Evaluation of Vehicle Bottom for the Placement of HF-VHF Antennas

The bottom side of a vehicle is assessed for mounting HF-VHF antenna systems in terms of omni-directionality, efficiency and propagation loss. Accurate and numerically efficient procedure for calculation of propagation loss associated with sources electrically close to real grounds is proposed and carefully validated. It is shown that even though bottom sources cannot compete with conventionally mounted antennas in terms of far field omni-directionality and efficiency, in the near field region propagation loss margins are comparable for distances shorter than 10 m and frequencies from 20 to 100 MHz. The result points to the frequency range where antennas can be concealed at the bottom side and still used for emerging short distance applications.