High-Efficiency and Wideband Coaxial Dual-Tube Hybrid Monopole Water Antenna

A coaxial dual-tube monopole water antenna with high efficiency and wideband characteristics is presented. On the basis of the original single-tube monopole salty-water antenna, a coaxial tube filled with distilled water is inserted inside, acting as a dielectric loading of the feeding probe to introduce another mode. The distilled water column acts as the loading part rather than the radiation factor to guarantee high radiation efficiency. Both dual-tube and single-tube antennas are fabricated and compared. The simulated and measured results show reasonably good agreement. By employing the dual-tube technique, the radiation efficiency is increased from 15% to 47% and 52% to 84% in the operating frequency range. Furthermore, the impedance bandwidth of |S₁₁| <; -15 dB is increased from 38.24% to 57.27%.