JP5601881B2 - Passive radar system and passive radar method - Google Patents

Description

  The present invention does not transmit radio waves by itself and receives scattered waves generated when radio waves that already exist around itself (existing radio waves) hit a moving target, while radio wave sources of radio waves that already exist A passive radar system and a passive radar that receive a direct wave coming directly from the satellite and locate the position of the moving target based on the arrival time difference between the scattered wave and the direct wave, the Doppler frequency difference, and the angle measured by the own array antenna It is about the method.

  FIG. 10 is an internal configuration diagram of a conventional passive radar device (see, for example, Patent Document 1). The conventional passive radar device 100 in FIG. 10 includes a first antenna 11a to 11d, a second antenna 11e, a first receiver 13a to 13d, a second receiver 13e, and a first A / D converter 14a. To 14d, a second A / D converter 14e, a first storage unit 15a, a second storage unit 15b, a cross-correlation calculating unit 16, and a target locating unit 17. Moreover, the array antenna 12 is comprised by the 1st antennas 11a-11d.

  The passive radar device 100 receives the scattered wave 1 and the direct wave 2. The scattered wave 1 is received by the first receivers 13a to 13d via the array antenna 12 having the first antennas 11a to 11d, and A / D conversion is performed by the first A / D converters 14a to 14d. And stored in the first storage unit 15a in association with the numbers (element numbers) of the first antennas 11a to 11d included in the array antenna 12.

  On the other hand, the direct wave 2 is received by the second receiver 13e via the second antenna 11e, A / D converted by the second A / D converter 14e, and stored in the second storage unit 15b. The Here, the second antenna 11e, the second receiver 13e, and the second A / D converter 14e are respectively a first antenna 11a to 11d, a first receiver 13a to 13d, and a first A. This has the same function as the / D converters 14a to 14d.

Next, a general target orientation principle of a conventional passive radar device will be described.
The scattered wave 1 arrives at the passive radar device 100 when the radio wave transmitted from the radio wave source hits the target. Therefore, although it has the same waveform specifications as compared with the direct wave arriving at the passive radar device 100 directly from the radio wave source, the arrival time is delayed.

  When the target is moving, the frequency of the radio wave hitting the moving target is shifted according to the moving speed of the target. This is called a Doppler frequency difference. The cross-correlation calculating means 16 in the passive radar device 100 uses the time series data of the scattered wave 1 stored in the storage unit 15a and the time series data of the direct wave 2 stored in the storage unit 15b, using the following formula ( The calculation related to the evaluation function 1) is performed.

Here, each symbol in the above formula (1) means the following.
s (t): scattered wave reception signal d (t): direct wave reception signal t: A / D converter sample number T: number of data samples used in one observation frame P: evaluation function τ: scattered wave reception signal Arrival time difference between s (t) and direct wave reception signal d (t) Δf: Doppler frequency difference between scattered wave reception signal s (t) and direct wave reception signal d (t)

  As described above, when the arrival time difference is τ, the evaluation function takes a maximum value of s (t) × d (t−τ). At the same time, in order to correct the Doppler frequency difference of the scattered wave 1, in the above equation (1), correction is performed by exp (−j2πΔft). In this case, it is assumed that the moving target remains at a certain fixed point during the observation time t = 1 to T.

  FIG. 11 is an explanatory diagram showing the search range of the evaluation function in the cross-correlation calculating means 16 of the conventional passive radar device. Since the cross-correlation calculating means 16 scans within the range of the estimated arrival time difference τ and the Doppler frequency difference Δf with respect to the evaluation function of the above equation (1), a two-dimensional full-scale search is performed as shown in FIG. Necessary. As a result, a large amount of computation must be processed.

  FIG. 12 is an explanatory view showing an example of the calculation result of the evaluation function in the cross correlation calculation means 16 of the conventional passive radar device as a three-dimensional graph. As shown in FIG. 12, first, many reactions with a Doppler frequency difference = 0 are observed. This is due to reflection by a fixed object such as a mountain or an artificial building, and corresponds to an obstacle (fixed clutter) when viewed from a radar device that targets a moving target.

It should be noted that a peak other than Doppler frequency difference = 0 can be seen in a portion surrounded by a dotted-line ellipse in FIG. This is a reaction by the moving target that is the target of orientation, and the arrival time difference τ ₁ and the Doppler frequency difference Δf ₁ with respect to the moving target can be obtained from this peak position.

Next, the operation of the target locating means 17 will be described. FIG. 13 is an operation image diagram of a conventional passive radar system. Specifically, the method of locating the moving target 30 by the target locating means 17 in one passive radar device 100 is illustrated. The target locating unit 17 generates a candidate having a target from the arrival time difference τ ₁ obtained by the cross correlation calculating unit 16.

Here, in order to simplify the explanation, this problem is considered on a two-dimensional plane. In general, since the positions of the radio wave source 20 and the passive radar device 100 are known, candidates for which the arrival time difference is τ ₁ are limited to an ellipse with the position of the radio wave source 20 and the passive radar device 100 as a focal point. This ellipse is called an equidistant ellipse.

  Finally, the intersection of the equidistant ellipse and the arrival direction is specified as the estimated position of the moving target 30 by obtaining the arrival direction of the scattered wave 1 from the measured angle value by the array antenna 12 provided in the passive radar device 100. Is done.

JP 2008-134256 A

However, the prior art has the following problems.
In the conventional passive radar device, the information of the Doppler frequency difference Δf ₁ output from the cross-correlation calculating means 16 is used only to separate the moving target from the fixed clutter in FIG. The speed specifications (movement speed, direction, etc.) of the movement target are obtained only from the rate of change of position in a plurality of observation frames (corresponding to the speed calculation formula in Table 3 of Patent Document 1). Therefore, the speed specification of the moving target obtained in the conventional technique is an average moving vector derived from positions in a plurality of frames, and an instantaneous speed vector cannot be obtained.

  In general, radio wave sources when passive radar devices are operated are fair to all-round users (viewers) such as FM broadcast waves, analog television broadcast waves, digital television broadcast waves, and mobile phone base station radio waves. In most cases, the transmission antenna of the radio wave source is omnidirectional so that the radio wave can reach. In this case, since the transmission power is regulated to a certain value, the energy is dispersed all around.

  Therefore, a radar device (referred to as a monostatic radar device in a narrow sense) that can transmit the transmission energy in a concentrated manner by changing the characteristics of the antenna provided for itself in a specific direction or region. The power concentration effect (transmitting antenna directivity gain) cannot be obtained.

  For this reason, passive radar equipment has extremely low reflected power from a moving target that exists in a specific direction or region compared to radar equipment that can transmit its transmission energy in a concentrated manner. A method of gaining integral gain using is essential.

  On the other hand, in order to obtain long-time observation data and obtain an efficient integral gain, it is necessary to estimate the instantaneous velocity vector (moving velocity and direction at that moment) of the moving target. This is because even if it is assumed that the moving target remains at a fixed point in one observation frame data t = 1 to T, if this is performed in a plurality of observation frames (that is, long-time observation), This is because this assumption does not hold.

  That is, the position of the moving target changes from the first observation frame to the last observation frame. For example, in the case of a civil aircraft moving at a speed of 300 m / sec, the change in position for an observation frame of 1 msec is 0.3 m.

However, if this observation frame is repeated 1000 times and equivalent to observation for 1 second as a whole, the change in position of the moving target at the beginning and end of the observation increases to 300 m. If the conversion speed of the A / D converter 14 in the passive radar device 100 is 100 MHz, one range bin is 1 / (100 × 10 ⁶ ) × light velocity≈3 m. For this reason, a single observation frame of 1 msec fits within one range, but the entire observation of 1 second actually moves about 100 range bins. This is called a range walk.

Next, I will explain why it is inconvenient if there is a range walk.
Assume that the evaluation function P is obtained from the above equation (1) using observation time series data for 1 second. At this time, since the moving target does not continue to exist at the same position, the arrival time difference τ ₁ of the scattered wave s (t) changes every moment.

On the other hand, the value of the evaluation function P obtained by applying the direct wave d (t−τ) is dispersed from τ ₁ (1) at the start of observation to τ ₁ (T) at the end, and t = 1. The integration effect of ~ T will be weakened. As a result, the reaction of the movement target obtained as a peak in FIG. 12 becomes a low peak or a gentle hill shape.

  This may be buried in the floor noise of FIG. 12 depending on the observed S / N ratio of the environment and the scattering cross section (RCS) of the moving target, and the moving target cannot be detected. It means the problem of end.

  The present invention has been made to solve the above-described problems. The sharpness of the evaluation function P does not deteriorate even during long-time integration, and the movement of the low RCS such as in a low S / N environment or a stealth target is achieved. An object of the present invention is to obtain a passive radar system and a passive radar method that can improve detection / location accuracy even for a target.

The passive radar system according to the present invention includes a first antenna that receives a scattered wave generated when an existing radio wave hits a moving target without radiating the radio wave, and a plurality of first antennas. An array antenna composed of antennas, a plurality of first receivers that are individually provided for each element of the array antenna, and that extract signals in a desired frequency band from the received signals of the array antenna, and a plurality of first receptions A plurality of first A / D converters for converting each of the output signals of the unit into digital data, and time series data output by the plurality of first A / D converters are associated with the element numbers of the array antenna. A first storage unit that is stored, a second antenna that receives a direct wave from a radio wave source that transmits an existing radio wave, and a signal in a desired frequency band from a reception signal of the second antenna A second receiver to be extracted, a second A / D converter that converts the output signal of the second receiver into digital data, and time-series data output from the second A / D converter are stored. It is assumed that the time-series data for the number of elements read from the second storage unit and the first storage unit is the same time-series data read from the second storage unit as two variables of time and frequency. Cross-correlation is calculated by searching the entire range to calculate cross-correlation, and the arrival time difference and Doppler frequency difference with respect to the moving target are specified as observation information, observation information output from the cross-correlation calculation means, and angle measurement by the array antenna A passive radar system comprising a plurality of passive radar devices arranged at different positions and having target locating means for obtaining unknown parameters such as position, altitude and angle of a moving target using value information. Each of the passive radar devices transmits the observation information specified by its own cross-correlation calculation means to other passive radar devices and receives the observation information specified by the cross-correlation calculation means of the other passive radar devices. The apparatus further comprises communication means and instantaneous speed vector estimation means for estimating the instantaneous speed vector of the moving target based on the respective observation information specified by all the passive radar devices, and the cross-correlation calculation means is configured to estimate the instantaneous speed vector. Using the instantaneous velocity vector estimated by the means, predicting the presence position of the moving target in the next observation frame, calculating the arrival time difference and the Doppler frequency difference with respect to the moving target at the predicted existence position as second observation information; Match the calculated second observation information with the observation information specified for the current observation frame By performing such correction processing and specifying the second observation information after the correction processing as observation information in the next observation frame, observation information equivalent to a long-time cross-correlation calculation between frames is acquired. Is.

In addition, the passive radar method according to the present invention receives the scattered waves generated when the existing radio waves in the surrounding space of the self hit the moving target without radiating the radio waves via the array antenna. The direct wave from the radio wave source that transmits the signal is received via the antenna, the cross-correlation calculation processing is performed based on the scattered wave and the direct wave, and the arrival time difference and the Doppler frequency difference with respect to the moving target are specified as observation information. A passive radar method using a plurality of passive radar devices that calculate unknown parameters such as the position, altitude, and angle of a moving target using identified observation information and angle measurement value information from an array antenna. Obtaining observation information identified by cross-correlation calculation processing by a passive radar device via a communication means; That based on the respective observation information identified in all the passive radar system including observation information specified in the mutual correlation operation, estimating the instantaneous velocity vector of the moving target, which is estimated by estimating instantaneous Using the velocity vector, the location of the moving target in the next observation frame is predicted, the arrival time difference and the Doppler frequency difference with respect to the moving target at the predicted location are calculated as second observation information, and the calculated second observation By performing correction processing to match the information with the observation information specified for the current observation frame, and specifying the second observation information after the correction processing as observation information in the next observation frame, And a correction step for obtaining observation information equivalent to performing cross-correlation calculation over a long period of time .

  According to the passive radar system and the passive radar method of the present invention, long-time integration is performed by performing integration while estimating the instantaneous velocity vector of the moving target based on observation information from two or more passive radar devices. A passive radar system and a passive radar method capable of improving detection / positioning accuracy even for a low RCS moving target such as a low S / N environment or a stealth target without the sharpness of the evaluation function P being deteriorated sometimes. Can be obtained.

It is an operation | movement image figure of the passive radar system of Embodiment 1 of this invention. It is a figure which shows the internal structure of the passive radar apparatus of Embodiment 1 of this invention. It is a figure explaining the projection to the vector B of the instantaneous velocity vector v of a movement target. It is a figure which defines the arrangement | positioning and angle of each component in the passive radar system of Embodiment 1 of this invention. It is an operation | movement image figure of the passive radar system of Embodiment 2 of this invention. It is a figure explaining the integral gain improvement in the passive radar system of Embodiment 3 of this invention. It is a figure explaining performing integral gain improvement in a passive radar system of Embodiment 3 of the present invention to a plurality of observation frames. It is a figure explaining the execution content of the cross correlation calculation means of the passive radar apparatus of Embodiment 4 of this invention in contrast with FIG. It is a figure which shows the internal structure of the passive radar apparatus of Embodiment 5 of this invention. It is a figure which shows the internal structure of the conventional passive radar apparatus. It is the figure which imaged the execution content of the cross correlation calculation means of the conventional passive radar apparatus. It is an example of the calculation result output by the cross correlation calculation means of the conventional passive radar apparatus. It is an operation image figure of the conventional passive radar system.

  Hereinafter, preferred embodiments of a passive radar system and a passive radar method of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is an operation image diagram of the passive radar system according to Embodiment 1 of the present invention. The passive radar system illustrated in FIG. 1 illustrates a case where the passive radar system is configured to include two passive radar devices 10a and 10b, a radio wave transmission source 20, and a moving target 30. Compared with the configuration of FIG. 13 showing the conventional passive radar system, the configuration of FIG. 1 showing the passive radar system of the first embodiment is different in that it includes two passive radar devices 10a and 10b. The technical feature is that the instantaneous velocity vector v of the moving target 30 can be obtained by this configuration.

  The first passive radar device 10 a receives the scattered wave 1 a that the radio wave 3 transmitted from the radio wave transmission source 20 is scattered by the moving target 30 and the direct wave 2 a that directly arrives from the radio wave transmission source 20. . On the other hand, the second passive radar device 10b generates a scattered wave 1b in which the radio wave 3 transmitted from the radio wave transmission source 20 is scattered by the moving target 30 and a direct wave 2b that arrives directly from the radio wave transmission source 20. Receive.

The cross-correlation calculating means 16a in the first passive radar device 10a calculates the equidistant ellipse 40a obtained from the arrival time difference τ ₁ between the scattered wave 1a and the direct wave 2a as described in the prior art. Similarly, the cross correlation calculating means 16b in the second passive radar device 10b also calculates the equidistant ellipse 40b obtained from the arrival time difference τ ₂ between the scattered wave 1b and the direct wave 2b.

  FIG. 2 is an internal configuration diagram of the passive radar device according to the first embodiment of the present invention, and shows a configuration common to the first passive radar device 10a and the second passive radar device 10b shown in FIG. ing.

  The passive radar device 10 according to the first embodiment in FIG. 2 includes a first antenna 11a to 11d, a second antenna 11e, a first receiver 13a to 13d, a second receiver 13e, and a first A / A. D converters 14a to 14d, second A / D converter 14e, first storage unit 15a, second storage unit 15b, cross-correlation calculating unit 16, target locating unit 17, communication unit 18, and instantaneous velocity vector Estimating means 19 is provided. Moreover, the array antenna 12 is comprised by the 1st antennas 11a-11d.

  Compared with the configuration of FIG. 10 showing a conventional passive radar device, the configuration of FIG. 2 showing the passive radar device of the first embodiment further includes a communication means 18 and an instantaneous velocity vector estimation means 19. Is different. A technical feature is that the instantaneous velocity vector v of the moving target 30 can be obtained by this configuration. Therefore, the following description will focus on such a different configuration.

The communication means 18 is means for communicating the mutual observation information 4 between the first passive radar device 10a and the second passive radar device 10b. Here, the observation information 4 exchanged between the communication means 18a in the first passive radar device 10a and the communication means 18b in the second passive radar device 10b is the same between the passive radar devices 10a. 10b, corresponding to the information of the arrival time difference τ _m and the Doppler frequency difference Δf _m detected by the cross-correlation calculating means 16a, 16b in 10b (m represents the individual number of the passive radar device, where m = 1, 2) To do.

The instantaneous velocity vector estimation means 19 estimates the instantaneous velocity vector v of the moving target 30 using the arrival time difference τ _m and the Doppler frequency difference Δf _m which are observation information exchanged between the two passive radar devices 10a and 10b. To do.

Next, the instantaneous speed vector estimation operation will be described in detail.
The principle by which the conventional passive radar device 100 determines the position of the moving target 30 is as already described in the background art. However, in the prior art, among the passive radar system TDOA tau ₁ for the mobile target 30 detected by the cross-correlation calculation means 16 of the 100 and the Doppler frequency difference Delta] f _1, for the arrival time difference tau ₁ generates the equidistant ellipse 40 Used for.

On the other hand, the Doppler frequency difference Δf ₁ is used only for separating the moving target 30 having a Doppler frequency difference other than 0 from the fixed clutter in FIG. 12 representing the calculation result of the evaluation function P. . As for the speed specifications of the movement target 30, only the average movement vector obtained from the position change rate between a plurality of observation frames was obtained. On the other hand, in the present invention, the instantaneous velocity vector is obtained by utilizing both the arrival time difference τ and the Doppler frequency difference Δf.

  FIG. 3 is an explanatory diagram relating to the projection of the instantaneous velocity vector v of the moving target onto the vector B. As shown in FIG. 3, if the positions of the passive radar device 10, the radio wave transmission source 20, and the moving target 30 are known, the Doppler frequency difference Δf1 detected by the cross-correlation calculating means 16 in the passive radar device 10 is It can be expressed by the following formula (2) using the positional relationship.

Here, each symbol in the above formula (2) means the following.
v _x , v _y : X axis and Y axis element of the instantaneous velocity vector v of the moving target 30 λ: Transmission wavelength of the radio wave transmission source 20 β ₁ : Formed by the moving target 30, the radio wave transmission source 20, and the passive radar device 10. Angle of the vertex of the triangle with respect to the moving target 30 φ ₁ : Angle formed by the vector B and the X axis The vector B is generally referred to as a Biscientistic Detector.

On the right side of FIG. 3, a deformed vector diagram is shown so that the positional relationship and the angular relationship can be easily understood. Doppler frequency difference Delta] f ₁ observed in first unit of the passive radar device 10a, each element v _x of the instantaneous velocity vector v of the moving target _30, the v _y, the inner product of the projection (vector v and the vector B to vector B ).

Now, what is required here is to obtain the instantaneous velocity vector v of the moving target 30. In the above equation (2), λ is known. Further, the position of the moving target 30 is also known from the equidistant ellipse 40 based on the arrival time difference τ ₁ detected by the cross-correlation calculating means 16 and the angle measurement value of the array antenna 12. Therefore, if the positions of the radio wave transmission source 20 and the passive radar device 10 are measured in advance, β ₁ can be obtained by calculation.

If β ₁ is obtained, an angle φ ₁ formed with the X axis can also be obtained. Further, the Doppler frequency difference Δf ₁ is also obtained from the cross correlation calculating means 16. Then, the unknown variable is two elements v _x and v _y of the instantaneous velocity vector v. For two unknown variables, it cannot be solved by only one equation of the above equation (2).

  Therefore, as shown in FIG. 1, the passive radar system of the present invention uses the two passive radar devices 10a and 10b to increase the amount of observation information, thereby increasing the instantaneous velocity vector v of the moving target 30. It is possible to perform integration while estimating.

  FIG. 4 is a diagram for defining the arrangement and angle of each component in the passive radar system according to the first embodiment of the present invention. More specifically, it is a diagram showing the positional relationship and angular relationship of the first passive radar device 10a and the second passive radar device 10b, the radio wave transmission source 20, and the moving target 30.

  First, the observation equation of the above equation (2) is obtained by the first passive radar device 10a. Similarly, the second passive radar device 10b also obtains the observation equation (3) from the relationship shown in FIG.

In the above formula (3), λ is already known. Further, the position of the moving target 30 is also known from the equidistant ellipse 40b based on the arrival time difference τ ₂ detected by the cross-correlation calculating means 16b and the angle measurement value of the array antenna 12b. Therefore, if the positions of the radio wave transmission source 20 and the passive radar device 10b are measured in advance, β ₂ can be obtained by calculation.

If β ₂ is obtained, an angle φ ₂ formed with the X axis can also be obtained. Further, the Doppler frequency difference Δf ₂ is also obtained from the cross-correlation calculating means 16b. As a result, for the two unknown variables v _x and v _y , the number of equations is two, the above equation (2) and the above equation (3), so that the variable can be uniquely solved. In this way, the instantaneous velocity vector v of the moving target 30 can be obtained.

However, in order to make the two equations (2) and (3) simultaneous, the arrival time difference τ _m and the Doppler frequency difference detected by the cross-correlation calculation means 16a and 16b between the passive radar devices 10a and 10b. The information of Δf _m must be shared (m is the individual number of the passive radar device, where m = 1, 2). For this purpose, the two passive radar devices 10a and 10b of the present invention are provided with communication means 18 for exchanging observation information 4 with each other as shown in FIG.

  As described above, according to the first embodiment, the instantaneous velocity vector of the moving target can be estimated based on the observation information from the two passive radar devices. As a result, the sharpness of the evaluation function P does not deteriorate even during long-time integration, and the passive radar that can increase the detection / location accuracy even for a low RCS moving target such as a low S / N environment or a stealth target. A system and passive radar method can be obtained.

Embodiment 2. FIG.
FIG. 5 is an operation image diagram of the passive radar system according to Embodiment 1 of the present invention. The passive radar system shown in FIG. 5 illustrates a case where the passive radar system is configured to include three passive radar devices 10a, 10b, and 10c, a radio wave transmission source 20, and a moving target 30. Compared with the configuration of FIG. 1 showing the passive radar system of the first embodiment, the configuration of FIG. 5 showing the passive radar system of the second embodiment further includes a third passive radar device 10c. The difference is that the estimation accuracy of the instantaneous velocity vector is improved.

  The three passive radar devices 10a, 10b, and 10c in the second embodiment all have the same configuration, and the internal configuration is the same as that in FIG. 2 in the previous first embodiment. In the first embodiment, to simplify the description, it is assumed that the movement target 30, the radio wave transmission source 20, and the passive radar devices 10a and 10b are all on the same plane. However, actually, the moving target 30 is different from the radio wave transmission source 20 and the passive radar devices 10a and 10b installed on the land, and is flying at a certain altitude.

  Therefore, the second embodiment can be expanded to a more realistic three-dimensional problem by providing three passive radar devices 10a, 10b, and 10c, and will be described in detail below. explain.

First, the Doppler frequency difference Δf ₁ of the moving target 30 detected by the cross-correlation calculation means 16a in the first passive radar device 10a is expressed by the following equation (4) from the above equation (2) specialized for the two-dimensional problem. ).

Here, ψ ₁ is an elevation angle. Note that the equidistant ellipse 40a generated based on the arrival time difference τ ₁ output from the cross-correlation calculating means 16a becomes a three-dimensional ellipsoid when considered in terms of a three-dimensional problem. On the other hand, the position of the moving target 30 can be specified even on a three-dimensional curved surface by making both the horizontal angle and the elevation angle measurable by making the array antenna 12a a planar array. Become.

  Similarly, in the second passive radar device 10b and the third passive radar device 10c, the following observation equations (5) and (6) can be obtained.

In the above formulas (4) to (6), λ is known. Further, φ _m , β _m , and ψ _m can be obtained by the same method as in the first embodiment (m represents the individual number of the passive radar device, where m = 1, 2, 3). Therefore, there are three unknown variables: the elements v _x , v _y , and v _z of the instantaneous velocity vector v.

  For the three unknown variables, the number of equations is 3 in the above formulas (4) to (6), so that the variables can be uniquely solved. Therefore, even when extended in three dimensions, the instantaneous velocity vector v of the moving target 30 can be estimated by providing the three passive radar devices 10a, 10b, and 10c and exchanging observation information with each other.

  As described above, according to the second embodiment, the instantaneous velocity vector of the moving target can be estimated based on the observation information from the three passive radar devices. As a result, even when extended to three dimensions, the sharpness of the evaluation function P does not deteriorate even during long-time integration, and even for low RCS moving targets such as low S / N environments and stealth targets, It is possible to obtain a passive radar system and a passive radar method capable of increasing the positioning accuracy.

Embodiment 3 FIG.
In the third embodiment, a method for improving the detection / location accuracy of the moving target by estimating the observation information of the (N + 1) th observation frame based on the observation information of the Nth observation frame and increasing the amount of information will be described. To do. The configuration of the passive radar system in the third embodiment is the same as the configuration in FIG. 5 in the second embodiment.

  Next, a series of operations of the passive radar system according to the third embodiment will be described using a flowchart. FIG. 6 is an explanatory diagram regarding the integral gain improvement in the passive radar system according to the third embodiment of the present invention.

As described in the second embodiment, the arrival time difference τ _m (N) and the Doppler frequency difference Δf _m (N) that are observation information of the Nth observation frame in the three passive radar devices 10a, 10b, and 10c. Can be used to estimate the position p (N) of the moving target 30 and the instantaneous velocity vector v (N) (step S601).

Therefore, using p (N) and v (N), the position p (N + 1) of the moving target 30 in the next observation frame (assuming the time lag from the current observation frame to the next observation frame is known) is estimated. can do. Furthermore, if the positions of the radio wave transmission source 20 and the three passive radar devices 10a, 10b, and 10c are known and the position p (N + 1) of the moving target 30 in the next frame can be estimated, the (N + 1) th is calculated by geometric calculation. ) The arrival time difference τ _m (N + 1) and the Doppler frequency difference Δf _m (N + 1) in the observation frame can be estimated (step S602).

  However, this time lag is not very long, and it is assumed that the instantaneous velocity vector of the moving target 30 does not change suddenly during the time lag. In fact, if the time lag is less than about 1 msec, this assumption holds even if civil aircraft or fighter class aircraft do not make a sharp turn or climb.

  As described above, it is indispensable to obtain an integral gain by long-time integration for detection / location of a low RCS target having a stealth performance or the S / N ratio of scattered waves deteriorates depending on the reception environment. Here, an object is to double the sharpness of the peak of the evaluation function P with respect to the moving target 30 by using two observation frames of the Nth observation frame and the (N + 1) th observation frame.

Assuming that the predicted position p (N + 1) extends over several range bins, the arrival time difference τ _m (N + 1) detected in the (N + 1) th observation frame and the Doppler frequency difference Δf _m (N + 1) are detected in the Nth observation frame. Different from the arrival time difference τ _m (N) and the Doppler frequency difference Δf _m (N). As a result, the peak is broken into two, and the sharpness is deteriorated.

Therefore, using the predicted position p (N + 1), the arrival time difference τ _m (N + 1) and the Doppler frequency difference Δf _m (N + 1) with respect to the (N + 1) th observation frame estimated in the previous step S602 are determined as the Nth observation frame. Is made to coincide with the arrival time difference τ _m (N) and the Doppler frequency difference Δf _m (N). This means that the displacement (range walk) of the position of the moving target 30 is canceled. Specifically, the operation of the following expression (7) is performed by the calculation of the above expression (1) (step S603).

Here, each symbol in the above formula (7) means the following.
P _{N + 1} : Evaluation function of the (N + 1) th observation frame

  In this way, by correcting the cross-correlation calculation for the (N + 1) th observation frame and using the data of the Nth and (N + 1) th observation frames as continuous data, it is possible to perform integration that corrects the range walk of the moving target. (Step S604). As a result, the integral gain can be doubled, the sharpness of the evaluation function P can be doubled, and the detection probability of the moving target 30 and the positioning accuracy can be improved (step S605).

  FIG. 7 is an explanatory diagram when the integral gain improvement is performed for a plurality of observation frames in the passive radar system according to the third embodiment of the present invention. FIG. 7 shows the process between the two frames shown in FIG. 6 developed over four frames. Specifically, FIG. 7 is an image diagram for treating the data from the Nth observation frame to the (N + 3) th observation frame as continuous data, quadrupling the integral gain and quadrupling the sharpness of the evaluation function. Is shown.

The operation being performed is the same as that described in the flowchart of FIG. 6, while correcting the arrival time difference τ _m (N) and the Doppler frequency difference Δf _m (N) for each observation frame. The cross-correlation calculation is performed.

  As described above, according to the third embodiment, even when a moving target performs a range walk over a plurality of observation frames, correction is performed by using the instantaneous velocity vector v of the moving target in the observation frame. Integration with long-term observation data becomes possible.

Embodiment 4 FIG.
In the fourth embodiment, a measure for reducing the calculation load by the cross correlation calculation means 16 will be described. The configuration of the entire system in the fourth embodiment is the same as the configuration of FIG. 5 in the second embodiment. The internal configuration of each of the passive radar devices 10a, 10b, and 10c is the same as that shown in FIG.

Next, a specific policy regarding reduction of calculation load by the cross correlation calculation means 16 will be described. In the cross-correlation calculating means 16 of the conventional passive radar device 100, as shown in FIG. 11, the two-dimensional entire search is performed within the range of the expected arrival time difference τ and the Doppler frequency difference Δf. The arrival time difference τ ₁ and the Doppler frequency difference Δf ₁ were detected.

  Such a two-dimensional full-scale search has a very high calculation load, and causes an increase in the scale of the passive radar device 100 as a whole, and a reduction in reaction time (time from obtaining observation data until an answer is obtained). There was a problem.

  Even if the instantaneous velocity vector v of the moving target 30 can be estimated, the cost impact of the entire passive radar system is large if these problems are carried over. Therefore, it is important to improve the calculation load related to the cross-correlation calculation and to reduce the size and price of the apparatus.

  In the passive radar system according to the fourth embodiment, the position p (N) of the moving target 30 with respect to the Nth observation frame can be estimated by the first passive radar device 10a alone. The position p (N) of the moving target 30 can also be obtained by the second passive radar device 10b alone and the third passive radar device 10c alone. However, the position p (N) obtained by the passive radar devices 10b and 10c can be said to be a backup for system construction, and can also be used to verify the position estimation accuracy of the first passive radar device 10a. However, it can be said that it is redundant at the same time.

  Accordingly, if the installation positions of the second passive radar device 10b and the third passive radar device 10c are known, the position p (N) of the moving target 30 determined by the first passive radar device 10a. The relative positional relationship between the second passive radar device 10b and the third passive radar device 10c can be obtained by geometric calculation.

Then, the distance between each of the second passive radar device 10b and the third passive radar device 10c and the moving target 30 is also known. Therefore, the arrival time differences τ ₂ and τ ₃ can be known without searching by the cross-correlation calculating means 16b of the second passive radar device 10b and the cross-correlation calculating means 16c of the third passive radar device 10c. End up.

FIG. 8 is a diagram illustrating the execution contents of the cross-correlation calculating means 16 of the second and subsequent passive radar devices according to the fourth embodiment of the present invention, and is a diagram contrasted with the conventional FIG. As shown in FIG. 8, the cross-correlation calculating means 16b in the second passive radar device 10b and the cross-correlation calculating means 16c in the third passive radar device 10c have the arrival time difference τ and the Doppler frequency difference Δf. The normal cross-correlation calculation, which was a two-dimensional whole search, can be suppressed to a one-dimensional search by Δf, with the time direction being a fixed value of τ ₂ or τ ₃ .

  Therefore, the cross-correlation calculating means 16b and 16c of the second passive radar device 10b and the third passive radar device 10c can keep the calculation load low. As a result, the reaction time can be improved by reducing the size and weight of the arithmetic device and shortening the arithmetic time.

  As described above, according to the fourth embodiment, when using a plurality of passive radar devices, the cross-correlation calculation is suppressed to a one-dimensional search except for the first passive radar device, thereby reducing the size of the arithmetic device. It is possible to obtain a passive radar system and a passive radar method in which the reaction time is improved by reducing the weight and shortening the calculation time.

Embodiment 5 FIG.
In the previous fourth embodiment, the countermeasure for reducing the calculation load of the cross correlation calculation means 16 has been described. On the other hand, in the fifth embodiment, the hardware of the second and third passive radar devices is compared with the first passive radar device, using an example in which three passive radar devices are used. A case will be described in which the size of the apparatus is reduced by reducing the size of the apparatus, thereby reducing the size and weight, reducing the power consumption, and improving the portability.

  The configuration of the entire system in the fifth embodiment is the same as the configuration in FIG. 5 in the second embodiment. The internal configuration of the first passive radar device 10a is the same as that in FIG.

  FIG. 9 is an internal configuration diagram of the second and subsequent passive radar devices according to the fifth embodiment of the present invention. The second and subsequent passive radar devices 10b (10c) of the fifth embodiment in FIG. 9 include a first antenna 11a, a second antenna 11e, a first receiver 13a, a second receiver 13e, 1 A / D converter 14 a, second A / D converter 14 e, first storage unit 15 a, second storage unit 15 b, cross-correlation calculation unit 16, target orientation unit 17, communication unit 18, and instantaneous A velocity vector estimation means 19 is provided.

  Compared with the internal configuration of FIG. 2 showing the first passive radar device 10a, the internal configuration of FIG. 9 showing the second and subsequent passive radar devices 10b, 10c is the first antenna 11b-10d, The difference is that one receiver 13b to 13d and the first A / D converters 14b to 14d are not provided, and the reception system for the scattered wave 1 is composed of one system.

Next, simplification of the configuration of the second and subsequent passive radar devices 10b and 10c will be described.
In the passive radar system of the present invention, the position p (N) of the moving target 30 with respect to the Nth observation frame can be estimated by the first passive radar device 10a alone. The position p (N) of the moving target 30 can be obtained even with the second passive radar device 10b alone and the third passive radar device 10c alone. However, the position p (N) obtained by the passive radar devices 10b and 10c can be said to be a backup for system construction, and can also be used to verify the position estimation accuracy of the first passive radar device 10a. However, it can be said that it is redundant at the same time.

  That is, if the first passive radar device 10a alone can estimate the position p (N) of the moving target 30 from the solid equidistant ellipsoid and the measured values of the horizontal and elevation angles, the second passive radar device 10a can be used. In the radar apparatus 10b and the third passive radar apparatus 10c, the angle measurement function by the array antenna 12 is redundant.

  The purpose of installing the second passive radar device 10b and the third passive radar device 10c is to obtain an observation equation related to the Doppler frequency difference of the above equations (5) and (6). The angle measuring function becomes unnecessary, and the array antenna 12 is unnecessary. That is, the first antenna 11 may be only one element (first antenna 11a). This also brings about the effect of reducing the number of first receivers 13 and first A / D converters 14 following the first antenna 11 and further suppressing the storage capacity of the first storage unit 15a.

  As described above, according to the fifth embodiment, when a plurality of passive radar devices are used, the second and subsequent passive radar devices are specialized in obtaining an observation equation relating to the Doppler frequency difference, Can be simplified. As a result, it is possible to estimate the position p (N) of the moving target and the instantaneous velocity vector v (N), while reducing the scale of the second and subsequent passive radar devices, reducing the size and weight, reducing power consumption, and allowing A passive radar system and a passive radar method with improved portability can be obtained.

  The radio waves already present in the vicinity of the target of the passive radar system of the present invention include FM broadcast waves, analog television broadcast waves, digital television broadcast waves, mobile phone base station radio waves, satellite broadcast waves, Any one or a combination of HF (short wave) broadcast waves, known radar devices, and other available radio waves can be used.

  However, the size of the antenna device changes with respect to the frequency band of the radio wave used, the pass / stop band of the receiver changes, and the conversion speed of the A / D converter changes. These are all grounds for selection in terms of operation such as conditions such as a high S / N ratio of radio waves in the surrounding environment, installation area, and portability as a passive radar system. However, since the basic operation principle is the same, the passive radar system of the present invention operates effectively for any radio wave.

  Further, in the passive radar system of the present invention, the angle measurement method is not particularly stated, but monopulse angle measurement, DBF (Digital Beam Forming), MUSIC (Multiple Signal Classification), ESPRIT (Estimation of Signal Parameters). (Techniques), and a super-resolution angle measuring method such as a maximum likelihood method.

  10, 10a, 10b, 10c passive radar device, 11 antenna, 11a-11d first antenna, 11e second antenna, 12, 12a, 12b array antenna, 13 receiver, 13a-13d first receiver, 13e 2nd receiver, 14 A / D converter, 14a-14d 1st A / D converter, 14e 2nd A / D converter, 15 memory | storage part, 15a 1st memory | storage part, 15b 2nd Storage unit 16, 16a, 16b, 16c Cross-correlation calculating means, 17 Target locating means, 18 Communication device, 19 Instantaneous velocity vector estimating device, 20 Radio wave transmission source (radio wave source), 30 Moving target.

Claims (9)

A first antenna that receives a scattered wave generated when an existing radio wave hits a moving target without radiating the radio wave,
An array antenna composed of a plurality of the first antennas;
A plurality of first receivers that are individually provided for each element of the array antenna and extract a signal in a desired frequency band from the reception signal of the array antenna;
A plurality of first A / D converters for converting each of output signals of the plurality of first receivers into digital data;
A first storage unit that stores time-series data output from the plurality of first A / D converters in association with element numbers of the array antenna;
A second antenna for receiving a direct wave from a radio wave source for transmitting the existing radio wave;
A second receiver for extracting a signal of a desired frequency band from the received signal of the second antenna;
A second A / D converter for converting the output signal of the second receiver into digital data;
A second storage unit for storing time-series data output from the second A / D converter;
Search the time series data for the same number of elements read from the second storage unit in the time series data for the number of elements read from the first storage unit, and search the entire range within the range assumed as two variables of time and frequency. Cross-correlation, and cross-correlation calculating means for specifying the arrival time difference and the Doppler frequency difference with respect to the moving target as observation information;
A passive radar apparatus comprising: target locating means for obtaining unknown parameters such as the position, altitude, and angle of the moving target using the observation information output from the cross-correlation calculating means and angle measurement value information from the array antenna Is a passive radar system in which multiple units are arranged at different positions,
Each of the plurality of passive radar devices transmits observation information specified by its own cross-correlation calculating means to another passive radar device, and observation information specified by the cross-correlation calculating means of the other passive radar device Communication means for receiving,
An instantaneous velocity vector estimating means for estimating an instantaneous velocity vector of the moving target based on observation information specified by all passive radar devices ; and
The cross-correlation calculating means predicts the position of the moving target in the next observation frame using the instantaneous speed vector estimated by the instantaneous speed vector estimating means, and An arrival time difference and a Doppler frequency difference are calculated as second observation information, and correction processing is performed so that the calculated second observation information matches the observation information specified for the current observation frame, and the correction is performed. Passive radar characterized by acquiring second observation information after processing as observation information in the next observation frame, thereby obtaining observation information equivalent to performing a long-time cross-correlation calculation between frames system. A first antenna that receives a scattered wave generated when an existing radio wave hits a moving target without radiating the radio wave,
An array antenna composed of a plurality of the first antennas;
A plurality of first receivers that are individually provided for each element of the array antenna and extract a signal in a desired frequency band from the reception signal of the array antenna;
A plurality of first A / D converters for converting each of output signals of the plurality of first receivers into digital data;
A first storage unit that stores time-series data output from the plurality of first A / D converters in association with element numbers of the array antenna;
A second antenna for receiving a direct wave from a radio wave source for transmitting the existing radio wave;
A second receiver for extracting a signal of a desired frequency band from the received signal of the second antenna;
A second A / D converter for converting the output signal of the second receiver into digital data;
A second storage unit for storing time-series data output from the second A / D converter;
Search the time series data for the same number of elements read from the second storage unit in the time series data for the number of elements read from the first storage unit, and search the entire range within the range assumed as two variables of time and frequency. Cross-correlation, and cross-correlation calculating means for specifying the arrival time difference and the Doppler frequency difference with respect to the moving target as observation information;
A passive radar apparatus comprising: target locating means for obtaining unknown parameters such as the position, altitude, and angle of the moving target using the observation information output from the cross-correlation calculating means and angle measurement value information from the array antenna Is a passive radar system in which multiple units are arranged at different positions,
Each of the plurality of passive radar devices transmits observation information specified by its own cross-correlation calculating means to another passive radar device, and observation information specified by the cross-correlation calculating means of the other passive radar device Communication means for receiving,
An instantaneous velocity vector estimating means for estimating an instantaneous velocity vector of the moving target based on observation information specified by all passive radar devices ; and
The communication means in the second and subsequent passive radar devices are the unknown parameters obtained by the target locating means in the first passive radar device via the communication means in the first passive radar device. Get
The cross-correlation calculating means in the second and subsequent passive radar devices obtains the arrival time difference with respect to the moving target as a fixed value from the acquired relative parameters and the relative positional relationship of each passive radar device, and uses it as a variable of frequency A passive radar system characterized in that the observation information is specified by performing a one-dimensional search within an assumed range, calculating a cross-correlation, and obtaining a Doppler frequency difference with respect to a moving target . A first antenna that receives a scattered wave generated when an existing radio wave hits a moving target without radiating the radio wave,
An array antenna composed of a plurality of the first antennas;
A plurality of first receivers that are individually provided for each element of the array antenna and extract a signal in a desired frequency band from the reception signal of the array antenna;
A plurality of first A / D converters for converting each of output signals of the plurality of first receivers into digital data;
A first storage unit that stores time-series data output from the plurality of first A / D converters in association with element numbers of the array antenna;
A second antenna for receiving a direct wave from a radio wave source for transmitting the existing radio wave;
A second receiver for extracting a signal of a desired frequency band from the received signal of the second antenna;
A second A / D converter for converting the output signal of the second receiver into digital data;
A second storage unit for storing time-series data output from the second A / D converter;
Search the time series data for the same number of elements read from the second storage unit in the time series data for the number of elements read from the first storage unit, and search the entire range within the range assumed as two variables of time and frequency. Cross-correlation, and cross-correlation calculating means for specifying the arrival time difference and the Doppler frequency difference with respect to the moving target as observation information;
A passive radar apparatus comprising: target locating means for obtaining unknown parameters such as the position, altitude, and angle of the moving target using the observation information output from the cross-correlation calculating means and angle measurement value information from the array antenna Is a passive radar system in which multiple units are arranged at different positions,
Each of the plurality of passive radar devices transmits observation information specified by its own cross-correlation calculating means to another passive radar device, and observation information specified by the cross-correlation calculating means of the other passive radar device Communication means for receiving,
An instantaneous velocity vector estimating means for estimating an instantaneous velocity vector of the moving target based on observation information specified by all passive radar devices ; and
The second and subsequent passive radar devices are configured so that the number of elements of the first antenna is only one element,
The target locating means in the second and subsequent passive radar devices does not calculate the unknown parameters based on the angle measurement value information . The passive radar system according to any one of claims 1 to 3 ,
The cross-correlation calculating means repeats the correction process over a plurality of observation frames of three or more, thereby obtaining observation information equivalent to performing a long-time cross-correlation calculation between the plurality of observation frames of three or more. A passive radar system characterized by The passive radar system according to any one of claims 1 to 4 ,
The passive radar system is composed of two passive radar devices,
At least one instantaneous velocity vector estimation means of the two passive radar devices includes observation information specified by its own cross-correlation calculation means and observation information specified by another cross-correlation calculation means. A passive radar system characterized in that a two-dimensional instantaneous velocity vector of the moving target is estimated based on. The passive radar system according to any one of claims 1 to 4 ,
The passive radar system is composed of three passive radar devices,
At least one instantaneous velocity vector estimation means of the three passive radar devices includes observation information specified by its own cross-correlation calculation means and observation information specified by the other two cross-correlation calculation means. A passive radar system, wherein a three-dimensional instantaneous velocity vector of the moving target is estimated based on. The passive radar system according to any one of claims 1 to 6 ,
The existing radio waves in the surrounding space of the self are FM broadcast waves, analog television broadcast waves, digital television broadcast waves, mobile phone communication waves, satellite broadcast waves, HF (short wave) broadcast waves, and known radar transmission waves. A passive radar system characterized in that one or a combination of two or more of the above is used. The passive radar system according to any one of claims 1 to 7 ,
A passive radar system characterized by applying MUSIC, ESPRIT, or super-resolution angle measurement by maximum likelihood estimation as the angle measurement method by the array antenna. It does not radiate radio waves, but receives scattered waves generated by the existing radio waves in its surrounding space when it hits a moving target via an array antenna, and receives direct waves from a radio wave source that sends the existing radio waves. The reception time difference and Doppler frequency difference with respect to the moving target are identified as observation information by performing cross-correlation calculation processing based on the scattered wave and the direct wave received via an antenna, the identified observation information, and A passive radar method using a plurality of passive radar devices for calculating unknown parameters such as position, altitude, and angle of the moving target using angle measurement value information by an array antenna,
Obtaining observation information identified by cross-correlation calculation processing by another passive radar device via communication means;
Estimating the instantaneous velocity vector of the moving target based on the respective observation information specified by all the passive radar devices including the observation information specified by the cross-correlation calculation processing by the own passive radar device ;
Using the instantaneous velocity vector estimated in the estimating step, the presence position of the moving target in the next observation frame is predicted, and an arrival time difference and a Doppler frequency difference with respect to the moving target at the predicted existence position are calculated as a second value. Correction processing is performed so that the calculated second observation information matches the observation information specified for the current observation frame, and the second observation information after the correction processing is obtained. A passive radar method comprising: a correction step of acquiring observation information equivalent to performing long-time cross-correlation calculation between frames by specifying as observation information in the next observation frame .

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