Estimation of HF radar mixed-media path loss using the millington method

In order to predict the performance of a coastal high-frequency surface-wave radar (HFSWR) when the antenna must be located some distance back from the ocean, measurements of the path loss over beach sand at 13 and 25 MHz were made at several locations on beaches near Rotterdam, Netherlands in September 2014. The measured mixed-media path loss was compared with estimates made using a procedure developed by Millington in 1949 and were found to agree within 1-2 dB over a total range of 30 dB, even though the distances of a few hundred meters were much shorter than the several kilometers usually employed by the Millington method. Using this method along with the measured loss, it is possible to predict the degradation in achievable range for a coastal HF radar when the path to the sea includes a significant segment of low-conductivity soil, such as dry sand. Example calculations are included for 13 and 25 MHz.