High-Efficiency Miniaturized Dipole Antenna for Single-Sided Metal Wall Environment Inside Inspection Vehicle

To achieve high aperture efficiency and miniaturization for a dipole antenna operating in an environment with a single-sided metal wall inside an inspection vehicle, this paper analyzes and optimizes the antenna’s performance using multi-arm folding and current control methods. First, based on the effective current length theory, a four-arm folded dipole antenna fed by a vertical microstrip line is proposed. While maintaining the effective current length, the radiating arms are folded horizontally and vertically, respectively, achieving antenna miniaturization. Second, a back cavity is added beneath the antenna, and a horizontal strip is introduced to concentrate the resonant current in the radiation plane, thus improving the aperture efficiency and gain of the four-arm dipole antenna. Finally, to address the impedance mismatch and radiation pattern distortion caused by the single-sided metal wall inside the inspection vehicle, the four-arm folded dipole antenna is further redesigned. A shorting patch is introduced to suppress surface currents on the side nearest the wall, while the vertical arm nearest the wall is extended to suppress undesired current excitation, thus mitigating the effects of the metal wall on the antenna’s impedance and radiation pattern performance. Both antennas have been fabricated and measured. The results show that the antenna size is reduced from a half-wavelength to approximately 1/4 wavelength, achieving a reduction of 50%. The measured bandwidth is 410–447 MHz with good impedance matching. The antenna can effectively suppress the effects of the single-sided metal wall, with a peak gain of 5.5 dBi, cross-polarization levels below −10 dB, backlobe levels below −10 dB, and radiation efficiency above 80%, meeting the requirements of the wireless transmission system inside the inspection vehicle.