Influence of the Earth in the HF transmission of LPD antennas

Log-periodic dipole (LPD) arrays have important applications in HF transmission for their large bandwidths and rather high gain. The nonideal terrain around the antenna gives a strong degradation of the radiation pattern at low elevation angles where the antenna is used in HF in order to utilize the ionospheric refraction. The problem is discussed, and the possible means for improving such situations are compared (e.g., the raising of the antenna, the use of metallic ground screen of different characteristics around the antenna, and the use of horizontal dipole arrays), giving consideration also to the cost.