JP2010071889A - Radar system mounted on movable body and calibration method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct displacement of the wave front of an antenna while a movable body mounted therewith is on the move. <P>SOLUTION: In a radar signal processor R, the direction of a known directional target is measured prior to usual operation. A direction correcting value is calculated on each of antenna elements from a measurement result and stored in a storage circuit 141. The phases of signals received by the elements are controlled based on the correcting value stored during actual operation. At the usual operation stage, an aimed target is disposed in a known direction to emit pulses in the direction while measuring an incoming direction from a target based on a target reflected signal received via the antenna. In a module correction quantity calculation circuit 151, a correction value is calculated with respect to the amplitude/phase difference of a synthetic output of respective sub-modules Li so as to null a difference between a measured incoming direction and a known target direction, and stored in a memory 1512. During actual operation, a correction value for a phase error is found from the memory 1512 to correct the displacement of the wave front, the phase error caused by body deformation of each of the respective sub-modules Li with respect to a beam pointing direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a radar device that receives a radar signal using an antenna device that is mounted on a moving body such as an aircraft and is mounted on the surface thereof, and an antenna device by correcting a change in the element array plane shape of the antenna device. The present invention relates to a calibration method for avoiding deterioration of antenna performance when a device mounting surface is deformed.

  2. Description of the Related Art In recent years, in radar devices mounted on aircraft, development of an antenna device using an active phased array in which an array antenna is divided into a number of flexible submodules and distributed along the shape of the airframe surface has been underway. This antenna apparatus is expected to obtain an arbitrary directivity as a whole and to increase the radar aperture by individually and selectively controlling individual modules.

  By the way, in a radar apparatus using an active phased array antenna, the directivity of the array antenna is controlled in order to increase the gain of the antenna reception signal. The directivity of the array antenna is controlled by adjusting the amplitude and phase with an amplitude adjuster and a variable phase shifter attached to each antenna, thereby obtaining a desired directivity pattern and frequency characteristics.

  However, the array antenna has a problem that the operating characteristics of each antenna element are different due to variations in circuit characteristics corresponding to each antenna element, variations in element arrangement, and the like. Thus, if there are variations in circuit characteristics and variations in element arrangement, the wavefront of the antenna will be shifted by the phase difference corresponding to these variations. For this reason, in the past, a phase difference corresponding to these variations is obtained in advance as a correction value, and when obtaining the azimuth, the correct azimuth is obtained by performing so-called calibration that corrects the wavefront of the antenna using the correction value. ing. There are some report cases (for example, Non-Patent Document 1) as the calibration method.

  Specifically, the calibration procedure usually measures the orientation with respect to a target placed in a known orientation before operation, and corrects the orientation (phase difference) so that the measured orientation becomes a predetermined orientation. A value is obtained for each antenna element and stored in a storage device in the radar device. In this storage device, correction values that take into account the influence on the phase difference due to temperature and frequency characteristics are generally stored. In the operation stage, the wavefront of the antenna can be accurately matched by calculating using the correction value obtained by this calibration.

  However, when considering a radar device in which an antenna device is mounted on the surface of an aircraft body, the problem becomes complicated.

Generally, it is known that the surface of an aircraft body is deformed during flight. The antenna placement error due to the deformation of the airframe surface has little effect on the characteristics of the antenna itself, but in the case of a radar using an array antenna composed of thousands of antenna elements such as active phased array radar, the effect is Appears prominently. In the conventional calibration method, corrections are made for variations in element positions and arrangement errors in a single antenna, but phase correction corresponding to the entire radar aperture caused by airframe deformation is not taken into consideration. For this reason, the correction value measured before normal operation has a problem that the performance deteriorates due to the deviation of the wavefront of the antenna.
Nobuyoshi Kikuma, "Adaptive signal processing by array antenna", Science and Technology Publishing Co., Ltd., November 1998, p.13-66.

  As described above, in the radar device mounted on a moving body using a conventional active phased array antenna, since the deformation of the antenna mounting surface during movement of the mounted moving body is not taken into consideration, even if calibration is performed, The wave front of the antenna during movement cannot be accurately matched.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a mobile-mounted radar device that can adjust the wavefront of an antenna even when the mounted mobile body is moving, and a calibration method thereof. To do.

  In order to solve the above problems, a radar mounted on a moving body according to the present invention is an array that is mounted in a distributed manner on the surface of the moving body, has an individual microwave reception function, and is directed independently of each other. A plurality of sub-modules based on an antenna structure; scanning control means for controlling a beam scanning angle by controlling phases of individual antenna elements in the plurality of sub-modules based on a directed directivity direction; and the plurality of sub-modules Receiving beam forming means for combining the received signals obtained in step (1) to form a received beam, and directivity control means for controlling the direction of the received beam in units of submodules for the plurality of submodules. The control unit is configured to control the phase for each of the plurality of submodules based on the reception signal of the reception beam formed by the reception beam forming unit. The corrected, characterized in that to adjust the deviation of the wavefront due to the fuselage deformation of the movable body.

  In addition, the calibration method used in the mobile radar device having the above configuration emits a pulse to the direction of a reference target having a high SNR arranged in a known direction, and estimates the direction of arrival of the radio wave based on the reflected wave. Calculate the azimuth correction value for each submodule so that the difference between the azimuth from the target obtained by the method and the known target azimuth is zero, and convert this azimuth correction value into the phase correction amount in the submodule. It is characterized by doing.

  That is, the present invention has been made in view of the above-described problems, and does not provide a phase correction value only for a single antenna, but a combined output of a plurality of array antenna units (submodules) that are gathered to some extent. Perform phase correction.

  First, regarding the derivation of the correction value for each antenna, the azimuth of each antenna element with respect to a target placed in a known azimuth is measured before normal operation of the radar apparatus so that the measured azimuth becomes a predetermined azimuth. Then, a correction value for the azimuth (phase difference) is calculated. In addition to the correction value, a correction value that takes into account the effects of temperature and frequency characteristics is recorded in the phase correction amount storage device.

  Next, with respect to phase correction in units of submodules, a target having a high SNR is arranged in a known direction in a normal operation stage, and a pulse is emitted in that direction. Based on the target reflection signal of the radar pulse received via the antenna, the difference between the arrival direction from the target and the known target direction obtained by the radio wave arrival direction estimation method (for example, Beamformer method, Capon, MUSIC, ESPRIT, etc.) A correction value for the phase difference is calculated for the combined output of each sub-module so as to be zero, and stored in the radar apparatus. By applying this calibration method, it is possible to obtain a correction value for the phase error due to the deformation of the airframe, and to avoid the wavefront shift performance deterioration with respect to the problem.

  Therefore, according to the present invention, it is possible to provide a mobile mounted radar apparatus and a calibration method thereof that can match the wavefront of the antenna even while the mounted mobile body is moving.

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

  FIG. 1 is a perspective view showing an antenna mounting image of an aircraft on which a radar apparatus according to the present invention is mounted. In this aircraft, receiving sub-modules L1 to Ln using a large number of thin and flexible antennas are mounted at arbitrary locations on the surface of the aircraft.

  As shown in FIG. 2, each receiving sub-module Li (i is 1 to n) selects N antenna elements (element numbers # 1 to #N) 111 to 11N, excitation of each element, and reception of the element. Switching, and adjusting the phase and amplitude, and distributing the power of the microwave excitation signal to each of the microwave modules 121 to 12N and combining the received outputs from the modules 121 to 12N / Combining circuit 13, and scanning controller 14 for scanning control of the directivity direction of the antenna beam according to beam scanning angle information for power distribution / combining circuit 13 and microwave modules 121 to 12N. The scanning controller 14 stores the amplitude / phase correction amount of each antenna element given to each of the reception submodules L1 to Ln in the module correction amount storage circuit 141, and based on the correction amount stored here. It has a function of correcting the amplitude and phase of the combined output during reception beam formation.

  The n reception submodules Li are connected to the radar signal processing device R. This radar signal processing apparatus R calculates the amplitude / phase correction amount for each antenna element according to the beam forming direction, sends it to each receiving submodule Li, stores it in the storage circuit 141, and stores the amplitude / phase correction amount for each submodule. A radar signal processing unit 15 including a module correction amount calculation circuit 151 that calculates a phase correction amount, and an excitation signal are sent to the power distribution / combination circuit 13 of each submodule Li, and a combined received signal from the power distribution / synthesis circuit 13 Is provided on the basis of the amplitude / phase correction amount calculated by the module correction amount calculation circuit 151, and an excitation receiving unit 16 for combining and outputting.

  Here, in the active phased array radar, for example, an aperture surface is configured by a planar array antenna in which M array antennas of N elements arranged in the vertical direction are arranged in the horizontal direction. In the present invention, the planar array antenna is divided into a plurality of parts, each of which is configured as a receiving submodule Li. FIG. 3 shows a receiving submodule when the radar aperture is divided in units of (n = 8, m = 8).

  In the above configuration, specific processing contents will be described below.

  First, with reference to a configuration diagram of an array antenna including a plurality of antenna elements shown in FIG. The array configuration is assumed to be an equispaced linear array for ease of explanation.

In FIG. 4, N (n: 1 ... N) is the number of antenna elements, d _n is the distance of the n-th element position from the reference point, theta ₀ is radio wave arrival direction, c is the speed of light. A _{1 to} A _N are amplitude adjusters, δ _{1 to} δ _N are variable phase shifters, and Σ is an adder. Received data in each array element is obtained by the following equation.

Here, λ is the wavelength of the incoming wave, s (t) is the complex amplitude of the incoming wave, and n _n (t) is the thermal noise generated in each antenna element.

The output value of the array is expressed by the following equation.

Here, w is a weight vector whose element is a weighting coefficient for each element. The output power is obtained by the following equation.

Here, E [•] is an ensemble average.

Although described in detail in Non-Patent Document 1, the Beamformer method is the most basic arrival direction estimation method, which scans the main beam of the array antenna in all directions and searches for a direction in which the output power of the array increases. is there. In order to direct the main beam of the array antenna to the angle θ, the weight vector is set as follows from the common phase condition (condition for aligning the phases to be in phase).

The angle θ is changed from −90 ° to 90 °, and the peak of the output power of the array is searched. The weight vector having the above weight component has an angle θ as a variable and is called a mode vector or a steering vector. The combined output of the array is given by

  As each antenna calibration procedure, a reflector is installed in a certain known direction, and radio waves are transmitted in that direction. The reflected signal from the reflector is received by the array antenna, and the peak of the array output power is searched by the Beamformer method. For example, as shown in FIG. 5, when there is an angle difference (azimuth error) between the peak angle of the output power and the radiation angle of the radio wave, the amplitude / phase correction amount is calculated so that the angle difference is zero and the correction is made Treat as a value.

  According to the present invention, the amplitude / phase correction for each antenna element is performed using the correction value calculated in the inspection process before normal operation, and the secondary amplitude / phase correction is performed for each sub-module in the upper system. As described above, a module correction amount calculation circuit 151 is prepared in the radar signal processing unit 15. FIG. 6 shows a schematic system diagram for correction in units of submodules.

In FIG. 6, the excitation receiving unit 16 takes in the received signals from the respective receiving submodules Li via the amplitude / phase controller 161 i and sequentially adds and synthesizes them with the adder (Σ) 162. On the other hand, in the module correction amount calculation circuit 151, when the beam scanning angle information (θ _AZ , θ _EL ) is given, the calculation circuit 1511 calculates the amplitude / phase amount corresponding to the beam direction.

  Here, in the calculation circuit 151, the amplitude / phase correction amount of each submodule measured in advance for each beam directing direction is stored in the memory 1512. When the correction amount reading circuit 1513 is given beam scanning angle information, The memory 1512 is accessed to read out the amplitude / phase correction amount for each submodule in the corresponding beam directing direction. The read amplitude / phase correction amount is sent to the adder 1514 and added to the amplitude / phase amount obtained by the arithmetic circuit 1511 for each submodule. The amplitude / phase amount for each sub-module corrected in this way is sent to the amplitude / phase controller 161i of the corresponding system of the excitation receiver 161, and used for the amplitude / phase control processing.

  FIG. 7 is a flowchart showing a specific processing procedure of radar signal processing in the configuration shown in FIG. First, when signal reception of each antenna element is performed in each submodule Li (step S1), the amplitude correction amount for each submodule is read from the memory 1512, and amplitude correction is executed in the corresponding submodule (step S2). . Subsequently, the phase correction amount for each sub-module is read from the memory 1512, and the phase correction is executed by the corresponding sub-module (step S3).

  RF synthesis is performed through the correction processing in units of submodules (step S4), the synthesized output is A / D converted (step S5), and the phase of the entire antenna is corrected in accordance with the beam directing direction (step S6). Beam synthesis is performed (step S7), and a radar output Y (t) is obtained.

  In this way, the amplitude / phase correction amount is calculated for the combined output from each sub-module, and this correction amount is converted into the amplitude / phase correction amount for each sub-module and subjected to the amplitude / phase control and combined. More accurate angle measurement is possible.

  In summary, the conventional radar device mounted on a moving object using an active phased array antenna does not take into account the deformation of the antenna mounting surface during movement of the mounted moving object. The wave front of the antenna cannot be matched accurately.

  Therefore, in the present invention, amplitude / phase correction is performed on the combined output of a plurality of array antenna units (submodules) collected to some extent, instead of giving amplitude / phase correction values only to a single antenna.

  First, regarding the derivation of the correction value of each antenna element, the radar signal processing apparatus R measures the azimuth of each antenna element with respect to a target placed in a known azimuth before normal operation. Then, the module correction amount calculation circuit 151 calculates a correction value for the azimuth (phase difference) so that the measured azimuth becomes a predetermined azimuth, and further adds a correction value considering the influence of temperature and frequency characteristics. Thus, the phase of the received signal of each element is controlled based on the phase correction amount stored in the module correction amount storage circuit 141 of each submodule Li and stored in actual operation.

  Next, with respect to phase correction in units of submodules, a target having a high SNR is arranged in a known direction in a normal operation stage, and a pulse is emitted in that direction. In the radar signal processing device R, based on the target reflected signal of the radar pulse received via the antenna, the arrival direction from the target obtained by the radio wave arrival direction estimation method (for example, Beamformer method, Capon, MUSIC, ESPRIT, etc.) taking measurement. Then, the module correction amount calculation circuit 151 calculates a correction value for the amplitude / phase difference for the combined output of each submodule Li so that the difference between the measured arrival direction and the known target direction becomes zero. And stored in the memory 1512. By applying such a calibration method, it is possible to obtain a correction value of the phase error due to the airframe deformation of each submodule Li with respect to the beam directing direction from the memory 1512 during actual operation, and avoid performance degradation due to wavefront deviation. It becomes possible to do.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The perspective view which shows the antenna mounting image of the aircraft in which the radar apparatus based on this invention is mounted. The block diagram which shows the specific structure of the receiving submodule and the radar signal processing apparatus in the radar apparatus of FIG. The conceptual diagram for demonstrating the array antenna structure of the receiving submodule shown in FIG. The block diagram for demonstrating the control procedure of the beam directivity in a common array antenna. The figure which shows the beam pattern by Beamformer method in case there exists an angle difference (azimuth | direction error) in the peak angle of output electric power and the radiation angle of an electromagnetic wave in the array antenna shown in FIG. FIG. 2 is a block diagram showing a schematic system configuration for performing amplitude / phase correction in units of submodules according to the present invention in the radar apparatus shown in FIG. 1. 7 is a flowchart showing a specific processing procedure of radar signal processing in the configuration shown in FIG. 6.

Explanation of symbols

L1 to Ln: reception submodule, 111 to 11N ... antenna element, 121 to 12N ... microwave module, 13 ... power distribution / combination circuit, 14 ... scan controller, 141 ... module correction amount storage circuit, R ... radar signal processing 15: Radar signal processing unit, 151 ... Module correction amount calculation circuit, 1511 ... Arithmetic circuit, 1512 ... Memory, 1513 ... Correction amount reading circuit, 1514 ... Adder, 16 ... Excitation receiving unit, 161i ... Amplitude / phase control , A _{1 to} A _N ... Amplitude adjuster, δ _{1 to} δ _N ... Variable phase shifter, Σ.

Claims (4)

A plurality of sub-modules having an array antenna structure that is mounted in a distributed manner on the surface of the moving body, each having a microwave reception function and independently controlled to direct each other,
Scanning control means for controlling the beam scanning angle by controlling the phase of each antenna element in the plurality of sub-modules based on the indicated directivity direction;
Receiving beam forming means for combining the received signals obtained by the plurality of submodules to form a receiving beam;
Directivity control means for performing directivity control of the received beam in units of submodules for the plurality of submodules;
The directivity control unit corrects the phase amount for each of the plurality of submodules based on the reception signal of the reception beam formed by the reception beam forming unit, and adjusts the deviation of the wavefront accompanying the deformation of the mobile body. A radar device mounted on a moving body.   2. The directivity control unit includes a correction phase calculation circuit unit that calculates an azimuth correction value for each of the plurality of submodules and converts the azimuth correction value into a phase correction amount for each submodule. The mobile radar device according to the description.   The directivity control means further emits a pulse to a high SNR reference target arranged in a known azimuth, and based on the reflected wave, an arrival azimuth from the target obtained by a radio wave arrival direction estimation method An azimuth correction value is calculated for each submodule so that a known target azimuth difference is zero, and calibration is performed to convert this azimuth correction value into a phase correction amount for each submodule. The mobile unit-mounted radar device according to claim 2.   A plurality of sub-modules having an array antenna structure that are mounted in a distributed manner on the surface of the moving body, each having a microwave reception function and independently controlled in directivity, and the plurality of sub-modules based on the indicated directivity direction Scanning control means for controlling the beam scanning angle by controlling the phase of each antenna element in the sub-module, and reception beam forming means for combining the reception signals obtained by the plurality of sub-modules to form a reception beam; Directivity control means for performing directivity control of the received beam in units of submodules with respect to the plurality of submodules, wherein the directivity control means converts the received signal of the received beam formed by the received beam forming means. Based on the movement, the phase amount for each of the plurality of submodules is corrected to adjust the wavefront displacement accompanying the airframe deformation of the moving body. A pulse is radiated to the direction of a high SNR reference target placed in a known azimuth used in an on-board radar device, and the arrival azimuth from the target determined by the radio wave arrival direction estimation method based on the reflected wave is known. A mobile-mounted radar device characterized in that an azimuth correction value is calculated for each sub-module so that a difference in target azimuth of the sub-module becomes zero, and the azimuth correction value is converted into a phase correction amount in the sub-module. Calibration method.

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