Antenna phase center calibration method based on spherical near-field measurement

Abstract

The invention discloses an antenna phase center calibration method based on spherical near-field measurement, and belongs to the field of antenna measurement. According to the method, phase pattern measurement and phase center calculation capabilities of a multi-probe spherical near field are utilized to test the azimuth rotation capability of the rotary table and the design height value from the table top of the rotary table to the center of the field; the method comprises the following steps: respectively measuring discrete position points of a fixed point on an arc movement track and a linear movement track under a site coordinate system, fitting circles and straight lines from the discrete position points according to the movement tracks, respectively determining a Z axis and an X axis of a measured site, and further obtaining a multi-probe spherical near-field site coordinate system. And determining the phase center of the to-be-tested antenna in the field coordinate system according to the phase pattern of the to-be-tested antenna, thereby calibrating the relative position relationship between the phase center of the to-be-tested antenna and the reference point, namely obtaining the offset of the phase center of the to-be-tested antenna.

Description

Technical Field

[0001] The invention relates to an antenna phase center calibration method based on spherical near-field measurement, and belongs to the field of antenna measurement. Background Art

[0002] Carrier phase measurement has important applications in the precise positioning of satellite navigation systems. In radio systems that use carrier phase as an observation, the measured pseudorange and carrier phase values ​​are the distances between the phase center of the receiver antenna and the phase center of the satellite transmitting antenna. Usually, there is a certain deviation between the phase center of the antenna and its geometric center. The impact of this deviation on the relative positioning result can reach more than ten millimeters or even several centimeters depending on the stability of the antenna phase center. For measurements with high accuracy requirements, its impact cannot be ignored. Therefore, the antenna phase center is an extremely important parameter in navigation and positioning applications, which directly affects the accuracy of the navigation and positioning measurement system. Usually, the reference point that makes the phase distribution of the radiation field the flattest within the main lobe of the antenna is defined as the apparent phase center. From the definition, it can be seen that the apparent phase center is the phase center in the sense of least squares, which measures the phase distribution within the range of interest. Since the antenna phase center depends on the phase distribution within the range of interest, antenna phase measurement is the key link in determining the phase center of the antenna to be measured.

[0003] The traditional measurement of the antenna phase center is carried out in the far field using a far-field darkroom. With the development of testing technology, near-field measurement technology is increasingly being used. This technology can achieve high-precision measurements in a microwave darkroom, eliminating the difficulty of building a large darkroom. Spherical near-field measurement is an important branch of the near-field measurement field and is widely used in measuring antenna amplitude and phase. The first developed technology is the single-probe spherical near-field measurement technology. In order to solve the problem of low efficiency of single-probe measurement, a multi-probe spherical near-field measurement system has emerged and is widely used. The multi-probe spherical near-field measurement system is characterized by converting the two-dimensional mechanical scanning in the spherical near-field measurement into one-dimensional electrical scanning and one-dimensional mechanical scanning. By arranging low-scattering scanning probes at equal intervals on a circular scanning frame, the electronic scanning is realized by using a multiplexed network system and sequential electronic modulation technology, which greatly improves the measurement speed. The multi-probe spherical near-field can easily measure the far-field pattern information of the main radiation direction of the antenna to be tested, including the far-field phase information. By utilizing the spherical near-field antenna phase pattern measurement capability and mathematical calculations, the position of the antenna phase center in the site coordinate system can be directly obtained. However, what is actually needed in engineering applications is the position of the antenna phase center relative to the antenna reference point, that is, the phase center offset.

[0004] In recent years, many sets of multi-probe spherical near-field measurement systems have been established in China. The multi-probe spherical near-field test system generally includes a circular scanning frame and a test turntable. The circular scanning frame is built on the turntable. The probes are evenly spaced on the scanning ring and aligned with the center of the site. The site coordinate system is based on the turntable. The scanning ring surface and the rotation axis of the turntable are theoretically in the same plane. These can be used as conditions for restoring the site coordinate system. Using this system for phase center calibration has the advantages of high measurement accuracy, low test cost and wide-range promotion. The currently built multi-probe spherical near-field measurement system usually does not give an accurate site coordinate system, making it difficult to directly calibrate the antenna phase center. The phase data of the antenna to be tested measured by the multi-probe spherical near-field measurement system is based on the site coordinate system, and the phase center calculated using the phase pattern is also the result of the site coordinate system. To obtain the phase center offset required for engineering applications, it is necessary to convert the phase center in the site coordinate system to the antenna body coordinate system. The premise of the coordinate system conversion is to obtain the test field coordinate system first. Whether the site coordinate system of the multi-probe spherical near field can be accurately restored has become an important factor affecting whether the system can be used to accurately calibrate the antenna phase center. Summary of the invention

[0005] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and propose an antenna phase center calibration method based on spherical near-field measurement, to restore the spherical near-field coordinate system through spatial point coordinate measurement and data processing, and then to calibrate the phase center offset of the antenna to be measured by using the spherical near-field measurement of the antenna phase direction and the antenna position measurement.

[0006] The technical solution of the present invention is:

[0007] A method for calibrating an antenna phase center based on spherical near-field measurement, comprising:

[0008] Rotate any fixed point on the observation turntable around the turntable to obtain the arc trajectory of the fixed point, and calculate the normal line through the center of the arc. The normal line is the rotation axis of the observation turntable and also the Z axis of the site coordinate system;

[0009] An auxiliary circularly polarized antenna is set up on the observation turntable, and the auxiliary circularly polarized antenna is moved to multiple positions along a horizontal straight line in the site, and the phase center of the auxiliary circularly polarized antenna in the site coordinate system at each position is measured and calculated, and a straight line is fitted according to the phase center, and the angle between the straight line and the X-axis of the site coordinate system is calculated; the coordinates of any fixed point on the auxiliary circularly polarized antenna are measured when it is moved to different positions, and a straight line is fitted again; according to the parallelism of the two straight lines, the angle between the straight line fitted by the fixed point and the X-axis of the site coordinate system is obtained, and then the X-axis direction of the site coordinate system is found;

[0010] Calculate the position of the origin of the site coordinate system on the Z axis, project the X axis of the site coordinate system toward the Z axis, and intersect the Z axis through the origin of the coordinate system. Then fine-tune the Z and X axis directions through coordinate axis fitting to make the two axes strictly perpendicular. Obtain the corrected Z and X axes of the site coordinate system, and then determine the Y axis of the site coordinate system according to the right-hand rule.

[0011] Remove the auxiliary circularly polarized antenna, set up the antenna to be tested on the observation turntable, obtain the far-field phase pattern of the antenna to be tested, and calculate the phase center coordinates of the test frequency point of the antenna to be tested in the corrected site coordinate system;

[0012] Measure the position of the reference target sphere on the antenna to be tested in the corrected site coordinate system, and then combine it with the phase center coordinates to calculate the position of the phase center of the antenna to be tested relative to the reference target sphere, which is the phase center offset.

[0013] Furthermore, any fixed point on the observation turntable is rotated around the turntable to obtain the arc trajectory of the fixed point movement, and the normal line passing through the center of the arc is calculated. The specific method is:

[0014] Set up the laser tracker, fix the target ball on the target ball base, then fix the target ball base on the extension arm and install it on the top of the observation turntable calibration tooling;

[0015] The observation turntable is rotated to different angles, the position of the target ball at different angles is measured, and the circle formed by the target ball at each position is fitted. The straight line passing through the center of the circle and perpendicular to the circular surface is the normal line.

[0016] Furthermore, the observation turntable is rotated to different angles to measure the position of the target ball at different angles, and the circle formed by the target ball at each position is fitted. The fitting method is:

[0017] Assume the radius of the circle is R, and the circle equation is expressed as:

[0018] R 2 =(xA) 2 +(yB) 2

[0019] Further simplified to:

[0020] x 2 +y 2 +ax+by+c=0

[0021] The target ball position (X i ,Y i ) to the center of the fitting circle i The difference between the square of and the square of the radius is:

[0022] δ i =d i 2 -R2 =(X i -A) 2 +(Y i -B) 2 -R 2 =X i 2 +Y i 2 +aX i +bY i +c

[0023] Make δ i Minimum, solve the partial differential equation to calculate the coefficients a, b and c.

[0024] Furthermore, the phase center of the auxiliary circularly polarized antenna in the site coordinate system at each position is calculated using the following calculation method:

[0025] Assume that the vector r′ from the origin of the site coordinate system to the phase center is:

[0026]

[0027] Among them, (Δx, Δy, Δz) are the phase center coordinates of the auxiliary circularly polarized antenna in the site coordinate system, is the unit vector on the X, Y, and Z axes;

[0028] A certain direction in the distance in the site coordinate system The unit vector of the observation point P on is expressed as:

[0029]

[0030] Then the phase of the distant observation point P when the phase center is taken as the reference point is expressed as:

[0031]

[0032] in, is the space angle The phase value measured on the , k is the transmission coefficient; let:

[0033]

[0034] Among them, ψ 0 is the average equiphase surface, so When it is minimum, the phase center (Δx, Δy, Δz) of the auxiliary circularly polarized antenna in the site coordinate system is solved.

[0035] Furthermore, a rectangular tooling is used, on which no less than four antenna mounting holes arranged in a straight line are designed, and the rectangular tooling is set up on an observation turntable with the upper surface kept horizontal; the auxiliary circularly polarized antenna is fixed in different antenna mounting holes of the rectangular tooling to enable the auxiliary circularly polarized antenna to move along a horizontal straight line in the site.

[0036] Furthermore, the position of the origin of the field coordinate system on the Z axis is calculated. The calculation method is as follows: a calibration fixture is installed on the observation turntable mounting table, an extension arm is set up on the calibration fixture, and a target ball is fixed at the end of the extension arm; the position of the target ball is measured by a laser tracker, and then the target ball base height h, the calibration fixture length d are used to calculate the position of the target ball. 2 , the distance d between the test turntable surface and the origin of the site coordinate system 1 , calculate the distance between the target ball 7 and the origin of the coordinate system in the direction of the turntable rotation axis as d 1 -d 2 +h; Based on the known length of the observation turntable surface from the origin of the site coordinate system, the position of the coordinate origin on the Z axis is calculated.

[0037] Furthermore, a measuring fixture is used and installed on an observation turntable, and the antenna to be tested is connected to the testing fixture; a test cable is connected, and the test system is started to complete near-field data acquisition, and the far-field radiation pattern of the antenna to be tested is obtained through near-field to far-field transformation.

[0038] Furthermore, the test system includes a scanning ring and measuring probes. The measuring probes are evenly spaced on the scanning ring. The multiple probes obtain pitch data and observe turntable rotation data based on electrical scanning sampling, thereby realizing near-field data sampling in the entire space.

[0039] Furthermore, the test fixture is a columnar structure with flanges at both ends, and the two ends are respectively connected to the test turntable and the antenna to be tested, and the height is sufficient to set the antenna to be tested to the center of the scanning ring.

[0040] The advantages of the present invention compared with the prior art are:

[0041] (1) The present invention realizes the recovery of the site coordinate system and the calibration of the antenna phase center based on the existing turntable and measurement system of the multi-probe spherical near field.

[0042] (2) The present invention utilizes an accurate large-scale coordinate measuring instrument (such as the laser tracker in the embodiment) to measure the discrete position points of a fixed point under different moving trajectories in the field, and the position point measurement accuracy is high.

[0043] (3) The present invention utilizes rigorous mathematical processing methods to perform data fitting on phase measurement data and fixed point discrete position points, etc., to accurately obtain the required sphere, circle or straight line for calculating the phase center or analyzing the field coordinate axis.

[0044] (4) The present invention combines the spatial point measurement results of the coordinate measuring instrument with the existing conditions of the multi-probe spherical near-field site, and uses mathematical processing methods such as data fitting to accurately obtain the site coordinate system.

[0045] (5) After obtaining the multi-probe spherical near-field site coordinate system, the present invention utilizes the phase pattern measurement and phase center calculation capabilities of the measurement system and uses a high-precision large-size coordinate measuring instrument to obtain the phase center offset of the antenna to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0047] Figure 1 It is a schematic diagram of the multi-probe spherical near-field test system and the site coordinate system;

[0048] Figure 2 This is a schematic diagram of a laser tracker according to an embodiment of the present invention measuring the position of a target ball rotating around a turntable;

[0049] Figure 3 A schematic diagram of a laser tracker according to an embodiment of the present invention measuring the movement of a fixed point of an antenna along a straight line on a horizontally placed tooling;

[0050] Figure 4 This is a schematic diagram of measuring the position of a reference target sphere on an antenna to be measured in a site coordinate system using a laser tracker according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0052] The typical architecture and coordinate system definition of the scanning ring of a multi-probe spherical near-field test system are as follows: Figure 1 As shown, the measuring probes 2 are evenly spaced on the scanning ring 1, and the distance d between the surface of the test turntable 3 and the origin of the coordinate system is 1 And calibration tool 4 length d 2Known. The calibration tooling is a tooling that comes with the site, and is generally only used for site calibration. The tooling structure has high stability. When conducting an antenna radiation pattern test, it is first necessary to collect near-field data of the antenna 12 to be tested mounted on the test turntable 3, and then measure the antenna's far-field radiation pattern through a near-field to far-field transformation algorithm. The measurement system uses multiple probes 2 to implement electronic scanning sampling in pitch (θ), and combines the rotation of the turntable 3 in azimuth (φ) to achieve near-field data sampling in the entire space. The site's scanning system is established based on the turntable 3. According to the definition of the site coordinate system, the turntable's rotation axis is the Z axis of the site coordinate system (positive direction upward), the X axis is perpendicular to the Z axis in the annular surface where the probe is located, and the Y axis is perpendicular to the annular surface where the scanning ring probe is located. The distance between the coordinate origin and the test turntable surface and the height of the calibration tooling itself are known.

[0053] Aiming at the problem that the multi-probe spherical near-field site coordinate system is difficult to recover and its accuracy will directly affect the accuracy of antenna phase center calibration, the present invention proposes an antenna phase center calibration method based on spherical near-field measurement to realize the calibration of the phase center offset of the antenna to be measured.

[0054] The calibration method specifically includes the following steps:

[0055] Step 1: Determine the Z axis of the field coordinate system. According to the definition of the spherical near-field field coordinate system, the Z axis of the field coordinate system is the rotation axis of turntable 3. Observe the arc trajectory formed when a fixed point on turntable 3 rotates around the turntable, and then calculate the normal line passing through the center of the arc. According to this method, the rotation axis of the turntable can be determined, that is, the Z axis of the field coordinate system can be obtained.

[0056] S1.1: Set up the laser tracker 5 at a suitable position in the test site to ensure that the target ball 7 installed on the top of the calibration tool can be observed. Figure 2 As shown, the target ball 7 is fixed on the target ball base 8 (the height h of the target ball center point from the bottom of the target ball base is known), and then fixed on an extension arm 6 with a length of about 0.5m and installed on the top of the turntable calibration tooling 4.

[0057] S1.2: Establish the laser tracker 5's own coordinate system and measure the coordinates of the current position of the target ball 7, rotate the test turntable 3 to different angles, and measure the position coordinates of the target ball 7 at different rotation angles.

[0058] S1.3: Use the least squares method to perform circle fitting on the position of the target sphere 7 measured in the second step, find the center point of the fitting circle, and the straight line passing through the center point and perpendicular to the fitting circle is the rotation axis of the test turntable 3, that is, the Z axis of the multi-probe spherical near-field site coordinate system.

[0059] When performing circle fitting, let the circle radius be R, and the circle equation can be expressed as:

[0060] R2 =(xA) 2 +(yB) 2 (1)

[0061] Formula (1) can be further simplified as:

[0062] x 2 +y 2 +ax+by+c=0 (2)

[0063] Sample point (X i ,Y i ) to the center of the fitting circle i The difference between the square of and the square of the radius is:

[0064] δ i =d i 2 -R 2 =(X i -A) 2 +(Y i -B) 2 -R 2 =X i 2 +Y i 2 +aX i +bY i +c (3)

[0065] Make δ i Minimum, solving the partial differential equation can calculate the coefficients a, b and c.

[0066] Step 2: Determine the X-axis direction of the site coordinate system. With the help of the measuring tool, move the antenna to multiple positions along a horizontal straight line in the site, measure and calculate the phase center of the antenna in the site coordinate system at each position, fit a straight line based on the phase center, and calculate the angle between the straight line and the X-axis; measure the coordinates of a fixed point on the antenna when it moves to different positions, and then fit a straight line. Since the two straight lines are theoretically parallel, the angle between the straight line fitted by the fixed point and the X-axis of the site coordinate system can be obtained, and then the X-axis direction of the site coordinate system can be obtained.

[0067] In this embodiment, a rectangular fixture 9 is used to set up an auxiliary circular polarization antenna 10 at a suitable height. The laser tracker 5 is used to measure the coordinates of the antenna target sphere 11 fixed to the antenna base, and then the test system is used to obtain the far-field phase pattern of the antenna and calculate the phase center. The antenna is moved along a straight line in a nearly horizontal direction on the rectangular fixture 9 to different positions and the same measurement is performed. The moving trajectory of the antenna target sphere 11 can fit a straight line L 1 , the antenna phase center can be fitted with a straight line L 2, and obtain its relationship with the X axis of the site coordinate system. Ignore the phase center error obtained when the antenna is installed in different hole positions, the relative position of its phase center and the antenna target ball 11 should remain unchanged and L 1 and L 2 should be parallel, and using this relationship we can get L 1 The relationship with the X-axis of the site coordinate system is used to find the direction of the X-axis.

[0068] S2.1: Design at least 4 antenna mounting holes arranged in a straight line on the rectangular fixture 9. Set up the fixture on the adapter column of the test turntable 3, keeping the upper surface horizontal. The setting state is as follows: Figure 3 Select an auxiliary circular polarization antenna 10, fix the antenna at position 1 of the rectangular fixture 9, and then fix the antenna target sphere 11 at a position suitable for ground observation on the side of the antenna base.

[0069] S2.2: Use the laser tracker 5 to measure the antenna target sphere 11 fixed on the side of the antenna to be tested to obtain its coordinates, use the test system to measure the far-field phase pattern of the antenna to be tested, and then move the antenna along the test fixture to the remaining positions and repeat this coordinate measurement process.

[0070] S2.3: Using the least squares-based antenna phase center calculation method, the phase center of each frequency point in the site coordinate system at different installation positions of the antenna is calculated for the phase pattern radiated within the range of ±60 degrees in the maximum radiation direction.

[0071] The phase center calculation method based on least squares is briefly described as follows:

[0072] When calculating the phase center based on least squares, the vector from the origin of the site coordinate system to the phase center is assumed to be:

[0073]

[0074] The unit vector of the distant observation point P in the site coordinate system is expressed as:

[0075]

[0076] Then the phase of the distant observation point P when the phase center is used as the reference point can be expressed as:

[0077]

[0078] in, is the space angle The phase value measured on , k is the transmission coefficient. Let

[0079]

[0080] Among them, ψ 0is the average equiphase surface, so When it is minimum, the phase center (Δx, Δy, Δz) of the antenna to be tested in the site coordinate system can be solved.

[0081] S2.4: Using the coordinate points of the antenna target sphere 11 measured in S2.2, the straight line L is obtained by fitting the one-dimensional data 1 The phase center calculated by S2.3 is used to fit the straight line L 2 , and get L 2 The angle with the X axis of the site coordinate system. 1 and L 2 Parallel, get L 1 The angle between the X axis and the site coordinate system is used to obtain the X axis direction of the site coordinate system.

[0082] Step 3: Determine the origin of the site coordinate system. The origin of the site coordinate system should be located on the Z axis determined in step 1. Using the condition that the distance between the origin of the site coordinate system and the installation surface of the test turntable 3 is known (given during site construction), the origin of the coordinate system can be determined on the Z axis. Combined with the Z and X axis directions obtained in steps 1 and 2, the site coordinate system can be finally determined using the right-hand rule.

[0083] S3.1: Install the calibration fixture 4 on the mounting table of the test turntable 3, set up an extension arm 6 on the calibration fixture 4, fix a target ball 7 at the end of the extension arm, and use the laser tracker 5 to measure the position of the target ball 7. Then, according to the height h of the base 8 of the target ball 7 and the length d of the calibration fixture 4, the position of the target ball 7 is measured. 2 And the distance d between the test turntable 3 and the origin of the site coordinate system 1 , the distance between the target ball 7 and the origin of the coordinate system in the direction of the turntable rotation axis can be calculated as d 1 -d 2 +h. Further, the position of the coordinate origin on the turntable rotation axis (Z axis) can be calculated.

[0084] S3.2: Project the X-axis direction obtained in step 2 toward the Z-axis of the coordinate system obtained in step 1, and intersect the Z-axis through the coordinate origin. Then fine-tune the Z-axis and X-axis directions through coordinate axis fitting to make them strictly perpendicular, determine the Z-axis and X-axis of the site coordinate system, and then determine the Y-axis of the coordinate system according to the right-hand determination.

[0085] S3.3: The antenna 12 to be tested is measured using a multi-probe spherical near-field measurement system to obtain its far-field phase pattern, and then the phase center calculation method based on least squares is used to calculate the phase center of the antenna 12 to be tested in the site coordinate system.

[0086] Step 4: Use a multi-probe spherical near-field measurement system to measure the antenna 12 to be tested, use the software provided by the measurement system to calculate the far-field phase pattern, and then use the least squares-based phase center calculation method to calculate the phase center coordinates of the antenna 12 to be tested in the site coordinate system.

[0087] S4.1: The test fixture 13 is installed on the test turntable of the multi-probe spherical near field, and then the antenna to be tested 12 is connected to the test fixture 13, such as Figure 4 As shown, it is located close to the center of the scanning ring 1. The test fixture 13 is a columnar structure with flanges at both ends, and the two ends are respectively connected to the test turntable 3 and the antenna to be tested 12. The height is sufficient to set the antenna to be tested 12 to the center of the scanning ring 1. Connect the test cable, start the test system to complete the near-field data acquisition, and then use the system's own near-field to far-field transformation software to obtain the far-field radiation pattern of the antenna to be tested.

[0088] S4.2: Using the antenna phase center calculation method based on least squares, the phase center coordinates of the test frequency of the antenna to be tested in the site coordinate system can be calculated based on the far-field phase pattern data measured in the previous step.

[0089] Step 5: Use large-scale coordinate high-precision measurement methods to measure the position of the reference point on the antenna to be tested 12 in the site coordinate system. Combined with the coordinates of the phase center in the site coordinate system obtained in step 4, the position of the phase center of the antenna to be tested relative to the reference point on the antenna to be tested can be calculated.

[0090] S5.1: A laser tracker 5 is set up in the field, and the position of the reference target sphere 14 on the antenna to be tested in the field coordinate system can be measured using the field coordinate system obtained in step 3.

[0091] S5.2: Combining the position of the phase center of the antenna to be tested in the site coordinate system obtained in step 4 and the position of the reference target sphere 14 on the antenna in the site coordinate system, the position of the phase center of the antenna to be tested relative to the reference target sphere, that is, the phase center offset, can be obtained through coordinate transformation.

[0092] The present invention proposes a method for calibrating a multi-probe spherical near-field site coordinate system. The phase pattern measurement and phase center calculation capabilities of the multi-probe spherical near-field are used to test the azimuth rotation capability of the turntable and the design height value of the turntable table from the site center. With the auxiliary measurement of a high-precision large-size coordinate measuring instrument, discrete position points on the circular arc movement trajectory and the straight line movement trajectory of the fixed point in the site coordinate system are measured respectively. Then, circles and straight lines are fitted to the discrete position points according to the movement trajectory. The Z axis and X axis of the measured site can be determined respectively, and then the multi-probe spherical near-field site coordinate system can be obtained.

[0093] The present invention proposes a method for calibrating the phase center offset of an antenna to be tested. The method utilizes the phase pattern measurement capability of a multi-probe spherical near field and a method for determining a multi-probe spherical near field site coordinate system, and with the help of a high-precision large-size coordinate measuring instrument, measures the position of a reference point on the antenna to be tested in the site coordinate system. Then, a phase center calculation method based on least squares is used to determine the phase center of the antenna to be tested in the site coordinate system based on the phase pattern of the antenna to be tested, thereby calibrating the relative position relationship between the phase center of the antenna to be tested and the reference point, that is, obtaining the phase center offset of the antenna to be tested.

[0094] The above-described embodiments are only preferred specific implementations of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calibrating the antenna phase center based on spherical near-field measurement, characterized in that: include: Rotate any fixed point on the observation turntable around the turntable to obtain the arc trajectory of the fixed point, and calculate the normal line through the center of the arc. The normal line is the rotation axis of the observation turntable and also the Z axis of the site coordinate system; An auxiliary circularly polarized antenna is set up on the observation turntable, and the auxiliary circularly polarized antenna is moved to multiple positions along a horizontal straight line in the site, and the phase center of the auxiliary circularly polarized antenna in the site coordinate system at each position is measured and calculated, and a straight line is fitted according to the phase center, and the angle between the straight line and the X-axis of the site coordinate system is calculated; the coordinates of any fixed point on the auxiliary circularly polarized antenna are measured when it is moved to different positions, and a straight line is fitted again; according to the parallelism of the two straight lines, the angle between the straight line fitted by the fixed point and the X-axis of the site coordinate system is obtained, and then the X-axis direction of the site coordinate system is found; Calculate the position of the origin of the site coordinate system on the Z axis, project the X axis of the site coordinate system toward the Z axis, and intersect the Z axis through the origin of the coordinate system. Then fine-tune the Z and X axis directions through coordinate axis fitting to make the two axes strictly perpendicular. Obtain the corrected Z and X axes of the site coordinate system, and then determine the Y axis of the site coordinate system according to the right-hand rule. Remove the auxiliary circularly polarized antenna, set up the antenna to be tested on the observation turntable, obtain the far-field phase pattern of the antenna to be tested, and calculate the phase center coordinates of the test frequency point of the antenna to be tested in the corrected site coordinate system; Measure the position of the reference target sphere on the antenna to be tested in the corrected site coordinate system, and then combine it with the phase center coordinates to calculate the position of the phase center of the antenna to be tested relative to the reference target sphere, which is the phase center offset.

2. The antenna phase center calibration method based on spherical near field measurement according to claim 1 is characterized in that: Rotate any fixed point on the observation turntable around the turntable to obtain the arc trajectory of the fixed point movement, and calculate the normal line through the center of the arc. The specific method is: Set up the laser tracker, fix the target ball on the target ball base, then fix the target ball base on the extension arm and install it on the top of the observation turntable calibration tooling; The observation turntable is rotated to different angles, the position of the target ball at different angles is measured, and the circle formed by the target ball at each position is fitted. The straight line passing through the center of the circle and perpendicular to the circular surface is the normal line.

3. The antenna phase center calibration method based on spherical near field measurement according to claim 2 is characterized in that: Rotate the observation turntable to different angles, measure the position of the target ball at different angles, and fit the circle formed by the target ball at each position. The fitting method is: Assume the radius of the circle is R, and the circle equation is expressed as: R 2 =(x-A) 2 +(y-B) 2 Further simplified to: x 2 +y 2 +ax+by+c=0 The target ball position (X i ,Y i ) to the center of the fitting circle i The difference between the square of and the square of the radius is: δ i =d i 2 -R 2 =(X i -A) 2 +(Y i -B) 2 -R 2 =X i 2 +Y i 2 +aX i +bY i +c Make δ i Minimum, solve the partial differential equation to calculate the coefficients a, b and c.

4. The antenna phase center calibration method based on spherical near field measurement according to claim 1 is characterized in that: Calculate the phase center of the auxiliary circularly polarized antenna in the site coordinate system at each position. The calculation method is: Assume that the vector r′ from the origin of the site coordinate system to the phase center is: Among them, (Δx, Δy, Δz) are the phase center coordinates of the auxiliary circularly polarized antenna in the site coordinate system, is the unit vector on the X, Y, and Z axes; A certain direction in the distance in the site coordinate system The unit vector of the observation point P on is expressed as: Then the phase of the distant observation point P when the phase center is taken as the reference point is expressed as: in, is the space angle The phase value measured on the , k is the transmission coefficient; let: Among them, ψ0 is the average isophase surface, so that δ ij 2 When it is minimum, the phase center (Δx, Δy, Δz) of the auxiliary circularly polarized antenna in the site coordinate system is solved.

5. The antenna phase center calibration method based on spherical near field measurement according to claim 1 or 4, characterized in that: A rectangular tooling is used with no less than four antenna mounting holes arranged in a straight line designed on the rectangular tooling. The rectangular tooling is set up on the observation turntable with the upper surface kept horizontal. The auxiliary circularly polarized antenna is fixed in different antenna mounting holes of the rectangular tooling to realize the movement of the auxiliary circularly polarized antenna along a horizontal straight line in the site.

6. The method for calibrating the antenna phase center based on spherical near-field measurement according to claim 1, characterized in that: Calculate the position of the origin of the site coordinate system on the Z axis. The calculation method is as follows: install a calibration fixture on the observation turntable installation table, set up an extension arm on the calibration fixture, and fix a target ball at the end of the extension arm; use a laser tracker to measure the position of the target ball, and then calculate the distance between the target ball 7 and the origin of the coordinate system in the direction of the turntable rotation axis as d1-d2+h based on the target ball base height h, the calibration fixture length d2, and the distance d1 between the test turntable table and the origin of the site coordinate system; based on the known length of the observation turntable table from the origin of the site coordinate system, calculate the position of the coordinate origin on the Z axis.

7. The antenna phase center calibration method based on spherical near field measurement according to claim 1 is characterized in that: Use a measuring fixture, install the measuring fixture on the observation turntable, and connect the antenna to be tested to the testing fixture; Connect the test cable and start the test system to complete near-field data acquisition. Through near-field to far-field transformation, the far-field radiation pattern of the antenna to be tested is obtained.

8. The method for calibrating the antenna phase center based on spherical near-field measurement according to claim 7, characterized in that: The test system includes a scanning ring and measuring probes. The measuring probes are evenly spaced on the scanning ring. Multiple probes obtain pitch data and observe turntable rotation data based on electronic scanning sampling, thereby realizing near-field data sampling in the entire space.

9. The method for calibrating the antenna phase center based on spherical near-field measurement according to claim 1, characterized in that: The test fixture is a columnar structure with flanges at both ends. The two ends are respectively connected to the test turntable and the antenna to be tested. The height is sufficient to set the antenna to be tested to the center of the scanning ring.

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