United States Navy AN/TPS-71 ROTHR (Relocatable Over-the-Horizon Radar) Receiver Site (Juana Díaz)

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This AN/TPS-71 radar array is the receiver site of the ROTHR (Relocatable Over the Horizon Radar) located in Vieques and Juana Díaz. It is the third and final of its type to be installed, extending counterdrug surveillance past the equator, deep into South America.

Fleet Surveillance Support Command was established in July 1987 to operate the Navy's Relocatable Over-the-Horizon Radar (ROTHR) in support of Fleet units worldwide. This unique radar system was originally designed to provide tactical warning to battle group commanders of air and surface threats at an extended range allowing time for responsive engagement. Two US Navy high-frequency (HF) over-the-horizon (OTH) radars known as ROTHR (Relocatable Over-the-Horizon Radar) are operated at Corpus Christi TX and Chesapeake VA, with coverage of the Caribbean Sea and portions of the Atlantic Ocean and the Gulf of Mexico. The ROTHRs in Virginia and Texas are presently in full-time use for counter-narcotics surveillance, and a third is scheduled for installation in Puerto Rico in the near future.

The High Frequency Band (3 to 30 MHz) is a candidate for radar because it enables surface to surface radar to target distances well beyond the horizon. Radar to target ranges of 1000 nmi and more are typical. Use of the 10 to 60 meter wavelengths associated with HF radar requires physically large antennas. Each ROTHR achieves a nominal half degree azimuth angular resolution with a 2.58-km-long linear phased receiving array consisting of 372 twin-monopole elements. Each monopole pair has a receiver and analog-to-digital converter attached to it. A digital beamformer forms 18 beams which are then Doppler processed to separate the moving targets from the ground clutter. Range resolution is achieved by transmitting a 25-kHz continuous frequency-modulated waveform. A radar resolution cell on the ocean surface is therefore about 6 km in range by about 15 km in azimuth, for the frequency and range used. Radar frequency is variable and is selected using real-time sweep frequency ionospheric soundings.

www.fas.org/nuke/guide/usa/airdef/an-tps-71.htm