A high-precision wide-band circularly polarized antenna far-field test system and method

Abstract

The present invention relates to the field of microwave darkroom antenna testing technology, and discloses a high-precision wide-band circularly polarized antenna testing system and method. The testing system adopted by the method comprises: an antenna stand, an antenna array, and an elevator. The antenna stand is an arc antenna stand with a far-field test distance as a radius, and narrow-band circularly polarized antennas are installed at equal intervals on the antenna stand. The antenna stand is arranged at the top of the elevator. The arc antenna stand uses a section of an arc-shaped stand with a far-field test distance radius as the front frame of the antenna stand, and a fixed horizontal bar is arranged between the front frame and the straight rear frame to reinforce the antenna stand. The center of the antenna stand is fixed on the elevator as the main support point. The present invention can conduct tests conveniently, quickly, accurately, and efficiently. It overcomes the defects of a large number of antennas and a large number of lifting and lowering times in microwave darkroom antenna testing, greatly shortens the time, simplifies the operation, and improves the test efficiency of the wide-band circularly polarized antenna far-field test system.

Description

Technical Field

[0001] The present invention relates to the technical field of antenna testing in a microwave anechoic chamber, and particularly to a testing system and method for a high-precision wide-band circularly polarized antenna, which can perform testing conveniently, quickly, accurately and efficiently. Background Art

[0002] High-precision testing of antennas needs to be carried out in a microwave anechoic chamber. A microwave anechoic chamber is an electromagnetic measurement environment that can shield external electromagnetic interference, suppress internal electromagnetic multipath reflection, and almost completely absorb electromagnetic waves. According to "GJB3071-97 Radar Antenna Subsystem Performance Testing Method", the test distance for far-field testing is calculated according to (1) and (2):

[0003] R≥2(D + d) 2 / λ (1)

[0004] When d << D, R≥2D 2 / λ (2)

[0005] In the formula: D is the maximum size of the aperture (equivalent aperture) of the antenna under test, m; d is the size of the aperture (equivalent aperture) of the source antenna, m; λ is the shortest operating wavelength, m; R is the distance between the geometric centers of the source antenna and the antenna under test, m.

[0006] Polarization refers to the trajectory described by the tip of the electric field vector when it changes for one period in a plane perpendicular to the wave propagation direction. If the trajectory described by the tip is a straight line, it is called linear polarization; if the trajectory described by the tip is a circle, it is called circular polarization; if the trajectory described by the tip is an ellipse, it is called elliptical polarization.

[0007] The axial ratio of elliptical polarization is defined as the ratio of the major axis to the minor axis, represented by r. Then the axial ratio AR expressed in decibels is:

[0008] AR = 20log(R) (3)

[0009] Circular polarization and linear polarization are two special cases of elliptical polarization, that is, when r = 1 or AR = 0dB, it is circular polarization; when r = ∞ or AR = ∞, it is linear polarization. Any circular polarization can be decomposed into a linear polarization wave or a circular polarization wave. Therefore, the gain of an elliptical polarization antenna can be expressed as:

[0010] G = 10log(G a +G b ) (4)

[0011] In the formula, G a and G b respectively represent the partial gains of the orthogonal polarization components. For the linear polarization decomposition method, G a and G bRepresent the long axis gain and short axis gain respectively; for circular polarization decomposition method, G a and G b They represent the gain of the circular polarization part with larger amplitude and the gain of the part with smaller amplitude respectively.

[0012] High-precision testing of circularly polarized antennas requires circularly polarized source antennas with good axial ratios. Only when the frequency band of the circularly polarized antenna is made narrow enough can the axial ratio be good enough and the axial ratio r be infinitely close to 1. Therefore, high-precision testing of wide-band circularly polarized antennas often requires a large number of narrow-band circularly polarized source antennas. Usually, a far-field test system set up in a microwave darkroom is Figure 1 As shown, a standard gain antenna or a wide-band antenna to be tested is set up on a one-dimensional directional turntable, and a narrow-band antenna is set up on the elevator. In order to meet the far-field test conditions, it is necessary to meet the test requirements such as far-field distance, equal-height installation, and polarization consistency. After the installation is completed, directional optical alignment is required, and then the test is carried out. An example used in the present invention: a broadband circularly polarized antenna with a frequency of (2-12) GHz, the test requires 14 narrow-band circularly polarized source antennas, including 7 left-handed circularly polarized antennas and 7 right-handed circularly polarized antennas. In the test process, after each set of data is tested, another narrow-band circularly polarized source antenna needs to be replaced, and the elevator needs to be lowered, disassembled and replaced with another narrow-band antenna, and then the elevator is raised, and the antenna is aligned again, and then the test is carried out. The main problems with the original test conditions and methods are: first, a lot of manpower is required to cooperate, and multiple people are required to cooperate in the lifting and lowering of the elevator, and the disassembly and installation of the antenna; second, it takes a long time, and it takes a lot of time to lift and disassemble the antenna, which is inefficient. Summary of the invention

[0013] In order to overcome the shortcomings of the background technology, the present invention provides a high-precision wide-band circularly polarized antenna far-field test system and method based on a microwave darkroom, which can test the wide-band antenna more conveniently, quickly, accurately and efficiently, greatly shorten the test time, and can reduce the number of lifting and lowering times from the original 14 times (using the data in the above example) to the current 1 time, saving more than 90% of the lifting and installation time. All test antennas can be installed at one time. After the installation is completed, there is no need to repeatedly raise and lower the lifting frame. The antenna can be selected by software operation, which reduces the number of operators and improves the level of automation and test efficiency.

[0014] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0015] A high-precision wide-band circularly polarized antenna far-field test system, comprising: an antenna stand, an antenna array, and an elevator, wherein the antenna stand is an arc antenna stand with a far-field test distance as a radius, and narrow-frequency-band circularly polarized antennas are arranged on the antenna stand at equal intervals, and the antenna stand is arranged at the top of the elevator; the arc antenna stand uses an arc-shaped stand with a radius of the far-field test distance as a front frame of the antenna stand, and a fixed horizontal bar is arranged between the front frame and the straight rear frame to reinforce the antenna stand, and the center of the antenna stand is fixed on the elevator as a main support point;

[0016] The front frame is symmetrically provided with antennas of different polarizations on both sides with the main supporting point as the midpoint, including a left-hand circularly polarized antenna group and a right-hand circularly polarized antenna group; the left-hand circularly polarized antenna group is composed of left-hand circularly polarized antenna 1 to left-hand circularly polarized antenna 7, and the right-hand circularly polarized antenna is composed of right-hand circularly polarized antenna 1' to right-hand circularly polarized antenna 7', and each left-hand circularly polarized antenna and right-hand circularly polarized antenna is fixed on the arc of the front frame through an antenna fixing point;

[0017] Each antenna of the left-hand circularly polarized antenna group and the right-hand circularly polarized antenna group is arranged in the order from low frequency to high frequency from the middle to both sides according to the technology of center of gravity balance, with low frequency antenna being relatively large and high frequency antenna being relatively small.

[0018] The left-hand circular polarization antenna group and the right-hand circular polarization antenna group are connected to an antenna array circuit, and the antenna array circuit consists of a radio frequency switching switch matrix, a power amplifier, and a signal source.

[0019] A high-precision wide-band circularly polarized antenna far-field test system, wherein the radio frequency switching switch matrix comprises a three-select-one radio frequency switch SP3T and a five-select-one radio frequency switch SP5T, wherein the three output ends of the three-select-one radio frequency switch SP3T are respectively connected to the five-select-one radio frequency switch SP5T through radio frequency cables, and the five output ends of each five-select-one radio frequency switch SP5T are respectively connected to the corresponding load, namely, the antenna through radio frequency cables; the input end of the three-select-one radio frequency switch SP3T is connected to a power amplifier circuit through radio frequency cables; the three-select-one radio frequency switch SP3T is placed at the center of an antenna frame, and each five-select-one radio frequency switch SP5T is placed at the center of three equally divided areas; the radio frequency selection switch matrix is ​​controlled by an industrial computer, and the relay board on the industrial computer is an RS485 communication interface, which is used for operating to realize the selection of different frequency and polarization narrow frequency antennas.

[0020] A test method for a high-precision wide-band circularly polarized antenna far-field test system: The antenna gain is measured using a comparison method, and the steps are as follows:

[0021] 1) Preparation: First, install all narrow-band source antennas on the antenna rack of the elevator, then raise the elevator, set the standard gain antenna or the wide-band circularly polarized antenna to be tested on the one-dimensional turntable, and after optical alignment, the axis of the standard gain antenna or the wide-band circularly polarized antenna to be tested and the narrow-band circularly polarized source antenna can be on the same horizontal line;

[0022] 2) During the test, after the lift is raised, ensure that the axis of the installed source antenna can maintain horizontal signal transmission, be in the same plane as the axis of the standard antenna or the antenna under test, and point in the direction of the standard gain antenna / the center of the broadband antenna under test on the one-dimensional turntable;

[0023] The switch matrix must select the source antenna one by one as required. The signal sent by the signal source is amplified by the power amplifier and then transmitted to the selected source antenna. The receiving end is a standard gain antenna or a wide-band circularly polarized antenna under test. The signal received by the receiving antenna passes through a low-noise amplifier and a spectrum analyzer. The frequency of the receiving end is consistent with the frequency of the transmitting end. The antenna radiation pattern of the test end can be obtained by scanning the turntable for one rotation. The data of the maximum power point is the test value A2 of the tested antenna, or the test value A1 of the standard antenna.

[0024] When the standard gain antenna is a linearly polarized antenna, a gain synthesis value is required. Assuming the gain of the standard gain antenna is G0, the gain value of the antenna under test at this frequency can be calculated according to formula (5):

[0025] G=G0+[A2-A1] (5).

[0026] By adopting the technical solution, the present invention has the following advantages:

[0027] A high-precision wide-band circularly polarized antenna far-field test system overcomes the drawbacks of a large number of circularly polarized source antennas, the need to repeatedly raise and lower a lift and replace source antennas, and the need for multiple people to operate in a microwave darkroom antenna test. All test antennas can be installed at one time. After the installation is completed, there is no need to repeatedly raise and lower the lift. Only software operation is required to achieve the selection of narrow-band circularly polarized source antennas, which greatly shortens the time, simplifies the operation, improves the automation level of the system, and greatly improves the test efficiency of the wide-band circularly polarized antenna far-field test system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the original microwave darkroom antenna test system

[0029] Figure 2 Design plan for the antenna rack

[0030] Figure 3 Design diagram for antenna RF switch matrix

[0031] Figure 4This is a test principle diagram of the present invention applied in a microwave darkroom. DETAILED DESCRIPTION

[0032] like Figure 2 , 3 As shown in Figure 4, a high-precision wide-band circularly polarized antenna far-field test system, the antenna frame on the elevator is an arc antenna frame with a radius of the far-field test distance, narrow-band circularly polarized antennas can be installed at equal intervals on the antenna frame, the antenna frame can be installed on the top of the elevator, after the elevator is raised, it is necessary to ensure that the axis of the installed source antenna can maintain a horizontal transmission signal, and is in the same plane as the axis of the standard antenna or the antenna being tested, and the direction points to the center of the standard gain antenna / the broadband antenna being tested on the one-dimensional turntable. Figure 2 As shown in the figure, a circular arc-shaped frame with a radius of 30 meters is designed as the front frame 8 of the antenna frame, and the length is as follows: Figure 2 The straight rear frame 11 shown has a fixed horizontal bar 10 in the middle to reinforce the antenna frame. The center of the entire frame is fixed on the elevator with the main support point as the center. The antenna group 13 is installed symmetrically on both sides with the main support point 12 as the midpoint. Different polarized antennas are installed on both sides. Antenna 1 to antenna 7 are left-hand circular polarization antennas, and antenna 1' to antenna 7' are right-hand circular polarization antennas. Since the low-frequency antenna is relatively large and the high-frequency antenna is relatively small, considering the center of gravity balance, the antennas are installed from the middle to the sides in the order from low frequency to high frequency. Each left-hand circular polarization antenna and right-hand circular polarization antenna are fixed on the arc of the front frame 8 through the antenna fixing point 9.

[0033] The antenna array needs to design a radio frequency switching circuit to realize the selection of different antennas, and realize the switching of different frequencies and polarizations of the antennas in sequence through the operating software. Figure 3 As shown, a RF switch matrix is ​​designed for 14 narrow-band antenna arrays. Combined with the frequency, power and isolation indicators, a mechanical switch that meets the requirements is selected. In this case, 1 SP3T and 3 SP5T, 4 switch installation boxes and related connection plug-ins, RF cables (1 power amplifier-SP3T, 3 SP3T-SP5T, 15 SP5T-antenna), 1 high-power load, 1 switch power supply and control system, 1 set of control software are required. The switch layout adopts the SP3T switch placed at the center of the antenna, and the 3 SP5T switches are placed at the center of 3 equally divided areas. At the same time, the length of the RF cable should be reduced. 1 load is used for antenna array shutdown and maintenance backup. The RF selection switch is for power control, the relay board is the RS485 communication interface, and the RS485 board is installed on the industrial computer. The selection of narrow frequency antennas with different frequencies and polarizations is realized through the control software operation.

[0034] According to the technical solution of the present invention, the test is carried out and the gain of the antenna is measured by the comparison method. First, all the narrow-band source antennas are installed on the antenna frame of the elevator, and then the elevator is raised, and the standard gain antenna or the wide-band circularly polarized antenna to be tested is set on the one-dimensional turntable, and after optical alignment, the axis of the standard gain antenna or the wide-band circularly polarized antenna to be tested and the narrow-band circularly polarized source antenna can be on the same horizontal line. During the test, the switch matrix must select the source antenna one by one as required. The signal sent by the signal source is amplified by the power amplifier and then transmitted to the selected source antenna. The receiving end is a standard gain antenna or a wide-band circularly polarized antenna under test. The signal received by the receiving antenna passes through a low noise amplifier and a spectrum analyzer. The frequency of the receiving end is consistent with the frequency of the transmitting end. The antenna radiation pattern of the test end can be obtained by scanning the turntable for one rotation. The data of the maximum power point is A2 (test value of the tested antenna) or A1 (test value of the standard antenna. If the standard gain antenna is a linearly polarized antenna, a gain synthesis value is required). Assuming that the gain of the standard gain antenna is G0, the gain value of the tested antenna at this frequency can be calculated according to formula (5):

[0035] G=G0+[A2-A1] (5).

Claims

1. A high-precision wide-band circularly polarized antenna far-field test system, characterized by: include: Antenna stand, antenna array, and elevator, wherein the antenna stand is an arc antenna stand with a radius of a far-field test distance, and narrow-frequency circularly polarized antennas are installed at equal intervals on the antenna stand, and the antenna stand is arranged at the top of the elevator; The arc antenna rack uses an arc-shaped rack with a radius of the far-field test distance as the front frame of the antenna rack, and a fixed horizontal bar is arranged between the front frame and the straight rear frame to reinforce the antenna rack. The center of the antenna rack is fixed on the elevator as the main support point; The front frame is symmetrically provided with antennas of different polarizations on both sides with the main supporting point as the midpoint, including a left-hand circularly polarized antenna group and a right-hand circularly polarized antenna group; the left-hand circularly polarized antenna group is composed of left-hand circularly polarized antenna 1 to left-hand circularly polarized antenna 7, and the right-hand circularly polarized antenna is composed of right-hand circularly polarized antenna 1' to right-hand circularly polarized antenna 7', and each left-hand circularly polarized antenna and right-hand circularly polarized antenna is fixed on the arc of the front frame through an antenna fixing point; Each antenna of the left-hand circularly polarized antenna group and the right-hand circularly polarized antenna group is arranged in the order from low frequency to high frequency antenna from the middle to both sides according to the technology of relatively large low frequency antenna and relatively small high frequency antenna, and the center of gravity is balanced; the left-hand circularly polarized antenna group and the right-hand circularly polarized antenna group are connected to the antenna array circuit, and the antenna array circuit is composed of a radio frequency switching switch matrix, a power amplifier, and a signal source; The radio frequency switching switch matrix includes a three-select-one radio frequency switch SP3T and a five-select-one radio frequency switch SP5T. The three output ends of the three-select-one radio frequency switch SP3T are respectively connected to the five-select-one radio frequency switch SP5T through radio frequency cables, and the five output ends of each five-select-one radio frequency switch SP5T are respectively connected to the corresponding load-antenna through radio frequency cables; the input end of the three-select-one radio frequency switch SP3T is connected to the power amplifier circuit through the radio frequency cable; the three-select-one radio frequency switch SP3T is placed at the center of the antenna rack, and each five-select-one radio frequency switch SP5T is placed at the center of three equally divided areas; the radio frequency selection switch matrix is ​​controlled by an industrial computer, and the relay board on the industrial computer is an RS485 communication interface, which is used to operate and realize the selection of different frequency and polarization narrow frequency antennas; The test method of the high-precision wide-band circularly polarized antenna far-field test system uses a comparison method to measure the gain of the antenna, and the steps are as follows: 1) Preparation: First, install all narrow-band source antennas on the antenna rack of the elevator, then raise the elevator, set the standard gain antenna or the wide-band circularly polarized antenna to be tested on the one-dimensional turntable, and after optical alignment, the axis of the standard gain antenna or the wide-band circularly polarized antenna to be tested and the narrow-band circularly polarized source antenna can be on the same horizontal line; 2) During the test, after the lift is raised, ensure that the axis of the installed source antenna can maintain horizontal transmission signals, be in the same plane as the axis of the standard antenna or the antenna under test, and point in the direction of the standard gain antenna of the one-dimensional turntable or the center of the broadband antenna under test; The switch matrix must select the source antenna one by one as required. The signal sent by the signal source is amplified by the power amplifier and then transmitted to the selected source antenna. The receiving end is a standard gain antenna or a wide-band circularly polarized antenna under test. The signal received by the receiving antenna passes through a low-noise amplifier and a spectrum analyzer. The frequency of the receiving end is consistent with the frequency of the transmitting end. The antenna radiation pattern of the test end can be obtained by scanning the turntable for one rotation. The data of the maximum power point is the test value A2 of the tested antenna, or the test value A1 of the standard antenna. When the standard gain antenna is a linearly polarized antenna, a gain synthesis value is required. Assuming the gain of the standard gain antenna is G0, the gain value of the antenna under test at this frequency can be calculated: G = G0 + [A2-A1] (5).

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