JPH04102085A - Radar device - Google Patents

Abstract

PURPOSE:To enable an optimum integration value to be specified and detection probability to be improved by determining the optimum integration value from S/N per pulse of a received signal according to a bandwidth of a Doppler spectrum of the received signal. CONSTITUTION:An A/D converter 1 converts a received signal to a digital signal. Then, each range pin 2 divides the digital signal from the converter 1 for each distance to a target. Each received signal bandwidth measurement means 8 measures the bandwidth of a Doppler spectrum of the received signal from an output signal of each pin 2. Then, a coherent integrator 7a determines an optimum integration value from S/N per pulse of received signal which is output from each pin 2 according to the bandwidth of Doppler spectrum of the received signal which is output from the means 8. Then, a non-coherent integrator 5 allows output signal of each amplitude detector 4 to be subjected to non-coherent integration. Then, a threshold detector 6 detects presence of an object to be detected when the output signal of the integration 5 exceeds a threshold level.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a radar device for detecting a detection target.
In particular, it relates to a radar device using pulse integration.

[Conventional technology]

FIG. 5 is a block diagram showing the configuration of a radar device disclosed in Japanese Patent Application No. 02-51108.

In the figure, 1 is an A/D (analog/digital) converter,
2 is a range bin, 4 is an amplitude detector, 5 is a non-coherent integrator, 6 is a threshold detector, 7 is a coherent integrator having means for determining the optimum number of integrations, 8 is a received signal bandwidth measuring means, and 9 is a transmitter. , 10 is a transmission/reception switch, 11
12 is a transmitting and receiving antenna, 12 is a receiver, and 13 is a display device. Note that the operations of the above-mentioned components will be described in the operation description below.

Next, the operation will be explained. In FIG. 5, a transmission signal is transmitted from a transmitter 9 to a transmitter/receiver switch 10. Transmitting/receiving antenna 11
The signal radiated to the outside via the detection target and reflected by the detection target is transmitted to the transmitting/receiving antenna 11. The received signal enters the receiver 12 as a received signal via the transmitter/receiver switch 10, is converted into a complex video signal, and is then converted into a digital signal by the A/D converter 1. This digital signal is divided into M range bins 2 for each distance, and is input to a received signal bandwidth measuring means 8 connected to each range bin 2, and is also input to a coherent integrator 7 having means for determining the optimum number of integrations. Ru. As shown in the flowchart of FIG. 7, the received signal bandwidth measuring means 8 performs Fourier transform in step 23, and in step 24 calculates the bandwidth BW of the Doppler spectrum of the received signal normalized by the pulse repetition frequency (PRF). seek.

The coherent integrator 7 determines the optimum number of integrations NF according to the flowchart of FIG. 6, which will be explained later, and performs coherent integration.

Next, each coherent integrator output signal is subjected to amplitude detection by an amplitude detector 4, and then non-coherent integration (post-detection integration) is performed by a non-coherent integrator 5. At this time, the number of non-coherent integrals is the number obtained by dividing the total number of pulse hints P by the optimal number of integrals N7.

P / N P (not shown), when the output (t) of the non-coherent 8 minute W5 exceeds the threshold level of the threshold detector 6, the presence of the detection target is detected and the display 13 shows Is displayed.

Here, a method for determining the optimal number of integrals N for the above-mentioned coherent integration will be explained. Figure 8 shows an example of the relationship between the SN ratio (signal power to noise power ratio after coherent integration) and the number of coherent integrations N, when the SN ratio per pulse of the received signal is set to a certain value. , when there is no fluctuation in the received signal (received signal bandwidth BW=O), the SN ratio after coherent integration improves in proportion to the number N of coherent integrations. In this case, under a given false alarm probability PN, the coherent integral number N that maximizes the detection probability P,
is known to be equal to the total number of pulse hints P.

On the other hand, when there is fluctuation in the received signal due to irregular movement of the detection target, even if the number N of coherent integrations is increased, the effect of improving the SN ratio by coherent integration cannot be obtained above a certain value.

α and β in FIG. 8 each indicate the value of the coherent integration number N at which the SN ratio improvement effect by coherent integration is no longer obtained when there is fluctuation in the received signal, and these values can be expressed as 1/BW.

Figure 9 shows the detection probability PD versus the number of coherent integrals N when the SN ratio per pulse of the received signal is set to a certain value and the received signal bandwidth is changed under a given false alarm probability PM.
(The number of non-coherent integrals can be expressed as P/N) is shown as an example of the relationship, and shows calculation results by computer simulation.

Similarly to FIG. 9 above, the relationship between the detection probability P0 and the number of coherent integrals N is determined each time by keeping either the SN ratio per pulse of the received signal or the received signal bandwidth constant and changing the other. From these, the coherent integral number N, (-optimal integral number NF) for which the detection probability po takes the maximum value can be determined.

When this optimal integral number NF is placed on the top of FIG. 8, it is a value smaller than the above-mentioned 1/BW.

BN after coherent integration for this optimal integration number N
The ratio is defined as SNP, which is determined in advance and stored in the computer. In the coherent integrator 7, the received signal bandwidth and the target word l! are measured online! 1 (expressed by converting the SN ratio per pulse of the received signal into the target distance), the optimal integral number N2 determined by the value N2 can be extracted from the table.

Next, the operation of the coherent integrator 7 will be explained in detail along the flowchart shown in FIG.

In step 14, range bin number m is detected, and in step 1
In step 5, the target word fiR is obtained from the following equation.

R=cmτ/2-(1
1 Here, C is the speed of light (-3×10' m/s), m is the range bin number, and τ is the transmission pulse width.

Next, in step 16, 1 is set as the initial value of the coherent integral number N, and in step 17, SN
Calculate the ratio.

S N = P t ηF Gy G* λ2σN/(4
π) 3R' (NF)kTBL - (21 where,
When N=1, the SN ratio per pulse of the received signal is determined, and when N=n, the SN ratio after coherent integration of the number of integrals n is determined. It is assumed that the target to be detected is a specific one, and that the radar cross section of the target is known.

PL is the transmission pulse peak power, η is the pulse compression ratio, G7
is the transmitting antenna gain, GR is the receiving antenna gain, λ is the transmitting wavelength, R is the distance between the detection target and the radar, NF is the receiver noise figure, k is the Boltzmann constant, T is the absolute temperature, and B is the receiver band width, σ is the radar cross section of the detected target, N is the coherent 41 number, and L is the system loss.

Since the value of system loss changes depending on the number of pulse integrations and the received signal bandwidth, it should be stored in the computer in advance and retrieved from the table during calculation.

Next, in step 22, the received signal bandwidth normalized by the pulse repetition frequency (PRF) obtained in step 24 of FIG. 7 is compared with l/BW and the coherent integral number N using BW. If N is greater than 1/BW, the process ends; if N is less than l/BW, the process proceeds to step 18.

In step 18, the total number of pulse hints P is compared with the number of coherent integrals N. If NSP, the process proceeds to step 19, and if N>P, the process ends. In step 19, the SN ratio obtained in step 17 and the optimal integral number NF determined by the received signal bandwidth measured online and the target distance are extracted from the storage table and compared, and until the SN ratio reaches SNp, step 20.21 , the coherent integral number N
Continue coherent integration by increasing .

When the S/N ratio reaches S N p, the L coherent integrators 7 calculate the detection probability PD according to the S/N ratio per pulse and the received signal bandwidth under the given false alarm probability PM. The coherent integration of the coherent integration number N, (=optimal integration number NF), in which the number takes the maximum value, is completed.

[Problem to be solved by the invention]

In conventional radar equipment, the number of coherent integrals (optimal integral number) that maximizes the detection probability is obtained through the processing described above, but the means for determining this optimal number of integrals is not clear, and the detection probability The problem was that it was difficult to make improvements.

This invention has been made to solve the above-mentioned problems, and it is an object of the present invention to clarify the unclear means for determining the optimal number of integrals in conventional devices, and to provide a radar device that can improve the detection probability. With the goal.

[Means to solve the problem]

The radar device according to the present invention includes an analog/digital converter 1 that converts a received signal into a digital signal, each range bin 2 that divides the digital signal from the analog/digital converter 1 by distance to a target, and Each received signal bandwidth measuring means 8 measures the Doppler spectrum bandwidth of the received signal from the output signal of each range bin 2, and the Doppler spectrum band of the received signal output from each received signal bandwidth measuring means 8. S per pulse of the received signal output from each range bin 2 according to the width
A coherent integrator 7a having means for determining an optimal number of integrals from the N ratio and performing coherent integration of a received signal according to the optimal number of integrals, and each coherent integral signal corresponding to each received signal output from the coherent integrator 7a. each amplitude detector 4 that amplitude-detects the amplitude, each non-coherent integrator 5 that non-coherently integrates the output signal of each of the above-mentioned amplitude detectors 4, and when the output signal of each of the above-mentioned non-coherent integrators 5 exceeds a threshold level. and a threshold detector 6 for detecting the presence of a detection target.

[Effect]

Analog/digital converter 1 converts the received signal into a digital signal. Each range bin 2 separates the digital signal from the analog/digital converter 1 by distance to the target. Each received signal bandwidth measuring means 8 measures the bandwidth of the Doppler spectrum of the received signal from the output signal of each range bin 2. The coherent integrator 7a performs optimal integration from the SN ratio per pulse of the received signal outputted from each range bin 2 according to the bandwidth of the Doppler spectrum of the received signal outputted from each received signal bandwidth measuring means 8. The received signal is coherently integrated according to the optimum integration number. Each amplitude detector 4 amplitude-detects each coherent integrated signal corresponding to each received signal output from the coherent integrator 7a. Each non-coherent integrator 5 non-coherently integrates the output signal of each amplitude detector 4. A threshold detector 6 detects the presence of a target to be detected when the output signal of each non-coherent integrator 5 exceeds a threshold level.

〔Example〕

FIG. 1 is a block diagram showing the configuration of a radar device according to an embodiment of the present invention. In Figure 1, 1 is an A/D (analog/digital) converter that converts the received signal into a digital signal, 2 is each range bin that divides the digital signal from A/D converter 1 by distance, and 8 is each range bin. 2
Each received signal bandwidth measuring means measures the bandwidth of the Doppler spectrum of the received signal from the output signal of the received signal; 7a measures the bandwidth of the Doppler spectrum of the received signal output from each received signal bandwidth measuring means 8; a coherent integrator that has means for determining an optimal number of integrations from the SN ratio per pulse of the received signal output from each of the range bins 2, and performs coherent integration of the received signal according to the optimal number of integrations; 4;
5 is each amplitude detector that amplitude-detects each coherent integrated signal corresponding to each received signal output from the coherent integrator 7a, 5 is each non-coherent integrator that non-coherently integrates the output signal of each amplitude detector 4, 6 1 is a threshold detector that detects the presence of a detected target when the output signal of each non-coherent integrator 5 exceeds a threshold level; 13 is a display that displays the detected target; 9 is a transmitter that generates a transmission signal; 10 1 is a transmitting/receiving switch for switching transmission/reception, 11 is a transmitting/receiving antenna, and 12 is a receiver for receiving a signal reflected by a detected target.

Next, the operation will be explained. In FIG. 1, a transmission signal is transmitted from a transmitter 9 to a transmission/reception switch 10 and a transmission/reception antenna 1
The signal radiated to the outside via 1 and reflected by the detection target enters the receiver 12 as a received signal via the transmitting/receiving antenna 11 and the transmitting/receiving switch 10, and the received signal is converted into a complex video signal. It is converted into a digital signal by an A/D converter l. This digital signal is divided into M range signals 2 for each distance, and is input to a received signal bandwidth measuring means 8 connected to each range bin 2, and is also input to a coherent integrator 7a having means for determining the optimum number of integrations. . As shown in the flowchart of FIG. 3, the received signal bandwidth measuring means 8 performs Fourier transform in step 23, and in step 24 calculates the Doppler spectrum bandwidth BW of the received signal normalized by the pulse repetition frequency (PRF).
seek.

The coherent integrator 7a determines the optimal number N of coherent integrals and the optimal number K of non-coherent integrals according to the flowchart of FIG. 2, which will be explained later, and performs coherent integration.

Next, each coherent integrator output signal is subjected to amplitude detection by an amplitude detector 4, and then a coherent integrator 7a having means for determining the optimum number of integrals performs non-coherent integration of the number of times determined by the number of non-coherent integrals. is performed by the non-coherent integrator 5. Non-coherent integrator 5
When the output signal exceeds the threshold level of the threshold detector 6, the presence of the detection target is detected and displayed on the display 13.

Here, a method for determining the above-mentioned optimal integral numbers N and K will be explained. There is a coefficient U depending on the received signal bandwidth BW, and there is a coefficient between the signal-to-noise ratio per pulse (SNRI) and the ratio of the total number of pulse hints P to the optimal non-coherent fraction that maximizes the detection probability. As shown in FIG. 4, the following relationship holds true.

K/P#tX (SNRI) u-
(3) Therefore, the optimal number of non-coherent integrals is the following formula % = the nearest integer (tX (SNR,)”xp)−・
(4) Moreover, the optimal non-coherent integral number N is given by the following equation.

N=P/K
-(51) Next, the operation of the coherent integrator 7a is
A detailed explanation will be given according to the ml-chart shown in the figure.

In step 25, range bin number m is detected, and in step 2
In step 6, find the target road MR using the following equation.

R=cmτ/2·−(6) Here, C is the speed of light (=3×10” m/s), m is the range bin number, and τ is the transmission pulse width.

Next, in step 27, the SN ratio per pulse is calculated using equation (7).

SNR, = PtηP GT GR S2 σ/(4π)'
R' (NF) kTB - (71 Here, it is assumed that the target to be detected is a specific one, and the radar cross section of the target to be detected is known.

Pt is the transmission pulse peak power, η is the pulse compression ratio, Ct
is the transmitting antenna gain, GR is the receiving antenna gain, λ is the transmitting wavelength, R is the distance between the detection target and the radar device, NF is the receiver noise figure, k is the Boltzmann constant, T is the absolute temperature,
B is the receiver bandwidth and σ is the radar cross section of the detected target.

Next, in step 28, the received signal bandwidth normalized by the pulse repetition frequency (PRF) obtained in step 24 of FIG. 3, the coefficient determined by BW, and U are read from a storage table (not shown).

In step 29, the optimum non-coherent integral number K is calculated using equation (4). In step 30, the non-coherent integral number is compared with 0, and if K=O, step 31
After the process proceeds to step 32, if K≠0, the process proceeds to step 32. In step 31, K is set to 1. In step 32, the optimum number N of non-coherent integrations is calculated using equation (5), and in step 33, coherent integration is performed N times, and the process ends.

Figure 4 shows the relationship between the ratio of the optimal number of non-coherent integrals to the total number of pulse hints and the S/N ratio per pulse, given the false alarm value rate P and later, when the received signal bandwidth BW is set to a certain value. This is an example.

In the radar device of the embodiment configured as described above, a means for measuring the received signal bandwidth connected to each range bin and a coherent integrator are provided with a means for measuring the received signal bandwidth, and a means for measuring the SN per pulse of the received signal according to the received signal bandwidth. A given false alarm probability PH
Under these conditions, determine the optimal number of coherent integrals N and the optimal number of non-coherent integrals K that maximize the detection probability according to the received signal bandwidth and the S/N ratio per pulse of the received signal, and perform pulse integration. I can do it.

That is, the radar device of the above embodiment utilizes the fact that the ratio of the optimal number of non-coherent integrals to the total number of pulse hints for the S/N ratio per pulse is expressed by an equation according to the received signal bandwidth. The detection probability is improved by selecting the distribution of the number of pulse integrals that maximizes the detection probability.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a received signal bandwidth measuring means for measuring the bandwidth of the Do-7-Pler spectrum of the received signal output from each range bin, and Since the system is equipped with a coherent integrator that has means for determining the optimal number of integrals from the S/N ratio of , this has the effect of improving the detection probability.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a radar device according to an embodiment of the present invention, FIG. 2 is a flowchart showing the operation of the coherent integrator in FIG. 1, and FIG. 3 is a received signal in FIG. FIG. 4 is a flowchart showing the operation of the bandwidth measuring means. FIG. 4 is a diagram showing the relationship between the ratio of the optimal number of non-coherent integrals to the total number of pulse hints and the S/N ratio per pulse in this embodiment. FIG. 6 is a flowchart showing the operation of the coherent integrator in FIG. 5; FIG. 7 is a flowchart showing the operation of the received signal bandwidth measuring means in FIG. 5; FIG. 8 is a diagram showing the relationship between the SN ratio (after coherent integration) and the number of coherent integrals, and FIG. 9 is a diagram showing the relationship between the detection probability and the number of coherent integrals. DESCRIPTION OF SYMBOLS 1... Analog/digital converter, 2... Range bin, 4... Amplitude detector, 5... Non-coherent integrator, 6... Threshold detector, 7a... Optimal integration number determining means a coherent integrator with 8...
- Received signal bandwidth measurement means. Agent Patent Attorney Jun Miyazono Figure 1 SNI of Pulscoli? (dB) Figure 8 Figure 1, Statement of the case (spontaneous) July 1991 Japanese Patent Application No. 2-220539 5 Column for detailed explanation of the invention in the specification subject to amendment. G Correction details + 11 Specification page 6 line 7 rBN ratio" rS
Correct it as "N ratio". (2) In the same book, page 15, line 3, and page 16, line 15, "Non-coherent integral number" is corrected to "coherent integral number." 3.Representative of the person making the amendment4.

Claims (1)

[Claims] An analog/digital converter that converts the received signal into a digital signal, each range bin that divides the digital signal from this analog/digital converter according to the distance to the target, and the Doppler spectrum of the received signal from the output signal of each range bin. and one pulse of the received signal output from each of the range bins according to the bandwidth of the Doppler spectrum of the received signal output from each of the received signal bandwidth measuring means. a coherent integrator that has means for determining an optimal number of integrals from a given SN ratio and performs coherent integration of a received signal according to the optimal number of integrals; and each coherent integral signal corresponding to each received signal output from the coherent integrator. and each non-coherent integrator that non-coherently integrates the output signal of each of the above-mentioned amplitude detectors, and detects the detected target when the output signal of each of the above-mentioned non-coherent integrators exceeds a threshold level. A radar device comprising a threshold detector for detecting the presence of.