JP2013113722A - Radar system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a radar system which accomplishes both clutter suppression performance and a target signal storage performance and can suppress a stationary clutter and a moving clutter, at the same time.SOLUTION: The radar system includes an FIR filter 2 for suppressing a stationary clutter of a reception signal, an MTI filter 3 for suppressing a stationary clutter of the reception signal, an FIR filter 14 for moving clutters for using a filter coefficient adjusted by a notch frequency correction part 13 to suppress a moving clutter of an output signal of the FIR filter 2, a first FFT processing part 5a for performing coherent integration of an output signal of the FIR filter 2 or the FIR filter 14 for moving clutters, a second FFT processing part 5b for performing coherent integration of an output signal of the MTI filter 3, and an FFT output selection part 6 for selecting either output signal between an output signal from the first FFT processing part 5a and an output signal from the second FFT processing part 5b on the basis of a detection result of a moving clutter peak detection part 12.

Description

  The present invention relates to a radar device, and in particular, receives a reflected radio wave by irradiating a target with pulse radio waves from an antenna, and suppresses clutter that is an unnecessary reflected echo from a stationary object (other than the target) included in the received signal. The present invention relates to a radar device that detects a target.

  In general, radar devices radiate pulsed radio waves into the space, extract echoes from the target, and perform distance measurement. At the time of reception, in addition to the reflected echo from the target, a target called clutter In many cases, unnecessary reflected echoes from other objects are also received at the same time. In particular, reflected echo from an object that does not move, such as the ground surface, is called stationary clutter. Since such clutter hinders accurate target detection processing, for example, a search system radar apparatus has conventionally been provided with, for example, MTI (Moving Target Indicators) as a method of suppressing stationary clutter (see, for example, Patent Document 1). ).

MTI suppresses only static clutter by utilizing the fact that "Doppler frequency is generated for echoes from moving targets, but no Doppler frequency is generated for static clutter that is echoes from the ground or buildings." It is a kind of high-pass filter. In other words, MTI is a method of suppressing clutter in which power is concentrated in the vicinity of a Doppler frequency of 0 by subtracting the received signal delayed by one pulse from the received signal of each range bin. As a commonly used MTI, an MTI whose transfer function is represented by “1-z ⁻¹ ” is called a single eraser, and is represented by (1−z ⁻¹ ) ^M (M> 1). The MTI is called a multiple eraser.

  In MTI, the multiplexing (increasing the filter order) tends to increase the stopband width, increase the stopband attenuation, and increase the clutter suppression performance. However, the stopband attenuation is adjusted only by multiplexing the zeros of the filter, and MTI having a high order exhibits high clutter suppression performance, but has a drawback that the passband width is narrow. That is, while clutter is suppressed by MTI, the target signal is highly likely to be attenuated by MTI processing.

  On the other hand, a clutter suppression filter such as MTI can also be realized by a general transversal FIR (Finite Impulse Response) filter. If the filter order is increased, it is possible to widen the passband width while maintaining the suppression performance. However, depending on the design method, a large ripple may be generated in the passband and the target signal power may be reduced.

JP 58-55474 A

  Since the conventional radar apparatus is configured as described above, when the static clutter is suppressed by the MTI filter, the target signal is greatly attenuated by the MTI filter depending on the moving speed of the target, making it difficult to detect the target. There was a problem. In addition, when an FIR filter with a wide pass band is used as a static clutter suppression filter, there is a problem that target detection is greatly attenuated due to the influence of ripple in the pass band, and target detection becomes difficult. The MTI filter placed in the area cannot suppress the moving clutter, which is an unnecessary reflection echo from the moving object, and therefore the target detection performance deteriorates when not only the stationary clutter but also the moving clutter are received simultaneously. there were.

  The present invention has been made to solve the above-described problems. It is an object of the present invention to obtain a radar apparatus that can suppress both the clutter suppression performance and the target signal storage performance, and at the same time suppress static clutter and moving clutter. Objective.

  A radar apparatus according to the present invention includes transmission / reception processing means for transmitting / receiving pulse radio waves and generating a reception signal, spectrum calculation means for performing frequency analysis of the reception signal generated by the transmission / reception processing means, and frequency analysis results of the spectrum calculation means The moving clutter peak detecting means for detecting the moving clutter of the received signal and detecting the peak frequency of the detected moving clutter, the FIR filter for suppressing the stationary clutter of the received signal, and the stationary clutter of the received signal are suppressed. Based on the detection result of the MTI filter, the moving clutter peak detecting means, the output control means for controlling the outputs of the FIR filter and the MTI filter, and the filter coefficient based on the peak frequency of the moving clutter detected by the moving clutter peak detecting means. Notch frequency correcting means and notch frequency correcting means An FIR filter for moving clutter that suppresses moving clutter of the output signal of the FIR filter using the adjusted filter coefficient, and first FFT processing means for performing coherent integration on the output signal of the FIR filter or the FIR filter for moving clutter And a second FFT processing means for performing coherent integration on the output signal of the MTI filter, and a switch for storing a switching frequency value indicating switching to an output signal from a filter having a high amplitude gain among the FIR filter and the MTI filter. Based on the frequency database and the detection result of the moving clutter peak detecting means, the output signal from the first FFT processing means and the second FFT processing means in accordance with the switching frequency value set with reference to the switching frequency database. FFT output selection to select one of the output signals And the step, in which and a target detection means for FFT output selecting means detects the target from the output signal selected.

According to the present invention, it is possible to achieve both the clutter suppression performance and the target signal storage performance by combining the MTI filter and the FIR filter having a wider pass bandwidth than the MTI filter. In addition, by providing an FIR filter corresponding to moving clutter, both stationary clutter and moving clutter can be suppressed even when moving clutter is received at the same time, and target detection performance can be improved. it can.

1 is a block diagram showing a configuration of a radar apparatus according to Embodiment 1. FIG. It is a figure which shows the amplitude characteristic of the FIR filter and MTI filter of the radar apparatus by Embodiment 1. It is a figure which shows the filter switching frequency of the radar apparatus by Embodiment 1. FIG. 1 is a diagram illustrating a configuration of a transversal filter of a radar device according to Embodiment 1. FIG. It is a figure which shows the amplitude characteristic of the FIR filter for moving clutters of the radar apparatus by Embodiment 1. FIG. FIG. 5 is a block diagram showing a configuration of a radar apparatus according to a second embodiment. It is a figure which shows the characteristic of the FIR filter for stationary / moving clutter of the radar apparatus by Embodiment 2. FIG.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a radar apparatus according to Embodiment 1 of the present invention. In FIG. 1, a radar apparatus 100 includes a transmission / reception circuit (transmission / reception unit) 1, an FIR filter 2, an MTI filter 3, a spectrum calculation unit (spectrum calculation unit) 11, a moving clutter peak detection unit (moving clutter peak detection unit) 12, and a switch. Unit (switching means) 4, notch frequency correction unit 13, moving clutter FIR filter 14, first FFT processing unit 5a, second FFT processing unit 5b, FFT output selection unit 6, target detection unit 7, display unit ( Output means) 8 and a switching frequency database 9.

  The transmission / reception circuit 1 includes a transmission antenna that transmits a pulsed radio wave and a reception antenna that receives a reflected wave of the radio wave. Further, the received reflected wave is converted into a received signal. The FIR filter 2 is a first clutter suppression filter that suppresses clutter of the received signal input from the transmission / reception circuit 1. The MTI filter 3 is a second clutter suppression filter that suppresses clutter of the received signal input from the transmission / reception circuit 1.

  The spectrum calculation unit 11 performs frequency analysis of the reception signal input from the transmission / reception circuit 1. The moving clutter peak detector 12 detects the peak frequency of the moving clutter based on the frequency analysis result output from the spectrum calculator 11. The switch unit 4 refers to the detection result of the moving clutter peak detection unit 12 and performs switching control of the output destinations of the FIR filter 2 and the MTI filter 3. The notch frequency correction unit 13 adjusts the filter coefficient based on the frequency value output from the moving clutter peak detection unit 12. The moving clutter FIR filter 14 is a third clutter suppression filter that suppresses the moving clutter in the signal output from the switch unit 4 using the filter coefficient output from the notch frequency correction unit 13.

  The first FFT processing unit 5a Fourier-transforms the output signal of the FIR filter 2 or the output signal of the moving clutter FIR filter 14. The second FFT processing unit 5b performs Fourier transform on the output signal of the MTI filter 3. The FFT output selection unit 6 receives the output results of the first FFT processing unit 5a and the second FFT processing unit 5b, and selects the FFT output result used for the subsequent target signal detection from the output result. The target detection units 7a, 7b,..., 7n automatically detect the target signal based on the FFT output result of the FFT output selection unit 6. The display unit 8 displays the target detection results input from the target detection units 7a, 7b, ..., 7n on a display such as a display. In addition to displaying on the display, notification by voice output may be used. The switching frequency database 9 stores the switching frequency used in the FFT output selection unit 6.

Next, the operation of the radar apparatus according to the first embodiment will be described with reference to FIGS.
FIG. 2 is an example showing amplitude characteristics of the FIR filter and the MTI filter of the radar apparatus according to the first embodiment. FIG. 3 is a diagram illustrating calculation of the switching frequency of the radar apparatus according to the first embodiment. FIG. 4 is a diagram showing a configuration of a transversal filter of the radar apparatus according to the first embodiment. FIG. 5 is a diagram showing amplitude characteristics of the FIR filter for moving clutter of the radar apparatus according to the first embodiment.

  A pulsed radio wave is radiated from the transmission antenna of the transmission / reception circuit 1, and a reflected wave obtained by reflecting the radiated radio wave by the target is received by the reception antenna of the transmission / reception circuit 1. The received reflected wave is phase-detected and converted into a baseband received signal in the transmission / reception circuit 1, then sampled and quantized, and converted into a digital signal. The digitally converted received signal retains the phase of the received radio wave, and is a complex signal having an I signal (In-phase signal) and a Q signal (Quadrature-phase signal) in the real part and the imaginary part, respectively. is there.

The sampling of the signal is performed at the same timing for all the received signals, and is performed at a constant period after a predetermined time from the time of transmitting the transmission signal. From one received signal, a total of k digital received signals indicated by x ₁ (n), x ₂ (n),..., X _k (n) are generated. Here, “n” is called a hit number and is treated as a parameter representing a time factor of the received signal. “K” is called a range bin number and is treated as a parameter indicating the sampling order (distance from the radar).
The digital reception signal x _k (n) obtained by the above processing becomes an input signal to the subsequent configuration of the transmission / reception circuit 1.

The reception signal x _k (n) output from the transmission / reception circuit 1 is branched and output to the FIR filter 2, the MTI filter 3, and the spectrum calculation unit 11. First, the spectrum calculator 11 performs Fourier transform on the received signal x _k (n) by applying FFT (Fast Fourier Transform) processing or the like, and converts the received signal x _k (n) into a frequency component. The conversion to the frequency component is not limited to the Fourier transform, and can be changed as appropriate.

The moving clutter peak detection unit 12 performs peak detection processing on the converted received signal x _k (n) input from the spectrum calculation unit 11 except for the vicinity of Doppler frequency 0 indicating the peak of the static clutter. Further, the detected peak frequency is set as the center frequency of the moving clutter. If the detected peak intensity is greater than or equal to an arbitrary value, it is determined that moving clutter exists. The arbitrary value is set as appropriate, for example, 10 dB compared to the receiver noise power.

Hereinafter, the case where the moving clutter peak detector 12 determines that no moving clutter exists and the case where it is determined that moving clutter exists will be described separately.
(I) When it is determined that there is no moving clutter This is a case where there is no moving clutter, that is, when the intensity of the peak detected by the moving clutter peak detector 12 is smaller than an arbitrary value, and only a single clutter exists. The operation in the mode will be described.
The detection result in the moving clutter peak detection unit 12 is output only to the switch unit 4. The switch unit 4 connects the output side of the MTI filter 3 to the first FFT processing unit 5b, and connects the output side of the FIR filter 2 to the first FFT processing unit 5a. That is, the output of the FIR filter 2 does not pass through the FIR filter 14 for moving clutter.

When the switching control of the switch unit 4 is completed, the MTI filter 3 starts processing the received signal x _k (n). As the MTI filter 3, a general multiple eraser will be described here as an example. The transfer function F (z) of the MTI filter 3 is expressed by the following equation (1).
F (z) = (1−z ⁻¹ ) ^L (1)
In Expression (1), L indicates the multiplicity of the MTI filter 3 and is the filter order. An example of the amplitude characteristic of the fourth-order MTI filter 3 is indicated by a dotted line in FIG. In the filter amplitude characteristic of FIG. 2, only the range of 0 to 0.5 of the frequency normalized by the pulse repetition frequency is displayed.

式（２）において、αはフィルタ係数正規化のための定数であり、ＬはＦＩＲフィルタ全体の次数であり、ＭはＦＩＲフィルタの零点多重度を示す。ａ（ｍ）はフィルタの通過域幅を調整するための０でない定数である。なお、式（２）で示す伝達関数Ｇ（ｚ）を持つフィルタを用いる理由は、以下の２点である。 Simultaneously with the processing of the MTI filter 3, the FIR filter 2 starts processing of the received signal x _k (n). As the FIR filter 2, an FIR filter having a transfer function G (z) expressed by the following equation (2) is used to widen the passband width of the received signal x _k (n).

In Equation (2), α is a constant for normalizing the filter coefficient, L is the order of the entire FIR filter, and M is the zero multiplicity of the FIR filter. a (m) is a non-zero constant for adjusting the passband width of the filter. The reason for using the filter having the transfer function G (z) represented by the equation (2) is the following two points.

First, as reason 1, by forming a single or multiple blocking zero at z = 1 (f = 0), it is possible to reduce the filter gain near the center frequency of the clutter spectrum and increase the clutter suppression ratio. It is. The reason 2 is that the clutter suppression ratio is inferior to that of the multiple eraser, but by providing the second term (Σ term) on the right side of Equation (2), the passband width can be widened, and the moving target (Doppler frequency is This is because the possibility that the target signal (which is not 0) is attenuated by the filter is reduced.
A design in which no blocking zero is set at f = 0 is also possible. For example, both sides of f = 0, i.e. f = set the zero point to ± δ _f (δ _f is very small real number). In this case, a filter having a wider passband width than Expression (2) can be designed, but the clutter suppression ratio becomes small.

The second term (Σ term) on the right side of Equation (2) is determined by how the filter passband characteristics are set. In the radar apparatus 100 according to the present invention, the second term (Σ term) on the right side of the equation (2) is important because it emphasizes the effect of widening the filter passband with the lowest possible order and with as few design parameters as possible. , A (0) = 1 and a (1) = r. At this time, the expression (2) is expressed by the following expression (3).
G (z) = α (1-Z ⁻¹ ) ^M · (1 + rz ⁻¹ ) (3)
An example of the amplitude characteristic of the fourth-order FIR filter 2 having the transfer function G (z) represented by the equation (3) is shown by the solid line in FIG.

  In the above equation (3), the passband width of the clutter suppression filter can be changed by adjusting the newly provided variable r. The first term on the right side of Equation (3) has the same form as the multi-order MTI filter 3, and has the effect of significantly reducing the filter gain at the Doppler frequency 0 and suppressing the ground clutter. The second term on the right side of Equation (3) shows the same characteristics as the first-order filter in which the gain of the region serving as the passband is intentionally lowered in the MTI filter 3. By multiplying the two, it is possible to widen the passband width correspondingly by sacrificing the passband gain of the region where the amplitude characteristic of the MTI filter 3 has shown a peak. The larger the variable r is, the more effective it is to widen the passband width. On the other hand, the clutter suppression performance deteriorates because the stopband width becomes narrower. Therefore, it is necessary to confirm that the designed FIR filter 2 has the required static clutter suppression performance.

出力信号ｙ_k（ｎ）は、静止クラッタが抑圧された信号となる。 The transfer functions of the MTI filter 3 of the equation (1) and the FIR filter 2 of the equation (3) can be transformed into a transfer function of a transversal filter as shown in FIG. Assuming that the filter coefficient at that time is h _k (l), the output signal y _k (n) after the L-th order filter processing is expressed by the following equation (4).

The output signal y _k (n) is a signal in which stationary clutter is suppressed.

式（５）において、Ｎは受信信号ｘ_k（ｎ）のヒット数、Ｐはフーリエ変換点数を表す。 Next, a coherent integration process is performed on the signal subjected to the clutter suppression process in the first FFT processing unit 5a and the second FFT processing unit 5b in order to improve the S / N. Discrete Fourier transform is performed based on the following formula (5). Here, FFT processing capable of performing discrete Fourier transform at high speed is used.

In Expression (5), N represents the number of hits of the received signal x _k (n), and P represents the number of Fourier transform points.

In the following description, in order to distinguish between the output signal of the MTI filter 3 and the output signal of the FIR filter 2, the result of FFT of the output signal of the MTI filter 3 is MF _k (p), and the output signal of the FIR filter 2 is The result of the FFT is FF _k (p).

  FIG. 2 shows an example of amplitude characteristics of the fourth-order MTI filter 3 and the fourth-order FIR filter 2 in the radar apparatus 100 shown in FIG. In FIG. 2, for ease of explanation, the frequency range is normalized from 0 to 0.5. The amplitude characteristics of the fourth-order MTI filter 3 and the fourth-order FIR filter 2 intersect at a normalized frequency of 0.38. Therefore, it can be seen that in the frequency range 0 to 0.38, the amplitude gain of the FIR filter 2 is higher and the passband is wider than that of the MTI filter 3. On the other hand, it can be seen that the amplitude gain of the MTI filter 3 is higher in the frequency range of 0.38 to 0.5.

  Due to these characteristics, the FFT output selection unit 6 sets a frequency value (normalized frequency 0.38) at which the amplitude characteristics of the MTI filter 3 and the FIR filter 2 intersect as a switching frequency as shown in FIG. Depending on the set switching frequency, one of the output results of the first FFT processing unit 5a and the second FFT processing unit 5b is selected. In the calculation of the output result, the output result of the moving clutter peak detector 12 is also referred to. The switching frequency is calculated in advance and stored in the switching frequency database 9. Therefore, the FFT output selection unit 6 searches the switching frequency database 9 for a switching frequency value corresponding to the corresponding filter order and parameter, and reads the corresponding value. If the value of this switching frequency is β (> 0), the FFT output selection unit 6 selects an output signal based on the following condition (A) or condition (B) and selects the target detection units 7a, 7b,. -Output to 7n.

・ Condition (A)
When the frequency channel (p / P) takes a value from 0 to β, or takes a value from 1 to β to 1.0, the FIR filter 2 is selected and FFk (p) is set to the target detection unit 7a, 7b,..., 7n.
・ Condition (B)
When the frequency channel (p / P) takes a value from β to 1-β, the MTI filter 3 is selected and MFk (p) is output to the target detectors 7a, 7b,.
When the frequency channel (p / P) = β, either the FIR filter 2 or the MTI filter 3 may be selected.

  FIG. 3 shows an example in which the switching frequency β takes a value of 0.38. However, the switching frequency β varies depending on the orders of the MTI filter 3 and the FIR filter 2 and parameters when designing the FIR filter. For this reason, it is necessary to calculate the amplitude characteristics of a filter obtained by combining these parameters in advance, and store the calculated amplitude characteristics in the switching frequency database 9 for each parameter.

(Ii) When it is determined that moving clutter exists Next, when moving clutter exists, that is, when the intensity of the peak detected by the moving clutter peak detector 12 is greater than or equal to an arbitrary threshold, The operation in the double clutter mode in which both moving clutters exist will be described.
The detection result in the moving clutter peak detection unit 12 is output to the switch unit 4 and the notch frequency correction unit 13. The switch unit 4 opens the output side of the MTI filter 3 and connects the output side of the FIR filter 2 to the moving clutter filter 64. The notch frequency correcting unit 13 adjusts the filter coefficient of the moving clutter FIR filter 14 based on the frequency value output from the moving clutter peak detecting unit 12. Moving clutter is suppressed by connecting the FIR filter 2 and the moving clutter filter 64. Since the output signal of the FIR filter 2 has already suppressed the static clutter, the output signal of the moving clutter FIR filter 14 is a signal in which two clutters are suppressed.

式（６）において、Ｌはフィルタ次数、ｈは調整後のフィルタ係数、ｈｈは調整前のフィルタ係数、ｋは抑圧処理を行うレンジビン番号、ｆ₀は移動クラッタの中心周波数を示す。 FIG. 5 shows amplitude characteristics of a fourth-order FIR filter as an example of the FIR filter 14 for moving clutter. FIG. 5 shows the amplitude characteristics of the fourth-order FIR filter when the normalized Doppler frequency of the clutter is 0.2. The FIR filter used as the moving clutter FIR filter 14 is designed as a filter having a notch frequency of 0 and is adjusted to a filter coefficient whose notch frequency matches the center frequency of the moving clutter according to the following equation (6). .

In Equation (6), L is the filter order, h is the filter coefficient after adjustment, hh is the filter coefficient before adjustment, k is the range bin number for performing the suppression process, and f ₀ is the center frequency of the moving clutter.

  The signal subjected to the clutter suppression processing in the moving clutter FIR filter 14 is subjected to coherent integration processing in the first FFT processing unit 5 a and is output to the FFT output selection unit 6. Since the output side of the MTI filter 3 is open, only the processing result of the first FFT processing unit 5a is input to the FFT output selection unit 6. The subsequent processing is the same as the processing in (i) described above.

  As described above, in the radar apparatus 100 according to the first embodiment, different processes are performed when only the static clutter is received and when the static clutter and the moving clutter are simultaneously received.

  By performing the above-described processing for all range bins k, the output of the FFT output selection unit 6 becomes two-dimensional data of distance and frequency. The target detection units 7a, 7b,..., 7n detect a target signal larger than the receiver noise level by performing automatic detection processing such as CFAR (Constant False Alarm Ratio) in the distance direction for each frequency channel. . As a result, the distance to the target and the moving speed of the target are calculated. The target detection units 7a, 7b,..., 7n are assumed to perform one-dimensional target detection processing in consideration of the processing load, but may be configured to perform two-dimensional target detection processing. The display unit 8 displays information related to the target signal detected by the target detection units 7a, 7b, ..., 7n.

As described above, according to the first embodiment, the clutter suppression process is performed by combining the FIR filter 2 with a wide filter passband and the MTI filter 3 with a high filter passband gain. It is possible to achieve both suppression performance and target signal storage performance. Further, compared with the case where the MTI filter 3 is used alone, the degradation of the target signal power due to the filter amplitude characteristic is reduced, and the target detection performance can be improved.

  Further, according to the first embodiment, the FFT for selecting whether to output the processing result of the first FFT processing unit 5a or the processing result of the second FFT processing unit 5b based on the switching frequency. Since the output selection unit 6 is provided, an optimum filter processing result can be selected according to the frequency channel of the received signal.

  Further, according to the first embodiment, since the FIR filter 14 for moving clutter is separately provided, even when stationary clutter and moving clutter are received simultaneously, stationary and moving clutter can be suppressed, The target detection performance can be ensured.

Embodiment 2. FIG.
In the first embodiment described above, the radar apparatus 100 having good target detection performance even when stationary clutter and moving clutter are received simultaneously has been described. However, in order to suppress stationary clutter and moving clutter with different filters, two stages are used. It was necessary to perform the clutter suppression processing. Therefore, in the second embodiment, a radar apparatus is described in which stationary clutter and moving clutter are suppressed by the same filter, and the clutter suppression processing can be simplified and resources can be effectively used.

  FIG. 6 is a block diagram showing the configuration of the radar apparatus according to Embodiment 2 of the present invention. In the radar apparatus 100 ′ of the second embodiment, instead of the notch frequency correction unit 13 and the moving clutter FIR filter 14 of the radar apparatus 100 of the first embodiment shown in FIG. A filter selection unit 22 and a filter coefficient storage unit 23 are additionally provided. Further, as the number of filters increases, the switch of the switch unit 4 'is also added. In the following description, the same or corresponding parts as those of the radar apparatus according to the first embodiment are denoted by the same reference numerals as those used in the first embodiment, and description thereof is omitted or simplified.

The stationary / moving clutter FIR filter 21 is a fourth clutter suppression filter that receives the received signal x _k (n) input from the transmission / reception circuit 1 and suppresses the clutter. A significant difference from the first embodiment is that a static / moving clutter FIR filter 21 is provided, and the static clutter and the moving clutter can be simultaneously suppressed by one filter. The switch unit 4 ′ refers to the detection result of the moving clutter peak detecting unit 12 and performs switching control of the output destinations of the FIR filter 2, the MTI filter 3, and the stationary / moving clutter FIR filter 21.

  Based on the frequency value output from the moving clutter peak detection unit 12, the filter selection unit 22 selects the coefficient of the stationary / moving clutter FIR filter 21 to be used from the filter coefficient storage unit 23, and selects the selected filter coefficient Set to the FIR filter 21 for moving clutter. The filter coefficient storage unit 23 holds filter coefficients of a plurality of types of FIR filters 21 for stationary / moving clutter designed in advance. The third FFT processing unit 5c Fourier-transforms the output signal of the stationary / moving clutter FIR filter 21. The FFT output selection unit 6 ′ is configured to output an FFT output result used for detecting a target signal in the subsequent stage from the processing results input from the first FFT processing unit 5 a, the second FFT processing unit 5 b, and the third FFT processing unit 5 c. Select. The target detection unit 7 automatically detects the target signal based on the output result of the FFT output selection unit 6 ′.

  First, the design of the filter coefficient stored in the filter coefficient storage unit 23 will be described. The radar apparatus 100 ′ assumes a certain amount of the Doppler frequency interval between the stationary clutter and the moving clutter in advance, and calculates the maximum number of combinations of the stationary clutter Doppler frequency and the moving clutter Doppler frequency based on the assumption. One filter that forms a notch for the combination of Doppler frequencies is designed, and the filter coefficient of the designed filter is stored in the filter coefficient storage unit 23.

  The filter selection unit 22 selects from the filter coefficient storage unit 23 an FIR filter that forms a notch at the peak frequency (center frequency) of the moving clutter output from the moving clutter peak detection unit 12 and the frequency 0. If there is no matching peak frequency, an FIR filter having a notch frequency as close to the peak frequency as possible is selected. Based on the selection result of the filter selection unit 22, the stationary / moving clutter FIR filter 21 simultaneously suppresses the stationary clutter and the moving clutter in the received signal, and outputs them to the third FFT processing unit 3 c via the switch unit 4 ′. To do.

The switch unit 4 ′ refers to the detection result of the moving clutter peak detecting unit 12 and performs switching control of the output destinations of the FIR filter 2, the MTI filter 3, and the stationary / moving clutter FIR filter 21.
When the moving clutter is not detected, the output sides of the FIR filter 2 and the MTI filter 3 are connected, and the output side of the stationary / moving clutter FIR filter 21 is opened. The subsequent processing is performed in the same manner as (i) of the first embodiment. On the other hand, when a moving clutter is detected, the output sides of the FIR filter 2 and the MTI filter 3 are opened, and the output side of the FIR filter 21 for stationary / moving clutter is connected. Thereby, both the static clutter and the moving clutter received simultaneously can be suppressed.

  The signal subjected to the clutter suppression processing in the stationary / moving clutter FIR filter 21 is subjected to coherent integration processing in the third FFT processing unit 5 c and is output to the FFT output selection unit 6. Since the output sides of the FIR filter 2 and the MTI filter 3 are open, only the processing result of the third FFT processing unit 5c is input to the FFT output selection unit 6. Subsequent processing is the same as that of the first embodiment.

  As described above, in the radar apparatus according to the second embodiment, when only the static clutter is received, the same operation as that of the first embodiment is performed. In addition, when the moving clutter is also received at the same time, the static clutter and the moving Both clutters can be suppressed.

  Further, with the configuration of the second embodiment, it is possible to reduce the number of hits spent on the clutter suppression processing. When the Doppler frequencies of the moving clutter and the stationary clutter are separated, the same processing is performed when the moving clutter and the stationary clutter are suppressed by two different filters and when they are suppressed by one filter having two notch frequencies. Results are obtained. However, as shown in FIG. 7, when the Doppler frequencies of the moving clutter and the stationary clutter are relatively close, the use of two filters increases the proportion of the two filter stopbands overlapping, It has been found that the stopband width of the filter is widened with respect to the notch frequency. In the example shown in FIG. 7, the center frequencies of the moving clutter and the stationary clutter are 0 and −0.1, but this tendency becomes stronger as the distance becomes closer.

  Here, the orders of the suppression filter having a notch at normalized Doppler frequency 0 and the suppression filter having a notch at normalized Doppler frequency −0.1 are La and Lb, respectively. Also, let Lc be the order of a suppression filter having two notches as shown in FIG. If the order of each filter is set under the condition that the required suppression coverage is satisfied, the condition of La + Lb ≧ Lc is satisfied. Therefore, by using a suppression filter having two notches, a clutter suppression process similar to the individual process with a filter having a small order can be realized, and the number of hits consumed in the suppression process can be reduced. In other words, the target detection performance can be improved because the number of hits used in the subsequent integration process increases.

  As described above, according to the second embodiment, when the moving clutter peak detection unit 12 detects the peak frequency of the moving clutter, the filter that forms a notch with respect to the stationary clutter and the Doppler frequency of the moving clutter is used. Since the FIR filter 21 for stationary / moving clutter that simultaneously suppresses the static clutter and the moving clutter is provided, the static clutter and the moving clutter can be suppressed by one-stage clutter suppression processing. As a result, suppression processing can be simplified and resources can be used effectively. In addition, the clutter suppression process can be realized with a filter having a low order, and the number of hits consumed in the suppression process can be reduced.

  In the second embodiment described above, a case where one stationary clutter and one moving clutter are received has been described. However, when a plurality of types of moving clutter are received, a plurality of moving clutters have notches. This can be dealt with by using a filter.

  In the first and second embodiments described above, the configuration has been described in which the switch units 4 and 4 'are provided to substantially switch the connection destination. However, the movement can be performed by providing a control means such as a filter output control unit. A signal to be output to the subsequent stage may be controlled based on the detection result of the clutter peak detector 12.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 1 Transmission / reception circuit, 2 FIR filter, 3 MTI filter, 4 switch part, 5a 1st FFT process part, 5b 2nd FFT process part, 5c 3 FFT process part, 6 FFT output selection part, 7 target detection part, 8 Display section, 9 Switching frequency database, 11 Spectrum calculation section, 12 Moving clutter peak detection section, 13 Notch frequency correction section, 14 FIR filter for moving clutter, 21 FIR filter for stationary / moving clutter, 22 Filter selection section, 23 Filter Coefficient storage unit, 100 Radar device.

Claims (6)

Transmission / reception processing means for transmitting / receiving pulsed radio waves and generating reception signals;
Spectrum calculation means for performing frequency analysis of the received signal generated by the transmission / reception processing means;
Moving clutter peak detecting means for detecting a moving clutter of the received signal with reference to a frequency analysis result of the spectrum calculating means and detecting a peak frequency of the detected moving clutter;
An FIR filter for suppressing stationary clutter of the received signal;
An MTI filter for suppressing stationary clutter of the received signal;
Output control means for controlling the outputs of the FIR filter and the MTI filter based on the detection result of the moving clutter peak detection means;
Notch frequency correcting means for adjusting a filter coefficient based on the peak frequency of the moving clutter detected by the moving clutter peak detecting means;
An FIR filter for moving clutter that suppresses moving clutter of the output signal of the FIR filter using the filter coefficient adjusted by the notch frequency correcting means;
First FFT processing means for performing coherent integration on an output signal of the FIR filter or the FIR filter for moving clutter;
Second FFT processing means for performing coherent integration on the output signal of the MTI filter;
A switching frequency database for storing a switching frequency value indicating switching to an output signal from a filter having a high amplitude gain among the FIR filter and the MTI filter;
Based on the detection result of the moving clutter peak detecting means, the output signal from the first FFT processing means and the second FFT processing means in accordance with the switching frequency value set with reference to the switching frequency database. FFT output selection means for selecting one of the output signals;
A radar apparatus, comprising: target detection means for detecting a target from the output signal selected by the FFT output selection means. Transmission / reception processing means for transmitting / receiving pulsed radio waves and generating reception signals;
Spectrum calculation means for performing frequency analysis of the received signal generated by the transmission / reception processing means;
Moving clutter peak detecting means for detecting a moving clutter of the received signal with reference to a frequency analysis result of the spectrum calculating means and detecting a peak frequency of the detected moving clutter;
An FIR filter for suppressing stationary clutter of the received signal;
An MTI filter for suppressing stationary clutter of the received signal;
Filter coefficient storage means for storing a plurality of types of filter coefficients capable of simultaneously suppressing stationary clutter and moving clutter;
Filter selection means for selecting a filter coefficient from the filter coefficient storage means based on the detection result of the moving clutter peak detection means;
An FIR filter for stationary moving clutter that suppresses stationary clutter and moving clutter of the received signal with the filter coefficient selected by the filter selection means;
Output control means for controlling outputs of the FIR filter, the MTI filter and the stationary moving clutter FIR filter based on the detection result of the moving clutter peak detecting means;
First FFT processing means for performing coherent integration on the output signal of the FIR filter;
Second FFT processing means for performing coherent integration on the output signal of the MTI filter;
Third FFT processing means for performing coherent integration on the output signal of the FIR filter for stationary moving clutter;
A switching frequency database for storing switching frequency values indicating switching to an output signal from a filter having a high amplitude gain among the first FFT processing means or the third FFT processing means, and the second FFT processing means;
Based on the detection result of the moving clutter peak detecting means, a switching frequency value is set with reference to the switching frequency database, an output signal from the first FFT processing means according to the set switching frequency value, the first FFT output selection means for selecting one of the output signals from the two FFT processing means or the output signal from the third FFT processing means;
A radar apparatus, comprising: target detection means for detecting a target from the output signal selected by the FFT output selection means. When no moving clutter is detected by the moving clutter peak detecting means,
The output control means outputs the output signal of the FIR filter to the first FFT processing means, and outputs the output signal of the MTI filter to the second FFT processing means. The radar apparatus according to claim 2. When moving clutter is detected by the moving clutter peak detecting means,
The output control means inputs the output signal of the FIR filter to the FIR filter for moving clutter,
2. The radar apparatus according to claim 1, wherein the moving clutter FIR filter suppresses the moving clutter of the input output signal and outputs an output signal in which the moving clutter is suppressed to the first FFT processing means. When moving clutter is detected by the moving clutter peak detecting means,
The radar apparatus according to claim 2, wherein the output control means outputs an output signal of the FIR filter for the stationary moving clutter to the third FFT processing means.   6. The radar apparatus according to claim 1, further comprising an output unit that outputs a detection result of the target detection unit.

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