JP4005007B2 - Radar signal processing device - Google Patents

Description

  The present invention relates to a radar signal processing apparatus that detects a target using Doppler generated by movement of the target.

  Conventionally, a radar signal processing device used in a radar device is known. The radar signal processing device transmits a transmission pulse signal toward a target, processes a reception signal obtained by reflecting the transmission pulse signal on the target, extracts a Doppler component due to the movement of the target, and performs the Doppler component. The moving target is detected based on the above.

  The configuration of such a conventional radar signal processing apparatus is shown in FIG. This radar signal processing apparatus includes a transmission seed signal generator 10, a D / A converter 11, a local oscillator 12, a mixer 13, a transmission amplifier 14, a circulator 15, an antenna 16, a reception amplifier 17, a mixer 18, and an A / D converter. 19, a pulse compression processing unit 20, a discrete Fourier transform (DFT) processing unit 21, and a target detection processing unit 22.

  The transmission type signal generator 10 has a pulse repetition frequency (abbreviated as PRF) and generates a transmission type signal (chirp signal) as a wide pulse width signal whose frequency band is expanded by modulation. For example, as shown in FIG. 5A, a chirp (linear FM modulation) signal having a transmission pulse width T (T >> τ) and a frequency bandwidth Δf (= 1 / τ) is generated.

  The D / A converter 11 converts the chirp signal from the transmission seed signal generator 10 into an analog signal. The mixer 13 mixes the local signal from the local oscillator 12 with the chirp signal from the D / A converter 11 and converts it into a high frequency signal.

  The transmission amplifier 14 amplifies the high frequency signal from the mixer 13 to a predetermined level. The circulator 15 outputs a high-frequency signal from the transmission amplifier 14 to the antenna 16 and performs signal switching for outputting a reception signal from the antenna 16 to the reception amplifier 17. The antenna 16 is composed of, for example, an array antenna or the like. The antenna 16 transmits a high-frequency signal input from the transmission amplifier 14 via the circulator 15 toward the target, receives a reflected wave from the target, and transmits the received signal to the circulator. 15 is output.

  The reception amplifier 17 amplifies the reception signal input from the antenna 16 via the circulator 15 with low noise. The mixer 18 converts the reception signal from the reception amplifier 17 and the local signal from the local oscillator 12 into an intermediate frequency signal.

The A / D converter 19 converts the intermediate frequency signal from the mixer 18 into a quadrature digital (I, Q) signal x (t). The pulse compression processing unit 20 performs pulse compression processing on the quadrature digital (I, Q) signal x (t) from the A / D converter 19. Pulse compression is a technology that converts a wide pulse width signal that has been modulated at the time of transmission into a narrow pulse width signal through correlation processing in the range (distance) direction at the time of reception. Tj and the received pulse signal as a function x (t−tj) of time t, this is multiplied by the reference signal x ^* (− t) ( ^* : complex conjugate) in the frequency domain, and the phase component of the spectrum Is made constant over the entire frequency and further returned to the time domain, the signal energy is concentrated in one place and converted into a narrow pulse width signal. A chirped compression pulse waveform is shown in FIG.

The discrete Fourier transform (DFT) processing unit 21 converts time data into frequency data by performing Fourier transform on the signal from the pulse compression processing unit 20. That is, in order to detect the target relative speed, the received signal is decomposed into a Doppler component which is a target speed component. The target detection processing unit 20 extracts the movement target by extracting the Doppler component from the DFT processing unit 21 (see Patent Document 1).
JP-A-4-357485

  The radar signal processing apparatus described above utilizes the fact that the reflected wave from the moving target undergoes frequency shift due to Doppler, and as shown in FIG. 6, the transmission pulse is transmitted at each pulse repetition period (PRI). And receiving a reception signal corresponding to the transmission pulse within the PRI period, and performing a Fourier transform on each reception signal between the PRIs, thereby obtaining a phase variation (frequency shift) of each reception signal between the PRIs, A Doppler component is detected based on this phase variation. In this Fourier transform, as shown in FIG. 7, a target Doppler component is detected by, for example, filter bank 4 using a plurality of filter banks having different center frequencies in a frequency range of 0 to 1 / PRI (= PRF). ing. For this reason, the Doppler frequency that can be detected is determined by the PRF, and a Doppler frequency higher than the PRF is turned back into the PRF. That is, when a low PRF radar is used, an ambiguity (false image) is generated at a Doppler frequency due to target movement or the like, and a high Doppler frequency is mistaken as a low Doppler frequency.

  Further, in order to suppress the occurrence of Doppler frequency ambiguity due to target movement or the like, a high PRF radar is required. That is, with a high PRF radar, the frequency is not folded back, and a high Doppler frequency can be measured accurately. However, in a high PRF radar, when the target is relatively far away, a transmission pulse is transmitted a plurality of times, so that ambiguity occurs in the distance. For this reason, it is impossible to suppress the occurrence of ambiguity in both the Doppler and the target distance due to the movement of the target.

  The present invention has been made to solve the above-described problems, and provides a radar signal processing apparatus capable of accurately detecting a target by obtaining a Doppler component having no ambiguity at a low pulse repetition frequency. There is to do.

  In order to achieve the above object, a radar signal processing apparatus according to a first aspect of the invention includes a transmission means for generating and transmitting a wide pulse width signal having a frequency band expanded by modulation, and a wide pulse width signal from the transmission means. , And a receiving means for processing a wide pulse width signal from the antenna, and a wide pulse width signal from the transmitting means is output to the antenna. Switching means for switching a signal for outputting a wide pulse width signal from the antenna to the receiving means, and a pulse for converting the wide pulse width signal from the receiving means into a narrow pulse width signal using a reference signal Compression processing means, complex conjugate signal generating means for generating a complex conjugate signal that is complex conjugate with respect to a wide pulse width signal from the transmitting means, and complex conjugate signal generating means from the complex conjugate signal generating means. Characterized in that it comprises extraction means for extracting the Doppler signal due to the movement of the target based on the wide pulse width signal from the conjugate signal and the receiving means.

  The radar signal processing apparatus according to the second aspect of the invention is characterized by comprising wavelet transform means for detecting a Doppler frequency by performing wavelet transform on the Doppler signal extracted by the extraction means.

  According to the present invention, since the extraction means extracts the Doppler signal due to the target movement based on the complex conjugate signal and the wide pulse width signal, the Doppler component due to the target movement without ambiguity even at a low pulse repetition frequency is obtained. Thus, it is possible to provide a radar signal processing apparatus that can obtain the target and accurately detect the target.

  In addition, since the wavelet transform improves the resolution as the frequency is lower, the target Doppler frequency can be efficiently detected by performing the wavelet transform on the Doppler signal by the wavelet transform means.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals as those used in the column of the conventional technology are used for the parts corresponding to the components described in the column of the conventional technology.

  FIG. 1 is a block diagram showing a configuration of a radar signal processing apparatus according to an embodiment of the present invention. The radar signal processing device generates a Doppler signal of only the Doppler component in the received pulse from the complex conjugate signal that is the complex conjugate of the transmission pulse signal with respect to the received signal, performs wavelet transform on the Doppler signal, and performs the Doppler frequency. Is detected.

  The radar signal processing apparatus shown in FIG. 1 includes a transmission seed signal generator 10, a D / A conversion unit 11, a local oscillator 12, a mixer 13, a transmission amplifier 14, a circulator 15, an antenna 16, a reception amplifier 17, a mixer 18, and an A / A. It comprises a D converter 19, a pulse compression processing unit 20, a first target detection processing unit 22a, a second target detection processing unit 22b, a complex conjugate signal generator 30, a multiplication unit 31, and a wavelet conversion unit 32.

  The transmission type signal generator 10 has a pulse repetition frequency (abbreviated as PRF) and generates a transmission type signal (chirp signal) as a wide pulse width signal whose frequency band is expanded by modulation. For example, as shown in FIG. 5A, a chirp (linear FM modulation) signal having a transmission pulse width T (T >> τ) and a frequency bandwidth Δf (= 1 / τ) is generated.

  The D / A converter 11 converts the chirp signal from the transmission seed signal generator 10 into an analog signal. The mixer 13 mixes the local signal from the local oscillator 12 with the chirp signal from the D / A converter 11 and converts it into a high frequency signal.

  The transmission amplifier 14 amplifies the high frequency signal from the mixer 13 to a predetermined level. The circulator 15 outputs a high-frequency signal from the transmission amplifier 14 to the antenna 16 and performs signal switching for outputting a reception signal from the antenna 16 to the reception amplifier 17. The antenna 16 is composed of, for example, an array antenna or the like. The antenna 16 transmits a high-frequency signal input from the transmission amplifier 14 via the circulator 15 toward the target, receives a reflected wave from the target, and transmits the received signal to the circulator. 15 is output.

  The reception amplifier 17 amplifies the reception signal input from the antenna 16 via the circulator 15 with low noise. The mixer 18 converts the received signal from the receiving amplifier 17 and the local signal from the local oscillator 12 into an intermediate frequency signal. The A / D converter 19 converts the intermediate frequency signal from the mixer 18 into a quadrature digital (I, Q) signal x (t).

The pulse compression processing unit 20 performs compression processing on the quadrature digital (I, Q) signal x (t) from the A / D converter 19. Pulse compression is a technology that converts a wide pulse width signal that has been modulated at the time of transmission into a narrow pulse width signal through correlation processing in the range (distance) direction at the time of reception. Tj and the received pulse signal as a function x (t−tj) of time t, this is multiplied by the reference signal x ^* (− t) ( ^* : complex conjugate) in the frequency domain, and the phase component of the spectrum Is made constant over the entire frequency and further returned to the time domain, the signal energy is concentrated in one place and converted into a narrow pulse width signal. A chirped compression pulse waveform is shown in FIG.

  The first target detection processing unit 22 a detects the target position based on the signal from the pulse compression processing unit 20, and outputs the detected target detection position information to the multiplication unit 31. The complex conjugate signal generator 30 receives the chirp signal generated by the transmission seed signal generator 10 and generates a complex conjugate signal that is complex conjugate to the chirp signal.

  The multiplier 31 multiplies the complex conjugate signal from the complex conjugate signal generator 30 by the reception signal from the A / D converter 19 to obtain a Doppler signal having only a Doppler component due to target movement. The wavelet transform unit 32 detects a target Doppler frequency by performing wavelet transform on the Doppler signal from the multiplier 31.

  The second target detection processing unit 22b determines whether or not the Doppler frequency from the wavelet transform unit 32 is equal to or higher than a predetermined threshold value. If the Doppler frequency is equal to or higher than the threshold value, the target is determined to be a moving target. If the Doppler frequency is less than the threshold value, it is determined that there is a false alarm due to a ground clutter or the like.

  Next, the operation of the radar signal processing apparatus according to the embodiment of the present invention configured as described above will be described.

ここで、Δｆは掃引周波数（周波数帯域幅）を表し、Ｔは送信パルス幅を表す。 First, the transmission seed signal generator 10 generates a chirp signal which is a wide pulse width signal having a wide frequency band by modulation. This chirp signal is expressed by equation (1).

Here, Δf represents the sweep frequency (frequency bandwidth), and T represents the transmission pulse width.

  Next, the chirp signal generated by the transmission seed signal generator 10 is converted into an analog signal by the D / A converter 11, and this analog signal is mixed with the local signal from the local oscillator 12 by the mixer 13. Converted to a high frequency signal. The high frequency signal from the mixer 13 is amplified to a predetermined level by the transmission amplifier 14 and then transmitted from the antenna 16 to the target via the circulator 15.

  Next, the received signal input from the antenna 16 is amplified with low noise by the receiving amplifier 17 via the circulator 15 and mixed with the local signal from the local oscillator 12 by the mixer 18 to obtain an intermediate frequency signal. Converted.

ここで、Δｆは掃引周波数を表し、ｆｄは目標の移動等によるドップラ周波数を表し、φは初期位相を表し、Ｔは送信パルス幅を表す。 The intermediate frequency signal from the mixer 18 is converted into an orthogonal digital (I, Q) signal x (t) by an A / D converter 19. This quadrature digital signal is expressed by equation (2).

Here, Δf represents the sweep frequency, fd represents the Doppler frequency due to target movement, etc., φ represents the initial phase, and T represents the transmission pulse width.

  Next, the orthogonal digital signal x (t) is input to a system that performs intra-pulse Doppler detection by wavelet transform and a system that performs pulse compression processing.

  First, a signal input to a system that performs pulse compression processing is converted into a narrow pulse width signal by the pulse compression processing unit 20, and the target position is determined by the first target detection processing unit 22a based on the narrow pulse width signal. Detected. The detected target position information is input to a multiplier 31 which is a system that performs intra-pulse Doppler detection.

ここで、目標の移動等により発生するドップラ周波数ｆｄは、Ａ／Ｄ変換器１９のサンプリング周波数に比較して小さい。 On the other hand, in the system that performs intra-pulse Doppler detection, as shown in FIG. 3, the complex conjugate signal from the complex conjugate signal generator 30 and the received signal from the A / D converter 19 are multiplied by a multiplier 31, A Doppler signal having a Doppler frequency fd is obtained. Thereby, the received signal x (t) becomes as shown in Expression (3).

Here, the Doppler frequency fd generated by the movement of the target is smaller than the sampling frequency of the A / D converter 19.

ここで、Ψ（ω）はψ（ｔ）の周波数スペクトルを表す。この基本ウェーブレットを伸縮・移動させたものを式（６）に示す。

このψ_ａ，ｂ（ｔ）もウェーブレットである。ここで、ａはウェーブレットの伸縮を表すスケールパラメータであり、ｂはウェーブレットの位置を示すシフトパラメータである。また、１／（ａ）^１／２はウェーブレットの有するエネルギーを一定にするための正規化定数である。同一の基本ウェーブレットから作られたスケール及びシフトの異なる二つのウェーブレットの内積が０、即ち式（７）が成立するとき、

このウェーブレットを直交ウェーブレットという。ここで、δはクロネッカーのデルタを表す。関数ｆ（ｔ）のウェーブレット変換Ｗ（ａ，ｂ）は、式（８）で定義される。

ここで、＊は複素共役を表す。 Next, the Doppler signal from the multiplier 31 is wavelet transformed by the wavelet transform unit 32 to detect a target Doppler frequency. The wavelet transform performs time-frequency analysis of a signal and is performed as follows. First, the wavelet ψ (t) is defined as a waveform that satisfies the conditions as shown in the equations (4) and (5).

Here, ψ (ω) represents the frequency spectrum of ψ (t). The basic wavelet is expanded / contracted / moved as shown in equation (6).

This ψ _{a, b} (t) is also a wavelet. Here, a is a scale parameter indicating the expansion and contraction of the wavelet, and b is a shift parameter indicating the position of the wavelet. 1 / (a) ^1/2 is a normalization constant for making the energy of the wavelet constant. When the inner product of two wavelets with different scales and shifts made from the same basic wavelet is 0, that is, when the equation (7) is satisfied,

This wavelet is called an orthogonal wavelet. Here, δ represents the Kronecker delta. The wavelet transform W (a, b) of the function f (t) is defined by equation (8).

Here, * represents a complex conjugate.

  The orthogonal mirror filter is a power bank of 2 on the frequency axis, that is, an octave division filter bank, and an orthogonal wavelet is used as an impulse response of the filter. In other words, a circuit that performs orthogonal wavelet transform of a signal is an orthogonal mirror filter.

  FIG. 2 is a diagram for explaining the orthogonal mirror filter. FIG. 2A shows a configuration of an orthogonal mirror filter, and a discrete signal f (n) (n = 0, 1, 2,...) Input to the filter has a low frequency with an impulse response of h (n). The filter LPF (transfer function is H (ω)) and g (n) high-pass filter HPF (transfer function is G (ω)). Then, the signals that have passed through each filter are thinned out one by one and become the filter output. At this time, the sampling frequency of the signal is halved by the thinning.

  The high-pass filter output is the bank # 1 output. The low-pass filter output is further converted to a low-pass filter LPF (transfer function is H (ω)) with an impulse response of h (n) and a high-pass filter HPF with g (n). Through (transfer function is G (ω)), data is thinned out one by one. This is repeated thereafter.

This operation is described as follows on the frequency axis in FIG. The frequency region up to the sampling frequency is first divided into a low frequency part (banks # 2, # 3...) And a high frequency part (corresponding to bank # 1). Next, the low frequency part (banks # 2, # 3...) Is further divided into a low frequency part (bank # 3...) And a high frequency part (bank # 2). Hereinafter, by repeating this j times, information of the 1/2 ^j region of the original frequency region can be obtained.

  Since the filter bank by such an orthogonal mirror filter is formed at equal intervals on the logarithmic frequency axis, the low frequency region is fine and the high frequency region is rough. In other words, since the wavelet transform can constitute an octave division filter with respect to the frequency, the resolution can be improved as the frequency becomes lower. Therefore, when the wavelet transform process is performed on the Doppler signal obtained by Expression (3), only the target Doppler frequency is obtained in the frequency region of the bank 3 as shown in FIG. That is, the target Doppler frequency can be detected efficiently.

  Next, the second target detection processing unit 22b determines whether the Doppler frequency from the wavelet transform unit 32 is equal to or higher than a predetermined threshold value. As shown in FIG. 3, when the Doppler frequency is equal to or higher than the threshold value, the target is determined as a moving target, and when the Doppler frequency is lower than the threshold value, it is determined as a false alarm. Thereby, false alarms due to ground clutter or the like can be reduced.

  As described above, according to the radar signal processing device according to the embodiment of the present invention, the multiplier 31 includes the complex conjugate signal from the complex conjugate signal generator 30 and the wide pulse width from the A / D converter 19. Since only the Doppler signal due to the movement of the target is generated by multiplying the signal, the Doppler frequency of the Doppler signal is not related to the PRF. For this reason, the Doppler component due to the movement of the target having no ambiguity can be obtained even at a low pulse repetition frequency, and thus the target can be accurately detected. In addition, since the wavelet transform improves the resolution as the frequency is lower, the target Doppler frequency can be efficiently detected by performing wavelet transform on the Doppler signal by the wavelet transform unit 32.

  The present invention is applicable to a radar apparatus including a radar signal processing apparatus.

It is a block diagram which shows the structure of the radar signal processing apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the orthogonal mirror filter in the radar signal processing apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the extraction process of a Doppler signal and the wavelet transformation process in the radar signal processing apparatus which concerns on embodiment of this invention. It is a block diagram for demonstrating the conventional radar signal processing apparatus. It is a figure which shows each signal waveform of a chirp system. It is a figure which shows each pulse repetition period and each received signal in the conventional radar signal processing apparatus. It is a figure which shows the target Doppler component obtained by the filter bank of the DFT process part in the conventional radar signal processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmission type signal generator 11 D / A converter 12 Local oscillators 13 and 18 Mixer 14 Transmission amplifier 15 Circulator 16 Antenna 17 Reception amplifier 19 A / D converter 20 Pulse compression processing part 21 DFT processing part 22 Target detection processing part 22a First target detection processing unit 22b Second target detection processing unit 30 Complex conjugate signal generator 31 Multiplication unit 32 Wavelet transform unit

Claims (3)

Transmitting means for generating and transmitting a wide pulse width signal having a frequency band expanded by modulation;
An antenna that radiates a wide pulse width signal from the transmission means toward a target and receives a reflected wave from the target;
Receiving means for processing a wide pulse width signal from the antenna;
Switching means for switching a signal for outputting a wide pulse width signal from the transmitting means to the antenna and outputting a wide pulse width signal from the antenna to the receiving means;
A pulse compression processing means for converting a wide pulse width signal from the receiving means into a narrow pulse width signal using a reference signal;
Complex conjugate signal generating means for generating a complex conjugate signal that is complex conjugate with respect to the wide pulse width signal from the transmission means;
Extracting means for extracting a Doppler signal due to the movement of the target based on a complex conjugate signal from the complex conjugate signal generating means and a wide pulse width signal from the receiving means;
A radar signal processing apparatus comprising:   The radar signal processing apparatus according to claim 1, further comprising: a wavelet transform unit that detects a Doppler frequency by performing wavelet transform on the Doppler signal extracted by the extraction unit. Is detected Doppler frequency is determined whether or above the threshold by the wavelet transform unit, and a goal detection processing means you determined movement target the target when the Doppler frequency is equal to or greater than the threshold value the radar signal processing apparatus according to claim 2 Symbol mounting, characterized in that.

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