A method for testing polarization pattern of shortwave antenna

Abstract

The present invention discloses a method for testing the polarization pattern of a shortwave antenna. The method adopts a calibrated three-coordinate electric small loop antenna carried by an unmanned aerial vehicle to synchronously and independently receive three orthogonal electric field components in space, and obtains polarization parameters such as total electric field strength, polarization inclination angle, and axial ratio according to the received three orthogonal electric field components and a theoretical correction model. The method for testing the polarization pattern of a shortwave antenna disclosed in the present invention can obtain the polarization characteristics of the entire upper half space of the shortwave antenna in a field environment through a complete flight test. Compared with the existing shortwave antenna pattern testing method, the method of the present invention can obtain the polarization characteristics of the shortwave antenna in any direction in the upper half space in a field environment, thereby obtaining a complete description of the far-field radiation pattern of the shortwave antenna.

Description

Technical Field

[0001] The invention belongs to the field of shortwave antenna testing, and in particular relates to a method for testing a polarization pattern of a shortwave antenna in the field. Background Art

[0002] Shortwave antennas are usually large and complex in structure, not easy to move or rotate, and their radiation performance is closely related to the installation environment. Therefore, the radiation field test of shortwave antennas is often carried out at the installation site using the fixed antenna method.

[0003] The fixed antenna method is divided into ground testing and aerial testing. The ground test is to select a series of azimuth test points in a sector or circular area with a radius of r on the ground plane with the antenna to be tested as the center, and measure at each point to obtain the directional pattern characteristics of the ground plane. However, the ground test is limited to horizontal plane testing and vertical plane testing is not possible. In addition, since the main lobe of the shortwave antenna is often not in the ground plane and generally has a certain elevation angle, it is difficult to obtain the true main lobe characteristics with this method.

[0004] Relatively speaking, the aerial test method is more comprehensive and flexible, and is a test method commonly used at home and abroad. In this method, the antenna to be tested is still fixed, and the auxiliary antenna is installed on a balloon, airship, airplane or other aircraft. The aircraft carries a receiving or transmitting device, which moves in a circle around the antenna to be tested in the plane to be tested, thereby obtaining the directional characteristics of the plane. Except for very low elevation angles, the aerial test method can test the far-field characteristics of the entire upper half of the shortwave antenna. This method is more flexible and convenient in the selection of the measurement route, is less affected by the ground environment, and has a lower measurement error.

[0005] In 1973, the Stanford Research Institute in the United States developed a shortwave antenna pattern measurement system (XELEDOP), which uses a helicopter to tow horizontal and vertical polarized antennas to fly on a spherical surface at a certain distance from the antenna to be tested and transmit signals, and can measure the different polarization patterns of the antenna to be tested. However, the posture of the towed antenna is easily affected by the flight speed and environmental conditions, and there is a polarization mismatch error; the radiation gain of the vertically polarized antenna relative to the antenna to be tested is different at different elevation angles, and needs to be normalized according to the theoretical value.

[0006] Since 2005, China has adopted aerial testing methods, using tethered airships, manned airships and fixed-wing drones to carry vertical or horizontal polarization antennas to conduct on-site far-field radiation pattern tests on domestic shortwave log-periodic antennas, horizontal dipole array antennas, etc. However, due to polarization mismatch and many influences of the flight platform, the actual test results are not ideal.

[0007] Since the above method uses a single linearly polarized auxiliary antenna for testing, it can only measure the field component of the corresponding polarization, and cannot measure the gain pattern of the shortwave antenna, let alone the polarization pattern of the shortwave antenna. This is an incomplete description of the antenna radiation pattern, because the shortwave horizontally polarized antenna installed on the actual ground has cross-polarization components, and the cross-polarization components in different directions are different in size. A complete description of the radiation pattern requires measuring the polarization characteristics as a function of direction, especially in the direction deviating from the main lobe of radiation, the polarization characteristics may be very different from the design value. To date, no public reports have been found on the test method of the polarization pattern of shortwave antennas on the actual ground. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for testing the polarization pattern of a shortwave antenna in a field environment.

[0009] The present invention adopts the following technical solution:

[0010] A method for testing the polarization pattern of a shortwave antenna uses a calibrated three-coordinate electric small loop antenna carried by an unmanned aerial vehicle to synchronously and independently receive three orthogonal electric field components in space, and obtains polarization parameters such as total electric field strength, polarization inclination angle, and axial ratio based on the received three orthogonal electric field components and a theoretical correction model. Since the three orthogonal electric field components can fully describe the spatial field strength of any polarization, the unmanned aerial vehicle, with the shortwave antenna to be tested as the center, can measure the polarization pattern within the corresponding beam solid angle range and the radiation field strength amplitude and polarization inclination angle of the upper half of the shortwave antenna in a single aerial flight, including the following steps:

[0011] Step 1: Design a three-coordinate electric small loop antenna as an auxiliary receiving antenna. The three-coordinate electric small loop antenna includes three electric small loop antennas. The diameters and matching networks of the three electric small loop antennas are exactly the same. The three electric small loop antennas are assembled in three orthogonal directions with the center of the circle at the same point. Calibrate the antenna coefficient of each electric small loop antenna at 3MHz to 30MHz to ensure that the antenna coefficients of the three electric small loop antennas are the same, that is:

[0012] K x =K y =K z =K (1)

[0013] Step 2: Take the common point of the three-coordinate electric small loop antenna of the auxiliary receiving antenna as the origin and establish Figure 3 The spherical coordinate system shown in the figure, the radiation field strength E of a point in the far area of ​​the shortwave antenna to be measured is expressed as:

[0014]

[0015] in, is the amplitude of the radiation field strength of the antenna to be measured, -kr is the phase of the radiation field strength changing with the distance r, and k is the spatial propagation constant;

[0016] In actual testing, the shortwave antenna to be tested is located in the lower half space of the three-coordinate electric small loop antenna. Assuming 90°≤θ≤180°, the azimuth angle is set to: The polarization tilt angle is set to: 0°≤τ≤180°;

[0017] Step 3: The radiation field strength at a certain point in the far field of the shortwave antenna to be tested can be expressed in the wavefront plane as the horizontal polarization field strength E H and the vertical polarization field strength E V Decompose the coordinate base. Since the radiation field of the shortwave antenna to be tested in the far area is an elliptically polarized wave, such as Figure 4 As shown, let the major axis of the elliptically polarized wave be E m , the minor axis is E n , long axis E m With the horizontal polarization field strength E H The angle between is the polarization tilt angle τ, then:

[0018] E m =E H cos τ+E V sinτ (3)

[0019] E n =E H sinτ+E V cosτ (4)

[0020] make for Figure 3 The three orthogonal coordinate bases in the rectangular coordinate system shown, φ H ,φ V is the horizontal polarization field strength E H and the vertical polarization field strength E V The phase of E H and E V In rectangular coordinates it is:

[0021]

[0022]

[0023] Substituting equations (5) and (6) into equations (3) and (4), we can obtain:

[0024]

[0025]

[0026]

[0027] The three-coordinate electric small loop antennas correspond to the receiving E x , E y , E z , and due to the conservation of power of radio waves, we have:

[0028] |E| 2 =|E x | 2 +|E y | 2 +|E z | 2 =|E H | 2 +|E V | 2 (10)

[0029] Step 4: Select a drone with a gimbal and fix the three-coordinate electric small loop antenna in the gimbal of the drone. The automatic tracking function of the gimbal ensures that the relative posture of the three-coordinate electric small loop antenna and the shortwave antenna to be tested remains stable.

[0030] Step 5: Based on the relative positions of the three-coordinate electric small loop antenna and the UAV in step 4, theoretical simulation is performed on the three-coordinate electric small loop antenna at any position by the UAV, wireless data transmission, and global positioning equipment. The influence of directional radiation field strength, denoted as ΔE x , ΔE y , ΔE z ;

[0031] Step 6: According to equation (1) and step 5, the voltages of the three-coordinate electric loop antenna and the three-channel receiver for independently receiving the electric field components are expressed as:

[0032] U x =(E x +ΔE x ) / K (11)

[0033] U y =(E y +ΔE y ) / K (12)

[0034] U z =(E z +ΔE z ) / K (13)

[0035] Step 7: The shortwave antenna to be tested transmits the test frequency signal of interest. The UAV takes the shortwave antenna to be tested as the sphere center and performs circular flight on the spherical surface with a radius R of the far field of the shortwave antenna to be tested. R is not less than 10 times the wavelength. The angle of the UAV relative to the shortwave antenna to be tested at any point on the flight trajectory is recorded. And the corresponding U x , Uy , U z ;

[0036] During the test, only the relative position of the three-coordinate electric small loop antenna and the shortwave antenna to be tested changes. When the initial condition is that the X-axis directions of the two coordinate systems are opposite and the Z-axis directions are the same, assuming that the UAV rotates counterclockwise at an angle of δ, then and There are the following relations:

[0037] θ=180°-θ′ (14)

[0038]

[0039] Step 8, compare the U recorded in step 7 x , U y , U z The magnitude of the three received voltage components, select the largest field strength component max{|KU x -ΔE x |、|KU y -ΔE y |、|KU z -ΔE z |}, and using the corresponding equations (7), (8), (9), and (10) of the field strength component, the test results show that the shortwave antenna under test has any angle in the upper half space. The radiation field intensity polarization tilt angle τ, and |E H |、|E V |、φ H ,φ V , choosing the maximum voltage component can effectively avoid the test error caused by the possible minimum value; let Δφ=φ V -φ H ,

[0040]

[0041]

[0042] Step 9, repeat step 8, according to the recorded And calculate the far-field radiation intensity of the shortwave antenna to be tested The polarization tilt angle τ of the elliptically polarized wave, The ellipticity angle is When Δφ>0, the polarization ellipse is right-hand polarization, and ε takes a "-" sign. When Δφ<0, the polarization ellipse is left-hand polarization, and ε takes a "+" sign.

[0043] When Δφ=±nπ,n=0,1,2,…,elliptically polarized wave degenerates into linearly polarized wave, and the polarization inclination angle is τ; when |E H |=|E V|, When , the elliptically polarized wave degenerates into a circularly polarized wave, where When is right-hand circularly polarized wave, When is left-hand circularly polarized wave;

[0044] Therefore, the polarization mode of the far-field radiation field of the shortwave antenna to be tested can be determined based on the test results, and the polarization pattern of the antenna at different frequencies can be drawn.

[0045] Step 10, end.

[0046] The beneficial effects of the present invention are:

[0047] The test method for the polarization pattern of a shortwave antenna disclosed in the present invention can obtain the polarization characteristics of the entire upper half space of the shortwave antenna in a real environment through a complete flight test. Compared with the existing shortwave antenna pattern test method, the method of the present invention can obtain the polarization characteristics of the shortwave antenna in any direction in the upper half space in a real environment, thereby being able to obtain a complete description of the far-field radiation pattern of the shortwave antenna. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the testing process of the method of the present invention;

[0049] Figure 2 It is a schematic diagram of the structure of the three-coordinate electric small loop antenna in the method of the present invention;

[0050] Figure 3 It is a schematic diagram of a spherical coordinate system established with the common center of the three-coordinate electric small loop antenna as the origin;

[0051] Figure 4 is the polarization ellipse of the far-field radiation field of the shortwave antenna to be tested;

[0052] Figure 5 is a schematic diagram of the flight trajectory of the UAV in the method of the present invention;

[0053] Figure 6(a) is a theoretical simulation model of the effect of the distance change between the UAV and the three-coordinate electric small loop antenna on the radiation field strength;

[0054] Figure 6(b) is a simulation of the effect of the 0.8m (3.2dB) center distance between the drone and the three-coordinate electric small loop antenna on the radiation field strength;

[0055] Figure 6(c) is a simulation of the effect of a 2.5-meter (0.5 dB) center distance between the drone and the three-coordinate electric small loop antenna on the radiation field strength;

[0056] Figure 7 is a schematic diagram of an antenna unit;

[0057] Figure 8It is a curve showing the variation of the antenna ellipticity angle with the azimuth angle at a frequency of 14.87 MHz when the vertical logarithmic periodic antenna is tested using the method of the present invention;

[0058] Fig. 9 The present invention is a theoretical simulation of the variation curve of the ellipticity angle of the polarized wave of the far field of the vertical logarithmic periodic antenna with the azimuth angle at 10MHz;

[0059] Fig.10 It is the phase difference between the vertical polarization field intensity and the horizontal polarization field intensity of the far-field polarization wave of the vertical logarithmic periodic antenna at 10MHz in the theoretical simulation of the present invention. DETAILED DESCRIPTION

[0060] 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.

[0061] Figure 1 The figure is a schematic diagram of the whole process of testing the polarization pattern of the shortwave antenna to be tested in the present invention. In the shortwave antenna polarization pattern test experiment, in order to obtain the three-dimensional pattern of the shortwave antenna to be tested in the whole space, it is always hoped that the airborne receiving antenna will make a circular motion in the whole sphere. However, due to the existence of the ground, we often only care about the pattern of the upper half of the shortwave antenna space. Moreover, for the aircraft, this ideal spherical flight trajectory is difficult to achieve. In actual measurement, the airborne receiving antenna is used. Figure 5 The spherical spiral line shown is used as its test trajectory. When the UAV flies along the spherical spiral line, the flight trajectory of each point is on a spherical surface with a radius of R, thereby ensuring that the distance between the receiving antenna and the shortwave antenna to be tested remains unchanged.

[0062] Design and manufacture a 25cm diameter three-coordinate electric small loop antenna. The radiator of the loop antenna uses a copper wire with a diameter of φ3, and the supporting structure uses non-conductive fiberglass rods, such as Figure 2 As shown, three electric small loop antennas are assembled in three orthogonal positions with the same center. After matching each electric small loop antenna with reference to GJB / J5410-2005, the antenna coefficient is calibrated at 3MHz to 30MHz. The consistency error of the antenna coefficient K of the three electric small loop antennas is less than 0.5dB.

[0063] Take the common center of the three-coordinate electric small loop antenna as the origin and establish Figure 3 According to the established spherical coordinate system, the radiation field strength vector E of a certain point in the far field of the shortwave antenna to be measured is decomposed in three dimensions orthogonally. Then, the three-coordinate electric small loop antenna corresponds to the receiving E x , E y , E z .like Figure 4As shown in the figure, the elliptically polarized radiation field of the shortwave antenna to be tested in the far area is horizontally polarized in the wavefront plane with field strength E H and the vertical polarization field strength E V Decompose into coordinate basis.

[0064] A small UAV is selected as the aerial mobile test platform, and the three-coordinate electric small loop antenna and the three-channel receiving module are installed in the UAV's gimbal. The automatic tracking function of the gimbal can ensure that the relative posture of the three-coordinate electric small loop antenna and the shortwave antenna to be tested remains stable. According to the relative position of the three-coordinate electric small loop antenna and the UAV, the UAV system is theoretically simulated, including the UAV, gimbal, wireless data transmission, global positioning equipment, etc., to measure the three-coordinate electric small loop antenna at any position. The influence of directional radiation field strength is expressed as (ΔE x , ΔE y , ΔE z ), simulation model and results can be found in Figure 6(a) , 6(b) and 6(c).

[0065] The shortwave antenna to be tested transmits the test frequency signal of interest. The UAV test platform takes the shortwave antenna to be tested as the sphere center and performs circular flight on the spherical surface with a radius R of the far field of the shortwave antenna to be tested. The angle of any point on the flight trajectory relative to the shortwave antenna to be tested is according to and The angle relationship is recorded to record the angle of the drone relative to the shortwave antenna to be tested. And the corresponding (U x , U y , U z ). Thus, the angle of any angle in the upper half space relative to the shortwave antenna to be tested can be obtained. The electric field radiation intensity.

[0066] Compare x , U y , U z ) the magnitudes of the three received voltage components,

[0067] Select the largest field strength component max{|KU x -ΔE x |、|KU y -ΔE y |、|KU z -ΔE z |}, and using the corresponding expressions (7), (8), (9), (10) of this component, the angle of the upper half space of the shortwave antenna to be tested can be obtained. The radiation field intensity polarization tilt angle τ, and |E H |、|E V |、φ H ,φV According to expressions (16) (17) and step 9, the polarization mode of the far-field radiation field of the shortwave antenna to be tested can be determined, and the polarization patterns of the antenna at different frequencies can be plotted.

[0068] Example 1: Using the test method of the present invention, the polarization pattern of the vertical log-periodic antenna is tested. Figure 7 The schematic diagram of the antenna unit is shown in Figure 1. At a frequency of 14.87 MHz, the received field strength value of the upper coordinate of the three-coordinate electric small loop antenna is recorded and measured in the test, such as Figure 8 As shown, the curve of the variation of the ellipticity angle of the vertical logarithmic periodic antenna with the azimuth angle at this frequency can be measured by data processing using the theoretical formula.

[0069] Example 2, using the test method of the present invention, theoretically simulates the polarization pattern of the vertical log-periodic antenna, Fig. 9 The curve of the ellipticity angle of the polarized wave in the far field of the vertical logarithmic periodic antenna changing with the azimuth angle at 10MHz. Fig.10 It is the phase difference between the vertically polarized field intensity and the horizontally polarized field intensity of the far-field polarized wave of the vertical log-periodic antenna at 10MHz.

Claims

1. A method for testing the polarization pattern of a shortwave antenna. It is characterized in that The steps include: Step 1: Design a three-coordinate electric small loop antenna as an auxiliary receiving antenna. The three-coordinate electric small loop antenna includes three electric small loop antennas. The diameters and matching networks of the three electric small loop antennas are exactly the same. The three electric small loop antennas are assembled in three orthogonal directions with the center of the circle at the same point. Calibrate the antenna coefficient of each electric small loop antenna at 3MHz to 30MHz to ensure that the antenna coefficients of the three electric small loop antennas are the same, that is: K x =K y =K z =K (1) Step 2: Take the common point of the three-coordinate electric small loop antenna of the auxiliary receiving antenna as the origin and establish a spherical coordinate system. Then the radiation field strength E of a certain point in the far area of ​​the shortwave antenna to be measured is expressed as: in, is the amplitude of the radiation field strength of the antenna to be measured, -kr is the phase of the radiation field strength changing with the distance r, and k is the spatial propagation constant; In actual testing, the shortwave antenna to be tested is located in the lower half space of the three-coordinate electric small loop antenna. Assuming 90°≤θ≤180°, the azimuth angle is set to: The polarization tilt angle is set to: 0°≤τ≤180°; Step 3: The radiation field strength at a certain point in the far field of the shortwave antenna to be tested can be expressed in the wavefront plane as the horizontal polarization field strength E H and the vertical polarization field strength E V As the coordinate basis, the radiation field of the shortwave antenna to be tested in the far field is an elliptically polarized wave, and the major axis of the elliptically polarized wave is E m , the minor axis is E n , long axis E m With the horizontal polarization field strength E H The angle between is the polarization tilt angle τ, then: AND m =And H cosτ+E V sinτ (3) AND n =And H sinτ+E V cosτ (4) make is the three orthogonal coordinate basis in the rectangular coordinate system, φ H ,φ V is the horizontal polarization field strength E H and the vertical polarization field strength E V The phase of E H and E V In rectangular coordinates it is: Substituting equations (5) and (6) into equations (3) and (4), we can obtain: The three-coordinate electric small loop antennas correspond to the receiving E x , E y , E z , and due to the conservation of power of radio waves, we have: |E| 2 =|And x | 2 +|And y | 2 +|And z | 2 =|And H | 2 +|And V | 2 (10) Step 4: Select a drone with a gimbal and fix the three-coordinate electric small loop antenna in the gimbal of the drone. The automatic tracking function of the gimbal ensures that the relative posture of the three-coordinate electric small loop antenna and the shortwave antenna to be tested remains stable. Step 5: Based on the relative positions of the three-coordinate electric small loop antenna and the UAV in step 4, theoretical simulation is performed on the three-coordinate electric small loop antenna at any position by the UAV, wireless data transmission, and global positioning equipment. The influence of directional radiation field strength, denoted as ΔE x , ΔE y , ΔE z ; Step 6: According to equation (1) and step 5, the voltages of the three-coordinate electric loop antenna and the three-channel receiver for independently receiving the electric field components are expressed as: U x =(E x +ΔE x ) / K (11) U y =(E y +ΔE y ) / K (12) U z =(E z +ΔE z ) / K (13) Step 7: The shortwave antenna to be tested transmits the test frequency signal of interest. The UAV takes the shortwave antenna to be tested as the sphere center and performs circular flight on the spherical surface with a radius R of the far field of the shortwave antenna to be tested. R is not less than 10 times the wavelength. The angle of the UAV relative to the shortwave antenna to be tested at any point on the flight trajectory is recorded. And the corresponding U x , U y , U z ; During the test, only the relative position of the three-coordinate electric small loop antenna and the shortwave antenna to be tested changes. When the initial condition is that the X-axis directions of the two coordinate systems are opposite and the Z-axis directions are the same, assuming that the UAV rotates counterclockwise at an angle of δ, then and There are the following relations: θ=180°-θ′ (14) Step 8: Compare the U recorded in step 7 x , U y , U z The magnitude of the three received voltage components, select the largest field strength component max{|KU x -ΔE x |、|KU y -ΔE y |、|KU z -ΔE z |}, and using the corresponding equations (7), (8), (9), and (10) of the field strength component, the test results show that the shortwave antenna under test has any angle in the upper half space. The radiation field intensity polarization tilt angle τ, and |E H |、|E V |、φ H ,φ V , let Δφ=φ V -φ H , Step 9, repeat step 8, according to the recorded And calculate the far-field radiation intensity of the shortwave antenna to be tested The polarization tilt angle τ of the elliptically polarized wave, The ellipticity angle is When Δφ>0, the polarization ellipse is right-hand polarization, and ε takes the "-" sign; when Δφ<0, the polarization ellipse is left-hand polarization, and ε takes the "+" sign; When Δφ=±nπ,n=0,1,2,…,elliptically polarized wave degenerates into linearly polarized wave, and the polarization inclination angle is τ; when |E H |=|E V |, When , the elliptically polarized wave degenerates into a circularly polarized wave, where When is right-hand circularly polarized wave, When is left-hand circularly polarized wave; Therefore, the polarization mode of the far-field radiation field of the shortwave antenna to be tested can be determined based on the test results, and the polarization pattern of the antenna at different frequencies can be drawn.

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