Emerson Electric's AN/APQ-153 was an I band radar system developed for the Northrop F-5E fighter aircraft. Required to fit into the tight confines of the originally radar-less F-5, the system offered relatively simple air-to-air modes and a short detection range. The AN/APQ-157 was a similar system with dual displays and controls for the twin-seat F-5F trainer. Many of the F-5's still flying have been upgraded to the improved AN/APQ-159.
The APQ-153 was a relatively simple Pulse-Doppler radar intended to improve gunnery on the F-5. It offered four modes of operation; AA1 and AA2 air-to-air target search at different ranges, "dogfight" which locked onto the closest target and offered ranging and gun cueing, and finally a missile bore-sight cueing mode that calculated the engagement envelope of the AIM-9 Sidewinder and gave the pilot directional cues to help them fly into the envelope.
The antenna was necessarily small, a 12 by 16 inches (30 × 41 cm) parabolic dish that was stabilized to account for maneuvering. This was connected to a small 5-inch (13 cm) B-Scope display in the cockpit.