Launching of HF surface waves

A technique for obtaining approximately 3 dB improvement in HF signal strength at ground level over that obtained from a vertically polarised dipole has been described. This use of inductive loading has been shown to be relatively broadband. The work described in this paper forms part of an ongoing programme of research for communication and radar applications for the efficient utilisation of HF antennas, which has particular reference to coastal sites. At such sites the antenna must be placed with the driven elements some distance back from the tide-line, and the intervening ground is often overlaid by a wire grid screen. The principles described shows that by adding a second ´layer´ to the ground, an enhancement in the radiated field relative to the perfect conductor is possible. Future tests will involve the use of shipborne measurements with the ground loading turned round so as to direct radiation over the sea rather than over the land.<>