Note: This article discusses the radar modes in modern fighter jets including air to air, air to sea & air to ground modes of modern radars.
Modern Fighters Have Following Air-To-Air Radar Modes (Among Others)
Range While Scan (RWS): The radar beam proceeds across the sky in a zig-zag motion. Each time a return is detected, its range is calculated using time delay and its location is plotted on the B-scope. The return “decays” off the scope after a period of time, so that trends in target motion can be clearly seen in successive overlapping returns. Closure rate can also be calculated in this mode using Doppler analysis. The pulse repetition frequency (PRF — how long a radar will wait after sending out a pulse to listen for a response) can be varied to detect more distance or closer targets.
Track While Scan (TWS)
This mode is similar to RWS except that the radar creates a “track file” for each new target it sees. The track file stores the target’s location, and successive returns from the same target are appended to its track file’s history. (The radar must use some guesswork in deciding if two nearby subsequent returns came from the same target or not.) By analyzing the recent history of a track file, the radar can interpolate other information about the target, such as its velocity and heading. The number of simultaneous track files that can be open is limited by fire control computer memory.
Situational Awareness Modes (SAM)
This is a hybrid of one of the previous modes (RWS or TWS) and a single-target track mode. In this mode, a single target is periodically scanned by the radar in between sweeps of the sky.
Single-Target Track (STT)
The radar focuses its entire energy on a single target. The beam points directly at the target, “jittering” occasionally to ensure that the lock is not lost in case the target maneuvers. A single track file is kept for the target and the track data is high-resolution and highly accurate.
Velocity Search and Ranging (VSR)
This is an adaptation of RWS where the y-axis of the B-scope is not range (as calculated by time delay) but velocity (as calculated by Doppler shift). Thus, targets with faster closure rates appear at the top of the scope.
Range Gated High (RGH)
This is an adaptation of RWS that automatically filters out targets that do not have a high closure rate.
Vector (VCTR)/Ultra-Long-Range Scan (ULS)
In this mode, the radar beam travels half as quickly as it would in RWS mode, the extra time spent processing the radar image to detect more distant targets.
Auto-Acquisition (AACQ)/Air Combat Maneuvering (ACM) Modes
In these modes, the radar searches a fixed section of the sky (examples: bore sighted directly ahead, in a single vertical line, in a small box representing the pilot’s forward view) very quickly. Any targets detected are automatically locked and transferred to STT mode.
In this mode the radar uses enhanced frequency agility and other techniques to “burn through” a radar-jamming environment.
Radars also often support the following Air-to-Ground radar modes (among others)
Ground Mapping (GM)/Real Beam Map (RBM)
In this mode the radar scans the terrain ahead to produce a 3D map of the topography. Pilots can use this map for terrain avoidance or as a “picture” of the ground ahead of them for target detection. For higher resolution, a Doppler-beam sharpening (DBS)/high resolution map (HRM) mode can be used.
Ground Moving Target (GMT)
This mode uses a Doppler notch to detect only moving targets on the ground, filtering out clutter from buildings, trees, and terrain.
Interleaved Ground Moving Target (IGMT)
This mode is a combination of the above two modes. The radar does one scan to create a picture of the terrain, and another scan to detect moving targets and display them on top of the terrain.
Sea-Surface Search (SSS)
This mode uses enhanced image processing to detect ships and boats on the water. The enhanced processing is necessary to account for the increased reflectivity of the water.
Beacon (BCN) Search
This mode is a passive radar mode that detects transmitting radar beacons placed by ground personnel. These beacons are programmed to emit certain codes that the radar can search for.
Air-To-Ground Ranging (AGR)
This radar mode is used to assist in aerial gunnery and visual bombing. The radar maintains a continuous single beam on the aircraft’s line-of-sight, and the fire control computer uses the range information to calculate a fire solution for the guns or bombs.
Air To Sea Modes
Real Beam Mapping(RBM)
It is the simplest radar ground- mapping mode used. In a typical real beam mapping mode, the radar repetitively sweeps an arc firing pulse trains frequently enough to produce a viewable map of the terrain.
Doppler Beam Sharpening(DBS)
A coherent ground map mode which provides higher azimuth resolution by processing the radar return signal phase to exploit the doppler dependency on azimuth angle. The. DBS mode is defined as having constant angular resolution, as opposed to the constant cross-range resolution of. SAR
Fixed Target Track (FTT)
This mode can automatically maintain an accurate track on a stationary target for fix-taking and weapons delivery. FTT is accessible from the GM, GM EXP, SEA, SEA EXP, and DBS modes. Slow-moving targets can be acquired from GM or SEA modes using FTT mode.
Ground Moving Target Indication (GMTI)
This detects moving targets such as cars, trucks, tanks, other military vehicles, ships, and taxiing aircraft on land or sea out to 40 nautical miles. GMTI mode can also be used to detect moving surface targets in high sea-states. The Freeze option is available.
Beacon (BCN) Search
This mode is a passive radar mode that detects transmitting radar beacons placed by ground personnel. These beacons are programmed to emit certain codes that the radar can search for
TA (Terrain Avoidance)
This mode is available in A/G as a means to fly Nap-of-the-earth (NOE) in limited visibility. TA cannot be coupled to the autopilot. It is strictly a visual aid designed to assist the pilot in avoiding terrain in front of the aircraft. In the TA mode, the Radar computes two altitude clearance planes. While the aircraft is in level flight or climbing, terrain that is above the aircraft’s altitude is displayed at an intermediate intensity on the display, and terrain that is within 500 feet of the aircraft’s altitude is displayed at a lower intensity.
Terrain more than 500 feet below the aircraft is not displayed at all. When the aircraft is climbing, the two clearance planes remain horizontal. However, when the aircraft is diving, the two clearance planes are tilted downward parallel to the aircraft’s flight path angle. The idea is to fly the aircraft so that no intermediate intensity video appears in close proximity to the aircraft’s ground track.