Adaptive Active Phased Array Radars
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Introduction
Over the years radar systems have been changing on account of the requirements caused by:
a) Increase in the number of wanted and unwanted targets.
b) Reduction in target size either due to physical size reduction due to the adoption of stealth measures.
c) The need to detect unwanted targets in even more sever levels of clutter and at longer ranges.
d) The need to adapt to a greater number of and more sophisticated types of electronic counter measures.
Radar designers addressed these needs by either designing radars to fulfill a specific role, or by providing user selectable roles within single radar. This process culminated in the fully adaptive radar, which can automatically react to the operational environment to optimize performance. Conventional radars fall into two categories independent of what functions they perform. The first category has fixed antenna with centralized transmitters which produce patterns by reflector or passive array antennas. The beaming being fixed, scanning can only be achieved by physically moving the antenna. Typically surveillance radar will produce a fan shaped beam with a fixed elevation illumination profile, the azimuth scanning being achieved by rotating the antenna. Tracking radar will have a pencil beam that is used to track targets by the use of mechanical tracking mount. Because of the limitations imposed on such radars by their design such radars are "single-function radars".
ACTIVE ARRAYS:
A major reason for the large size and power requirements of a conventional phased array radar is the need to overcome the loss in their RF signal between the bulk transmitter and the antenna, and between the antenna and the receiver. Losses typically can be 7dB and in some compiled designs can reach as much as 10dB. Typically 95 % of the prime power and 80 % of the effective transmitter power is lost, with only 20 % being used for detection.
VOLUME SURVEILLANCE:
The AAPAR can provide a number of operating mode to tailor surveillance volumes to the system or mission requirements. Energy usage is optimizes and the probability of target determination is maximized by the management of radar waveforms and beams. Volume surveillance can be managed in order to cope with varying threats - lower priority surveillance tasks can be traded for higher priority tasks such as short range surveillance or target tracking as the threat scenario changes.
DETECTION AND CONFIRMATION:
A look back beam using the position data derived from the detection beam can immediately confirm each detection that is not associated with a target already in current track files this significantly reducing the track confirmation delay.
TARGET TRACKING:
Separate tracking beams can be used to maintain target positions and velocity date. Targets with low maneuvering capability and those that are classified as friendly or neutral may be tracked using track-while-scanning techniques during normal surveillance.
TARGET IDENTIFICATION:
Cooperative technique use an IFF (Identification: Friend or Foe) integrated system controlled by a radar. Defending on the role of the radar, integration of target is performed only when the demanded, or on a continuous 'Turn and Burn' basis. Selective integration is used to minimize transmission from the radar to reduce the probability of ESM (Electronic Surveillance Measures) intercepts and is merely always used when mode 4; the secure IFF mode, is being used . Non cooperative technique extract additional data from radar returns by extracting features and comparing them with information held on threat date bases. A correlation process is used that finds the best fit to the data. This method can provide good accuracy in recognizing a target from a class of targets, or a specific type of targets.
TARGET TRAJECTORY CALCULATION:
Calculation of an impact point is one input to the threat assessment process and the radar can assist by adapting to a mode that fits the trajectory to a complex curve fitting law. This process is more effectively performed by the AAPAR since it can adapt its tracking priorities and parameters and form the date quickly to the required accuracy.
TRACKING OF ECM EMISSIONS:
Receive-only beams can be formed with an active array, giving all the normal receive processes without the need for transmitted RF. Utilizing these beams, sources of in band radiation can be accurately tracked in two dimensions. The track data can be correlated with strobes from other sensors to enable the positions of the jamming sources to be determined and tracked in conditions in which the presence of jamming may prohibit the formation of tracks.
KILL ASSESSMENT:
It is possible to use a radar sensor to give some information to the kill assessment process. The radar can only be used in two ways. Firstly, it can determine whether the trajectory or track vector has changed sufficiently to indicate that the threat has aborted its mission or been damaged sufficiently to lose control. Secondly, the radar can form a high resolution image of the target to determine if it has been fragmented.
MISSILE COMMUNICATION:
In a system, where an interception is being performed by surface-to-air missile, the multifunction radar is likely to be located in a position where it has good visibility of both the targets and the outgoing missile. In this system the ground-to-missile communication's link. Used to control the missile in its various stages of flight could be performed by the radar