Receiving beam pattern forming device

Abstract

To form transmission / reception beam patterns, in which a clutter is suppressed in its electric power distribution direction while a target is extracted in a desired direction, without any deterioration in beam width through real-time processing of a radar device (not limited to meteorological uses) using an array antenna.SOLUTION: Information on an electric power distribution of a clutter is acquired, and then reception excitation coefficients of respective elements are calculated such that a reception beam pattern while forming a main lobe in a desired direction forms null in an electric power distribution direction of the clutter. The information on the electric power distribution of the clutter is acquired, and then transmission excitation coefficients of the respective elements are calculated such that a transmission beam pattern while forming a main lobe in a desired direction forms null in the electric power distribution direction of the clutter.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a technique for forming transmit and receive beam patterns for an array antenna. [Background technology]

[0002] Weather radar systems that use parabolic antennas to observe rainfall distribution are commonly used. Weather radar systems that use parabolic antennas require mechanical rotation in the elevation direction and cannot scan all elevation directions at high speed, but they can narrow the main lobe of the transmitting and receiving beam pattern, suppress the side lobes of the transmitting and receiving beam pattern, and increase the resolution in the elevation direction. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Morotomi, K., Shimamura, S., Kobayashi, F., Takamura, T., Takano, T., Higuchi, A., & Iwashita, H., “Evolution of a Tornado and Debris Ball Associated With Super Typhoon Hagibis 2019 Observed by X‐Band Phased Array Weather Radar in Japan”, Geophysical Research Letters, 47(24), 2020. [Non-patent document 2] Yoshikawa, E., Ushio, T., & Kikuchi, H., “A Study of Comb Beam Transmission on Phased Array Weather Radars”, IEEE Transactions on Geoscience and Remote Sensing, 59(8), 2021. [Non-patent document 3] Yoshikawa, E., Ushio, T., Kawasaki, Z., Yoshida, S., Morimoto, T., Mizutani, F., & Wada, M., “MMSE Beam Forming on Fast-Scanning Phased Array Weather Radar”, IEEE Transactions on Geoscience and Remote Sensing, 51(5), 2013. Summary of the Invention [Problem to be solved by the invention]

[0004] Weather radar devices that observe rainfall distribution using an array antenna are disclosed in Non-Patent Documents 1 and 2. Weather radar devices that use an array antenna do not require mechanical rotation in the elevation direction and can perform high-speed scanning in all elevation directions. The weather radar device disclosed in Non-Patent Document 1 forms a fan beam pattern as the transmission beam pattern. The weather radar device disclosed in Non-Patent Document 2 forms a comb beam pattern as the transmission beam pattern.

[0005] Figure 1 shows a conventional fan beam pattern. The transmit beam pattern F1 (black) is a fan beam pattern with a wide main lobe. The receive beam pattern F2 (black) narrows the main lobe in the elevation direction selected from the transmit beam pattern F1 through software processing. The combined transmit and receive beam pattern F3 (black) can narrow the main lobe, but cannot suppress the side lobes and does not provide high resolution in the elevation direction. However, by simply forming the transmit beam pattern F1, dense observation in the elevation direction is possible and the observation time can be shortened.

[0006] Figure 2 shows a conventional comb beam pattern. The transmit beam pattern C1 (black) is a comb beam pattern with a narrow main lobe. The receive beam pattern C2 (black) narrows the main lobe in the elevation direction selected from the transmit beam pattern C1 through null formation processing. The combined transmit and receive beam pattern C3 (black) can narrow the main lobe, suppress side lobes, and increase the resolution in the elevation direction. However, unless multiple transmit beam patterns C1 are formed, dense observation in the elevation direction is not possible, and the observation time cannot be shortened.

[0007] A simulation of rainfall distribution observation using the conventional technology is shown in Figure 3. In the left column of Figure 3, the distance and height of rainfall R and the ground surface G were set. In the middle column of Figure 3, rainfall R was observed using transmit beam pattern F1 and receive beam pattern F2, but the side lobes of the total transmit and receive beam pattern F3 could not be suppressed, and a strong false image due to ground clutter C appeared, significantly interfering with the observation of rainfall R. In the right column of Figure 3, rainfall R was observed using transmit beam pattern C1 and receive beam pattern C2, and while the side lobes of the total transmit and receive beam pattern C3 could be suppressed, a weak false image due to ground clutter C appeared, somewhat interfering with the observation of rainfall R.

[0008] Therefore, weather radar devices using array antennas suppress the side lobes of the receiving beam pattern by window function processing or adaptive signal processing (see Non-Patent Document 3). Meanwhile, weather radar devices using parabolic antennas suppress the side lobes of the transmitting and receiving beam pattern by appropriate antenna design. However, weather radar devices using array antennas degrade the beam width of the receiving beam pattern by window function processing, deteriorating observation performance, and adaptive signal processing requires processing of each received signal data from each element, making them unsuitable for real-time processing. Meanwhile, weather radar devices using parabolic antennas cannot suppress the side lobes of the transmitting and receiving beam pattern beyond the design value at the time of antenna design.

[0009] Therefore, in order to solve the above problems, it is an object of the present disclosure to achieve high-speed omnidirectional scanning, improved resolution in each direction, and dense observation in each direction in a radar device (not limited to meteorological applications) using an array antenna. And, in order to solve the above problems, it is an object of the present disclosure to form, by real-time processing, a transmit / receive beam pattern without degradation of the beam width, in a radar device (not limited to meteorological applications) using an array antenna, such that a target is extracted in a desired direction while clutter is suppressed in its power distribution direction. [Means for solving the problem]

[0010] In order to solve the above problem, information on the power distribution of clutter is acquired, and then the receiving excitation coefficient of each element is calculated so that the receiving beam pattern forms a main lobe in the desired direction while forming a null in the direction of the clutter power distribution.

[0011] Specifically, the present disclosure provides a receive beam pattern forming device comprising: a clutter power distribution acquisition unit that acquires information on the power distribution of clutter; a receive excitation coefficient calculation unit that calculates a receive excitation coefficient of each element of the array antenna based on a transmit beam pattern of the array antenna and the power distribution of the clutter, or based on the power distribution of the clutter, such that a receive beam pattern of the array antenna forms a main lobe in a desired direction while forming a null in the direction of the power distribution of the clutter; and a receive signal calculation unit that calculates a receive signal in each direction of the array antenna based on the receive signal and receive excitation coefficient of each element of the array antenna, such that a target is extracted in the desired direction while the clutter is suppressed in the direction of the power distribution of the clutter.

[0012] According to this configuration, in a radar device using an array antenna (not limited to meteorological applications), a receiving beam pattern can be formed by real-time processing without degradation of the beam width, so that targets are extracted in the desired direction while clutter is suppressed in the direction of its power distribution.

[0013] The present disclosure also provides a receiving beam pattern forming device further comprising: an adaptive signal processing unit that calculates a receiving signal in each direction of the array antenna in accordance with a receiving signal of each element of the array antenna so that side lobes are suppressed in undesired directions; and a receiving excitation coefficient updating unit that causes the receiving excitation coefficient calculation unit to update the receiving excitation coefficient of each element of the array antenna based on a new power distribution of the clutter when a difference between the receiving signal in each direction of the array antenna calculated by the receiving signal calculation unit and the receiving signal in each direction of the array antenna calculated by the adaptive signal processing unit is equal to or greater than a predetermined value.

[0014] According to this configuration, even if the reflection intensity and appearance position of the clutter change slightly after the information on the power distribution of the clutter is acquired, the receiving excitation coefficient of each element can be updated.

[0015] The present disclosure also provides a receiving beam pattern forming device characterized in that the transmitting beam pattern of the array antenna is a comb beam pattern in directions requiring high-precision observation, and a fan beam pattern in directions not requiring high-precision observation.

[0016] This configuration allows a radar device (not limited to meteorological applications) using an array antenna to simultaneously achieve high-speed scanning in all directions, improved resolution in each direction, and dense observation in each direction.

[0017] In order to solve the above problem, information on the power distribution of clutter is acquired, and then the transmit excitation coefficient of each element is calculated so that the transmit beam pattern forms a main lobe in the desired direction while forming a null in the direction of the clutter power distribution.

[0018] Specifically, the present disclosure provides a transmission beam pattern forming device comprising: a clutter power distribution acquisition unit that acquires information on the power distribution of clutter; and a transmission excitation coefficient calculation unit that calculates a transmission excitation coefficient of each element of the array antenna based on a transmission beam pattern of the array antenna (before null formation for the clutter) and the power distribution of the clutter, or based on the power distribution of the clutter, such that the transmission beam pattern of the array antenna (after null formation for the clutter) forms a main lobe in a desired direction while forming a null in the direction of the power distribution of the clutter.

[0019] According to this configuration, in a radar device using an array antenna (not limited to meteorological applications), a transmit beam pattern can be formed by real-time processing without degradation of the beam width, so that targets are extracted in the desired direction while clutter is suppressed in the direction of its power distribution.

[0020] The present disclosure also provides a transmission beam pattern forming device, further comprising a transmission excitation coefficient updating unit that causes the transmission excitation coefficient calculation unit to update the transmission excitation coefficient of each element of the array antenna based on a new power distribution of the clutter when a difference between the reception signals in each direction of the array antenna calculated by the reception signal calculation unit included in the reception beam pattern forming device and the reception signals in each direction of the array antenna calculated by the adaptive signal processing unit included in the reception beam pattern forming device is equal to or greater than the predetermined value.

[0021] According to this configuration, even if the reflection intensity and appearance position of the clutter change slightly after the information on the power distribution of the clutter is acquired, the transmission excitation coefficient of each element can be updated.

[0022] The present disclosure also provides a transmission beam pattern forming device characterized in that the transmission beam pattern of the array antenna is a comb beam pattern in directions requiring high-precision observation, and a fan beam pattern in directions not requiring high-precision observation.

[0023] This configuration allows a radar device (not limited to meteorological applications) using an array antenna to simultaneously achieve high-speed scanning in all directions, improved resolution in each direction, and dense observation in each direction.

[0024] In order to solve the above problem, we have decided to take advantage of the respective advantages of comb and fan beam patterns, forming a comb beam pattern as a transmit beam pattern in directions where high-precision observation is required (directions depending on the application and situation), while forming a fan beam pattern as a transmit beam pattern in directions where high-precision observation is not required (directions depending on the application and situation).

[0025] Specifically, the present disclosure relates to a radar device characterized in that the transmission beam pattern of the array antenna is a comb beam pattern in directions where high-precision observation is required, and a fan beam pattern in directions where high-precision observation is not required.

[0026] This configuration allows a radar device (not limited to meteorological applications) using an array antenna to simultaneously achieve high-speed scanning in all directions, improved resolution in each direction, and dense observation in each direction. [Effects of the Invention]

[0027] In this way, the present disclosure enables a radar device (not limited to meteorological applications) using an array antenna to simultaneously achieve high-speed scanning in all directions, improved resolution in each direction, and dense observation in each direction. Furthermore, the present disclosure enables a radar device (not limited to meteorological applications) using an array antenna to form, through real-time processing, a transmit / receive beam pattern without degradation of beam width, such that a target is extracted in a desired direction while clutter is suppressed in its power distribution direction. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 illustrates a prior art fan beam pattern. [Figure 2] FIG. 1 illustrates a prior art comb beam pattern. [Figure 3]FIG. 1 is a diagram showing a simulation of rainfall distribution observation using the prior art. [Figure 4] 1 is a diagram illustrating a configuration of a weather radar device according to the present disclosure. [Figure 5] 1A and 1B are diagrams illustrating transmission beams in the elevation direction according to the present disclosure and the comparative example. [Figure 6] FIG. 10 is a diagram showing transmit beam patterns according to the present disclosure and the comparative example. [Figure 7] FIG. 10 is a diagram showing the total transmit and receive beam patterns of the present disclosure and the comparative example. [Figure 8] FIG. 10 is a diagram showing the procedure of a receive beam pattern forming process according to the present disclosure. [Figure 9] FIG. 1 illustrates a transmit / receive / total transmit / receive beam pattern of the present disclosure. [Figure 10] FIG. 1 illustrates a transmit / receive / total transmit / receive beam pattern of the present disclosure. [Figure 11] FIG. 1 illustrates a transmit / receive / total transmit / receive beam pattern of the present disclosure. [Figure 12] FIG. 1 illustrates a transmit / receive / total transmit / receive beam pattern of the present disclosure. [Figure 13] FIG. 10 is a diagram showing the procedure of a transmit beam pattern forming process according to the present disclosure. [Figure 14] FIG. 1 illustrates a transmit / receive / total transmit / receive beam pattern of the present disclosure. [Figure 15] FIG. 1 illustrates a transmit / receive / total transmit / receive beam pattern of the present disclosure. [Figure 16] FIG. 1 illustrates a transmit / receive / total transmit / receive beam pattern of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0029]

[0023] The following embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of implementation of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0030] (Configuration of the weather radar device of the present disclosure) The configuration of the weather radar device of the present disclosure is shown in Fig. 4. The weather radar device W includes an array antenna 1, a weather radar transmitting and receiving device 2, and a transmitting and receiving beam pattern forming device 3, and removes clutter on the earth's surface G when observing a signal of precipitation R. The transmitting and receiving beam pattern forming device 3 includes a clutter power distribution acquisition unit 31, a receiving excitation coefficient calculation unit 32, a receiving signal calculation unit 33, an adaptive signal processing unit 34, a receiving excitation coefficient update unit 35, a transmitting excitation coefficient calculation unit 36, and a transmitting excitation coefficient update unit 37, and can be realized by installing a receiving beam pattern forming program and a transmitting beam pattern forming program shown in Fig. 8 and Fig. 13, respectively, on a computer.

[0031] The transmission beams in the elevation angle direction for the present disclosure and the comparative example are shown in Figure 5. In the present disclosure, by taking advantage of the respective advantages of comb and fan beam patterns, a comb beam pattern is formed as the transmission beam pattern in the low elevation angle direction, while a fan beam pattern is formed as the transmission beam pattern in the high elevation angle direction. In the comparative example, because the number of transmitting elements is smaller than the number of receiving elements, a fan beam pattern is formed as the transmission beam pattern in the low elevation angle direction, and a fan beam pattern is also formed as the transmission beam pattern in the high elevation angle direction.

[0032] In the present disclosure, in the low elevation angle direction, since the observation distance is long and the clutter from the Earth's surface G is strong, a comb beam pattern is formed as the transmit beam pattern to increase the resolution in the elevation angle direction and the gain in each elevation angle direction (see FIG. 2). On the other hand, in the high elevation angle direction, since the observation distance is short and the clutter from the Earth's surface G is weak, scanning in all elevation angle directions can be made faster and the gain in each elevation angle direction can be made lower, so a fan beam pattern is formed as the transmit beam pattern (see FIG. 1).

[0033] In the present disclosure, the following transmit beam patterns are formed: Comb beam pattern No. 1 at an elevation angle of 0° and 3°, Comb beam pattern No. 2 at an elevation angle of 1° and 4°, Comb beam pattern No. 3 at an elevation angle of 2° and 5°, Comb beam pattern No. 4 at elevation angles of 6°, 9°, . . . , and 24°, Comb beam pattern No. 5 at elevation angles of 7°, 10°, . . . , and 25°, Comb beam pattern No. 6 at elevation angles of 8°, 11°, . . . , and 23°, and Fan beam pattern No. 7 at elevation angles of 26° to 55°. Note that a Taylor window is applied in forming the transmit beam pattern, and a Taylor window is also applied in forming the receive beam pattern.

[0034] In the comparative example, the following transmit beam patterns are formed: fan-type beam pattern No. 1 at an elevation angle of 0° to 1°, fan-type beam pattern No. 2 at an elevation angle of 2° to 3°, fan-type beam pattern No. 3 at an elevation angle of 4° to 5°, fan-type beam pattern No. 4 at an elevation angle of 6° to 10°, fan-type beam pattern No. 5 at an elevation angle of 11° to 18°, fan-type beam pattern No. 6 at an elevation angle of 19° to 31°, and fan-type beam pattern No. 7 at an elevation angle of 32° to 55°. Note that when forming the transmit beam pattern, a Taylor window is not applied, and a co-phase mode is applied, while when forming the receive beam pattern, a Taylor window is applied.

[0035] The transmit beam patterns of the present disclosure and the comparative example are shown in Fig. 6. The transmit excitation coefficient calculation unit 36 ​​calculates the transmit excitation coefficient of each element so as to form the transmit beam pattern shown in Fig. 6 (see Fig. 13). In the present disclosure, comb beam patterns No. 1 to No. 3 have a higher gain than comb beam patterns No. 4 to No. 6, and therefore have a smaller number of beams.

[0036] The total transmit and receive beam patterns of the present disclosure and the comparative example are shown in Fig. 7. The receive excitation coefficient calculation unit 32 calculates the receive excitation coefficient of each element so as to form a receive beam pattern in each elevation angle direction (see Fig. 8). In the present disclosure, the resolution is higher, particularly in the low elevation angle direction, and the side lobes in the low elevation angle direction and the high elevation angle direction are more suppressed than in the comparative example.

[0037] In this way, the weather radar device W using the array antenna 1 can simultaneously achieve high-speed scanning in all elevation directions, improved resolution in the elevation directions, and dense observation in the elevation directions.

[0038] As a variant, the transmission beam pattern of the array antenna 1 may be a comb beam pattern in directions where high-precision observation is required (directions depending on the application and situation), or a fan beam pattern in directions where high-precision observation is not required (directions depending on the application and situation). In this way, a radar device (not limited to meteorological applications) using the array antenna 1 can simultaneously achieve high-speed scanning in all directions, improved resolution in each direction, and dense observation in each direction.

[0039] (Procedure of receiving beam pattern formation process according to the present disclosure) The procedure for the receive beam pattern forming process of the present disclosure is shown in Fig. 8. Steps S1 to S5 are an application of the null forming process of Non-Patent Document 2. Steps S6 to S10 are an application of the adaptive signal processing of Non-Patent Document 3. Steps S1 to S5 and steps S6 to S10 are executed in parallel. The process will be explained below in the order of the steps.

[0040] The clutter power distribution acquisition unit 31 acquires information on the power distribution of clutter on the ground surface G (step S1). Here, in order to observe the power distribution of clutter on the ground surface G without being affected by the power distribution of the signal of precipitation R, step S1 is executed in advance under clear skies.

[0041] The receiving excitation coefficient calculation unit 32 calculates the receiving excitation coefficient of each element based on the transmitting beam pattern and the power distribution of clutter on the ground surface G (steps S2 and S3) so that the receiving beam pattern forms a main lobe in the desired direction while forming a null in the direction of the power distribution of clutter on the ground surface G. Steps S2 and S3 will be explained below using equations 1 to 3.

[0042] First, calculate y' in Equation 1. Here, y TX is the transmit beam pattern, and yCL is the power distribution of clutter on the ground surface G. E is a diagonal matrix, with the diagonal elements corresponding to the desired direction being 0 and the diagonal elements corresponding to other directions being 1. Furthermore, y TX for y CL The weighting of is set taking into consideration the signal-to-noise ratio of the clutter and the depth of the null.

number

[0043] In addition, y TX When a comb beam pattern is used as the transmit beam pattern, it is easy to form a null in the receive beam pattern in the elevation direction far from the main lobe of the receive beam pattern (see Figure 2). TX When a fan-shaped beam pattern is used as the transmit beam pattern, a null must be formed in the receive beam pattern even in the elevation direction close to the main lobe of the receive beam pattern, making it difficult to form a null in the receive beam pattern (see Figure 1).

[0044] Next, in Equation 2, R y’ Here, H is the complex conjugate transpose, the circle marks are the Hadamard product, and I is the identity matrix, which, together with the Hadamard product, gives y' y' H Extract the diagonal elements of y' y' H Zero out the off-diagonal elements of

number

[0045] Next, calculate x^ in Equation 3. Here, y a is a beam pattern that forms a main lobe in the desired direction. S is a steering matrix that converts the excitation coefficients of each element into a beam pattern. Therefore, x^ is the desired receiving excitation coefficient of each element. The desired receiving excitation coefficient of each element is then stored as an excitation coefficient table.

number

[0046] Here, the diagonal components of E corresponding to the desired direction are set to 0, and the diagonal components corresponding to other directions are set to 1 (see Equation 1). y’ ) -1 increases the diagonal component corresponding to the desired direction and decreases the diagonal component corresponding to other directions (see Equation 2). Therefore, x^ increases the component corresponding to the desired direction and decreases the components corresponding to other directions (see Equation 3).

[0047] The received signal calculation unit 33 calculates the received signals for each elevation angle direction based on the received signals of each element and the receiving excitation coefficients (excitation coefficient table) so that the rainfall R is extracted in the desired direction while the clutter on the ground surface G is suppressed in the power distribution direction (steps S4 and S5).

[0048] In steps S2 and S3, the receiving excitation coefficient calculation unit 32 calculates the desired receiving excitation coefficient of each element based on the transmit beam pattern and the power distribution of clutter on the ground surface G. As a modified example, the receiving excitation coefficient calculation unit 32 may calculate the desired receiving excitation coefficient of each element based only on the power distribution of clutter on the ground surface G without using the transmit beam pattern.

[0049] The transmit / receive / total transmit / receive beam patterns of the present disclosure are shown in Fig. 9 to Fig. 12. Fig. 9 to Fig. 12 show the results of executing the processes of steps S1 to S5 in Fig. 8.

[0050] In Figure 9, the power distribution of clutter from the ground surface G is not observed in all elevation angle directions. In the upper part of Figure 9, the transmit beam pattern forms a comb beam pattern at elevation angles of 10°, 20°, and 30°. In the middle part of Figure 9, the receive beam pattern forms a main lobe at an elevation angle of 10° and nulls at elevation angles of 20° and 30°. In the lower part of Figure 9, the combined transmit and receive beam pattern forms a main lobe at an elevation angle of 10°.

[0051] In FIG. 10, the relative power of clutter from the ground surface G is 0 dB and is observed at elevation angles of 0° to 5°. In the upper part of FIG. 10, the transmit beam pattern forms a comb beam pattern at elevation angles of 10°, 20°, and 30°. In the middle part of FIG. 10, the receive beam pattern forms a main lobe at an elevation angle of 10°, forms nulls at elevation angles of 20° and 30°, and forms shallow nulls corresponding to clutter power of 0 dB at elevation angles of 0° to 5°. In the lower part of FIG. 10, the combined transmit and receive beam pattern forms a main lobe at an elevation angle of 10°, and forms shallow nulls corresponding to clutter power of 0 dB at elevation angles of 0° to 5°.

[0052] In Figure 11, the relative power of clutter from the ground surface G is 10 dB, and is observed at elevation angles of 0° to 5°. In the upper part of Figure 11, the transmit beam pattern forms a comb beam pattern at elevation angles of 10°, 20°, and 30°. In the middle part of Figure 11, the receive beam pattern forms a main lobe at an elevation angle of 10°, forms nulls at elevation angles of 20° and 30°, and forms a medium null corresponding to the clutter power of 10 dB at elevation angles of 0° to 5°. In the lower part of Figure 11, the combined transmit and receive beam pattern forms a main lobe at an elevation angle of 10°, and forms a medium null corresponding to the clutter power of 10 dB at elevation angles of 0° to 5°.

[0053] In FIG. 12, the relative power of clutter from the ground surface G is 30 dB, and is observed at elevation angles of 0° to 5°. In the upper part of FIG. 12, the transmit beam pattern forms a comb beam pattern at elevation angles of 10°, 20°, and 30°. In the middle part of FIG. 12, the receive beam pattern forms a main lobe at an elevation angle of 10°, forms nulls at elevation angles of 20° and 30°, and forms a deeper null corresponding to the clutter power of 30 dB at elevation angles of 0° to 5°. In the lower part of FIG. 12, the combined transmit and receive beam pattern forms a main lobe at an elevation angle of 10°, and forms a deeper null corresponding to the clutter power of 30 dB at elevation angles of 0° to 5°.

[0054] After acquiring information on the power distribution of clutter on the ground surface G (step S1), the reflection intensity and appearance position of clutter on the ground surface G may change slightly depending on the season, weather, or time of day. This effect is more apparent in low elevation angle directions than in high elevation angle directions.

[0055] The adaptive signal processing unit 34 calculates the received signal for each elevation angle direction so that side lobes are suppressed in undesired directions, adaptively adapting to the received signal for each element (steps S6 and S7). Here, in order to form the receive beam pattern in real time, step S6 is not executed for each data of the received signal for each element, but is executed periodically according to the season, weather, or time of day.

[0056] The receiving excitation coefficient update unit 35 calculates (step S8) the difference between the received signal in each elevation angle direction calculated by the received signal calculation unit 33 (step S4) and the received signal in each elevation angle direction calculated by the adaptive signal processing unit 34 (step S6). If the difference is equal to or greater than a predetermined value (step S9, YES), the receiving excitation coefficient update unit 35 causes the receiving excitation coefficient calculation unit 32 to update the receiving excitation coefficient of each element based on the new power distribution of clutter on the ground surface G (step S10).

[0057] In this embodiment, the present disclosure is applied to a weather radar device W, but as a modified example, the present disclosure may be applied to a radar mounted on a drone, etc. In this embodiment, clutter on the ground surface G is removed, but as a modified example, clutter on the sea surface, etc. may be removed.

[0058] In this way, in a radar device (not limited to meteorological applications) using the array antenna 1, a receiving beam pattern can be formed by real-time processing without degradation of the beam width, so that targets are extracted in the desired direction while clutter is suppressed in its power distribution direction.

[0059] After acquiring information on the power distribution of clutter, even if the reflection intensity and appearance position of the clutter change slightly, the receiving excitation coefficient of each element can be updated.

[0060] (Procedure of transmit beam pattern formation process of the present disclosure) The procedure for the transmit beam pattern forming process of the present disclosure is shown in Fig. 13. Steps S11 to S13 are an application of the null forming process of Non-Patent Document 2. Steps S14 to S18 are an application of the adaptive signal processing of Non-Patent Document 3. Steps S11 to S13 and steps S14 to S18 are executed in parallel. The process will be explained below in the order of the steps.

[0061] The clutter power distribution acquisition unit 31 acquires information on the power distribution of clutter on the ground surface G (step S11). Here, in order to observe the power distribution of clutter on the ground surface G without being affected by the power distribution of the signal of precipitation R, step S11 is executed in advance under clear skies.

[0062] The transmission excitation coefficient calculation unit 36 ​​calculates the transmission excitation coefficient of each element (steps S12 and S13) based on the transmission beam pattern (before forming a null for clutter on the ground surface G) and the power distribution of the clutter on the ground surface G, so that the transmission beam pattern (after forming a null for clutter on the ground surface G) forms a main lobe in a desired direction while forming a null in the direction of the power distribution of the clutter on the ground surface G. Steps S12 and S13 will be explained below using equations 4 to 6.

[0063] First, calculate y' in Equation 4. Here, y TX is the transmit beam pattern, and y CL is the power distribution of clutter on the ground surface G. E is a diagonal matrix, with the diagonal elements corresponding to the desired direction being 0 and the diagonal elements corresponding to other directions being 1. Furthermore, y TX for y CL The weighting of is set taking into consideration the signal-to-noise ratio of the clutter and the depth of the null.

number

[0064] In addition, y TXWhen a comb beam pattern is used as the transmit beam pattern, it is easy to form a null in the transmit beam pattern in the elevation direction far from the main lobe of the transmit beam pattern (see Figure 2). TX When a fan-shaped beam pattern is adopted as the transmit beam pattern, a null must be formed in the transmit beam pattern even in the elevation direction close to the main lobe of the transmit beam pattern, which makes it difficult to form a null in the transmit beam pattern (see Figure 1).

[0065] Next, in Equation 5, R y’ Here, H is the complex conjugate transpose, the circle marks are the Hadamard product, and I is the identity matrix, which, together with the Hadamard product, gives y' y' H Extract the diagonal elements of y' y' H Zero out the off-diagonal elements of

number

[0066] Next, calculate x^ in Equation 6. Here, y a is a beam pattern that forms a main lobe in the desired direction. S is a steering matrix that converts the excitation coefficients of each element into a beam pattern. Therefore, x^ is the desired transmit excitation coefficient of each element. The desired transmit excitation coefficient of each element is then stored as an excitation coefficient table.

number

[0067] Here, the diagonal components of E corresponding to the desired direction are set to 0, and the diagonal components corresponding to other directions are set to 1 (see Equation 4). y’ ) -1 increases the diagonal components corresponding to the desired direction and decreases the diagonal components corresponding to other directions (see Equation 5). Therefore, x^ increases the component corresponding to the desired direction and decreases the components corresponding to other directions (see Equation 6).

[0068] The reason for adding λI in Equation 6 is as follows. That is, when a transmission beam pattern is formed, the number of main beams formed is greater than when a reception beam pattern is formed. Therefore, in Equation 6, (S H R y’ S) -1 Therefore, in Equation 6, (S H R y’ S+λI) -1 Here, λ is set to a value that is neither too small nor too large so that the transmit beam pattern formation does not become unstable and a clutter null is formed after the transmit beam pattern formation.

[0069] In steps S12 and S13, the transmit excitation coefficient calculation unit 36 ​​calculates the desired transmit excitation coefficient of each element based on the transmit beam pattern and the power distribution of clutter on the ground surface G. As a modified example, the transmit excitation coefficient calculation unit 36 ​​may calculate the desired transmit excitation coefficient of each element based only on the power distribution of clutter on the ground surface G without using the transmit beam pattern.

[0070] The transmit / receive / total transmit / receive beam patterns of the present disclosure are shown in Fig. 14 to Fig. 16. Fig. 14 to Fig. 16 show the results of executing the processes of steps S11 to S13 in Fig. 13.

[0071] In Fig. 14, the transmit beam pattern does not form a clutter null at the ground surface G. In the upper part of Fig. 14, the transmit beam pattern forms a seven-comb beam pattern at an elevation angle of 0° to 20°. In the middle part of Fig. 14, the receive beam pattern forms a main lobe at an elevation angle of 16°, forms a null at an elevation angle of 0° to 20° (excluding 16°), and forms a null corresponding to the clutter power at an elevation angle of 30° to 35° (see Fig. 8). In the lower part of Fig. 14, the total transmit and receive beam pattern forms a main lobe at an elevation angle of 16°, and forms a null corresponding to the clutter power at an elevation angle of 30° to 35°.

[0072] In FIG. 15, the clutter null of the ground surface G is formed in the transmit beam pattern, but λI in Equation 6 is not added. In the upper part of FIG. 15, the transmit beam pattern is H R y’ S) -1 14. In the middle of FIG. 15, the receive beam pattern is significantly different from the middle of FIG. 14 due to instability in the formation of the transmit beam pattern. In the bottom of FIG. 15, the total transmit and receive beam pattern is significantly different from the bottom of FIG. 14 due to instability in the formation of the transmit beam pattern and the receive beam pattern.

[0073] In FIG. 16, a clutter null of the ground surface G is formed in the transmit beam pattern, and λI in Equation 6 is added. In the upper part of FIG. 16, the transmit beam pattern forms a seven-comb beam pattern at an elevation angle of 0° to 20°, and forms a null corresponding to the clutter power at an elevation angle of 30° to 35°. In the middle part of FIG. 16, the receive beam pattern forms a main lobe at an elevation angle of 16°, forms a null at an elevation angle of 0° to 20° (excluding 16°), and forms a null corresponding to the clutter power at an elevation angle of 30° to 35° (see FIG. 8). In the lower part of FIG. 16, the transmit / receive total beam pattern forms a main lobe at an elevation angle of 16°, and forms a null corresponding to the clutter power at an elevation angle of 30° to 35°. The clutter null is deeper in the lower part of FIG. 16 than in the lower part of FIG. 14.

[0074] After acquiring information on the power distribution of clutter on the ground surface G (step S11), the reflection intensity and appearance position of clutter on the ground surface G may change slightly depending on the season, weather, or time of day. This effect is more apparent in low elevation angle directions than in high elevation angle directions.

[0075] The adaptive signal processing unit 34 calculates the received signal for each elevation angle direction, adaptively adapting to the received signal of each element, so that side lobes are suppressed in undesired directions (steps S14 and S15). Here, in order to form the transmit beam pattern in real time, step S14 is not executed for each data of the received signal of each element, but is executed periodically according to the season, weather, or time of day.

[0076] The transmission excitation coefficient update unit 37 calculates (step S16) the difference between the reception signal for each elevation angle calculated by the reception signal calculation unit 33 (step S4) and the reception signal for each elevation angle calculated by the adaptive signal processing unit 34 (step S14). If the difference is equal to or greater than a predetermined value (step S17, YES), the transmission excitation coefficient update unit 37 causes the transmission excitation coefficient calculation unit 36 ​​to update the transmission excitation coefficient of each element based on the new power distribution of clutter on the ground surface G (step S18).

[0077] In this embodiment, the present disclosure is applied to a weather radar device W, but as a modified example, the present disclosure may be applied to a radar mounted on a drone, etc. In this embodiment, clutter on the ground surface G is removed, but as a modified example, clutter on the sea surface, etc. may be removed.

[0078] In this way, in a radar device (not limited to meteorological applications) using the array antenna 1, a transmit beam pattern can be formed by real-time processing without degradation of the beam width, such that targets are extracted in the desired direction while clutter is suppressed in its power distribution direction.

[0079] After acquiring information on the power distribution of clutter, even if the reflection intensity and appearance position of the clutter change slightly, the transmission excitation coefficient of each element can be updated. [Industrial Applicability]

[0080] The receive beam pattern forming device and transmit beam pattern forming device of the present disclosure can form receive beam patterns and transmit beam patterns while forming nulls in the power distribution direction of clutter such as the ground surface or sea surface, etc. The radar device of the present disclosure can form receive beam patterns and transmit beam patterns while simultaneously achieving high-speed scanning, improved resolution, and dense observation. [Explanation of symbols]

[0081] F1: Transmit beam pattern F2: Receiving beam pattern F3: Total beam pattern for transmission and reception C1: Transmit beam pattern C2: Receiving beam pattern C3: Total beam pattern for transmission and reception R:Rainfall G: Ground surface C: Ground clutter W: Weather radar equipment 1: Array antenna 2: Weather radar transmitter and receiver 3: Transmitting and receiving beam pattern forming device 31:Clutter power distribution acquisition section 32: Receiving excitation coefficient calculation unit 33: Received signal calculation unit 34: Adaptive signal processing unit 35: Receiving excitation coefficient update unit 36: Transmit excitation coefficient calculation unit 37: Transmission excitation coefficient update unit

Claims

1. a clutter power distribution acquisition unit that acquires information on the power distribution of clutter; a receiving excitation coefficient calculation unit that calculates, using a beam-null forming technique, a receiving excitation coefficient for each element of the array antenna based on a transmitting beam pattern of the array antenna and a power distribution of the clutter, or based on the power distribution of the clutter, such that a receiving beam pattern of the array antenna forms a main lobe in a desired direction while forming a null in the direction of the power distribution of the clutter; a received signal calculation unit that calculates received signals in each direction of the array antenna based on received signals and receiving excitation coefficients of each element of the array antenna, such that the target is extracted in the desired direction while the clutter is suppressed in the power distribution direction of the clutter; an adaptive signal processing unit that uses adaptive beamforming technology to adapt to the received signals of each element of the array antenna and calculates received signals in each direction of the array antenna so that side lobes in undesired directions are suppressed; a receiving excitation coefficient updating unit that causes the receiving excitation coefficient calculating unit to update the receiving excitation coefficient of each element of the array antenna based on a new power distribution of the clutter when a difference between the received signal in each direction of the array antenna calculated by the received signal calculating unit and the received signal in each direction of the array antenna calculated by the adaptive signal processing unit is equal to or greater than a predetermined value; A receiving beam pattern forming device comprising:

2. The transmitting beam pattern of the array antenna is a comb beam pattern in a direction where high accuracy observation is required, and a fan beam pattern in a direction where high accuracy observation is not required.

2. The receiving beam pattern forming device according to claim 1, wherein:

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