JPS62225979A - Radar equipment - Google Patents

Abstract

PURPOSE:To achieve a higher visual recognition property of a moving target, by classifying the searching area of a radar into that where ground clutters exist, that where clutters other than the ground clutters exist and that where no clutters exist to suppress the clutters adapted to each area. CONSTITUTION:An area where ground clutters are always generated is detected on a screen of a display and is initialized to automatically detect clutters (e.g. weather clutters) other than ground clutters. This is used to classify the searching area by a radar into that where ground clutters exist, that where clutters other than ground clutters and that where no clutters exist. The control of a signal processing adapted to each area enables the optimization of the visual recognition property of a moving target such as aircraft.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radar device, and particularly to a radar device that performs signal processing to suppress clutter.

[Conventional technology]

Conventionally, in radar devices that display moving targets such as aircraft of this type, ground clutter (fixed clutter) is a signal reflected from the ground, buildings, mountains, etc.; weather clutter is a signal reflected from rain clouds or the sea surface. In order to detect and display moving targets such as aircraft by removing moving clutter such as sea surface clutter, which is a reflected signal from the ocean, various clutter removing means or suppressing means are available.

However, although there are suppression means that are suitable for the fixed clutter and moving clutter mentioned above, it is necessary to manually select the clutter suppression means based on the operator's judgment based on changes in the clutter situation. Many of them are in the best condition.

[My point while the invention is trying to solve]

The problem with the conventional technology that the present invention aims to solve is that, as described above, a corresponding means for removing clutter is prepared, and the operator judges the situation and adjusts the selected clutter suppression means. This makes it difficult to finely adapt to one local area and to quickly follow and adapt to changes in the environment over time, making it difficult to maintain the best visibility of moving targets such as aircraft. There is a point.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a radar device that overcomes the above-mentioned drawbacks.

[Means for solving problems]

The radar device of the present invention includes a first determining means for manually initializing the area where ground clutter exists, a second setting means for automatically detecting and setting the area where all the clutter exists, and the first determining means for automatically initializing the area where ground clutter exists. and separating the search area from the setting area of the second setting means into an area where ground clutter exists, an area where clutter other than ground clutter exists, and an area where clutter does not exist, and suppresses clutter adapted to each area. and a control means for controlling signal processing.

〔Example〕

Next, the present invention will be described in detail with reference to drawings showing embodiments of the present invention.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the process of creating a clutter map from a video signal of the present invention, and FIG. 3 is a clutter setting method of the present invention and its process. A chart showing the control contents of signal processing corresponding to the type of region to be set; FIGS.
The figure is a chart showing changes in characteristics of the grip interpolator in the azimuth direction.

゛The outline of the present invention is to first detect a ground clutter area that regularly occurs on a display screen, make initial settings for that area, and then automatically detect clutter other than ground clutter (such as weather clutter). It is something to do. This allows the radar search area to be
The area is classified into areas where ground clutter exists, areas where clutter other than ground clutter exists, and areas where clutter does not exist. The radar device is capable of performing the signal processing shown in FIG. 3 that is adapted to each of these areas.

First, a method for determining each area will be described.

As shown in FIG. 3, the first step is to set the area where ground clutter exists. PP the received normal video signal
A fan-shaped area is set one by one to encompass the clutter area observed and displayed by the I-scope, and is overlapped to form a map. (First MTI map).

Second, all clutter areas are automatically detected.

In advance, the entire search area is plotted in the azimuth direction (B-
(Ba direction) at a constant unit angle (2.8 degrees in this example) and a constant unit distance (1 nautical mile in this example) in the distance direction (A-Aa direction). (referred to as a cell). A predetermined threshold is applied to the received normal video to quantize the signal. The threshold is usually set to the lowest possible level of receiver noise level, and correlation detection processing is performed on the quantized signal in order to detect clutter and distinguish it from noise. It is desirable to perform correlation processing by measuring the number of hits of the quantized signal within a cell and determining that clutter is present when the number of hits is greater than or equal to the predicted value in the case of receiver noise. However, in Fig. 2, as a simple method, /16
The number of hits is determined, and K(
This example shows means for determining that clutter is present when there is a number of hits equal to or greater than 4). When it is determined that clutter is present in this manner, the clutter map is turned on for the corresponding cell, and a clutter map is formed for the entire search range.

By combining the first MTI map and the clutter map, the entire search area is divided into three areas. That is, the area where the first MTI map is on is called the ground clutter area, and the area where the first MTI map is off and the clutter map is on is called the area where clutter other than ground clutter exists, and the area where the first MTI map is off and the clutter map is on is called the area where clutter other than ground clutter exists. An area where both clutter maps are off is determined to be an area where clutter does not exist.

Next, signal processing suitable for each region will be described. First, in the ground clutter region, the Doppler frequency of the ground clutter is O, so the MTI canceller is activated, and the Doppler filter (hereinafter referred to as filter) is
By using a low sideloop filter compatible with ground clutter, as shown in FIG. 3(a), the clutter reception power is largely removed, and the residual level is suppressed by CFAR processing. Furthermore, among the outputs of a plurality of filters excluding the output of the filter corresponding to Doppler frequency=O, the one with the largest amplitude is selected and further blip interpolation is performed to prevent cracking or missing blips.

Second, in areas where clutter other than ground clutter exists, the Doppler frequency of moving clutter generally changes due to changes in environmental conditions such as wind speed. Use low sidelobe filters. Regarding the selection of channels for the filter, the channel that exhibits the maximum value of amplitude among all channels is selected because there is no ground clutter.

Thirdly, in the region where there is no clutter, the Doppler filter does not have clutter, so 8. /N In order to maximize the degree of improvement, the DFT filter shown in FIG. 4(c) is used, and the filter channel exhibiting the maximum value of amplitude is selected.

Next, the above-mentioned MTI canceller, Doppler filter, CF
If ground clutter remains even after the clutter suppression means of AR processing is performed (i.e., if the received clutter power exceeds the clutter suppression ability by signal processing, and depending on the amplitude distribution characteristics of clutter, CF
'AI? , if the receiver noise characteristics cannot be suppressed in the same way by processing), further processing is performed using the second MTI map. This converts the processed video after the signal processing mentioned earlier into PP
Observe on the I scope and remove the remaining generation area from the first MT.
Set it in the same way as I map. This is the second MTI
CFAR for the area within this map.
The process is similar to the case where ground clutter exists in the first MTI map, except that a predetermined threshold is applied after processing to remove clutter.

The present invention thus performs clutter adaptive signal processing.

Next, an embodiment of the present invention will be described, focusing on its configuration and operation.

As shown in FIG. 1, this embodiment includes a transmitter 1, a circulator 2, an antenna 3, a receiver 4, and an MTI canceller 5.
, Doppler filters 6A to 6N, CFAR processor processing-7A to 7N, Rechehold processors 88 to 8N, filter selector 9, blip interpolator 10, display 11, and clutter area setter 12. It is equipped with a clutter map memory 13 and a clutter detector 14.

The transmitted pulses output from the transmitter 1, which transmits pulses at preset intervals, are input to the antenna 3 via the circulator 2, are emitted as short pulse-shaped radio waves, and are reflected back from the target. The radio waves are received again by the antenna 3 and sent to the receiver 4 via the circulator 2.
Enter.

The receiver 4 mixes the transmission frequency components and performs phase detection on the frequency components that are different from the transmission frequency to produce a coherent video.
A normal video with amplitude detection is generated, and A/
The digital coherent video is input to the MT1 canceller 5, and canceller processing is performed only in the first MTI map based on the IIjlJ all signal from the controller] 7.

The Doppler filters 68 to 6NI/l then select one of the three types of filters preset for each of the three regions mentioned above based on the control signal from the controller 17. It is conventional to separate and extract only the signal components within the pre-designed bus band frequency band, and then to suppress the energy components that spread in the distance direction. It's similar to technology.

Furthermore, in order to remove residual clutter signals that cannot be suppressed to the same amplitude characteristics as noise by the MTI canceller, Doppler filter, and CFAR processing, threshold processors 8A to 31L171- are provided with a second A predetermined threshold is applied only within the MTI map of 2 to remove the remaining clutter signal below the threshold level, and this signal is input to the filter selector 9. Here, for each range bin, the one with the maximum amplitude among the output signals of the threshold processors 98 to 9N is output as the filter selector output signal 101, that is, the prep interpolator input signal.

The filter selector output signal 101 is sequentially input to the prep interpolator 10, which compares the output signals for each of three adjacent orientations corresponding to successive orientations and at the same distance. The signal level corresponding to the central direction among the three consecutive directions is lower than the signal level corresponding to the directions before and after it,
And only when the signal level in the front and rear directions has a signal strength equal to or higher than the noise level, the amplitude interpolated signal in which the signal level corresponding to the central direction is replaced with the average signal level of the signal levels corresponding to the front and rear directions is The signal will be as shown in FIG. This amplitude interpolation signal is smoothed by a built-in smoothing integrator to form a waveform that is convenient for display without causing any splitting of the voltage on the display, that is, a voltage output signal 102 from the voltage interpolator as shown in FIG. It is output and displayed on the display 11. Furthermore, the maximum values of the filter selector output signal Φ amplitude interpolator output signal and smoothing integrator output signal in FIG.
Although there is generally a delay such as -32 due to calculation time, it can be dealt with by correcting the angle signal.

Next, a method for determining the type of search area will be described.

In the present invention, when there is a ground clutter in the search area,
When there is no ground clutter but there are other clutters,
It is determined that there is no clutter, and signal processing that is appropriate for this is performed.

First, in order to manually initialize the area where ground clutter exists, the normal video tP of the output of the receiver 4 is
The area setter 12 sets fan-shaped areas one by one and overlays them so as to include the ground clutter observed on Pl. In order to save the area even when the power is turned off, the specified area is written to the EEPROM (electrically erasable and programmable read-only memory) of the clutter map memory 13, and the first MTI map shown in FIG. Set. The data is sent to the controller 17
It is stored in the memory and used to command the necessary signal processing.

Next, in order to automatically detect and set the areas where all clutter exists, the clutter map shown in FIG. 2 mentioned above is created. First, the search area t - a cell as shown in Figure 2 (in this case, a fan-shaped area of 3.8 degrees in the azimuth direction and 1 nautical mile in the distance direction)
The received signal (referred to as low video signal) 100 obtained when searching in the A-Aa direction is input to the clutter detector 14, and as described above, the clutter area is detected and the clutter map is created according to the procedure shown in FIG. Create. In this way, the clutter map memory 13 has a total of three types of map memories: the first MTI map, the clutter map, and the second MTI map, and in order to control each process according to the algorithm shown in FIG. The controller 17 inputs three types of map information, performs timing adjustment that matches the timing of each process, and outputs a control signal for each processor. That is, from the controller 17, the MTI canceller 5, Doppler filters 6A to 6N, and CFAR processor processing -7A to 7N
Signifold processors 8 to 8N, filter selector 9,
The prep interpolator 10 is controlled according to FIG. By performing signal processing adapted to the clutter area using the method described above, clutter can be effectively suppressed.
Observation of the target can be easily achieved in the best condition.

[Effects of the Invention] As described above in detail, the radar device of the present invention divides the radar search area into an area where ground clutter exists, an area where clutter other than ground clutter exists,
Since signal processing can be performed to suppress clutter by classifying it into regions where clutter does not exist and suppressing clutter in accordance with each region, the visibility of a moving target such as an aircraft can be easily brought to the best possible state.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the process of creating a clutter map from a video signal of the present invention, and FIG. 3 is a clutter setting method of the present invention. Figure 4 (a) is a diagram showing the types of areas set by
) to (c) are charts showing examples of characteristics of a Doppler filter according to an embodiment of the present invention, and FIG. 5 is a chart showing changes in characteristics of a prep interpolator in the azimuth direction. 1...Transmitter, 2...Circulator, 3...Antenna, 4...Receiver, 5...
...MTI canceller, 68~6N...
Doppler filter, 7A~7N...CFAR processing! , 8A to 8N...threshold processor,
9...Filter selector, 10...Blip interpolator, 11...Display, 12...
...Clutter area setter, 13...Clutter map, memory, 14...Clutter detector, 17...Controller.ノθθ, ゛ Uke 4 Shishu (゛ Yori 劃 /ρ/, ゛ PrL ta selection 11, but rarely 3 ridges 1 time ridges Z increments nido) Uenri Kanekyo 20? 70 feet from the exit of b taxi 5. 't-(h'z)

Claims (1)

[Claims] In a radar device, a first setting means for manually initializing an area where ground clutter exists; a second setting means for automatically detecting and setting an area where all clutter exists; Separate the search area from the setting areas of the first and second setting means into an area where ground clutter exists, an area where clutter other than ground clutter exists, and an area where no clutter exists, and suppress clutter adapted to each area. 1. A radar device comprising: control means for controlling signal processing.