AN/ASG-18

Manufacturer: Hughes
IEEE Band:
NATO Band: I Band (9350-9400 MHz)
Pulse Repetition Frequency: 980 to 1020 pps
Pulse Repetition Interval: 980.392 to 1020.408 microseconds
Pulse Duration: 0.150 to 0.250 microseconds
Elevation: +/- 45 degrees
Minimum Altitude:
Maximum Altitude:
Maximum Tracks:
Maximum Engagements:
Detection Example 1:
Detection Example 2:
Track While Scan Range:

NOTES: The AN/ASG-18 was the United States' first pulse doppler radar, and had look-down/shoot-down capability (for only one target track at a time)

Addena

Page 65 onwards from Valkryie - North American's Mach 3 Superbomber:

The fire control system was built around a 40-inch-diameter antenna and could detect B-47-size targets at a range of over 100 nautical miles at all altitudes. The radar was capable of look-down or lookup operation, but could only track a single target at a time because of limited computer power. The ASG-18 employed a liquid-cooled transmitter consisting of two traveling wave tube amplifiers in tandem to provide the desired gain, and analog circuitry for generating and processing the coherent high-pulse repetition frequency waveform. The radar consisted of 41 separate units weighing nearly 2,100 pounds that occupied most of the nose of the F-108. The entire package included a solid-state digital computer for navigation and firing solutions, an analog-attack steering computer, and an infrared search-and-track system capable of being slaved to the radar.

The new radar included an inherent self-test capability, both on the ground and in flight. Prior to takeoff, circuits in each electronics bay would test the equipment and display a "readily visible go-no-go" indicator to the maintenance crew. This was a tremendous improvement over the MX-1179 and earlier systems where large and cumbersome ground test equipment was required. The in-flight self-test would be initiated by the weapons system officer, who would perform a final check of the system before the F-108 entered combat. If the results were negative, this information could be automatically relayed to the SAGE network so that a "substitute F-108" could be vectored to the battle. All of the equipment would also have time-in-service clocks and would be removed at predetermined intervals corresponding to its demonstrated mean-time-between-failure rate (in spite of its apparent operating condition). North American believed this would "help maintain confidence level and mission reliability" of all the systems.

Tests of the ASG-18 continued using the B-25 and T-29 surrogates against a variety of targets, including a B-57, DC-3, and Aero Commander. All of the targets were "augmented" to provide an "equivalent reflecting area of 343 square feet" which apparently corresponded to the anticipated Soviet threat. The prototype radar was demonstrating a decent ability to find the targets, but the ranges were usually less than 40 nautical miles, substantially less than the actual requirement. The testing included an ability to find and lock onto a target dropping chaff, plus look-down acquisitions of targets in ground clutter. Flights were made over various terrain features around Southern California to collect clutter data to improve the algorithms being used.

The IRST system was to be capable of detecting a tail-aspect B-47-size target at a range of 34.8 nautical miles at 45,000 altitude. From directly ahead of the bomber, the detection range was to be 10.3 nautical miles. A Mach 3 bomber - a very large target because of heat from skin friction - was to be detected at 76.5 nautical miles from any aspect. This convinced North American that lowering the infrared signature of the B-70 was essential, since it was known that the Soviets included IRST systems on virtually all of their interceptors.