This disclosure relates to receivers including, but not limited to, radar systems and traffic collision and avoidance systems. More particularly, this disclosure relates to sensing an angle-to-target using a multiple antenna system.
Systems can be utilized to sense the presence and location of targets. According to one exemplary application, airborne radar systems can be utilized to detect and locate ground and air targets. The location of the ground and air targets can be displayed to a crew in an aircraft on a two-dimensional map display showing range and bearing to the target or can be used by an on-board or off-board computing system. Targets can be other aircraft, ground structures, vehicles, obstacles, terrain, etc.
Monopulse radar systems generally utilize multiple aperture antennas and include multiple receiver channels. Monopulse radar systems operate in a search mode to identify targets and a track operation to more accurately estimate the angle-to-target. Search mode generally uses Doppler filtering to both increase signal to noise and to allow radar returns to be separated by their Doppler signatures. A detection while searching is generally declared when power in a given radar range, azimuth, elevation, frequency, or location is greater than other returns taken from neighboring range, azimuth, elevation, frequency, or location. Detections may be required to be confirmed by other pulse and process activities, but information related to the target's range, its angular position, and its relative movement either toward or away from the radar can be garnered form the initial detection. These four parameters from the initial detection may not produce an unambiguous understanding of the target's movement or have desired accuracy.
The angle-to-target parameter can have limited accuracy. The accuracy of the angle-to-target parameter from the initial detection is generally limited to the target being within the beam of the radar signal. Since the beam is not a narrow line but has a response several degrees wide, the angle-to-target parameter only can indicate that the target is within several degrees from the beam center.
Thus, there is a need for a reliable low-cost system for and method of making an angle-to-angle target estimate without using a microwave monopulse comparator. Further, there is a need for a radar or traffic collision avoidance system and method that can more accurately estimate angles-to-targets. Further still, there is a need for a radar system and method capable of calibrating mismatch errors in sum and difference channels to estimate an angle-to-target for targets in the area.
Yet further still, there is a need for a radar system for and method of utilizing a search operation to estimate angles to target by adjusting for gain mismatch. Further still, there is a need for a reliable system for and method of compensating for mismatch errors and computing angle-to-target parameters. Yet further still, there is a need for a radar system and/or traffic collision avoidance system (TCAS) that achieves the advantages of high speed angle estimation for multiple targets. Thus, there is a need for a system for and method of producing accurate angle estimates without servoing the antenna to be centered on the received target. Further still, there is a need for a high speed system for and a method of providing accurate angle estimates to multiple targets in a target rich environment. Further still, there is a need for a system for and method of calibrating a lobing or monopulse system so that the antenna does not have to servo to the point to the target.