JP2005249629A - Electric wave incoming direction specifying system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve accuracy of specifying a position of a electric wave source over a wide range and to avoid error of antenna element position and phase error. <P>SOLUTION: An electric wave incoming direction specifying system for specifying an incoming direction of electric wave is provided with a high altitude platform 11 for flying or staying at high altitude, an array antenna 12 for receiving electric wave of an optional format in a predetermined frequency range transmitted from an electric wave source 10 of which position is unknown and outputting the received signal and an incoming direction specifying means for conducting a predetermined signal process to information of amplitude and phase obtained from the received signal of the array antenna 12 and specifying the incoming direction of the electric wave transmitted from the electric wave source 10 of which position is unknown within a predetermined error range. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radio wave arrival direction specifying system for specifying a radio wave arrival direction.

  In recent years, a radio wave arrival direction identifying system has been proposed as a concept that uses a high altitude platform that flies or stays at high altitude when specifying the direction of arrival of radio waves transmitted from a radio source of unknown position.

Several techniques for specifying the direction of arrival of the above-mentioned radio wave have been proposed. As a first conventional technique, disclosed in the following Patent Document 1, “Phased Array Antenna Device and Beam Direction Direction Calibration of Phased Array Antenna” There is a "method". This technology consists of an antenna panel that forms an array antenna, a reference plate that does not deform, and a plurality of sensors that measure the amount of distortion between the antenna panel and the reference plate. The amount of phase shift of each antenna element is controlled by measuring the amount of change in shape due to mechanical strain.
JP 2002-171115 A

  In the first prior art described above, even if the shape of the array antenna is distorted for some reason, the amount of phase shift for compensating for the distortion can be set in each antenna element. It has the feature that the error can be reduced.

Next, as a second conventional technique, there is a “array antenna calibration method” disclosed in Patent Document 2 below. In this technique, when there is an amplitude and phase non-uniformity between systems of each antenna element of a receiving array antenna, a signal from a calibration reference station in a known direction is received by the array antenna, and each antenna element A calibration coefficient for canceling the non-uniformity of the amplitude and phase is obtained by performing predetermined digital signal processing operation on the output of the received signal.
Japanese Patent No. 3138728

  In the second prior art described above, even if the amplitude and phase inside the circuit connected to each antenna element constituting the array antenna have an unknown error, a complex weight for canceling this can be obtained. The characteristic deterioration and the error of the beam directing direction can be reduced.

As a third prior art, there is “Regarding a super-resolution array calibration method using a known wave source” disclosed in Non-Patent Document 1 below. This technology is an array antenna that applies a super-resolution method for measuring the direction of arrival of radio waves with high accuracy, and the amplitude and phase errors of each antenna element, which are unknown parameters that cause the direction measurement accuracy to deteriorate. The degree of influence due to the coupling between the antenna elements is simultaneously estimated by solving simultaneous equations created using received data vectors from wave sources installed in a plurality of known directions.
Arai et al., "Super resolution array calibration method using known wave source" IEICE Transactions B, Vol. J86-B, no. 3, pp. 527-535, March 2003

  In the third prior art described above, not only the amplitude and phase error / variation of each antenna element, but also the presence of electromagnetic coupling between antenna elements, these parameters are estimated and compensated simultaneously to compensate for the super resolution. It has a feature that an error in measuring the direction of arrival of radio waves by applying the solution method can be reduced.

  However, the first prior art requires a structure called a hard reference plate whose shape does not change, and the change in sensor output corresponds to the positional deviation of each antenna element constituting the array antenna on a one-to-one basis. However, there was a problem that strict calibration had to be performed in advance. In addition, when the number of sensors is small, if the antenna panel has a relatively soft structure, the error in measuring the position error of the antenna element located away from the sensor becomes large, and if the number of sensors is increased, Along with the amount of data lines for sucking up sensor data, there is a problem that the system becomes complicated and heavy. In addition, this technique does not correct amplitude and phase errors in the circuit connected to each antenna element, and it is necessary to provide these correction techniques separately to correct these. It was.

  Further, the second prior art has a problem that it can correct the error in the amplitude and phase in the circuit connected to each antenna element of the array antenna, but cannot correct the error in the position of each antenna element.

  The third prior art can correct the amplitude and phase errors in the circuit connected to each antenna element of the array antenna and the coupling between the antenna elements, but cannot correct the position error of each antenna element. The necessary known wave source is greater than or equal to {(N / 2 + 1) N−1} / (N−1), where N is the number of antenna elements and the number of wave sources to be measured in the direction of arrival of radio waves is 1. There is a problem that the number of known wave sources is required as the number of antenna elements increases as the number of antenna elements increases.

  Furthermore, in the first, second, and third prior arts, since the antenna elements are densely arranged, it is necessary to consider the influence of mutual coupling between the antenna elements. Contributed to the complexity.

  The present invention has been proposed in view of the above, and it is possible to increase the accuracy with which a radio wave source position can be specified over a wide range, and it is not necessary to consider the influence of mutual coupling between antenna elements, and the radio wave arrival direction is specified. In this case, a rigid reference plate that does not change its shape and a sensor for measuring the amount of distortion are not required, and errors in the position of each antenna element that constitutes the array antenna can be corrected. It is an object of the present invention to provide a radio wave arrival direction specifying system capable of correcting an error in amplitude and phase in a circuit with a small number of known radio wave sources.

  In order to achieve the above object, an invention according to claim 1 is a radio wave arrival direction specifying system for specifying a radio wave arrival direction, and is installed in the high altitude platform for flying or stopping at high altitude, For an array antenna that receives radio waves of an arbitrary format within a predetermined frequency range, transmitted from an unknown radio source, and outputs the received signal, and amplitude and phase information obtained from the received signal of the array antenna And arrival direction specifying means for performing predetermined signal processing and specifying the arrival direction of the radio wave transmitted from the radio wave source whose position is unknown within a predetermined error.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, one or a plurality of radio sources with unknown positions are provided, and the received signal of the array antenna is an array antenna. Is a signal received by each of the antenna elements constituting the.

  Further, in the invention described in claim 3, in addition to the configuration of the invention described in claim 1 or 2, the antenna elements of the array antenna are arranged as much as possible in the place where the platform can be installed at most. A necessary and sufficient number over a wide range is installed in a linear, curved, flat or curved shape according to the shape of the platform, and the array antenna has a wide aperture surface. Based on the received signal from the array antenna on the surface, the arrival direction of the radio wave is specified one-dimensionally or two-dimensionally within a predetermined error.

  In addition to the configuration of the invention described in any one of claims 1 to 3, the invention described in claim 4 is located away from the array antenna and installed at a known position, and One or a plurality of calibration reference stations that transmit radio waves modulated in a predetermined format are provided, and the arrival direction specifying means includes a position of each antenna element constituting the array antenna and a receiving circuit connected to each antenna element. When the amplitude and phase of the antenna fluctuate with time, by performing predetermined signal processing on the received signal from the calibration reference station received by the array antenna, the position of each antenna element and the inside of the receiving circuit connected to each antenna element By calculating the influence of fluctuation in amplitude and phase, and calibrating with the fluctuation influence, the direction of arrival of radio waves transmitted from radio sources with unknown positions is within a specified error. Identifying, it is characterized by.

  Further, in the invention described in claim 5, in addition to the configuration of the invention described in any one of claims 1 to 4, the arrival direction specifying means is provided in the platform at most and is obtained by the arrival direction specifying means. It is characterized in that only information on the direction of arrival of radio waves is transmitted to the ground station.

  Further, in the invention described in claim 6, in addition to the configuration of the invention described in any one of claims 1 to 4, the arrival direction specifying means is provided in the ground station, and from the array antenna of the platform at most The received signal is multiplexed and transmitted to the ground station, and the arrival direction specifying means of the ground station separates the multiplexed received signal and then specifies the arrival direction of the radio wave.

  In the invention according to claim 7, in addition to the configuration of the invention according to any one of claims 1 to 6, when the position of the altitude platform changes with time, the direction-of-arrival specifying means includes the altitude platform. The radio wave arrival direction is specified in each of a plurality of different known positions, and the three-dimensional position of the radio wave source is obtained with high accuracy using each radio wave arrival direction.

  According to an eighth aspect of the invention, in addition to the configuration of the invention according to any one of the first to sixth aspects, the direction-of-arrival determination is performed when the high-altitude platform is at two or more known positions different from each other. The means is characterized in that the three-dimensional position of the radio wave source is obtained with higher accuracy by using the radio wave arrival direction specified by each of the altitude platforms.

  Further, in the invention described in claim 9, in addition to the configuration of the invention described in any one of claims 1 to 8, the altitude platform includes a manned or unmanned fixed-wing aircraft, helicopter, balloon, airship, And any one of artificial satellites.

  In the first and second aspects of the present invention, when the direction of arrival of a radio wave from a radio source with an unknown position is specified, the radio wave is received at most by an array antenna provided on the platform. The accuracy that can be specified can be increased over a wide range. In addition, a rigid reference plate that does not change its shape and a sensor for measuring the amount of distortion are not required, and the direction of arrival of radio waves can be specified with a simple configuration.

  According to the third aspect of the present invention, each antenna element of the array antenna is installed in a linear shape, a curved shape, a planar shape, or a curved shape over a wide range as much as possible in a place where the platform can be installed at most. Since the antenna has a wide aperture, the direction of arrival of radio waves can be specified with high accuracy in one or two dimensions within a predetermined error.

  In addition, since the distance between the antenna elements of the array antenna mounted on the platform is sufficiently long compared to the wavelength, there is almost no need to consider the influence of mutual coupling between the antenna elements.

  According to the fourth aspect of the present invention, the radio wave from the calibration reference station is received to determine the position of each antenna element and the fluctuation effect of the amplitude and phase in the receiving circuit connected to each antenna element. Since the direction of arrival of radio waves is calibrated, it is possible to correct the position error of each antenna element that constitutes the array antenna, and to correct the error in the amplitude and phase inside the circuit connected to each antenna element. Can be performed by a known radio wave source (calibration reference station).

  In addition, the direction of the radio wave source (target radio wave source) whose position is unknown can be specified with high accuracy without strictly fixing the position of each antenna element of the array antenna installed on the platform.

  In addition, even if the position of each antenna element of the array antenna installed on the platform fluctuates in time and is unknown, if the calculation speed is sufficient, the direction of the target radio wave source can be achieved with high accuracy and in real time. Can be specified.

  In addition, the direction of the target radio wave source can be specified with high accuracy regardless of the arrangement method of the array antennas installed on the platform at a high level or unknown.

  Furthermore, even if there are unknown variations in the amplitude and phase inside the circuit connected to each antenna element of the array antenna installed on the platform, and even if they change over time, there should be sufficient calculation speed. Thus, the direction of the target radio wave source can be specified with high accuracy and real time.

  In addition, if the relative positioning method is applied to the transmission signal of the appropriate at least one of the calibration reference stations whose positions are known and the relative positioning method is applied, there is an error in the platform position and attitude information at most. However, the influence of the error can be offset and the direction of the target radio wave source can be specified.

  According to the fifth aspect of the present invention, since the arrival direction specifying means is provided in the platform at most, and only the information on the direction of arrival of the radio wave is transmitted to the ground station, the amount of feeder link data from the platform can be reduced, and the ground The hardware configuration of the station can be simplified.

  According to the sixth aspect of the present invention, the arrival direction specifying means is provided in the ground station, and the received signals are multiplexed and transmitted to the ground station from the array antenna of the altitude platform, so that the system mounted on the altitude platform is reduced in weight. In addition, since the signal processing apparatus that is a complicated system can be installed on the ground, maintenance can be easily performed.

  In claim 7 of the present invention, the position of the platform is changed with time, the arrival direction of the radio wave is specified at each position, and the position of the target radio wave source is obtained by using the arrival direction of each radio wave. The position of the target radio wave source can be specified three-dimensionally. Further, it is possible to specify the target radio wave source with higher accuracy than in the case where the target radio wave source is specified by one high-level platform that stops at a certain place. Furthermore, in that case, the number of altitude platforms required can be increased by one.

  According to claim 8 of the present invention, when two or more high-altitude platforms are in different known positions, the position of the target radio wave source is obtained using the radio wave arrival direction specified by each of the high-altitude platforms. The position of the target radio wave source can be specified three-dimensionally. Further, it is possible to specify the target radio wave source with higher accuracy than in the case where the target radio wave source is specified by one high-level platform that stops at a certain place. Furthermore, in that case, the platform need not be moving at all.

  According to the ninth aspect of the present invention, any one of a manned or unmanned fixed-wing aircraft, helicopter, balloon, airship, and artificial satellite is used as the altitude platform. If the source location needs to be urgently identified with high accuracy, a manned aircraft, helicopter or balloon can be used. In addition, when it is necessary to specify the position of the radio wave source from a low altitude to a high altitude within a certain range continuously for a long time without being influenced by the weather, it is possible to turn or stop at a high degree. Possible unmanned aircraft or airships can be used. Furthermore, the position of radio sources from low altitudes to high altitudes in a wide range on a global scale is not required to be as accurate as the location from the above-mentioned aircraft or airship, but it is higher than the location of radio sources by conventional satellites. When accuracy is required continuously, a radio wave source localization system can be constructed by installing an array antenna over the widest possible area of an artificial satellite, such as a solar cell panel.

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

  Example 1 shown in FIG. 1 is a diagram showing a configuration of a radio wave arrival direction identifying system using a high-altitude platform according to the present invention. The configuration of the present invention includes a radio wave source 10 in an unknown location such as the ground, an aircraft, a ship, a high altitude platform 11 that flies or stops at high altitude, and a receiving array installed in a predetermined range of the high altitude platform 11. And an antenna 12. As the altitude platform 11, a manned or unmanned fixed wing aircraft, helicopter, balloon, airship, or artificial satellite can be used.

  In the first embodiment, the receiving array antenna 12 receives radio waves of an arbitrary format within a predetermined frequency range transmitted from the radio wave source 10, and performs predetermined signal processing on the amplitude and phase information obtained from the received signals. By performing the above, the function of specifying the direction of arrival of the radio wave emitted from the radio wave source 10 whose position is unknown within a predetermined error, as viewed from the platform 11 at the highest level, is provided. It is assumed that the position and posture of the platform 11 itself are already known by other means such as GPS and gyro. As the predetermined signal processing, for example, a known super resolution method such as the MUSIC method can be applied.

  In this way, when specifying the direction of arrival of a radio wave from a radio source of unknown position (target radio source), the radio wave is received at most by the array antenna provided on the platform, so the radio source position is specified. The possible range can be wide.

  FIG. 2 is a diagram showing an example of an array antenna installation method when a large airship and an unmanned maneuvering solar plane are used as a high-altitude platform in the first embodiment. FIG. 2A is a case of a large airship, the left side is a front view and the right side is a side view. FIG. 2B is a solar plane, and shows a front view of the main wing.

  In the case of a large airship, antenna elements 21 and 22 are dispersedly installed on the outer surface of the main body of the airship 20 to constitute an array antenna. Since an airship can usually secure a wide antenna element arrangement range not only in the long axis direction but also in the short axis direction, for example, if the antenna elements 21 and 22 are arranged in a cross shape as shown in FIG. A function for specifying the direction two-dimensionally is provided.

  In the case of an unmanned solar plane, antenna elements 24 are distributed on the surface of the main wing 23 to form an array antenna. In either case, the high altitude platform often becomes a large aircraft to obtain sufficient buoyancy or lift at high altitude. High enough by arranging the antenna elements in a straight line, curved line, flat surface or curved surface according to the platform shape as much as necessary over a wide range as much as possible, and widening the opening surface of the array antenna The direction of arrival of radio waves can be specified one-dimensionally or two-dimensionally with accuracy.

  As an arrangement method of the antenna elements, the number of necessary antenna elements can be reduced by arranging them at unequal intervals so that the uncertainty of the arrival direction of radio waves does not occur.

  In addition, the normal array antenna is affected by the amplitude and phase inside the circuit connected to each antenna element, the displacement of the position of the antenna element, and the mutual coupling between the antenna elements. All these unknown parameters are calibrated. If not, the estimation accuracy of the direction of arrival of radio waves deteriorates. However, in this embodiment, in order to obtain the highest possible resolution, it is assumed that the antenna elements are arranged at intervals of a half wavelength or more over a wide area on the platform, The effect of mutual coupling is almost negligible, and calibration of mutual coupling is unnecessary.

  FIG. 3 shows parameters for illustrating a calibration method in the case where an unknown position displacement occurs in the antenna element on the platform in Example 1 and an unknown phase displacement also occurs in the circuit connected to the antenna element. FIG. In the present calibration method, when the antenna element 30 installed on the platform is displaced to the position 30 'at high level and the position displacement vector is unknown, four calibration reference stations are distributed and installed at known positions on the ground. By receiving the calibration signals transmitted from 31, 32, 33, and 34 by the antenna elements 30, 30 ′, the reception phase displacement when the signal is assumed to arrive from an arbitrary direction is calculated. The array antenna is calibrated by calculating and determining the steering vector in any direction of the array antenna on the high-altitude platform with unknown position displacement and phase displacement for each antenna element.

  Here, the steering vector means a vector composed of elements corresponding to the number of antenna elements in which the arrival direction of radio waves or the beam direction of the array antenna is expressed by using a phase difference between the antenna elements of the array antenna.

  In the following, based on FIG. 3, attention is paid to one antenna element constituting the array antenna, and when this is accompanied by an unknown position displacement and phase displacement, an expression for calculating a received phase displacement when a signal comes from an arbitrary direction Is derived.

First, each parameter shown in FIG. 3 is defined. It is assumed that the position displacement vector when the antenna element 30 is displaced to the position 30 ′ is a vector d, the phase displacement inside the receiving circuit connected to the antenna element is φ, and these quantities are unknown. Next, unit vectors in the respective directions of the four calibration reference stations 31, 32, 33, and 34 viewed from the antenna element 30 are set as unit vectors e1, e2, e3, and e4, respectively. In addition, an angle parameter in steering vector scanning for estimating the direction of the detection target radio wave source is θ, and a unit vector in the direction 35 of an arbitrary azimuth angle θ is eθ. The scanning direction of the angle θ may be arbitrary, but the direction of the target radio wave source can be estimated with high resolution with respect to θ by setting the direction of the largest aperture of the array antenna. In FIG. 3, as an angle parameter for polar coordinate display in an arbitrary direction 36, the direction indicated by 37 is θ, and the direction indicated by 38 orthogonal thereto is ψ. At the same time, the direction of the largest aperture of the array antenna is taken as the x-axis, the vertically downward direction is taken as the y-axis, and the direction orthogonal to the x-axis and the y-axis is taken as the z-axis. At this time, the unit vectors e1, e2, e3, and e4 are expressed by the following equations using the x component, the y component, and the z component, respectively.

で表されるものとする。 Further, regarding the position displacement vector d from the antenna element 30 to 30 ′, which is an unknown parameter,

It shall be represented by

Further, projection vectors in the direction of the respective unit vectors e1, e2, e3, e4 and eθ relating to the position displacement vector d are respectively set as vectors δ1, δ2, δ3, δ4 and δθ, and the magnitudes thereof are expressed by phase displacements. These are set as δ1, δ2, δ3, δ4, and δθ. Note that the phase displacement actually observed by detecting the received signal of the antenna element is the same as that in the circuit that contributes to the above-mentioned δ1, δ2, δ3, δ4, and δθ in common for signals incident from any direction. The phase displacement φ is added, and this is expressed as follows.

  Here, when the distance from the antenna to the target radio wave source is sufficiently large compared to the antenna aperture length on the platform, the displacement in the direction of the target radio wave source viewed from the antenna element due to the displacement of the antenna element position is sufficiently negligible Since the relative positional relationship between the four calibration reference stations and the altitude platform is always known among the parameters of Equation 1, the vectors e1, e2, e3, e4, which are parameters related to these calibration reference stations, are always known. The values of can all be known, and δ'1, δ'2, δ'3 and δ'4 respectively measure the received phase displacement of the calibration signal transmitted by each calibration reference station at the antenna element. Can know.

ただし、（ ・ ）は内積、Ｔは転置を表す。回路内部の位相変位φが存在する場合、実際に観測される各方向の位相変位は数１ないし数５から、次式で表される。

ここで、行列Ｅｒ’およびベクトルδｒ’、ベクトルｄ’を次のように定義する。

Next, from these known parameters, an equation for deriving the sum δ′θ = δθ + φ of δθ and φ under the condition that the vectors d and φ are unknown is derived. First, since δ1 to δ4 and δθ are projections of the vector d in the direction of the unit vectors e1 to e4 and eθ, respectively, the following equation is obtained.

However, (·) represents an inner product, and T represents transposition. When there is a phase displacement φ inside the circuit, the phase displacement actually observed in each direction is expressed by the following equation from Equation 1 to Equation 5.

Here, the matrix Er ′, the vector δr ′, and the vector d ′ are defined as follows.

Rewriting Equation 6 using Equation 8 yields the following equation.

ただし、

とおいている。 Equation 7 is given by the following equation.

However,

I keep it.

Therefore, the following equation for obtaining δ′θ is obtained from Equation 9 and Equation 10.

  That is, if signals of at least four calibration reference stations installed at different known locations are received at most by each antenna element on the platform and their reception phases are measured, the phase displacement inside the receiving circuit is calculated using Equation 12. And the phase displacement δ′θ in the arbitrary direction θ including the phase displacement due to the positional displacement of the antenna element can be obtained.

  In order to select the signal of one calibration reference station from the signals received by each antenna element and measure the phase and amplitude, it is described in Japanese Patent No. 3096733 “Beam-forming method of array antenna”. The following known methods similar to the existing methods can be used.

ここで￣はｎサンプル分の平均値、＊は複素共役を表す。受信複素系列ｓ（ｎ）と既知のデータ系列ｒｉ（ｎ）の間でタイミングを１サンプルずつずらしながら演算し、ｗｉが最大値ｗｉ，ｐｅａｋとなったとき、次式を計算する。

ここでａｒｇは複素数の偏角、｜ ｜は複素数の絶対値を表す。 Each calibration reference station modulates and transmits different known calibration data series, and there is an i-th (i = 1, 2, 3,...) Calibration reference station selected on the platform at most. A complex data sequence of a predetermined number n of samples is set to ri (n), and signals transmitted from all at least four calibration reference stations are simultaneously received on the platform at most, and the number of samples n is detected from the signal detected up to the baseband. Let s (n) be the extracted complex sequence. It is assumed that the phase of the locally transmitted signal in detection is completely synchronized with all antenna elements. At this time, in order to select only the signal transmitted from the i-th calibration reference station from the received sequence s (n) and obtain the phase displacement δi ′ and the amplitude ai, the received complex sequence s (n) and the known data The following complex correlation calculation is performed between the series ri (n).

Here, ￣ represents an average value for n samples, and * represents a complex conjugate. The calculation is performed while shifting the timing between the received complex sequence s (n) and the known data sequence ri (n) by one sample, and when wi reaches the maximum value wi, peak, the following equation is calculated.

Here, arg represents the argument of the complex number, and || represents the absolute value of the complex number.

Arithmetic as seen from the array antenna is performed by performing the above-described operations of Formulas 12 to 14 for the received signals of all antenna elements, the calibration data series from all calibration reference stations, and all directions viewed from the array antenna. The steering vector in each direction is calculated, and the angle can be detected by the super resolution method that scans the direction of the steering vector. As a super-resolution method for specifying the direction of arrival of radio waves by scanning a steering vector, a known MUSIC method or the like is already known. In this case, the number of antenna elements is m, and the phase displacement corresponding to the θ direction calculated by Expressions 12 to 14 for the k-th (1 ≦ k ≦ m) antenna element is calculated by δθ ′ (k) and Expression 14. If the received signal amplitude at the k-th antenna element calculated from any i-th calibration reference station is ai (k), the steering vector Aθ corresponding to the θ direction is calculated by the following equation.

  When the calibration data transmitted from the calibration reference station is repeatedly transmitted at a predetermined cycle, and the position displacement of the antenna element, the phase displacement inside the circuit, and the amplitude change dynamically by repeatedly executing the above calculation. However, if there is a sufficient calculation speed, the steering vector can be obtained in real time.

  Next, performance examples of the first embodiment will be shown by simulation.

FIG. 4 is a diagram showing a model for simulation. This model is described below. Assume that the platform is stationary at an altitude of 20 km, and the antenna elements of the array antenna 40 are arranged on the surface of the platform in a curved line at an opening diameter of 70 m. Each antenna element is assumed to be randomly displaced in the vertical direction, and there is also a random phase displacement inside the circuit connected to each antenna element. However, the amplitude displacement inside each circuit is not assumed here. It is assumed that three calibration reference stations 41 to 43 are installed at known positions in order to calibrate the array antenna on the ground, and two detection target radio wave sources 44 are in close positions on the ground, and have the same frequency in the 900 MHz band. It is assumed that an arbitrary waveform is transmitted. Note that the angle difference seen from the platform of the two radio wave sources is 0.03 degrees. This angle difference corresponds to about 10 m in terms of distance. In the simulation, for simplification, it is assumed that each antenna element of the array antenna, the three calibration reference stations, and the two detection target radio wave sources all exist in the same plane. In this case, since the antenna element position displacement is changed from the normal three-dimensional to two-dimensional, the number of unknown variables is reduced by one. Therefore, three calibration reference stations are sufficient. Table 1 shows the main specifications of the simulation model.

  FIG. 5 is a diagram showing the results of simulation. FIG. 5A shows the result of obtaining the MUSIC spectrum by applying the MUSIC method without performing calibration with respect to the position of the antenna element or the phase shift in the circuit. It can be seen that no peaks appear in the directions of the two target radio wave sources, that is, the directions of 10.000 degrees and 10.03 degrees, and the radio wave source direction cannot be measured. On the other hand, FIG. 5 (b) shows the result of calibration using the signal from the calibration reference station, and the MUSIC spectrum is obtained. Peaks appear in the directions of the two target radio sources, and each direction can be accurately identified. It can be seen that these two directions are clearly disassembled.

  Since the simulation uses a model on a plane as described above, three calibration reference stations are sufficient. However, in the case of a three-dimensional space, adding another calibration reference station allows the array antenna to be Can be calibrated.

  In the simulation, there is no amplitude displacement inside the circuit connected to each antenna element of the array antenna. However, even if this is present at random, this is calibrated by means of Equations 13 and 14, and the target radio wave source The direction can be specified with high accuracy.

  The means for determining the direction of the target radio wave source by scanning the steering vector is simultaneously applied to the transmission signal of at least one of the four calibration reference stations, and the direction of the target radio wave source is known. If the already known relative positioning method, which is obtained as relative coordinates from the direction of the calibration reference station in Fig. 1, is applied, even if there is an error in the platform position and orientation information, the influence of the error is offset and the target radio wave The direction of the source can be specified.

  In this way, by receiving the radio wave from the calibration reference station, the position of each antenna element and the influence of fluctuation of the amplitude and phase inside the receiving circuit connected to each antenna element are obtained, and the direction of arrival of the radio wave is determined by the fluctuation influence. Since the calibration is performed, the position error of each antenna element constituting the array antenna can be corrected, and the correction of the amplitude and phase error in the circuit connected to each antenna element can be corrected with a small number of known radio wave sources. (Calibration reference station).

  In addition, the direction of the radio wave source (target radio wave source) whose position is unknown can be specified with high accuracy without strictly fixing the position of each antenna element of the array antenna installed on the platform.

  In addition, even if the position of each antenna element of the array antenna installed on the platform fluctuates in time and is unknown, if the calculation speed is sufficient, the direction of the target radio wave source can be achieved with high accuracy and in real time. Can be specified.

  In addition, the direction of the target radio wave source can be specified with high accuracy regardless of the arrangement method of the array antennas installed on the platform at a high level or unknown.

  Furthermore, even if there are unknown variations in the amplitude and phase inside the circuit connected to each antenna element of the array antenna installed on the platform, and even if they change over time, there should be sufficient calculation speed. Thus, the direction of the target radio wave source can be specified with high accuracy and real time.

  The above-described steering vector of the array antenna scans along the direction with the largest aperture diameter and simultaneously scans along the other direction, so that the direction of the target radio wave source can be obtained two-dimensionally. Naturally, when the aperture surface of the array antenna is two-dimensionally expanded and a large aperture diameter can be obtained in a plurality of directions, the two-dimensional identification accuracy in the direction of the target radio wave source is increased.

  FIG. 6 shows means for specifying the direction of the target radio wave source on the ground within a predetermined error range two-dimensionally when the aperture of the array antenna on the platform is only one-dimensionally widened. This means is composed of an array antenna 60 installed on the platform at a high level, and a target radio wave source 61 in an unknown place on the ground. It is assumed that the direction of the target radio wave source obtained by the MUSIC method is within the range of θ1 ± Δθ1 by scanning the steering vector indicated by 63 along the direction 62 in which the largest aperture of the array antenna 60 is obtained. However, Δθ1 is a direction specifying error. At this time, the position of the target radio wave source on the ground is included in a certain band-like region 64, and the position of the target radio wave source cannot be specified as one place only by this. Next, the direction of the target radio wave source obtained by the MUSIC method is θ2 ± Δθ2 by scanning the steering vector indicated by 66 along another direction 65 rotated by a predetermined angle γ in the horizontal direction from the direction 62. It is assumed that it is within the range. At this time, the position of the target radio wave source on the ground is included in another band-shaped region 67. Therefore, by scanning the steering vector in the two different directions, it is specified that the direction of the target radio wave source exists in the direction of the region 68 where the two band-like regions 64 and 67 intersect.

  In this way, the array antenna steering vector is scanned along the direction having the largest aperture diameter, and at the same time along the other direction, so that only when the array antenna having a two-dimensional spread is used. In addition, the direction of the target radio wave source can be obtained two-dimensionally even when an array antenna having only one-dimensional expansion is used.

  As described above, according to the first embodiment, even when the position of each antenna element of the array antenna installed on the platform and the amplitude and phase inside the receiving circuit connected to each antenna element fluctuate arbitrarily with time, the above-mentioned The position of each antenna element and the influence of fluctuations in amplitude and phase inside the receiving circuit connected to each antenna element can be simultaneously removed or reduced, and the radio wave arrival direction can be specified with high accuracy. In addition, since a calculation method that basically considers the influence of the position displacement of the antenna element is included, the arrangement method of the antenna element may be arbitrary, such as an equidistant arrangement, an unequal arrangement, an arrangement on a curved surface, a cross arrangement It can be applied to any arrangement such as a circular arrangement, and the position of each antenna element does not need to be accurately grasped in advance.

  Example 2 shown in FIG. 7 is a diagram showing an example of a signal transmission method from the on-board sensor system on the platform to the ground base station. In the present embodiment, an array antenna 71 installed on the platform 70 at a high degree, an A / D converter 72 that samples and digitizes received signals at each antenna element of the array antenna on the platform 70, respectively, are digitized. Digital signal processing is performed on the signal to calibrate the array antenna and calculate the direction of the target radio wave source 79, and the digital signal processing device 73 on the platform 70 multiplexes the calculated direction data of the target radio wave source to a predetermined radio frequency. Multiplexer / transmitter 74 on platform 70 for modulating, transmit antenna 75 on platform 70 for transmitting the modulated signal toward the ground, and installed on the ground for receiving the transmitted signal on the ground Receiving antenna 76, and demodulating the received signal And receiving and separating apparatus 77 installed on the ground to obtain the direction specification results direction data were respectively separated and recovered in the standard radio sources, and a.

  In the second embodiment, signals received by the antenna elements of the array antenna 71 on the platform 70 are AD-converted on the platform, and the calculation of the array antenna calibration and the arrival direction of the radio wave is performed. Although only the direction data of the radio wave source is multiplexed and modulated into a radio signal and transmitted to the receiving station on the ground, the weight of equipment mounted on the platform is increased and complicated, but the radio between the platform and the ground The data line does not require a lot of bandwidth, and the ground facilities are simple.

  Example 3 shown in FIG. 8 shows another example of a signal transmission method from the on-board sensor system on the platform to the base station on the ground. This embodiment includes an array antenna 81 installed on the platform 80 at a high level, an A / D converter 82 that samples and digitizes received signals at each antenna element of the array antenna on the platform 80, and each digitized signal. A multiplexing / transmission device 84 that multiplexes the received signals of the antenna elements as they are and transmits them to the ground, a transmission antenna 85 on the platform 80 that transmits the multiplexed signals toward the ground, and the transmitted signals. A receiving antenna 86 installed on the ground for receiving on the ground, a receiving / separating device 87 for separating the received signals and restoring received signals from the antenna elements on the platform 80 on the ground, and being separated / restored Using the measured signal, the array antenna is calibrated and the direction of radio wave arrival is calculated. A digital signal processor 83 to obtain the direction specification results of the target radio sources, in constructed.

  In the third embodiment, the calibration of the array antenna and the calculation for determining the arrival direction of the radio wave are not performed on the platform, and the digital signal obtained by AD-converting the reception signal of each antenna element is directly multiplexed and sent to the ground. It is characterized by simplifying the platform-equipped device and reducing the weight by performing the calibration of the signal and calculating the direction of arrival of the radio wave. In addition, although the bandwidth required to multiplex and transmit the received signals of all antenna elements to the wireless data line from the platform to the ground is required, and the ground equipment becomes complicated and large-scale, Therefore, the maintenance is easy. In this embodiment, in transmitting a multiplexed signal from the platform to the ground, it is necessary to accurately store the amplitude and phase information of the received signal at each antenna element on the platform. As a method of multiplexing the reception signal of each antenna element on the platform, a method such as parallel / serial conversion of a digital signal obtained by sampling the reception signal of each antenna element can be used.

  In the fourth embodiment shown in FIG. 9, when the platform flies around a certain range at high altitude and changes its position with time, the position of the target radio wave source including the altitude direction is three-dimensionally utilized by changing the position. The means to specify is shown. In this embodiment, one altitude platform equipped with an array antenna moves sequentially from position P1 to position P4 with time, and at the same time, the direction of the target radio wave source 92 at each position P1, P2, P3, P4 is sequentially set to 911. 914 to 914, and the range of the position where the target radio wave source exists is calculated from the position information of each platform and the result of specifying the direction of each target radio wave source. Give the means to seek.

  Only the array antenna on one high altitude platform can only determine the direction of the target radio source as viewed from the platform, it cannot identify the position in three dimensions, and the target radio source height is another means in advance. However, in the fourth embodiment, the height of the target radio wave source can be determined by specifying the direction of the target radio wave source from a plurality of positions using the movement of the platform. Even if it is unknown in advance, the three-dimensional position can be specified within a predetermined error range.

  Also, instead of the one high-altitude platform that moves, there are at least two high-altitude platforms in advance, and if these platforms can receive the transmission radio waves of the target radio wave source, the position of the target radio wave source can be similarly used using these platforms. Can be specified three-dimensionally. In this case, it is possible to specify the position more quickly than when the one platform moves, and the platform may not be necessarily moved but may be stopped at a predetermined position.

It is a figure which shows the structure of the electromagnetic wave arrival direction identification system by the high altitude platform which concerns on this invention. It is a figure which shows the example of the installation method of the array antenna at the time of using a large airship and an unmanned operation solar plane as a high altitude platform. It is a figure which shows each parameter for showing the calibration method when an unknown position displacement arises in the antenna element on a platform, and an unknown phase displacement also arises in the circuit connected to an antenna element. It is a figure which shows the model for simulation. It is a figure which shows the result of simulation. It is a figure which shows the means to specify the direction of the target radio wave source on the ground within a predetermined error range two-dimensionally when the aperture of the array antenna on the platform is only one-dimensionally widened. It is a figure which shows an example of the signal transmission method from the mounted sensor system on a high altitude platform to a ground base station. It is a figure which shows another example of the signal transmission method from the mounted sensor system on a high-altitude platform to a ground base station. FIG. 5 is a diagram showing a means for three-dimensionally specifying the position of a target radio wave source including the altitude direction using a change in position when the platform changes its position with time by turning and flying over a predetermined range at a high altitude. .

Explanation of symbols

10, 44, 61, 79, 92 Radio wave source 11, 70, 80 High altitude platform 12, 40, 60, 71, 81 Array antenna 20 Airship 21, 22, 24, 30, 30 'Antenna element 23 Main wing 31, 32, 33 , 34 Calibration reference station 35, 36, 62, 65 Direction 41, 42, 43 Calibration reference station 44 Radio wave source 60 Array antenna 61 Radio wave source 64, 67, 68 Area 72, 82 A / D converter 73, 83 Digital signal processing device 74,84 Multiplexer / transmitter 75,85 Transmit antenna 76,86 Receive antenna 77,87 Receiver / separator 93 Range 911, 912, 913, 914 Direction P1, P2, P3, P4 Position of platform

Claims (9)

In the radio wave arrival direction identification system that identifies the arrival direction of radio waves,
An altitude platform to fly or park at altitude,
An array antenna that is installed on the above-mentioned high altitude platform, receives radio waves of an arbitrary format within a predetermined frequency range, and is transmitted from a radio source of unknown position, and outputs the received signal;
Direction-of-arrival specification that performs predetermined signal processing on the amplitude and phase information acquired from the received signal of the array antenna, and specifies the direction of arrival of radio waves transmitted from radio sources of unknown position within a predetermined error Means,
A radio wave arrival direction identifying system comprising:   The radio wave arrival direction identifying system according to claim 1, wherein one or a plurality of radio sources having unknown positions are provided, and a received signal of the array antenna is a signal received by each antenna element constituting the array antenna. Each antenna element of the above array antenna is linear, curved, planar, or curved according to the shape of the high-altitude platform in a necessary and sufficient number over the widest possible range where the high-level platform can be installed. Installed in a wide area of the array antenna,
The arrival direction specifying means specifies the arrival direction of a radio wave one-dimensionally or two-dimensionally within a predetermined error based on a received signal from an array antenna having a wide aperture surface. Radio wave arrival direction identification system. One or more calibration reference stations that are located away from the array antenna, are installed at known positions, and transmit radio waves modulated in a predetermined format;
When the position of each antenna element constituting the array antenna and the amplitude or phase inside the receiving circuit connected to each antenna element fluctuate with time, the direction-of-arrival specifying means receives from the calibration reference station received by the array antenna. By applying predetermined signal processing to the signal, the position of each antenna element and the amplitude and phase fluctuation effects in the receiving circuit connected to each antenna element are obtained and calibrated with the fluctuation influence parts to The radio wave arrival direction specifying system according to any one of claims 1 to 3, wherein an arrival direction of a radio wave transmitted from an unknown radio wave source is specified within a predetermined error.   The radio wave arrival direction specifying system according to any one of claims 1 to 4, wherein the arrival direction specifying means is provided at a platform at a high degree and transmits only the information on the radio wave arrival direction obtained by the arrival direction specifying means to the ground station.   The arrival direction specifying means is provided in the ground station, and the received signals are multiplexed and transmitted from the array antenna of the platform to the ground station. The arrival direction specifying means of the ground station separates the multiplexed received signals. The radio wave arrival direction specifying system according to any one of claims 1 to 4, wherein the radio wave arrival direction is specified.   When the position of the high altitude platform changes with time, the arrival direction specifying means specifies the radio wave arrival direction in each of cases where the altitude platform is at a plurality of different known positions, and uses each radio wave arrival direction to The radio wave arrival direction identifying system according to any one of claims 1 to 6, wherein the three-dimensional position of the source is obtained with high accuracy.   When the altitude platform is at two or more known positions different from each other, the arrival direction specifying means uses the radio wave arrival direction specified by each of the altitude platforms to increase the three-dimensional position of the radio wave source. The radio wave arrival direction specifying system according to any one of claims 1 to 6, wherein the radio wave arrival direction specifying system is obtained with accuracy.   The radio wave arrival direction identifying system according to any one of claims 1 to 8, wherein the altitude platform is one of a manned or unmanned fixed-wing aircraft, a helicopter, a balloon, an airship, and an artificial satellite.

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