A method and a test system for testing the antenna pattern of a terahertz compact range

Abstract

A method for testing the antenna pattern of a terahertz compact range, comprising: installing the antenna under test, and determining the relationship between the coordinate system of the antenna under test and the coordinate system of the site; controlling the turntable to rotate, obtaining the far-field amplitude pattern data and phase pattern data of the antenna under test, and further obtaining the complex electric field value; multiplying the complex electric field value by an imaginary coefficient and then performing a fast Fourier transform to determine the pattern coefficient; expanding the pattern coefficient and then performing the inverse transform of the fast Fourier transform to obtain the encrypted complex electric field value. The present invention utilizes ordinary compact range test equipment, without the need to add additional hardware devices, and only obtains higher-resolution pattern data through data processing and calculation, improving the test accuracy of the antenna. The encryption of the present invention belongs to lossless encryption, and can achieve a completely coincident effect with the pattern obtained by actually increasing the sampling density, which is very different from ordinary numerical interpolation algorithms, especially for the null depth of the pattern, lossless restoration can be achieved.

Description

Technical Field

[0001] The present invention relates to a method and a test system for testing the radiation pattern of a terahertz compact range antenna, belonging to the technical field of antenna measurement. Background Art

[0002] With the development of terahertz antennas, their apertures are getting larger and larger, and the beam widths are getting narrower and narrower. For example, a 200 GHz front-fed Cassegrain antenna has an aperture of 2.5 m and a beam width of less than 0.05 degrees. If a far-field test of the antenna radiation pattern is to be carried out, the sampling interval needs to be at least less than 0.005 degrees. For antennas with requirements for beam pointing accuracy, according to the 1% accuracy requirement, the sampling interval needs to reach 0.0005 degrees to meet the accuracy requirement. This requirement poses very high requirements for ordinary antenna test turntables, and conventional turntables can no longer meet it. Currently, only some rotating devices used in optical projects, such as "six-degree-of-freedom turntables", can meet such sampling interval requirements.

[0003] Although there are currently devices that can meet this requirement, this solution sacrifices a great deal of test time, and the test speed needs to be reduced to 1 / 10 or even 1 / 100 of the original test. The test efficiency will decrease significantly, and the hardware cost will also increase accordingly.

[0004] Although near-field testing is not affected by resolution, such large-aperture high-frequency antennas have very high requirements for the dynamic range of terahertz radio frequency devices. For the same large-aperture antenna, the free-space loss test in a compact range test and a planar near-field test differs by at least more than 40 dB, which poses a great pressure on the radio frequency of the test system. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and solve the problem of testing the radiation pattern of a terahertz compact range antenna under high-precision resolution of an analog turntable.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A method for testing the radiation pattern of a terahertz compact range antenna includes:

[0008] Install the antenna to be tested and determine the relationship between the coordinate system of the antenna to be tested and the coordinate system of the site;

[0009] Control the turntable to rotate, obtain the far-field amplitude radiation pattern data and phase radiation pattern data of the antenna to be tested, and further obtain the complex electric field value;

[0010] Multiply the complex electric field value by an imaginary coefficient and then perform a fast Fourier transform to determine the radiation pattern coefficient;

[0011] The radiation pattern coefficient is extended, and then the inverse fast Fourier transform is performed to obtain the encrypted complex electric field value.

[0012] Preferably, after performing the fast Fourier transform on the complex electric field value, the sequence number of the radiation pattern coefficient is n, and the range of n is -N / 2 to N / 2. When extending the radiation pattern coefficient, (M - 1)*N / 2 zeros are added before -N / 2 and after N / 2 respectively, so that the range of n is extended to -M*N / 2 to M*N / 2.

[0013] Preferably, when obtaining the far-field amplitude radiation pattern data and phase radiation pattern data of the antenna under test, they are obtained separately according to different polarization directions.

[0014] Preferably, according to different polarization directions, the complex electric field values of different polarizations are obtained by using the far-field amplitude radiation pattern data and phase radiation pattern data of the antenna under test.

[0015] Preferably, according to different polarization directions, the corresponding radiation pattern coefficients are determined and the corresponding radiation pattern coefficient extension is performed.

[0016] Preferably, when obtaining the far-field amplitude radiation pattern data and phase radiation pattern data of the antenna under test, polarization conversion is completed by rotating the feed angle or reinstalling the feed.

[0017] Preferably, when rotating the feed angle, rotate 90 degrees clockwise facing the feed.

[0018] Preferably, when obtaining the far-field amplitude radiation pattern data and phase radiation pattern data of the antenna under test, the interval should be less than where is determined by the following formula:

[0019]

[0020] where k is the wave number corresponding to the test frequency, f is the test frequency, c is the speed of light in vacuum, the calculation result is an angle, π is the pi, and d is the maximum distance from the outermost edge of the antenna under test to the center of rotation of the turntable.

[0021] Preferably, the three axes of the coordinate system of the antenna under test and the site coordinate system are correspondingly parallel.

[0022] A terahertz compact range antenna radiation pattern test system includes a reflector, a feed, a feed turntable, an antenna under test turntable, a radio frequency instrument, and a test device;

[0023] The reflector converts the spherical electromagnetic wave emitted by the feed into a quasi-plane electromagnetic wave;

[0024] The feed turntable and the antenna under test turntable are respectively used to carry the feed and the antenna under test;

[0025] The test device is used to control the feed turntable, the antenna under test turntable, the feed, and the RF instrument; acquire, collect, and store test data;

[0026] The RF instrument is used for monitoring, processing, and collecting RF signals during wired transmission;

[0027] The said test system conducts tests by using the above-mentioned test method.

[0028] The present invention has the following beneficial effects compared with the prior art:

[0029] (1) The present invention utilizes ordinary compact range test equipment, without the need to add additional hardware devices, and only obtains higher-resolution pattern data through data processing and calculation, improving the test accuracy of the antenna.

[0030] (2) The encryption of the present invention belongs to lossless encryption, and the pattern obtained by actually increasing the sampling density can achieve a completely coincident effect, which is very different from ordinary numerical interpolation algorithms. In particular, for the null depth of the pattern, lossless restoration can be achieved.

[0031] (3) The technology of the present invention can not only be applied to the test results of the compact range pattern, but also be applied in the antenna far-field test system.

[0032] (4) The present invention is not only effective for one-dimensional patterns, but also can be similarly extended and applied to two-dimensional patterns.

[0033] (5) The present invention is not only effective for amplitude patterns, but also for phase patterns, and can complete interpolation without any special processing of the phase (the original winding state of the phase), which cannot be achieved by ordinary interpolation algorithms. Description of the Drawings

[0034] Figure 1 It is the flowchart of the method steps of the present invention;

[0035] Figure 2 It is the comparison diagram for verifying the algorithms of the co-polarization and cross-polarization amplitude patterns;

[0036] Figure 3 The comparison diagram for verifying the algorithm of the co-polarization phase pattern;

[0037] Figure 4 The comparison diagram for verifying the algorithm of the cross-polarization phase pattern. Detailed Embodiments

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will further describe the embodiments of the present invention in detail with reference to the drawings.

[0039] A terahertz compact range antenna pattern test method and system, including

[0040] The terahertz compact range consists of a reflecting surface, a feed, a feed turntable, a DUT (Device Under Test) antenna turntable, RF instruments, test software, etc. to form a test system. The reflecting surface converts the spherical electromagnetic wave emitted by the feed into a quasi-plane wave. The DUT antenna is placed on the DUT turntable and located within the quasi-plane wave. The feed is placed on the feed turntable. The RF system generates, transmits, and acquires electromagnetic wave signals in the required test frequency band, and the test software is responsible for coordinating each hardware for automated operation.

[0041] Generally, the turntable consists of three axes: azimuth, elevation, and polarization. In the plane formed by the azimuth rotation of the turntable (generally parallel to the ground), the direction perpendicular to the Z-axis is the X-axis, and the Y-axis is determined by the right-hand rule, which is the elevation of the turntable. The coordinate origin O is the intersection of the rotation centers of each axis.

[0042] Generally, field calibration is required for testing. Field calibration is to establish a definite relationship between the DUT antenna coordinate system and the field coordinate system or adjust them to be parallel to each other axis by axis. The adjustment process can be assisted by mechanical measuring devices such as theodolites and laser trackers.

[0043] The specific steps for testing the antenna in the compact range are as follows:

[0044] (1), Install the DUT antenna and perform field calibration according to the compact range test method to establish a compact range test environment;

[0045] (2), Set the scan range, sampling interval, and test frequency. The scan range is the range to be investigated corresponding to the antenna pattern; the sampling interval is the position density for collecting the antenna pattern, generally required to be no greater than one-tenth of the beam width. For example, if the beam width of the antenna pattern is 5 degrees, the sampling interval setting cannot be greater than 0.5 degrees. However, for the requirements of the algorithm of the present invention, the interval should also be less than Δθ max , where Δθ max is determined by the following formula.

[0046]

[0047] In the formula, k is the wave number corresponding to the test frequency, f is the test frequency, c is the speed of light in vacuum, d is the maximum distance from the outermost edge of the DUT antenna to the center of rotation of the turntable, and the calculation result is an angle; the test frequency is a typical frequency value within the nominal frequency working range of the antenna. These frequencies can be equally spaced or non-equally spaced. For example, when the antenna frequency range is 1.1 GHz to 1.46 GHz, it is a list of frequencies to be tested for this antenna, such as: 1.1 GHz, 1.2 GHz, 1.32 GHz, 1.4 GHz, 1.46 GHz, etc.;

[0048] (3), Perform the test of the first polarization of the DUT antenna.

[0049] (4) Rotate the transmitting feed by 90 degrees.

[0050] (5) Conduct the test of the second polarization of the antenna under test.

[0051] (6) Input the results or perform linear-circular polarization synthesis and output the results.

[0052] Generally, for the universality of the antenna test system, a single linear polarization feed is adopted in the compact range. When conducting antenna tests, two tests (for two polarizations) are carried out separately, and then the circular polarization pattern is obtained by synthesizing through data processing. The specific synthesis method is as follows:

[0053] Let the amplitude pattern collected for the first polarization be amH, the phase pattern be phH, the amplitude pattern collected for the second polarization be amV, and the phase pattern be phV. After circular polarization synthesis, the amplitude and phase patterns for right-handed rotation are am_R and ph_R, and the amplitude and phase patterns for left-handed rotation are am_L and ph_L.

[0054] First, both the amplitude and phase are converted to complex field strength representation.

[0055]

[0056]

[0057] Then, linear-circular polarization synthesis is carried out.

[0058]

[0059]

[0060] Finally, the complex field strength is further converted back to amplitude and phase representation.

[0061] am_R = 20log 10 (abs(ER))

[0062] am_L = 20log 10 (abs(EL))

[0063] ph_R = angle(ER) / π·180

[0064] ph_L = angle(EL) / π·180

[0065] Integrating the calculation process gives the following results.

[0066]

[0067]

[0068]

[0069]

[0070] where abs is for modulo value calculation, angle is for phase operation, and 20log 10 is for performing logarithm operation with base 10 and multiplying by 20.

[0071] According to the cylindrical near-field measurement theory, the far-field pattern can be expressed as the following formula:

[0072]

[0073] In the formula: is the electric field corresponding to point r, k is the wave number, e is the natural base, and are unit vectors representing directions, and d is the maximum distance from the outermost edge of the antenna under test to the center of rotation of the turntable.

[0074] The far-field pattern of the antenna can be expressed as the superposition of cylindrical waves. By measurement, the cylindrical wave coefficients are solved using the orthogonality of the vector function in the above formula, and thus the far-field pattern is obtained. Under the far-field conditions of an anechoic chamber, the two polarization components in the above formula are orthogonal and independent. At the same time, when calculating for a cross-section, kcosθ is a constant, and the compensation problem of the near-field test probe does not need to be considered. Therefore, the far-field pattern can be expressed in the form of cylindrical wave coefficients as the following formula:

[0075]

[0076]

[0077] In the formula is the electric field pattern of the polarization component, E θ is the electric field pattern of the θ polarization component, is the azimuth angle of the cylindrical coordinate system, corresponding to the azimuth angle of the azimuth turntable in the anechoic chamber, θ is the angle between the pitch direction of the cylindrical coordinate system and the vertical axis, k is the wave number, a n is the cylindrical wave coefficient corresponding to the n component, and b

[0078] As shown in the above formula, as long as the pattern coefficients are obtained, the pattern data at any position can be obtained, and the directivity coefficient is solved using the following formula.

[0079]

[0080]

[0081] The sampling interval should be less than where is determined by the following formula.

[0082]

[0083] In the formula, k is the wave number corresponding to the test frequency, f is the test frequency, c is the speed of light in vacuum, the calculation result is in degrees, and d is the maximum distance from the outermost edge of the antenna under test to the center of rotation of the turntable;

[0084] Based on the above principle analysis, the present invention proposes a method for testing the antenna pattern of a terahertz compact range, combined with Figure 1 The specific process is as follows:

[0085] (1) Install and calibrate the site for the antenna under test to establish a terahertz compact range test environment. Among them, the terahertz compact range consists of a reflector, a feed source, a feed source turntable, an antenna turntable under test, a radio frequency instrument, a test software, etc. to form a test system. The reflector converts the spherical electromagnetic wave emitted by the feed source into a quasi-plane electromagnetic wave, and the incoming wave direction is the Z axis. Generally, the turntable consists of three axes: azimuth, elevation, and polarization. The direction perpendicular to the Z axis in the plane formed by the azimuth rotation of the turntable (generally parallel to the ground) is the X axis, and the Y axis is determined by the right-hand rule as the elevation of the turntable. The coordinate origin O is the intersection of the rotation centers of each axis. The antenna under test is installed on the antenna turntable under test, and the site calibration is to establish a definite relationship between the coordinate system of the antenna under test and the site coordinate system or adjust it to be parallel to the corresponding three axes. Install the compact range feed source corresponding to the frequency on the compact range feed source turntable.

[0086] (2) Use the compact range test software to automatically rotate the turntable and control the radio frequency transmission signal while collecting and recording data, and complete the test of the first polarization pattern of the antenna under test point by point to obtain the far-field amplitude pattern data amH and phase pattern data phH of the first polarization.

[0087] (3) Rotate the compact range feed source or reinstall it to make it 90 degrees with the original polarization direction. If the original polarization is horizontal polarization and the rotated polarization is vertical polarization, note that the rotation direction is recommended to be clockwise facing the feed source for rotation.

[0088] (4) Refer to step (2) to conduct the second polarization test on the antenna under test to obtain the far-field amplitude pattern amV and phase pattern phV of the second polarization.

[0089] (5) Use the following formula to calculate the results obtained in (2) and (4) to obtain the corresponding complex electric field value.

[0090]

[0091]

[0092] In the formula, EH represents the complex electric field of the first polarization of the antenna, and j represents the complex number symbol. EV represents the complex electric field of the second polarization of the antenna. is the angular position corresponding to the radiation pattern.

[0093] The radiation pattern coefficient is calculated using the following formula.

[0094]

[0095]

[0096] In the formula, a n represents the radiation pattern coefficient corresponding to the electric field EH, and b n represents the radiation pattern coefficient corresponding to the electric field EV, and fft represents the fast Fourier transform. represents the angular value corresponding to the electric field during antenna testing. n represents the coefficient serial number. According to the principle of fast Fourier transform calculation, n and satisfy the following relationship, and the range of n is -N / 2 to N / 2, corresponding to to the maximum angle That is, n and have the same number N. have the same number N.

[0097] After obtaining the coefficients, the radiation pattern at any angle can be calculated using the following formula. However, calculating the radiation pattern at each position requires an integration, and the operation speed is slow. The present invention uses the method of virtually expanding the number of radiation pattern coefficients and performs fast calculation using the inverse fast Fourier transform.

[0098]

[0099]

[0100] On the left and right sides of the sequences a n and b n that is, in front of -N / 2 and behind N / 2, add (M - 1)*N / 2 zeros to make a n and b n sequences become A n and B n Then the range of this n is -M*N / 2 to M*N / 2.

[0101] Then, the electric field is recalculated using the following formula.

[0102]

[0103]

[0104] Where EH’ and EV’ are the encrypted electric fields, and ifft is the inverse transform of the fast Fourier transform.

[0105] amH′ = 20log 10 (abs(E′ H ))

[0106] amV′ = 20log 10 (abs(E′ V ))

[0107] phH′ = angle(E′ H ) / π·180

[0108] phV′ = angle(E′ V ) / π·180

[0109] abs is the operation of taking the modulus of a complex number.

[0110] angle is the operation of taking the phase angle of a complex number.

[0111] Then changes from the original interval to Thus, the purpose of pattern encryption is achieved.

[0112] (6) If it is a linearly polarized antenna, the result obtained in step (5) is the final pattern test result of the antenna under test. If it is a circularly polarized antenna, the result obtained in step (5) is used for linear-circular polarization synthesis to obtain the final pattern test result of the antenna under test.

[0113]

[0114]

[0115]

[0116]

[0117] In the formula:

[0118] am_R is the amplitude of the right-handed circular polarization after circular polarization synthesis.

[0119] am_L is the amplitude of the left-handed circular polarization after circular polarization synthesis.

[0120] ph_R is the phase of the right-handed circular polarization after circular polarization synthesis.

[0121] ph_L is the phase of the left-handed circular polarization after circular polarization synthesis.

[0122] abs is the operation of taking the modulus of a complex number.

[0123] The "angle" operation is to take the phase angle of a complex number.

[0124] "j" is the complex number symbol j 2 = -1

[0125] "π" is the pi value of 3.1415926.

[0126] The above method of the present invention details the encryption of the one-dimensional pattern. For the two-dimensional pattern, only by encrypting each one-dimensional pattern in each dimension of the two-dimensional pattern using the method of the present invention can a two-dimensional encrypted pattern be obtained, which will not be elaborated here. Figure 2 It is a comparison diagram for verifying the algorithm of the co-polarization and cross-polarization amplitude patterns; where the solid line is the pattern after encryption by the method of the present invention, the star points are the results of the coarsely sampled patterns, and the dashed line is the result of the actually densely sampled pattern. It can be seen from the results that whether it is the co-polarization or cross-polarization amplitude pattern, the coincidence degree after encryption with the actual encrypted sampling is very high, verifying the effectiveness of the present invention. Figure 3 It is a comparison diagram for verifying the algorithm of the co-polarization phase pattern; where the solid line is the pattern after encryption by the method of the present invention, the star points are the results of the coarsely sampled patterns, and the dashed line is the result of the actually densely sampled pattern. It can be seen from the results that the co-polarization phase pattern also has a very high coincidence degree with the actual encrypted sampling after being encrypted by the method of the present invention, verifying the effectiveness of the present invention for encrypting the phase pattern. Figure 4 It is a comparison diagram for verifying the algorithm of the co-cross-polarization phase pattern. Figure 3 The same as above, for the cross-polarization phase with lower energy, the present invention is still effective.

[0127] The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

[0128] Although the present invention has been disclosed above with preferred embodiments, it is not used to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modification, equivalent change, and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention all belong to the protection scope of the technical solution of the present invention.

Claims

1. A method for testing the antenna pattern of a terahertz compact range, characterized in that, Including: Install the antenna under test and determine the relationship between the coordinate system of the antenna under test and the site coordinate system; Control the turntable to rotate, obtain the far-field amplitude pattern data and phase pattern data of the antenna under test, and further obtain the complex electric field value; Multiply the complex electric field value by an imaginary coefficient and then perform a fast Fourier transform to determine the pattern coefficient; Expand the pattern coefficient and then perform the inverse transform of the fast Fourier transform to obtain the encrypted complex electric field value; The specific process is as follows: (1) Install and calibrate the site for the antenna under test to establish a terahertz compact range test environment; determine the relationship between the coordinate system of the antenna under test and the site coordinate system; (2) Rotate the turntable and control the RF transmission signal while performing data acquisition and recording, and complete the test of the first polarization pattern of the antenna under test point by point to obtain the far-field amplitude pattern data amH and phase pattern data phH of the first polarization; (3) Rotate the compact range feed or reinstall it to make it 90 degrees with the original polarization direction; (4) Referring to step (2), perform the second polarization test on the antenna under test to obtain the far-field amplitude pattern amV and phase pattern phV of the second polarization; (5) Use the following formula to perform operations on the results obtained in (2) and (4) to obtain the corresponding complex electric field value; Where, E H represents the complex electric field of the first polarization of the antenna, j represents the complex number symbol, E V represents the complex electric field of the second polarization of the antenna, π is the pi, is the angular position corresponding to the radiation pattern; Use the following formula to calculate the pattern coefficient: Where a n represents the pattern coefficient corresponding to the electric field E H and b n represents the pattern coefficient corresponding to the electric field E V ; fft represents the fast Fourier transform, n represents the coefficient sequence number. According to the principle of the fast Fourier transform calculation, n and satisfy the following relationship, and the range of n is -N / 2 to N / 2, corresponding to the to the maximum angle That is, n and have the same number N; Adopt the method of virtually expanding the number of pattern coefficients and use the inverse transform of the fast Fourier transform for fast calculation; At both sides of sequences a n and b n , that is, adding (M - 1)*N / 2 zeros at the front side of -N / 2 and the back side of N / 2, making a n and b n sequences become A n and B n , then the range of this n is -M*N / 2 to M*N / 2; Through the following formula, recalculate the electric field; where E H ’ and E V ’ are the encrypted electric fields, and ifft is the inverse transform of the fast Fourier transform.

2. The test method according to claim 1, wherein When rotating the feed angle, rotate 90 degrees clockwise facing the feed.

3. The test method according to claim 1 or 2, characterized in that When obtaining the far-field amplitude pattern data and phase pattern data of the antenna under test, the interval should be less than where is determined by the following formula: where k is the wave number corresponding to the test frequency, f is the test frequency, c is the speed of light in vacuum, the calculation result is in degrees, and d is the maximum distance from the outermost edge of the antenna under test to the center of rotation of the turntable.

4. The test method according to claim 1 or 2, characterized in that The three axes of the coordinate system of the antenna under test and the site coordinate system are correspondingly parallel.

5. A terahertz compact range antenna pattern test system, characterized in that, Including a reflector, a feed, a feed turntable, an antenna under test turntable, RF instruments, and a test device; The reflector converts the spherical electromagnetic wave emitted by the feed into a quasi-plane electromagnetic wave; The feed turntable and the antenna under test turntable are respectively used to carry the feed and the antenna under test; The test device is used to control the feed turntable, the antenna under test turntable, the feed, and the RF instruments; Obtain test data acquisition and storage; The RF instruments are used for monitoring, processing, and acquisition of RF signals under wired transmission; The said test system performs tests using the test method described in claim 1 or 2.

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