Under the initial 1965 design concept the Perimeter Acquisition Radar, or PAR, was an adjunct component of the NIKE-X system, specifically an unhardened, early warning VHF radar. Two years later, however, after the I-67 System deployment study, later known as the Sentinel system, the PAR transitioned from an early warning radar to a radar "which could provide initial target detection, discrimination and tracking for long-range Spartan intercepts."With this newly defined area defense mission, the PAR became a hardened UHF radar. The subsequent PAR configuration built upon the earlier Multifunction Array Radar and incorporating available components in the UHF band, "was considered to be 'off the shelf.'"Based on these factors, "development of a complete prototype system… was deemed unnecessary."
The research and development PAR therefore would be constructed at a site where it would later become part of the operational system. Thus the test conducted 20 July, 1973 was a significant step in the history of the PAR.Beginning in June 1973 announcements appeared in the North Dakota newspapers advising residents of the upcoming radar tests at the PAR facility constructed near Concrete, N.D. The community was notified that within 30 days the radar would be turned on and would begin transmissions at various levels of power for varying lengths of time.They were also warned of possible interference with electronic, but not electric, equipment. Any problems were to be reported to the Safeguard personnel.A unique five-story structure, the PAR's antenna measured 113 feet in diameter and contained 6,192 elements. The PAR system operated in the UHF and was designed to radiate 10.5 megawatts peak power, with an average power of 520 kilowatts.Power was supplied by traveling wave tubes, or TWTs, arranged in 16 transmitter groups, each group with 8 TWTs, or 128 TWTs for the -6 db system. Radiation at full power from all transmitters was actually achieved soon after the announcements were made during testing in June.The next step came in July. Could the radar detect a target in space? On July 20, 1973, the PAR demonstrated that the system did work as it detected its first satellite. Within two weeks, the PAR had also completed its first track of a satellite on Aug. 5. In subsequent test runs, satellite tracking exercised the maximum to minimum range of the PAR and the entire visibility angle for which it was designed. At the same time, the PAR demonstrated a capability to verify and track satellites as small as a basketball and as large as any in orbit.The satellite tests went beyond simply locating and tracking a satellite. This series of satellite tests incorporated both the PAR test software and the PAR weapons process. As the radar tracked the satellites' orbit, the range and angle accuracies were determined. At the same time, the radar's sensitivity, amplitude jitter, atmospheric effects, and absolute measurement accuracies of the radar were defined.In September 1973, Lt. Gen. Walter Leber the Safeguard System Manager, announced the radar was "successfully doing the job it was designed to do -- find and track objects traveling through space at ballistic speeds out to ranges of more than 1,000 miles."In fact, according to the official Safeguard history, the results of all these tests "indicated that the radar itself had not only met but exceeded design specifications.