JP2021047105A - Passive type radar device, and passive type radar signal processing method - Google Patents

Abstract

To identify a target position even in an environment where a direct wave cannot be obtained from a transmitting station.SOLUTION: A passive type radar device according to an embodiment, in an environment where a direct wave of a radar wave transmitted from a transmitting station whose transmission sources are known cannot be obtained, receives an indirect wave reflected on a target, opens a gate, and extracts a target detection signal from an indirect wave reception signal. A control unit sets a target moving speed and a temporary value of distance to set the gate in accordance with a scan rate based on known information on the transmission sources of the transmitting station. The passive type radar device establishes a target track from a target detection signal extracted at the scan rate, repeatedly performs derivation of vector information on the target track within a distance range of a radar coverage area and derivation for vector information on a target movement model based on the known information, derives a differential value between results of derivation of each vector information, derives a position vector in which the differential value becomes the minimum value, and inputs an initial position based on the position vector with the minimum differential value to the target track to estimate a target position.SELECTED DRAWING: Figure 4

Description

An embodiment of the present invention relates to a passive radar device and a passive radar signal processing method.

In a passive radar device that detects a target by radio waves using another radar as a transmitting station, the azimuth angle and elevation angle are derived by angle measurement processing for the target detection signal, and the wave and target are reflected directly from the transmitting station. By deriving the distance from the detection time difference from the indirect wave, the position with respect to the detection signal assumed to be the target is estimated.

As described above, in deriving the distance at the time of estimating the position of the passive radar device, it is necessary to grasp the time difference between the reception time of the direct wave and the detection time of the indirect wave. If the transmitting station is located outside the line of sight of the radio waves of the passive radar device, or in an environment where direct waves cannot be obtained on the passive radar device side, it becomes difficult for the passive radar device to calculate the distance. It becomes impossible to estimate the position of the target. Therefore, the passive radar device has a problem that the operating range is limited to the range where the direct wave of the transmitting station can reach (for example, Line Of Sight).

Japanese Unexamined Patent Publication No. 2016-138787 JP-A-2002-3111132

M. I. Skolnik, “Radar Handbook,” Third edition, pp. 23.1-23.13, McGraw-Hill, New York, N. J. Wills, “Bistatic Radar,” Second edition, Silver Spring, MD: Technology Service Corp., 1995. Corrected and republished by Raleigh, NC: SciTech Publishing, Inc., 2005

As described above, the conventional passive radar device has a problem that the operating range is limited to the range where the direct wave of the transmitting station can reach.

An embodiment of the present invention provides a passive radar device and a passive radar signal processing method capable of specifying a target position even in an environment where a direct wave required for synchronization with a transmitting station cannot be obtained. The purpose is.

The passive radar device according to the embodiment receives an indirect wave in which the radar wave is reflected by a target in an environment where a direct wave of a radar wave transmitted from a transmission station whose transmission specifications are known cannot be obtained. It is a device for detecting the position of a target, and includes a receiving unit, a control unit, and a signal processing unit. The receiving unit receives the indirect wave, opens the gate, and extracts a target detection signal from the received signal of the indirect wave. Based on the known information of the transmission specifications of the transmitting station, the control unit sets temporary values of the target moving speed and distance according to the scan rate, and sets the gate in the receiving unit. The signal processing unit establishes a target track from the target detection signal extracted at the scan rate in the receiving unit, derives vector information of the target track within the range of the radar coverage, and targets based on the known information. The vector information of the movement model is repeatedly derived, the difference value of the derivation result of each vector information is derived, the position vector at which the difference value is the minimum value is derived, and the initial position based on the position vector is derived from the target track. Is input to estimate the target position.

FIG. 1 is a conceptual diagram showing a configuration of a radar system including a passive radar device to which the present embodiment is applied. FIG. 2 is a block diagram showing a configuration of a passive radar device to which the present embodiment is applied. FIG. 3 is a diagram showing a distance calculation method using a passive radar device to which the present embodiment is applied. FIG. 4 is a flowchart showing a radar signal processing procedure when a direct wave cannot be obtained in the passive radar device according to the present embodiment. FIG. 5 is a conceptual diagram for explaining the target track imaging of the passive radar device according to the present embodiment. FIG. 6 is a conceptual diagram showing a virtual image of a moving model of the passive radar device according to the present embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram showing a configuration of a radar system including a passive radar device (hereinafter, passive radar) 100 to which the present embodiment is applied. In FIG. 1, the passive radar 100 receives the direct wave W1 that directly receives the transmitted wave transmitted from the transmitting station 200 and the indirect wave W2 that is reflected by the target T and arrives, and from the angle and time difference of each received wave. Identify the position of the target T.

FIG. 2 is a block diagram showing the configuration of the passive radar 100. In FIG. 2, the passive radar 100 includes a first antenna unit 101, an indirect wave signal processing unit 102, a cumulative unit 103, a synthesis unit 104, and a target position specifying unit 105. Further, the passive radar 100 includes a second antenna unit 106, a direct wave signal processing unit 107, and a control unit 108. The cumulative unit 103, the combining unit 104, the target position specifying unit 105, and the control unit 108 can be realized by a computer device having functions as an arithmetic circuit and a control circuit.

The first antenna unit 101 includes an antenna element that captures an incoming wave and obtains a received signal. Under the control of the control unit 108, the indirect wave signal processing unit 102 extracts a signal (indirect wave signal) during the period when the indirect wave W2 arrives from the received signals obtained by the first antenna unit 101. The indirect wave signal is subjected to reception processing such as limiter processing, amplification processing, filter processing, and A / D conversion processing. The indirect wave signal that has undergone reception processing is output to the cumulative unit 103.

The accumulation unit 103 is an arithmetic unit that accumulates the signal values of the indirect wave signals during the cumulative period controlled by the control unit 108, and accumulates the signal values of the input indirect wave signals.

The second antenna unit 106 includes an antenna element that captures the incoming wave and obtains a received signal, in addition to the first antenna unit 101 (which may be shared or partially used). The direct wave signal processing unit 107 extracts a signal (direct wave signal) during the period when the direct wave W1 arrives from the received signals obtained by the second antenna unit 106, and performs limiter processing on the direct wave signal. Receive processing such as amplification processing, filtering processing, and A / D conversion processing is performed. The direct wave signal that has undergone reception processing is output to the control unit 108.

The control unit 108 obtains the arrival timing of the direct wave W1 and the start timing of the interval based on the direct wave signal obtained by the direct wave signal processing unit 107, and extracts the indirect wave signal based on the arrival timing of the direct wave W1. The period (the arrival period of the indirect wave W2) is controlled. Further, the control unit 108 controls the cumulative period of the indirect wave signal in the cumulative unit 103.

The synthesis unit 104 synthesizes the results accumulated by the accumulation unit 103. The target position specifying unit 105 specifies the position of the target T based on the result synthesized by the synthesis unit 104. The position information of the target T specified by the target position specifying unit 105 is output to the outside and displayed as a detection result of the target T, for example.

In the passive radar 100 having the above configuration, the azimuth angle θ and the elevation angle φ are derived by angle measurement processing for the detection signal of the target T, and as shown in FIG. 3, the reception time t _{1 of the direct wave of the transmitting station 200 is derived.} By deriving the distance R _r from the time difference ΔT _rt (= t _2- t ₁ ) between the indirect wave and the detection time t _{2 , the position (R r} , θ,) with respect to the detection signal assumed to be the target T φ) is estimated. The following equation is applied to derive the distance.

Here, c is the speed of light, L is the distance between the passive radar 100 and the transmission station 200 (baseline), and α is the angle measurement angle of the passive radar 100 (the angle between the transmission station 100 and the target T as seen from the passive radar 100). ).

As a precondition of this embodiment, the passive radar 100 has known transmission specifications (transmission station position, scan rate, pulse timing (PRI (Pulse Repeat Interval), number of pulses, etc.)) of the transmission station 200. It is assumed that.

In the radar system, the processing flow of the present embodiment will be described below with reference to FIG. FIG. 4 is a flowchart showing a radar signal processing procedure by the control unit 108 when the passive radar 100 is placed in an environment where the direct wave required for synchronization with the transmission station 200 cannot be obtained.

In FIG. 4, when the control unit 108 determines that the environment is such that a direct wave signal cannot be obtained, it inputs an indirect wave signal to extract a target detection signal (step S11), and the target detection signal and transmission specifications. Based on the known information of the above, a temporary value of the moving speed and the distance is set to establish the target track (step S12). As a means for establishing a track, it is assumed that a general tracking radar TWS (Track While Scan) method (a method of tracking on data based on the obtained target information) is applied. In the TWS tracking, the gate is opened with the target speed assumed centering on the detection signal as a parameter. Here, the gate corresponds to the maximum range in which the detection target can move in the time until the next detection opportunity (in this embodiment, the scan rate of the transmitting station 200).

When the target track is established in step S12, the vector information of the target track is derived (step S13). Next, the derivation of the vector information of the target movement model based on the known information (step S14) and the derivation of the difference value of the vector information (step S15) are repeatedly executed within the distance range of the search coverage area (for example, 50 km ≦ R ≦ 250 km). To do. After that, the position vector R having the minimum difference value is derived (step S17), and the initial position corresponding to the position vector R is input to the target track to estimate the position of the target position (step S18).

The above processing will be specifically described.

First, the target track is established based on the target detection signal. In order to establish a wake, the gate is opened at the scan rate of the transmitting station 200 with the target speed assumed centering on the target detection signal in the TWS method as a parameter. When the target detection signals raised in the next scan enter the gate, these detection signals are connected as the same target. Based on the movement amount of the connected detection target, the gate for the next scan is opened, and then the target track is connected by repeating these processes.

On the other hand, in the passive radar 100 of the present embodiment, assuming a situation where it is difficult to calculate the distance, since the distance of the target T in which the signal is detected is unknown, the gate that opens even if the assumed target speed is set is wide. The exact gate size cannot be determined (because the exact gate size varies depending on the relative distance between the passive radar and the signal-detected target T). Therefore, for example, the middle of the distance that is the maximum diameter of the search coverage area (150 km in the middle when 50 km to 250 km is the search distance) is set as a provisional value, and the assumed target speed is set for the distance. Apply the method of determining the size of the gate.

The distance set as the temporary value can be set variably depending on the purpose of the system. For example, if the system can tolerate wakes, set the farthest distance in the coverage and open the gate wide, and if the system does not allow wakes, set a relatively short distance and open the gate narrowly. And so on.

Next, the initial position is estimated for the established track. An image of the established target wake is shown in FIG. Here, the directional θ and the elevation angle φ of each detection target T of the target track are the results of the angle measurement processing of the passive radar 100, and are values including an error. Although the distance is unknown, the moving distance component can be estimated from the time difference between the nth scan and the n + 1th scan, so the moving distance component is calculated.

The vector information of the target track is shown below. Here, N (n = 1 to N) represents a scan number corresponding to the scan rate of the transmitting station 200, θ _{n + 1} is the orientation information of the detection target of the n + 1th scan, and φ _{n + 1} is the detection target of the n + 1th scan. The elevation angle information, ΔR _{n + 1,} is the difference between the distance information of the detection target of the nth scan and the distance information of the detection target of the n + 1th scan.

Next, assume a target movement model. The target movement model sets the initial position and the movement direction, and derives the target detection assumed position where the target detection is raised at the scan rate of the transmitting station 200. The moving direction may be obtained by linear approximation or the like from the information of the target track vector already obtained. The vector information (θ, φ, ΔR) of the assumed target movement model is shown below.

Further, a hypothetical image of the moving model is shown in FIG.

The initial position of the target track is estimated based on the difference value of the vector information of the target movement model assumed to be the vector of the target track established earlier. By setting the initial position vector Rn of the assumed target movement model, the vector information of the target movement model is derived. Therefore, the estimation formula of the movement model that minimizes the error is expressed as follows.

Using the vector Rn in the above equation as a parameter, the vector information of the target movement model is derived for each vector Rn, the difference value from the vector information of the target track is calculated, and the target movement model with the minimum difference value is searched. In addition, α, β, and γ are weighting coefficients for smoothing the degree of difference due to the difference in information characteristics of azimuth, elevation, and distance. The initial position vector Rn of the target movement model that minimizes the searched difference value becomes the initial position of the previously established target track. By specifying the initial position of the target track, the current position of the target T can be specified.

Therefore, according to the passive radar according to the present embodiment, the target position can be specified even in an environment where the direct wave required for synchronization with the transmitting station cannot be obtained.

The present invention is not limited to the above-described embodiment as it is, and at the implementation stage, the components can be modified and embodied within a range that does not deviate from the gist thereof. In addition, various inventions can be formed by an appropriate combination of the plurality of components disclosed in the above-described embodiment. For example, some components may be removed from all the components shown in the embodiments. In addition, components across different embodiments may be combined as appropriate.

100 ... Passive radar, 101 ... First antenna unit, 102 ... Indirect wave signal processing unit, 103 ... Cumulative unit, 104 ... Synthesis unit, 105 ... Target position identification unit, 106 ... Second antenna unit, 107 ... Direct wave Signal processing unit, 108 ... Control unit. 200 ... Transmitting station.

Claims (4)

A passive radar device that detects the position of a target by receiving the indirect wave reflected by the target in an environment where the direct wave of the radar wave transmitted from a transmission station whose transmission specifications are known cannot be obtained. And
A receiver that receives the indirect wave, opens the gate, and extracts a target detection signal from the received signal of the indirect wave.
Based on the known information of the transmission specifications of the transmitting station, a control unit that sets a temporary value of the target moving speed and a distance according to the scan rate and sets the gate in the receiving unit.
The target track is established from the target detection signal extracted at the scan rate in the receiving unit, the vector information of the target track is derived within the distance range of the radar coverage, and the vector information of the target movement model based on the known information. The derivation is repeated, the difference value of the derivation result of each vector information is derived, the position vector whose difference value is the minimum value is derived, and the initial position based on the position vector is input to the target track to enter the target position. A passive radar device including a signal processing unit that estimates the position of the vector. The control unit sets a gate corresponding to the maximum range in which the target can move in the time until the next detection of the target, using the movement speed of the target assumed at the center of the target detection signal as a parameter. 1 The passive radar device according to 1. The first aspect of the present invention, wherein the signal processing unit sets the middle of the distance to be the maximum diameter of the radar covering area as the provisional value, sets an assumed target speed for the distance, and determines the width of the gate. Passive radar device. In an environment where direct waves of radar waves transmitted from transmission stations with known transmission specifications cannot be obtained.
The radar wave receives the indirect wave reflected by the target and receives the indirect wave.
Open the gate and extract the target detection signal from the received signal of the indirect wave.
Based on the known information of the transmission specifications of the transmission station, the gate is set by setting temporary values of the target movement speed and distance according to the scan rate.
Establish a target track from the target detection signal extracted at the scan rate,
The vector information of the target track and the vector information of the target movement model based on the known information are repeatedly derived within the distance range of the radar coverage area.
The difference value of the derivation result of each of the vector information of the target track and the vector information of the target movement model is derived.
Derivation of the position vector at which the difference value is the minimum value is derived.
A passive radar signal processing method for estimating the position of a target position by inputting an initial position based on the position vector into the target track.

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