Electromagnetic wave processing system

Abstract

The present invention provides an electromagnetic wave processing system that can perform all-round observations with only one device. The electromagnetic wave processing system is mounted on a spacecraft having multiple antennas, and comprises: a measuring device that processes measurement signals of electromagnetic waves obtained by the multiple antennas; a posture detection device that detects the posture of the spacecraft; a rotation control device that controls the rotation of the spacecraft; and a computing device, wherein the rotation control device causes the spacecraft to rotate around the center of gravity with multiple rotation axes relative to the inertial space, the measuring device performs measurements in multiple postures that change due to the rotation, and the computing device uses interference waveforms obtained by multiplying measurement signals obtained from different antennas among the measurement signals obtained in the multiple postures to calculate the intensity distribution of electromagnetic waves obtained by the multiple antennas.

Description

Technical Field

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

[0002] In the field of remote sensing using mobile objects such as artificial satellites and aircraft, a method for grasping the position of electromagnetic wave sources is an important technology. With the ability to conduct wide-area and high-frequency observations through formation flying and constellations of artificial satellites, the application of this technology is expected. Specifically, in the field of interferometer-type radio wave radiometers, a method for grasping the direction of arrival of electromagnetic waves by observing phase differences and the like by using interference processing of signals received by multiple antennas has been proposed.

[0003] For example, Patent Document 1 discloses a method for estimating the arrival direction of a target signal using an array of measuring antennas of a satellite in Earth orbit. In addition, Patent Document 2 discloses a control device having a plurality of antennas facing different directions within a plane, searching for the arrival direction of electromagnetic waves and controlling the movement of a moving body.

[0004] Patent Document 1: US2015 / 0355312

[0005] Patent Document 2: Japanese Patent Application Publication No. 2019-56656 Summary of the invention

[0006] The interferometer-type radio wave radiometer carried on an artificial satellite (or also called a satellite) or a mobile body such as an airplane (hereinafter referred to as a spacecraft in the present invention) implements an open synthesis process based on an orbital motion with a fixed baseline length, and does not use the rotation (autorotation) of the artificial satellite, so the observation range is restricted. For example, it is difficult to simultaneously implement observations in the direction of the surface of the earth including land and ocean and in the direction of the space opposite to the surface of the earth from the earth's orbit. In order to realize a rotating radio wave interferometer that performs all-round observations only with one mobile body, for example, it is necessary to rotate multiple antennas installed on an artificial satellite around multiple arbitrary axes, and perform measurements in multiple postures that change due to the rotation of the satellite and analysis of the measurement signals. However, in Patent Document 1, since it is not envisioned to rotate the satellite around an arbitrary axis, there is no description of this topic. In addition, Patent Document 2 envisions an antenna mounted on a flying device such as a drone, and does not record the idea of ​​rotating the device itself through multiple axes.

[0007] Based on the above, the present invention aims to provide an electromagnetic wave processing system that can perform all-round observation with only one device.

[0008] According to the above, in the present invention, "an electromagnetic wave processing system is carried on a spacecraft having multiple antennas, and the electromagnetic wave processing system comprises: a measuring device, which processes measurement signals of electromagnetic waves obtained by multiple antennas; a posture detection device, which detects the posture of the spacecraft; a rotation control device, which controls the rotation of the spacecraft; and a computing device, the rotation control device causes the spacecraft to rotate around the center of gravity with multiple rotation axes relative to the inertial space, the measuring device performs measurements in multiple postures changed by the rotation, and the computing device calculates the intensity distribution of electromagnetic waves obtained by the multiple antennas using interference waveforms obtained by multiplying measurement signals obtained from different antennas in the measurement signals obtained in the multiple postures with each other."

[0009] According to the present invention, the satellite rotates on multiple rotation axes to take various postures, and measurements are performed in each posture, thereby performing all-round observation with only one satellite. In this case, the rotation operation and measurement on multiple axes can be appropriately controlled to perform observations taking into account the state of the satellite's posture. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a diagram showing a schematic configuration example of a spacecraft.

[0011] Figure 2 This is a diagram showing a basic configuration example of an electromagnetic wave processing system 30 according to the first embodiment of the present invention.

[0012] Figure 3 This is a flowchart schematically showing the processing contents in the computing device 20 of the electromagnetic wave processing system 30 according to the first embodiment of the present invention.

[0013] Figure 4 It is a flowchart showing a detailed specific example of the content of the rotation measurement processing in the calculation device 20.

[0014] Figure 5 Yes means Figure 4 A diagram showing the timing of the measurement process.

[0015] Figure 6 This is a diagram showing the antenna structure and the positional relationship of the electromagnetic wave source when performing rotation measurement.

[0016] Figure 7 This is a diagram showing a theoretical interference variation pattern obtained from the time series variation of interference fringes.

[0017] Figure 8 It means execution Figure 3 FIG. 1 is a diagram of the rotation axis during processing step S33.

[0018] Fig. 9 3 is a diagram showing an example of the interference waveform Rij(t) observed by the processing of the processing step S34.

[0019] Fig.10 3 is a diagram showing an example of an interference fringe pattern obtained by the process of step S35.

[0020] Fig.11 Yes means Figure 2 FIG. 2 is a diagram showing an example of a process of electromagnetic wave source reconstruction in the radio wave source identification unit 23.

[0021] Fig.12 It is a diagram showing a simulation setup.

[0022] Fig.13 This is a diagram showing the position coordinates of the electromagnetic wave source and the antenna.

[0023] Fig.14 It is a diagram showing the simulation results of estimating the position of the radio wave source.

[0024] Fig.15 The diagram shows a simplified flow of electromagnetic wave source reconstruction processing and an example of two-dimensional map creation.

[0025] Fig.16 This is a diagram showing a basic configuration example of an electromagnetic wave processing system 30 according to a second embodiment of the present invention.

[0026] Fig.17 This is a diagram showing the timing of rotation measurement in Example 2.

[0027] Fig.18 It is a diagram showing an example of detecting a moving electromagnetic wave source.

[0028] Fig.19 This is a diagram showing a method of tracking a moving electromagnetic wave source.

[0029] Fig. 20 is a diagram showing multiple spacecraft tracking the same target while flying in formation.

[0030] Fig.21 It is a figure which shows the measurement result in the rotation under different conditions.

[0031] Fig. 22 This is a flowchart schematically showing the processing contents in the computing device 20 of the electromagnetic wave processing system 30 according to the seventh embodiment of the present invention. DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0033] [Example 1]

[0034] Figure 1The figure shows a schematic configuration example of a spacecraft. For example, a spacecraft 1 as an artificial satellite has a plurality of antennas AN (in the example shown, planar antennas ANA and polar antennas ANB) arranged around a spacecraft shell 2 via a tension member 4, and is equipped with a solar panel 5 for solar power generation.

[0035] In addition, Spacecraft 1 will Figure 2 The illustrated electromagnetic wave processing system 30 is installed in the spacecraft housing 2, and radio wave sources distributed omnidirectionally on the ground and in outer space are observed by the electromagnetic wave processing system 30. The solar cell panel 5 supplies the electric power used for this.

[0036] Here, the planar antenna ANA is a patch antenna arranged in a film shape and having three sides formed by a tension member 4 (cable) as a member having tension. The polar antenna ANB is arranged on a compressive material having a compressive force. The shell 2 of the spacecraft 1 is in the center, and a solar cell panel 5 is arranged on the surface of the shell 2. In addition, the film portion may also have a solar cell panel 5 in a place where the planar antenna ANA is not arranged.

[0037] Figure 2 1 is a diagram showing a basic configuration example of an electromagnetic wave processing system 30 mounted on a spacecraft 1. The electromagnetic wave processing system 30 is configured to include: a plurality of antennas AN (AN1 ···ANN); a measuring device 10 that processes measurement signals of electromagnetic waves obtained by the plurality of antennas AN; a posture detecting device 9 that detects the posture of the spacecraft 1; a rotation control device 8 that controls the rotation, i.e., the self-rotation, of the spacecraft 1; and a computing device 20 that is configured using a computer.

[0038] Among them, the posture detection device 9 is constructed to include a star tracker, a sun sensor, an earth sensor, a magnetic sensor, etc. for judging the posture, and the rotation control device 8 is constructed to include a reaction wheel, a momentum wheel, a magnetic torquer, a thruster, etc., thereby enabling the posture control of the spacecraft 1.

[0039] according to Figure 2 The electromagnetic wave processing system 30 of the invention rotates the spacecraft about the center of gravity at multiple rotation axes relative to the inertial space by the rotation control device 8, performs measurements at multiple postures changed by the rotation by the measurement device 10, and calculates the interference intensity distribution of electromagnetic waves obtained by multiple antennas by the calculation device 20 using interference waveforms obtained by multiplying measurement signals obtained from different antennas AN among the measurement signals obtained in multiple postures. In addition, the rotation control device 8 is controlled according to the instruction from the calculation device 20, and the posture control is performed to position the spacecraft 1 at an appropriate position.

[0040] In addition, in the measuring device 10, in order to measure in multiple postures that change due to rotation, the measurement signals of the multiple antennas AN are first amplified by the amplifier 11. The frequency of the local oscillator 15 and the target frequency are integrated by the mixer 12, and the intermediate frequency filter 13 is applied to extract the difference frequency (intermediate frequency). By converting the measurement signals of the multiple antennas AN into low frequencies in this way, the subsequent processing is easy. After that, the AD converter 14 performs AD conversion and inputs it to the operation device 20.

[0041] It is assumed that the processing in the measuring device 10 is implemented in simulation, but the processing in the computing device 20 can be set as computer processing. In this case, the computing device 20 has a storage device 21, an output device 24, and the functions of the interference waveform calculation unit 22 and the radio wave source identification unit 23 as the processing functions of the computing unit of the computer.

[0042] Figure 3 1 is a flowchart showing the outline of the processing contents in the computing device 20 of the electromagnetic wave processing system 30. In the first processing step S31 of the processing in the computing device 20, the measurement conditions are set or received. The measurement conditions include the rotation axis, the order of the rotation axes used, and the rotation speed when measuring the electromagnetic wave. It is also possible to pre-set the predetermined conditions stored in the internal memory of the computing device 20, or to have a communication device and set them by receiving instructions from the ground station.

[0043] Next, in processing step S32, a posture reference direction is set or received from the outside. The posture reference direction refers to the posture direction at the start and end of the rotation. In order to make the measurement start time consistent, it is set to the same direction in each rotation. For example, in the x, y, and z axes defined by the body coordinate system of the spacecraft, the x, y axes and the x, y axes of the inertial coordinate system (for example, the geocentric coordinate system) can also be set as the posture reference direction.

[0044] Next, in processing step S33 , a command is issued to the rotation control device 8 to rotate the spacecraft 1 about a plurality of axes, and measurement information from the measurement device 10 and posture information from the posture detection device 9 are acquired.

[0045] In the processing step S34, each posture / time information is associated with the electric field waveform measured by each antenna AN, the signal is multiplied for each antenna pair, and an interference waveform is calculated by applying a low-pass filter.

[0046] Next, in processing step S35, the theoretical interference intensity variation pattern is calculated or read in according to the posture change. Next, in processing step S36, the interference waveform at each moment is multiplied by the theoretical interference intensity variation pattern corresponding to each moment, and accumulated in the time direction, thereby reconstructing the electromagnetic wave source direction.

[0047] According to the above processing, it is possible to perform omnidirectional observation with only one spacecraft. Even when the number of antennas is limited, by increasing the rotation axis, it is possible to increase the length of the baseline or the type of the baseline vector, and omnidirectional observation can be performed. It is also possible to combine antennas with different directivity patterns to obtain polarization information of the electromagnetic wave source.

[0048] also, Figure 2 The processing of the interference waveform calculation unit 22 is equivalent to Figure 3 The processing steps S33 and S34, Figure 2 The processing of the radio wave source identification unit 23 is equivalent to Figure 3 Processing steps S35 and S36.

[0049] Figure 4 FIG. 2 is a flowchart showing a detailed example of the rotation measurement processing content in the computing device 20 of the electromagnetic wave processing system 30. Figure 4 In the example of , the measurement content and the posture reference direction are obtained in processing steps S31 and S32. Figure 4 In the processing step S33, a series of steps when performing rotation measurement are specifically described as processing steps S33a-S33e. In addition, processing step S48 is Figure 3 The processing contents of the processing steps S34 and S35 are further supplemented with the processing of the item α described in the processing frame along with the rotation measurement. The processing step S49 is Figure 3 The processing content of the processing step S36 is further accompanied by the rotation measurement and the processing of the item β described in the processing box is added. In this way, the processing of the processing step S33 is repeatedly executed while changing the conditions of the rotation measurement, and the processing steps S48 and S49 are executed as the electromagnetic wave source identification processing after the rotation measurement.

[0050] The processing of processing step S33 is described in detail. First, in processing step S33a, the rotation control device 8 uses the posture information obtained by the posture detection device 9 to issue a command to the rotation control device 8, and the rotation control device 8 stops rotating after performing rotation control in the posture reference direction. In processing step S33b, the rotation axis is set for one of the N repetitions, and in processing 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 processing step S33d, the posture detection device 9 detects that the predetermined rotation angle has been reached. The processing of the above processing steps S33a-S33d is continued with the changed conditions until the measurement of the N rotation axis amounts is completed in processing step S33e.

[0051] Then, in processing step S48, Figure 3 The processing step S34 (matching each posture / time information with the electric field waveform measured by each antenna AN, and calculating the interference waveform by multiplying the signal by the antenna pair) and the processing step S35 (calculating or reading the theoretical interference intensity change pattern according to the posture change), and the processing of item α (reconstructing the electromagnetic wave source based on the interference waveform obtained by multiplying the data of all antenna pairs of each rotation axis) are performed at this time.

[0052] Furthermore, in processing step S49, in addition to Figure 3 In addition to the processing of step S36 (multiplying the interference waveform at each moment by the theoretical interference intensity change pattern corresponding to each moment, and accumulating in the time direction to reconstruct the electromagnetic wave source), item β is also implemented (integrating the electromagnetic wave source data of all rotating axes to reconstruct the electromagnetic wave source).

[0053] about Figure 4 The specific measurement processing shown, in summary, is to start / stop the control of rotation on multiple axes in sequence based on the rotation angle recognized by the posture detection device 9, and then reconstruct the electromagnetic wave source for each rotation axis using the interference waveform of the antenna pair used in the analysis. The electromagnetic wave source is reconstructed by aligning all the rotation axes, and the idea is to select desirable rotational symmetry axes as rotation axes in sequence and rotate them.

[0054] According to the above processing, by determining the rotation axis, the posture can be determined continuously and with high precision in time, and the measurement data corresponding to each posture can be obtained. Moreover, by rotating around the rotational symmetry axis, stable rotation can be achieved. Since there are many options for the rotation axis, an axis with lower energy consumption and other costs can be selected.

[0055] Figure 5 Yes means Figure 4The horizontal axis represents time, and the vertical axis represents multiple antennas AN (here, six antennas AN1 to AN6), the axis selected by the rotation control device 8, the start timing, and the output of the posture detection device 9 in order from the top.

[0056] Thus, the posture detection device 9 sends a start signal at an appropriate timing of several degrees, and the rotation control device 8 initially rotates the rotating shaft 1 according to the start timing, and starts rotating and measuring at the same time. At this time, in the multiple antennas AN (here, 6 antennas AN1 to AN6), the electric field waveform Ex (t, Oy) observed at the antenna X (AN1 to AN6) during the rotation action Oy is obtained.

[0057] Similarly, the rotation measurement is started at the start timing of the start signal from the posture detection device 9, and the rotation and measurement are started while rotating the rotating shaft 2 next time. At this time, the electric field waveform Ex (t, Oy) is also obtained in the same way. The process of changing the axis is synchronously performed by multiple antennas, and finally the electric field waveform is measured until the rotation about all the rotating axes is completed (until the axis 13 in the case shown in the figure) and there is no rotation.

[0058] In addition, the rotation operation method at this time is set to repeat in the manner of stationary (reference posture) → rotation axis 1 → stationary (reference posture) → rotation axis 2 → stationary → ..., or repeat in the manner of rotation axis 1 → transitional rotation → rotation axis 2 → transitional rotation → .... In addition, as a rotation control method, in order to make the acceleration and deceleration smooth and suppress vibration, the rotation can be stopped, and when the rotation is started, the speed change can be smoothed (acceleration and attenuation are performed in a manner such that the differential of acceleration = jerk = jerk is less than a predetermined value).

[0059] According to the processing in this sequence, data acquired through a plurality of rotation operations can be processed as independent baseline data, and the baseline in radio wave interference measurement can be increased.

[0060] Next, use Figure 6-Figure 8 An example of antenna and baseline vector configuration for electromagnetic wave source search is described.

[0061] Here, the baseline vector of antenna ij is changed over time (recorded as Bij(t, Oy)) by the rotation operation Oy, and the interference waveform Bij(t, Oy) of the radio wave phase difference 2πBij(t, Oy)·s / λ from the radio wave source to antenna ij is observed.

[0062] first, Figure 6 It means execution Figure 3 , Figure 4 The antenna structure and the positional relationship of the electromagnetic wave source during the rotation measurement in the processing step S33 are shown in FIG. Figure 6The observation technique is described below. Here, for simplicity, it is assumed that the electromagnetic wave source from the array antenna is stationary on the three-dimensional celestial sphere. In the radio wave interferometer, the position of the radio wave source is determined by the intensity pattern (hereinafter referred to as fringe) when the electromagnetic waves from the electromagnetic wave source to the array antenna pair are interfered and output.

[0063] That is, since the rotation angle and posture of the spacecraft change according to time t, the distance vector or baseline vector between the array antennas (antenna i and antenna j) is called. Due to the difference between Bij(t) and the direction vector s of the electromagnetic wave source, a phase difference between the antennas is generated in the incoming electromagnetic wave. Therefore, for example, when it is assumed that the electromagnetic wave source is stationary at a predetermined position in the form of a point radiation source, if it is assumed that the observation is performed in an antenna pair fixed at a predetermined position, then Figure 7 Theoretical interference fringes as shown.

[0064] Figure 7 Indicates from Figure 3 The theoretical interference variation pattern obtained by the time series variation of the interference fringes in the processing step S35. When the point radiation source is located between the lines of the fringes, the interference output observed in the antenna pair is weak, and when it is located on the line of the fringes, the output becomes strong. Here, as described above, the array antenna can measure while rotating, so the baseline vector becomes a function of time. Therefore, the direction vector of the fringes in the celestial sphere also becomes a function of time, and as a result, the strength of the interference output (fringe pattern) is generated in a time series according to the rotation.

[0065] Figure 8 It means execution Figure 3 In the case of a 6-channel array antenna, a total of 15 (= 6 C 2 ) kinds. Therefore, by observing and analyzing these 15 kinds of fringe patterns under a total of 14 rotation operations, it is possible to map (matching) the direction of the radio wave source in all solid angles of 4π steradians. The total of 14 rotation operations refers to, for example Figure 8 There are a total of 14 states, including 4 C3 rotation axes, 3 C4 rotation axes, 6 C2 rotation axes, and static.

[0066] Fig. 9 An example of the interference waveform Rij(t) observed by the processing of step S34 is shown. Here, ω = 0.1 rad / s, B = 0.5 m. This interference waveform Rij(t) represents the interference waveform Rij(t) when the antenna AN1 and the antenna pair AN2-6 are used, and AN1-2 is based on the antenna AN1 and AN2.

[0067] As in this waveform example, interference fringes obtained by radio wave interference change with time as the base line vector moves due to rotation. Therefore, the position of the radio wave source can be reversely identified based on this waveform.

[0068] In addition, Fig.10 , which illustrates an example of an interference fringe diagram obtained by processing step S35. In which, B=0.5m, (a) represents the interference fringes when the antennas AN1 and AN2 are matched with AN1-2, (b) represents the interference fringes when the antennas AN1 and AN3 are matched with AN1-3, (c) represents the interference fringes when the antennas AN1 and AN4 are matched with AN1-4, and (d) represents the interference fringes when the antennas AN1 and AN5 are matched with AN1-5.

[0069] In the processing step S35, when the electromagnetic wave source (point source) is at an azimuth angle θ and an elevation angle When , the theoretical interference fringes obtained by interference between antennas ij in the rotation operation O are defined by equation (1). This is the case where the antenna pattern is assumed to be isotropic.

[0070] [Formula 1]

[0071] R PSij( θ,φ,t,O)=cos[2πB ij (t,O)·s(θ,φ,t,O) / λ]…(1)

[0072] By plotting equation (1), the spatial fringe pattern under the initial condition (time t = 0) can be visualized. Fig.10 The processing result is illustrated in FIG.

[0073] Fig.10 The interference fringes (spatial fringe pattern) rotate with the rotation of the array. In addition, when Fig.10 When the dense part of the fringe pattern overlaps with the electromagnetic wave source, the observed interference waveform becomes larger. In addition, as described later, Fig.11 The interference fringe pattern shown as the integration result is Fig.10 The weighted sum of the spatial patterns shown, the interference fringes (spatial fringe pattern), can be regarded as a spatial basis function representing the distribution of radio wave sources.

[0074] In this case, if the antenna pattern is assumed to be a half-wavelength dipole antenna, a patch antenna, or the like, the directivity (polarization direction) of the electromagnetic wave can also be detected from the pattern. The characteristics of the object can be acquired from the polarization direction.

[0075] Next, explain Figure 2 The processing of electromagnetic wave source reconstruction in the electromagnetic wave source identification unit 23 is Figure 3In the processing step S36, the radio wave source is reconstructed by the following method using the measurement data based on multiple rotation axes, assuming that the radio wave source is stationary. Figure 2 The output data of each antenna is stored in the storage device 21, and the product (interference waveform) Rij(t, O) is calculated between each channel.

[0076] Theoretically, as shown in the following equation (2), Rij is related to the intensity distribution I(s) of the unknown radio wave source in the s direction within the antenna beam directivity range and the theoretical interference intensity R PSij It is proportional to the value obtained by integrating the product of.

[0077] [Formula 2]

[0078]

[0079] 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 ij, Bij(t, O) is the baseline vector between antennas ij, beam is the integration range (the directional range of the antenna beam, or a sphere if it is isotropic), I(s) is the intensity distribution of the radio wave source in the direction of the vector s, and R PSij (θ, t, O) is the angle of the radio wave source (point source (PS)) at azimuth angle θ and elevation angle The theoretical waveform (interference fringes) obtained by interference between antennas ij.

[0080] In equation (1), it is known that the intensity distribution I(s) of the radio wave source can be estimated by the correlation Cij of the following equation (3). That is, the correlation Cij between the interference waveform Rij and the theoretical interference fringe Rps can be calculated to obtain the electromagnetic wave source direction reconstruction pattern.

[0081] [Formula 3]

[0082]

[0083] Here, Cij(θ, O), in Figure 4 In the processing step S48, the sum of all antenna pairs is obtained by equation (4), and then the sum of all rotation axes is obtained. Figure 4 In the processing step S49, the radio wave source position is calculated and estimated by equation (5), thereby improving the estimation accuracy.

[0084] [Formula 4]

[0085]

[0086] [Formula 5]

[0087]

[0088] In addition, here, the position of the time integration can also extract multiple peak times existing in Rij(t) and implement the time integration at this time point. In addition, the method using correlation is described here, but the method using fast Fourier transform (FFT) can also be used. In addition, the following method can also be used: an input device or a receiving device with a set shape or size of the electromagnetic wave source is used, and the reconstructed electromagnetic wave source is deconvolved by software processing to reconstruct the electromagnetic wave source. As a result, it is expected that the direction estimation accuracy can be improved.

[0089] As described above, by reconstructing the electromagnetic wave source using data obtained by a plurality of rotation operations, it is possible to estimate the electromagnetic wave source with further improved accuracy.

[0090] Fig.11 express Figure 2 An example of processing of electromagnetic wave source reconstruction in the radio wave source identification unit 23. Fig.11 The processing unit is composed of a correlation calculation unit 51, an antenna pair addition unit 52 and an inter-axis addition unit 53.

[0091] The correlation calculation unit 51 is configured for each axis rotation and antenna pair, so 15 types of processing are performed for all antenna pair combinations for the axis 1 rotation. Here, the axis 1 rotation is recorded as 51-1, and further marked as 51-1m to distinguish the 15 antenna pair combinations. The maximum value of m is 15. In addition, the axis N rotation is marked as 51-Na to 51-Nm.

[0092] In the figure, the processing of 51-1a is shown as a representative example. As a result, the correlation calculation unit 51 executes equation (3) through the processing of processing step S36. Here, the antenna electric field Ei(t, O) obtained in processing step S34 and the posture information R obtained in processing step S35 are PSij The direction of the reconstructed electromagnetic wave source is estimated by taking the product of (θ, t, O).

[0093] The antenna electric field Ei(t, O) is obtained as an interference waveform obtained by applying LPF to the product of the antenna electric field Ei(t, O), and the posture information R PSij (θ, t, O) is obtained as the theoretical interference fringe of a point radiation source. In addition, the direction of the reconstructed electromagnetic wave source is visualized by the shades on the spherical surface, and the greater the brightness difference between the bright part and the dark part, the more reliable the information can be.

[0094] The reconstructed electromagnetic wave source direction obtained for each antenna pair in each axis rotation is obtained by performing addition averaging for each axis in the antenna pair adding section 52 (52a-52m). Figure 4 It is obtained by equation (4) in the processing step S48.

[0095] Then, the reconstructed electromagnetic wave source direction obtained by adding and averaging for each axis is added and averaged by the inter-axis adding unit 53 to obtain a comprehensive result. Figure 4 It is obtained by equation (5) in the processing step S49.

[0096] The above processing is described in detail as follows. First, when performing the kth rotation, the electric field E measured by the i-th antenna i It depends on the attitude of the spacecraft caused by the time t and the rotation operation k, and obtains time series data as a voltage value found by an analog-to-digital (AD) converter in the subsequent stage of the antenna.

[0097] Interference waveform R between the i-th antenna and the j-th antenna pair ij For example, through the electric field E i and the electric field E j The interference waveform can be obtained by arithmetic processing of the digital data after AD conversion, or by obtaining the interference waveform through analog accumulation processing using a mixer in an electronic circuit, etc., and then performing AD conversion processing after passing through a low-pass filter.

[0098] Next, the theoretical interference fringes are calculated based on the positional relationship of the antenna pair obtained from the spacecraft's posture or the vector connecting the antenna pair, i.e., the baseline vector, when a point radiation source is assumed. The theoretical interference fringes whose patterns change in time series are obtained by mapping the interference intensity of electromagnetic waves of a predetermined frequency from a point radiation source located at an infinite distance in each direction (azimuth, elevation) onto a spherical surface.

[0099] After the above processing, the change in interference intensity at each moment is used as a weight to superimpose the theoretical interference fringes at each moment, thereby reconstructing the electromagnetic wave source.

[0100] As an effect of the above processing, by reconstructing the electromagnetic wave source using data obtained by a plurality of rotation operations, ghosting (artifacts) can be reduced. In addition, by using rotation, the number of electromagnetic wave sources that can be resolved increases, so a plurality of electromagnetic wave sources can be reconstructed.

[0101] use Fig.12 , Fig.13 , Fig.14The simulation and results of the radio wave source detection based on the rotational radio wave interference processing of the present invention described above are described. The concept here is to observe the radio waves while rotating the array antenna, determine the radio wave source position based on the interference fringe pattern of each antenna pair, and use the simulation device as Fig.12 Such a spacecraft equipped with antennas has multiple antennas in three-dimensional directions (X, Y, Z), and the distance between antennas in the same direction is set to B = 0.5m, and receives 2GHz radio waves from the electromagnetic wave source on the upper right.

[0102] Fig.13 It represents the position coordinates of the electromagnetic wave source and the antenna. In this simulation, the antenna has omnidirectionality, the electromagnetic wave source has the waveform of an omnidirectional sine wave source, and the position of the electromagnetic wave source is stationary.

[0103] Fig.14 The simulation results of radio wave source position estimation are shown, showing the Z-axis rotation, 3-axis rotation, and 3-axis rotation / vertex rotation from the left. The brighter the sphere, the more accurate the estimation can be. A graph showing the sum of normalized correlation coefficients on the celestial sphere around the spacecraft (can also be a 2D graph (θ, )). Thus, it is considered that the position of the radio wave source at an elevation angle of 45 degrees can be properly estimated. In addition, by overlapping various rotations, ghosting is reduced and the position estimation accuracy is improved.

[0104] Fig.15 The figure shows a simplified flow of electromagnetic wave source reconstruction processing and an example of two-dimensional image creation. The intensity of the interference waveform obtained by the rotation observation in each posture is used as a weight, and the 4π spatial interference fringes ( 6 C 2 = 15 kinds) are weightedly added to obtain the visualization result of radio wave source distribution.

[0105] In this display, the electric field of each antenna is measured by rotating on each rotation axis (13 axes) and in a stationary state (1 axis). In the electric field measurement, the time series reception intensity obtained by the high frequency receiving circuit after the antenna is A / D converted.

[0106] At the same time, the time-series attitude change of the spacecraft can be calculated by the reference attitude direction and the rotation start time. The theoretical interference fringes can be calculated in the 4π space (full solid angle space) when a point radio wave source is assumed, depending on each attitude. The theoretical interference fringes displayed on the two-dimensional map are fringes calculated as a function of the azimuth and elevation angle to determine which direction the radio wave source strongly interferes when the two antenna reception waveforms interfere in this attitude, and they change in a time series.

[0107] By superimposing the theoretical interference fringes using the weight of W, a two-dimensional radio wave source distribution is obtained. Here, W uses the interference intensity (R ij )

[0108] According to the present invention, the satellite rotates on multiple rotation axes to take various postures, and measurements are performed in each posture, thereby performing all-round observation with only one satellite. At this time, the rotation operation and measurement on multiple axes can be appropriately controlled to perform observation taking into account the posture state of the satellite.

[0109] [Example 2]

[0110] In the second embodiment, the main factor of the angular velocity is added to the processing of the first embodiment to achieve a more accurate estimation method. Figure 2 Compared with the structure of the present invention, 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 of the results of each axis are added as processing of the operation device 20. In addition, when the rotation control device 8 is driven, the timing of the AD conversion in the AD converter is adjusted by the newly added measurement / rotation operation signal output unit 28.

[0111] According to this configuration, the information from the angular velocity detection device 29 can be used to start measurement in a state where a predetermined angular velocity is reached in the rotation state determination unit 25 of the computing device 20. The measurement / rotation operation signal output unit 28 controls the rotation control device 8 and performs measurement control via the timing control of the AD converter 14, thereby reliably obtaining data in which the posture state and the electric field data correspond in time.

[0112] The electric field data from each antenna is converted into a digital signal by AD conversion, and the delay processing unit 26 of the computing device may be used to compensate for the influence of the delay as needed. This has the effect of being able to delete unnecessary time portions and reduce memory.

[0113] Fig.17 This is a diagram showing the timing of rotation measurement in Example 2. Here, the various devices related to the control of this case are described on the horizontal axis, and the vertical axis is used as the time axis to show the order of processing performed by each device in time series.

[0114] According to this time sequence, first, the measurement / rotation operation signal output unit 28 issues a measurement start signal (processing step S20), and the rotation control device 8 starts to move to a predetermined posture (processing step S21). After that, the computing device 20 uses the predetermined posture detected by the posture detection device (processing step S22) and the information that the angular velocity detected by the angular velocity detection device is zero (processing step S23) to determine whether the predetermined posture and angular velocity meet the respective conditions (processing step S24), and instructs the measurement / rotation operation signal output unit 28 to start rotation / measurement according to the conditions being met (processing step S25), and the measurement / rotation operation signal output unit 28 provides the rotation start to the rotation control device 8 (processing step S26), and the rotation control device 8 starts to rotate (processing step S27). That is, after determining that the posture is in a stationary state and is a predetermined reference posture, the measurement / rotation operation signal output unit 28 synchronously outputs a measurement start signal and a rotation start signal. As a result, there is an effect that the measurement conditions can be made the same even in the data between different rotation operations, and interference operation can be easily performed even between the data of different rotation operations.

[0115] On the other hand, if 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 / rotation operation signal output unit 28 issues a measurement start signal (processing step S29), the posture is saved in the posture detection device 9 (processing step S31), and AD conversion is started in the AD converter 14 (processing step S30). For example, the measurement / rotation operation signal output device 28 outputs a measurement start signal after determining that the rotation speed maintains a predetermined stability at a predetermined rotation speed. Thus, there is an effect of being able to maintain stable data acquisition in radio wave measurement.

[0116] After that, when the predetermined posture is detected in the posture detection device 9 (processing step S32), the measurement / rotation operation signal output unit 28 issues a measurement end signal (processing step S33), the rotation is stopped in the rotation control device 8 (processing step S35), and the AD conversion is completed in the AD converter 14 (processing step S34). In addition, when the rotation is stopped by the rotation control device 8 (processing step S35), the computing device 20 repeatedly executes the above series of processes (processing step S36) until the rotation of the N axis is completed.

[0117] [Example 3]

[0118] In Example 3, a method for identifying a mobile electromagnetic wave source is described. This identification process is performed in three steps.

[0119] In step 1, the interference waveform (interference fringes) is observed. The electric field product is calculated from the electric field Ei(t, O) by equation (6). Here, I(s) is the intensity distribution of the radio wave source on the celestial sphere (unknown quantity).

[0120] [Formula 6]

[0121] R ij (t,O)[=∫(s)cos{2πB ij (t, O)·s / λ}ds]…(6)

[0122] In step 2, the running correlation coefficient is calculated. When the electromagnetic wave source is fixed, the correlation is obtained by integrating all the time. When the electromagnetic wave source is moving, in order to track the movement of the electromagnetic wave source, the electromagnetic wave source is obtained by integrating only during a predetermined period, so that the window function that determines the period is staggered in time, thereby continuously measuring the electromagnetic wave source. The integral amplitude at this time is weighted by the window function. Window functions include rectangular window (or square window), Hanning window, Hamming window, Gaussian window, etc.

[0123] [Formula 7]

[0124]

[0125] Formula (7) is one example.

[0126] 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, t, O) is when the electromagnetic wave source (Point source) is at azimuth θ and elevation When the rotation operation O is performed, the theoretical interference fringes are obtained by the interference between the antennas ij. W(t) is the observation window function (applied to the moving radio wave source), which is omitted when the radio wave source is fixed. As the window function, any rectangular window (or square window), Hanning window, Hamming window, Gaussian window, etc. are sufficient. In addition, the position of the time integration in the simulation is to extract the multiple peak times existing in the time series interference intensity Rij(t, O) and implement the time integration at that time point.

[0127] In step 3, the sum of the correlation coefficients is calculated, for example, using equation (8).

[0128] [Formula 8]

[0129]

[0130] Fig.18This shows an example of detecting a moving electromagnetic wave source. In the case of a stationary electromagnetic wave source, the analysis is performed using the entire time, but the analysis is performed by dividing the time. Here, the relationship between the azimuth angle / π on the horizontal axis and the elevation angle / π on the vertical axis is shown, and it is observed that the azimuth angle / π of the bright point when the time passes sequentially from the top is shifted to the left. From this, the speed of the moving electromagnetic wave source can also be estimated.

[0131] [Example 4]

[0132] In the fourth embodiment, a method of switching the tracking of an object from a rough search to a detailed search by combining antennas having different spatial resolutions or directivity will be described.

[0133] Here, after narrowing down the target from all-around observation using an antenna array based on a beam member (eg, dipole antenna, monopole antenna, etc.), the object is tracked using a large aperture antenna array (patch antenna array) (high resolution) on the membrane surface.

[0134] Fig.19 This is a diagram showing the tracking method. On the left side, as an omnidirectional observation based on the beam component antenna, the spacecraft 1 performs rotation / measurement control and omnidirectional observation, and as shown on the right side, it shifts to detailed observation (target pointing control) based on the membrane surface antenna.

[0135] According to the fourth embodiment, by shifting from a rough observation using a dipole antenna to a detailed observation, it is possible to increase the gain of a target and perform a radio wave source search more efficiently and at a higher speed.

[0136] [Example 5]

[0137] In Example 5, a description is given of extending the baseline length (improvement of angular resolution) by combining formation types.

[0138] Therefore, in the sixth embodiment, the spacecraft are formed into a formation and the measurement of the baseline length (arrival time difference) between the spacecraft is extended. Each spacecraft is also equipped with a radio clock for time synchronization. Alternatively, the spacecraft communicate with each other to synchronize the time.

[0139] Fig. 20 Shown is tracking the same target as a surveillance target during formation flying of multiple spacecraft.

[0140] Thereby, the angular resolution “∝λ / B (wavelength / base line length)” can be improved.

[0141] [Example 6]

[0142] In Embodiment 6, the number of rotation axes to be used can be selected.

[0143] As a solution, the measurement mode is set based on the input of the electromagnetic wave source identification number, the measured variance value (distribution), and the time change (whether there is an object whose position changes over time), and high-speed measurement is achieved with the minimum necessary rotation. The rotation axis with the minimum cost is selected from 13 rotational symmetry axes.

[0144] Fig.21 The measurement results under different rotation conditions are shown. The left figure is obtained from the rotation result around the Z axis in the simple high-speed measurement mode, which is the observation result of residual asymmetry. The center figure is obtained from the rotation result around the three axes of X, Y, and Z in the high-speed measurement mode. By setting it to three axes, the measurement time can be shortened with the minimum measurement. The right figure is obtained from the rotation result around the three axes of X, Y, and Z and the four axes around the vertex diagonal in the high-precision measurement mode. By setting it to 7-axis to 14-axis, the symmetry is increased.

[0145] Therefore, it is possible to efficiently perform measurements according to the purpose, for example, when high-speed measurement is desired or when it is assumed that the number of radio wave sources is small, the rotation is limited to three axes, and the number of axes is increased for detailed measurement.

[0146] [Example 7]

[0147] In Example 7, using Fig. 22 This section describes a flowchart for determining the number of rotation axes to be used while judging the reconstruction results.

[0148] exist Fig. 22 In the process of , after executing the processing steps S31 and S32, the processing of the processing step S33 is executed as follows. In this processing, in the processing step S331, the rotation control is performed toward the posture reference position and the rotation is stopped, in the processing step S332, the rotation axis of one of the N repetitions is set, in the processing step S333, the timing of starting the rotation of one of the N repetitions is synchronized with the timing of starting the measurement, and in the processing step S334, the posture detection device detects that the predetermined rotation angle has been reached.

[0149] Next, in processing step S335, one measurement is used to reconstruct the electromagnetic wave source, in processing step S336, the number of electromagnetic wave sources is used for clustering processing, and in processing step S337, the electromagnetic wave source data of the measured rotation axis is integrated to reconstruct the electromagnetic wave source. On this basis, in processing step S338, it is determined whether the evaluation amount (e.g., the spatial variance value of the electromagnetic wave intensity) is greater than a predetermined value, or whether the measurement is completed on all rotation axes, and the process is repeated until the measurement is completed on all rotation axes.

[0150] According to the seventh embodiment, the number of rotation axes to be used can be determined while judging the reconstruction result.

[0151] Explanation of symbols

[0152] 1: Spacecraft

[0153] 2: Spacecraft shell

[0154] 4: Tension components

[0155] 5: Solar Panels

[0156] 8: Rotary Controls

[0157] 9: Posture detection device

[0158] 10: Measuring device

[0159] 20: Computing device

[0160] 30: Electromagnetic wave processing system

[0161] AN: Antenna.

Claims

1. An electromagnetic wave processing system, mounted on a spacecraft having a plurality of antennas, characterized in that: The electromagnetic wave processing system comprises: a measuring device that processes the measurement signals of the electromagnetic waves obtained by the plurality of antennas; a posture detection device that detects the posture of the spacecraft; a rotation control device that controls the rotation of the spacecraft; and a computing device. The rotation control device causes the spacecraft to rotate about its center of gravity at multiple rotation axes relative to the inertial space. The measuring device performs measurement in the plurality of postures changed by the rotation, and the computing device calculates the intensity distribution of electromagnetic waves obtained by the plurality of antennas using interference waveforms obtained by multiplying measurement signals obtained from different antennas among the measurement signals obtained in the plurality of postures.

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

3. The electromagnetic wave processing system according to claim 1, characterized in that: The electromagnetic wave source is reconstructed based on the time integral or correlation diagram of the product of the theoretical interference intensity assuming that a point radiation source exists at each position on the celestial sphere and the interference waveform, wherein the theoretical interference intensity is an interference fringe or fringe pattern.

4. The electromagnetic wave processing system according to claim 3, characterized in that: The electromagnetic wave processing system has an input device or a receiving device for setting the shape or size of the electromagnetic wave source, and reconstructs the electromagnetic wave source by deconvolving the reconstructed electromagnetic wave source.

5. The electromagnetic wave processing system according to claim 1, characterized in that: The electromagnetic wave processing system includes a measurement / rotation operation signal output device, and after determining that the posture is a stationary state and a predetermined reference posture, the device synchronously outputs a measurement start signal and a rotation start signal.

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

7. The electromagnetic wave processing system according to claim 1, characterized in that: The velocity of a source of electromagnetic waves in relative motion with respect to the spacecraft is estimated.

8. The electromagnetic wave processing system according to claim 1, characterized in that: Calculate the polarization direction of the electromagnetic wave radiated by the electromagnetic wave source.

9. The electromagnetic wave processing system according to claim 1, characterized in that: The electromagnetic wave processing system has a first antenna array and a second antenna array, the first antenna array has a first directional pattern, and the second antenna array has a second directional pattern, The object is tracked by combining identification of the target electromagnetic wave source direction based on substantially omnidirectional observation using the first antenna array and identification of the target electromagnetic wave source direction based on high-precision observation using the second antenna array.

10. The electromagnetic wave processing system according to claim 1, characterized in that: The electromagnetic wave processing systems are respectively mounted on a plurality of mobile bodies flying in formation, and are synchronized with each other at the same time to perform measurement with a prolonged baseline length.

11. The electromagnetic wave processing system according to claim 1, characterized in that: The electromagnetic wave processing system is configured to be able to select a rotation axis to be used from a plurality of rotationally symmetric axes or to select the number of rotation axes when performing measurement.

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