High Frequency Surface Wave Radar (HFSWR)
US Navy ships have made only limited progress toward improving self-defense capabilities, since most shipborne sensors are limited by the horizon. Lockheed Sanders has developed the High Frequency Surface Wave Radar (HFSWR) as an Advanced Technology Development (ATD) for the US Navy. The HFSWR is designed to detect low-flying, low-signature ASCMs and tactical ballistic missiles. The system operates between 3 and 30 MHz to detect low-flying objects at over-the-horizon ranges.
On 02 February 1996 Lockheed Sanders, Incorporated, Surveillance Systems Division, Nashua, New Hampshire, was awarded a $6,471,031 modification to previously awarded contract N66001-95-C-0160 for research and development services, specifically for the fabrication, integration, and testing under Phase II of the High Frequency Surface Wave Radar design and system development program. Work was performed in Hudson, New Hampshire, and was expected to be completed by February 1998. Contract funds in the amount of $3,000,000 expired at the end of fiscal year 1996. This contract was competitively procured by a request for proposals and six offers were received. The Naval Command, Control and Ocean Surveillance Center RDT&E Division, San Diego, California, was the contracting activity.
Funding was first cut, then restored, and only limited testing continued. LSD-45 Comstock was to be equipped with a prototype Sanders HFSWR High Frequency Surface Wave Radar, with vertical transmitting antennas in fixed structures on the sides of the superstructure and in 24 small receiving array boxes along either side of the upper deck.
High Frequency (HF) radars are sometimes referred to as over-the-horizon (OTH) radars because of their capacity to receive target echoes over much longer distances than microwave radars, which are restricted to distances defined by the line-of-sight or the horizon. The most common type of HF radar operates in the sky wave mode, which receives radar echoes through reflection from the ionosphere. HF radar can also operate in the surface wave mode, which provides coverage in the order of several hundred kilometers. Signals propagate efficiently in the surface wave mode only at vertical polarization and require a conducting surface along the signal path. This makes the HFSWR practical at coastal installations where the ocean surface serves as the conducting surface.
An operational HFSWR must be able to operate in congested signal spectrum with limited signal bandwidth, and in the presence of sea clutter, ionospheric interference and external natural and man-made noise. Before an operational HFSWR system can be implemented, it must demonstrate detection capability under a wide range of signal and physical environments.
HFSWR is the only sensor that can measure temporal and spatial ocean properties simultaneously over thousands of square kilometers with resolutions less that 1 km. HFSWR is normally deployed as a pair of land stations with overlapping coverage, but can operate from ships or, with reduced capabilities, from a single land station. Oceanographic measurements include surface current, vertical current shear, directional wave height spectra, wind direction, detection of fronts and eddies, and measurement of bathymetry in the littoral zone.
The pace of modern military operations and the over-the-horizon range capability of many weapons systems impose heavy demands on real-time surveillance and intelligence support. For operations in the littoral zone, there is a clear requirement for a relocatable, shore-based sensor which can provide reliable all-weather detection of small surface and aerial targets of interest out to ranges in excess of 100 kilometres from the coast. HF surface-wave radar (HFSWR) may well provide the most cost-effective solution to this requirement, given the results of recent trials of experimental land-based systems developed in Australia and in Canada.
