JP2010096615A - Radar system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To observe a time change of the polarization characteristic of a detected signal by transmitting and receiving a plurality of pulses, and to determine a multipath wave and a direct wave, based on the amount of change thereof. <P>SOLUTION: This radar system includes two antennas 10 and 11 having polarization characteristics intersecting at right angles, a polarization switch 9 which drives either one of the two antennas in transmission and both of them in reception and collects a scattering vector of an observation object, a memory 13 which temporarily accumulates reception signals obtained by the transmission and reception of the plurality of pulses, a target detecting part 14 which detects a target signal by applying target detection processing to the reception signals read from the memory, a polarization degree calculating part 15 which calculates the degree of polarization of the detected target signal, and a polarization degree utilizing multipath determining part 16 which determines whether the detected target signal is obtained from the multipath wave or the direct wave, by using the value of the calculated degree of polarization. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radar apparatus for the purpose of discriminating between multipath waves and direct waves, and more particularly to a method for discriminating between multipath waves and direct waves using polarization information.

  When a target existing near the ground surface is observed using a radar, the target detection performance and target tracking performance of the radar deteriorate due to the influence of multipath waves generated on the ground surface. Therefore, a method for discriminating between direct waves and multipath waves from the target is required.

  Here, the definition of the direct wave and the multipath wave in this specification will be described. When considering the path from when the radio wave transmitted from the radar device is scattered and received by the target, the radio wave transmitted from the radar device to the direct wave path that reciprocates the straight path that connects the radar and the target After being scattered at the target, it is reflected again on the ground surface, or conversely, the wave path scattered on the target after being reflected at the ground surface is defined as a single-reflection multipath wave path, and the radio wave transmitted from the radar device is The path of the wave that is reflected by the target and then scattered by the target and then reflected again by the ground surface is defined as the path of the twice reflected multipath wave. In the following, the single reflection multipath wave and the double reflection multipath wave may be collectively referred to as a multipath wave.

  As a method of discriminating a multipath wave from a direct wave, there is a method of comparing the intensity of vertical polarization and horizontal polarization of a received wave and determining the presence of the multipath wave based on the magnitude relationship (for example, Patent Documents). 1).

JP 2000-28714 A

  However, the conventional method of comparing the intensity of the vertical polarization and horizontal polarization of the received wave and determining the presence of the multipath wave based on the magnitude relationship between the vertical polarization and the horizontal polarization causes the vertical polarization to be affected by the target polarization characteristics themselves. When there is a difference between the intensity and the intensity of horizontal polarization, there was a problem that multipath waves and direct waves could not be judged correctly.

  The present invention has been made to solve the above-described problem. A plurality of pulses are transmitted / received, a time change in the polarization characteristic of the detected signal is observed, and a multipath wave is based on the change amount. An object of the present invention is to obtain a radar apparatus capable of directly determining a wave.

  A radar apparatus according to the present invention includes two antennas having polarization characteristics orthogonal to each other, and drives either one of the two antennas for transmission and both for reception, A polarization switching device that collects the scattering vector of the signal, a memory that temporarily stores received signals obtained by transmitting and receiving a plurality of pulses, and a target detection process applied to the received signals read from the memory Using target detection means for detecting a signal, polarization degree calculation means for calculating the degree of polarization of the target signal detected by the target detection means, and the value of the degree of polarization calculated by the polarization degree calculation means And a degree-of-polarization multipath determination means for determining whether the target signal detected by the target detection means is a multipath wave or a direct wave.

  Alternatively, an entropy calculating unit that calculates an entropy of a target signal detected by the target detecting unit is provided instead of the degree of polarization calculating unit, and the entropy calculation is performed instead of the polarization degree using multipath determining unit. An entropy-based multipath determination unit that determines whether the target signal detected by the target detection unit is a multipath wave or a direct wave using the entropy value calculated by the unit.

  Alternatively, in place of the polarization degree calculation means, the apparatus includes a polarization channel correlation calculation means for calculating a correlation between polarization channels of the target signal detected by the target detection means, and uses the polarization degree multipath determination. Instead of the means, whether the target signal detected by the target detection means using the value of the correlation between polarization channels calculated by the correlation calculation means between the polarization channels is a multipath wave or a direct wave. Correlation using multipath determination means for determining is provided.

  According to the present invention, it is possible to transmit and receive a plurality of pulses, observe a temporal change in the polarization characteristics of the detected signal, and determine a multipath wave and a direct wave based on the change amount.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a radar apparatus according to Embodiment 1 of the present invention. The radar apparatus shown in FIG. 1 generates a pulse signal and radiates it from the first or second polarization transmitting / receiving antenna 10 or 11 to the space via the transmission / reception switch 8 and the polarization switch 9, and Of the first and second polarization transmitting / receiving antennas 10 and 11 having the polarization characteristics orthogonal to each other and the first and second polarization transmitting / receiving antennas 10 and 11, either one is used for transmission and both are used for reception. The polarization switch 9 that drives and collects the scattering vector to be observed, and the reception signals of the scattered waves received by the antennas 10 and 11 are received via the polarization switch 9 and the transmission / reception switch 8, respectively. The receiver 12, a memory 13 for temporarily storing signals obtained by transmitting and receiving a plurality of pulses, and an object for detecting the target signal by applying target detection processing to the received signal read from the memory 13 The detection unit 14, the polarization degree calculation unit 15 that calculates the degree of polarization of the signal detected by the target detection unit 14, and the target detection unit using the value of the polarization degree calculated by the polarization degree calculation unit 15 And a degree-of-polarization multipath determination unit 16 that determines whether the signal detected by 14 is a multipath wave or a direct wave.

  In FIG. 1, when the transmitter 7 generates a pulse signal, the transmission / reception switch 8 sends the pulse signal to the polarization switch 9. The polarization switch 9 drives the first polarization transmitting / receiving antenna 10 to radiate the pulse signal from the first polarization transmitting / receiving antenna 10 to the space. The pulse signal radiated into space is scattered by the observation target.

  When the polarization switching unit 9 drives both the first polarization transmitting / receiving antenna 10 and the second polarization transmitting / receiving antenna 11 and receives the scattered waves scattered by the observation target, the received signals of the scattered waves are received. Are sent to the receiver 12 via the transmission / reception switch 9. Here, the polarization characteristics of the first polarization transmitting / receiving antenna 10 and the second polarization transmitting / receiving antenna 11 are orthogonal to each other. Examples of combinations of orthogonal polarization characteristics in the first polarization transmitting / receiving antenna 10 and the second polarization transmitting / receiving antenna 11 include a combination of vertical polarization and horizontal polarization, and right-handed circular polarization and left-handed circular polarization. Combinations of these are possible.

The receiver 12 performs phase detection processing, A / D conversion processing, and range compression processing on each of the received signals of the scattered waves received by the first polarization transmitting / receiving antenna 10 and the second polarization transmitting / receiving antenna 11. , digital reception signal _X 1mn indicating the amplitude and phase of each received _signal, and outputs the _{X 2mn.} Output from the receiver 12 the received signal _{X 1mn, X 2mn} is transmitted to a memory 13, is temporarily stored. X _pmn is the p-th polarization channel (p = 1, 2, 3, 4, details will be described later) of the received signal of the mth (m = 0, 1,..., M−1) pulse. It is a value in the nth (n = 0, 1,..., N−1) range cell. Here, M is the number of pulses, and N is the number of range cells. The timing for transmitting and receiving M pulses will be described later.

Similarly, the pulse generated by the transmitter 7 is sent to the polarization switch 9 via the transmission / reception switch 8, and is irradiated to the observation target from the second polarization transmission / reception antenna 11. The reception signals X _3mn and X _4mn are obtained by repeating the same processing for the reception signals of scattered waves received by the first polarization transmission / reception antenna 10 and the second polarization transmission / reception antenna 11 by the receiver 12. . The received signals X _3mn and X _4mn output from the receiver 12 are sent to the memory 13 and temporarily stored.

  Here, the reception signal of the first polarization channel is a reception signal transmitted by the first polarization transmission / reception antenna 10 and received by the first polarization transmission / reception antenna 10, and the reception signal of the second polarization channel is: The received signal is transmitted by the first polarized wave transmitting / receiving antenna 10 and received by the second polarized wave transmitting / receiving antenna 11, and the received signal of the third polarization channel is transmitted by the second polarized wave transmitting / receiving antenna 11 and second received. The reception signal received by the polarization transmission / reception antenna 11 is defined as the reception signal of the fourth polarization channel, which is defined as the reception signal transmitted by the second polarization transmission / reception antenna 11 and received by the first polarization transmission / reception antenna 10.

FIG. 2 is a diagram for explaining the operation of the radar apparatus according to Embodiment 1 of the present invention, and shows the operation modes of the first polarization transmitting / receiving antenna 10 and the second polarization transmitting / receiving antenna 11 at each time. Interval in the figure, the received signal _{X 1mn, X 2mn, X 3mn} , a lump of processing required to obtain a set of _{X 4mn.} The interval time is T [seconds]. By repeating this interval M times, signals of each polarization channel are acquired for M pulses.

When the radar device has a monostatic configuration in which the positions of the transmitting and receiving antennas are equal, the fact that the received signals X2mn and X4mn are equal is described in the literature "Radar polarimetry for geoscience applications" (Ulaby et al., Artech House Inc., 1990). It is shown and is well known. Therefore, in the following description, the received signal _{X 4mn} without using the received signal _X 1mn three polarization _channels, X _{2mn, X 3 mn} only used. It should be noted that expansion in the case where the number of polarization channels is other than three is easy. The M pulse and N range cell signals of the polarization channel 3 channels acquired as described above are temporarily stored in the memory 13.

The target detection unit 14 _responds to the received signal X _pmn (p = 1, 2, 3; m = 0,..., M−1; n = 0,..., N−1) read from the memory 13. Then, the target signal is detected by applying the target detection process. The target detection processing is performed using, for example, CFAR processing described in the document “Radar signal processing” (edited by the Institute of Electronics, Information and Communication Engineers, Corona). Note that any method may be used as the target detection method in the target detection unit 14. The target detection unit 14 outputs a reception signal in the range cell nt where the target signal is detected. Hereinafter, the signal output from the target detection unit 14 is represented as S _pm (p = 1, 2, 3; m = 0,..., M−1). However, S _pm satisfies the relationship of the received signal X _pmn and the following equation (1).

The polarization degree calculator 15 calculates the degree of polarization using the signal _Spm output from the target detector 14. A procedure for calculating the degree of polarization will be described. First, a matrix M as shown in the following equations (2) and (3) is calculated from the received signal. A matrix such as M represents an average polarization characteristic of scattering of an observation target, and is called a Mueller matrix.

Next, an arbitrary incident polarization state is represented by a Stokes vector g _i , and a Stokes vector g _s representing a scattered polarization state when g _i is incident is calculated by the following equation (4).

The degree of polarization D (g _i ) is calculated from the Stokes vector g _s calculated as described above by the following equation (5). Incidentally, notation D (g _i) is derived from the degree of polarization is a function of the incident polarization state g _i.

If there is no change in the polarization characteristics of the target signal for M pulses, the degree of polarization D (g _i ) calculated here takes a maximum value of 1. If polarization characteristics change for each pulse, Henhado D (g _i) takes a value from 0 to less than 1, the larger the degree of change, the value of Henhado D (g _i) is smaller Become. The polarization degree calculator 15 outputs the polarization degree D (g _i ) calculated as described above.

Here, as the incident polarization state g _i, an arbitrary state may be selected, but a plurality of states may be set. In that case, the degree of polarization is calculated for each incident polarization state. Therefore, for example, when H states of g _i1 , g _i2 ,..., G _iH are set as the incident polarization states, the polarization degree calculation unit 15 performs polarization corresponding to each incident polarization state. Degrees D (g _i1 ), D (g _i2 ),..., D (g _iH ) are output.

  Details regarding the definition of the Mueller matrix, Stokes vector, polarization degree, etc. are detailed in the document “Radar polarimetry for geoscience applications” (Ulaby et al., Artech House Inc., 1990).

The degree of polarization D (g _ih ), (h = 1, 2,..., H) output from the degree of polarization calculation unit 15 is sent to the degree-of-polarization multipath determination unit 16. The polarization degree using multipath determination unit 16 compares the value of the input polarization degree D (g _ih ) with a preset threshold value. In the following description, the number of incident polarization states set in the polarization degree calculation unit 15 is one (H = 1) and a plurality (H> 1).

When H = 1, the input polarization degree is one value of D (g _i1 ). By comparing this with a preset threshold value T (g _i1 ), a determination is made as follows.
D (g _i1 ) <T (g _i1 ) ⇒ Multipath wave D (g _i1 ) ≧ T (g _i1 ) ⇒ Direct wave

  In the case of H> 1, since there are a plurality of input polarization degree values, the average value of the input polarization degrees is compared with the threshold value T as follows.

  Alternatively, once a determination is made for each incident polarization state, a final determination is made by majority vote or the like. In this case, the number of incident polarization states is desirably an odd number.

[Number of incident polarization states satisfying D (g _ih ) <T (g _ih )]
> [Number of incident polarization states satisfying D (g _ih ) ≧ T (g _ih )] ⇒ Multipath wave [Number of incident polarization states satisfying D (gih) <T (gih)]
≦ [Number of incident polarization states satisfying D (g _ih ) ≧ T (g _ih )] ⇒ Direct wave

  As is apparent from the above, according to the radar apparatus according to the first embodiment of the present invention, a direct wave and a multipath wave are determined based on the amount of change in the polarization characteristic between them by transmitting and receiving a plurality of pulses. Therefore, when the direct wave and the multipath wave are discriminated using the polarization information, there is an effect that the influence of the target polarization characteristic can be reduced.

  That is, since the multipath wave is reflected a plurality of times between the target and the surrounding environment, it is expected that the amount of time change of the polarization characteristic is larger than that of the direct wave. Therefore, the influence of the target polarization characteristic itself can be reduced by determining that a signal having a relatively large amount of time change is due to a multipath wave.

Embodiment 2. FIG.
FIG. 3 is a block diagram showing a configuration of a radar apparatus according to Embodiment 2 of the present invention. In FIG. 3, the same parts as those shown in FIG. 3 differs from the configuration shown in FIG. 1 in that an entropy calculation unit 17 that calculates the entropy of the signal detected by the target detection unit 14 is provided instead of the polarization degree calculation unit 15, and the degree of polarization is used. Instead of the multipath determination unit 16, an entropy-based multiplayer that determines whether the signal detected by the target detection unit 14 is a multipath wave or a direct wave using the entropy value calculated by the entropy calculation unit 17. The path determination unit 18 is provided.

The entropy calculation unit 17 calculates the entropy amount using the signal _Spm output from the target detection unit 14. The entropy amount is an amount that takes a real value between 0 and 1, and is an index for achieving variation in the polarization characteristics of the detected signal. The entropy calculation procedure in the entropy calculation unit 17 will be described. First, the following covariance matrix C is calculated from the received signal.

Next, eigenvalue decomposition of the covariance matrix C is performed to calculate _three eigenvalues λ ₁ , λ ₂ , and λ ₃ . Using these eigenvalues, entropy H is calculated by the following equation.

  The entropy calculation unit 17 outputs the entropy H calculated as described above. The closer the entropy value is to 1, the greater the time change of the polarization characteristics of the detected signal. Further, when the entropy is 0, it means that there is no time change of the polarization characteristic. The output entropy H is sent to the entropy utilization multipath determination unit 18. The entropy utilization multipath determination unit 18 compares the input entropy H with a preset threshold value T and performs determination as follows.

H> T⇒ Multipath wave H ≦ T⇒ Direct wave

  As is apparent from the above, according to the radar apparatus of the second embodiment of the present invention, a plurality of pulses are transmitted and received, and direct waves and multipath waves are determined based on the amount of change in polarization characteristics between them. Therefore, when the direct wave and the multipath wave are discriminated using the polarization information, an effect of reducing the influence of the target polarization characteristic is obtained.

Embodiment 3 FIG.
FIG. 4 is a block diagram showing a configuration of a radar apparatus according to Embodiment 3 of the present invention. 4, parts that are the same as the parts shown in FIG. 1 are given the same reference numerals, and explanation thereof is omitted. 4 differs from the configuration shown in FIG. 1 in that a polarization channel correlation calculation unit 19 calculates a correlation between polarization channels of a signal detected by the target detection unit 14 instead of the polarization degree calculation unit 15. And the signal detected by the target detection unit 14 using the value of the correlation between polarization channels calculated by the correlation calculation unit 10 between polarization channels instead of the multipath determination unit 16 using the polarization degree A correlation-use multipath determination unit 20 is provided for determining whether a path wave or a direct wave is used.

The polarization channel correlation calculation unit 19 calculates the correlation between the polarization channels using the signal Spm output from the target detection unit 14. The correlation between the polarization channels is an amount that takes a real value between 0 and 1, and is an index for achieving variation in the polarization characteristics of the detected signal. In the polarization channel correlation calculation unit 19, the polarization channel correlation Z _pq is calculated by the following equation.

The polarization channel correlation calculation unit 19 outputs the polarization channel correlation Z _pq calculated as described above. It shows that the time change of the polarization characteristic of the detected signal is so large that the value of the correlation between polarization channels is near zero. Further, when the polarization channel correlations Z ₁₂ , Z ₁₃ , and Z ₂₃ are all 1, it means that there is no temporal change in the polarization characteristics. The output polarization channel correlation Zpq is sent to the correlation use multipath determination unit 20. The correlation-use multipath determination unit 20 compares the input polarization channel correlation Z _pq with a preset threshold value T _pq and performs the determination as follows, for example.

Z ₁₂ <T ₁₂ and Z ₁₃ <T ₁₃ and Z ₂₃ <T ₂₃ ⇒ multipath wave Z ₁₂ ≧ T ₁₂ or Z ₁₃ ≧ T ₁₃ or Z ₂₃ ≧ T ₂₃ ⇒ direct wave

Note that cross-polarization component intensity in consideration that generally lower, may be used to determine only the Z _23. In this case, the determination is performed as follows.

Z ₁₃ <T ₁₃ ⇒ Multipath wave Z ₁₃ ≧ T ₁₃ ⇒ Direct wave

  As is apparent from the above, according to the radar apparatus of the third embodiment of the present invention, a plurality of pulses are transmitted and received, and direct waves and multipath waves are determined based on correlation values between polarization channels between them. Therefore, when the direct wave and the multipath wave are discriminated using the polarization information, an effect of reducing the influence of the target polarization characteristic is obtained.

  As described above, the present invention can discriminate between a multipath wave and a direct wave signal in a radar reception signal. In particular, a target such as a vehicle or an aircraft exists near the ground surface, and a multipath occurs. It is suitable for application to a radar apparatus that detects and tracks a target in an easy environment.

It is a block diagram which shows the structure of the radar apparatus by Embodiment 1 of this invention. It is a figure explaining operation | movement of the radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the structure of the radar apparatus by Embodiment 2 of this invention. It is a block diagram which shows the structure of the radar apparatus by Embodiment 3 of this invention.

Explanation of symbols

  7 transmitter, 8 transmission / reception switch, 9 polarization switch, 10 first polarization transmission / reception antenna, 11 second polarization transmission / reception antenna, 12 receiver, 13 memory, 14 target detection unit, 15 calculation of polarization degree Unit, 16 polarization degree use multipath determination unit, 17 entropy calculation unit, 18 entropy use multipath determination unit, 19 polarization channel correlation calculation unit, 20 correlation use multipath determination unit.

Claims (6)

Two antennas having polarization characteristics orthogonal to each other;
Of the two antennas, one of the two antennas is driven for transmission and the other is driven for reception to collect a scattering vector to be observed;
A memory for temporarily storing received signals obtained by transmitting and receiving a plurality of pulses;
Target detection means for detecting a target signal by applying target detection processing to the received signal read from the memory;
A degree of polarization calculating means for calculating the degree of polarization of the target signal detected by the target detecting means;
Polarization degree-based multipath determination for determining whether the target signal detected by the target detection means is a multipath wave or a direct wave using the polarization degree value calculated by the polarization degree calculation means A radar apparatus comprising: means. The radar apparatus according to claim 1, wherein
The radar apparatus according to claim 1, wherein the polarization degree calculating means sets a plurality of incident polarization states and calculates a polarization degree corresponding to each incident polarization state. The radar apparatus according to claim 2, wherein
When the average value of the polarization degree corresponding to the plurality of incident polarization states calculated by the polarization degree calculation unit is smaller than a predetermined threshold, A radar apparatus, wherein the target signal detected by the detecting means is determined to be due to a multipath wave. The radar apparatus according to claim 2, wherein
The polarization degree using multipath determination means compares the polarization degrees corresponding to a plurality of incident polarization states calculated by the polarization degree calculation means with a predetermined threshold value and is a number when the polarization degree is smaller than the threshold value. When the number exceeds the number of cases where the value is larger than the threshold, it is determined that the target signal detected by the target detection means is due to a multipath wave. Two antennas having polarization characteristics orthogonal to each other;
Of the two antennas, one of the two antennas is driven for transmission and the other is driven for reception to collect a scattering vector to be observed;
A memory for temporarily storing received signals obtained by transmitting and receiving a plurality of pulses;
Target detection means for detecting a target signal by applying target detection processing to the received signal read from the memory;
Entropy calculating means for calculating entropy of the target signal detected by the target detecting means;
A radar comprising entropy-use multipath determination means for determining whether the target signal detected by the target detection means is a multipath wave or a direct wave using the entropy value calculated by the entropy calculation means apparatus. Two antennas having polarization characteristics orthogonal to each other;
Of the two antennas, one of the two antennas is driven for transmission and the other is driven for reception to collect a scattering vector to be observed;
A memory for temporarily storing received signals obtained by transmitting and receiving a plurality of pulses;
Target detection means for detecting a target signal by applying target detection processing to the received signal read from the memory;
A polarization channel correlation calculating means for calculating a correlation between polarization channels of the target signal detected by the target detection means;
Correlation-based multi-use that determines whether the target signal detected by the target detection means is a multipath wave or a direct wave using the value of the correlation between polarization channels calculated by the correlation calculation means between the polarization channels A radar apparatus comprising: path determination means.

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