The AN/APG-76 radar is a pulse Doppler Ku band multi-mode radar developed and manufactured by Northrop Grumman.
AN/APQ-92
The first radar of the radar family AN/APG-76 belongs to is AN/APQ-92, which equipped A-6A. AN/APQ-92 is a search and navigational radar, with function called search radar terrain clearance (SRTC) to generate a synthetic terrain display on the pilot's Vertical Display Indicator (VDI), which is a large cathode ray tube (CRT) display in the center of the pilot's console, right under the gun sight. The display showed vertical terrain development in a 53 degree x 26 degree window about the projected flight path. If the Intruder was heading for a valley between two hills, the pilot would see return generally in the shape of two hills (one on either side of the display), with a curving "V" notch in the center between them. The limitation of SRTC is in its inability to detect smaller artificial features - like cables suspend across a valley.
AN/APQ-92 is part of DIANE (Digital Integrated Attack/Navigation Devices), which consists of multiple radars: the Norden AN/APQ-92 search and navigation radar, the separate AN/APQ-88 for tracking/attacking, AN/APN-141 radar altimeter, & AN/APN-122 navigational radar to provide position updates to the AN/ASN-31 inertial navigation system.
AN/APQ-103
AN/APQ-103 is the successor of AN/APQ-92, and it is used in conjunction with AN/APN-153 Doppler navigational radar that replaced earlier AN/APN-122, and AN/APQ-112 radar replaced AN/APQ-88. The APQ-103/APN-153/APQ-112 upgrade is part of the improvement of DIANE installed on A-6B.
AN/APQ-112
AN/APQ-112 is a tracking radar that replaced earlier AN/APQ-88 radar developed by Naval Avionics. While the AN/APQ-88 could only track moving targets, the APQ-112 could track stationary targets as well, and it had slightly better resolution and greater reliability than AN/APQ-88.
AN/APQ-112 not only could perform all functions of AN/APQ-88, but was also capable of performing some functions of AN/APQ-103. As more advanced version of AN/APQ-112 was developed, it replaced AN/APQ-103. However, the attempt to replace two separate radars failed at the time due to increased mission requirement, and a separate dedicated fire control radar was needed. As a result, the vastly improved Sperry Corporation AN/APQ-127 was adopted, while AN/APN-186 navigational radar replacing earlier AN/APN-153 in earlier A-6B. APN-186/APQ-112/APQ-127 suit is designed as part of A-6C specially dedicated for night attack missions against the Ho Chi Minh Trail in Vietnam.
AN/APQ-129
AN/APQ-129 is a derivative of AN/APQ-112 for EA-6A, allowing EA-6A to fire AGM-45 Shrike anti-radiation missile (ARM), though this was never done in real combat.
AN/APQ-148
The J-band AN/APQ-148 is the first one in the radar family that had achieved the capability to replace two separate radars with a single multi-function radar. AN/APQ-148 was the original radar on board the A-6E.
AN/APQ-156
AN/APQ-156 is the development of AN/APQ-148, and it is used in conjunction with Target Recognition and Attack Multi-Sensor" (TRAM) system starting to be installed on A-6E in 1979 during upgrades. The bombardier/navigator could use both TRAM imagery and radar data for extremely accurate attacks, and the radar has an Airborne Moving Target Indicator (AMTI), which allowed the aircraft to track a moving target (such as a tank or truck) and drop ordnance on it even though the target was moving.
AN/APS-130
AN/APS-130 is a derivative of AN/APQ-156 and the upgrade of AN/APQ-129, by applying the knowledge gained from AN/APQ-156 to improve AN/APQ-129. AN/APS-130 is fitted on EA-6B, enable the aircraft to fire AGM-88 HARM.
AN/APS-146
AN/APS-146 is a simplified version of AN/APQ-156/APS-130, with the interferometer omitted, but added a weather avoidance pencil beam, and replaced the reflector antenna with a planar antenna.
AN/APQ-173
AN/APQ-173 is the development of AN/APQ-156 with the addition to include synthetic aperture radar (SAR). and multi-function cockpit displays – the APQ-173 would have given the Intruder air-to-air capacity with provision for the AIM-120 AMRAAM. AN/APQ-173 was designed for A-6F/G which were cancelled.