Electronic Design

Design Of Arecibo Radar On Schedule

By early next spring, the huge 430-mc radar being built near Arecibo, Puerto Rico, for the Advanced Research Projects Agency of the Defense Department should be collecting data on electron density in the iono-sphere. This is an estimate made in Arecibo earlier this month by scientists of Cornell University's Center for Radiophysics and Space Research, the prime contractor to the Air Force Cambridge Research Laboratory for design and construction of the radar system. The installation is part of Project Defender, designed to minimize danger from missile attack.

Difficulties in transforming a Puerto Rican valley into a 1000-ft-diam, mesh-lined dish have postponed operation from July of this year to 1962, but design of the electronic equipment is proceeding according to plan, Cornell scientists report.

Although the 1/6-deg beam transmitted by the radar will be able to cover the sky only within 20 degrees of zenith, the facility will be useful for experiments involving the major planets, the moon, and some space vehicles. The fixed spherical reflector of the radar will be fed by a line feed supported above it on a rotating azimuth truss. The feed will be capable of all types of polarization and will fully illuminate the aperture, which will have a radius of curvature of 870 ft, and a surface tolerance of ±0.1 ft. Achieving this tolerance is expected to be one of the main structural-design problems connected with the project.

Design goals for the transmitter include: a peak power output of 2.5 megawatts at 430 mc, and an average power of 150 kw, with pulse-to-pulse stability of 0.2 db. Pulse lengths of 2 to 10,000 µsec are to be available with a repetition rate of 1 to 1,000 pps.

Though the feed, which will hang from tower-supported cables about 430 ft above the reflector surface, will weigh less than five tons, the entire feed-supporting structure will weigh about 450 tons. The feed is being designed to operate in 30-mph winds, and to survive 140-mph hurricanes. (The photo shows one of the three 250-ft towers that will support the feed hanging from a network of cables. The dish cavity is visible in the foreground.) (Electronic Design, September 27, 1961, p. 8)

The sheer size of this antenna still amazes me, and it's still in operation. There's an interesting wrapup on the antenna at the Web site: http://astronomica.org/Gallery/seti/seti10.html. The Web site's photo gives a good view of the pylons and the suspended feed as they look today.

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