Single-Mast Transmit-Receive Antenna for Long-Range Coastal HF Radars Below 11 MHz

The U.S. High Frequency Radar (HFR) network contains more than 140 coastal stations that provide hourly two-dimensional coastal surface currents. Approximately one-third of these are Long Range (LR) systems that transmit in the 4 – 5.5 MHz frequency band and have nominal offshore ranges and resolutions of 160-220 km and 3 – 6 km, respectively. The data provided by the network has numerous applications but is most critical to Coast Guard search & rescue and oil spill response [Harlan, et al, 2010]. HFR stations operating below 11 MHz, presently require separate transmit and receive antennas spaced approximately 60 m, which precludes mounting on structures such as buildings or platforms and limits most to ground mounts close to the water. During Hurricanes Irene (2011) and Sandy (2012), HFR was shown to be a key observation tool, along with others, to better predict intensity of approaching hurricanes before they make landfall [Glenn, et al, 2016]. Sandy’s storm surge destroyed the stations that were installed in the most vulnerable low-lying coastlines. CODAR proposes to redesign LR HFR antenna(s) to fit on a single mast so that these systems can be installed on platforms such as weather-hardened Sentinel water level monitoring stations, reducing risk of loss.