JPH0242438B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a radar system.

Radar systems that use directional antennas and pulsed radio waves to obtain information regarding the direction and distance of a target are well known.

In the radar system, pulsed radio waves are transmitted and received via a directional beam pattern formed by a directional antenna, and in addition to azimuth and distance data as position information regarding the target reflector, the azimuth and distance of this reflector are also obtained. Information on the spread of directions and information on the intensity is obtained, but the directional beam pattern formed by the directional antenna has side lobes in addition to the main lobe, and it is difficult to detect the reflected target. When the target becomes large enough to a certain extent, this large reflecting target is also received by transmission via side lobes, and the accuracy of azimuth measurement decreases because the received signal is captured by the side lobes close to the main lobe. Along with this, false images (ghosts) appear due to sidelobe reception, making it difficult to identify the target, and especially when it comes to automatic radar data processing, errors in target acquisition/tracking are likely to occur. It has some disadvantages.

FIG. 1 is a general characteristic diagram of a directional beam pattern.

The directional beam pattern shown in Figure 1 has side lobes d as well as a main lobe D, which has directional characteristics corresponding to conditions such as the structure of the directional antenna and the pulse radio frequency.
In addition to the images captured corresponding to the main lobe D, the images displayed on the screen of the Ray Tube (ray tube) also display the images received by the side lobe d.

Target Q is a large reflective target, for example, an extremely large target of several hundred thousand tons in sea area such as a port, and the receiving input is
Considering the case where it is displayed on a CRT screen,
Such a large reflective target is often also received by the side lobe d and is displayed together with the received signal by the main lobe in response to the rotational scanning of the beam pattern, resulting in the above-mentioned drawbacks.

The antenna gain ratio between the main lobe and side lobe of a directional antenna, the so-called side lobe ratio, is usually suppressed to a level of about 20 to 30 dB. Although it is easy to set the reception sensitivity so that reception due to side lobes is impossible for targets whose size falls within a limited range, for example ships, which range from several tons to hundreds of thousands of It can be said that it is basically impossible to set the receiving sensitivity to eliminate reception via side lobes when the size is extremely wide, such as a ton or more. In such cases, large reflective targets are received not only through the main lobe, but also through side lobes, which may appear as artifacts on the CRT screen, making it difficult to identify the target, or may also be automatically detected from the received signal. As mentioned above, many problems such as erroneous acquisition/tracking occur in the radar data automatic processing for tracking a target based on the received target information extracted in the above-mentioned manner.

FIG. 2 is a sidelobe reception characteristic diagram showing a typical example of sidelobe reception of a large reflective target.

The image of a large reflective target displayed on the CRT screen P is not only the main lobe image V _n but also the side lobe image V _s displayed by the received signal from the side lobe that rotates and scans together with the main lobe. is displayed on a substantially concentric circle from the center O to V _n as shown in FIG. This sidelobe image V _s is generated in response to the sidelobe ratio, transmission level, reception sensitivity, etc. If the sidelobe ratio is constant, it can be generated by increasing the transmission level and/or reception sensitivity. In extreme cases, they can often occur around the entire circumference of concentric circles.

Conventional radar systems have not taken countermeasures against sidelobe reception for large reflecting targets that would cause obvious drawbacks, and as a result, the above-mentioned drawbacks cannot be avoided.

The purpose of the present invention is to eliminate the above-mentioned drawbacks and to provide a large reflective target that exhibits a high reflected power level that may cause sidelobe reception from received echoes in a radar system that uses a directional antenna to obtain target position information. In addition, in a predetermined scanning area set based on reflection information regarding these large reflective targets, a means is provided to reduce reception sensitivity to a predetermined level in successive radar scans in order to suppress sidelobe reception. This greatly improves the accuracy of azimuth measurement for large reflective targets, basically eliminates the generation of false images due to sidelobe reception, greatly facilitates target identification, and eliminates the possibility of false targets when automatically processing radar data. The object of the present invention is to provide a radar system that can basically eliminate acquisition/tracking.

The method of the present invention is a radar method that determines the direction of a target by transmitting and receiving radio waves through a directional antenna, and also receives signals using side lobes of a directional beam pattern formed by the directional antenna. Detecting and storing reflection information regarding the distance, extent, and intensity of a large reflecting target exhibiting a large reflected power for each radar scan, and eliminating reception of the large reflecting target due to the side lobe in successive radar scans. The apparatus includes a receiving sensitivity control means for controlling the receiving sensitivity to be lowered to a predetermined level in each predetermined scanning area set based on the reflection information.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 3 is a block diagram showing one embodiment of the present invention.

The radar system of the present invention shown in FIG. 3 includes a detector 1, OR circuits 2 and 3, memories 4 and 5, a counter circuit 6, a flip-flop circuit 7, a NOT circuit 8,
It is configured to include a selector 9 and an attenuator 10.

In FIG. 1, a radar reception signal input through an input terminal 101 is transmitted to a detector 1 and an attenuator 1.
0.

Detector 1 sets the reception sensitivity so that only large reflecting targets are received by the main lobe formed by the directional antenna of the radar device, and then selects high-resolution signals from the received signal that may cause sidelobe reception. This is a detector that detects echoes due to level reflection targets.

Detector 1 detects the received signal using a low-sensitivity amplifier with a suppressed gain so that the sidelobe reception is approximately below the receiver noise level, and is aimed at a preset standard high-level reflection target. The sensitivity is set to such a low level that there is no sidelobe reception, and therefore, all targets having a target size larger than this reference high-level reflection target will be detected as high-reflection targets.

The output of detector 1 is via output line 102
It is supplied as one input to OR circuits 2 and 3.

The OR circuit 2 sends the addition result of the detection output supplied from the detector 1 and the output of the memory 4 to the memory 4, and the memory 4 sends the detection output thus sent out from the counter circuit 6 to the output line 603. One scan is written in and read out in the following manner by a memory addressing signal supplied through the memory addressing signal and a write/read signal supplied from the flip-flop circuit 7 through an output line 702.

That is, the counter circuit 6 is supplied with a clock signal via the input terminal 601, and the counter circuit 6 is supplied with a clock signal via the input terminal 601.
The OR circuit 2 is supplied with a radar trigger signal that triggers the transmission of the radar device via an output line 603, and after counting a clock signal of a predetermined frequency every time the radar trigger signal is input, outputs it as a memory address signal to the memories 4 and 5 via an output line 603. Specifies the address at which the output of detector 1 input via is to be stored for each sweep.

The memory 4 having the memory address thus designated is supplied with a write/read signal supplied from the flip-flop circuit 7 via an output line 702.

The write/read signal is composed of binary logic values “1” level and “0” level that are alternately repeated every radar scan of the CRT, and memories 4 and 5 both have the logic value “1” level. It operates in write mode when it is receiving the signal, and operates in read mode when it is at the logic "0" level.

The flip-flop circuit 7 connects North (North) in the radar scan via an input terminal 701.
It repeats setting and resetting every time it receives a source reference pulse supplied from the radar device for each sweep corresponding to the north) direction, and outputs a logic value "1" level write signal to the output line when in the set state. . This write signal continues for one radar scan period until the flip-flop circuit 7 is reset in response to the next north reference pulse. Therefore, the memory 4 receives the write signal and continues for one radar scan period to control the output of the OR circuit 2. Each sweep will be stored.

In this way, the received signal data stored one sweep at a time in the memory 4 is fed back to the OR circuit 2 as another input to the OR circuit 2, and the sweep integral for one radar scan (received signal data for each sweep) is fed back to the OR circuit 2 as another input to the OR circuit 2. The data is converted into time series data corresponding to the radar range by performing OR addition for one radar scan period for each sweep, and is stored in the memory 4. Therefore, this time-series data is composed of highly reflective targets with a possibility of sidelobe reception in the echoes included in the received signal.

In this way, the time series data obtained by performing sweep integration for one radar scan is read out in the next radar scan by a read signal with a logic value of "0" supplied via the output line 702, and is sent to the selector. Sent on 9th.

The selector 9 corresponds to the binary logical value "1" or "0" output from the NOT circuit 8, and selects the output of the memory 4 when the output is at the "1" level, and selects the output from the memory 4 when the output is at the "0" level. The output of the memory 5 is selected and supplied to the attenuator 10. When the output of the NOT circuit 8 is at the "1" level, the output of the flip-flop circuit 7 is at the "0" level, that is, the memory 4 is in the read mode, the memory 5 is in the write mode, and the output of the NOT circuit 8 is at the "0" level. When it is at the "0" level, the output of the flip-flop circuit 7 is at the "1" level, the memory 5 is in the read mode, the memory 4 is in the write mode, and the contents of the memory 5 are selectively output.

FIG. 4 is a time series data formation diagram showing an example of time series data formation by sweep integration for one radar scan in the embodiment of FIG.
4 is a radar image diagram showing an example of a CRT image obtained by one radar scan, and FIG. 4B is a characteristic diagram of time-series data based on echoes in the radar image of FIG. 4A.

In Fig. 4A, the sweep line that is swept around the screen from the center point O of the CRT screen P in synchronization with the transmission by the radar trigger signal is set at a constant point N on the screen P, which corresponds to the north direction, as a reference point. Complete one radar scan by turning 360 degrees in the direction of the arrow at turning speed.

In FIG. 4A, for example, if a, b, and c are three large reflective targets with sidelobe reception, these are the results of sweep integration by OR circuit 2 and memory 4, or OR circuit 3 and memory 5. , time series data arranged on time T corresponding to the sweep length as shown in Figure 4B.
converted to a′, b′ and c′. The sweep length indicated by time T corresponds to the radar range, and the time series data a', b', and c' are large reflecting targets whose side lobe reception should be suppressed during reception in this radar range. It gives information about the number, distance and level of targets as well as the size of the target.

Now, the selector 9 outputs time series data as shown in FIG.
Send to 0.

The attenuator 10 applies an attenuation amount corresponding to the distance, time width, and level of each large reflecting target indicated by the supplied time-series data to the radar reception signal, and outputs this to the output terminal 100.
1 to the radar receiver, the gain is attenuated in the range where sidelobes can be received due to large reflecting targets, thereby suppressing sidelobe reception. In this case, information on determining whether to perform reception sensitivity control to suppress sidelobe reception in all directions for each target large reflecting target, or to use a preset characteristic azimuth range centered on the target large reflecting target is sent to the input terminal 100 via the console of the radar device, etc. together with information regarding the level of reduction in reception sensitivity to be controlled.
2 to the attenuator 10, and is also separately given to the receiver, CRT display circuit, etc. as a system operation control signal, and one radar scan stored based on the received signal acquired by one radar scan in this way. The so-called feed control suppresses sidelobe reception in the next radar scan over a desired scanning area based on the sweep integral data of a large reflecting target with the possibility of sidelobe reception.
Forward-like sidelobe reception control becomes possible.

Note that although the processing example of this embodiment explained with reference to FIGS. 3 and 4 is based on the case where there are three large reflecting targets for which sidelobe reception is possible, the number of large reflecting targets that can receive sidelobes is It is clear that it can be implemented in the same way.

As explained above, according to the present invention, the receiving sensitivity of the large reflecting target detection range in the next radar scan can be adjusted to a desired level based on the data regarding the distance and spread of the large reflecting target that may cause sidelobe reception in the received signal. By providing a means for suppressing sidelobe reception by reducing the area in different areas, the accuracy of azimuth measurement for large reflective targets can be greatly improved, and false images caused by sidelobe reception can be basically eliminated to identify the target. The present invention has the advantage that it is possible to realize a radar system that greatly facilitates the process of acquisition and tracking of targets, and that can greatly reduce errors in target acquisition/tracking performed through automatic processing of radar data.

[Brief explanation of drawings]

Figure 1 is a general characteristic diagram of a directional beam pattern.
Fig. 2 is a sidelobe reception characteristic diagram showing a typical example of sidelobe reception of a large reflective target, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4A is a CRT image obtained by one radar scan. FIG. 4B, which is a radar image diagram showing an example, is a characteristic diagram of time-series data due to echoes in the radar image of FIG. 4A. 1...Detector, 2,3...OR circuit, 4,5...
...Memory, 6...Counter circuit, 7...Flip-flop circuit, 8...NOT circuit, 9...Selector,
10...Attenuator.

Claims (1)

[Claims] 1 In a radar system that determines the direction of a target by transmitting and receiving radio waves via a directional antenna, a reflection of a size that can also be received by a side lobe of a directional beam pattern formed by the directional antenna. Reflection information regarding the distance, spread, and intensity of a large reflecting target that indicates power is detected and stored for each radar scan, and in successive radar scans, reception sensitivity is adjusted so as to eliminate reception of the large reflecting target due to the side lobe. A radar system comprising: a receiving sensitivity control means for controlling reception sensitivity to a predetermined level over a predetermined scanning area set based on the reflection information.