JP2014222168A - Radar system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a radar system capable of performing highly accurate target detection and range-finding even when the SNR of a signal in the frequency region is low.SOLUTION: There is provided a frequency region conversion unit 9 which converts a reception video signal V(n, m) generated by a signal reception processing unit 7 into a frequency region signal F(n, k) by chirp z transformation (CZT) processing so that the same target Doppler frequency belongs to the same bin number even when the frequency fof a transmission RF signal changes. A coherent integration processing unit 11 performs coherent integration of the frequency region signal F(n, k) converted by the frequency region conversion unit 9.

Description

  In the present invention, after transmitting a transmission signal in the air at a predetermined interval, the transmission signal reflected and returned by the target is received, and signal processing of the received signal is performed, thereby measuring the target with high resolution. The present invention relates to a radar device that travels.

For example, in the radar device disclosed in Patent Document 1 below, a transmission signal having a transmission frequency changed in a step shape at a pulse repetition period (PRI) is transmitted and received.
The radar device performs FFT (Fast Fourier Transform) processing on the received signal of the same transmission frequency in the pulse hit direction to convert it to a frequency domain signal, and then converts the frequency domain signal strength. The target Doppler frequency is calculated by detecting the target based on this.
Further, after performing Doppler correction on a frequency domain signal using a target Doppler frequency, MUSIC (Multiple Signal Classification) processing is applied to the frequency domain signal after Doppler correction of a different transmission frequency. To measure the distance.

  In this radar apparatus, even in the case of a constant velocity target, the Doppler frequencies of received signals of the same target having different transmission frequencies are different. Therefore, in order to coherently integrate received signals of different transmission frequencies (denoted as coherent integration on behalf of the frequency analysis method. However, in this radar apparatus, this is equivalent to MUSIC processing), it is necessary to doppler correct the received signal. However, before the MUSIC process, the target is detected, the target Doppler frequency is calculated, and the Doppler correction is performed using the Doppler frequency.

JP 2010-175457 (FIG. 1)

  Since the conventional radar apparatus is configured as described above, when the signal-to-noise ratio (SNR) of the signal in the frequency domain is low, the target detection performance deteriorates and Doppler correction is performed. There are times when you can't. In such a case, there was a problem that the distance measurement performance deteriorated.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a radar apparatus capable of performing target detection and ranging with high accuracy even when the SNR of a frequency domain signal is low. To do.

  The radar apparatus according to the present invention includes a signal transmission unit that radiates a transmission signal in the air while changing the frequency of the transmission signal at predetermined intervals, and the signal that is radiated from the signal transmission unit to the air and then reflected back to the target. The signal receiving means for receiving the transmitted signal and converting the received signal into a received video signal, and even if the frequency of the transmitted signal changes, the same target Doppler frequency belongs to the same bin number. A frequency domain converting means for converting the received video signal converted by the signal receiving means into a frequency domain signal, and the coherent integrating means coherently integrates the frequency domain signal converted by the frequency domain converting means. It is a thing.

  According to this invention, even if the frequency of the transmission signal changes, the frequency at which the received video signal converted by the signal receiving means is converted into a frequency domain signal so that the same target Doppler frequency belongs to the same bin number. Since the domain conversion unit is provided and the coherent integration unit is configured to coherently integrate the frequency domain signal converted by the frequency domain conversion unit, even when the SNR of the signal after the frequency domain conversion is low, it is highly accurate. There is an effect that target detection and distance measurement can be performed.

It is a block diagram which shows the radar apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the transmission / reception sequence of the radar apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the frequency domain conversion result with respect to the received video signal of the same transmission frequency by FFT and CZT (when Doppler frequency 0-PRF / 2 is displayed). It is explanatory drawing which shows the frequency domain conversion result with respect to the received video signal of the same transmission frequency by FFT and CZT. It is explanatory drawing which shows the integration performance after the coherent integration by the influence of a target relative speed. It is explanatory drawing which shows the ranging performance after the coherent integration by the influence of a target relative speed. It is explanatory drawing which shows signal _FFFT (l, k) after the coherent integration by the coherent integration process part 11 of this Embodiment 1. FIG. It is explanatory drawing which shows the detection performance of the signal F _FFT (l, k) after the signal after pulse hit direction FFT by the radar apparatus currently disclosed by patent document 1, and the coherent integration by this Embodiment 1. FIG. It is a block diagram which shows the radar apparatus by Embodiment 2 of this invention. It is explanatory drawing which shows the transmission / reception sequence of the radar apparatus by Embodiment 2 of this invention. According to a second embodiment of the present invention is an explanatory diagram showing a transmission frequency f _n and transmission sequence of the radar device.

Embodiment 1 FIG.
1 is a block diagram showing a radar apparatus according to Embodiment 1 of the present invention.
In FIG. 1, a signal transmission processing unit 1 is composed of a multi-frequency local oscillator 2, a pulse modulator 3, and a transmitter 4, and the transmission is performed while changing the frequency of a transmission RF signal (transmission signal) at a predetermined interval. The process which outputs RF signal to the antenna 6 via the transmission / reception switching part 5 is implemented.
Multi-frequency local oscillator 2 of the signal transmission processing unit 1 is the local oscillation signal _{L 0 (t, n, m} ) is a signal source for generating a frequency of the local oscillation signal _{L 0 (t, n, m} ) at a predetermined interval Implement the process to change.
In the first embodiment, an example will be described in which the multi-frequency local oscillator 2 changes the frequency of the local oscillation signal L ₀ (t, n, m) in ascending or descending order at a predetermined interval.

The pulse modulator 3 performs pulse modulation on the local oscillation signal L ₀ (t, n, m) generated by the multi-frequency local oscillator 2 and transmits the pulse-modulated local oscillation signal L ′ ₀ (t, n, m). Processing to output to the machine 4 is performed.
The transmitter 4 outputs the pulse-modulated local oscillation signal L ′ ₀ (t, n, m) output from the pulse modulator 3 to the transmission / reception switching unit 5 as a transmission RF signal Tx (t, n, m). Thus, the process of radiating the transmission RF signal Tx (t, n, m) from the antenna 6 into the air is performed.

The transmission / reception switching unit 5 outputs the transmission RF signal Tx (t, n, m) output from the transmitter 4 to the antenna 6, while receiving the reflected RF signal incident from the antenna 6 as the reception RF signal Rx (t, n, m). m), a process of outputting to the signal reception processing unit 7 is performed.
The antenna 6 radiates the transmission RF signal Tx (t, n, m) output from the transmission / reception switching unit 5 into the air, while the reflection of the transmission RF signal Tx (t, n, m) is reflected back to the target. This is a transmitting / receiving antenna that receives an RF signal.
The signal transmission processing unit 1, the transmission / reception switching unit 5 and the antenna 6 constitute a signal transmission means.

The signal reception processing unit 7 includes, for example, a receiver, a phase detector, and the like, and uses the local oscillation signal L ₀ (t, n, m) generated by the multi-frequency local oscillator 2 to transmit and receive from the transmission / reception switching unit 5. The received reception RF signal Rx (t, n, m) is down-converted, and the down-converted signal is passed through a narrowband filter, and then subjected to amplification processing and phase detection processing, whereby the reception video signal V ( n, m) is generated.
The transmission / reception switching unit 5, the antenna 6 and the signal reception processing unit 7 constitute a signal receiving means.

The signal processor 8 includes a frequency domain conversion unit 9, a velocity compensation processing unit 10, a coherent integration processing unit 11, a target candidate detection unit 12, and a target candidate relative speed / relative distance calculation unit 13, and the signal reception processing unit 7. The target candidate is detected from the received video signal V (n, m) generated by the above.
Here, each of the frequency domain conversion unit 9, the speed compensation processing unit 10, the coherent integration processing unit 11, the target candidate detection unit 12, and the target candidate relative speed / relative distance calculation unit 13 which are components of the signal processor 8 is dedicated. However, the signal processor 8 may be constituted by a computer. However, the signal processor 8 may be constituted by a computer.
When the signal processor 8 is composed of a computer, the processing contents of the frequency domain conversion unit 9, the speed compensation processing unit 10, the coherent integration processing unit 11, the target candidate detection unit 12, and the target candidate relative speed / relative distance calculation unit 13 May be stored in the memory of a computer, and the CPU of the computer may execute the program stored in the memory.

The frequency domain converter 9 of the signal processor 8 receives the signal so that the same target Doppler frequency belongs to the same bin number even if the transmission frequency f _n of the transmission RF signal Tx (t, n, m) changes. The received video signal V (n, m) generated by the processing unit 7 is converted into a frequency domain signal F _CZT (n, k) by chirp z conversion processing, for example. The frequency domain conversion unit 9 constitutes frequency domain conversion means.
The speed compensation processing unit 10 performs a speed compensation process on the frequency domain signal F _CZT (n, k) converted by the frequency domain conversion unit 9, and the signal F ′ _CZT (n, k) after the speed compensation process is coherent. The process which outputs to the integration process part 11 is implemented. The speed compensation processing unit 10 constitutes speed compensation means.

The coherent integration processing unit 11 coherently integrates the signal F ′ _CZT (n, k) after the speed compensation processing output from the speed compensation processing unit 10, and uses the signal F _FFT (l, k) after the coherent integration as a target candidate. A process of outputting to the detection unit 12 is performed. The coherent integration processing unit 11 constitutes coherent integration means.
The target candidate detection unit 12 detects a target candidate based on the signal strength of the signal F _FFT (l, k) after the coherent integration output from the coherent integration processing unit 11, and the sampling number k ′ of the target candidate in the velocity direction. Then, a process of outputting the sampling number l ′ in the distance direction to the target candidate relative speed / relative distance calculation unit 13 is performed. The target candidate detection unit 12 constitutes a target candidate detection unit.

The target candidate relative speed / relative distance calculation unit 13 calculates the target candidate relative speed v ′ _tgt from the sampling number k ′ in the speed direction of the target candidate output from the target candidate detection unit 12, and outputs it from the target candidate detection unit 12. The target candidate relative distance R ′ _tgt is calculated from the sampling number l ′ of the target candidate in the distance direction. The target candidate relative speed / relative distance calculation unit 13 constitutes a target relative speed relative distance calculation unit.
The display device 14 is composed of, for example, a liquid crystal display and displays the relative distance R ′ _tgt and the relative distance R ′ _{tgt of} the target candidate calculated by the target candidate relative speed / relative distance calculation unit 13 on the screen.

FIG. 2 is an explanatory diagram showing a transmission / reception sequence of the radar apparatus according to Embodiment 1 of the present invention.
In FIG. 2, f ₀ is a transmission minimum frequency, f _n is a transmission frequency, n is a transmission frequency number, N is the number of transmission frequencies, m is a hit number of the same transmission frequency, M is a hit number of the same transmission frequency, and Δf is A transmission frequency interval, T _f is a transmission frequency switching interval, T _pri is a pulse repetition interval (PRI), T _p is a pulse width, Δt is a pulse repetition interval of the same transmission frequency, and T _cpi is an observation time.

In the first embodiment, as shown in FIG. 2, a transmission RF signal in which the transmission frequency switching interval T _{f is set} to the pulse repetition period T _pri and the transmission frequency f _n is changed in ascending order by the transmission frequency interval Δf is emitted into the air. It shall be. Further, it is assumed that the transmission RF signal changed in ascending order is repeatedly emitted into the air.
In the first embodiment, the transmission RF signal in which the transmission frequency f _n is changed in ascending order by the transmission frequency interval Δf is shown in the air, but the transmission frequency f _n is changed in descending order by the transmission frequency interval Δf. The transmission RF signal may be emitted into the air.

式（１）において、Ａ_Ｌは局部発振信号の振幅、φ_０は局部発振信号の初期位相である。 Next, the operation will be described.
The multi-frequency local oscillator 2 of the signal transmission processing unit 1 generates a local oscillation signal L ₀ (t, n, m) whose frequency changes at the transmission frequency switching interval T _f shown in FIG.
That is, the multi-frequency local oscillator 2 generates a local oscillation signal L ₀ (t, n, m) represented by the following expression (1), and pulses the local oscillation signal L ₀ (t, n, m). Output to the modulator 3 and the signal reception processing unit 7.

In Expression (1), A _L is the amplitude of the local oscillation signal, and φ ₀ is the initial phase of the local oscillation signal.

When the pulse modulator 3 receives the local oscillation signal L ₀ (t, n, m) from the multi-frequency local oscillator 2, the pulse modulator 3 performs pulse modulation on the local oscillation signal L ₀ (t, n, m). The local oscillation signal L ′ ₀ (t, n, m) after pulse modulation represented by 2) is output to the transmitter 4.

The transmitter 4 transmits the local oscillation signal after pulse modulation from the pulse modulator _{3 L '0 (t, n} , m) receives a local oscillation signal after pulse modulation _{L' 0 (t, n,} m) a The RF signal Tx (t, n, m) is output to the transmission / reception switching unit 5.
When the transmission / reception switching unit 5 receives the transmission RF signal Tx (t, n, m) from the transmitter 4, the transmission / reception switching unit 5 outputs the transmission RF signal Tx (t, n, m) to the antenna 6.
Thereby, the transmission RF signal Tx (t, n, m) is radiated from the antenna 6 into the air.

式（３）において、Ａ_Ｒは反射ＲＦ信号の振幅、Ｒ_０は初期目標相対距離、ｖは目標相対速度、ｃは光速である。 A part of the transmission RF signal Tx (t, n, m) radiated into the air is reflected by the target, and the transmission RF signal Tx (t, n, m) reflected by the target is expressed by the following equation (3). The reflected RF signal Rx (t, n, m) represented is incident on the antenna 6.

In Expression (3), _AR is the amplitude of the reflected RF signal, R ₀ is the initial target relative distance, v is the target relative speed, and c is the speed of light.

式（４）において、Ａ_Ｖは受信ビデオ信号の振幅である。
ここでは、信号受信処理部７が狭帯域フィルタを用いている例を示しているが、ＰＲＩ内をサンプリングした受信ビデオ信号を生成するようにしてもよい。 The transmission / reception switching unit 5 outputs the reflected RF signal Rx (t, n, m) incident from the antenna 6 to the signal reception processing unit 7 as a reception RF signal Rx (t, n, m).
When receiving the reception RF signal Rx (t, n, m) from the transmission / reception switching unit 5, the signal reception processing unit 7 uses the local oscillation signal L ₀ (t, n, m) generated by the multi-frequency local oscillator 2. The received RF signal Rx (t, n, m) is down-converted.
In addition, the signal reception processing unit 7 passes the down-converted signal through a narrowband filter, and then performs amplification processing and phase detection processing, so that the received video signal V ( n, m) is generated, and the received video signal V (n, m) is output to the signal processor 8.

In equation (4), _AV is the amplitude of the received video signal.
Here, an example is shown in which the signal reception processing unit 7 uses a narrowband filter, but a reception video signal obtained by sampling the PRI may be generated.

When the signal processor 8 receives the received video signal V (n, m) from the signal reception processing unit 7, the signal processor 8 performs predetermined signal processing on the received video signal V (n, m) to thereby obtain a target candidate. _Is detected, and the relative speed v ′ _{tgt of the} target candidate and the relative distance R ′ _tgt of the target candidate are calculated.
Hereinafter, the processing contents of the signal processor 8 will be specifically described.

FIG. 3 is an explanatory diagram showing frequency domain conversion results for received video signals of the same transmission frequency by FFT and chirp z-transform (CZT: Chirp Z-Transform) (when Doppler frequencies 0 to PRF / 2 are displayed).
FIG. 4 is an explanatory diagram showing a frequency domain conversion result for a received video signal having the same transmission frequency by FFT and CZT.
The frequency domain transform unit 9 receives the received video signal V (n, m) output from the signal reception processing unit 7, and the Doppler frequency f _d (n, v) of the transmission frequency f _n with respect to the target relative speed v is Since it is expressed by the following equation (5), it can be seen that the Doppler frequency f _d (n, v) varies depending on the transmission frequency f _n .

Therefore, as in the radar apparatus disclosed in Patent Document 1, when the received video signal V (n, m) having the same transmission frequency f _n is converted into a frequency domain signal by fast Fourier transform (FFT), As shown in FIG. 3A and FIG. 4A, the frequency domain signal is sampled at the same frequency sampling interval Δf _FFT regardless of the transmission frequency f _n .
As a result, when the transmission frequency f _{n of} the transmission RF signal Tx (t, n, m) changes, the same target Doppler frequency belongs to different bin numbers as shown in FIGS. 3 (a) and 4 (a). As a result, the target cannot be coherently integrated. It is also difficult to perform non-coherent integration.

Therefore, the frequency domain transforming unit 9 transforms the received video signal V (n, m) into a frequency domain signal for the purpose of enabling the subsequent coherent integration processing unit 11 to coherently integrate the same target. In this case, the signal is converted into a frequency domain signal F _CZT (n, k) by chirp z conversion (CZT) processing instead of FFT.
That is, the frequency domain transform unit 9 changes the CZT conversion function according to the transmission frequency f _n , thereby transmitting the transmission RF signal Tx (t, n, as shown in FIGS. 3B and 4B. , M), the received video signal V (n, m) generated by the signal reception processing unit 7 is changed to the frequency domain so that the same target Doppler frequency belongs to the same bin number even if the transmission frequency f _n changes. Signal F _CZT (n, k).
Specifically, the frequency domain transform unit 9 performs chirp z transform (CZT) processing on the received video signal V (n, m) generated by the signal reception processing unit 7 as shown in the following equation (6). The frequency domain signal F _CZT (n, k) is converted into a frequency domain signal F _CZT (n, k) and the speed compensation unit 10 is output.

ここで、ｚ_ｎ ^−ｍは送信周波数ｆ_ｎに対応するＣＺＴの変換関数、Ａ_ｎは送信周波数ｆ_ｎに対応する変換開始位相（式（７）を参照）、Ｗ_ｎ ^−ｋは送信周波数ｆ_ｎに対応するＣＺＴの変換範囲関数（式（８）を参照）である。
また、ｖ_ｓｔは変換開始速度、ｖ_ｅｎは変換終了速度、Ｍ_ｃｚｔはチャープｚ変換後のサンプリング数、ｆ_ｓａｍｐはサンプリング周波数（式（９）を参照）である。

_Here, (see Equation ₍₇₎₎ ^{z n -m} conversion function CZT corresponding to the transmission frequency _{f n, A n} is conversion start phase corresponding to the transmission frequency _{f n,} ^{W n -k} transmission frequency f CZT conversion range function corresponding to _n (see equation (8)).
Also, v _st is the conversion start speed, v _en is the conversion end speed, M _czt is the number of samples after chirp z conversion, and f _samp is the sampling frequency (see equation (9)).

As shown in FIG. 4B, the signal of the frequency domain is converted from the conversion start speed _vst at any transmission frequency f _n by the processing of the frequency domain conversion unit 9 according to the equations (6) to (9). The same target is sampled into the same Doppler velocity bin, sampled at the same velocity sampling interval Δv _czt until the end velocity v _en .
Further, the sampling number M _czt after the chirp z conversion can be arbitrarily set, and a desired sampling interval can be obtained. Conversion start velocity v _st or conversion end speed v _en, it becomes possible to arbitrarily set the relative speed to be assumed.
Therefore, compared to the FFT in the pulse hit direction performed by the radar apparatus disclosed in Patent Document 1, it is possible to easily perform high sampling.

式（１０）において、＊は畳み込みを表わす記号である。 Here, the frequency domain conversion unit 9 converts the received video signal V (n, m) generated by the signal reception processing unit 7 into a frequency domain signal F _CZT (n, k) by chirp z conversion (CZT) processing. However, the received video signal V (n, m) may be converted into a frequency domain signal F _CZT (n, k) by a discrete Fourier transform (DFT) process.
However, the chirp z-transform (CZT) represented by the equation (6) is converted into a frequency domain using a fast Fourier transform (FFT) and an inverse fast Fourier transform (IFFT: Inverse FFT) represented by the following equation (10). By realizing the convolution integration, processing can be performed at a higher speed than the discrete Fourier transform (DFT).

In the formula (10), * is a symbol representing convolution.

Here, the frequency domain conversion unit 9 converts the received video signal V (n, m) generated by the signal reception processing unit 7 into a frequency domain signal F _CZT (n, k) by chirp z conversion (CZT) processing. However, there is a _possibility that the frequency domain signal F _CZT (n, k) may be buried in a side lobe such as a clutter.
In such a case, the frequency domain transform unit 9 shows the following equation (11) before transforming the received video signal V (n, m) into a frequency domain signal F _CZT (n, k). As described above, the window function process is performed on the received video signal V (n, m) to generate the received video signal V ′ (n, m) after the window function process.
As a window function used in this window function processing, a Hamming window w _ham (m) represented by the following equation (12) can be considered.

As described above, by performing the window function processing, the side lobe in the speed direction of the signal in the frequency domain is reduced, so that a situation where the target is buried in the side lobe can be avoided.
When the frequency domain transform unit 9 performs window function processing on the received video signal V (n, m), the received video signal V ′ (n) after the window function processing is used instead of the received video signal V (n, m). , M) is substituted into Equation (6) or Equation (10) to convert it to a frequency domain signal F _CZT (n, k).

式（１３）において、ｖ_ｃｚｔ（ｋ）は下記の式（１４）で表わされる速度補償処理後の信号Ｆ’_ＣＺＴ（ｎ，ｋ）のドップラ速度ビンｋに対応する相対速度である。

式（１４）において、Δｖ_ｃｚｔは下記の式（１５）で表わされる速度補償処理後の信号Ｆ’_ＣＺＴ（ｎ，ｋ）の速度サンプリング間隔である。

Speed compensation processing unit 10 receives the signal in the frequency domain _F CZT (n, k) from frequency domain transform section 9, as shown in the following equation (13), the frequency region of the signal _F CZT (n, k) The speed compensation process is performed on the signal F, and the signal F ′ _CZT (n, k) after the speed compensation process is output to the coherent integration processing unit 11.

In the equation (13), v _czt (k) is a relative velocity corresponding to the Doppler velocity bin k of the signal F ′ _CZT (n, k) after the velocity compensation processing represented by the following equation (14).

In Expression (14), Δv _czt is a speed sampling interval of the signal F ′ _CZT (n, k) after the speed compensation processing expressed by the following Expression (15).

In the first embodiment, since the transmission frequency f _n during the pulse repetition interval Δt of the same transmission frequency is a change only in ascending order, the phase difference between the transmission frequency f _n and the transmission frequency f _{n + 1} is substantially the same. When the phase difference is very small, it is not necessary to perform speed compensation processing.
Here, the effect of the speed compensation process performed when the phase difference cannot be ignored will be described.
As shown in FIG. 4 (b), the chirp z transform of the frequency domain transform unit 9 transforms to the frequency domain so that the same target Doppler velocity bins are the same (after frequency domain transform of different transmission frequencies). Therefore, it is not necessary to detect the target candidate and calculate the relative speed of the target candidate before the speed compensation process. Therefore, since target candidate detection processing can be performed after performing speed compensation processing and coherent integration, it is possible to obtain a radar apparatus with improved target detection performance.

Further, when coherent integration is performed on the frequency domain signal F _CZT (n, k) in the transmission frequency direction, there is a concern that the integration efficiency may deteriorate due to the influence of the target relative speed. By performing the speed compensation process, the influence of the target relative speed is reduced, and the integration efficiency is improved. FIG. 5 shows the integration performance after coherent integration due to the influence of the target relative speed.
In addition, when performing the ranging process after performing coherent integration of the frequency domain signal F _CZT (n, k) in the transmission frequency direction, there is a concern that the ranging performance may deteriorate due to the influence of the target relative speed. However, when the speed compensation processing unit 10 performs the speed compensation process, the influence of the target relative speed is reduced, and the ranging performance is improved. FIG. 6 shows the ranging performance after coherent integration due to the influence of the target relative speed.

式（１６）において、Ｎ_ＦＦＴは送信周波数方向のＦＦＴ点数、Ｒ_ａｍｂは式（１７）で表わされるコヒーレント積分後の信号Ｆ_ＦＦＴ（ｌ，ｋ）の曖昧さなく計測が可能な距離である。
また、ΔＲは式（１８）で表わされるコヒーレント積分後の信号Ｆ_ＦＦＴ（ｌ，ｋ）の距離分解能、ΔＲ_ＦＦＴは式（１９）で表わされるコヒーレント積分後の信号Ｆ_ＦＦＴ（ｌ，ｋ）の距離方向のサンプリング間隔である。 When the coherent integration processing unit 11 receives the signal F ′ _CZT (n, k) after the speed compensation processing from the speed compensation processing unit 10, as shown in the following equation (16), the signal F ′ after the speed compensation processing _CZT (n, k) is coherently integrated, and the signal F _FFT (l, k) after the coherent integration is output to the target candidate detection unit 12.

In Expression (16), N _FFT is the number of FFT points in the transmission frequency direction, and R _amb is a distance that can be measured without ambiguity in the signal F _FFT (1, k) after coherent integration represented by Expression (17).
ΔR is the distance resolution of the signal F _FFT (l, k) after coherent integration represented by the equation (18), and ΔR _FFT is the signal F _FFT (l, k) after coherent integration represented by the equation (19). This is the sampling interval in the distance direction.

The coherent integration processing unit 11 sets 0 to the signal F ′ _CZT (n, k) after the speed compensation processing when the number of FFT points N _{FFT in the} transmission frequency direction is larger than the number N of transmission frequencies (N _FFT > N). The distance direction of the signal F _FFT (l, k) after the coherent integration is set to high sampling. However, when the distance direction of the signal F _FFT (l, k) after the coherent integration is highly sampled, the chirp z-transform may be applied.
Although the equation (16) is described by the discrete Fourier transform, the signal F ′ _CZT (n, k) after the speed compensation process may be integrated coherently by the fast Fourier transform process.
When the target number is known or the SNR is such that the target number can be calculated, the signal F ′ _CZT (n, k) after the speed compensation process may be integrated coherently in the MUSIC process. .

Here, the SNR of a signal for detecting a target candidate will be described, and the effect of coherent integration by the coherent integration processing unit 11 will be described.
FIG. 7 is an explanatory diagram showing the signal F _FFT (l, k) after coherent integration by the coherent integration processing unit 11 of the first embodiment.
As shown in FIG. 7, the signal F _FFT (l, k) after the coherent integration has an SNR improvement degree SNR_imp _{czt +} fft expressed by the following equation (20) as compared with the input SNR in the SNR of the signal for detecting the target candidate. Only improve.

On the other hand, the SNR of the signal after the pulse hit direction FFT by the radar device disclosed in Patent Document 1 is expressed by the following equation (21) as compared with the input SNR only by the effect of the pulse hit direction FFT of one transmission frequency. to improve only SNR improvement SNR_imp _fft represented.
Further, the SNR after performing non-coherent integration (average processing or PDI (Post Detection Integration)) on the signal after the pulse hit direction FFT of N transmission frequencies is compared with the input SNR as follows: It is improved by the SNR improvement degree SNR_imp fft _{+ pdi} expressed by 22).

図８は特許文献１に開示されているレーダ装置によるパルスヒット方向ＦＦＴ後の信号と、この実施の形態１によるコヒーレント積分後の信号Ｆ_ＦＦＴ（ｌ，ｋ）の検出性能を示す説明図である。 Therefore, the relationship between the SNRs at the time of target candidate detection in this Embodiment 1 and Patent Document 1 is expressed as the following Expression (23), and therefore, in this Embodiment 1, it is disclosed in Patent Document 1. It can be seen that the detection performance of the target is improved as compared with the radar device. For this reason, the radar apparatus which can detect the target candidate of a lower SNR is obtained.

FIG. 8 is an explanatory diagram showing the detection performance of the signal after the pulse hit direction FFT by the radar apparatus disclosed in Patent Document 1 and the signal F _FFT (l, k) after the coherent integration according to the first embodiment. .

Here, the coherent integration processing unit 11 has shown that the signal F ′ _CZT (n, k) after the speed compensation processing is integrated coherently, but the signal F _FFT (l, k) after the coherent integration is the clutter. There is a possibility that it is buried in the side lobe.
In such a case, the coherent integration processing unit 11 performs speed compensation processing as shown in the following equation (24) before coherently integrating the signal F ′ _CZT (n, k) after the speed compensation processing. after implementing the window function processing for the signal _{F 'CZT (n, k)} , it generates a signal _{F "CZT} after the window function processing (n, k).
As a window function used in this window function processing, a Hamming window w _ham (n) represented by the following equation (25) can be considered.

As described above, by performing the window function processing, the side lobes in the distance direction of the signal after the coherent integration are reduced, so that a situation where the target is buried in the side lobes can be avoided.
When the window function process is performed on the signal F ′ _CZT (n, k) after the speed compensation process, the coherent integration processing unit 11 uses the window function instead of the signal F ′ _CZT (n, k) after the speed compensation process. The processed signal F ″ _CZT (n, k) is substituted into the equation (16) to integrate coherently.

When the target candidate detection unit 12 receives the signal F _FFT (l, k) after the coherent integration from the coherent integration processing unit 11, the target candidate detection unit 12 detects the target candidate based on the signal intensity of the signal F _FFT (l, k), The target candidate speed direction sampling number k ′ and the distance direction sampling number l ′ are output to the target candidate relative speed / relative distance calculation unit 13.
As target candidate detection processing, for example, CA-CFAR (Cell Average Constant False Alarm Rate) processing can be considered.

表示器１４は、信号処理の結果として、目標候補相対速度・相対距離算出部１３により算出された目標候補の相対距離Ｒ’_ｔｇｔや相対距離Ｒ’_ｔｇｔを画面上に表示する。 When the target candidate relative speed / relative distance calculation unit 13 receives the sampling number k ′ in the speed direction and the sampling number l ′ in the distance direction of the target candidate from the target candidate detection unit 12, as shown in the following equation (26). Then, the relative speed v ′ _tgt of the target candidate is calculated from the sampling number k ′ in the speed direction of the target candidate.
Further, as shown in the following equation (27), the relative distance R ′ _tgt of the target candidate is calculated from the sampling number l ′ in the distance direction of the target candidate.

As a result of the signal processing, the display 14 displays the relative distance R ′ _tgt and the relative distance R ′ _tgt of the target candidate calculated by the target candidate relative speed / relative distance calculation unit 13 on the screen.

As apparent from the above, according to the first embodiment, even if the frequency f _{n of} the transmission RF signal Tx (t, n, m) changes, the same target Doppler frequency belongs to the same bin number. In addition, a frequency domain conversion unit 9 is provided for converting the received video signal V (n, m) generated by the signal reception processing unit 7 into a frequency domain signal F _CZT (n, k) by chirp z conversion (CZT) processing. The coherent integration processing unit 11 is configured to coherently integrate the frequency domain signal F _CZT (n, k) converted by the frequency domain conversion unit 9, and thus the frequency domain signal F _CZT (n, k). Even when the SNR is low, it is possible to perform target detection, distance measurement and speed measurement with high accuracy.
Also, by coherently integrating the received video signal V (n, m) changing in ascending order at the transmission frequency interval Δf, it is equivalent to using a wideband receiver even if the receiver band is small. There is an effect that the hardware scale required to obtain a high distance resolution can be reduced.

In addition, according to the first embodiment, before the frequency domain converting unit 9 converts the received video signal V (n, m) into the frequency domain signal F _CZT (n, k), the received video signal V Since the window function process for (n, m) is performed to generate the received video signal V ′ (n, m) after the window function process, side lobes in the velocity direction of the frequency domain signal are reduced. And the effect which can avoid the situation where a target is buried in a side lobe is produced.

Further, according to the first embodiment, the speed compensation processing unit 10 performs the speed compensation process on the frequency domain signal F _CZT (n, k) transformed by the frequency domain transform unit 9, and after the speed compensation process The signal F ′ _CZT (n, k) is output to the coherent integration processing unit 11, so that the target detection performance is improved and the influence of the target relative speed is reduced. The effect of improving performance is obtained.

Further, according to the first embodiment, before the coherent integration processing unit 11 coherently integrates the signal F ′ _CZT (n, k) after the speed compensation process, the signal F ′ _CZT ( Since the window function processing is performed on n, k) to generate the signal F ″ _CZT (n, k) after the window function processing, the side lobe in the distance direction of the signal after the coherent integration is reduced. As a result, it is possible to avoid the situation where the target is buried in the side lobe.

Embodiment 2. FIG.
FIG. 9 is a block diagram showing a radar apparatus according to Embodiment 2 of the present invention. In the figure, the same reference numerals as those in FIG.
The multi-frequency local oscillator 2a is a signal source that generates a local oscillation signal L ₀ (t, n, m), and performs a process of changing the frequency of the local oscillation signal L ₀ (t, n, m) at a predetermined interval. To do.
In the first embodiment, the multi-frequency local oscillator 2 changes the frequency of the local oscillation signal L ₀ (t, n, m) in ascending or descending order at a predetermined interval. In the multi-frequency local oscillator 2a, for example, the local oscillation signal L ₀ (t, n,) is transmitted at a predetermined interval such that the transmission frequency f _n in the pulse repetition interval Δt of the same transmission frequency alternately changes in ascending order and descending order. The frequency of m) is changed according to a predetermined rule.

Similar to the speed compensation processing unit 10 of FIG. 1, the speed compensation processing unit 10a performs speed compensation processing on the frequency domain signal F _CZT (n, k) transformed by the frequency domain transformation unit 9, and after the speed compensation processing The signal F ′ _CZT (n, k) is output to the coherent integration processing unit 11. The mathematical expression representing the speed compensation process is slightly different from that of the speed compensation processing unit 10 of FIG. The speed compensation processing unit 10a constitutes speed compensation means.

Next, the operation will be described.
Except for the multi-frequency local oscillator 2a and the speed compensation processing unit 10a, the processing is the same as that of the first embodiment. Therefore, only the processing contents of the multi-frequency local oscillator 2a and the speed compensation processing unit 10a will be described here.
FIG. 10 is an explanatory diagram showing a transmission / reception sequence of the radar apparatus according to the second embodiment of the present invention.
FIG. 10 illustrates the case where the number of transmission frequencies N = 8.

As shown in FIG. 10, if the pulse number n ′ between the pulse repetition intervals Δt of the same transmission frequency is an even number, the multi-frequency local oscillator 2a changes the transmission frequency f _n in ascending order to generate the local oscillation signal L _0. If (t, n, m) is generated and the pulse number n ′ is an odd number, the transmission frequency f _n is changed in descending order to generate the local oscillation signal L ₀ (t, n, m).
Since the generation processing of the local oscillation signal L ₀ (t, n, m) by the multi-frequency local oscillator 2a combines ascending order and descending order, it changes to either ascending order or descending order as in the first embodiment. Compared to the case of making it, it is more complicated. Further, the transmission frequency f _n of continuous pulses changes more greatly. For this reason, the effect of reducing the influence of the secondary clutter and the effect of concealing the use frequency of the radar device are improved as compared with the first embodiment.

The multi-frequency local oscillator 2a generates a local oscillation signal L ₀ (t, n, m) represented by the following equation (28), and the local oscillation signal L ₀ (t, n, m) is converted into a pulse modulator. 3 and the signal reception processing unit 7.
The local oscillation signal L ₀ (t, n, m) generated by the multi-frequency local oscillator 2a has a sequence of transmission frequencies f _n as shown in FIG.

In the second embodiment, since the transmission frequency f _n in the pulse repetition interval Δt of the same transmission frequency changes alternately in ascending order and descending order, and the change in the transmission frequency f _n is not continuous, speed compensation Processing needs to be performed.
Speed compensation processing section 10a receives the signal _F CZT in the frequency domain from the frequency domain transform section 9 (n, k), as shown in the following equation (29), the frequency region of the signal _F CZT (n, k) The speed compensation process is performed on the signal F, and the signal F ′ _CZT (n, k) after the speed compensation process is output to the coherent integration processing unit 11.

As apparent from the above, according to the second embodiment, the multi-frequency local oscillator 2a increases the transmission frequency f _n in ascending order if the pulse number n ′ between the pulse repetition intervals Δt of the same transmission frequency is an even number. To generate a local oscillation signal L ₀ (t, n, m). If the pulse number n ′ is an odd number, the transmission frequency f _n is changed in descending order to generate the local oscillation signal L ₀ (t, n). , M) is generated, it is possible to increase the effect of reducing the influence of the secondary clutter and the effect of concealing the use frequency of the radar apparatus.

In the second embodiment, if the multi-frequency local oscillator 2a has an even pulse number n ′ during the pulse repetition interval Δt of the same transmission frequency, the transmission frequency f _n is changed in ascending order, and the pulse number n ′ if but odd, showed a change pattern of changing the transmission frequency f _n in descending order, as long the transmission frequency f _n in which varying according to a predetermined rule, change patterns of the transmission frequency f _n is the It is not limited to things.

  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 Signal transmission process part (signal transmission means), 2, 2a Multi-frequency local oscillator, 3 Pulse modulator, 4 Transmitter, 5 Transmission / reception switching part (Signal transmission means, Signal reception means), 6 Antenna (Signal transmission means, Signal Receiving means), 7 signal receiving processing section (signal receiving means), 8 signal processor, 9 frequency domain converting section (frequency domain converting means), 10, 10a speed compensation processing section (speed compensating means), 11 coherent integration processing section (Coherent integration means), 12 target candidate detection section (target candidate detection means), 13 target candidate relative speed / relative distance calculation section (target relative speed relative distance calculation means), 14 display.

Claims (15)

Signal transmitting means for radiating the transmission signal in the air while changing the frequency of the transmission signal at a predetermined interval;
Signal receiving means for receiving the transmission signal that has been radiated from the signal transmitting means into the air and then reflected back to the target, and converts the received signal into a received video signal; and
Frequency domain conversion means for converting the received video signal converted by the signal receiving means into a frequency domain signal so that the same target Doppler frequency belongs to the same bin number even if the frequency of the transmission signal changes. ,
A radar apparatus comprising: coherent integration means for coherently integrating the frequency domain signal converted by the frequency domain conversion means.   2. The radar apparatus according to claim 1, further comprising target candidate detection means for detecting a target candidate from a signal after coherent integration by the coherent integration means.   3. The radar apparatus according to claim 2, further comprising target relative speed relative distance calculating means for calculating a relative speed and a relative distance of the target candidate detected by the target candidate detecting means.   The radar apparatus according to any one of claims 1 to 3, wherein the signal transmission means changes the frequency of the transmission signal in ascending order or descending order at predetermined intervals.   The radar apparatus according to any one of claims 1 to 3, wherein the signal transmission means changes the frequency of the transmission signal at a predetermined interval according to a predetermined rule.   6. The frequency domain transforming means transforms the received video signal converted by the signal receiving means into a frequency domain signal by chirp z conversion processing. Radar device.   6. The frequency domain transforming means transforms the received video signal transformed by the signal receiving means into a frequency domain signal by discrete Fourier transform processing. Radar device.   The frequency domain converting means performs window function processing on the received video signal converted by the signal receiving means, and converts the received video signal after the window function processing into a frequency domain signal. 8. The radar device according to any one of items 7.   9. A speed compensation unit that performs speed compensation processing on the frequency domain signal transformed by the frequency domain transforming unit and supplies the signal after the speed compensation processing to the coherent integration unit. The radar device according to any one of the above.   10. The radar apparatus according to claim 1, wherein the coherent integration unit coherently integrates the frequency domain signal converted by the frequency domain conversion unit by a discrete Fourier transform process. .   10. The radar apparatus according to claim 1, wherein the coherent integration unit coherently integrates the frequency domain signal converted by the frequency domain conversion unit by a fast Fourier transform process. .   12. The radar apparatus according to claim 10, wherein the coherent integration unit performs coherent integration with a number of points larger than the number of transmission frequencies of the frequency domain signal converted by the frequency domain conversion unit.   The radar apparatus according to any one of claims 1 to 9, wherein the coherent integration means coherently integrates the frequency domain signal converted by the frequency domain conversion means by chirp z conversion processing. .   The radar apparatus according to any one of claims 1 to 9, wherein the coherent integration unit coherently integrates the frequency domain signal converted by the frequency domain conversion unit by MUSIC processing.   The coherent integration unit performs window function processing on the frequency domain signal converted by the frequency domain conversion unit, and coherently integrates the signal after the window function processing. The radar device according to any one of the above.

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