JPH08160121A - Instrument and method for finding range using multi-prf method - Google Patents

Abstract

PURPOSE: To prevent the occurrence of a large error in the measured results of a range finder even when an error is contained at the time of measuring the apparent time difference between a received pulse and transmitted pulse. CONSTITUTION: At the time of deciding the cycle period of a first transmitting pulse in a first transmission-reception step (411-417), the cycle period is switched by making increment of i1 and referring to a previously prepared table N1 in 414. The cycle period is decided to n1 at which the expected value of the greatest common measure(GCM) of n1 and n2 becomes the largest out of the cycle periods in which clutters can be suppressed and the received power can be secured. At the time of deciding the cycle period of a second transmitting pulse in a second transmission-reception step (421), n2 at which the greatest common measure of n1 and n2 becomes the largest is preferentially used against the n1 used for the first transmitting pulse by referring to another table N2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device and a distance measuring method using a multi-PRF method mounted on a high speed moving body such as an aircraft.

[0002]

2. Description of the Related Art In a pulse Doppler radar device mounted on an aircraft, in order to secure a clutter suppression characteristic of a moving target indicator (hereinafter, referred to as MTI) filter, a repetition period of a transmission signal (hereinafter, referred to as PRI as appropriate). Note that there is a limit and must be short. Therefore, the range in which the distance can be determined is significantly narrowed by distance measurement using a transmission signal of one type of repeating cycle. If FM ranging cannot be applied, a multi-PRF (pulse repetition frequency) method is used to determine a target distance by switching a plurality of transmission signals having different repetition periods in order to expand the limit of the fixed distance.

As a radar apparatus using the multi-PRF method, there is one disclosed in Japanese Patent Application No. 55-59361, for example. The configuration of a conventional distance measuring device using the multi-PRF method will be described below by taking a radar device having the configuration shown in FIG. 15 as an example. In the figure, 251 is a transmitter, 252 is a receiver, 253 is a transmission / reception switch (circulator), 254 is an antenna, 255 is a reference signal generator, and 256 is MTI.
A filter 257 is a distance correlation circuit, 258 is a signal processing device, and 259 is a display device. Reference signal generator 255
Determines the repetition period of the transmitted pulse, which is transmitted by the transmitter 251.
The signal is modulated and amplified by and the radio wave is emitted from the antenna 254 toward the target. The reflected wave is received by the antenna 254, demodulated and amplified by the receiver 252, and filtered by the MTI filter 256 based on the repetition cycle of the transmission pulse determined by the reference signal generator 255, whereby the ground surface, weather, etc. Suppress clutter. With respect to the clutter-suppressed received pulse, the distance correlation circuit 257 obtains an apparent target distance obtained from the received signal, and the signal processor 258 obtains the true target distance.

Next, the operation of the conventional distance measuring apparatus using the multi-PRF method will be described with reference to the flowchart shown in FIG. 271 is a process of determining T ₁ , which is the repeating period of the _first transmission pulse, and transmitting and receiving in this repeating period, 272 is a process of measuring an apparent target distance X ₁ from the transmission pulse, the reception pulse, and the timing, 273. process to determine the T ₂ is a repetition period of the second transmission pulse, the processing of transmitting and receiving at the repetition period, 274 for measuring the target distance X ₂ the apparent 2
75 calculates the correlation signal between the first reception pulse and the second reception pulse at the same timing using X ₁ and X ₂ .
This is a process of calculating the true target distance X ₀ from this correlation signal. At 275, the time difference X ₀ of E in FIG. 17 is measured from the position of the peak of the received pulse correlation signal, and this is multiplied by 2 and the speed of light c to uniquely determine the target distance.

FIG. 17 is a timing chart of a transmission signal and a reception signal for explaining the operation of the conventional example shown in the above document. Here, for the sake of simplicity, a method of determining the distance to the target by using two types of pulses having different repetition periods will be described. In the figure, A is a first transmission pulse with a repetition period of T ₁ , B is a reception pulse for A, C is a second transmission pulse with a repetition period of T ₂ , D is a reception pulse for B, E Is a transmission pulse after the correlation processing of the first transmission pulse A and the second transmission pulse C, and F is the first reception pulse B
And the second received pulse D after the correlation processing. The horizontal axis directly indicates time t, but the distance is 2 at time t.
Since it can be converted by multiplying by and the speed of light c, it can be understood that the horizontal axis indicates the target distance. In order to secure the clutter suppression characteristic as described above, T ₁ and T ₂ have an upper limit shown by the following equation. T ₁ , T ₂ ≤λ / 2v (1) where λ is the wavelength and v is the speed of the platform of the radar device. When determining the repeating period (= T) of the transmission pulse (A or C in FIG. 17) by the reference signal generator 255 in FIG. 15, or by determining T ₁ and T ₂ in steps 271 and 273 in FIG. In doing so, the clutter suppression characteristic is ensured by satisfying the expression (1).

Next, the basic principle of the distance measuring method based on the multi-PRF method will be described with reference to FIG. If it is attempted to measure the target only with the received pulse shown in B without switching the repetition cycle, the limit of the fixed distance of the target is 2 cT.
Becomes ₁ . In an airborne pulse Doppler radar, λ / 2v in equation (1) is generally much shorter than the maximum range of range finding, and thus 2cT ₁ is not a sufficient limit for the target deterministic range. For a target exceeding 2 cT ₁ , as shown by B ₁ , B ₂ , ..., B ₅ in the figure, a plurality of target echoes appear and are uncertain. Therefore, the repeating cycle is switched, T ₁ and T ₂ are determined so that each repeating cycle does not become an integral multiple of the other repeating cycle (in the figure, the relationship between A and C), and each receiving cycle is determined. The correlation signal of the pulses B and D is obtained like F, and the target distance is determined from the time difference X ₀ between F and E. The limit of the fixed distance at this time is the period T _{0 of} E, which is sufficiently expanded as compared with 2cT ₁ .

When T ₁ and T ₂ are respectively expressed as an integral multiple of the unit time Δ as follows, T ₁ = Δ · n ₁ and T ₂ = Δ · n ₂ (2) T ₀ is given by the following equation. To be T ₀ = Δ · LCM (n ₁ , n ₂ ) (3) Here, LCM (n ₁ , n ₂ ) means the least common multiple of the integers n ₁ , n ₂ .

However, in the above-mentioned conventional distance measuring method of the multi-PRF method, the error e ₁ , in the target distances X ₁ , X ₂ which is the apparent time difference between the received pulse and the transmitted pulse in FIG.
e ₂ is included, and the timings of the received pulses B and D are shifted by an error. Depending on the directions and the magnitudes of the errors e ₁ and e ₂ , as shown in FIG. 18, the calculated target distance R ₀ has a large error (represented by e ₀ in the figure) for a number of repeating cycles. Will end up. This is because the errors e ₁ and e ₂ cause the received pulses of B and D to coincide with each other at a position far away from the true target distance, and a peak of the correlation signal occurs at that position.
Further, when the received pulses B and D are deviated due to an error and the correlation signal peak does not appear in F, the time difference X ₀ cannot be obtained and the target distance cannot be determined. Also, in general pulse Doppler radar, in order to share the transmitting and receiving antennas, and to secure a sufficient maximum detection distance and detection probability,
The duty ratio (= pulse width / repetition cycle) may be set high. In this case, the influence of eclipse becomes particularly large, and it is necessary to switch the repetition cycle many times to avoid eclipse. It takes a long time to observe the target distance. In addition, when the apparent time difference between the received pulse and the transmitted pulse is measured using a distance discretization, if the reception power of the discreet reception gate is insufficient, it is necessary to switch the repeating cycle many times. It takes a long time to observe the target distance.

[0009]

The conventional distance measuring apparatus and distance measuring method using the multi-PRF method are configured as described above, and the error contained in the apparent time difference between the received pulse and the transmitted pulse causes There is a problem that a large error may occur in the target distance measurement result. Further, there is a problem that the target distance may not be determined due to an error included in the apparent time difference between the received pulse and the transmitted pulse. Also, when the duty ratio (= pulse width / repetition period) is high, the effect of eclipse is large, and when the time difference between the received pulse and the transmitted pulse is measured using the distance discreet, the reception When the received power of the gate is insufficient, it is necessary to switch the repetition cycle many times, and there is a problem that it takes a long time to observe the target distance.

The present invention has been made to solve the above problems. Even when an apparent time difference between a reception pulse and a transmission pulse includes an error, a large error does not occur in a target distance measurement result. An object is to obtain a distance measuring device and a distance measuring method. It is another object of the present invention to provide a distance measuring method that enhances the degree to which the target distance can be reliably determined even when the apparent time difference between the received pulse and the transmitted pulse includes an error. Also, when the influence of Eclipse becomes large,
It is an object of the present invention to obtain a distance measuring method that can determine a target distance by observing in a short time even when the reception power of a reception gate of a distance discrepancy is insufficient.

[0011]

In order to achieve the above object, a range finder using the multi-PRF method of the invention according to claim 1 has the following components (a), (b) and (c). Is provided. The repetition period of the transmission signal is represented by the product of an integer n _j (j = 1, 2) and the unit time Δ (hereinafter,
(Repetition cycle is represented by an integer n _j ), (a) second transmission signal selectable with respect to repetition cycle n ₁ of the first transmission signal in determining the repetition cycle of the first transmission signal Repeat cycle n ₂
In order to preferentially use n ₁ in descending order of the expected value of the greatest common divisor GCM (n ₁ , n ₂ ) of the set, and when determining the repetition period of the second transmission signal, Transmitting means for preferentially using n ₂ in the order in which the value of the greatest common divisor of the set of the repeating period n ₂ of the second transmitting signal is higher than n ₁ used as the repeating period, (b) each of the transmitting signals Receiving means for receiving a reflected wave from the target, and (c) signal processing for calculating a target distance using the correlation signal of the first and second received signals which is the reflected wave of the first and second transmitted signals. means.

The multi-PR of the invention according to claim 2
The distance measuring method using the F method has the following steps (a), (b), and (c). The repetition cycle of the transmission signal is represented by the product of an integer n _j (j = 1, 2) and the unit time Δ (hereinafter, the repetition cycle is represented by an integer n _j ), (a) first
The common divisor GCM (n ₁ , n ₁ of the set of the repetition cycle n ₂ of the second transmission signal selectable with respect to the repetition cycle n ₁ of the transmission signal of
a first transmission / reception step in which n ₁ is preferentially used in descending order of the expected value of n ₂ ) to determine the repetition cycle of the transmission signal;
(B) The greatest common divisor GCM (n ₁ , n) with respect to the repetition cycle n ₁ of the first transmission signal used in the first transmission / reception step.
₂ ) The second transmission / reception step of determining the repetition period of the transmission signal by preferentially using n ₂ in descending order of the value, (c) the reception signals obtained in the first and second transmission / reception steps. A signal processing step of calculating a target distance using the correlation signal.

Further, the multi-PR of the invention according to claim 3
The distance measuring method using the F method has the following steps (a), (b), and (c). The repetition cycle of the transmission signal is represented by the product of an integer n _j (j = 1, ..., J) and the unit time Δ (hereinafter, the repetition cycle is represented by an integer n _j ), (a)
The first transmission / reception step in which the repetition cycle of the first transmission signal is n ₁ , (b) and each of the first to (j−1) th transmission / reception steps (j = 2, ..., J) the repetition period of the transmission signal n _1, n _2, ..., as n _(j-1) represents the least common multiple thereof in LCM _(j-1), the greatest common divisor of the LCM _(j-1) and n _j Where GCM (LCM _(j-1) , n ₂ ) is represented, the integer n _j is preferentially used in descending order of the value of GCM (LCM _(j-1) , n _j ) to repeat the transmission signal. A j-th (j = 2, ..., J) transmission / reception step for determining a period, (c)
From the first transmission / reception step, the j-th (j = 2, ..., J)
Signal processing step of calculating the target distance using the correlation signal of the received signal obtained in each transmission and reception step up to.

Also, the multi-PR of the invention according to claim 4
The distance measuring method using the F method has the following steps (a), (b), and (c). The repetition cycle of the transmission signal is represented by the product of an integer n _j (j = 1, 2) and the unit time Δ (hereinafter, the repetition cycle is represented by an integer n _j ).
_1, represents the greatest common divisor of n ₂ GCM and (n _1, n _2),
(A) function for the set of repetition periods n ₂ of the first transmission signal second transmission signal that can be selected for repetition period n ₁ of [G
CM (n ₁ , n ₂ ) / (n ₁ + n ₂ )], the first transmission / reception step of determining the repetition cycle of the transmission signal by preferentially using n ₁ in the order of higher expected value of (b) Priority is given to n ₂ in descending order of the value of the function [GCM (n ₁ , n ₂ ) / (n ₁ + n ₂ )] with respect to the repetition cycle n ₁ of the first transmission signal used in the first transmission / reception step. A second transmission / reception step for determining a repetition period of a transmission signal by using (c) the first and second
A signal processing step of calculating a target distance using the correlation signal of the received signal obtained in the transmitting and receiving step.

Further, the multi-PR of the invention according to claim 5
The distance measuring method using the F method has the following steps (a), (b), and (c). The repetition cycle of the transmission signal is represented by the product of an integer n _j (j = 1, ..., J) and the unit time Δ (hereinafter, the repetition cycle is represented by an integer n _j ), (a)
The repetition cycle of the first transmission signal is determined to be n ₁ , the target existence region width σ ₁ of the first reception signal, which is a reflected wave from the target of the first transmission signal, is determined, and A first transmission / reception step of calculating a first target existence region within a range of ± σ ₁ from each echo center, (b) a repetition cycle of a j-th (j = 2, ..., J) transmission signal is set to n _j The target existence region width σ of the j-th received signal that is the reflected wave from the target of the j-th transmitted signal determined
_j is determined, the j-th target existence area in the range of ± σ _j from each echo center of the j-th received signal is calculated, and the target existence areas of the first to (j−1) th received signals are calculated. J th
When the j-th transmission / reception step for obtaining the correlation of the received signal with the target presence area, (c) the j-th target presence area after the correlation processing obtained in the j-th transmission / reception step indicates one target presence area, A signal processing step of calculating a target distance using the correlation signal.

Further, the multi-PR of the invention according to claim 6
The distance measuring method using the F method has the following steps (a), (b), and (c). The repetition cycle of the transmission pulse is represented by the product of an integer n _j (j = 1, ..., J) and the unit time Δ (hereinafter, the repetition cycle is represented by an integer n _j ), (a) the first transmission pulse N ₁ is determined as the repeating cycle of the first transmission pulse, and the target existence region width σ ₁ of the first reception pulse, which is a reflected wave from the target of the first transmission pulse, is set to a value shown in (a1) below. A first transmission / reception step of calculating a first target existence region within a range of ± σ ₁ from each echo center of the reception pulse; (a1) a pulse width of the first transmission pulse is τ ₁ ;
Let SNR _{1 be} the signal power to noise power ratio of the first received pulse, which is a reflected wave from the target of the transmission pulse of, and a be an appropriate positive proportional constant, and let σ ₁ be the following equation: σ ₁ = a · [Τ ₁ / (SNR ₁ ) ^1/2 ] (b) The repetition period n _j of the j-th (j = 2, ..., J) transmission pulse is determined and the reflection of the j-th transmission pulse from the target is determined. The target existence area width σ _j of the jth received pulse, which is a wave, is set to a value shown in (b1) below, and the jth target existence area in the range of ± σ _j from each echo center of the jth received pulse is calculated. In addition, a j-th transmission / reception step of obtaining a correlation between the target existence region of the first to (j−1) th received pulses and the target existence region of the j-th received pulse, (b1) j-th transmission pulse of the pulse width tau _j, a signal to noise ratio of the received pulse of the j is the reflection wave from the target of the transmission pulse of the j NR _j, the appropriate positive constant of proportionality as a, a sigma _j and the following equation was determined by transmitting and receiving step of _{σ j = a · [τ j} / (SNR j) 1/2] (c) the first j When the j-th target existence area after the correlation processing indicates one target existence area,
A signal processing step of calculating a target distance using the correlation signal.

Further, the multi-PR of the invention according to claim 7
The distance measuring method using the F method has the following steps (a), (b), and (c). (A) A first transmission / reception step of obtaining a time difference X ₁ between the transmission pulse and a reception pulse which is a reflected wave from a target by using a first transmission pulse having a repetition cycle T ₁ , and (b) a second The predicted loss power EC _m of the second received pulse due to eclipse is obtained by the following (b1) process with the repetition cycle of the transmission pulse as T ₂ , and the predicted loss power E
A second transmission / reception step in which a small average value of C _m for m is preferentially used for T ₂ , and a time difference X ₂ between the transmission pulse and the reception pulse is obtained, (b1) The candidate for T ₂ is set as TC _2. , M are positive integers, and [X ₁ + (m-1) T
_1] determine the remainder MB _m about TC _2, the predicted loss of the second received pulse by Eclipse from MB _m power EC _m
The calculated signal processing step of calculating processing for calculating an average value for m of the predicted power loss EC _m, the target distance obtaining a correlation of the received pulses obtained in (c) the first and second transmitting and receiving steps.

Further, the multi-PR of the invention according to claim 8
The distance measuring method using the F method has the following steps (a), (b), and (c). (A) a first transmission / reception step in which a time difference X ₁ between the transmission pulse and a reception pulse which is a reflected wave from the target is obtained by using a distance discretion using a first transmission pulse having a repetition period T ₁ . (B) With the repetition cycle of the second transmission pulse set to T ₂ , the following (b1) process sets T ₂ to a value with a large average value of m of the predicted reception power PG _m of the reception gate of the distance discretization. A second transmission / reception step in which the time difference X ₂ between the transmission pulse and the reception pulse which is a reflected wave from the target of the transmission pulse is preferentially used, (b1) The candidate for T ₂ is set to TC ₂ , and m is positive. An integer, [X ₁ + (m-1)
T _1] seek remainder MB _m about TC ₂ of, determine the predicted received power PG _m distance discriminator reception gate from MB _m, processing for obtaining the average value for m of PG _m, and (c) the first A signal processing step in which the target distance is calculated by obtaining the correlation of the received pulses obtained in the second transmission / reception step.

[0019]

In the distance measuring device of the invention according to claim 1 configured as described above, the transmitting means determines the first and second transmission signals when determining the repetition cycle of the first and second transmission signals. By setting the priority order so that the greatest common divisor of the repetition cycle of becomes large, correlation is less likely to occur in the signal processing means except at the timing of the true target distance, the allowable amount for measurement error increases, and the distance measurement result increases. It is possible to make a big error less likely to occur.

Further, in the measuring method of the invention according to claim 2, in the first and second transmitting / receiving steps, the first and second
When determining the repetition period of the transmission signal, the priority is determined so that the greatest common divisor of the repetition periods of the first and second transmission signals becomes large. Correlation is less likely to occur at timings other than, the tolerance for measurement error is increased, and a large error in the distance measurement result is less likely to occur.

In the measuring method according to the third aspect of the invention, when the repeat cycle of the first transmission signal is set to n ₁ in the first transmitting / receiving step, the j-th (j = 2, ..., J) )
In the transmission / reception step of, the repetition cycle of each transmission signal used in the first to (j−1) th transmission / reception steps (j = 2, ..., J) is n ₁ , n ₂ , ..., N _{(j-1 )} , The least common multiple thereof is represented by LCM _(j-1) , and LCM _(j-1)
And the greatest common divisor of n _j is represented by GCM (LCM _(j-1) , n ₂ ), the integers n _j are preferentially used in _descending order of GCM (LCM _(j-1) , n _j ). By configuring the steps so as to determine the repetition cycle of the j-th transmission signal, it becomes difficult for correlation to occur at times other than the timing of the true target distance during distance measurement, and the tolerance for measurement error increases. , It is possible to prevent a large error in the distance measurement result.

In the measuring method of the invention according to claim 4, the greatest common divisor of the repeating cycles n ₁ and n ₂ is GCM (n ₁ ,
n ₂ ), in the first transmission / reception step, the first
Second selectable for the repetition period n ₁ of the transmission signal of
For each set of repetition cycle n ₂ of the transmission signal of
_{(N 1, n 2) /} (n 1 + n 2)] expected value with priority using n ₁ at a high order of, so as to determine the repetition period of the first transmission signal, second transmission and reception step , The function [GCM (n ₁ , n ₂ ) / (n ₁ + n) with respect to the repetition cycle n ₁ of the first transmission signal used in the first transmission / reception step.
₂₎ the value preferentially using n ₂ in descending order of, by constructing the steps to determine the repetition period of the second transmission signal, the time of distance measurement, the timing of the true target distance In other cases, the correlation is less likely to occur, the tolerance for the measurement error is increased, and a large error in the distance measurement result is less likely to occur.

Further, in the measuring method of the invention according to claim 5, in the first transmitting / receiving step, the repeating cycle of the first transmission signal is determined as n ₁ , and the first transmission signal and the first reception signal are determined. The first target existing area in the range of ± σ ₁ from each echo center of the first received signal is calculated with σ ₁ as the upper limit value of the time difference measurement error. Similarly, in the jth transmission / reception step, n _j is determined as the repeating cycle of the jth (j = 2, ..., J) transmission signal, and the time difference between the jth transmission signal and the jth reception signal is measured. the upper limit of the magnitude of the error as a sigma _j, a signal in the range of ± sigma _j from each echo center of the received signal of the j to calculate a target existing area of the j, the received signal from the first through j When the target existence area after the above correlation processing is narrowed down to one,
By configuring the step to calculate the target distance using the peak of the correlation signal, even if there is a measurement error in the timing of the received signal, because of the margin σ _j , disappearance of the peak of the correlation signal is less likely to occur, The target distance can be calculated reliably.

Further, in the measuring method of the invention according to claim 6, in the first transmitting / receiving step, the repetition period n ₁ of the first transmission pulse is determined, and the first transmission pulse and the first reception pulse are combined. Let τ _{1 be} the pulse width of the first transmission pulse, SNR _{1 be} the signal power to noise power ratio of the first reception pulse, and a be a predetermined proportional constant independent of j as the upper limit value of the time difference measurement error. The following equation is used to calculate the first target existence region within a range of ± σ ₁ from each echo center of the first received pulse. σ ₁ = a · [τ ₁ / (SNR ₁ ) ^1/2 ] Similarly, in the j-th transmission / reception step, the j-th (j =
2, ..., J) The repetition period n _j of the transmission pulse is determined, and
And transmit pulses and the magnitude of upper limit value of the time difference measurement error between the received pulse of the j by the following equation, calculates a target existing area of the j ranging from ± sigma _j from each echo center of the received pulse of the j . _{σ j = a · [τ j} / (SNR j) 1/2] Furthermore, correlates target existence region of the received pulses of the first through j, target presence region after the correlation processing is narrowed down to one If the step is configured to calculate the target distance using the peak of the above correlation signal, even if there is a measurement error in the timing of the received pulse, the margin σ _j causes the peak of the correlation signal to disappear. Is less likely to occur, and the target distance can be calculated reliably.

Further, in the measuring method of the invention according to claim 7, the candidate of the repetition cycle T ₂ of the second transmission pulse is set to TC ₂ , and the first reception is performed before the second transmission pulse is transmitted. seeking the echo center time B _m of pulses, the B _m TC ₂
Seeking remainder MB _m relates obtains a power loss EC _m of the second received pulse by Eclipse from MB _m, average determined for m of EC _m, first by giving priority to the average value is less TC ₂ of the EC _m Since the step is configured to be used for the repetition cycle T ₂ of the second transmission pulse and the expected value of the Eclipse is reduced when the second reception pulse is received, the loss of the reception power is reduced and the second transmission pulse Repeat cycle T
Since the number of times ₂ is switched is reduced, the target distance can be determined by observing in a shorter time.

Further, in the measuring method of the invention according to claim 8, the candidate of the repetition cycle T ₂ of the second transmission pulse is set as TC ₂ , and the first reception is performed before the second transmission pulse is transmitted. seeking the echo center time B _m of pulses, the B _m TC ₂
Seeking remainder MB _m relates obtains the received power PG _m distance discriminator reception gate from MB _m, average determined for m of PG _m, the average value is large TC ₂ of the PG _m
Is configured to be used for the repetition period T ₂ of the second transmission pulse with priority, and the expected value of the gate reception power is increased when the second reception pulse is received. Since the number of times to switch the repeating cycle T ₂ is reduced,
The target distance can be determined by observing in a shorter time.

[0027]

【Example】

Example 1. A first embodiment of the present invention will be described with reference to the drawings.
First Embodiment FIG. 1 is a block diagram of a distance measuring device using a multi-PRF method showing a first embodiment of the present invention. In the figure, 251 is a transmitter, 252 is a receiver, 253 is a transmission / reception switch (circulator), 254 is an antenna, 256 is an MTI filter,
257 is a distance correlation circuit, 258 is a signal processing device, and 259.
Is a display device, 1601 is a reference signal generator, and 1602 is P
It is a RI reference table. The reference signal generator 1601 determines the repetition cycle of the transmission pulse, modulates and amplifies it with the transmitter 251, and emits a radio wave from the antenna 254 toward the target. This reflected wave is received by the antenna 254, and the receiver 2
The signal is demodulated and amplified at 52, and filtered by the MTI filter 256 based on the repetition cycle of the transmission pulse determined by the reference signal generator 1601 to suppress clutter such as the ground surface and weather. With respect to the clutter-suppressed received pulse, the distance correlation circuit 257 obtains the apparent target distances X ₁ and X ₂ obtained from the received signal, and the signal processor 258 obtains the true target distance X ₀ . The above reference signal generator 1601 has a PRI reference table 1602, and the PRI reference table 1602 is a table showing the priority order of switching the transmission pulse repetition period. The reference signal generator 1601 refers to this table. Determine the repetition period of the successive transmission pulse. Here, 251, 253, 254, 1601, 1
602 constitutes a transmitting means, 252, 253, 254 and 256 constitute a receiving means, and 257, 258 and 259 constitute a signal processing means.

Embodiment 2 FIG. Second Embodiment FIG. 2 is a flowchart showing a distance measuring method using a multi-PRF method showing a second embodiment of the present invention. In the flowchart of FIG. 2, first, 411
Set the integer i ₁ to the minimum value I _min , fetch the i ₁ -th integer value N ₁ (i ₁ ) from the one-dimensional table N _{1 in} 412, and multiply it by the unit time Δ and send the first value. The pulse repetition period is set to T ₁ , and at 413, the current flight speed v of the platform is referenced to confirm whether T ₁ satisfies the condition (1) for clutter suppression.
A pulse of ₁ is transmitted, the received signal waveform is stored at 213, the received signal waveform is stored, the presence or absence of received power is determined at 214, the integer i ₁ is incremented at 414, and the apparent target distance X ₁ (at FIG. 17) is incremented at 216. , B), and at 417 the integer i
Remember ₁ 421, 423, 222, 223, 22
4,424,226,427 are 411 and 41, respectively.
3,212,213,214,414,216,417
Apparent target distance X ₂ according to (see D in Fig. 17)
Is a processing step of measuring and storing. 422 is an integer value N of the i _1st row i _2nd row from the two-dimensional table N _2
2 (i ₁ , i ₂ ) is taken out, and a value obtained by multiplying it by a unit time Δ is set in T ₂ which is the second transmission pulse repetition period. The first received pulse stored in 201 (see B in FIG. 17) and the second received pulse (see FIG. 17)
(See F in FIG. 17) (see F in FIG. 17), and a target distance is calculated from the received pulse correlation signal in 202. One-dimensional table N ₁ , 2 referred to by 412 and 422
The dimension table N ₂ is created in advance. In the above processing steps, 411, 412, 413, 212, 2
13, 214, 414, 216, and 417 are the first transmission / reception step in which T ₁ which is the repetition cycle of the first transmission pulse is determined and transmission / reception is performed in this repetition cycle of T _1.
1,422,423,222,223,224,42
4, 226 and 427 are the second transmission / reception steps for determining T ₂ which is the repetition cycle of the second transmission pulse and transmitting / receiving in this repetition cycle, and 201 and 202 are the above X ₁ and X.
_This is a signal processing step for calculating the true target distance X ₀ using ₂ (see FIG. 16).

FIG. 3 shows a multi-P system according to the second embodiment of the present invention.
An example of a flow chart for creating the tables N ₁ and N ₂ to be referred to in the distance measuring method using the RF method will be shown. The tables N ₁ and N ₂ obtained here are also used in the PRI reference table 1602 of the distance measuring apparatus using the multi-PRF method of the first embodiment shown in FIG. In FIG. 3, first, 502 sets an integer value i ₁ to the i ₁ -th element N ₁ (i ₁ ) of the one-dimensional table N ₁ , and 504 is the i ₁ -th row i ₂ -th of the two-dimensional table N ₂ . Element N ₂ (i
₁ , i ₂ ) is set to an integer value i ₂ , and 505 is i ₁ , i
_In this processing, the least common multiple (LCM) of ₂ is calculated, and a value obtained by multiplying this value by Δ is set in T ₀ . 506 multiplies T ₀ by (c / 2) and compares it with the minimum target fixed distance limit R _lim to be secured, and 507 calculates the greatest common divisor (GCM) of i ₁ and i ₂ , and this value is Processing for setting the i _1st row i _2nd element F (i ₁ , i ₂ ) of the dimensional array F, 5
08 is a process for setting 0 in the two-dimensional array F (i ₁ , i ₂ ), and 509 and 512 are i ₂ and i ₁ with the maximum value I, respectively.
A process 510 for determining whether or not _max has been reached is performed by comparing the size of the corresponding F (i ₁ , i ₂ ) of each row of the table N ₂ with elements N ₂ (i ₁ , i ₂ ) in descending order of F. ) Sort processing 511, each row of the array F, element F
The process of obtaining the average value of i ₂ of (i ₁ , i ₂ ) and setting it to the i _1- th element G (i ₁ ) of the one-dimensional array G, 513 sets the size of G (i ₁ ). By comparison, a process 514 of sorting the elements N ₁ (i ₁ ) of the table N ₁ in order of increasing G compares the sizes of G (i ₁ ) and the rows of the table N ₂ in order of increasing G. This is a process of sorting N ₂ (i ₁ , i ₂ ) row by row. Where I _min and I _max
Are lower and upper limits of integers that can be used for i ₁ and i ₂ , respectively.

Next, the process of creating the table N ₁ and the table N ₂ according to FIG. 3 will be described with reference to I _min = 8, I _max = 10,
Numerical examples in which R _lim /(Δc/2)=33.5 will be described with reference to Tables 1 to 7. Table 1 is shown in FIG.
502 shows a one-dimensional table N ₁ (i ₁ ) after processing. Table 2 is a two-dimensional table N ₂ (i
₁ , i ₂ ) is shown.

[0031]

[Table 1]

[0032]

[Table 2]

Table 3 shows LC in 505 processing in FIG.
The value of M (i ₁ , i ₂ ) is shown. Table 4 shows 509 in FIG.
The two-dimensional array F (i ₁ , i ₂ ) after processing is shown.

[0034]

[Table 3]

[0035]

[Table 4]

Table 5 shows the two-dimensional table N ₂ (i ₁ , i ₂ ) after the processing 510 in FIG.

[0037]

[Table 5]

Table 6 shows the one-dimensional array G (i ₁ ) after the 511 processing in FIG. Table 7 shows the one-dimensional table N ₁ (i ₁ ) after the 513 process in FIG. Table 8 is shown in FIG.
A two-dimensional table N ₂ (i ₁ , i ₂ ) after 514 processing is shown.

[0039]

[Table 6]

[0040]

[Table 7]

[0041]

[Table 8]

In FIG. 3, at 506, it is a judgment as to whether or not the determinable target distance determined by N ₁ and N ₂ can secure the minimum _limit R _lim.
(I _1, i ₂₎ in giving the greatest common divisor of N ₁ and N ₂ (GCM), given in a case that can not be secured 508 F (i _1, i ₂₎ 0. Therefore, the two-dimensional array F (i ₁ , i ₂ ) has the values shown in Table 4. Two-dimensional table N ₂ (i ₁ , i ₂ )
Is the element N ₂ for each row by the processing of 510 in FIG.
Since (i ₁ , i ₂ ) is sorted in the order of the size of F (i ₁ , i ₂ ), the order changes from Table 2 to Table 5. For example, the row of i ₁ = 8 is shown in Table 2 as N ₂ (8,8) = 8, N ₂ (8,9) = 9, N ₂ (8,
10) = 10, but in Table 4, F (8,8) = 0, F (8,9) = 1, F (8,10)
Therefore, in Table 5, N ₂ (8,8) = 10, N ₂ (8,9) = 9, N
_The order changes to ₂ (8, 10) = (not used). Therefore, this order (the order in the row direction of the table N ₂ shown in Table 5) is such that N ₁ and N ₂ which secure the minimum _limit R _lim of the target distance that can be determined with respect to the corresponding N _1.
Among the combinations of, the greatest common divisor (GCM) is in descending order. Table 6 shows the average values in the row direction of Table 4. For example, the row of i ₁ = 9 is shown in Table 4 as follows: F (9,8) = 1, F (9,9) = 0, F (9,10)
Since = 1, G (9) = 0.66. In FIG. 5, 51
By the processing of 3, N ₁ (i ₁ ) is sorted in the order of the size of G (i ₁ ), so that the order changes from Table 1 to Table 6. Therefore, the order of the table N ₁ shown in Table 6 is the order of the largest expected value of the greatest common denominator (GCM).
The processing of 514 is to change the order of i ₁ of the table N ₂ in accordance with the processing of changing the order of the table N ₁ of 513. In this numerical example, N ₁ of table N ₁ in 513
(9) and N ₁ (10) were exchanged, so table N ₂
Is the row N _{2 with} i ₁ = 9 (9, i ₂ ) and the row N ₂ with i ₁ = 10
It is changed as shown in Table 8 by exchanging (10, i ₂ ). Table 7 is the final result of Table N ₁ and Table 8 is the final result of Table N ₂ .

Next, an outline of a distance measuring method using the multi-PRF method according to the second embodiment will be described with reference to FIGS. 412 indicates the first transmission pulse repetition period T ₁
However, as i ₁ is incremented by 414, the repeat cycle T ₁ is switched in the order of the table N ₁ previously created in FIG. Therefore, 21
In the first reception pulse used when measuring the apparent target distance X ₁ in 6, the maximum agreement between n ₁ and n _{2 in} the repetition cycle in which clutter can be suppressed and reception power is secured. The repetition period with the highest expected number (GCM) is used. Similarly, 422 determines T ₂ which is the second transmission pulse repetition cycle, but as i ₂ is incremented by 414, the table N created in advance in FIG.
Repetitive cycles in ₂ of the i ₁ row order is switched. This row selection number i ₁ is the value stored in 417. Therefore, in the second reception pulse used when measuring the apparent target distance X ₂ in 226, the first reception pulse is included in the first reception pulse in the repetition cycle in which the clutter can be suppressed and the reception power can be secured. For the n ₁ used, the repetition period with the highest greatest common divisor (GCM) of n ₁ and n ₂ is used. That is, in the multi-PRF method of the embodiment, n ₁ and n ₂ which determine the repeating period of two pulses used for distance measurement are the greatest common divisor (GC) among combinations satisfying given conditions.
The one having the highest M) is used.

Next, the greatest common divisor (GCM) of n ₁ and n ₂
A description will be given of the fact that a large error is less likely to occur in the distance measurement result when the is set higher. In FIG. 17, the timing of B ₄ of the received pulse 1 and the timing of D ₃ of the received pulse 2 coincide with each other on the true target distance, and other combinations of the received pulses, B ₁ and D ₁ , B ₂
It is a condition for obtaining a correct distance measurement result that there is no correlation between D ₁ and D ₁ , B ₂ and D ₂ , B ₃ and D ₂ , B ₅ and D ₄ , and B ₁ and D ₄ . In FIG. 18, B2 and D are due to the measurement errors e ₁ and e _2.
The timing of 1 coincided with each other, resulting in a large error in the distance measurement result. Conversely, the combination of received pulses, B ₁ and D ₁ ,
B ₂ and D ₁ , B ₂ and D ₂ , B ₃ and D ₂ , B ₅ and D ₄ , B
_The larger the time difference between ₁ and D _4, the less likely the target ranging result will be.

Bi of the received pulse 1 (i = 1, 2, ...,
The time difference X _1i between 5) and the transmission pulse at t = 0 is expressed by the following equation using the apparent target distance X ₁ and T ₁ as the repetition period. X _1i = X ₁ + (i−1) T ₁ (4) Similarly, Dj of received pulse 2 (j = 1, 2, ..., 4)
The time difference X _{2j of} is expressed by the following equation. X _2j = X ₂ + (j−1) T ₂ (5) Since the ranging principle of the multi-PRF method is to search for pulses whose timings match each other, X _1i = X _{2j, that} is, X ₁ + (i− 1) Obtaining i or j that satisfies T ₁ = X ₂ + (j−1) T ₂ (6), and substituting this i or j into equation (4) or equation (5), or X _1i or X
_This is equivalent to setting _2j as the target distance. Where equation (6)
Taking the remainders with respect to T ₂ on both sides of j, j is eliminated and equation (6) is replaced by the following equation. X ₂ = MB _i (7) MB _i = MOD [X ₁ + (i−1) T ₁ , T ₂ ] (i = 1, 2, ..., 5) (8) MOD [*, T ₂ ] is It means the remainder with respect to T ₂ . That is, received pulses B ₁ and D ₁ , B ₂ and D ₁ , B ₂ and D ₂ ,
The larger time difference between B ₃ and D ₂ , B ₅ and D ₄ , and B ₁ and D ₄ is equivalent to the wide spacing between MB _i (i = 1, 2, ..., 5). . Therefore, widening the MB _i intervals is equivalent to making it difficult for a large error to occur in the target distance measurement result.

The position of MB _i defined by equation (8) is indicated by G in FIG. As is clear from FIG. 4, MB
_{The i} intervals are equal to each other, and this is indicated by δ. δ is, in the example of FIG. 4, δ = MB ₁ −MB ₂ = MB ₅ −MB ₂ = MB ₄ −MB ₅ =
_{MB 3 -MB 4 = (MB 2} + T 2) -MB _3. The number of MB _i is T ₀ / T from B and C in FIG.
₁ and MB _i equally divides the interval 0 to T ₂ by δ. Therefore, the interval δ of MB _i from each other is given by the following equation. δ = T ₂ / (T ₀ / T ₁ ) (9) Now, using the mutually prime integers k ₁ and k ₂ , T ₀ ,
When T ₁ and T ₂ are expressed, the following relational expressions hold from Expressions (2) and (3). Here, LCM (n ₁ , n ₂ ) means the least common multiple of integers n ₁ , n ₂ , and GCM (n ₁ , n ₂ ) means the greatest common divisor of integers n ₁ , n ₂ . Therefore, in equation (9), equation (10),
Substituting (11), δ = GCM (n ₁ , n ₂ ) (12) holds. That is, the mutual intervals of MB _i are given by the greatest common divisor of the first transmission pulse and the second transmission pulse.

As described above, in the present embodiment, the repeating period is used so that the greatest common divisor of the first transmission pulse and the second transmission pulse has a value as high as possible. A large error is less likely to occur in the distance result. In this embodiment, the tables N ₁ and N ₂ are created in advance, but they may be created by calculation in real time.

Further, in this embodiment, the repetition cycle of the first transmission pulse is set to the first and second repetition cycles together with the repetition cycle of the second transmission pulse.
Although it is determined that the highest common divisor of the repetition cycle is preferentially used in the descending order, the same effect can be expected when the selection order of only the repetition cycle of the second transmission pulse is determined.

As described above, in the second embodiment, as the distance measuring method using the multi-PRF method, the case where two kinds of PRFs different from each other are used has been described. A selection method can be adopted. For example, when three types of PRFs are used, the following equation is used as a method for selecting the third repetition period, and T ₃ (=
By determining Δ · n ₃ ), even if an apparent time difference between the reception pulse and the transmission pulse includes an error, a large error is unlikely to occur in the distance measurement result. δ3 = GCM (LCM (n ₁ , n ₂ ), n ₃ ) where LCM (n ₁ , n ₂ ) is the least common multiple of the integers n ₁ and n ₂ , and GCM (n ₁ , n ₂ ) is the integer n ₁ , N _{2 is} the greatest common divisor of n ₂ .

Further, in general, there are J types (j = 1, 2, ...
, J) PRF is used, the following equation is used as a method for selecting the J-th repeating cycle, and T _J (= Δ is the repeating cycle of the J-th transmission pulse in order of increasing δJ).・ N _J )
By determining, even when an apparent time difference between the reception pulse and the transmission pulse includes an error, a large error is unlikely to occur in the distance measurement result. δJ = GCM (LCM _(J-1) , n _J ) where LCM _(J-1) is an integer n ₁ , n ₂ , ..., N _(J-1)
The least common multiple of GCM (n ₁ , n ₂ ) is an integer n ₁ , n _2.
Means the greatest common divisor of.

Example 3. Embodiment 3 of the present invention
Explain. FIG. 5 shows a multi-P system according to the third embodiment of the present invention.
Table N to be referred to in the distance measuring method using the RF method
₁, Table N₂Shows an example of a flow chart for creating
You. The third embodiment has a repetition cycle longer than that of the second embodiment.
Even if it is changed, the maximum detection distance and
The duty ratio (= pulse width / repetition cycle) depends on the repetition cycle
Keep an apparent target distance X_jThe distance
For pulse Doppler radar that measures using discreet
This is a distance measuring method. In FIG. 5, 707 is i₁, I₂of
The greatest common divisor (GCM) is calculated, and this value is (i₁+
i₂) Divided by i in the two-dimensional array F₁Line i₂Th
Element F (i₁, I ₂). Figure
In the figure, the same steps as those in FIG.
I do. Therefore, the table N obtained from FIG.₁, N
₂Is GCM (n₁, N₂) / (N₁+ N₂) Are in descending order of expected value.

When the duty ratio is D, the pulse width of the jth transmission pulse is τ _j , and the repetition period of the jth transmission pulse is T _j , τ _j is given by the following equation. τ _j = D · T _j (13)

Steps 216 and 226 for measuring the apparent target distances X ₁ and X ₂ in the flowchart showing the distance measuring method using the multi-PRF method of FIG. 2 showing the second embodiment.
When using a distance discriminant, for example, DK
BARTON: “MODERN RADAR SYSTEM ANALYSIS”, ARTECH HO
USE, pp.379-383 (1988), the expected value <| e _j |> of the magnitude of the measurement error e _j of X _j is the pulse width τ.
proportional to _j . Therefore, <e _j > is expressed as <| e _j |> = Ae · T _j (14) using the proportional constant Ae. Since a T _j = Δ · n _j as defined in formula 2, the measurement error e ₁ and the second according to the first received pulse
The expected value of the sum of the measurement error e ₂ concerning the received pulse of is given by the following equation. <| E ₁ + e ₂ |> ≦ Δ · (n ₁ + n ₂ ) (15) That is, when the repetition period of the transmission pulse is increased, the greatest common divisor tends to increase, but The error included in the apparent time difference also increases. Therefore, in the third embodiment, the greatest common divisor GCM (n ₁ , n ₂ ) of the repeating cycles of the first and second transmission pulses is set to a high value with respect to the error magnitude (n ₁ + n ₂ ). Then, a large error is unlikely to occur in the target distance measurement result. Therefore, in the third embodiment, the following equation, which is an evaluation function, uses a repetition cycle having a value as high as possible, so that a large error is unlikely to occur in the target distance measurement result. GCM (n ₁ , n ₂ ) / (n ₁ + n ₂ )

Example 4. 6 and 7 show Embodiment 4 of the present invention.
5 is a flowchart of a distance measuring method using the multi-PRF method. FIG. 7 is a continuation of FIG. In this embodiment, a distance measuring method using the multi-PRF method having three different types of transmission signal repetition periods will be described as an example. Figure 6,
In the flowchart of FIG. 7, first, 411 to 21
Up to 6, the apparent target distance X is calculated based on the repetition cycle T ₁ of the first transmission pulse according to the description in FIG. 2 of the second embodiment.
_This is a processing step for measuring ₁ . In 813, the target existence region width σ ₁ of the first received pulse is calculated, and in 814, 216
Using the apparent target distance X ₁ measured in step ₁ and the target existing area width σ ₁ calculated in 813, the target existing area by the first received pulse is calculated. Then, the processing steps 421 to 226 are to measure the apparent target distance X ₂ based on the repetition cycle T ₂ of the second transmission pulse in accordance with the description of FIG. 2 of the second embodiment. At 823, the target existence area width σ ₂ of the second reception pulse is calculated, and at 824, the apparent target distance X ₂ measured at 226 and the target existence area width σ ₂ calculated at 823 are used to perform the second reception. The target existence area by the pulse is calculated. The target existing area by the second reception is calculated, and then the apparent target distance X3 is measured from 431 to 236 based on the repetition cycle T3 of the third transmission pulse according to the description in FIG. 2 of the second embodiment. Is a processing step to be performed. At 833, the target existence region width σ of the third reception pulse
₃ was calculated and 834 by using the target presence region width sigma ₃ calculated in apparent target distance X ₃ and 833 measured at 236, calculates the target presence region by the third received pulse.
At 801 a correlation signal between the target existing region by the first reception and the target existing region by the second reception is calculated, and at 802, the target existing region up to immediately before and the target presence region by the third reception and the correlation signal are calculated. To find a new target existence area,
In 03, it is determined whether the target existence area after the correlation calculation in 801 or 802 is narrowed down to one area, and in 804, the center position of the target existence area is obtained. In the figure, FIG.
The same steps as those in the flowchart of FIG. Note that the above-mentioned steps 812, 822, and 832 are processing steps for determining the repetition cycle of the first, second, and third transmission pulses, but the tables N ₁ , N ₂ , and N ₃ referred to here are Even if the same as the one obtained in the second embodiment is used, it is easy to use, for example, N ₁ (i ₁ ) = i ₁ , N
₂ (i ₂ ) = i ₂ and N ₃ (i ₃ ) = i ₃ may be used.

Next, a distance measuring method using the multi-PRF method shown in FIGS. 6 and 7 of the fourth embodiment will be described with reference to the timing chart shown in FIG. First in step 216 of FIG.
By obtaining the apparent target distance X ₁ of the reception pulse of B ₁ , the timing of B ₁ , B ₂ , ..., B ₅ shown by B in FIG. 8 is determined. The target existence area width σ ₁ due to the first received pulse obtained in step 813 of FIG. 6 is set to be the maximum value of σ ₁ > | e ₁ | (16) with respect to the measurement error e ₁ of the timing of the received pulse. Given. σ ₁ is generally different from the pulse width τ ₁ . First obtained in step 814 of FIG.
The target existence area by the received pulse of ± σ around the timing B _j (j = 1, 2, ..., 5) of the received pulse is ± σ
The interval is ₁ . That is, the target existence region by the first reception pulse is as shown in the hatched portion of B in FIG. 8, B _j −σ ₁ ≦ t ≦ B _j + σ ₁ (j = 1, 2, ..., 5) ) It is a plurality of sections of (17). Similarly, steps 823 and 8 in FIG.
In 24, similar processing is performed to calculate the target existing area by the second received pulse having the target existing area width σ ₂ as shown by the hatched portion of D in FIG. The target existence area after the correlation processing is shown in FIG.
Inside, it is narrowed down as shown in F. As described above, the target existence region has a width wider than the timing measurement errors e ₁ and e _{2 of the} received pulse, so that the correlation signal peak is not lost on the true target distance (F3 in F in FIG. 8). .
On the other hand, as shown by F1, F2, and F4 in F in FIG. 8, the correlation signal may have a peak at timings other than the true target distance, but at 834 in FIG. 7, a third received pulse is newly added. The target existence area (indicated by H in FIG. 8) is calculated and the correlation between F in FIG. 8 and H in FIG. 8 is calculated in 802 to obtain the target existence area as indicated by I in FIG. Can be narrowed down to one place. If it cannot be narrowed down to one location, the repetition cycle T ₃ of the third transmission pulse is switched so that the target existence area by the third reception pulse is set until the target existence area becomes one location. Perform correlation processing. At 804, the center point of the target existing region narrowed down to one place is obtained, and this is set as the estimated value R ₀ of the target distance.

As described above, according to the distance measuring method of the fourth embodiment, even if there is an error in measuring the timing of the received pulse, the target existing region has a width, so that the correlation signal is close to the true target distance. Does not lose its peak, and the target distance can be determined with certainty. In the fourth embodiment, the case where the target existence region width σ is larger than the pulse width τ has been described, but conversely, when the target existence region width σ is smaller than the pulse width τ, there is a relationship with the true target. The peak of the correlation signal is unlikely to appear at non-timing, the true target is narrowed down in a short time, and the search time is shortened.

Example 5. 6 and 7 show Embodiment 4 of the present invention.
5 is a flowchart of a distance measuring method using the multi-PRF method. The present invention is based on the apparent target distance X shown in FIGS.
This is a distance measuring method in which the processes 216 and 226 for measuring _j are performed using a distance discriminant. The expected value <| e _j ｜> of the absolute value of the measurement error when the apparent target distance X _j is measured by the distance discretization is, for example, DKBARTON: “MODERN RADAR
SYSTEM ANALYSIS ”, pp.379-383, ARTECH HOUSE (1988)
Is given by the following equation. <| E _j |> = τ _j / (SNR) ^1/2 (18) τ _j is the pulse width, and SNR is the signal-to-noise power ratio. Therefore, based on the equation (16), the target existing area width σ _j by the j-th reception is determined as the following equation. σ _j = a · τ _j / (SNR) ^1/2 (19) Here, a is a proportional constant that does not depend on j, and the measurement error is a Gaussian distribution.
Equation (16) is satisfied with a probability of 6%. Therefore, the peak of the correlation signal is not extremely lost near the true target distance, and the degree to which the target distance cannot be determined is extremely small.

In the fifth embodiment, the processing of step 813 in the flowcharts of FIGS.
By using the signal-to-noise power ratio (SNR) measured in step S1 and the pulse width τ ₁ obtained from the repeat cycle T ₁ determined in step 812, the target existence region width σ by the first reception is calculated. It is calculated by the following formula. σ ₁ = a · τ ₁ / (SNR) ^1/2 Similarly, in steps 823 and 833, the target existing region width σ is set to σ ₂ = a · τ ₂ / (SNR) ^1/2 σ ₃ = a · τ _{3 respectively.} Calculated as / (SNR) ^1/2 . The SNR changes depending on the apparent target distance X _j and the repeating cycle T _j , and is therefore calculated sequentially in step 214.

As described above, according to the distance measuring method of the fifth embodiment, the target existing region has a width even if there is an error in measuring the timing of the received pulse, similarly to the distance measuring method of the fourth embodiment. Therefore, the correlation signal rarely loses its peak near the true target distance, and the degree to which the target distance cannot be determined becomes extremely small. In the fifth embodiment, the constant a in the equation (19) is set to a = 2.0, but other positive constants have the same effect with a predetermined probability.

Example 6. FIG. 9 is a flowchart of a distance measuring method using the multi-PRF method according to a sixth embodiment of the present invention, showing a distance measuring method in a pulse Doppler radar sharing a transmitting / receiving antenna. In FIG. 9, first, steps 411 to 417 are steps of measuring and storing an apparent target distance X ₁ based on the repetition cycle T ₁ of the first transmission pulse described in FIG. 2 of the second embodiment. According to. At 1012, the table N ₁ is referred to, and a value obtained by multiplying the table N ₁ by the time unit Δ is set as the repetition cycle of the first transmission pulse.
In step 001, a table N ₂ is created based on the expected value of Eclipse, and in step 1022, the table N ₂ is referenced, and the value is multiplied by the time unit Δ to obtain the value of the repetition cycle of the second transmission pulse. Here, the same steps as those in FIG.

FIG. 11 is a flow chart showing an example of creating the table N _{2 in} step 1001 of FIG. 11, first, set the integer value i ₂ to 1201 in a one-dimensional table of N ₂ i ₂ th element N ₂ (i _2), multiplied by the time unit Δ in N ₂ (i ₂₎ at 1202 values was set to T _2, and sets a value obtained by dividing the T ₂ at Diyuti ratio D in tau _2, set to 0 to 1203 in a one-dimensional array E (i _2), is set to 1 m in 1204, 1205
By using T ₂ set in 1202 in FIG. 9, T ₁ set in 1012 in FIG. 9, and X ₁ measured in 216 in FIG. 9, MB _m is calculated as MB _m = MOD [X ₁ + (m−1 ) T ₁ , T ₂ ]. Using T ₂ and τ ₂ set in 1202 in 1206, the eclipse value Ec (MB _m ) at the reception timing MB _m is calculated, and Ec (MB _m ) obtained in 1206 in 1207 is set to E (i ₂ ). Then, it is determined whether or not the integer m has reached the value obtained by dividing T ₀ obtained in 505 by T ₁ set in 1012 of FIG. 9 in 1208, and incrementing the integer m in 1209,
E (i ₂ ) is divided by (T ₀ / T ₁ ) by 10 to obtain 1211
To set E (i ₂ ) to a sufficiently large value, and to E at 1212
The magnitudes of (i ₂ ) are compared, and N ₂ (i
₂ ) This is the process of sorting. Where I _min and I _max
Are lower and upper limits of integers that can be used for i ₂ . In the figure, the same steps as those in FIG.

An example of creating the table N ₂ shown in FIG. 11 will be described with reference to FIG. In a pulse Doppler radar that shares a transmission / reception antenna, the receiver is shut off during transmission in order to prevent damage to the receiver due to leakage of transmission signals. Therefore, even if the echo from the target is received by the antenna during transmission, it is cut into transmission pulses,
Received power loss occurs. This is called Eclipse. The received power loss Ec (X) due to eclipse is a function of the apparent target position X of the received pulse, and is uniquely determined as indicated by J in FIG. 10 if the repetition period and the pulse width τ are given. Now, assume that the second transmission pulse having the repetition period T ₂ is transmitted. If the apparent position of the first reception pulse at this time is X ₁ , the expected value <Ec> of the reception loss power Ec due to Eclipse is given by the following equation.

[0063]

[Equation 1]

Here, MB _m is the remainder with respect to T ₂ of the first received pulse position defined in equation (8), k ₂ is the number of MB _m , and T ₀ defined in equation (11). Is an integer given by: k ₂ = T ₀ / T ₁ (21) The derivation of equation (20) will be described with reference to FIG. The apparent position of the first received pulse is X
If it is ₁ , the target position always exists in _{one of} B _m = X ₁ + (m−1) T ₁ (m = 1, 2, ..., 5). At this time, since the apparent position X ₂ of the second received pulse is in the section 0 ≦ t ≦ T ₂ ,
Matches either the remainder of _m for T ₂ or MB _m . For example, if the target position is B ₄ ,
As shown in D, X ₂ is given by MB ₄ . That is, the apparent position X ₂ of the second received pulse is MB ₁ ,
It cannot be a value other than MB ₂ , ..., MB ₅ . Therefore,
Received loss power Ec due to eclipse of second received pulse
The values of Ec (MB ₁ ), Ec (MB ₂ ), ..., Ec
It becomes any one value of (MB ₅ ). MB ₁ , M
Since the probabilities that B ₂ , ..., MB ₅ are X ₂ are equal, the expected value <Ec> is given by equation (20). If T ₂ which is the repetition cycle of the second transmission pulse is changed, the value of MB _m is also changed, so that <Ec> is also changed.

[0065] With reference to FIG. 11, the first repetition period of T ₁
When the first reception pulse appears at the apparent target position X ₁ when the first transmission pulse is transmitted, what repetition period T _{2 is used} for the second transmission pulse, and the reception loss power Ec due to Eclipse is the most. Whether the expected value <Ec> of is small will be described. At 1201 and 1202, the value of T ₂ which is the repetition period which is a candidate for the second transmission pulse is obtained, and at 1205 MB _m
Look, T ₂ in 1206, Eclipse from τ ₂ Ec (M
B _m ). The Eclipse function Ec (X ₂ ) is, for example, as shown by J in FIG.

[0066]

[Equation 2]

Is given by Σ in equation (20) in 1207
Ec (MB _m ) is calculated, and ΣEc (MB _m ) is divided by 1210 by k ₂ . 1205, 1206, 1207, 120
The processing of 8, 1209, and 1210 calculates the equation (20) to obtain the expected value <Ec> of the power loss. 505
506 and 1211 are the minimum limit R of the target distance that can be determined.
_This is a process of eliminating T ₂ that cannot secure _min . 121
In step 2, N ₂ (i ₂ ) is sorted in ascending order of E (i ₂ ), so that the order of the table N ₂ (i ₂ ) changes to the order in which the expected value <Ec> of the reception power loss due to Eclipse is small.

A distance measuring method using the multi-repeat cycle shown in FIG. 9 will be described. In step 1022, the second transmission pulse repetition period T ₂ is determined.
As i ₂ is incremented at 24, the repeating cycle T ₂ is switched in the order of the table N ₂ calculated in FIG. Therefore, the repetition period of the second pulse transmitted at 222 is the expected value of the reception power loss due to Eclipse <E
c> is used from the smallest repetition period. Therefore, according to the distance measuring method of the present invention, when the second transmission pulse is transmitted, since the repetition period in which eclipse is unlikely to occur is used, the number of times to change the repetition period of the second transmission pulse may be small, It is possible to shorten the observation time to determine the target distance.

Step 1012 is a process for determining the repetition cycle of the first transmission pulse, and refers to the table N _{1 to be} referred to.
Is not limited to those referred to in FIG. 2, for example simply N ₁ (i
₁ ) = i ₁ may be used. Further, when calculating the reception loss power Ec due to eclipse, the apparent position X ₂ of the second reception pulse is set to T of the first reception pulse position B _m .
_It is calculated from the remainder for ₂ , that is, MB _m .
The received pulse position B _m may be converted. Also, 12
Although the duty ratio D is fixed when the pulse width τ ₂ is determined by 02, D may be changed for each pulse. In the description of the embodiment, as shown in FIG. 9, the case where the distance measurement is completed by using the pulses of the two types of repeating cycles is shown. However, as shown in FIGS. When completing the distance measurement using the pulse of, not only the second,
In the same way, by changing the use order of the repetition period used for the third and subsequent transmission pulses to reduce the expected value of the reception loss power due to the eclipse of the third and subsequent reception pulses, the observation up to the determination of the target distance is performed. The time can be shortened.

Example 7. FIG. 12 is a flowchart of a distance measuring method using the multi-PRF method according to the seventh embodiment of the present invention, showing a distance measuring method using a distance discriminant when measuring the apparent target distance X _m . In the figure, reference numeral 1301 denotes a process for creating the table N ₂ based on the expected value of the gate reception power. The same steps as those in FIGS. 2 and 9 are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 14 is a flowchart showing an example of creating the table N _{2 in} step 1301 of FIG. In the flowchart of FIG. 14, first, 150
6, the gate reception power Pg (MB _m ) at the reception position MB _m is calculated using T ₂ and τ ₂ set in 1202, and Pg (MB _m ) obtained in 1507 is calculated as Pg (MB _m ).
The process of adding to (i ₂ ), E (i ₂ ) is set to 0 in 1511, the size of E (i ₂ ) is compared in 1512, and E (i ₂ ) is compared.
Is a process of simultaneously sorting N ₂ (i ₂ ) in descending order. In the figure, the same steps as those in FIGS. 3 and 11 are designated by the same reference numerals, and the description thereof will be omitted.

An example of creating the table N ₂ shown in FIG. 14 will be described with reference to FIG. The reception gate of the distance discretization is opened at a timing synchronized with T ₂ of the second transmission pulse repetition period as shown by G in FIG. 13, for example. Therefore, even if the echo from the target is received by the antenna, the received power is lost due to the timing difference between the received pulse position and the receiving gate. The reception power Pg (X) captured by the reception gate is a function of the apparent target position X of the reception pulse and is uniquely determined as indicated by K in FIG. 13 if the repetition period and the pulse width τ are given. It Now, assume that the second transmission pulse is transmitted at T ₂ of the repetition period. If the apparent position of the first reception pulse at this time is X ₁ , the expected value of the gate reception power Pg <Pg
> Is given by the following equation.

[0073]

(Equation 3)

Here, MB _m is the remainder with respect to T ₂ of the first received pulse position defined in equation (8), and k ₂ is the number of MB _m and is given by equation (21). Formula (23)
The derivation of is explained. If the apparent position of the first received pulse is X ₁ , then the apparent position of the second received pulse is X _1.
2 cannot take values other than MB ₁ , MB ₂ , ..., MB ₅ . Therefore, the value of the gate reception power Pg is Pg (MB
₁ ), Pg (MB ₂ ), ..., Pg (MB ₅ ), the expected value <Pg> is given by the equation (23). If T ₂ of the repetition cycle of the second transmission pulse changes, the value of MB _m also changes, so <Pg> also changes.

[0075] With reference to FIG. 14, the first repetition period of T ₁
When the first received pulse appears at the apparent target position X ₁ when the second transmitted pulse is transmitted and what cycle T _{2 is used} for the second transmitted pulse, the expected value of the gate received power Pg is the most expected value. It will be described whether <Pg> becomes high. In the following description, the center position of the receiving gate is represented by Tg and the gate width is represented by the pulse width τg. At 1506, the gate reception power Pg (MB _m ) is calculated from T ₂ and τ ₂ , and the gate reception power Pg is, for example, as shown by K in FIG.

[0076]

[Equation 4]

Is given by 1205, 1506, 15
The processes of 07, 1208, 1209, and 1210 are expressed by the formula (2
The calculation of 3) is performed and the expected value of the gate reception power Pg <P
g> is calculated. At 1512, N ₂ (i ₂ ) is sorted in the descending order of E (i ₂ ), so table N ₂ (i ₂ )
The expected value <Pg> of the gate reception power Pg changes in the order of.

A distance measuring method using the multi-repeat cycle method of the sixth embodiment will be described with reference to FIG. First, in T 1322, T ₂ which is the second transmission pulse repetition period is determined.
As i ₂ is incremented by 4 in FIG.
The repeating cycle T ₂ is changed over in the order of the table N ₂ created in. Therefore, the repetition cycle of the second pulse transmitted at 222 is used from the repetition cycle with the largest expected value <Pg> of the gate reception power Pg. Therefore, according to the distance measuring method of the present embodiment, when the second pulse is transmitted, the gate reception power is used from the statistically high repetition period, so that the number of times of switching the repetition period of the second transmission pulse is reduced, It is possible to shorten the observation time to determine the target distance.

Reference numeral 1012 is a process for determining the first repetition cycle, but the reference table N ₁ is not limited to the one created in FIG. 3; for example, N ₁ (i ₁ ) = i ₁ can be simply set. It may be one. Also, when calculating the gate receiving power Pg, the position X ₂ of the apparent second received pulse, the remainder of the T ₂ of the first received pulse position B _m, i.e. determined from MB _m, direct B You may convert from _m . In the description of the embodiment, as shown in FIG. 12, the case where the distance measurement is completed by using the pulses of the two types of repeating cycles is shown.
In the case where the distance measurement is completed by using the pulses of the three types of repeating cycles as well, the order of use of the repeating cycles used for the third and subsequent transmission pulses is changed by the same method, and By increasing the expected value of the gate received power of the third and subsequent received pulses, it is possible to shorten the observation time until the target distance is determined.

[0080]

As described above, according to the invention of claim 1, the transmitting means repeats the first and second transmission signals when determining the repetition cycle of the first and second transmission signals. By determining the priority so that the greatest common denominator of the return cycle becomes a large value, correlation is less likely to occur in the signal processing means except at the timing of the true target distance, and the tolerance for measurement error increases, resulting in a distance measurement result. It is possible to obtain a distance measuring device using the multi-PRF method in which the occurrence of large errors is small.

According to the second aspect of the invention, in the first and second transmission / reception steps, the first and second transmission signals are determined when the repetition cycle of the first and second transmission signals is determined. The steps are configured to determine the priority order so that the greatest common divisor of the repetition cycle becomes a large value, and during distance measurement, correlation is less likely to occur except at the timing of the true target distance, and measurement error tolerance It is possible to obtain a distance measuring method using the multi-PRF method in which the frequency is increased and a large error does not occur in the distance measuring result.

According to the third aspect of the invention, when the repeat cycle of the first transmission signal is set to n ₁ in the first transmission / reception step, the j-th (j = 2, ..., J) In the transmission / reception step of, the repetition cycle of each transmission signal used in the first to (j−1) th transmission / reception steps (j = 2, ..., J) is n ₁ , n ₂ , ..., N _{(j-1 )} , The least common multiple thereof is represented by LCM _(j-1) , and the above LCM _(j-1) and n _j
When the greatest common divisor of GCM (LCM _(j-1) , n ₂ ) is represented, the integer n _j is preferentially used in _descending order of the GCM (LCM _(j-1) , n _j ), The steps are configured so as to determine the repetition cycle of the transmission signal of j, and during distance measurement, correlation is less likely to occur at timings other than the timing of the true target distance, the tolerance for measurement error increases, and the distance measurement result increases. It is possible to obtain a distance measuring method using the multi-PRF method in which a large error does not occur.

According to the fourth aspect of the invention, the greatest common divisor of the repeating cycles n ₁ and n ₂ is GCM (n ₁ , n ₂ )
In the first transmission / reception step, the function [GCM (GCM (is sent to each of the set of the repetition cycle n ₂ of the second transmission signal selectable for the repetition cycle n _{1 of the first} transmission signal. n ₁ , n
_{2) / (n 1 + n} 2)] expected value with priority using n ₁ in descending order, followed, in a second transceiver step, Repetitive of the first transmission signal used in the first transmission and reception step For the return cycle n ₁ , the function [GCM (n ₁ , n ₂ ) / (n ₁ +
n _2)] value is an n ₂ preferentially used in high order, each constitute a step to determine the repetition period of the first and second transmission signals, at the time of distance measurement, the true target It is possible to obtain a distance measuring method using the multi-PRF method in which a correlation is less likely to occur at a timing other than the distance timing, a tolerance for a measurement error is increased, and a large error does not occur in a distance measurement result.

Further, according to the invention of claim 5, in the first transmitting / receiving step, the repeating cycle of the first transmission signal is set to n ₁ and the first transmission signal and the first reception signal are combined. With the upper limit of the magnitude of the time difference measurement error being σ ₁ , the first target existing area in the range of ± σ ₁ from each echo center of the first received signal is calculated, and then in the j-th transmission / reception step, Let n _{j be} the repetition cycle of the transmission signal of j (j = 2, ..., J), and let σ _{j be} the upper limit of the time difference measurement error between the j-th transmission signal and the j-th reception signal. , A signal in the range of ± σ _j from each echo center of the j-th received signal is calculated as the j-th target existing area, and the target existing areas of the first to j-th received signals are correlated to obtain the above correlation. When the processed target existing area is narrowed down to one, the target distance is calculated using the above correlation signal. Configure step, multi that during distance measurement, even if there is a measurement error in the timing of the received signals, for margin sigma _j, hardly occur disappearance of the peak of the correlation signal, it is possible to reliably calculate the target distance PR
A distance measuring method using the F method can be obtained.

According to the invention of claim 6, in the first transmitting / receiving step, the repeating period n ₁ of the first transmission pulse is determined, and the time difference between the first transmission pulse and the first reception pulse is determined. The upper limit of the magnitude of the measurement error is calculated by the following equation using a predetermined proportional constant a that does not depend on the pulse width τ ₁ of the first transmission pulse, the signal power to noise power ratio SNR _{1 of} the first reception pulse, and j. And ± σ ₁ from the echo center of the first received pulse
The first target existence area in the range of σ ₁ = a [τ ₁ / (SNR ₁ ) ^1/2 ] is similarly calculated in the j-th transmission / reception step.
, J), the repeating period n _j of the transmission pulse is determined, and the upper limit value of the time difference measurement error between the j-th transmission pulse and the j-th reception pulse is defined as The j-th target existence area in the range of ± σ _j from the echo center is calculated. _{σ j = a · [τ j} / (SNR j) 1/2] Furthermore, correlates target existence region of the received pulses of the first through j, target presence region after the correlation processing is narrowed down to one When configured, the step is configured to calculate the target distance using the peak of the correlation signal, and even if there is a measurement error in the timing of the received pulse, because of the margin σ _j ,
It is possible to obtain a distance measuring method using the multi-PRF method, in which the peak of the correlation signal hardly disappears and the target distance can be calculated reliably.

According to the invention of claim 7, the candidate of the repetition cycle T ₂ of the second transmission pulse is TC ₂ ,
Before the second transmission pulse is transmitted, each echo center time B _m of the first reception pulse is obtained, the remainder MB _m of B _m with respect to TC ₂ is obtained, and the second MB _{m according} to Eclipse is calculated from MB _m .
Calculated power loss EC _m reception pulse, average determined for m of EC _m, the average value is smaller TC ₂ of the EC _m
Is configured to be used for the repetition period T ₂ of the second transmission pulse with priority, and the expected value of Eclipse is reduced when the second reception pulse is received. Since the number of times the cycle T ₂ is switched is reduced, it is possible to obtain a distance measuring method using the multi-PRF method that can determine the target distance by observing in a shorter time.

Further, according to the invention of claim 8, the candidate of the repetition cycle T ₂ of the second transmission pulse is TC ₂ , and
Before the second transmission pulse is transmitted, each echo center time B _m of the first reception pulse is obtained, the surplus MB _m of B _m with respect to TC ₂ is obtained, and the reception gate of the distance discretization from MB _m is received. calculated power PG _m, determine the average in the m of PG _m, constitutes a step to use the repetition period T ₂ of the average value is large TC ₂ of the PG _m with priority second transmission pulse, By increasing the expected value of the gate reception power at the time of receiving the second reception pulse, the number of times the repetition cycle T ₂ of the second transmission pulse is switched is reduced, so that the target distance can be determined by observing in a shorter time. A ranging method using the PRF method can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a distance measuring device using a multi-PRF method showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing a distance measuring method using a multi-PRF method showing a second embodiment of the present invention.

FIG. 3 is a flowchart illustrating an example of creating a reference table to be referred to in a second embodiment.

FIG. 4 is a diagram illustrating that the error tolerance increases when the greatest common denominator is increased in the second embodiment.

FIG. 5 is a flowchart illustrating an example of creating a reference table used for reference in a third embodiment.

FIG. 6 is a flowchart showing a distance measuring method using the multi-PRF method according to Examples 4 and 5 of the present invention.

FIG. 7 is a flowchart showing a distance measuring method using the multi-PRF method according to Examples 4 and 5 of the present invention. (Continued from Fig. 6)

FIG. 8 is a timing chart illustrating a distance measuring method using the multi-PRF method according to the fourth and fifth embodiments of the present invention.

FIG. 9 is a flowchart showing a distance measuring method using a multi-PRF method showing a sixth embodiment of the present invention.

FIG. 10 is a diagram illustrating that the observation time until the distance is determined can be shortened by reducing the influence of eclipse in the sixth embodiment.

FIG. 11 is a flowchart showing an example of the process of step 1001 of FIG.

FIG. 12 is a flowchart showing a distance measuring method using the multi-PRF method according to the seventh embodiment of the present invention.

FIG. 13 is a diagram illustrating that the observation time until the distance is determined can be shortened by increasing the reception power of the reception gate used in the distance discretization in the seventh embodiment.

14 is a flowchart showing an example of the processing of step 1301 in FIG.

FIG. 15 is a configuration diagram showing a distance measuring device using a conventional multi-PRF method.

FIG. 16 is a schematic flowchart showing a distance measuring method using the multi-PRF method.

FIG. 17 is a timing chart explaining the principle of a distance measuring method using the multi-PRF method.

FIG. 18 is a timing chart explaining a measurement error and a distance measurement error of a conventional distance measuring method using a multi-PRF method.

[Explanation of symbols]

 251 Transmitter 252 Receiver 253 Transmission / Reception Switch 254 Antenna 256 MTI Filter 257 Distance Correlation Circuit 258 Signal Processor 1601 Reference Signal Generator 1602 PRI Reference Table

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Okamura 5-1-1 Ofuna, Kamakura-shi Electronic Systems Research Laboratories, Mitsubishi Electric Corporation (72) Inventor Tetsuro Kirimoto 5-1-1 Ofuna, Kamakura-shi Mitsubishi Electric (72) Inventor Toshiki Ozaki 325 Kamimachiya, Kamakura City Mitsubishi Electric Corporation Kamakura Factory

Claims (8)

[Claims] 1. A range finder using the multi-PRF method, comprising the following components (a), (b) and (c), wherein the repetition period of a transmission signal is an integer n _j (j = 1, 2) and the unit time Δ (hereinafter, the repeating period is represented by an integer n _j ). (A) When determining the repeating period of the first transmission signal, The greatest common divisor GCM of the set of the repetition cycle n ₂ of the second transmission signal selectable with respect to the repetition cycle n ₁ .
N ₁ is preferentially used in the order of higher expected value of (n ₁ , n ₂ ), and then n is used as the repetition cycle of the first transmission signal in determining the repetition cycle of the second transmission signal. ₁
With respect to the second transmission signal, the transmitting means for preferentially using n ₂ in the order of the greatest common divisor of the set of the repetition period n ₂ of the _second transmission signal; (C) signal processing means for calculating the target distance using the correlation signal of the first and second received signals which is the reflected wave of the first and second transmitted signals. 2. A distance measuring method using a multi-PRF method, characterized by comprising the following steps (a), (b) and (c), wherein the repetition period of a transmission signal is an integer n _j (j = 1). , 2) and the unit time Δ (hereinafter, the repetition period is represented by an integer n _j ), (a) the second transmission selectable with respect to the repetition period n ₁ of the first transmission signal. The greatest common divisor GC of a set of signal repetition period n ₂
The first transmission / reception step of determining the repetition cycle of the transmission signal by preferentially using n ₁ in the order of higher expected value of M (n ₁ , n ₂ ), (b) used in the first transmission / reception step greatest common divisor GCM (n ₁ with respect to repetition period n ₁ of the first transmission signal, n
₂ ) A second transmission / reception step in which n ₂ is preferentially used in descending order of the value of ₂ ) to determine the repetition cycle of the transmission signal, and (c) the reception signals obtained in the first and second transmission / reception steps. A signal processing step of calculating a target distance using the correlation signal. 3. A distance measuring method using a multi-PRF method, characterized by comprising the following steps (a), (b) and (c), wherein the repetition period of a transmission signal is an integer n _j (j = 1). , ..., J) and a unit time Δ (hereinafter, the repetition period is represented by an integer n _j ), (a) a first transmission / reception step in which the repetition period of the first transmission signal is n _1. , (B) Next, the repetition cycle of each transmission signal used in the first to (j−1) th transmission / reception steps (j = 2, ..., J) is set to n.
Let _l , n ₂ , ..., N _(j-1) be their least common multiples L
If CM _(j-1) is expressed as GCM (LCM _(j-1) , n ₂ ) and the greatest common divisor of LCM _(j-1) and n _j is expressed as GCM (LCM _(j-1) , n ₂ ),
The integers n _{j in the} descending order of CM (LCM _(j-1) , n _j )
, Which determines the repetition period of the transmitted signal by using
(J = 2, ..., J) transmission / reception step, (c) From the first transmission / reception step to the j-th (j = 2, ...
, J), the signal processing step of calculating the target distance using the correlation signal of the received signal obtained in each transmission / reception step. 4. A distance measuring method using a multi-PRF method characterized by comprising the following steps (a), (b) and (c), wherein the repetition period of a transmission signal is an integer n _j (j = 1). , 2) and the unit time Δ (hereinafter, the repeating period is represented by an integer n _j ), and the greatest common divisor of the repeating periods n ₁ and n ₂ is GCM.
(N ₁ , n ₂ ), and (a) a function [G] for a set of repetition cycles n ₂ of the second transmission signal selectable with respect to the repetition cycle n _{1 of the first} transmission signal.
CM (n ₁ , n ₂ ) / (n ₁ + n ₂ )], the first transmission / reception step in which n ₁ is preferentially used in descending order of the expected value to determine the repetition period of the transmission signal, (b) A function [GCM (n ₁ , n ₂ ) is applied to the repetition cycle n ₁ of the first transmission signal used in the first transmission / reception step.
/ (N ₁ + n ₂ )] in the descending order of the value, preferentially using n ₂ in the second transmission / reception step of determining the repetition period of the transmission signal, (c) in the first and second transmission / reception steps A signal processing step of calculating a target distance using the obtained correlation signal of the received signal. 5. A distance measuring method using a multi-PRF method, characterized by comprising the following steps (a), (b) and (c), wherein a repetition period of a transmission signal is an integer n _j (j = 1). , ..., J) and the unit time Δ (hereinafter, the repetition period is represented by an integer n _j ), (a) The repetition period n ₁ of the first transmission signal is determined, and
The target existence region width σ ₁ of the first reception signal, which is a reflected wave from the target of the transmission signal of _1, is determined, and the first target existence region in the range of ± σ ₁ from each echo center of the first reception signal is calculated. A first transmission / reception step, (b) determining the repeating cycle n _j of the j-th (j = 2, ..., J) transmission signal, and the j-th transmission signal that is a reflected wave from the target. The target existence area width σ _j of the received signal is determined, the jth target existence area in the range of ± σ _j from each echo center of the jth received signal is calculated, and the first to (j−1) th The j-th target presence / absence step for obtaining the correlation between the target existence area of the received signal of No. 1 and the target existence area of the j-th received signal, When the area shows one target existence area,
A signal processing step of calculating a target distance using the correlation signal. 6. A distance measuring method using a multi-PRF method, characterized by comprising the following steps (a), (b) and (c), wherein the repetition period of a transmission pulse is an integer n _j (j = 1). , ..., J) and the unit time Δ (hereinafter, the repeating period is represented by an integer n _j ), (a) The repeating period of the first transmission pulse is determined as n _1, and The target existence region width σ ₁ of the first reception pulse, which is a reflected wave from the target of the transmission pulse, is set to a value shown in (a1) below, and the first range of ± σ ₁ from each echo center of the first reception pulse is set. The first transmission / reception step of calculating the first target existence area, (a1) the pulse width of the first transmission pulse is τ ₁ , and the signal power of the first reception pulse which is a reflected wave from the target of the first transmission pulse Let SNR _{1 be the} noise power ratio, a be a suitable positive proportional constant, and σ ₁ be the following expression: σ ₁ = a · [τ ₁ / (SNR ₁ ) ^1/2 ] (b) The repeating period of the j-th (j = 2, ..., J) transmission pulse is determined as n _j, and the j-th reception pulse is a reflected wave from the target of the j-th transmission pulse. The target existence area width σ _{j of} is set to a value shown in (b1) below, and the j-th target existence area in the range of ± σ _j from each echo center of the j-th received pulse is calculated. j-1) a j-th transmission / reception step of obtaining a correlation between the target existence region of the received pulse up to j-1) and the target existence region of the j-th received pulse, (b1) the pulse width of the j-th transmitted pulse is τ _j , the j-th SNR _j is the signal power-to-noise power ratio of the j-th received pulse, which is the reflected wave from the target of the transmission pulse, and a is an appropriate positive proportional constant, and σ _j is the following equation: σ _j = a · [Τ _j / (SNR _j ) ^1/2 ] (c) The j-th target existence region after the correlation processing obtained in the j-th transmission / reception step is 1 When showing two target existence areas,
A signal processing step of calculating a target distance using the correlation signal. 7. A distance measuring method using a multi-PRF method, comprising the following steps (a), (b) and (c): (a) a first transmission having a repetition period T _1. The first transmission / reception step for obtaining the time difference X ₁ between the above-mentioned transmission pulse and the reception pulse which is the reflected wave from the target using a pulse, (b) The repetition cycle of the second transmission pulse is T ₂ , and the following ( By the b1) processing, the predicted loss power EC _m of the second received pulse due to eclipse is obtained, and the predicted loss power E
A second transmission / reception step in which a small average value of C _m for m is preferentially used for T ₂ , and a time difference X ₂ between the transmission pulse and the reception pulse is obtained, (b1) The candidate for T ₂ is set as TC _2. , M are positive integers, and the remainder MB _{m of} [X ₁ + (m−1) T ₁ ] with respect to TC ₂
And the predicted loss power EC _m of the second received pulse due to Eclipse is calculated from MB _m , and the predicted loss power EC _m
(C) A signal processing step of calculating a target distance by calculating the correlation between the received pulses obtained in the first and second transmission / reception steps. 8. A distance measuring method using a multi-PRF method, comprising the following steps (a), (b) and (c), and (a) a first transmission having a repetition period T _1. A first transmission / reception step in which a time difference X ₁ between the above-mentioned transmission pulse and a reception pulse which is a reflected wave from the target is obtained by using a pulse, using a distance discretization, (b) the repetition cycle of the second transmission pulse is T ₂ , the following (b1) process is used to preferentially use T ₂ for which the average value of m of the predicted reception power PG _m of the reception gate of the distance discriminator is larger than the transmission pulse and the target of the transmission pulse. Second transmission / reception step of obtaining a time difference X ₂ from the received pulse which is the reflected wave of (b1) The candidate of T ₂ is TC ₂ , m is a positive integer, and [X ₁ + (m-1) T ₁ ] MB _m for TC ₂ of
To obtain the predicted reception power PG _m of the reception gate of the distance discretion from MB _m and obtain an average value of PG _m with respect to m, (c) reception obtained in the first and second transmission / reception steps A signal processing step of obtaining a target distance by obtaining a pulse correlation.