JP2006078270A - Radar device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress clutter by a method having a small processing scale, and to detect a target, even in the case where each Doppler velocity of the target and the clutter is similar in a clutter environment. <P>SOLUTION: When determining the number of pulse hits for determining the shape of a frequency filter of MTI 41, if the clutter is strong, the number of hits is determined from a viewpoint wherein the clutter is suppressed by increasing the number of hits of the MTI, and a suppression degree is enlarged to the clutter, and the MTI 41 is executed by a coefficient 44 determined so as not to suppress relative to the target near the clutter, and DFT 42 is executed relative to the signal. Thus, the number of hits for determining the shape of the frequency filter of the MTI 41 is increased, and a null shape to the clutter is sharpened, and a Doppler filter is formed by using the common MTI output. Consequently, coefficient control in each filter bank is not required, and the clutter can be suppressed by the method having the small processing scale, and the target having the similar Doppler frequency can be detected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radar apparatus in general for detecting a low-speed target in a clutter environment.

  If the target appears only instantaneously in a clutter environment, such as a hovering helicopter, perform DFT (Discrete Fourier Transform) or STFT (Short Time Fourier Transform) A method is adopted in which the number of hits is increased more than necessary for a signal that exists only instantaneously, and the number of hits is selected so as not to increase thermal noise, and the signal is detected. At this time, if the clutter is strong, a combination of several pulses of MTI (Moving Target Indicator) and DFT (or STFT) is performed to suppress the clutter.

  Here, when the Doppler frequency of the target and the clutter is separated, the clutter can be suppressed and the signal can be detected. However, when the target is close to the Doppler speed of the clutter as in the case where the target is low speed, not only the clutter but also the target is suppressed, so the target may not be detected by the MTI filter. .

In order to suppress clutter, there is a method of controlling the side lobe shape of the Doppler filter to form a deep null with respect to the clutter, but the filter coefficient is controlled for each Doppler filter, and the processing scale is increased. There was a problem of getting bigger.
Nobuyoshi Kikuma, “Adaptive signal processing by array antenna”, Science and Technology Publishing (1999), pp.67-86: MSN method Nobuyoshi Kikuma, "Adaptive signal processing by array antenna", Science and Technology Publishing (1999), pp. 35-37, 98-99: Direct solution method (SMI method, etc.) Tani, “Digital Signal Processing Theory”, Corona, pp.41-43 (1985): Inverse Fourier Transform (frequency filter)

  As described above, in the conventional radar device, when the clutter and the target Doppler speed are close to each other, the target is not detected because the MTI for suppressing the clutter suppresses the target. . In addition, there is a problem that the processing scale becomes large to control the coefficient for each filter bank of the Doppler filter in order to suppress the clutter.

  The present invention has been made in view of the above circumstances, and provides a radar apparatus capable of detecting a target by suppressing the clutter with a small processing scale even when the clutter and the target Doppler speed are close to each other. The purpose is to do.

  In order to solve the above problem, the radar apparatus according to the present invention is configured as follows.

  (1) Transmission / reception means for acquiring data between PRIs (Pulse Repetition Intervals) of a plurality of pulse hits, and MTI (Moving Target Indicator: Moving Target Indicator) in the data between PRIs obtained by the transmission / reception means. MTI processing means for detecting a target while suppressing the clutter component by processing, and a filter bank for converting the output data of the MTI processing means to the frequency domain and suppressing the clutter component by a plurality of filter banks having different frequency domains The MTI coefficient determined to increase the degree of suppression for clutter and not to suppress the target in the vicinity of the clutter is calculated for the processing means and the MTI processing means, and the MTI is calculated based on the MTI coefficient. And MTI coefficient calculation processing means for performing the above.

  In the radar apparatus having the configuration of (1), not only the thermal noise is not increased more than necessary when determining the number of pulse hits, but if the clutter is strong, the number of MTI hits is increased and the clutter is increased. The number of hits is determined from the viewpoint of suppressing the noise, the MTI is performed with a coefficient determined so as to increase the degree of suppression for the clutter and not to suppress the target in the vicinity of the clutter, and the DFT is applied to the signal. It is characterized by carrying out.

  That is, the number of hits that determine the shape of the MTI frequency filter can be increased, and the shape of the null relative to the clutter can be sharpened. By forming a Doppler filter using this common MTI output, each filter bank Coefficient control is not required, clutter can be suppressed by a method with a small processing scale, and targets close to Doppler frequencies can be detected.

  (2) In the configuration of (1), the mobile device further includes a speed detector for detecting the own machine speed, and the MTI coefficient calculation processing means suppresses the clutter of the installed machine according to the own machine speed. The notch position is determined.

  The radar apparatus having the configuration (2) is characterized in that, when mounted on a moving body, the center frequency of the clutter is calculated according to the speed of the own aircraft, and the position of the null point of the frequency filter of the MTI is set. Can be determined according to the speed of its own position, clutter can be suppressed, and a target with a Doppler frequency close to a target at a short distance can be detected.

  According to the present invention, in detecting a target that appears only instantaneously in a clutter environment, even when the target and the Doppler speed of the clutter are close to each other, it is possible to suppress the clutter and detect the target with a small processing scale. Can be provided.

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

(First embodiment)
FIG. 1 is a block diagram showing a configuration of a radar apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a planar antenna in which a plurality of antenna elements are arranged in an array, which repeatedly emits a transmission pulse output from the transmitter 2 in a specified direction and captures the reflected wave. The captured signal of the reflected wave is frequency-converted by the receiver 3, converted to a digital signal, and sent to the signal processor 4. This signal processor 4 removes clutter components by performing MTI processing on the input received signal based on the MTI coefficient from the MTI coefficient arithmetic processing unit 44 by the MTI processor 41, and the DFT processing unit 42 performs frequency conversion from the time domain. After conversion into the area, the target detection angle measuring processor 43 detects the target and obtains the azimuth elevation angle and outputs it as target information.

  In the above configuration, the processing operation of this embodiment will be described below.

In FIG. 1, a transmission signal input from the transmitter 2 to the antenna 1 is radiated to the space, the received signal is frequency-converted via the antenna 1 and the receiver 3, and further converted into a digital signal. Entered. Here, the received signal of N pulses is subjected to MTI processing for each M range cells of PRI (Pulse Repetition Interval) by the following equation.

  Here, in order to determine the MTI filter coefficient so as to suppress the clutter and not suppress the target signal whose clutter and Doppler frequencies are close to each other, as shown in FIG. Increased to the extent that is not dominant. Formulation for calculating M weight coefficients used in this MTI is performed.

  As the MTI coefficient, it is desirable to set the Doppler frequency of the clutter as fcst to fced, form a null in the range of fcst to fced, and improve the level as much as possible. For this purpose, three methods will be described.

As shown in FIG. 3, the first method is a method of calculating the MTI coefficient with a constraint condition. Generally, it is formulated when the amplitude level is constrained (the main lobe on the frequency axis is a constant value and the clutter range is null). First, the constraint condition is as follows.

The recurrence formula of the complex weight of the MTI when the constraint condition is added using this becomes the following formula.

Using the signal of the N ′ pulse after the MTI processing by this MTI coefficient, DFT is performed by the following equation.

Of course, this DFT processing may be FFT (Fast Fourier Transform).

  FIG. 4 shows the flow of processing until clutter is suppressed by the above processing and a target is detected.

  Here, when calculating the MTI weight, the MSN method (see Non-Patent Document 1) is used, but it goes without saying that other methods such as SMI (see Non-Patent Document 2) may be used.

The second method is a method using inverse Fourier transform to form an MTI filter as shown in FIG. 4 (see Non-Patent Document 3). If the desired filter response is bd, the complex weight (amplitude and phase weight) of the auxiliary beam that approximates the response is expressed as the inverse Fourier transform of bd by the following equation (see Non-Patent Document 3).

Needless to say, a window function may be applied in order to prevent ripples in the filter response after MTI when determining the desired filter response.

As shown in FIG. 5, the third method forms a signal that has a peak at the center frequency of null from the output of one pulse of m = 1 to M, and has an amplitude as shown in the following equation. In addition, a sharp null is formed by subtracting in accordance with the phase.

  DFT may be performed on this bnull signal.

  According to the above processing, when determining the number of pulse hits, not only the thermal noise is not increased more than necessary, but also when the clutter is strong, the number of MTI hits is increased to suppress the clutter. Determine the number of hits from the viewpoint. Then, MTI is performed with a coefficient determined so as to increase the degree of suppression for clutter and not suppress the target near the clutter, and DFT is performed on the signal. In the radar apparatus according to this configuration, the number of hits that determine the shape of the frequency filter of the MTI can be increased, the shape of the null with respect to the clutter can be sharpened, and a Doppler filter can be formed by using this common MTI output. Coefficient control for each filter bank is not required, clutter can be suppressed by a method with a small processing scale, and a target with a close Doppler frequency can be detected.

(Second Embodiment)
FIG. 6 is a block diagram showing the configuration of the radar apparatus according to the second embodiment of the present invention. In FIG. 6, the same parts as those in FIG. 1 are denoted by the same reference numerals, and different parts will be described here.

The radar apparatus shown in FIG. 6 is for mounting on an aircraft or the like, and includes a speed detector 5. The own speed obtained by the speed detector 5 is input to the MTI coefficient arithmetic processing unit 44, and the center frequency of the clutter is obtained. Is calculated by the following equation.

  By setting null for this clutter center frequency, a filter that suppresses clutter and detects a low-speed target can be formed by the same method as in the first embodiment. On the other hand, it is possible to detect a target having a close Doppler frequency.

  The above embodiment has been described in the case of a planar antenna, but it goes without saying that it is effective even in the case of a one-dimensional antenna.

  Further, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram showing a configuration of a radar apparatus according to a first embodiment of the present invention. The figure which shows the processing timing of MTI and STFT with respect to the target and clutter of the radar apparatus shown in FIG. The figure for demonstrating the process example for forming the sharp null in the radar apparatus shown in FIG. The figure for demonstrating the processing operation of the clutter suppression of the radar apparatus shown in FIG. 1, and target detection. The figure for demonstrating the other process example for forming the sharp null in the radar apparatus shown in FIG. The block diagram which shows the structure of the radar apparatus of 2nd Embodiment which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... Transmitter, 3 ... Receiver, 4 ... Signal processor, 41 ... MTI processor, 42 ... DFT processing part, 43 ... Target detection angle measuring processor, 44 ... MTI coefficient arithmetic processor, 5 ... speed detector.

Claims (2)

Transmitting / receiving means for acquiring data between PRIs (Pulse Repetition Intervals) of a plurality of pulse hits;
MTI processing means for detecting the target while suppressing the clutter component by performing MTI (Moving Target Indicator) processing on the inter-PRI data obtained by the transmission / reception means;
Filter bank processing means for converting output data of the MTI processing means into a frequency domain and suppressing clutter components by a plurality of filter banks having different frequency domains;
The MTI processing unit calculates an MTI coefficient determined to increase the degree of suppression for clutter and not to suppress the target in the vicinity of the clutter, and performs the MTI based on the MTI coefficient. A radar apparatus comprising: coefficient calculation processing means. In addition, for mobile mounting, equipped with a speed detector that detects the own machine speed,
The radar apparatus according to claim 1, wherein the MTI coefficient calculation processing means determines a notch position for clutter suppression of the on-board machine according to the speed of the own machine.

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