High-precision radar antenna leveling error compensation method

Abstract

The present invention relates to the field of radar detection technology, and in particular to a high-precision radar antenna leveling error compensation method. The method does not modify the radar platform leveling device in any way, but only uses the high-precision dual-axis tilt sensor installed inside the antenna to measure the tilt angle of the azimuth axis. By using the principle of beam space pointing invariance, the roll tilt error γ and the pitch roll tilt error δ are used as the polar coordinate value of the target antenna array surface (R m , ε z , β z ) are used to infer the target's radar polar coordinates (R, ε, β) through coordinate conversion. The target's coordinates in the north-east celestial coordinates are measured by a high-precision double differential positioning device (with positioning accuracy higher than that of radar) and converted into the coordinates in the radar polar coordinates (R o , ε o , β o ), the difference between the two (ΔR, Δε, Δβ) is the leveling error that needs to be compensated in the end.

Description

Technical field:

[0001] The invention relates to the field of radar detection technology, and in particular to a high-precision radar antenna leveling error compensation method. Background technology:

[0002] Since the phased array radar adopts the electronic scanning method, its antenna beam can realize inertia-free rapid scanning, has strong anti-interference ability, and can perform multi-target tracking and detection. It is impossible for the phased array antenna to achieve 360° scanning of the entire airspace. It requires a combination of mechanical scanning and electronic scanning that cooperates with the pitch tracking system and the azimuth tracking system to achieve 360° beam coverage of the entire airspace. The antenna beam can achieve accurate detection and tracking of the detected target, all based on the condition that the radar platform is absolutely horizontal. In actual situations, there is a certain error between the radar platform and the horizontal plane. When the azimuth tracking system or the pitch tracking system is running, the azimuth and depression angles measured by its angle measuring sensor are not the true angles between the radar antenna and the true north or horizontal direction, resulting in a large error between the actual detected target coordinate information and the required accuracy of the index, which seriously affects the overall working indicators of the radar.

[0003] In order to solve the impact of radar azimuth axis tilt error on target detection accuracy, the radar industry at home and abroad usually adopts two methods: using radar platform leveling device and radar platform tilt error compensation.

[0004] The radar platform leveling device uses the inclination measured by the inclination sensor installed on the platform to adjust the height of the three or four supporting legs to achieve the horizontal requirement of the radar platform. However, the structure of the leveling device is relatively complex, especially the algorithm of the closed-loop control system for leveling error adjustment is relatively complex, which makes the radar erection and withdrawal process complicated and time-consuming. In particular, due to the influence of the error clearance fit of the various components of the transmission mechanism of the leveling device, this limitation makes it difficult to improve the leveling accuracy. At present, the highest accuracy that domestic leveling devices can achieve is only 3' (the patent of the "Radar Digital Platform Leveling Device and Leveling Method" of the 206th Institute of China Ordnance Industry, the leveling range is -30°~30°). The measurement error of some high-precision radars is even less than 1', and the platform tilt accuracy obviously cannot meet the requirements of these high-precision radars.

[0005] Radar platform tilt error compensation, this method does not rely on the leveling device, avoiding the limitations of the leveling device. A high-precision dual-axis tilt sensor is used to measure the tilt of the radar platform with high precision, and a mathematical method is used to compensate the azimuth axis tilt error to the positioning error of the measured target. Although the high-precision tilt sensor has high accuracy (second level), the measurement range is usually narrow (less than 10°). However, it cannot be used normally when the radar platform is severely tilted.

[0006] Both of the above methods have their obvious limitations and are obviously unable to meet the requirements of today's phased array radars for high positioning accuracy of the targets being measured. Summary of the invention:

[0007] In view of this, in order to reduce the influence of the radar platform tilt error on the positioning accuracy of the detected target and avoid the limitations of the radar platform leveling device and the tilt error compensation method, the present invention provides a high-precision radar antenna leveling error compensation method, which does not make any modification to the radar platform leveling device, but only uses the high-precision dual-axis tilt sensor installed inside the antenna itself to measure the tilt angle of the azimuth axis.

[0008] In order to solve the problems existing in the prior art, the technical solution adopted by the present invention is: a high-precision radar antenna leveling error compensation method, characterized in that the steps are:

[0009] 1): After the radar platform is leveled, the pitch angle of the antenna's pitch follower is set to 0, that is, ε T =0, and locked state;

[0010] 2) The azimuth follower starts with a constant step angle β Ti Rotate, rotate one circle back to the initial point, when the azimuth follower stops, the two-dimensional inclination sensor measures a set of i longitudinal roll inclination angles δ i and the roll angle γ i Sequence, through the formula Calculate the azimuth axis tilt value θ of this point;

[0011] 3) Using the azimuth axis tilt value obtained in step 2), the formula Calculate the absolute value of the pitch angle at this time, and use the relationship between the pitch angle and the azimuth angle δ i =f1(β Ti ), determine the positive and negative sign of the pitch angle at this time

[0012]

[0013] 4) Establish a radar north-east celestial coordinate system (X, Y, Z) with the radar azimuth rotation center projected on the geodetic plane as the origin, and then calculate the radar polar coordinates (R, ε, β) with the same origin;

[0014] 5) Establish a rectangular coordinate system (X′, Y′, Z′) with the antenna array as the center, and use it to calculate the polar coordinates (R m , ε z , β z )form;

[0015] 6) Convert the radar north-east coordinate system (X, Y, Z) to the antenna array rectangular coordinate system (X′, Y′, Z′) to obtain the radar polar coordinates (R, ε, β) and the array polar coordinates (R m , ε z , β z ) corresponding relationship;

[0016] 7) According to the conclusion of step 6), the measured coordinates of the known target in the polar coordinates of the array (R m , ε z , β z ), converted into its radar polar coordinate value (R, ε, β);

[0017] 8) Use a high-precision positioning device to measure the known target's geodetic north-east celestial coordinates (X o , Y o , Z o ), and converted into the coordinate value (R) in the radar polar coordinate according to the method in step 4). o , ε o , β o );

[0018] 9) Subtract the two types of radar polar coordinate values ​​obtained in step 7) and step 8), and the difference between the two (ΔR, Δε, Δβ) is the leveling error to be compensated in the end.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The present invention breaks away from the inherent ideas of previous leveling error compensation methods, and introduces the orthogonal relationship between the roll tilt angle and the pitch roll tilt angle based on geometric principles. The pitch roll tilt angle of the antenna at different pitch angles and azimuth angles is derived by mathematical methods using the roll tilt angle, breaking through the limitations of the use conditions of high-precision tilt sensors.

[0021] 2) The present invention is different from various previous leveling devices and compensation methods in that the inclination sensor used in the previous leveling devices or error compensation methods is not installed on the radar platform, and only the inclination of the radar platform itself is measured. However, due to the error transmission between various components, there is a large error between the measured inclination and the actual azimuth axis inclination. The inclination sensor installed inside the antenna measures the inclination of the radar platform, the installation errors between the radar platform, the azimuth follower and the pitch follower, the azimuth bearing clearance fit error, etc., and measures the actual inclination of the azimuth axis, thereby obtaining the actual leveling error compensation value.

[0022] 3) The present invention does not modify the leveling device of the original radar platform, and only uses the two-dimensional tilt sensor of the radar antenna to measure the inclination of the azimuth axis. The method is easy to implement, has high reliability and low cost, and improves the accuracy of the leveling device and the compensation method from graded to second level. Description of the drawings:

[0023] Figure 1 It is a schematic diagram of the composition and layout of the radar leveling system;

[0024] Figure 2 It is a schematic diagram of the decomposition of the azimuth axis tilt error into two orthogonal errors;

[0025] Figure 3 This is a schematic diagram of the relationship between the north-east celestial coordinate system and the polar coordinate system with the radar as the center;

[0026] Figure 4 It is a schematic diagram of the relationship between the polar coordinate system of the antenna array and the rectangular coordinate system of the antenna array.

[0027] Marking instructions: 1. Radar platform 2. Azimuth follower 3. Pitch follower 4. Radar antenna 5. Two-dimensional tilt sensor; 6. Azimuth axis 7. Geodetic plane 8. Roll error reference axis Y 9. Longitudinal roll error reference axis X. Specific implementation method:

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] The principle of the present invention is as follows: the azimuth axis tilt angle is measured by a two-dimensional tilt sensor installed inside the antenna, and is decomposed into a roll tilt angle γ and a longitudinal roll tilt angle δ which are orthogonal to each other according to the geometric relationship. When the radar is working normally, the antenna attitude is an azimuth angle β T , depression angle ε T The roll angle measured by the inclination sensor is γ i , knowing the previously measured azimuth axis tilt angle θ, deduce the current pitch tilt angle δ i. The premise that the roll tilt angle γ and the longitudinal roll tilt angle δ are orthogonal to each other is based on the situation that the antenna array is an ideal rigid body. If the antenna array is rotated in pitch, the antenna array will be greatly twisted and deformed. If the deformation exceeds the maximum accuracy of the tilt sensor, it is meaningless to deduce the longitudinal roll tilt angle δ through the roll tilt angle γ. Therefore, it is necessary to analyze the maximum deformation of the antenna array due to its own gravity; the maximum deformation caused by wind load when working under the maximum allowable wind level; the maximum deformation of the array due to temperature changes. The superposition of the antenna array deformation caused by these three main factors must be less than one order of magnitude of the highest measurement accuracy of the tilt sensor. The change in the azimuth axis tilt angle caused by the array deformation will not affect the final measurement result.

[0030] Based on the principle of beam spatial pointing invariance, the roll tilt angle γ and the longitudinal roll tilt angle δ are used as the polar coordinates of the target antenna array (R m , ε z , β z ) are used to infer the target's radar polar coordinates (R, ε, β) through coordinate conversion. The target's coordinates in the north-east celestial coordinates are measured by a high-precision double differential positioning device (with positioning accuracy higher than that of radar) and converted into the coordinates in the radar polar coordinates (R o , ε o , β o ), the difference between the two (ΔR, Δε, Δβ) is the leveling error that needs to be compensated in the end.

[0031] The present invention provides a high-precision radar antenna leveling error compensation method, which adopts a radar leveling system such as Figure 1 As shown, the radar platform 1 is provided with an azimuth follower 2, the azimuth follower 2 is provided with a pitch follower 3, a radar antenna 4 is provided on the pitch follower 3, and a dual-axis tilt sensor 5 is provided inside the radar antenna 4. The present invention realizes leveling error compensation only through the high-precision two-dimensional tilt sensor 5 inside the radar antenna 4. The specific steps are as follows:

[0032] Step 1: After the radar platform 1 is leveled and locked, calibration is required: the two test reference axes (roll tilt angle reference axis Y8 and longitudinal roll tilt angle reference axis X9) of the dual-axis tilt sensor 5 are calibrated with the center normal of the antenna array and the antenna cross-section, that is, the X-axis of the sensor is parallel to the center normal of the antenna array, and the Y-axis is parallel to the antenna cross-section.

[0033] Step 2: Calibrate the radar pitch tracking photoelectric encoder, that is, the elevation angle ε T = 0°, the center normal of the antenna array is parallel to the XOY plane 7 of the earth, and the radar azimuth follower photoelectric encoder is calibrated, that is, the azimuth angle β T When =0°, the center normal of the antenna array points to due north.

[0034] Step 3: Lock the antenna pitch follower 3 to keep the pitch angle at 0°, start driving the azimuth follower 2 to rotate from 0 with a step of 2π / N, stop for t seconds after reaching the predetermined test point, record the longitudinal roll tilt angle data and the transverse roll tilt angle data of the dual-axis sensor, and calculate the average of these two sets of data, recorded as δ j and γ j , and then start rotating at an angle of 2π / N, repeat the previous step until it rotates to 360°, and record N+1 sets of data; calculate the expected value of the azimuth axis inclination angle by the following formula:

[0035]

[0036] The azimuth axis tilt angle is a systematic error, which is the result of the transmission and superposition of the three errors of the radar platform tilt error, the installation error between the radar platform 1, the azimuth follower 2, and the pitch follower 3, and the azimuth rotation mechanism bearing clearance. When the azimuth follower is working, the azimuth follower motor will vibrate; the relationship between the tilt error and the azimuth angle is not a straight line, but a curve with irregular ups and downs with θ as the center.

[0037] Step 4: Since the reference axes of the dual-axis sensor (the roll tilt angle reference axis Y8 and the longitudinal roll tilt angle reference axis X9) are orthogonal, the measured longitudinal roll tilt angle δ and the roll tilt angle γ are also orthogonal, that is, the azimuth axis tilt angle θ can be decomposed into two orthogonal errors, namely, the longitudinal roll tilt angle δ in the direction of the array normal and the roll tilt angle γ of the array transverse symmetry axis (such as Figure 2 ). The pitch angle can be derived from the known roll angle γ:

[0038]

[0039] Step 5: Pitch and roll angle δ j The positive and negative signs are directly related to the azimuth angle. The theoretical relationship equation between the azimuth angle and the roll angle is fitted by N+1 sets of data. j =f(β Tj ).

[0040] Assume the roll angle relationship equation

[0041] δ=θcos(k·β T +β o ) Formula 2

[0042] Pitch-roll and tilt angle relationship equation

[0043] γ=θsin(k·β T +β o ) Formula 3

[0044] The above formula can be derived through univariate linear regression analysis, but due to the nonlinearity of trigonometric functions, linear transformation is required. Let y = arccos (γ / θ), x j =β Tj Then δ l =θcos(k·β Tj +β o ) can be converted to y = kx j +β o .(Where K is the azimuth correction coefficient, β o Error equation initial azimuth)

[0045] y j =arccos(δ j / θ) where j = 1.2.3…N+1

[0046] Estimation of K

[0047] β o Estimated value of

[0048] The ideal roll angle fitting formula is:

[0049]

[0050] The theoretical roll angle is derived as

[0051]

[0052] Note: sign is the function sign.

[0053] Step 6: According to the working principle of radar, radar is based on the distance R of the target. m , azimuth ε m and the pitch angle β m Detection to determine its spatial coordinates (such as Figure 3 ). The distance R m is the straight-line distance from the target to the center of the array, and the azimuth ε m It is the angle between the line connecting the target to the center of the array and the longitudinal symmetry plane of the antenna. m It is the angle between the straight line from the target to the center of the array and the transverse symmetry plane of the antenna, from which the polar coordinate position of the target on the antenna array can be determined (R m ,ε z ,β zThe characteristic of antenna array coordinates is that they are only the relative position relationship between the target and the antenna array, and have nothing to do with the position of the radar and the antenna attitude. A rectangular coordinate system is established with the center of the antenna array as the origin O. The X' axis is the normal direction of the antenna array (pointing to the detection airspace), the Y' axis is the horizontal symmetry axis of the antenna array (left is positive), and the Z' axis is the vertical symmetry axis of the antenna (up is positive). The coordinate value of the target in the antenna rectangular coordinate system is (x', y'z') and its antenna array polar coordinate (R m ,ε z ,β z )

[0054]

[0055] In actual work, the conversion relationship between the north-east coordinate system with the radar as the origin and the antenna rectangular coordinate system is the radar antenna depression angle ε T , azimuth β T , and the antenna azimuth axis tilt angle θ. T , azimuth β T When both are 0° and the azimuth axis tilt angle is ignored, the antenna rectangular coordinate system is simply the result of translating the coordinates of the north-east sky coordinate system with the radar as the origin in the Z-axis direction. T , azimuth β T The attitude is facing the target. Due to the existence of radar platform leveling error, assembly error of each part and bearing clearance matching error, the azimuth axis tilt angle θ is generated. During radar calibration, the coordinates (X, Y, Z) of the target in the north-east celestial coordinate system with the radar as the origin are known. Through the following conversion: the radar north-east celestial coordinate is translated by Δh (vertical distance from the center of the array to the ground) and rotated around the Z (Z1) axis by β T is the radar azimuth (measured by the azimuth photoelectric encoder). Rotation around the new Y1 axis is ε T The radar depression angle (measured by the pitch photoelectric encoder) and the antenna longitudinal roll tilt angle δ (calculated in the second step) are also formed by rotating around the new Y1 axis. The actual depression angle should be ε T +δ. Rotate around the new X1 axis to γ ​​radar pitch angle antenna longitudinal roll tilt angle. (e.g. Figure 4 ) through the following conversion:

[0056]

[0057] The roll tilt angle γ measured by the tilt sensor and the theoretical longitudinal roll tilt angle δ are obtained through equation 5, and the antenna pitch angle ε T and azimuth β TSubstituting the height Δh of the center of the array from the ground into formula 8, we can get the real coordinate value of the target in the rectangular coordinate system of the antenna array. Substituting the calculated result into formula 7, we can get the theoretical polar coordinate value of the array (R m ,ε z ,β z ).

[0058] The polar coordinates of the target are known (R m ,ε z ,β z ) Through equation 6, the rectangular coordinates of the target antenna array surface (x′, y′, z′) can be obtained. Perform the inverse process of the above conversion:

[0059]

[0060] The roll tilt angle γ measured by the tilt sensor is combined with the theoretical longitudinal roll tilt angle δ obtained by equation 5, and the antenna pitch value ε T and the orientation value β T Substituting the height Δh from the center of the array to the ground into formula 9, the real coordinates (X, Y, Z) of the target in the radar's north-east coordinate system can be obtained.

[0061] Step 6: Usually, the display result of radar detection target is polar coordinates (R, ε, β) with the projection point of the center of the radar antenna array on the XOY plane of the earth's north-east celestial coordinate as the origin. Among them, R is the straight-line distance between the measured target and the projection point of the array center on the earth's XOY plane; the depression angle ε is the angle between the line between the target and the polar coordinate origin and the earth (if ε = 0, the target and the radar polar coordinate origin are at the same altitude); the azimuth angle β is the angle between the projection line of the line between the target and the polar coordinate origin on the ground and the true north direction (if β = 0, the target is in the north direction of the radar). With the projection point of the center of the radar antenna array on the XOY plane of the earth's north-east celestial coordinate as the origin, the relationship between the radar polar coordinates and the radar north-east celestial coordinates (the two have the same origin) is:

[0062]

[0063] also,

[0064]

[0065] Substituting the result of formula 9 into formula 10, the coordinates of the target measured in the radar polar coordinates (R, ε, β) can be obtained. The high-precision double differential positioning device can obtain the real coordinates of the target in the north-east coordinate system with the radar as the origin (Xo, Yo, Zo). Similarly, formula 10 can be used to obtain the real target coordinates in the polar coordinate system with the radar as the origin (R o ,ε o ,β o). Subtract the true value from the measured value: ΔR = Ro - R, Δε = ε o -ε,

[0066] Δβ=β o -β, and obtain the radar antenna leveling error compensation value (ΔR, Δε, Δβ).

[0067] The present invention does not make any structural changes to the radar platform leveling device, and only uses the high-precision dual-axis tilt sensor installed inside the antenna to measure the tilt angle of the azimuth axis. It avoids the new device error transmission caused by the bulky inertial navigation device installed outside the antenna in other existing technologies. The inertial navigation device can measure the absolute value angle of the three-axis tilt attitude of the object, but due to the low accuracy (in graded), the response time is relatively long. For the antenna array, the present invention only considers the longitudinal roll tilt angle and the transverse roll tilt angle. The longitudinal roll tilt angle is derived by mathematical methods using the rigid body characteristics of the antenna and the orthogonal relationship of the error. The addition of the longitudinal roll tilt angle and the relative pitch rotation angle measured by the high-precision pitch follow-up photoelectric encoder is the true angle between the center normal of the antenna array and the ground plane, so that the original leveling device or inertial navigation device can maintain the accuracy error level from graded to second level.

[0068] The content of the present invention is not limited to the embodiments listed, and any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the description of the present invention are covered by the claims of the present invention.

Claims

1. A high-precision radar antenna leveling error compensation method, characterized in that: The steps are: 1): After the radar platform (1) is leveled, the pitch angle of the antenna's pitch follower (3) is set to 0, i.e., ε T =0, and locked state; 2) The azimuth follower (2) starts to move at a constant step angle β Ti When the azimuth follower (2) stops, the two-dimensional inclination sensor (5) measures a set of i longitudinal roll inclination angles δ i and the roll angle γ i Sequence, through the formula Find the tilt value θ of the azimuth axis (6) at this point; 3) Using the azimuth axis tilt value obtained in step 2), the formula Calculate the absolute value of the pitch angle at this time, and use the relationship between the pitch angle and the azimuth angle δ i =f1(β Ti ), determine the positive and negative sign of the pitch angle at this time 4) Establish a radar north-east celestial coordinate system (X, Y, Z) with the radar azimuth rotation center projected on the geodetic plane as the origin, and then calculate the radar polar coordinates (R, ε, β) with the same origin; 5) Establish a rectangular coordinate system (X′, Y′, Z′) with the antenna array as the center, and use it to calculate the polar coordinates (R m , ε z , β z )form; 6) Convert the radar north-east coordinate system (X, Y, Z) to the antenna array rectangular coordinate system (X′, Y′, Z′) to obtain the radar polar coordinates (R, ε, β) and the array polar coordinates (R m , ε z , β z ) corresponding relationship; 7) According to the conclusion of step 6), the measured coordinates of the known target in the polar coordinates of the array (R m , ε z , β z ), converted into its radar polar coordinate value (R, ε, β); 8) Use a high-precision positioning device to measure the known target's geodetic north-east celestial coordinates (X o , Y o , Z o ), and converted into the coordinate value (R) in the radar polar coordinate according to the method in step 4). o , ε o , β o ); 9) Subtract the two types of radar polar coordinate values ​​obtained in step 7) and step 8), and the difference between the two (ΔR, Δε, Δβ) is the leveling error to be compensated in the end.

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