JP2010185700A - Radar system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radar system and a signal processing method which can perform simultaneous observation of a plurality of targets different in direction by a single body, and can acquire a high-resolution image of each target. <P>SOLUTION: In a system in which an aircraft 11 tracks an observation target 4 to make images, a pulse equal to or higher than LPRF is transmitted while a beam 12 is switched over one after another. That is, the beam 12 which is directed to the target ever since it is transmitted, in the present circumstances, is directed for observation to other observation targets located in other directions as well. In an ISAR image analysis, only a reflected wave from the observation target 4 is actually needed, and therefore a reception gate 14 can be made smaller enough than usual PRI 17 for one target by controlling the timing of opening the reception gate 14. Thus, a plurality of targets in many directions can be observed simultaneously by adding a beam control function and a timing control function. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radar system capable of acquiring a two-dimensional image while tracking a target, by performing pulse transmission at a period of LPRF (Low Pulse Repetition Frequency) or more while switching a beam at high speed, The present invention relates to a radar system that enables simultaneous observation of a plurality of targets.

  Conventionally, a technique called ISAR (Inverse Synthetic Aperture Radar) that uses rotation and movement of a target aircraft or ship as an image is used as a warning monitoring method using a radar.

  This technology is an image radar technology that applies the principle of SAR (Synthetic Aperture Radar) that can acquire a high-resolution two-dimensional image. In general, radar cross-range resolution is determined by the beam width. The larger the antenna aperture length, the narrower the beam width and the higher the resolution. SAR is a technique for obtaining high resolution in the cross range direction by combining received data of a small aperture antenna by signal processing as if it were acquired by a large aperture antenna.

  On the other hand, ISAR is a technique for generating a high-resolution image in a target azimuth direction using a Doppler frequency generated by a target rotational motion (see, for example, Patent Document 1). As an example of this technology, for example, an X-band synthetic aperture radar is mounted on an aircraft. With this radar, a navigating ship is tracked. For example, when the ship is performing yaw movement, a high-resolution image as if the ship was viewed from above is obtained by the Doppler frequency. Conventionally, only tracking and imaging of a single target has been performed, but it is possible to observe multiple targets. By this method, multiple target ISAR images existing in the same direction can be acquired.

Japanese Patent Laid-Open No. 11-248834

  In the system described above, LPRF is used for target observation. Therefore, even if a plurality of targets are observed simultaneously, it can be applied only when those targets exist in the same direction.

  Further, as a method for simultaneously observing targets existing in different directions, a method of combining a transmission fan beam and a reception multi-beam can be considered. During the observation, the reception gate is opened for one target (one direction).

  However, this method may cause low gain because the transmission is a fan beam, and in order to make the receiving system a multi-beam, the number of reception channels is required according to the target number, and the radar scale increases accordingly. turn into.

  The present invention has been made to solve the above-described problems, and is a radar system capable of tracking and imaging a plurality of targets existing in multiple directions with a single radar that maintains the conventional gain and radar scale. The purpose is to provide.

A radar system according to the present invention includes a transmission unit that transmits pulses having a low pulse repetition frequency or higher toward a plurality of observation targets while sequentially switching observation targets, and a reception unit that receives reflected waves from the plurality of observation targets. An ISAR processing unit for performing a supplement / tracking process based on a received signal received by the receiving unit to calculate position information and an ISAR imaging process;
A multi-target ISAR control unit that performs timing control of a reception gate so that transmission / reception timings do not collide based on position information from the ISAR processing unit, and performs integrated beam control for different-direction targets. .

  According to the present invention, the reception gate is opened only during the time when the target exists. The time generated by this is used for beam operation and pulse transmission / reception to other targets. As a result, multi-target tracking can be performed with a processing system of the same scale as the conventional system.

It is the block diagram and schematic block diagram for demonstrating embodiment which concerns on this invention. It is a schematic block diagram for demonstrating embodiment which concerns on this invention. It is explanatory drawing for demonstrating the pulse transmission / reception timing of embodiment which concerns on this invention. It is explanatory drawing for demonstrating the flow of the process of embodiment which concerns on this invention. It is a schematic block diagram for demonstrating embodiment which concerns on this invention. It is explanatory drawing for demonstrating the pulse transmission / reception timing of embodiment which concerns on this invention. It is a schematic block diagram for demonstrating embodiment which concerns on this invention. It is explanatory drawing for demonstrating the pulse transmission / reception timing of embodiment which concerns on this invention.

Embodiment 1 FIG.
A preferred embodiment of the present invention will be described with reference to the drawings. The radar system of the present invention may be used for observing a moving target with a radar capable of synthetic aperture processing. For example, the radar system can be applied to ship observation using an aircraft-mounted radar or aircraft observation using a ground control radar. However, in the following explanation, an example applied to an airborne radar will be introduced. That is, a system that enables tracking and imaging of a two-boat vessel will be described.

  FIG. 1 is a block diagram and schematic configuration of a radar system according to the present invention. In the conventional ISAR system, the excitation signal generated by the exciter 1 is converted into a transmission signal by the transmitter 2 and transmitted from the antenna 3 toward the observation target 4. Since pulses are transmitted at a constant pulse repetition frequency PRF, transmission timing control is unnecessary. The reflected wave from the observation target 4 is received again by the antenna 3 and converted into an IQ video signal by the receiver 5. Since the single target is continuously observed, it is not necessary to control the opening timing of the reception gate during observation.

  The IQ video signal is sent to the ISAR processing unit 6 where capture / tracking processing 6 is performed to calculate position information. Conventionally, beam control is performed based on this position information in order to track the movement of the observation target 4. Further, the ISAR imaging process 8 is performed simultaneously, and the generated ISAR image is displayed on the display 9.

  In the present invention, a multi-target ISAR control unit 10 is added to the above-described conventional radar system to enable tracking and imaging of two targets existing in different directions. First, the PRF must be doubled to accommodate two goals. In addition, in order to simultaneously observe the targets 4 having different azimuths, it is necessary to perform beam control on the antenna 3. Furthermore, since the reflected waves from two targets with different distances have different reception timings, reception gate control is also required. In this way, the multi-target ISAR control unit 10 integrally performs the timing control of the reception gate so that the transmission / reception timing does not collide and the beam control for the two targets of different directions.

FIG. 2 shows a schematic configuration of the present invention. In FIG. 2, an aircraft 11 is equipped with the radar system of the present invention shown in FIG. The ships 4a and 4b are observation targets, and the aircraft 11 simultaneously tracks and images the two targets while switching the beam 12. In FIG. 2, R _a and R _b indicate distances to the observation targets 4a and 4b, respectively.

FIG. 3 shows the operation concept of the two-target simultaneous observation in the present invention. The distances t _a (15a) and t _b (15b) between the transmission pulse 13 and the reception gate 14 of the observation targets 4a and 4b are expressed by the following equation (c: speed of light) depending on the distance to the target. Since the observation target 4a, the distance 4b different, _{t a} and _{t b} takes different values.

  Here, considering the size of the receiving gate from the size of the ship to be observed, the fact that it can be made sufficiently smaller than the conventional pulse repetition interval PRI (Pulse Repetition Interval) makes it possible to transmit and receive toward the observation target 4a. Even if it is delayed by half of the conventional PRI 17 and superimposed on the observation target 4b, the transmission pulse and the reception gate do not collide. Thus, if the combination of the observation targets 4 is such that the transmission / reception timing does not collide even if one of them is shifted, the PRI 16 can be reduced to half of the conventional PRI, that is, the PRI 17 per target.

  The operation will be described below. First, the aircraft 11 directs the beam 12b toward the observation target 4b and transmits a transmission pulse 13b. Thereafter, the direction of the beam is changed (12a), and the transmission pulse 13a is transmitted to the observation target 4a. Next, the direction of the beam is changed (12b), the reception gate 14b is opened, and the reflected wave from the observation target 4b is received. Finally, the direction of the beam is changed (12a), and the reception gate 14a is opened to receive the reflected wave from the observation target 4a. By repeating this operation, two targets are simultaneously observed while maintaining the conventional PRI per target.

  FIG. 4 shows the flow of processing for multi-target observation. First, an observation target area is searched and an observation target is selected (S100). Next, a timing chart is created according to the distance to each target (S101). Here, since simultaneous observation is impossible depending on the distance to the target, whether or not simultaneous observation is possible is determined (S102). Thereafter, beam control and timing control (S103) are performed. Therefore, the position data obtained by the capture / tracking process (S104) is fed back to the timing chart creation (S101), and the data obtained by the ISAR imaging (S105) is output as an image (S106).

  In the present invention, since transmission / reception is performed while switching the beam in a complicated manner, when one reflected wave is observed, the other reflected wave may enter the side lobe of the received beam. Therefore, in implementing this invention, it is necessary to take measures against unwanted waves from multiple targets such as using a low sidelobe beam or using a sidelobe canceller.

  In addition, as a countermeasure against the above-described unwanted waves, it is possible to reverse the chirp direction of the frequency modulation of the pulse, or apply a phase modulation to the pulse so that only necessary signals can be separated even if interference occurs. Good.

  Conventionally, multi-target tracking is enabled by system multiplexing, whereas in this embodiment, multi-target tracking is enabled by resource distribution. Conventionally, the scale of the processing system increases as the number of targets increases, but in this embodiment, the scale of the transmission / reception system does not change.

Embodiment 2. FIG.
In the following description, as in the above-described embodiment, an example applied to an aircraft-mounted radar will be introduced. That is, a system that enables tracking and imaging of a plurality of ships will be described.

FIG. 5 shows a schematic configuration of the present invention. In FIG. 5, the aircraft 11 is equipped with the radar system of the present invention. Assume that the ships 4a, 4b,..., 4N are observation targets in total N 艘, and the aircraft 11 tracks and images the plurality of targets simultaneously while switching the beam 12. _{R a,} R b in FIG. 5, showing ..., each _{R N} observation target 4a, 4b, ..., the distance to 4N.

FIG. 6 shows the operation concept of simultaneous observation of multiple targets in the present invention. The distances t _a , t _b ,..., TN (15) between the observation targets 4a, 4b,..., 4N transmission pulse 13 and the reception gate 14 are expressed by the following equation depending on the distance to the target. Since the observation target 4a, 4b, ···, the distance 4N _{different, t a, t b, ···} , t N takes a different value.

  Here, the PRI 16 is shortened to 1 / N (N: a natural number not including 0) of the conventional PRI 17, and N targets are simultaneously observed. For example, even if the transmission / reception of the observation target 4a is shifted by 1 * PRI and the transmission / reception of the observation target 4c is shifted by (N-1) * PRI respectively, There is no collision. In this way, if the combination of the observation targets 4 is such that the transmission / reception timing does not collide even if each of the PRIs 16 is shifted, the PRI 16 is reduced to 1 / N of the prior PRI, that is, the apparent PRI 17 per target. be able to.

  Therefore, simultaneous observation is possible if N satisfies the following conditions.

  The operation will be described below. First, the aircraft 11 directs the beam 12b toward the observation target 4b and transmits a transmission pulse 13b. Thereafter, the direction of the beam is changed (12a), and the transmission pulse 13a is transmitted to the observation target 4a. Next, the direction of the beam is changed (12N), the reception gate 14N is opened, and the reflected wave from the observation target 4N is received. The reflected wave from the observation target 4N is transmitted to the observation target 4N in the previous cycle of this one cycle, and transmission / reception can be assigned beyond the cycle in this way. Next, the direction of the beam is changed (12a), and the reflected wave from the observation target 4a is received by the receiving gate 14a. Similarly, the direction of the beam is changed (12b) and the reflected wave from the observation target 4b is received by the receiving gate 14b. Receive. Finally, the direction of the beam is changed (12N), the transmission pulse 13N is transmitted to the observation target 4N, and the observation of one cycle is completed. Naturally, a total of N transmissions / receptions are performed during these operations. By repeating this operation, N targets are simultaneously observed while maintaining the conventional PRI 17 per target.

Embodiment 3 FIG.
In the following description, as in the above-described embodiment, an example applied to an aircraft-mounted radar will be introduced. That is, a system that enables tracking and imaging of a plurality of ships will be described.

FIG. 7 shows a schematic configuration of the present invention. In FIG. 7, an aircraft 11 is equipped with the radar system of the present invention. Ships 4a, 4b, 4c, and 4d are, for example, a total of four observation targets, and aircraft 11 tracks and images the plurality of targets simultaneously while switching beams 12. In FIG. 7, R _a , R _b , R _c , and R _d indicate distances to the observation targets 4a, 4b, 4c, and 4d, respectively.

FIG. 8 shows the operation concept of simultaneous observation of multiple targets in the present invention. The distances t _a , t _b , t _c , and t _d (15) between the transmission pulses 13 of the observation targets 4a, 4b, 4c, and 4d and the reception gate 14 are expressed by the following equations depending on the distance to the target.

Since the distances of the observation targets 4a, 4b, 4c, and 4d are different, t _a , t _b , t _c , and t _d take different values. Here, a conventional system capable of simultaneously observing, for example, four targets with different azimuths by setting the pulse transmission interval 18 irregularly while maintaining the conventional PRI 17 per target. The transmission pulse interval 18 is shifted by an arbitrary time so that the transmission pulse 13 and the reception gate 14 do not collide. If the observation target 4 is not a combination that causes a collision no matter how it is shifted, it is possible to simultaneously observe a plurality of targets while maintaining the conventional PRI, that is, the apparent PRI 17 per target. By using irregular pulses, an increase in the number of observation targets N can be expected as compared with the case of using regular pulses.

  The operation will be described below. First, the aircraft 11 directs the beam 12a toward the observation target 4a and transmits a transmission pulse 13a. Thereafter, the direction of the beam is changed (12d), and the transmission pulse 13d is transmitted to the observation target 4d. Next, the direction of the beam is changed (12a), the reception gate 14a is opened, and the reflected wave from the observation target 4a is received. Next, the direction of the beam is changed (12c), and the transmission pulse 13c is transmitted to the observation target 4c. Next, the direction of the beam is changed (12b), the reception gate 14b is opened, and the reflected wave from the observation target 4b is received. The reflected wave from the observation target 4b is transmitted to the observation target 4b in the period before this one period, and transmission / reception can be assigned beyond the period in this way. Next, the direction of the beam is changed (12d), the reception gate 14d is opened, and the reflected wave from the observation target 4d is received. Next, the direction of the beam is changed (12b), and the transmission pulse 13b is transmitted to the observation target 4b. Finally, the direction of the beam is changed again (12c), the reception gate 14c is opened, the reflected wave from the observation target 4c is received, and one cycle of observation is finished. This operation is repeated to simultaneously observe a plurality of targets while maintaining the conventional PRI per target.

  In addition to ISAR, it is also possible to use a method using irregular pulses for transmission in order to integrate transmission and reception.

  4 observation target, 10 multi-target ISAR control unit, 11 aircraft, 12 beams, 13 transmission pulses, 14 reception gate, 16 PRI, 17 PRI per target, 18 pulse transmission interval.

Claims (5)

A transmission means for transmitting a pulse having a low pulse repetition frequency or more toward a plurality of observation targets while sequentially switching the observation target;
Receiving means for receiving reflected waves from a plurality of observation targets;
An ISAR processing unit for performing a supplement / tracking process based on a received signal received by the receiving unit to calculate position information and an ISAR imaging process;
A radar system comprising: a multi-target ISAR control unit that performs timing control of a reception gate so that transmission / reception timings do not collide based on position information from the ISAR processing unit, and performs integrated beam control for targets in different directions. The radar system according to claim 1, wherein
The multi-target ISAR control unit sets an interval t _N between transmission pulses and reception gates of a plurality of observation targets N (N: a natural number not including 0) to t _N = 2R _N / c (where _RN is a plurality of observations) The distance to the target, c is the speed of light), the pulse repetition interval PRI is set to 1 / N of the apparent pulse repetition interval PRI per target, and the apparent pulse repetition interval PRI is ≧ (pulse width + receiving gate width) + A beam switching time), and a radar system that performs simultaneous observation of a plurality of observation targets N. The radar system according to claim 1 or 2,
The radar system according to claim 1, wherein the multi-target ISAR control unit tracks and observes observation targets of different multi-directions. The radar system according to claim 3, wherein
The multi-target ISAR control unit irregularly sets the pulse transmission timing for multi-directional observation targets according to the distance to each observation target, and tracks multiple multi-directional multi-targets while switching the observation target one after another. A radar system characterized by image processing. The radar system according to any one of claims 1 to 4,
The multi-target ISAR controller has a sidelobe canceller, a function of reversing the direction of chirp of frequency modulation of the pulse, and a function of performing phase modulation on the pulse, and is generated by switching the beam to a plurality of directions. Radar system characterized by reducing or eliminating interference of received signal from

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