JP2009257884A - Radar device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a stepped multiple frequency ICW (Interrupted Continuous Wave) system is for a short range radar but it is not applicable to a search radar ranging from short to long range, while the stepped multiple frequency ICW system can separate a plurality of targets with the same velocity in a distance direction by stepwise changing a transmission frequency by a small frequency difference to convert transmission waves into a pulse form. <P>SOLUTION: An intra-pulse modulation means generates transmission signals by applying, through a transmitter, frequency conversion and amplification processing to signals that are obtained by applying transmission signal intra-pulse modulation to pulse-form transmission signals, emits the transmission signals from an antenna, and converts into digital signals at an A/D converter the reception signals from a receiver for receiving reflected waves from a target through the antenna. A modulated signal correlation means applies correlation processing to the digital signals using the intra-pulse modulation signals of the transmission signals. A frequency analyzing means analyzes the signals applied for correlation processing. A target detection means extracts target signals from a result obtained by the frequency analyzing means, and a target distance calculating means measures a distance to the target from the extraction result. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radar apparatus that irradiates a target with radio waves, receives a reflected wave from the target, and detects the speed of the target.

  A conventional search radar using the pulse Doppler method can easily detect a plurality of targets existing in different range bins. Even if multiple targets exist in the same range bin, they can be distinguished if the Doppler frequencies are different. However, it is not possible to individually detect a plurality of targets having the same Doppler frequency in the same range bin, for example, a group of aircraft moving in a formation.

  A multi-frequency stepped ICW (Interrupted Continuous Wave) method has been proposed as a radar method that can detect a plurality of targets that exist at the same distance and move at a constant speed (for example, Non-Patent Document 1). In this method, the transmission frequency is pulsed by changing the transmission frequency in steps with a fine frequency difference. After the received signal is frequency analyzed in the pulse direction, the peak detected distance is processed by super-resolution signal processing. Distance resolution is obtained.

Takayuki Inaba, “Multi-target separation method by multi-frequency step ICW radar”, IEICE B, Vol.J89-B No.3 pp.373-383.

There are FMCW (Frequency Modulated Continuous Wave) method and 2 frequency CW (Continuous Wave) method as a ranging method which is not so large and can be implemented at low cost. Since these are simple methods, they have the following problems.
The FMCW method generates a beat signal between a reception signal and a transmission signal obtained by receiving a reflected wave from a target in two observation periods, a frequency increase period and a frequency decrease period, and obtains a beat signal obtained in the frequency increase period. And a beat signal obtained during a frequency drop period to detect the relative speed and distance of the target. When reflected waves from a plurality of targets are received in this method, a pairing malfunction of the detected frequency may occur in the up sweep during the frequency increase period and the down sweep during the frequency decrease period.

On the other hand, the two-frequency CW method is a method in which transmission waves of _two frequencies f ₁ and f ₂ are transmitted for a predetermined period and a target is detected from frequency and phase information of each reception wave. The two-frequency CW method is effective as a radar method when cost reduction is prioritized because the transmission / reception system is simple and the signal processing load is the same as that of the FMCW method. However, since it is based on the principle of obtaining the distance from the phase difference between the target frequency components of the received signal for the two transmission frequencies, multiple waves (multiple waves of the same frequency with different phases) are present when there are multiple targets at the same speed. ) It becomes an environment, and the problem that malfunction occurs in distance measurement arises.

  On the other hand, the multi-frequency step ICW method can separate a plurality of constant speed targets in the distance direction by changing the transmission frequency in steps with a small frequency difference and pulsing the transmission wave. It has the characteristics.

  The radar using the multi-frequency step ICW method was developed considering application to a short-range radar, and is applied as it is to a radar that needs to search from a short distance to a long distance like a search radar. It was difficult.

  The present invention has been made to solve such problems. In other words, in a radar using the multi-frequency step ICW method, a long distance is provided by providing a modulation signal correlation means for transmitting a pulse signal with a wide pulse width and performing intra-pulse modulation, and performing a pulse compression process at the time of reception. A plurality of targets that are close in the distance direction can be separated and detected. In addition, it is possible to receive an echo of a target that is finely decomposed in the distance direction with respect to a single target at a long distance, and obtain a target distance profile. Furthermore, if the Doppler frequencies of a plurality of targets having the same distance are different, the distance profile of each target can be obtained individually. This result can be used for target recognition and identification.

The radar apparatus according to the present invention is
In-pulse modulation means for changing the frequency of the pulsed transmission signal to modulate the transmission signal pulse;
A transmitter that inputs a signal transferred from the intra-pulse modulation means, performs frequency conversion, amplification processing to generate a transmission signal, and radiates through an antenna;
An A / D converter that inputs a reception signal transferred from a receiver that receives a reflected wave from a target of a transmission signal via an antenna and converts it into a digital signal;
Modulated signal correlation means for performing correlation processing on the received digital signal converted by the A / D converter using the intra-pulse modulation signal of the transmission signal;
Frequency analysis means for frequency analysis of the signal transferred from the modulated signal correlation means;
Target detection means for extracting a target signal from the result of the frequency analysis means;
Target distance calculation means for measuring the distance from the result of the target detection means to the target;
Is provided.

  According to the radar apparatus of the present invention, the frequency of the pulsed transmission signal is changed, the signal modulated in the transmission signal pulse is radiated from the antenna, and the transmission signal reflected from the target received through the antenna is reflected. By converting the received wave signal into a digital signal and using the intra-pulse modulated signal of the transmitted signal to perform correlation processing on the received digital signal, multiple targets that are close to each other in the long distance direction are detected separately can do.

Embodiments of the present invention will be described below with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a radar apparatus according to Embodiment 1 of the present invention. Here, as an example of a transmission pulse intra-modulation method, a case where modulation by a code sequence is performed is treated as an example.
In the figure, 1 is a transmission / reception antenna, 2 is a circulator, 3 is a transmitter, 4 is a code modulator that performs intra-pulse modulation for each stepped frequency, 5 is a code sequence generator that generates a code such as a pseudo-random code, 6 is a step frequency generator that changes the frequency stepwise, 7 is a receiver, 8 is an A / D converter that converts the received signal into a digital signal, 9 is a modulation signal correlating means that performs pulse compression processing on the received signal, 10 Is a frequency analysis means for performing frequency analysis on the signal transferred from the modulation signal correlation means 9, 11 is a target detection means for extracting a target signal from the result of the frequency analysis means 10, and 12 is a target for calculating the distance of the detected target. It is a distance calculation means.
Reference numeral 20 denotes intra-pulse modulation means, which comprises a code modulator 4, a code sequence generator 5, and a step frequency generator 6.
FIG. 2 is a diagram illustrating transmission / reception timings of transmission signals in a multi-frequency step ICW method in which a transmission wave is modulated in a pulse on the premise of pulse compression processing on the reception side.

Next, the operation of the radar apparatus according to Embodiment 1 of the present invention will be described. Let T _C be the minimum observation time required on the principle of frequency analysis processing in order to satisfy the velocity resolution required for the radar apparatus.
The step frequency generator 6 repeatedly generates a transmission signal at the same center frequency for a fixed time and changes the frequency from f ₀ to f _N−1 as shown in FIG. The code sequence generator 5 generates a code sequence convenient for pulse compression processing such as a pseudo-random code, for example, a Barker code. The code modulator 4 performs modulation processing on the signal generated by the step frequency generator 6 based on the code sequence generated by the code sequence generator 5.

As shown in FIG. 2, the signal transmitted from the transmitter 3 repeats the frequency modulation process of increasing the frequency by Δf within T _C M times during the minimum observation time. Here, M is a natural number of 2 or more. FIG. 2 is a waveform diagram of the transmission signal generated in this way. The repeated frequency modulation process is to increase the frequency of the transmission signal by Δf over N stages (where N is a natural number of 2 or more) every time T _PRI . The time width T _S of one frequency modulation process is given by T _S = T _PRI × N. The range (bandwidth) B of the frequency to be modulated is obtained from B = Δf × N. The transmission signal is code-modulated with a sub-pulse width Tchip.
The transmission signal generated in this way is converted into a transmission signal in an RF (Radio Frequency) band, further pulsed into a transmission pulse signal, and radiated from the antenna 1 as a transmission wave. A part of the transmission wave irradiated to the target reaches the antenna 1 again as an echo (reflected wave).

  The circulator 2 is a switch that switches the connection between the transmitter 3 and the antenna 1 and the connection between the receiver 7 and the antenna 1 in a time division manner. That is, the transmitter 3 and the antenna 1 are directly connected at the timing when the target is irradiated with the transmission pulse signal generated by the transmitter 3 as a transmission wave. On the other hand, the receiver 7 and the antenna 1 are directly connected at the timing when the transmission wave is reflected by the target and returns to the antenna 1 as an echo. By doing so, the antenna 1 can be used for both transmission and reception, and the circuit scale and device scale can be reduced.

The antenna 1 receives the reflected wave and outputs an analog received signal in the RF band. The receiver 7 converts the RF band received signal transferred from the circulator 2 to a video band signal and performs baseband conversion so that the received signal can be processed by a lower speed signal processing circuit. It is.
The RF band analog received signal is subjected to frequency conversion and baseband conversion by the receiver 7. This converted signal is assumed to be x (t). The A / D converter 8 converts the analog reception signal into a digital signal. A distance gate is formed by the sampling interval at this time. Here, if the received signal expressed using the distance gate number r, the frequency modulation process number m, and the frequency step number n is X (n, m, r), X (n, m, r) is expressed by the following equation (1). It is represented by

Here, T ₀ is the time from when each pulse is transmitted until the reflected wave is received, and τ _s is the sampling interval when the received signal is captured as a digital signal.

The modulation signal correlator 9 performs pulse compression processing well known in radar signal processing. The multi-frequency step ICW method has a feature that high distance resolution can be obtained in a relatively narrow transmission / reception band, but ambiguity occurs in the distance when applied to a long-distance radar. Therefore, it is necessary to lengthen the pulse repetition period and eliminate the distance ambiguity as a pulse radar. Next, it is reasonable to adopt a method in which each transmission pulse is modulated in the pulse and the distance resolution is improved within the distance ambiguity of the multi-frequency step ICW method by pulse compression processing as preprocessing in the reception system. . Specifically, this is realized by partially overlapping the frequency range to be changed between adjacent transmission pulses.
The reception signal X _PC (n, m, r) after pulse compression by the modulation signal correlator 9 can be obtained from the code sequence F _PN generated by the code sequence generator 5 from the following equation.

The frequency analysis means 10 performs frequency analysis on the reception signal obtained from the reflected wave of the transmission signal modulated to the same step frequency over a plurality of frequency modulation processes. This process received signals X _PC after pulse compression, which is held (n, m, r) of the, by fixing the n for each of the range gates r, X _PC obtained for a plurality of m (n, This corresponds to acquiring m, r) and performing frequency analysis. If Fourier transform is used as the frequency analysis method, the frequency analysis result is expressed by Expression (3).

なお、以下の説明において、式（３）におけるｋを周波数成分番号と呼ぶ。

In the following description, k in Equation (3) is referred to as a frequency component number.

The target detection unit 11 detects the target from the frequency analysis result obtained by the expression (3). First, the sum of the amplitude values of F _k (n, r) represented by the equation (3) is calculated, for example, as in the equation (4).

Subsequently, the target detection unit 11 obtains a frequency component number k at which the value of G _k (r) in Expression (4) peaks. This process is performed by searching for a frequency component number k _peak (r) that maximizes the value of the left side G _k of equation (4). On the other hand, the peak frequency f _peak (n, r) of the received signal is given by equation (5).

The target detection means 11 obtains the relative speed v _i of the target from the peak frequency number that maximizes the formula (4) and the formula (5), and outputs this v _i as the relative speed.
Moreover, the information of the peak frequency used for calculation of this relative speed is output as frequency analysis information. The frequency analysis information refers to, for example, the frequency analysis result (result of expression (3)) output by the frequency analysis means 10 and the frequency component number (expression (4)) that is the peak of the amplitude value of this frequency analysis result. K).

  The target distance calculation means 12 also obtains the peak frequency over a plurality of frequency modulation processes obtained for one n in Equation (3) for the other n, and the interphase displacement (degree of change, change of each peak frequency). This is a part that separates the distances of a plurality of constant speed targets based on the rate. This process corresponds to obtaining the phase gradient of the peak frequency in the n direction when the step frequency is monotonously increased or monotonously decreased in the frequency modulation process.

  Specifically, the target distance calculation means 12 performs frequency analysis on the received signal obtained by receiving the echo of the transmission wave modulated to the same step frequency of a plurality of repeated frequency modulation processes using the super-resolution frequency estimation method. . Such super-resolution frequency estimation methods include MUSIC (Multiple Signal Classification) method, ESPRIT (Estimation of Signal Parameters via Rotational Invariance Technique) method, ML (Maximum Likelihood) method, Capon method, maximum entropy method, linear prediction method, Although a minimum norm method or the like can be used, a specific example of processing will be described here using the MUSIC method as an example.

First, one of the frequencies at which the amplitude value in the Fourier transform output by the frequency analysis unit 10 obtained by the target detection unit 11 reaches a peak is defined as a frequency number k _peak . The target distance calculation means 12 performs frequency averaging processing by combining the frequency component corresponding to the frequency number k _peak and several frequency components before and after this frequency component in the frequency analysis result.

In the following description, as an example, one frequency component corresponding to the frequency number k _peak and one frequency component before and after this frequency component are used. That is, three components are used: a frequency component corresponding to the frequency number k _peak −1, a frequency component corresponding to the frequency number k _peak, and a frequency component corresponding to the frequency number k _peak +1.

In order to separate the distance of each target when there are multiple targets in the frequency component of frequency number k _peak, the frequency between the received signals is separated between each step frequency part of the frequency modulation process of the transmission signal. There is a need to. In order to make it possible to separate frequencies having different step frequencies n (n = 1 to N) in the frequency modulation process, first, data sampling with different step frequency numbers n is set as a sub-matrix Fq composed of N _s .

And the average processing of the correlation matrix of the sub-matrix Fq is performed as shown in Equation (7).

Subsequently, the target distance calculation means 12 performs eigenvalue expansion of the correlation matrix R obtained by frequency averaging according to the equation (7), and the eigenvector e _α (α = 1,..., N _S −P corresponding to the noise eigenvalue. ) Noise space E = [e ₁ ... E _Ns−P ]. Here, P is the number of signals, and is obtained from, for example, the number of eigenvalues larger than the eigenvalue of noise.

  Thereafter, the target distance calculation means 12 performs frequency estimation processing to calculate the distances of the plurality of targets, respectively. This frequency estimation process is as follows. That is, a mode vector that maximizes the value of the evaluation function MUSIC (R) represented by the mode vector a (R) and the noise space E is calculated as in equation (8).

  Here, the mode vector a (R) is given by equation (9).

  In other words, a plurality of Rs that give the mode vector a (R) of Expression (9) that maximizes the evaluation function MUSIC (R) of Expression (8) are calculated, and these are output as the distances of the respective targets.

  As described above, according to the first embodiment of the present invention, it is possible to separately detect a plurality of targets that are close to each other in the long distance direction, which is difficult with the conventional multi-frequency step ICW method. .

  In the above description, the Fourier transform has been described as an example of the frequency analysis method, but it is also possible to perform frequency analysis by the super-resolution method.

  In the frequency modulation process, the transmitter 3 monotonically increases the frequency of the reference signal step by step by Δf. However, since the configuration required here is only to modulate to a plurality of frequencies, frequency modulation may be performed by other methods such as a configuration that monotonously decreases the frequency or a configuration that modulates to a random frequency.

  Further, the code pattern generated by the code sequence generator may be the same for each frequency to be stepped. However, by making the code pattern different for each frequency, an effect of reducing the influence of the secondary echo can be expected.

  In addition, as a method for intra-pulse modulation of a transmission pulse signal, the modulation method using a code sequence has been described as an example in the first embodiment. However, the same method may be used even when a modulation method that continuously changes the frequency like a chirp signal is used. The effect can be expected.

  In the first embodiment, the radar apparatus configured to share the transmitting antenna and the receiving antenna is presented. However, the same effect can be expected in a radar apparatus configured separately including the transmitting antenna and the receiving antenna.

Embodiment 2. FIG.
3 is a block diagram of a radar apparatus according to Embodiment 2 of the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts, and the description thereof is omitted. Compared with the radar apparatus according to the first embodiment, a characteristic part in the second embodiment is that a pulse repetition frequency switching means 30 and a new target detection means 31 are provided in place of the target detection means 11. The target detection unit 31 operates in the same manner as the target detection unit 11 of FIG. 1, but additionally holds a memory for storing the detected target speed and distance, and is controlled by the pulse repetition frequency switching unit 30. A function of transferring this to the target distance calculating means 12 by a signal is provided.

Next, the operation of the radar apparatus according to Embodiment 2 of the present invention will be described. The radar apparatus according to the second embodiment of the present invention operates by switching the pulse repetition period corresponding to T _PRI in FIG. A radar having a long pulse repetition period, that is, a low pulse repetition frequency is called an L-PRF (Low-Pulse Repetition Frequency) radar. On the other hand, a radar with a short pulse repetition period, that is, with a high pulse repetition frequency is called an H-PRF (High-Pulse Repetition Frequency) radar. Depending on the pulse repetition frequency, each radar has the following features. In the L-PRF radar, since the time interval for transmitting the pulse is long, the reflected wave from the target is received before the next pulse is transmitted. That is, there is no ambiguity in distance. On the other hand, the H-PRF radar has a short time interval for transmitting pulses and can receive a large number of pulses, so that the target speed range that can be measured is wide and there is no ambiguity in speed.

In the second embodiment, the feature due to the difference in these pulse repetition frequencies is used. As shown in the block diagram of FIG. 3, the radar using the multi-frequency pulse ICW method first performs target analysis by performing frequency analysis from the received signal. Therefore, when the target speed is detected by the frequency analysis, the target speed can be correctly measured by operating the radar in the H-PRF mode in which the measured speed has no ambiguity. At this time, since the ambiguity occurs at the target distance, the target distance calculation means 12 is not operated. The target speed and distance measured in the H-PRF mode are temporarily held in the target detection means 31.
Next, the mode is switched to the L-PRF mode. In the L-PRF mode, frequency analysis, target detection, and target distance calculation processing are performed. At this time, the target speed measured by the target detection means 31 is compared with the target speed measured in the H-PRF mode and held in the memory. To implement. If the two target speeds are significantly different, there is a possibility that speed ambiguity has occurred due to L-PRF, so the stored target speed data is transferred to the target distance calculation means 12.

  As described above, according to the second embodiment of the present invention, while avoiding the ambiguity of speed and distance, a plurality of close proximity in the long distance direction, which is difficult with the conventional multi-frequency step ICW method, is achieved. The target can be detected separately.

  The radar apparatus according to the present invention can detect and separate not only a short distance but also a plurality of long distance targets at the same time, so that it can be used not only for mounting on a vehicle such as an automobile but also for a general search radar for detecting an aircraft or the like. Is available.

It is a block diagram which shows the structure of the radar apparatus by Embodiment 1 of this invention. FIG. 3 is an explanatory diagram of transmission / reception timing of an intra-pulse modulated transmission signal of the radar apparatus according to the first embodiment. It is a block diagram which shows the structure of the radar apparatus by Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1; Transmission / reception antenna, 2; Circulator, 3; Transmitter, 4; Code modulator, 5; Code sequence generator, 6: Step frequency generator, 7: Receiver, 8; A / D converter, 9; Signal correlation means, 10; frequency analysis means, 11; target detection means, 12; target distance calculation means, 20; intra-pulse modulation means, 30; pulse repetition frequency switching means.

Claims (4)

In a radar device that generates a pulsed transmission signal and irradiates the target as a transmission wave, receives the reflected wave of the transmission wave reflected by the target, and calculates the relative speed and distance of the target.
In-pulse modulation means for modulating the transmission signal pulse by changing the transmission frequency;
A transmitter that inputs a signal transferred from the intra-pulse modulation means, performs frequency conversion, amplification processing to generate a transmission signal, and irradiates the target via an antenna;
An A / D converter that receives a received signal transferred from a receiver that receives a reflected wave from a target and converts it into a digital signal;
Modulation signal correlation means for performing correlation processing on the digital signal converted by the A / D converter using the intra-pulse modulation signal of the transmission signal,
Frequency analysis means for frequency analysis of the signal transferred from the modulated signal correlation means;
Target detection means for extracting a target signal from the result of the frequency analysis means;
Target distance calculation means for measuring the distance from the result of the target detection means to the target;
A radar apparatus comprising:   A control signal for changing the pulse repetition frequency is transferred to the transmitter, and pulse repetition frequency switching means for controlling the operations of the frequency analysis means, the target detection means, and the target distance calculation means according to the pulse repetition frequency of the transmitter is provided. The radar apparatus according to claim 1.   2. The intra-pulse modulation means partially overlaps a frequency range changed between adjacent transmission pulses, and widens the range of ambiguity than the pulse width compressed by the modulation signal correlation means. The radar apparatus according to claim 2.   The radar apparatus according to claim 1 or 2, wherein the intra-pulse modulation means performs intra-pulse modulation using a code sequence, and changes a code pattern for each frequency to be changed stepwise.

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