JPH06242233A - Radar apparatus for detecting moving target - Google Patents

Abstract

PURPOSE:To restrict unnecessary reflected signals from the ground (sea) surface where the Doppler frequency is low and to detect a target moving at low speed having a Doppler frequency considerably close to the frequency of the reflected signals, by providing a pulse transmitting/receiving means, a DPCA (Displaced Phase Center Antenna) processing means and an FFT (high-speed Fourier transform) processing means. CONSTITUTION:A DPCA processing device 132 delays one of the digital received signals by the amount corresponding to the PRI (repetition frequency cycle of transmission pulses) at a PRI delay circuit 132a, and subtracts the other receiving signal at a subtracting circuit 132b. The remainder output is sent to an FFT processing device 134 for an FFT treatment. The output data of the processing device 132 is updated every 2XT based on the timing of the Rx input data, FFT input data and FFT output data of the processing device 132 and therefore, the width of an FFT filter bank is 1/2, enhancing the resolution of the frequency. Accordingly, the FFT sampling time is elongated to the PRI delay time, so that the detection efficiency of a target moving at lower speed can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving target detecting radar apparatus which is mounted on a moving body such as an aircraft and which detects a small target which is moving on the sea surface at a low speed.

[0002]

2. Description of the Related Art As one of methods for detecting a moving target by a radar device mounted on a moving body, DPCA (Displaced
The processing called Phase Center Antenna) is known. FIG. 9 shows an example of the DPCA processing system.

In FIG. 9, the antenna device 11 is R, L2.
It has two antennas 111 and 112. These antennas 1
The reference numerals 11 and 112 are arranged parallel to the flight plane of the moving body and separated by an appropriate distance, and radiate and receive electric power with a predetermined beam width.

The transmitter / receiver 12 is provided with each antenna 111, 112.
Through, two pulses are repeatedly transmitted at a constant cycle, and the reflected signal is received. That is, transmission waveform generation, reception power amplification, frequency conversion, and quadrature detection are performed. The two received signals of L and R obtained by the transmitter / receiver 12 are both sent to the signal processor 13.

In the signal processing device 13, the A / D (analog / digital) converter 131 converts the two received signals into digital signals, which are then sent to the DPCA processor 132.
The DPCA processor 132 suppresses the clutter component by delaying one digital reception signal by a PRI (transmission pulse repetition period) delay circuit 132a by an amount corresponding to PRI and then subtracting the other digital reception signal by a subtraction circuit 132b. The target detector 133 detects the target signal after removing the residual clutter component from the output of the DPCA processor 132. The target signal thus obtained by the signal processing device 13 is sent to the display device 14 and displayed appropriately. Here, the ideal operation of the DPCA processor 132 will be described with reference to FIG.

In FIG. 10, when components from the direction perpendicular to the velocity direction of the mounted moving body are received in the reception beam as shown in (A0), as shown in (B0), components from directions other than the vertical direction are received. When receiving the components, each DPCA
The frequency response is illustrated in (A1) and (B1), the received reflection spectrum is illustrated in (A2, B2), and the spectrum after DPCA processing is illustrated in (A3) and (B3).

That is, the received signal from the direction perpendicular to the speed direction of the mounted moving body is not affected by Doppler due to its own movement, and unnecessary reflection (clutter) from the sea surface is Doppler 0.
The notch of the DPCA frequency response is formed at 0 [Hz] while spreading around [Hz].

On the other hand, a received signal from a direction other than the vertical direction is
Since it shifts on the frequency axis due to Doppler due to its own movement, the unnecessary reflection from the sea surface also shifts accordingly, and at the same time, the notch of the DPCA frequency response is formed at the center of the unnecessary reflection spectrum from the sea surface.

As described above, according to the DPCA processing method,
Since the notch of the DPCA frequency response and the center of the unwanted reflection spectrum from the sea surface overlap in all directions within the beam, it is possible to effectively suppress the unwanted reflection from all the sea surfaces within the beam.

By the way, in the conventional airborne radar device, the target moving target is usually a high-speed moving body such as an aircraft or a missile which exhibits a high Doppler frequency. Therefore, if the processing by DPCA is performed, only unnecessary reflection signals due to surface reflection or sea surface reflection can be effectively suppressed, and the target can be reliably detected. This state is shown in FIG.

However, when a low-speed moving target that moves slowly on the surface of the earth or the sea surface is used for detection, the Doppler frequency of the target itself is low and is close to the spread of the Doppler frequency of the unwanted reflection signal (in the case of Therefore, the power of the target signal is suppressed only by the DPCA process, and the target cannot be detected. This phenomenon is remarkable for a low speed target existing in an environment where the spread of the unwanted reflection signal spectrum is large (eg, on the sea surface). This state is shown in FIG.

[0012]

As described above, in the conventional moving object detecting radar device mounted on the moving body by the DPCA processing method, when an attempt is made to detect a low speed target on the surface of the earth or the sea surface, unnecessary reflection components are generated. Since the target signal is also suppressed when the signal is suppressed, it is difficult to detect the target.

The present invention has been made to solve the above problems, and suppresses an unnecessary reflection signal from the ground surface or the sea surface having a low Doppler frequency, while at the same time, a low-speed target having a Doppler frequency very close to the signal is suppressed. It is an object of the present invention to provide a moving target detection radar device that can detect accurately.

[0014]

In order to achieve the above-mentioned object, a radar for detecting a moving target mounted on a moving body according to the present invention transmits a transmission pulse at a constant cycle using a pair of antennas arranged at a predetermined interval. A pulse transmitting / receiving means for obtaining two received signals, and a DPCA for suppressing a clutter component by delaying one of the two received signals obtained by this means by a repetition period of a transmission pulse and performing subtraction processing with the other received signal. The processing means and the FFT processing means for performing fast Fourier transform on the processing result of the DPCA processing means to further suppress only the clutter component are provided, and the target is detected and displayed from the processing result of the FFT processing means. Is characterized by.

[0015]

In the radar apparatus for detecting a moving target having the above structure, the DPCA processing means and the FFT processing means are combined in series, and several FFT filter banks are provided within a range where the Doppler frequency of the low speed moving target is estimated to be obtained. ,
The frequency analysis in each bank is performed with high accuracy.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below with reference to FIGS. In FIGS. 1, 3, and 6, the same parts as those in FIG. 9 are designated by the same reference numerals, and different parts will be mainly described.

FIG. 1 shows a first embodiment of the radar device according to the present invention.
FFT (Fast Fourier Transform) in series with CA processor 132
A processor 134 is provided.

That is, two antennas 11 of R and L
The reflected signals received at 1 and 112 are frequency-converted into video signals in the R and L transmitting / receiving devices 12, respectively, and converted into digital signals in the A / D converter 131 in the input stage of the signal processing device 13.

DP to which these digital received signals are input
The CA processor 132 delays one of the received signals by an amount corresponding to PRI by the PRI delay circuit 132a, and then, the subtraction circuit 13
In 2b, the clutter component is suppressed by subtracting the other received signal.

Here, when targeting a low speed moving target,
As described above, since the received signal from the target has a low Doppler frequency, the attenuation of the target signal itself increases when DPCA processing is performed, and the required SC ratio (received signal from the target / received signal from the clutter) is improved. It is difficult to detect the target because it is not obtained.

Therefore, in the above embodiment, the DPCA processor 132 and the FFT processor 134 are combined in series, and several FFT filter banks are provided within the range in which the Doppler frequency of the slow moving target is estimated to be obtained. We decided to perform frequency analysis within each bank with high accuracy.

FIG. 2 shows the situation. FIG. 2A shows a frequency response of signal processing for a certain direction within the reception beam, where A is a DPCA response and B is a FFT filter bank response. Now
When there is a target signal component close to the frequency distribution of the sea surface clutter on the Doppler frequency axis as shown in FIG. 2 (b), the sea surface clutter component is DP as shown in FIG. 2 (c).
Although suppressed by the CA process, since the target component is in the FFT filter bank, almost the same power can be obtained by the filtering process and the required SC ratio improvement is achieved.

Therefore, in the radar apparatus having the above-mentioned structure, the target detector 133 can detect the target by performing processing such as peak detection, and thereby the position of the slow moving target can be displayed on the display 14. Can be displayed.

By the way, when it is desired to detect a moving target as slow as possible, the FFT processor 134 uses one FF.
The frequency width of the T filter bank may be narrowed. This can be realized by increasing the number of FFT points. However, since the processing time increases at the same time, real-time processing becomes difficult. In particular, when the target is searched while scanning the beam, the number of points cannot be increased because the FFT process must be completed in a short time. If the number of points is fixed, the frequency width of the filter bank can be narrowed by lengthening the sampling time. On the other hand, in the DPCA processing, it is desired to reduce the PRI delay time because it is desired to suppress the unnecessary reflection signal spread on the Doppler frequency axis as much as possible.

FIG. 3 shows the situation. First, when the PRI delay time is long, the notch of the DPCA frequency response becomes narrower with respect to the clutter component as shown in FIG. 3 (A1), and the residual clutter of the DPCA output becomes larger as shown in FIG. 3 (A2). Will end up. On the other hand, if the PRI delay time is shortened, as shown in FIG.
Since the A frequency response spreads in the frequency direction,
As shown in (B2), the residual clutter of the DPCA output can be reduced.

In the configuration of FIG. 1, one digital reception signal of the A / D converter 131 is Rx (R) data, the other digital reception signal is Rx (L) data, and the PRI delay time is Tx.
(1 / pulse repetition period) [sec] If constant, DP
Rx (R) data (R (t),
R (t + T), R (t + 2T), ...), Rx (L) data (L (t)
, L (t + T), L (t + 2T), ..., Input data of the FFT processor 134 (DO (t), DO (t + T), DO (t + 2T), ...)
And its output data (FO (t), FO (t + T), FO (t + 2
The timing relationship of T), ...) is as shown in FIG. In this case, FFTT sampling time (T ^* ) = PRI delay time (T).

Therefore, as shown in FIG. 5 (DPCA, frequency response characteristics of FFT), the filter bank of the FFT processor 134 has only the number of FFT points. The FFT frequency resolution fr at this time is about PRF.
/ P (P: number of FFT points), and there is a limit in detecting the low speed target in the PRF.

FIG. 6 shows a second embodiment in which the above points are taken into consideration. The antenna selector 15 is composed of two antennas 1.
11, 112 are selectively connected to the transmitter / receiver 12 at a pulse repetition period. The transmitter / receiver 13 obtains the Rx (R, L) time division received signal. In the signal processing device 13, the reception signal input by the A / D converter 131 having only one system is converted into a digital reception signal, and the DPCA processor 132 divides the digital reception signal into two systems, one of which is the PRI delay circuit 132a. Is delayed by an amount corresponding to PRI, the subtraction circuit 132b subtracts the other received signal, and the subtracted output is obtained by the FFT processor 1
It supplies to 34 and FFT processing is carried out.

In this configuration, the R of the DPCA processor 132 is
The timing relationship between the x input data, the FFT input data, and the FFT output data is as shown in FIG. in this case,
The output data of the DPCA processor 132 is updated every 2 × T (FFT sampling time is twice as long as the PRI delay time of DPCA processing).
As shown in FIG. 8, the width fr 'of the filter bank is 1/2 of fr in the case of the configuration of FIG. 1, and the frequency resolution can be improved.

Therefore, by increasing the FFT sampling time with respect to the PRI delay time of the DPCA process, it is possible to improve the target detection performance at a lower speed.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the DPC of 2 pulses is used.
Although the case where the A process is performed is described, it goes without saying that the present invention can be applied to the case of two or more pulses. Other than the above, various modifications may be made without departing from the scope of the present invention, and the same effects can be achieved.

[0032]

As described above, according to the present invention, while suppressing unnecessary reflection signals from the ground surface or the sea surface having a low Doppler frequency, it is possible to accurately detect a low speed target having a Doppler frequency very close to the signal. It is possible to provide a moving target detection radar device that can do so.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of a moving target detecting radar device according to the present invention.

FIG. 2 is a frequency characteristic diagram for explaining the signal processing operation of the same embodiment.

FIG. 3 is a frequency characteristic diagram for explaining a relationship between a DPCA processing rate and a processing result of the same embodiment.

FIG. 4 is a timing diagram showing a timing relationship between DPCA input / output data and FFT input / output data of the embodiment.

FIG. 5 is a frequency characteristic diagram for explaining the FFT frequency resolution of the same embodiment.

FIG. 6 is a block diagram showing the configuration of a second embodiment according to the present invention.

FIG. 7 is a timing chart showing a timing relationship between DPCA input / output data and FFT input / output data in the embodiment.

FIG. 8 is a frequency characteristic diagram for explaining the FFT frequency resolution of the same embodiment.

FIG. 9 is a block diagram showing the configuration of a conventional moving target detection radar device using a DPCA processing method.

FIG. 10 is a diagram for explaining an outline of the DPCA processing method.

FIG. 11 is a frequency characteristic diagram showing a DPCA processing result when the target is a high-speed moving body.

FIG. 12 is a frequency characteristic diagram showing a DPCA processing result when the target is a low-speed moving body.

[Explanation of symbols]

11 ... Antenna device, 111, 112 ... Antenna, 12 ... Transceiver device, 13 ... Signal processing device, 131 ... A / D converter, 132 ... DPCA processor, 132a ... PRI delay circuit, 132b ... Subtraction circuit, 133 ... Target Detector, 134
... FFT processor, 14 ... Display.

Claims (2)

[Claims] 1. A moving target detecting radar apparatus mounted on a moving body, comprising: pulse transmitting / receiving means for transmitting two transmission signals at a constant cycle using a pair of antennas arranged at predetermined intervals; Regarding the DPCA processing means for suppressing the clutter component by delaying one of the two received signals obtained by this means by the repetition period of the transmission pulse and subtracting from the other received signal, and the processing result of the DPCA processing means FFT that applies fast Fourier transform to further suppress only clutter component
And a processing means, wherein the target is detected and displayed from the processing result of the FFT processing means. 2. The moving target detecting radar apparatus according to claim 1, wherein the FFT sample time of the FFT processing means is set longer than the delay time of the DPCA processing means.