Radar systems and methods

Abstract

A radar system having side lobe blanking capability is disclosed. The system can include a single channel antenna and receiver system, the side lobe blanking system being time multiplexed, but requiring no dedicated guard channel data collection period such that the scan rate of the system is not degraded.

Claims

1. A method of blanking radar signals, the method comprising: displacing the azimuth position of a radar receiver according to a scan pattern through a plurality of bore sight positions and receiving at each of the plurality of bore sight positions a set of channel data; for a first bore sight position of the plurality of bore sight positions: combining two channel data sets taken at two bore sight positions of the plurality of different bore sight positions different from the first bore sight position to produce a first combined data set, wherein the first bore sight position is between the two bore sight positions used to produce the first combined data set; and comparing the channel data set taken at the first bore sight position with the first combined data set to blank detection of side lobe discretes for the first bore sight position; for a second bore sight position of the plurality of different bore sight positions: combining the channel data set taken at the first bore sight position within another channel data set from another bore sight position other than the second bore sight position of the plurality of bore sight positions to produce a second combined data set, wherein the second bore sight position is between the combined channel data sets used to produce the second combined data set; and comparing the channel data set taken at the second bore sight position with the second combined data set to blank detection of side lobe discretes for the second bore sight position.

Description

(1) The invention will now be described with reference to the accompanying diagrammatic drawings in which:

(2) FIG. 1 is a schematic drawing of the operation of the system. It can be seen that the target is only detected when the antenna beam is in the central position, whereas the sidelobe target is detected in all three antenna positions. By using data from the left hand (L) and right hand (R) beam positions the sidelobe detection can be eliminated when the beam is in the central position.

(3) FIG. 2 is a schematic drawing showing independent sliding window M/N and azimuth centroiding processes that are used to resolve the ambiguities and estimate azimuth position for the left hand (+) and right hand () sequence of schedules.

(4) In a system in accordance with one form of the invention, discussed above with reference to FIG. 1, channel data for a boresight of interest is compared with two sets of channel data acting as G channels, displaced in azimuth by, for example, +/10 degrees from the boresight position. Detection lists from the two G channels are then combined (OR-ed) together before being used to blank channel detections. After SLB, range and Doppler ambiguities are removed by typical signal processing means that are well-known in the art. Further control of side lobe discretes can be exercised through intelligent application of range-variable thresholds once the absolute range has been established.

(5) Note that the channel data may be processed in different ways depending on whether it is to be used for channel or G channel purposes, for example it may be advantageous to employ lower thresholds for the G channel.

(6) Two G channels are proposed to improve the G- ratio and exploit the fact that near-in side lobe levels are higher than far-out side lobe levels. Thus for a given position of side lobe discrete, with respect to the channel boresight, there is likely to be a positive G- ratio for one or other of the two G patterns.

(7) It will be appreciated that separating the two G patterns' by, for example, 20 degrees, will require a large number of coherent bursts of data to be held in memory. However this is unlikely to be an issue for modern digital processing systems.

(8) It will be appreciated that a number of considerations arise from this processing scheme as a result of data latency. For example, fixed frequency operation is assumed so that side lobe discretes do not become spatially decorrelated or migrate in Doppler bin number. Furthermore, as the data collected will effectively come from a 20 degree window, which corresponds to 0.33 second at 60 degree/sec scan rate, some consideration needs to be given to rangeDoppler migration over the period, which is not inconsiderable. For example, at 240 m/s target velocity, range migration lies within a 80 m to +80 m window for 360 degree scan excluding any effect of own ship motion.

(9) Moreover, large side lobe discretes can exhibit very angle-dependent patterns, with main beam RCS lobes typically extending over only 1-2 milliradians. Over a period of 0.3 seconds or so there is a possibility of decorrelation as a result of own ship motion, particularly for short range discretes.

(10) Preferably, in another form of the invention, the challenge of range migration and time decorrelation can be overcome by exploiting the capabilities of an electronically scanned antenna.

(11) In this form of the invention the and its associated G channel is acquired on a burst by burst time multiplexed basis and synchronised with electronic azimuth beam steps. Thus the equivalent time interval over which and its associated G data is obtained is now reduced to 2 bursts, effectively eliminating range migration and very significantly reducing the opportunity for decorrelation. This data pair effectively provides data simultaneously for two beam patterns separated in angle, and for each pattern the associated G data is derived from the other pattern of the data pair, e.g. the left hand pattern is associated with the right pattern acting as a G channel, whilst the right hand pattern is associated with the left hand pattern acting as a G channel.

(12) Preferably, the following points should also be considered.

(13) Firstly, the antenna pattern at, say, +/10 degree electronic squint angle will have higher side lobes than when pointing at 0 degrees. This may be undesirable when a 0 degree pattern is acting as G for a +/10 degree squint pattern. However, this effect may be reduced by avoiding the boresight position, and setting the and G position at, say, +/5 degrees respectively.

(14) Secondly, it may be desirable to position the and G channels asymmetrically around the boresight pattern to ensure optimal coverage of the side lobes by the G channel.

(15) Finally, the scan rate, beam width, schedule period, and angular position of the G beam patterns are tightly connected. Nominally the scan rate will be chosen to ensure that the time on target (2-way beam width/scan rate) is approximately equal to or slightly greater than the schedule period (the schedule comprising typically 8 bursts, each one at a unique PRF).