JP6980570B2 - Target detector and signal processing method - Google Patents

Description

Embodiments of the present invention relate to a target detection device and a signal processing method.

The monopulse angle measurement processing method and the interferometer processing method are known as an example of a signal processing method for obtaining the arrival direction of radio waves at the time of target detection. The interferometer processing is a method of obtaining the arrival direction of a radio wave based on the phase of the radio wave incident on the array antenna and the element spacing of the antenna elements.

Japanese Patent No. 5547012

Wing-Kin Ma,'DOA Estimation of Quasi-Stationary Signals With Less Sensors Than Sources and Unkown Spatial Noise Covariance: A Khatri-Rao Subspace Approach', IEEE Trans. Signal Process., Vol.58, no.4, pp.2168 -2180, April (2010) JIAN LI, PETER STOICA, ‘MIMO RADAR SIGNAL PROCESSING’, WILEY, pp. 1-5 (2009)

In the interferometer processing method, the angle measurement accuracy is improved as the distance between the antenna elements is widened. However, in a flying object or the like where the mounting space of the antenna is limited, the element spacing cannot be sufficiently widened, so that the angle measurement accuracy reaches a plateau. In such an environment, an active antenna or the like must be used in combination in order to improve the guidance accuracy of the flying object, which causes adverse effects such as an increase in weight, and therefore a countermeasure is desired.

An object of the present invention is to provide a target detection device and a signal processing method with improved accuracy within the constraints of mounting space.

According to the embodiment, the target detection device includes an array antenna including a plurality of antenna elements for capturing radio waves from the target, and an angle measuring unit. The angle measuring unit calculates a target target angle from each element signal of a plurality of antenna elements. In addition, the angle measurement processing unit calculates the target angle measurement value from each element signal, and forms a virtual array including a plurality of virtual antenna elements having a wider opening than the array antenna by matrix calculation based on each element signal. The ambiguity is excluded from the measured angle value, and the target angle is calculated from each element signal of the plurality of virtual antenna elements.

FIG. 1 is a diagram showing an example of an air vehicle equipped with the target detection device 4 according to the embodiment. FIG. 2 is a functional block diagram showing an example of the target detection device 4. FIG. 3 is a diagram showing an example of the first embodiment of the receiving antenna unit 11. FIG. 4 is a flowchart showing an example of the processing procedure of the angle measuring device 15. FIG. 5 is a diagram showing an example of a virtual antenna opening obtained by the expansion array forming process according to the embodiment. FIG. 6 is a diagram showing an example of a second embodiment of the receiving antenna unit 11.

<Structure>
[First Embodiment]
FIG. 1 is a diagram showing an example of an air vehicle equipped with the target detection device 4 according to the embodiment. As an example of the flying object, the flying object 1 is assumed in the embodiment, but it can also be applied to an flying object such as an aircraft or a drone.

The flying object 1 is composed of a guidance device 2 that guides the flying object 1 in the direction of arrival of radio waves, and a steering device 3 that changes the attitude of the flying object 1. The guidance device 2 outputs a guidance signal for guiding the flying object 1 toward the target 6 that emits radio waves. Here, target 6 is an object that radiates or reflects radio waves, and is typically a ground-based or carrier-based radar device. The steering device 3 controls the posture of the flying object 1 according to the guidance signal, and guides the flying object 1 in the direction of the target 6.

The guidance device 2 includes a target detection device 4 and a target follower device 5. The target detection device 4 receives a radio wave and detects a target from the received radio wave. The target tracking device 5 generates a guidance signal so as to follow the detected target, and outputs the guidance signal to the steering device 3.

FIG. 2 is a functional block diagram showing an example of the target detection device 4. The target detection device 4 includes a receiving antenna unit 11, a receiver 12, an A / D (analog / digital) converter 13, a detection processor 14, and an angle measuring processor 15. Of these, the receiver 12 is configured to include an analog circuit. Further, the detection processor 14 and the angle measuring processor 15 include, for example, a processor. The processor is, for example, a CPU (Central processing unit), a GPU (Graphics Processing Unit), an ASIC (Application Specific Integrated Circuit), a Programmable Logic Device (for example, a SPLD (Simple Programmable Logic Device), a CPLD (Complex Programmable Logic Device) or an FPGA. (Field Programmable Gate Array) etc.) means the circuit.

The receiving antenna unit 11 receives the radio wave from the target 6 and guides the received wave to the receiver 12. The receiver 12 detects the received wave output from the receiving antenna unit 11. The A / D converter 13 converts the detected received wave into a digital signal. The detection processor 14 analyzes the digital signal to detect the received wave from the target 6. The angle measuring device 15 obtains the direction of the target 6 and the frequency of the radio wave from the target from the output of the detection processing device 14.

FIG. 3 is a diagram showing an example of the receiving antenna unit 11. Receiving antenna unit 11 includes an antenna a, antenna b, and antenna c are arranged at predetermined intervals d _0, an array antenna. The antenna a, the antenna b, and the antenna c are antenna elements that capture radio waves from the target.

Of these, it is assumed that the antenna a and the antenna b are arranged along the azimuth (AZ) axis, and the antenna a and the antenna c are arranged along the elevation (EL) axis. That is, the receiving antenna unit 11 includes a plurality of antenna elements arranged along two axes that are different (orthogonal) from each other.

The radio wave from the target 6 is captured by the receiving antenna unit 11, and the element signals from the antennas a, b, and c are detected by the receiver 12. The detected received wave is converted into a digital signal by the A / D converter 13. The digital signal is taken into the detection processor 14.

The radio wave incident on the receiving antenna unit 11 is not limited to a single wave source. Therefore, the detection processor 14 analyzes the frequency, modulation method, etc., identifies and separates radio waves from a plurality of wave sources, and detects them as a plurality of target waves. As a method for separation / identification, for example, the method described in Patent Document 1 can be applied. Based on the result of separation / identification, the detection processor 14 determines the target wave to be angled among the plurality of target waves. The plurality of target waves selected as the angle measurement target are taken into the angle measuring device 15 one by one. The angle measuring device 15 calculates the arrival direction of each target wave to obtain the target angle of the target. Next, the operation in the above configuration will be described.

<Action>
FIG. 4 is a flowchart showing an example of the processing procedure of the angle measuring device 15. In FIG. 4, the angle measuring device 15 captures the target wave signal separated and identified by the detection processing device 14 (step S1). The target wave signal (complex number) can _{be expressed as xAZ and xEL in} each axial direction as shown in the following equation (1).

Here, x _a is a target wave signal (target wave signal) from the antenna a, x _b is a target wave signal from the antenna b, and x _c is a target wave signal from the antenna c.

Next, the angle measuring device 15 performs the first angle measuring processing (step S2). That is, the angle measuring device 15 calculates the arrival direction of the target wave for each axial direction by interferometer processing, and calculates the measured angle value of the target. In the interferometer, the arrival direction θ can be obtained from the relationship of the following equation (2).

Here, φ is the phase difference of the received signal between the two antennas, d is the distance between the two antenna elements, and λ is the wavelength of the received signal. When measuring the angle using the antennas a and b, or when measuring the angle using the antennas a and c, the element spacing is d = d ₀ .

Next, the angle measuring device 15 performs inter-element expansion processing (step S3). Here, angle measuring processor 15 _first, x _AZ, correlation matrix _R AZ of _{x EL,} obtained by following equation _{R EL} (3).

H in equation (3) represents the complex conjugate transpose. Here, the principle of Khatri-Rao product (KR product) (e.g. Non-Patent Document 1), the vector _V AZ represented by the following formula _(4), the _{V EL,} a target wave signal by a virtual receive antennas for each axis be able to. That is, the number of antenna elements per axis is expanded from the original two to three.

Further, _VAZ and _VEL are multiplied to obtain the following equation (5).

Each component of the 3 × 3 matrix represented by the equation (5) becomes a received signal of the virtual antenna.

FIG. 5 is a diagram showing an example of a virtual antenna opening obtained by the expansion array forming process according to the embodiment. Equation (5) indicates that an extended array (virtual receiving antenna) having nine virtual antenna elements as shown in FIG. 5 is equivalently formed. As shown in FIG. 5, the positions of the virtual antenna elements a to i _{correspond to the distance d 0} , and for example, the distance between the virtual antenna a and the virtual antenna c is 2 d ₀ . Therefore, the antenna opening of the extended array is larger than the opening of the receiving antenna unit 11 as a real array.

This corresponds to, for example, in the MIMO (Multi Input Multi Output) signal processing method disclosed in Non-Patent Document 2, a method of obtaining an N × M virtual array signal from an N-channel transmission signal and an M-channel reception signal. In normal MIMO, a multiplication operation is automatically performed on a signal to be transmitted and received, whereas in the embodiment, it corresponds to performing a reception × reception multiplication operation.

Next, the angle measuring device 15 performs the second angle measuring processing using the extended array (virtual receiving antenna) (step S4). That is, the angle measuring device 15 calculates the arrival direction of the target wave for each axial direction by interferometer processing, and calculates the target angle of the target. For example, when the received signals of the virtual antenna a and the virtual antenna c are used, the element spacing is d = 2d ₀ , which is wider than the first angle measurement process in step S2.

From the relationship of equation (2), if the wavelength and phase difference are constant, the wider the distance between the two antennas, the smaller the change in the arrival direction. That is, even if the phase difference includes an error due to noise, the error in the arrival direction can be reduced and the accuracy is improved. As described above, according to the first embodiment, it is possible to improve the angle measurement accuracy without changing the element spacing on the hardware by the arithmetic processing for forming the virtual antenna.

The AZ axis, virtual antennas a and c, d and f, are three solutions by calculation using the g and i is obtained as the element spacing 2d _0. Since these have the same true value, the accuracy can be further improved by averaging the three solutions.

Similarly, the EL axis, in such obtain virtual antennas a and g as the element spacing 2d _0, b and h, and three solutions by calculation using the c and i, taking the average of these three solutions, The accuracy can be further improved.

As the element spacing increases, the range that can be measured (the range where ambiguity does not occur) becomes narrower, but since the rough value (measured value) in the target direction can be obtained by the processing in step S2, it is possible to obtain a rough value (measured value). Ambiguity can be avoided from the result. If the principle of KR product is used, a false target may occur when a plurality of targets are included. However, in the first embodiment, the separation / identification process is performed by the detection processor 14 before applying the KR product principle. Therefore, even if there are multiple goals, there is no concern about the occurrence of false goals.

<Effect>
As described above, according to the first embodiment, the target angle measurement values are posted from the element signals from the antennas a, b, and c of the receiving antenna unit 11 as a real array, and then the extended array is posted. An expansion array is formed by the formation process. Then, the ambiguity was eliminated by the already calculated angle measurement value, and then the target angle was calculated from each element signal of the virtual antenna of the extended array. Since this is done, it is possible to perform angle measurement processing based on a virtual array signal having an opening wider than that of a real array, and to provide a target detection device and a signal processing method with improved accuracy under the constraint of mounting space. It will be possible.

That is, according to the first embodiment, even in an environment where the mounting space of the antenna is limited, such as a flying object, a virtual antenna spacing wider than the actual antenna element arrangement is performed by calculation using the principle of KR product. Antennas can be set. By increasing the number of virtual antenna elements in this way, it is possible to obtain the target angle with higher accuracy without expanding the hardware scale.

[Second Embodiment]
FIG. 6 is a diagram showing an example of the first embodiment of the receiving antenna unit 11. In FIG. 3, two antenna elements are arranged in each direction, but the present invention is not limited to this, and three or more antenna elements may be arranged as shown in FIG.

_{If the interval (arrangement) is, for example, d 0} = d ₁ + d _{2 in} comparison with FIG. 3, by preparing an element having a narrow element interval, the angle can be measured without causing ambiguity. Can be expanded.

_{The correlation matrix Rxx} for each axis at this time and the received signal V of the virtual antenna are shown in the equation (6).

Here, N is the number of antenna elements arranged on each axis. The spacing between each element is arbitrary. FIG. 6 corresponds to the element arrangement when N = 3 as an example. By increasing the number of antenna elements, it is possible to increase the number of angle measurement values that can be obtained at the same time in angle measurement using a virtual antenna, and therefore the accuracy can be further improved. From these facts, it is possible to provide the target detection device and the signal processing method which improved the accuracy under the constraint of the mounting space also by the 2nd Embodiment.

Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Flying body, 2 ... Guidance device, 2d ₀ ... Element spacing, 3 ... Steering device, 4 ... Target detection device, 5 ... Target tracking device, 6 ... Target, 11 ... Reception antenna unit, 12 ... Receiver, 13 ... A / D converter, 14 ... detection processor, 15 ... angle measuring device, a to i ... virtual antenna element.

Claims (8)

An array antenna equipped with multiple antenna elements that capture radio waves from the target,
It is provided with an angle measuring unit that calculates the target angle of the target from each element signal of the plurality of antenna elements.
The angle measuring unit is
The target angle measurement value is calculated from each element signal, and the target angle measurement value is calculated.
By matrix calculation based on each element signal, a virtual array including a plurality of virtual antenna elements having an opening wider than that of the array antenna is formed.
A target detection device that calculates the target angle from each element signal of the plurality of virtual antenna elements by eliminating ambiguity by the angle measurement value. The target detection device according to claim 1, wherein the array antenna includes an antenna element group arranged at a first interval and an antenna element group arranged at a second interval different from the first interval. .. Further, before the process of forming the virtual array, a detection processing unit for identifying the target from the element signals of the plurality of antenna elements is provided.
The target detection device according to claim 1 or 2, wherein the angle measuring unit forms the virtual array by a matrix operation based on each element signal after identifying the target. The target detection device according to claim 1, wherein the angle measuring unit calculates the measured value and the target angle by an interferometer processing method. A signal processing method performed by a processor connected to an array antenna with multiple antenna elements to capture radio waves from a target.
The processor
The target angle measurement value is calculated from each element signal of the plurality of antenna elements.
By matrix calculation based on each element signal, a virtual array including a plurality of virtual antenna elements having an opening wider than that of the array antenna is formed.
A signal processing method for calculating a target angle of a target from each element signal of the plurality of virtual antenna elements by eliminating ambiguity by the angle measurement value. The signal processing method according to claim 5, wherein the array antenna includes an antenna element group arranged at a first interval and an antenna element group arranged at a second interval different from the first interval. .. The processor identifies the target from each element signal of the plurality of antenna elements before the process of forming the virtual array.
The signal processing method according to any one of claims 5 or 6, wherein the virtual array is formed by a matrix operation based on each element signal after the target is identified. The signal processing method according to claim 5, wherein the processor calculates the measured angle value and the target angle by an interferometer processing method.

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