A New Method for Improving the Performance of Antennas Mounted on a Vehicle in the HF Band

Commonly, several antennas with different application are mounted on a vehicle for acting at HF band, such as monopole for ground wave communication and half-loop antennas for NVIS (Near Vertical Incident Sky wave) communication. Each of these antennas are applicable in different missions due to their different radiation patterns. Both of these antennas are electrically small due to small size in comparison to wave length and they have small gain, efficiency and bandwidth. Since there is electrically small space above the vehicle, these antennas are positioned closely together which increase the mutual coupling between them and influence on radiation properties of each other. The objective of this paper is improving the performance of the monopole antenna and half-loop antenna placed on a vehicle, by reducing the mutual coupling between the antennas. For this purpose, mantle cloak is employed to increase the isolation between the antennas. To design the cloak, the direction of the current induced on each antenna caused by stimulating of the other antenna is studied and an array of stripes are inserted perpendicular to the induced current direction. The induced current radiation is suppressed using these strips so, the radiation properties of the antennas, such as efficiency, directivity and radiation pattern in the presence of other antennas should be similar to the individual bare antennas. Suitable performance of the purposed method is proved using various simulations and it is shown that the communication range of the cloaked neighboring antennas will be increased since better radiation pattern is achieved using adding mantle cloak on the neighboring antennas in comparison to the co-site bare antennas.