Phased-array Radar System Improvements

image: AN/FPS-85 Radar Site

AN/FPS-85 Radar Site

image: replacement transmitter

Replacement Transmitter

The AN/FPS-85 (a computer-controlled, phased-array radar) searches, detects, identifies, and tracks satellites and other space objects. Built in the 1960s, this unique, high-power radar is located at Eglin Air Force Base in Florida. The radar incorporates separate transmitter and receiver arrays operating at 442 MHz. The Transmitter Array System comprises 5,184 radar transmitter units arranged in a 72-square matrix. Each radar transmitter unit delivers nearly 10 kilowatts of peak power into a dipole antenna yielding a collective beam peak power of more than 30 Megawatts.

SwRI Contracted to Study the AN/FPS-85

The U.S. Government contracted with Southwest Research Institute (SwRI) to study the Transmitter Array System for potential reliability improvements. Each day, an average of 20 transmitter units failed that required servicing by a dedicated, on-site, maintenance shop.

An SwRI failure analysis determined that six vacuum tubes within the transmitter contributed mostly to the transmitter reliability. Consequently, SwRI recommended replacing these tubes with more reliable solid-state technology. The project team proposed multiple design approaches and then prototyped and tested them in the system.

After careful analysis of factors such as cost, performance, expected reliability, and production risk, the project team selected a final design. The selected design represented a form, fit, and functional replacement of the original design. The design retained the original chassis and final-stage tube cavity, but solid-state RF signal processing and power amplifier circuits replaced the remaining five tubes and related circuitry.

SwRI delivered a production technical data package, and a production contractor has successfully completed the replacement of the original transmitters with the new SwRI design.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.