Electromagnetic wave processing system

Abstract

To provide an electromagnetic wave processing system capable of performing omnidirectional observation with only one machine.SOLUTION: An electromagnetic wave processing system mounted on a spacecraft with a plurality of antennas comprises a measuring device which processes electromagnetic wave measurement signals acquired by the plurality of antennas, an attitude detection device which detects the attitude of the spacecraft, a rotation control device which controls the rotation of the spacecraft, and an arithmetic device. The rotation control device rotates the spacecraft about the center of gravity along a plurality of rotational axes with respect to an inertial space. The measuring device performs measurements in a plurality of attitudes that change due to rotation. The arithmetic device calculates the intensity distribution of electromagnetic waves acquired by the plurality of antennas using interference waveforms obtained by multiplying measurement signals obtained from different antennas in the measurement signals obtained in the plurality of attitudes.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electromagnetic wave processing system mounted on a spacecraft for observing radio wave sources distributed in all directions on the earth and in outer space. [Background technology]

[0002] In the field of remote sensing using moving objects such as satellites or aircraft, a method for determining the location of an electromagnetic wave source is an important technology. As satellite formation flights and constellations enable wide-area and high-frequency observation, the use of this technology is expected. Specifically, in the field of interferometric radio radiometers, a method has been proposed for determining the direction of arrival of electromagnetic waves by observing phase differences, etc., through interference processing using signals received by multiple antennas.

[0003] For example, Patent Document 1 discloses a method for estimating the direction of arrival of a target signal with respect to an array of measurement antennas of a satellite in Earth orbit, while Patent Document 2 discloses a control device that includes multiple antennas facing different directions in a plane, searches for the direction of arrival of electromagnetic waves, and controls the movement of a mobile object. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US2015 / 0355312 [Patent Document 2] JP 2019-56656 A Summary of the Invention [Problem to be solved by the invention]

[0005] An interferometer-type radio radiometer mounted on a moving object such as an artificial satellite (or also called a satellite) or an aircraft (hereinafter referred to as a spacecraft in the present invention) performs aperture synthesis processing by orbital motion with a fixed baseline length, and does not use the rotation (rotation) of the artificial satellite, so that the observation range is limited. For example, it is difficult to simultaneously perform observation in the direction of the earth's surface including land and ocean and observation in the direction of outer space opposite to the earth's surface from an orbit around the earth. In order to realize a rotating radio interferometer that observes in all directions with only one moving object, for example, it is necessary to rotate multiple antennas attached to the artificial satellite around multiple arbitrary axes and perform measurements and analysis of the measurement signals in multiple attitudes that change due to the rotation of the satellite. However, Patent Document 1 does not assume that the satellite will be rotated around an arbitrary axis, so there is no description of this problem. In addition, Patent Document 2 assumes that an antenna will be mounted on a flying device such as a drone, and there is no description of the viewpoint of rotating the device itself around multiple axes.

[0006] In view of the above, an object of the present invention is to provide an electromagnetic wave processing system that enables omnidirectional observation using only one satellite. [Means for solving the problem]

[0007] In view of the above, the present invention is an electromagnetic wave processing system mounted on a spacecraft having multiple antennas, the electromagnetic wave processing system comprising a measurement device that processes measurement signals of electromagnetic waves acquired by the multiple antennas, an attitude detection device that detects the attitude of the spacecraft, a rotation control device that controls the rotation of the spacecraft, and a calculation device, wherein the rotation control device rotates the spacecraft around its center of gravity on multiple rotation axes with respect to inertial space, the measurement device performs measurements at multiple attitudes that change due to the rotation, and the calculation device calculates the intensity distribution of the electromagnetic waves acquired by the multiple antennas using an interference waveform obtained by multiplying measurement signals obtained from different antennas together in the measurement signals obtained at the multiple attitudes. Effect of the Invention

[0008] According to the present invention, the satellite rotates on multiple axes, assumes various attitudes, and performs measurements in each attitude, which leads to omnidirectional observation with only one satellite. In this case, the rotation operation and measurements on multiple axes can be appropriately controlled, and observations can be performed taking into account the state of the satellite's attitude. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of a schematic configuration of a spacecraft. [Diagram 2] FIG. 1 is a diagram showing an example of a basic configuration of an electromagnetic wave processing system 30 according to a first embodiment of the present invention. [Diagram 3] FIG. 2 is a flow chart showing an outline of the processing contents in the arithmetic device 20 of the electromagnetic wave processing system 30 according to the first embodiment of the present invention. [Figure 4] 4 is a flowchart showing a detailed example of the rotation measurement process in the calculation device 20. FIG. [Diagram 5] FIG. 5 is a diagram showing a time sequence in the measurement process described in FIG. 4. [Figure 6] FIG. 2 is a diagram showing the antenna configuration and the positional relationship of the electromagnetic wave source when performing rotation measurement. [Figure 7] FIG. 13 is a diagram showing a theoretical interference change pattern obtained from the time series change of interference fringes. [Figure 8] FIG. 4 is a diagram showing rotation axes when performing processing step S33 in FIG. 3. [Figure 9] FIG. 13 is a diagram showing an example of an interference waveform Rij(t) observed by the processing in processing step S34. [Figure 10] FIG. 13 is a diagram showing an example of an interference fringe map obtained by the processing in processing step S35. [Figure 11] 3 is a diagram showing an example of processing for reconstructing an electromagnetic wave source in the radio wave source identification unit 23 of FIG. 2; [Figure 12] Schematic showing the simulation setup. [Figure 13] FIG. 2 is a diagram showing the position coordinates of an electromagnetic wave source and an antenna. [Figure 14] FIG. 11 is a diagram showing a simulation result of radio wave source position estimation. [Figure 15]11A to 11C are diagrams showing a simplified flow of electromagnetic wave source reconstruction processing and an example of creating a two-dimensional map. [Figure 16] FIG. 1 is a diagram showing an example of a basic configuration of an electromagnetic wave processing system 30 according to a second embodiment of the present invention. [Figure 17] FIG. 11 is a diagram showing a time sequence of rotation measurement according to the second embodiment. [Figure 18] FIG. 13 is a diagram showing an example of detection of a moving electromagnetic wave source. [Figure 19] FIG. 1 is a diagram showing a method for tracking a moving electromagnetic source. [Figure 20] A diagram showing multiple spacecraft tracking the same target when flying in formation. [Figure 21] FIG. 13 is a diagram showing measurement results in rotation under different conditions. [Figure 22] FIG. 11 is a flow chart showing an outline of the processing contents in a calculation device 20 of an electromagnetic wave processing system 30 according to a seventh embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0011] 1 is a diagram showing an example of the schematic configuration of a spacecraft. For example, the spacecraft 1, which is an artificial satellite, has multiple antennas AN (in the illustrated example, a planar antenna ANA and a pole antenna ANB) arranged around the spacecraft housing 2 via tension members 4, and is also equipped with a solar panel 5 for solar power generation.

[0012] 2 is installed in the spacecraft casing 2, and radio wave sources distributed in all directions on the ground and in outer space are observed by the electromagnetic wave processing system 30. The solar panel 5 supplies power for this purpose.

[0013] Here, the planar antenna ANA is a patch antenna installed on a thin film having three sides formed by a tension member 4 (cable), which is a member having tension. The pole antenna ANB is installed on a compression member having compression. The housing 2 of the spacecraft 1 is located in the center, and a solar panel 5 is installed on the surface of the housing 2. The solar panel 5 may also be installed on the thin film portion in a place where the planar antenna ANA is not installed.

[0014] 2 is a diagram showing an example of a basic configuration of an electromagnetic wave processing system 30 mounted on the spacecraft 1. The electromagnetic wave processing system 30 is configured to include a plurality of antennas AN (AN1...ANN), a measurement device 10 that processes measurement signals of electromagnetic waves acquired by the plurality of antennas AN, an attitude detection device 9 that detects the attitude of the spacecraft 1, a rotation control device 8 that controls the rotation of the spacecraft 1, i.e., its axis, and an arithmetic device 20 configured using a computer.

[0015] Of these, the attitude detection device 9 is composed of a star tracker, a sun sensor, an earth sensor, a magnetic sensor, etc. for determining the attitude, and the rotation control device 8 is composed of a reaction wheel, a momentum wheel, a magnetic torquer, a thruster, etc., which enable the attitude control of the spacecraft 1.

[0016] 2, the rotation control device 8 rotates the spacecraft around the center of gravity on multiple rotation axes relative to the inertial space, the measurement device 10 performs measurements at multiple attitudes that change due to the rotation, and the calculation device 20 calculates the interference intensity distribution of the electromagnetic waves acquired by the multiple antennas using an interference waveform obtained by multiplying the measurement signals obtained at the multiple attitudes by the measurement signals obtained from different antennas AN. Also, the rotation control device 8 is controlled according to instructions from the calculation device 20, and attitude control is performed to position the spacecraft 1 at an appropriate position.

[0017] In order to perform measurements in multiple attitudes that change due to rotation, the measurement device 10 first amplifies the measurement signals of the multiple antennas AN in the amplifier 11. Similar to the principle used in FM receivers, the target frequency is multiplied by the frequency of a local oscillator 15 in a mixer 12, and an intermediate frequency filter 13 is applied to extract the difference frequency (intermediate frequency). In this way, the measurement signals of the multiple antennas AN are converted to low frequencies to facilitate subsequent processing. The signals are then AD converted in an AD converter 14 and input to a calculation device 20.

[0018] It is assumed that the processing in the measuring device 10 is performed in an analog manner, but it is preferable that the processing in the arithmetic unit 20 is performed by a computer. In this case, the arithmetic unit 20 has a storage device 21, an output device 24, and the functions of an interference waveform calculation unit 22 and a radio wave source identification unit 23 as processing functions of the arithmetic unit of the computer.

[0019] 3 is a flow diagram showing an outline of the processing contents in the arithmetic device 20 of the electromagnetic wave processing system 30. In the first processing step S31 of the processing in the arithmetic device 20, the measurement conditions are set or received. The measurement conditions include the rotation axis during electromagnetic wave measurement, the order of the rotation axes to be used, and the rotation speed. Predetermined conditions stored in advance in the internal memory of the arithmetic device 20 or the like may be set, or a communication device may be provided and the conditions may be set by receiving commands from a ground station.

[0020] Next, in processing step S32, the attitude reference direction is set or received from outside. The attitude reference direction is the attitude direction at the start and end of rotation, and is set to the same direction for each rotation to align the measurement start time. For example, the attitude reference direction can be set to a direction in which the x, y, and z axes defined in the body coordinate system of the spacecraft coincide with the x and y axes of the inertial coordinate system (for example, taken as a geocentric coordinate system), including the positive and negative directions.

[0021] Next, in process step S33, a command is issued to the rotation control device 8 to rotate the spacecraft 1 about multiple axes, and measurement information from the measurement device 10 and attitude information from the attitude detection device 9 are acquired.

[0022] In processing step S34, each attitude and time information is associated with the electric field waveform measured by each antenna AN, and an interference waveform is calculated by multiplying the signal for each antenna pair and applying a low-pass filter.

[0023] Next, in process step S35, a theoretical interference intensity change pattern is calculated or read from the posture change. Next, in process step S36, the interference waveform at each time is multiplied by the theoretical interference intensity change pattern corresponding to each time, and the result is integrated in the time direction to reconstruct the electromagnetic wave source direction.

[0024] According to the above process, it is possible to perform omnidirectional observation with only one spacecraft. Even if the number of antennas is limited, it is possible to increase the number of baseline lengths or types of baseline vectors by increasing the number of rotation axes, and thus perform omnidirectional observation. It is also possible to obtain polarization information of the electromagnetic wave source by combining antennas with different directivity patterns.

[0025] 2 corresponds to processing steps S33 and S34 in FIG. 3, and the processing of the radio wave source identification unit 23 in FIG. 2 corresponds to processing steps S35 and S36 in FIG.

[0026] FIG. 4 is a flow diagram showing a detailed example of the rotation measurement process in the arithmetic device 20 of the electromagnetic wave processing system 30. In the example of FIG. 4, the measurement contents and the attitude reference direction are obtained in the process steps S31 and S32. Next, in FIG. 4, as the process contents of the process step S33, a series of procedures when performing the rotation measurement is specifically described as the process steps S33a-S33e. In addition, in the process step S48, the item α described in the box is added to the process contents of the process steps S34 and S35 in FIG. 3 in association with the rotation measurement. In the process step S49, the item β described in the box is added to the process contents of the process step S36 in FIG. 3 in association with the rotation measurement. In this way, the process of the process step S33 is repeatedly executed while changing the conditions of the rotation measurement, and the process steps S48 and S49 are executed as the electromagnetic wave source identification process after the rotation measurement.

[0027] The process of process step S33 will be described in detail. First, in process step S33a, the rotation control device 8 issues a command to the rotation control device 8 using the attitude information acquired by the attitude detection device 9, and the rotation control device 8 controls the rotation in the attitude reference direction and then stops the rotation. In process step S33b, the rotation axis is set for one of the N repetitions, and in process step S33c, the timing of the start of rotation and the start of measurement are synchronized for one of the N repetitions. Under this condition, in process step S33d, the attitude detection device 9 detects that it has reached a predetermined rotation angle. The processes of the above process steps S33a-S33d are continuously performed by changing the conditions until the measurement of N rotation axes is completed in process step S33e.

[0028] Thereafter, in processing step S48, processing step S34 in FIG. 3 is performed (each attitude / time information is associated with the electric field waveform measured by each antenna AN, and an interference waveform is calculated by multiplying the signals for each antenna pair), and processing step S35 is performed (a theoretical interference intensity change pattern is calculated or read from the attitude change), while at this time processing item α is also performed (the electromagnetic wave source is reconstructed from the interference waveform obtained by multiplying the data of all antenna pairs for each rotation axis).

[0029] Furthermore, in processing step S49, in addition to the processing of processing step S36 in FIG. 3 (multiplying the interference waveform at each time by the theoretical interference intensity change pattern corresponding to each time and integrating it in the time direction to reconstruct the electromagnetic wave source), processing of item β (integrating and processing the electromagnetic wave source data for all rotation axes to reconstruct the electromagnetic wave source) is performed.

[0030] In short, the specific measurement process shown in FIG. 4 involves the attitude detection device 9 recognizing the rotation angle, controlling the start and stop of rotation around multiple axes in sequence, and further reconstructing the electromagnetic wave source for each rotation axis using the interference waveform of the antenna pair used in the analysis, and reconstructing the electromagnetic wave source by aligning all the rotation axes. The idea is to sequentially select possible rotationally symmetric axes as the rotation axes and rotate them.

[0031] According to the above process, by determining the rotation axis, it is possible to determine the attitude continuously and precisely over time, and to obtain measurement data corresponding to each attitude. Furthermore, by rotating around a rotationally symmetric axis, it is possible to rotate stably. Since there are many options for the rotation axis, it becomes possible to select an axis with lower costs such as energy consumption.

[0032] Fig. 5 is a diagram showing a time sequence in the measurement process described in Fig. 4. Here, the horizontal axis shows time, and the vertical axis shows multiple antennas AN (six antennas, AN1 to AN6 in this case), the axis selected by the rotation control device 8, the start timing, and the output of the attitude detection device 9, in order from the top.

[0033] According to this, the attitude detection device 9 issues a start signal at appropriate timing several times, and in response to the start timing, the rotation control device 8 first starts rotation and measurement while rotating the rotating shaft 1. At this time, the multiple antennas AN (here, six antennas, AN1 to AN6) each obtain an electric field waveform Ex(t, Oy) observed at antenna X (AN1 to AN6) during rotational motion Oy.

[0034] A similar rotation measurement is started next time while rotating axis 2 according to the start timing by the start signal from the attitude detection device 9. In the same manner, each electric field waveform Ex(t, Oy) is obtained at this time. The process of changing the axis is executed synchronously for multiple antennas, and the electric field waveform is measured until rotation is finally completed for all the rotation axes (up to axis 13 in the illustrated case) and there is no more rotation.

[0035] The rotation operation method at this time is to repeat the sequence of Stationary (Reference Position) → Rotation Axis 1 → Stationary (Reference Position) → Rotation Axis 2 → Stationary → ..., or Rotation Axis 1 → Transient Rotation → Rotation Axis 2 → Transient Rotation → .... As for the rotation control method, in order to smooth acceleration and deceleration and suppress vibration, it is recommended to perform operations such as smoothing the speed change when stopping and starting rotation (accelerating / decelerating so that the derivative of acceleration = jerk = jerk is below a predetermined value).

[0036] According to such a time sequence process, data acquired by a plurality of rotation operations can be treated as independent baseline data, and the number of baselines in radio interference measurement can be increased.

[0037] Next, examples of antenna and baseline vector arrangements for electromagnetic wave source detection will be described with reference to Figs.

[0038] In this example, the baseline vector of antenna ij is changed over time (denoted as Bij(t, Oy)) by a rotation operation Oy, and the interference waveform Bij(t, Oy) due to the phase difference of the radio waves arriving at antenna ij from the radio wave source, 2πBij(t, Oy) s / λ, is observed.

[0039] First, Fig. 6 is a diagram showing the antenna configuration and the positional relationship of the electromagnetic wave source when performing the rotation measurement in processing step S33 in Fig. 3 and Fig. 4. The observation technology will be explained using Fig. 6. For simplicity, it is assumed here that the electromagnetic wave source located in the direction vector s from the array antenna is stationary on the three-dimensional celestial sphere. In a radio interferometer, the position of the radio wave source is identified by using the intensity pattern (hereinafter, fringe) when the electromagnetic waves arriving from the electromagnetic wave source to the pair of array antennas are output as an interference output.

[0040] In other words, because the rotation angle and attitude of the spacecraft change with time t, a phase difference occurs between the antennas in the arriving electromagnetic waves due to the difference between the distance vector between the array antennas (antennas i and j), or the baseline vector, Bij(t), and the direction vector s of the electromagnetic wave source. For example, if we assume that the electromagnetic wave source is a point radiation source that is stationary in a predetermined position, and if we assume observation with an antenna pair fixed in a predetermined position, theoretical interference fringes such as those shown in Figure 7 will be obtained.

[0041] Figure 7 shows a theoretical interference change pattern obtained from the time series change of the interference fringes in processing step S35 of Figure 3. If a point radiation source is between the fringe lines, the interference output observed by the antenna pair is weak, and if it is on the fringe line, the output is strong. Here, as mentioned above, the array antenna can be rotated during measurement, so the baseline vector is a function of time. Therefore, the direction vector of the fringes on the celestial sphere is also a function of time, and as a result, the strength of the interference output (fringe pattern) occurs over time in response to rotation.

[0042] FIG. 8 is a diagram showing the rotation axis when performing the processing step S33 in FIG. 3. In the case of a 6-channel array antenna, there are a total of 15 fringe patterns (= 6 C 2 ) can be obtained. Therefore, by observing and analyzing these 15 fringe patterns under a total of 14 rotation operations, the direction of the radio wave source can be mapped within the full solid angle of 4π steradians. The total of 14 rotation operations are, for example, 14 states in total, including four C3 rotation axes, three C4 rotation axes, six C2 rotation axes, and stationary, as shown in Figure 8.

[0043] An example of the interference waveform Rij(t) observed by the processing in processing step S34 is shown in Fig. 9, where ω = 0.1 rad / s and B = 0.5 m. This interference waveform Rij(t) is displayed for AN2-6 which forms an antenna pair with antenna AN1, and shows that AN1-2 is the interference waveform Rij(t) when antennas AN1 and AN2 form a pair.

[0044] As shown in this waveform example, the interference fringes obtained by radio wave interference change over time as the baseline vector moves due to rotation, so the position of the radio wave source can be inversely identified from this waveform.

[0045] 10 shows an example of an interference fringe map obtained by processing in processing step S35, where B=0.5 m, (a) shows an example of interference fringes caused by pair AN1-2 of antennas AN1 and AN2, (b) shows an example of interference fringes caused by pair AN1-3 of antennas AN1 and AN3, (c) shows an example of interference fringes caused by pair AN1-4 of antennas AN1 and AN4, and (d) shows an example of interference fringes caused by pair AN1-5 of antennas AN1 and AN5.

[0046] In processing step S35, when an electromagnetic wave source (point source) is at an azimuth angle θ and an elevation angle φ, the theoretical interference fringes obtained by the interference between antennas i and j in a rotation operation O are defined by equation (1), which assumes that the antenna pattern is isotropic.

[0047]

number

[0048] By plotting equation (1), we can visualize the spatial fringe pattern at the initial condition (time t = 0). The result of this process is shown in Figure 10.

[0049] The interference fringes (spatial fringe pattern) in Figure 10 rotate as the array rotates. Furthermore, when the dark areas of the fringe pattern in Figure 10 overlap with the location of the electromagnetic wave source, the observed interference waveform becomes larger. As will be described later, the interference fringe map shown as the integration result in Figure 11 is the weighted sum of the spatial patterns shown in Figure 10, and the interference fringes (spatial fringe pattern) can be considered as a spatial basis function that indicates the distribution of radio wave sources.

[0050] In this case, if the antenna pattern is assumed to be a half-wave dipole antenna, patch antenna, etc., it is also possible to detect the directionality (polarization direction) of the electromagnetic wave according to the pattern. From the polarization direction, it is possible to obtain the characteristics of the target object.

[0051] Next, the process of reconstructing the electromagnetic wave source in the radio wave source identification unit 23 in Fig. 2 will be described. In processing step S36 in Fig. 3, the radio wave source is reconstructed by the following method using measurement data from multiple rotation axes, assuming that the radio wave source is stationary. In performing this process, the product (interference waveform) Rij(t, O) between each channel is calculated using the output data of each antenna stored in the storage device 21 in Fig. 2.

[0052] Theoretically, Rij is expressed as the unknown intensity distribution I(s) of the radio source in the s direction and the theoretical interference intensity R PSij is proportional to the integral of the product over the antenna beam directivity range.

[0053]

number

[0054] In these equations, t is time, O is the type of rotation operation (e.g., 13 rotation axes and no rotation), Rij(t, O) is the observed waveform obtained by multiplying the electric field waveform between antennas i and j, Bij(t, O) is the baseline vector between antennas i and j, beam is the integral range (the directivity range of the antenna beam, which is spherical if isotropic), I(s) is the intensity distribution of the radio wave source in the direction of vector s, R PSij (θ, φ, t, O) is the theoretical waveform (interference fringe) obtained by interference between antennas i and j when a radio wave source (point source (PS)) is at an azimuth angle of θ and an elevation angle of φ.

[0055] In equation (1), it is known that the intensity distribution I(s) of the radio wave source can be estimated by the correlation Cij in the following equation (3). In other words, the correlation Cij between the interference waveform Rij and the theoretical interference fringes Rps can be calculated to obtain a reconstruction pattern of the electromagnetic wave source direction.

[0056]

number

[0057] Here, Cij(θ, φ, O) is calculated for each rotation O, and the sum of all antenna pairs is found using equation (4) in processing step S48 of FIG. 4. Furthermore, the radio wave source position is found and estimated as the sum of all rotation axes using equation (5) in processing step S49 of FIG. 4, thereby improving the estimation accuracy.

[0058]

number

[0059]

number

[0060] In this case, the time integration may be performed by extracting the times of multiple peaks present in Rij(t) and performing time integration at those times. Although the method using correlation has been described here, a method using fast Fourier transform (FFT) may also be used. Furthermore, a method may be used in which an input device or a receiving device is provided for setting the shape or size of the electromagnetic wave source, and the reconstructed electromagnetic wave source is deconvoluted by software processing to reconstruct the electromagnetic wave source. This is expected to improve the accuracy of direction estimation.

[0061] As described above, by reconstructing the electromagnetic wave source using data acquired by multiple rotation operations, it is possible to estimate the electromagnetic wave source with higher accuracy.

[0062] Fig. 11 shows an example of processing for reconstructing an electromagnetic wave source in the radio wave source identification unit 23 in Fig. 2. The processing unit in Fig. 11 is made up of a correlation calculation unit 51, an antenna pair addition unit 52, and an inter-axis addition unit 53.

[0063] Among these, the correlation calculation unit 51 is configured for each axial rotation and each antenna pair, and therefore, processing of all 15 combinations of antenna pairs is performed for one axial rotation. Here, one axial rotation is represented as 51-1, and the 15 combinations of antenna pairs are represented as 51-1m to distinguish them. m is a maximum of 15. Note that N axial rotations are represented as 51-Na to 51-Nm.

[0064] In the figure, the process of 51-1a is shown as a representative example. The correlation calculation unit 51 ultimately executes equation (3) by the process of process step S36. Here, the antenna electric field Ei(t,O) calculated in process step S34 and the attitude information R calculated in process step S35 are PSij The reconstructed electromagnetic wave source direction is estimated as the product of (θ, φ, t, O).

[0065] The antenna electric field Ei(t, O) is calculated as an interference waveform obtained by applying an LPF to the product of the antenna electric fields Ei(t, O), and the attitude information R PSij (θ, φ, t, O) can be obtained as a theoretical interference pattern of a point radiation source. The direction of the reconstructed electromagnetic wave source is visualized by shading on a sphere, and the greater the difference in brightness between the bright and dark parts, the more reliable the information.

[0066] The reconstructed electromagnetic wave source direction calculated for each axis rotation and each antenna pair is calculated by averaging for each axis in antenna pair adder 52 (52a-52m). This process is performed in process step S48 of FIG. 4 using equation (4).

[0067] Further, the reconstructed electromagnetic wave source direction obtained by averaging for each axis is averaged by the inter-axis adder 53 to obtain a total result. This process is performed in process step S49 of FIG.

[0068] The above process is described in detail as follows. First, the electric field E measured by the i-th antenna after the k-th rotation is idepends on the spacecraft attitude due to time t and rotation operation k, and is obtained as time series data of voltage values ​​obtained by an analog-to-digital (AD) converter downstream of the antenna.

[0069] Interference waveform R between the i-th and j-th antenna pairs ij For example, the electric field E i and the electric field E j The interference waveform may be obtained by arithmetic processing of the digital data after AD conversion, or it may be obtained by analog integration processing using a mixer in an electronic circuit, and then AD conversion processing may be performed after passing through a low-pass filter.

[0070] Next, theoretical interference fringes assuming a point radiation source are calculated from the positional relationship of the antenna pair, which is determined from the attitude of the spacecraft, or the baseline vector, which is the vector connecting the antenna pair. By mapping the interference intensity when electromagnetic waves of a specified frequency arrive from a point radiation source located in each direction (azimuth angle, elevation angle) at infinity onto a spherical surface, theoretical interference fringes with a pattern that changes over time are obtained.

[0071] After the above processing, the electromagnetic wave source can be reconstructed by superimposing the theoretical interference fringes at each time using the change in interference intensity at each time as a weight.

[0072] The effect of the above process is that it is possible to reduce ghosts (artifacts) by reconstructing the electromagnetic wave source using data acquired by multiple rotation operations. Furthermore, the number of resolvable electromagnetic wave sources increases by using rotation, so it becomes possible to reconstruct a large number of electromagnetic wave sources.

[0073] A simulation of radio wave source exploration using the rotating radio wave interference processing according to the present invention described above and the results thereof will be described with reference to Figures 12, 13 and 14. The concept here is to observe radio waves while rotating the array antenna and identify the radio wave source position from the interference fringe pattern of each antenna pair, and the simulation setup is a spacecraft equipped with antennas as shown in Figure 12. It is equipped with multiple antennas in each of the three dimensional directions (X, Y, Z), the distance between antennas in the same direction is B=0.5m, and it is assumed that 2GHz radio waves are received from an electromagnetic wave source in the upper right.

[0074] FIG. 13 shows the position coordinates of the electromagnetic wave source and antenna. In this simulation, the antenna is omnidirectional, the radio wave source has an omnidirectional sinusoidal wave source waveform, and the radio wave source is stationary.

[0075] Figure 14 shows the results of a radio wave source location estimation simulation, and from the left, it shows Z-axis rotation, 3-axis rotation, and 3-axis rotation + vertex-to-vertex rotation. The greater the brightness and darkness on the sphere, the higher the accuracy of the estimation. A map of the normalized sum of correlation coefficients is displayed on the celestial sphere around the spacecraft (a 2D map (θ, φ) would also work). This suggests that the radio wave source location, located at an elevation angle of 45 degrees, can be estimated reasonably well. Also, by superimposing various rotations, ghosts are reduced and the accuracy of location estimation is improved.

[0076] FIG. 15 is a diagram showing a simplified flow of the electromagnetic wave source reconstruction process and an example of creating a two-dimensional map. 6 C 2 Each of the interference waveforms (15 combinations) was weighted and added together to obtain a visualization of the distribution of radio wave sources, using the intensity of the interference waveform at each attitude obtained from the rotation observations as a weight.

[0077] In this display, the electric field of each antenna is measured by rotating on each axis (13 types of axes) and in a stationary state (1 type). In the electric field measurement, it is sufficient to perform A / D conversion of the time series reception strength acquired by the high frequency receiving circuit after the antenna.

[0078] At the same time, the spacecraft's attitude change over time can be calculated from the reference attitude direction and the start time of rotation. Theoretical interference fringes can be calculated in 4π space (total solid angle space) assuming a point radio wave source depending on each attitude. The theoretical interference fringes displayed on a two-dimensional map are calculated as a function of azimuth and elevation angles to determine which direction the radio wave source will interfere most strongly when two types of antenna reception waveforms interfere in that attitude, and change over time.

[0079] The theoretical interference fringes are superimposed with weighting by W to obtain a two-dimensional radio source distribution. Here, W is the interference intensity (R ij ) can be used.

[0080] According to the present invention, the satellite rotates on multiple axes, assumes various attitudes, and performs measurements in each attitude, which leads to omnidirectional observation with only one satellite. In this case, the rotation operation and measurements on multiple axes can be appropriately controlled, and observations can be performed taking into account the state of the satellite's attitude. EXAMPLES

[0081] In the second embodiment, a factor of angular velocity is added to the processing of the first embodiment to provide a more accurate estimation method. Compared to the configuration of the first embodiment shown in Fig. 2, an angular velocity detection device 29 is added as an input, and a rotation state determination unit 25, a delay processing unit 26, and an integration processing unit 27 for each axis result are added as processing of the calculation device 20. In addition, when driving the rotation control device 8, a newly added measurement / rotation operation signal output unit 28 adjusts the timing of AD conversion in the AD converter.

[0082] With this configuration, the rotation state determination unit 25 of the calculation device 20 can start measurement when a predetermined angular velocity is reached, using information from the angular velocity detection device 29. The measurement and rotation operation signal output unit 28 controls the rotation control device 8 and performs measurement control via timing control of the AD converter 14, making it possible to reliably obtain data that has a temporal correspondence between the posture state and the electric field data.

[0083] The electric field data from each antenna is converted into a digital signal by AD conversion, and if necessary, a process to compensate for the effect of delay may be performed in the delay processing unit 26 of the calculation device. This has the effect of eliminating unnecessary time portions and reducing memory.

[0084] 17 is a diagram showing a time sequence of rotation measurement according to Example 2. Here, the horizontal axis describes each device involved in this control, and the vertical axis is the time axis, which shows the order in which the processes of each device are performed in chronological order.

[0085] According to this time sequence, first, the measurement and rotation operation signal output unit 28 issues a measurement start signal (processing step S20), and the rotation control device 8 starts moving to a predetermined posture (processing step S21). After that, the calculation device 20 uses the predetermined posture detected by the posture detection device (processing step S22) and the information of the zero angular velocity detected by the angular velocity detection device (processing step S23) to determine whether the predetermined designation and angular velocity match each condition (processing step S24), and instructs the measurement and rotation operation signal output unit 28 to start rotation and measurement according to the condition match (processing step S25), and the measurement and rotation operation signal output unit 28 gives a rotation start command to the rotation control device 8 (processing step S26), and the rotation control device 8 starts rotation (processing step S27). In other words, the measurement and rotation operation signal output device 28 determines that the posture is stationary and is a predetermined reference posture, and then outputs the measurement start signal and the rotation start signal in synchronization. This has the effect that the measurement conditions can be made equal even for data obtained from different rotation operations, and further, interference operations can be easily performed even for data obtained from different rotation operations.

[0086] In contrast, when the angular velocity detection device 29 detects a predetermined angular velocity as a result of the control of the rotation control device 8 (processing step S28), the measurement and rotation operation signal output unit 28 issues a measurement start signal (processing step S29), the attitude detection device 9 stores the attitude (processing step S31), and the AD converter 14 starts AD conversion (processing step S30). For example, the measurement and rotation operation signal output device 28 outputs a measurement start signal after determining that the rotation speed is maintaining a predetermined stability at a predetermined rotation speed. This has the effect of maintaining stable data acquisition in radio wave measurement.

[0087] Thereafter, when attitude detection device 9 detects a predetermined attitude (processing step S32), measurement / rotation operation signal output unit 28 issues a measurement end signal (processing step S33), rotation control device 8 stops rotation (processing step S35), and AD converter 14 ends AD conversion (processing step S34). Furthermore, when rotation control device 8 stops rotation (processing step S35), calculation device 20 repeatedly executes the above series of processes (processing step S36) until rotation of the N axis ends. EXAMPLES

[0088] A method for identifying a moving electromagnetic wave source will be described in Example 3. This identification process is carried out in three steps.

[0089] In step 1, the observed interference waveform (interference fringes) is observed. The electric field product is calculated from the electric field Ei(t, O) using equation (6), where I(s) is the radio source strength distribution (unknown quantity) on the celestial sphere.

[0090]

number

[0091] In step 2, a running correlation coefficient is calculated. When the electromagnetic wave source is fixed, the correlation is found by integrating over the entire time. When the electromagnetic wave source moves, the electromagnetic wave source is found by integrating only over a specified period so that the movement of the electromagnetic wave source can be tracked, and the window function that determines that period is shifted in time to measure the electromagnetic wave source continuously. The integration width at this time is weighted by the window function. Window functions include a rectangular window (or square window), Hanning window, Hamming window, and Gaussian window.

[0092]

number

[0093] Equation (7) is one example of this.

[0094] In equation (7), Rij(t, O) is the interference fringe obtained by the interference between antennas ij in the rotation operation O, and R PSij (θ, φ, t, O) are the theoretical interference fringes obtained by interference between antennas ij in rotation operation O when an electromagnetic wave source (point source) is at azimuth θ and elevation φ, and W(t) is the observation window function (applied to moving radio wave sources) and is omitted when the radio wave source is fixed. The window function may be a rectangular window (or square window), Hanning window, Hamming window, Gaussian window, etc. In the simulation, the time integration is performed by extracting the multiple peak times present in the time series interference intensity Rij(t, O) and performing time integration at those points.

[0095] In step 3, the sum of the correlation coefficients is calculated using, for example, equation (8).

[0096]

number

[0097] Figure 18 shows an example of detecting a moving electromagnetic wave source. In the case of a stationary radio wave source, the analysis was performed using the entire time, but in this example, the analysis was performed in sections. This shows the relationship between the azimuth angle / π on the horizontal axis and the elevation angle / π on the vertical axis, and it is observed that the azimuth angle / π of the bright point shifts to the left as time passes from the top. This also makes it possible to estimate the speed of the moving electromagnetic wave source. EXAMPLES

[0098] In the fourth embodiment, a method of combining antennas having different spatial resolutions or directivity performances and switching from a coarse search to a fine search to track an object will be described.

[0099] Here, the target is narrowed down through omnidirectional observation using an antenna array (e.g., dipole antenna, monopole antenna, etc.) on the beam member, and then the target is tracked by using a large aperture antenna array (patch antenna array) (high resolution) on the membrane surface.

[0100] Figure 19 shows the tracking method. On the left side, Spacecraft 1 performs rotation, measurement control, and omnidirectional observation using a beam antenna, and then shifts to detailed observation (target pointing control) using a membrane antenna as shown on the right side.

[0101] According to the fourth embodiment, by shifting from rough observation using a dipole antenna to detailed observation, the gain for the target can be increased, and radio wave source search can be performed more efficiently and quickly. EXAMPLES

[0102] In the fifth embodiment, a description will be given of extending the baseline length (improving angular resolution) by combining formation types.

[0103] For this reason, in the sixth embodiment, spacecraft are arranged in formation and measurements (arrival time difference) are combined to extend the baseline length between the spacecraft. Each spacecraft is additionally equipped with a radio clock for time synchronization. Alternatively, the time is synchronized by mutual communication.

[0104] Figure 20 shows multiple spacecraft flying in formation tracking the same target as a surveillance target.

[0105] This makes it possible to improve the angular resolution "∝λ / B (wavelength / baseline length)". EXAMPLES

[0106] In the sixth embodiment, the number of rotation axes to be used can be selected.

[0107] To solve this problem, the measurement mode is set based on the input of the electromagnetic wave source identification number, the measurement variance (degree of distribution) and time change (presence or absence of an object whose position changes over time) to achieve high-speed measurement with the minimum necessary rotations.The rotation axis with the lowest cost is selected from 13 types of rotational symmetry axes.

[0108] Figure 21 shows the measurement results for rotations under different conditions. The left is the result of rotation around the Z axis in simple high-speed measurement mode, and the observation result shows that asymmetry remains. The center is the result of rotation around three axes, X, Y, and Z, in high-speed measurement mode; by using three axes, it is possible to reduce measurement time with a minimum of measurements. The right is the result of rotation around four axes, the vertex diagonal, in addition to the three axes, X, Y, and Z, in high-precision measurement mode; by using 7-14 axes, symmetry has been increased.

[0109] This makes it possible to effectively perform measurements according to the purpose, such as rotating on only three axes when high-speed measurements are required or when the number of radio wave sources is assumed to be small, and increasing the number of axes when making detailed measurements. EXAMPLES

[0110] In the seventh embodiment, a flowchart for determining the number of rotation axes to be used while judging the reconstruction result will be described with reference to FIG.

[0111] 22, after steps S31 and S32, step S33 is performed as follows: In step S331, rotation is controlled to the attitude reference position and the rotation is stopped, step S332 sets the rotation axis for one of the N repetitions, step S333 synchronizes the start of rotation and the start of measurement for one of the N repetitions, and step S334 detects that the attitude detection device has reached a predetermined rotation angle.

[0112] Next, in process step S335, the electromagnetic wave sources are reconstructed using one measurement, in process step S336, clustering is performed by the number of electromagnetic wave sources, and in process step S337, the electromagnetic wave source data of the rotation axes that have already been measured is integrated and the electromagnetic wave sources are reconstructed. Then, in process step S338, it is determined whether the evaluation amount (e.g., spatial dispersion value of electromagnetic wave intensity) is equal to or greater than a predetermined value or whether measurements have been completed for all rotation axes, and this is repeatedly executed until measurements have been completed for all rotation axes.

[0113] According to the seventh embodiment, the number of rotation axes to be used can be determined while judging the reconstruction result. [Explanation of symbols]

[0114] 1: Spacecraft 2: Spacecraft housing 4: Tensile member 5:Solar panel 8: Rotation control device 9: Attitude detection device 10: Measurement equipment 20: Arithmetic device 30: Electromagnetic wave processing system AN: Antenna

Claims

1. An electromagnetic wave processing system mounted on a spacecraft having multiple antennas, The electromagnetic wave processing system includes a measurement device that processes measurement signals of electromagnetic waves acquired by the plurality of antennas, an attitude detection device that detects the attitude of the spacecraft, a rotation control device that controls the rotation of the spacecraft, and a calculation device; the rotation control device rotates the spacecraft about a center of gravity on a plurality of rotation axes with respect to an inertial space; The electromagnetic wave processing system is characterized in that the measurement device performs measurements in a plurality of postures that change due to the rotation, and the calculation device calculates the intensity distribution of the electromagnetic waves acquired by the plurality of antennas using an interference waveform obtained by multiplying measurement signals obtained from different antennas in the measurement signals obtained in the plurality of postures.

2. 2. The electromagnetic wave processing system according to claim 1, An electromagnetic wave processing system characterized in that the intensity distribution can be reconstructed on a celestial sphere or on a two-dimensional map of azimuth angle-elevation angle.

3. 2. The electromagnetic wave processing system according to claim 1, An electromagnetic wave processing system characterized by reconstructing an electromagnetic wave source from the time integral of the product of theoretical interference intensity (interference fringes or fringe pattern) and the interference waveform, assuming that a point radiation source exists at each position on the celestial sphere, or from a correlation map.

4. 4. The electromagnetic wave processing system according to claim 3, An electromagnetic wave processing system comprising an input device or a receiving device for setting an electromagnetic wave source shape or size, and for reconstructing an electromagnetic wave source by deconvoluting the reconstructed electromagnetic wave source.

5. 2. The electromagnetic wave processing system according to claim 1, An electromagnetic wave processing system comprising a measurement and rotation operation signal output device, which outputs a measurement start signal and a rotation start signal in synchronization with each other after determining that the posture is stationary and is a predetermined reference posture.

6. 6. The electromagnetic wave processing system according to claim 5, The electromagnetic wave processing system is characterized in that the measurement and rotation operation signal output device outputs a measurement start signal after determining that the rotation speed is maintained at a predetermined rotation speed and at a predetermined stability.

7. 2. The electromagnetic wave processing system according to claim 1, An electromagnetic wave processing system comprising: a spacecraft; a spacecraft receiving an electromagnetic wave from the spacecraft;

8. 2. The electromagnetic wave processing system according to claim 1, An electromagnetic wave processing system characterized by calculating the polarization direction of an electromagnetic wave radiated by an electromagnetic wave source.

9. 2. The electromagnetic wave processing system according to claim 1, a first antenna array having a first directional pattern and a second antenna array having a second directional pattern; An electromagnetic wave processing system characterized by tracking an object by combining and utilizing identification of the direction of a target electromagnetic wave source from approximately omnidirectional observation by a first antenna array and identification of the direction of a target electromagnetic wave source from high-precision observation by a second antenna array.

10. 2. The electromagnetic wave processing system according to claim 1, An electromagnetic wave processing system that is mounted on multiple moving objects flying in formation and performs measurements over an extended baseline length by synchronizing the time of each object with that of the other objects.

11. 2. The electromagnetic wave processing system according to claim 1, An electromagnetic wave processing system characterized in that it is configured so that, when performing measurement, a rotation axis to be used can be selected from a plurality of rotationally symmetric axes, or the number of rotation axes can be selected.

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