An adaptive tracking method for overhead targets using phased array radar

Abstract

The invention relates to a phased array radar over-the-top target adaptive tracking method. The method comprises the following steps: obtaining a target elevation threshold value by using an array face inclination angle and a beam scanning range; tracking by using a sum-difference beam angle measurement method when the target elevation value is less than the elevation threshold value; and adopting a target over-the-top tracking method when the target elevation value is greater than the elevation threshold value; transmitting and receiving in the over-the-top tracking method adopt a multi-beam form; compensating for Doppler frequency shift caused by radar platform movement; obtaining a target radial velocity threshold value by using a maximum Doppler frequency of clutter; removing clutter and detecting target echoes by using inter-pulse frequency agility, adaptive MTI in a pulse group, and inter-pulse accumulation when the target radial velocity is greater than the radial velocity threshold value; removing clutter and detecting target echoes by using inter-pulse frequency agility and inter-pulse accumulation when the radial velocity is less than the radial velocity threshold value; and finally obtaining an estimated value of the target position by using a multi-beam position aggregation with a target multi-beam echo amplitude as a weighted value, thereby realizing tracking of the over-the-top target.

Description

Technical Field

[0001] The invention belongs to the technical field of radar. Background Art

[0002] Phased array radar can achieve rapid beam scanning without mechanical rotation, thereby realizing high data rate tracking of the target. However, when the target moves to a very close position or even over the top, due to the limited angle range of the array scanning, the excessive elevation angle will cause the target to be lost, resulting in an over-the-top blind spot.

[0003] Regarding the problem of tracking targets passing overhead by phased array radar, the "Method for Tracking Targets Passing Over the Top with Multi-beam Spherical Phased Array Antenna" (CN108051803A) of the Southwest Institute of Electronic Technology (the 10th Institute of China Electronics Technology Group Corporation) discloses a method for tracking targets passing overhead by digital multi-beam spherical phased array antennas. This method uses a spherical phased array antenna to reduce the dynamic changes in azimuth and elevation angles by converting the coordinate system when the target passes overhead, thereby ensuring stable tracking of the target. Although this method uses a spherical phased array antenna to achieve overhead target tracking, spherical phased array antennas are rarely used in actual radar applications, and the partial antenna at the top of the sphere is less effective when the radar performs other tasks, so it is not universal.

[0004] The present invention can be used in a conventional planar phased array radar, and it is not necessary to use a special array surface form in order to track overhead targets. Summary of the invention

[0005] When a phased array radar tracks a target, if the target elevation angle is too high and exceeds the scanning range of the array beam, the target will be lost and a tracking blind spot will occur. The present invention provides a phased array radar over-the-top target adaptive tracking method. When tracking a radar over-the-top target, the two main problems to be solved are: one is that the directional pattern is distorted after the elevation angle is too high, the transmission and receiving gain at the target position is small, and the error in the estimation of parameters such as the position of the target will be large, which is easy to be lost due to the maneuvering of the target or the large deviation between the target position and the estimated position; the other problem is that when the beam scans a high-elevation target, a large amount of strong ground clutter will enter the side lobe, and the target echo may be covered by the clutter and cannot be detected.

[0006] The technical solution to realize the present invention is:

[0007] When tracking with sum-difference beam angle measurement, the target elevation angle and radial velocity are estimated, and the elevation angle threshold is set by the array inclination angle and the beam scanning range. The target elevation angle is compared with the elevation angle threshold. If it is lower than the threshold, the sum-difference angle measurement method is used for tracking, and if it is higher than the threshold, the over-the-top tracking method is used. When tracking over-the-top, both transmission and reception adopt multi-beam form, and the central beam is transmitted to the estimated position of the target, and then multiple beams are transmitted at equal intervals around the central beam. After compensating for the Doppler frequency shift caused by the motion state of the radar platform, the target radial velocity threshold is obtained from the maximum Doppler frequency of the clutter. When the radial velocity exceeds the radial velocity threshold, the frequency agility between pulse groups, adaptive MTI within the pulse group, and accumulation between pulse groups are used to achieve clutter removal and target echo detection. When the radial velocity is lower than the velocity threshold, the frequency agility between pulses and accumulation between pulses are used to achieve clutter removal and target echo detection. The over-the-top target is finally tracked by condensed angle measurement.

[0008] Furthermore, during overhead tracking, transmission is in multi-beam form, with the central beam of the multi-beam pointing to the estimated target position. Six beams are equally spaced around the beam, with adjacent beams overlapping and also overlapping with the central beam. The same multi-beam form is used during reception.

[0009] Furthermore, the radial velocity threshold is set by performing platform motion velocity compensation on the Doppler frequencies of the target echo and clutter, then estimating the maximum Doppler frequency of the clutter, and taking the maximum Doppler frequency of the clutter as a reference, multiplying it by a coefficient as the radial velocity threshold.

[0010] The present invention does not need to select a special phased array array form, and can realize the adaptive tracking of overhead targets by phased array radar only through scheduling control, signal processing and data processing methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a flow chart of the overhead target adaptive tracking method of the present invention.

[0012] Figure 2 It is a diagram of the multi-beam scanning method of the present invention, which is in the shape of a plum blossom, with beam 1 pointing to the estimated target position, and the remaining 6 beams surrounding beam 1 at equal intervals, and adjacent beams overlap and overlap with the central beam.

[0013] Figure 3 is the frequency response characteristic diagram of the adaptive MTI filter of the present invention, in which f d It is the Doppler frequency corresponding to the target radial velocity after platform motion velocity compensation. DETAILED DESCRIPTION

[0014] The present invention will be further explained below in conjunction with the accompanying drawings.

[0015] The present invention proposes a phased array radar over-the-top target adaptive tracking method. When the phased array radar tracks the target by sum and difference beam angle measurement, the radial velocity of the target is estimated, and the tracking is assisted by trajectory prediction. An elevation angle threshold is determined according to the array inclination angle and the array beam scanning range. When the target elevation angle estimation value is lower than the threshold, the sum and difference beam angle measurement method is continued to be used for tracking; when the target elevation angle estimation value is greater than the threshold, due to the distortion of the radiation pattern, the sum and difference beam angle measurement has a large error at this time, and the target position cannot be effectively estimated. At this time, the over-the-top target tracking method proposed by the present invention is used.

[0016] In order to achieve effective tracking, both transmission and reception adopt multi-beam form. In addition to transmitting the tracking beam to the estimated target position, multiple beams are also transmitted around the estimated target position to expand the scanning range, even if the actual position of the target deviates greatly from the estimated position or the target is maneuvering, it is still within the beam scanning range.

[0017] According to the motion state of the radar platform, platform velocity compensation is performed on the received target echo and clutter to offset the impact of platform motion on the target echo and clutter Doppler frequency. The maximum Doppler frequency of the clutter is estimated, and the maximum Doppler frequency of the clutter is multiplied by a coefficient to obtain the target radial velocity threshold.

[0018] According to the radial velocity of the target, it is determined whether to use the method of frequency agility between pulse groups plus adaptive MTI within the pulse group or the method of frequency agility between pulses to remove clutter. When the estimated radial velocity of the target is greater than the velocity threshold value, the target radial velocity is large and can be separated from the clutter by the MTI method. At this time, the frequency agility between pulse groups is first used for decorrelation, and then the adaptive MTI within the pulse group is used to filter out the clutter. The MTI filter coefficient is adjusted in real time according to the estimated radial velocity of the target, so that the center of the filter passband is always aligned with the Doppler frequency corresponding to the target radial velocity, and the filter stopband is aligned with the clutter. After the adaptive MTI, the detection probability is improved by accumulation between pulse groups. When the estimated radial velocity of the target is less than the velocity threshold value, the target radial velocity is small, and the frequency agility between pulses is used for decorrelation, and then accumulation between pulses is performed.

[0019] Then, the received multi-beam echo amplitude is condensed for angle tracking, and the amplitude of each beam is used as the weighted value of the beam position. Finally, the estimated position of the target is obtained, thereby realizing the tracking of the overhead target.

[0020] After the overhead tracking is successful, the target radial velocity continues to be estimated, and the tracking is assisted by trajectory prediction. According to the comparison result of the target elevation angle and the elevation angle threshold value, it is selected to return to the sum-difference beam angle measurement tracking mode or continue the overhead tracking mode proposed by the present invention, thereby achieving continuous tracking of the target without losing it.

[0021] In order to further illustrate the implementation steps of the embodiment, the following is described in detail with reference to the accompanying drawings:

[0022] 1. Phased array radar tracks distant targets by sum and difference beam angle measurement, estimates the target's radial velocity, and assists tracking by trajectory prediction. Set the elevation threshold value according to the array inclination angle and the beam scanning range. For example, if the array inclination angle is 20°, the elevation beam scanning range is ±50° on both sides of the array normal. At this time, the threshold value is the sum of the two, which is 70°. When the target elevation angle is lower than 70°, continue to track using the sum and difference beam angle measurement method. When the target elevation angle exceeds 70°, the target exceeds the normal scanning range of the array beam, and the overhead target tracking method proposed in the present invention is adopted.

[0023] 2. When the elevation angle exceeds the beam scanning range, both transmission and reception adopt multi-beam form, Figure 2 It is a multi-beam method with a plum blossom-shaped layout, where beam 1 points to the estimated target position, and the other six beams are equally spaced around beam 1. Adjacent beams are spaced 60° apart and overlap with each other, and also overlap with beam 1.

[0024] 3. Add a Doppler frequency shift compensation factor caused by the motion state of the radar platform to the Doppler frequency of the received clutter and target echo, and estimate the maximum Doppler frequency of the clutter after offsetting the motion state of the radar platform. Multiply the maximum Doppler frequency of the clutter by a coefficient to obtain the target radial velocity threshold value.

[0025] 4. When the target radial velocity is greater than the threshold value, the frequency agility between pulse groups is used, and adaptive MTI processing is adopted within the pulse group to adjust the filter coefficient in real time according to the target radial velocity. Figure 3 is the filter frequency response characteristic curve, and real-time adjustment is made so that the filter passband center is always aligned with the Doppler frequency f corresponding to the target radial velocity. d , stop band alignment clutter, filter out clutter and then perform pulse group accumulation. When the target radial velocity is less than the threshold value, use pulse-to-pulse frequency agility and then perform pulse-to-pulse accumulation to suppress clutter by decorrelation.

[0026] 5. Attachment Figure 2 The target echo amplitudes received by the 7 beams are x1, x2, ... x7, the azimuths of the 7 beam centers are A1, A2, ... A7, and the elevations of the 7 beam centers are E1, E2, ..., E7. Then the estimated azimuth of the target is and the elevation angle estimate They are:

[0027]

[0028]

[0029] The azimuth estimate and elevation estimate obtained by multi-beam focusing are used as the actual position of the target, thereby realizing the tracking of overhead targets.

[0030] 6. After successful tracking, the radial velocity of the target is continuously estimated, and tracking is assisted by trajectory prediction. The target elevation angle value is compared with the elevation angle threshold. If it is higher than the threshold value, the adaptive tracking method for overhead targets proposed by the present invention is continued to be used. If it is lower than the elevation angle threshold value, tracking is switched back to the sum-difference beam angle measurement method.

Claims

1. A phased array radar overhead target adaptive tracking method, characterized by: When tracking with the sum-difference beam angle measurement method, the target elevation angle and radial velocity are estimated. The elevation angle threshold is set by the array inclination angle and the beam scanning range. The target elevation angle is compared with the elevation angle threshold. If it is lower than the threshold, the sum-difference angle measurement method is used for tracking. If it is higher than the threshold, the over-the-top tracking method is used. When tracking over-the-top, both transmission and reception adopt multi-beam form. A central beam is transmitted to the estimated position of the target, and then multiple beams are transmitted at equal intervals around the central beam. After compensating for the Doppler frequency shift caused by the motion state of the radar platform, the target radial velocity threshold is obtained from the maximum Doppler frequency of the clutter. When the radial velocity exceeds the radial velocity threshold, the frequency agility between pulse groups, adaptive MTI within the pulse group, and accumulation between pulse groups are used to achieve clutter removal and target echo detection. When the radial velocity is lower than the velocity threshold, the frequency agility between pulses and accumulation between pulses are used to achieve clutter removal and target echo detection. The overhead target is finally tracked by condensed angle measurement.

2. The phased array radar overhead target adaptive tracking method according to claim 1, characterized in that: During overhead tracking, transmission is in multi-beam form. The central beam of the multi-beam points to the estimated target position. Six beams are equally spaced around the beam. Adjacent beams overlap and also overlap with the central beam. The same multi-beam form is used during reception.

3. The method for adaptively tracking overhead targets with a phased array radar according to claim 1 or claim 2, characterized in that: Setting of radial velocity threshold: The Doppler frequencies of target echo and clutter are compensated by platform motion velocity, and then the maximum Doppler frequency of clutter is estimated. The maximum Doppler frequency of clutter is used as a reference and multiplied by a coefficient as the threshold of radial velocity.

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