency achieves S11 = −21 dB, and the VSWR remains below 3 across the entire operating frequency band, meeting the impedance matching requirements of marine broadcasting systems. On this basis, we further conduct simulations under seawater loading. The results show that seawater induces a resonance down-shift and efficiency degradation; however, by adjusting the radiator length L, the resonance and matching can be restored to the target band while maintaining VSWR ≤ 3 and stable in-band radiation, thereby enabling a rapid, single-parameter, engineering-oriented retuning.