A method for off-center distance determination for far field spectral domain filtering

Abstract

The application discloses a kind of eccentric distance determination methods for far-field spectral domain filtering, specifically includes: obtaining the directional diagram data including environmental interference signal by far-field test;Directional diagram data is carried out spectral domain filtering processing, and directional diagram is reconstructed using retained main signal;By control variable method, the minimum offset distance required under different antenna size and different interference angle is analyzed;By fitting analysis, the relationship between offset distance and interference angle and antenna size is obtained, to determine the required offset distance;The accuracy of the relationship obtained is verified by bringing the relationship into another scene.The application first establishes the functional relationship of the minimum offset distance required by spectral domain filtering, and quickly determines the required minimum offset distance by antenna size and interference source angle;It is suitable for different types of antennas and has wide application value;Since the minimum offset distance is established, it provides guidance for the experiment, and the offset distance is shortened as much as possible under the premise that the interference can be offset, to reduce the number of sampling points.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless communication, and particularly relates to a method for determining eccentric distance for far-field spectral domain filtering. BACKGROUND

[0002] Antenna measurement is an indispensable part of antenna research and development. The radiation pattern reflects the antenna's radiation characteristics in space angle and is an important index for measuring the antenna's directional performance. Far-field measurement can obtain the antenna's far-field radiation pattern using simple test equipment and can provide one-dimensional radiation pattern cutting to minimize the measurement time and reduce the measurement complexity. However, there is a recognized disadvantage in directly measuring the antenna's radiation pattern, that is, the multipath effect will reduce the accuracy of the measurement results, and the multipath reflection is mainly caused by the aging of the absorbing material in the anechoic chamber and the bare part of the antenna turntable. The application of spectral domain filtering to filter out the interference of the multipath effect has been verified in the existing results, but the offset distance required by the AUT in the far-field spectral domain filtering has not been clearly specified, and the offset will directly affect the filtering accuracy and the measurement efficiency. When the offset is insufficient, the interference in the spectral domain cannot be separated; when the offset is too large, the number of sampling points will increase, thereby reducing the test efficiency. The determination of the offset distance is a key step in spectral domain filtering, but the existing solutions are mostly direct experience values, and there is no universal formula for the offset distance. SUMMARY

[0003] In order to overcome the above problems in the prior art, the present application provides a method for determining the eccentric distance for far-field spectral domain filtering.

[0004] The technical scheme adopted by the present application to solve the technical problems is: a method for determining the eccentric distance for far-field spectral domain filtering, comprising the following calculation steps:

[0005] Step 1: obtaining the radiation pattern data containing the environmental interference signal through far-field test;

[0006] Step 2: performing spectral domain filtering processing on the radiation pattern data obtained in step 1, and reconstructing the radiation pattern using the reserved main signal;

[0007] Step 3: analyzing the minimum offset distance required under different antenna sizes and different interference angles by the control variable method;

[0008] Step 4: obtaining the relationship between the offset distance and the interference angle and the antenna size through fitting analysis, and determining the required offset distance;

[0009] Step 5: bringing the relationship obtained in step 4 into another scene to verify the accuracy of the obtained relationship.

[0010] The eccentric distance determination method for far field spectral domain filtering, the relationship between the offset distance obtained in step 4 and the interference angle and the antenna size is as follows:

[0011]

[0012] Wherein, alpha is the interference offset angle, L is the antenna offset distance, and R is the antenna aperture radius.

[0013] The eccentric distance determination method for far field spectral domain filtering, the spectral domain filtering process in step 2 specifically includes:

[0014] Step 2.1, determining the offset according to the antenna aperture and the interference source angle;

[0015] Step 2.2, inputting the single-frequency point pattern data of the antenna to be measured after offset;

[0016] Step 2.3, transforming the near-far field pattern to obtain the far field pattern;

[0017] Step 2.4, differentiating the phase to translate the antenna limit center back to the rotation center;

[0018] Step 2.5, inverse Fourier transform to obtain the spectral domain mode coefficient;

[0019] Step 2.6, filtering out the high-order mode coefficient to retain the main signal;

[0020] Step 2.7, Fourier transform of the spectral domain data to reconstruct the far field pattern.

[0021] The eccentric distance determination method for far field spectral domain filtering, the single-frequency point pattern data in step 2.2 is processed by a fast Fourier algorithm to obtain spectral domain data.

[0022] The eccentric distance determination method for far field spectral domain filtering, the specific process of obtaining the far field pattern by near-far field pattern transformation in step 2.3 is as follows: according to the knowledge of cylindrical near-far field transformation, the calculation relationship of mode coefficients a n and b n is as follows:

[0023]

[0024]

[0025]

[0026]

[0027] Wherein, E z represents the component of the far field test field strength, denotes a n intermediate quantity, I z denotes b n intermediate quantity, p0 is the measurement radius, n denotes the order, j denotes the imaginary unit, k z =k0*cos theta, k0 denotes the free space wave number, p, and Z denote cylindrical coordinate system components, is the second kind Bessel function, in the far field, the second kind Bessel function has the following approximate expression:

[0028]

[0029] wherein,

[0030] The far field pattern can be obtained by simple summation of the mode coefficients, and each component is as follows:

[0031]

[0032]

[0033] E r =0

[0034] wherein theta, r, Phi denote spherical coordinate system components, E θ , E Φ , E r denote far zone radiation field strength components;

[0035] E θ , The two calculation formulas can be obtained by one-dimensional inverse Fourier transform, the maximum mode coefficient N is given by the following formula, the value of the sampling number needs to be greater than N, ceil denotes the function of rounding to the nearest integer to positive infinity, k0 denotes the free space wave number, a denotes the minimum cylindrical radius surrounding the antenna, n1 denotes the margin.

[0036] N=ceil(k0a)+n1

[0037] The above-mentioned eccentric distance determination method for far field spectral domain filtering, the step 2.4 shifts the antenna phase center back to the rotation center using the following formula:

[0038]

[0039] wherein, is the vector from the center of the measurement scanning surface to the center of the antenna aperture, is a unit vector, E1 denotes the far zone radiation field after differential phase change, E0 denotes the far zone radiation field obtained by near-far field transformation.

[0040] The eccentric distance determination method for far field spectral domain filtering, the high order mode coefficient n to be filtered out in step 2.6 is determined by the following formula:

[0041] n > k0r0

[0042] Wherein, r0 represents the minimum cylindrical radius surrounding the antenna.

[0043] The eccentric distance determination method for far field spectral domain filtering, the far field directional diagram is reconstructed by the following formula in step 2.7:

[0044]

[0045] Wherein, θ, r, Φ represent the spherical coordinate system components, E θ , E Φ , E r represent the far field radiation field strength components, b n ', a n ' represent the filtered mode coefficients.

[0046] The beneficial effects of the present application are that the present application firstly establishes the function relationship of the minimum offset distance required by spectral domain filtering, and quickly determines the required minimum offset distance through the antenna size and the interference source angle; the rule is suitable for different types of antennas and has wide application value; since the minimum offset distance is established, guidance is provided for experiments, and the offset distance is shortened as much as possible under the premise that the interference can be offset, so as to reduce the number of sampling points. BRIEF DESCRIPTION OF DRAWINGS

[0047] The present application is further illustrated below in combination with the drawings and examples.

[0048] Figure 1 The spectral domain filtering flowchart in the embodiment of the present application is shown in the figure;

[0049] Figure 2 The array antenna simulation model schematic diagram in the embodiment of the present application is shown in the figure;

[0050] Figure 3 The directional diagram data graph with or without metal plate interference in the embodiment of the present application is shown in the figure;

[0051] Figure 4 The spectral domain data with or without metal plate interference in the embodiment of the present application is shown in the figure;

[0052] Figure 5 The spectral domain filtering directional diagram of metal plate interference in the embodiment of the present application is shown in the figure;

[0053] Figure 6 The full wave simulation model in the embodiment of the present application is shown in the figure;

[0054] Figure 7 The metal plate interference spectrum domain data obtained by the full-wave simulation model in the embodiment of the application;

[0055] Figure 8 The metal plate interference spectrum domain filter pattern obtained by the full-wave simulation model in the embodiment of the application. DETAILED DESCRIPTION

[0056] In order for those skilled in the art to better understand the technical solutions of the application, the application will be described in detail below with reference to the drawings and specific embodiments.

[0057] The embodiment discloses a method for determining an eccentric distance for far-field spectrum domain filtering, comprising the following calculation steps:

[0058] Step 1: Obtain the pattern data containing the environmental interference signals by far-field testing;

[0059] Step 2: Perform spectrum domain filtering processing on the pattern data obtained in step 1, and reconstruct the pattern by using the reserved main signals;

[0060] Step 3: Analyze the minimum offset distance required under different antenna sizes and different interference angles by using the control variable method;

[0061] Step 4: Obtain the relationship between the offset distance and the interference angle and the antenna size by fitting analysis as follows:

[0062]

[0063] Wherein, α is the interference offset angle, L is the antenna offset distance, and R is the antenna aperture radius;

[0064] Step 5: Verify the accuracy of the relationship obtained in step 4 by bringing it into another scene.

[0065] In the embodiment, as shown in FIG. 1, the spectrum domain filtering processing in step 2 specifically comprises: Figure 1

[0066] When measuring in a darkroom, the test turntable drives the antenna under test (AUT) to rotate, samples according to fixed angle intervals, and measures the radiation field intensity at each angle, so as to obtain the antenna pattern. The minimum measurement distance between the test antenna and the antenna under test should satisfy:

[0067] F≥2D 2 / λ

[0068] Wherein, F is the distance between the test antenna and the antenna under test (m), D is the aperture of the antenna under test (m), and λ is the wavelength of the test frequency (m).

[0069] ​Spectral domain filtering was originally applied in near-field testing and was proven to be effective in suppressing multipath effects in one-dimensional far-field measurements. Pattern filtering is a filtering technique that processes frequency domain far-field data by using fast Fourier transform (FFT) algorithm, which converts single frequency point pattern data into spectral domain data for filtering, and then restores the filtered spectral domain data to obtain the pattern data without interference. In theory, this technique is applicable to various types of antennas.

[0070] In antenna testing, the number of wave spectra of a finite aperture antenna is related to the aperture size and the spatial scanning interval, as shown in equation (1), δ is the scanning interval, N max is the maximum number of wave spectra, a is the minimum spherical (or cylindrical) radius enclosing the antenna. In the measurement process, spectral domain filtering adopts a different measurement strategy from the conventional method, that is, the antenna is artificially offset from the rotation center, and a higher resolution scan is used to obtain the distribution of a larger range of aperture fields. Since the spatial region occupied by the antenna is limited, and the multiple scattering caused by various scatterers in the anechoic chamber is basically not limited in space, and the mode coefficients (and fields) associated with the antenna and the mode coefficients (and fields) associated with other scatterers are orthogonalized, the scattering interference can be effectively filtered out.

[0071]

[0072] Assuming that the far-field test field strength is used as a component E z , the calculation relationship of mode coefficients a n , b n is shown in equations (2), (3), (4), and (5),

[0073]

[0074]

[0075]

[0076]

[0077] wherein ρ0 is the measurement radius, and z respectively represent the cylindrical coordinate components, is the second kind of Bessel function, and in the far field, the second kind of Bessel function has an approximation as shown in equation (6),

[0078]

[0079] The far-field pattern can be obtained by simply summing the mode coefficients, and each component is shown in equations (7), (8), and (9),

[0080]

[0081]

[0082] E r = 0 (9)

[0083] Here, the formula (7) and (8) can be obtained by one-dimensional inverse Fourier transform, the maximum mode coefficient N is given by formula (1), the sampling number needs to be greater than N, ceil is a function of rounding to the nearest integer to positive infinity, k0 is the free space wave number, a is the minimum cylindrical radius surrounding the antenna, and n1 includes a margin of n1 which can be 10.

[0084] N = ceil(k0a) + n1 (1)

[0085] Since the spectral domain analysis measurement technology artificially moves the test antenna away from the rotation center, it leads to the increase of the minimum cylindrical radius a surrounding the antenna, and more mode coefficients are needed to represent the field, thereby leading to the decrease of the angular sample spacing and the increase of the amount of measurement data to be collected. After obtaining the far-field pattern, the antenna needs to be mathematically transformed to the origin of the coordinate system by differential phase transformation, as shown in formula (11), wherein, is the vector from the center of the measurement scanning surface to the center of the antenna aperture, is the unit vector.

[0086]

[0087] The differential phase transformation is to mathematically transform the antenna to the center of the measurement coordinate system, which is equivalent to converting the minimum cylindrical radius surrounding the antenna to the conceptual minimum value, and the number of mode coefficients needed to represent the antenna radiation field can be reduced accordingly. The equivalent cylindrical mode coefficients of the antenna can be obtained by the inversion of formula (7) and (8), as shown in formula (12) and (13), which can be numerically calculated by using one-dimensional inverse FFT,

[0088]

[0089]

[0090] After the antenna is restored to the ideal central position, the mode coefficients of the field outside the minimum cylindrical surface surrounding the antenna can be filtered out, that is, the mode coefficients irrelevant to the antenna are filtered out. The high-order mode coefficient n to be filtered out is determined by formula (14), and finally the filtered mode coefficients are used to reconstruct the far-field pattern by formula (7) and (8).

[0091] n > k0r0 (14)

[0092] Wherein, r0 represents the minimum cylindrical radius surrounding the antenna.

[0093] Firstly, the effect of spectral domain filtering in far-field test is verified. A simulation scene is constructed by using matlab as shown in Figure 2 The ideal point source 9-element array antenna is selected as the antenna under test, and the interval between the array elements is 30 mm. A reflectivity of 0.4 reflecting plate is placed on the side of the direct diameter to simulate the reflected interference, the interference angle θ is 45°, the direct diameter distance is measured as 8 m, the rotation center is located at the rear side of the antenna under test 0.6 m, the antenna under test is rotated by one degree for sampling, and the pattern data from-90° to 90° is collected at 3.3 GHz as the original data. The pattern data without the reflecting plate under the same conditions is used as the ideal data.

[0094] The simulation pattern information is shown in Figure 3 It can be observed that the original data has obvious interference. According to the spectral domain analysis method, the far-field pattern data is shifted to the spectral domain, and the spectral domain image is shown in Figure 4 By comparing the spectral domain data with and without the metal plate interference, it can be observed that most of the interference caused by the metal plate has been separated out.

[0095] The main signal around the narrow band of the spectral domain data n=0 is reserved, and the remaining interference signals are filtered, and then the pattern is reconstructed by the reserved main signal. After spectral domain analysis, the filtered pattern data is compared with the original pattern data and the ideal array antenna pattern data as shown in Figure 5 By comparing the ideal data with the spectral domain filtered data, it can be clearly found that the pattern data after spectral domain filtering is restored to the ideal state, and the two have high consistency. It is proved by simulation means that the spectral domain filtering method has significant effect in suppressing multipath signal interference.

[0096] In order to further analyze how to determine the offset distance, the simulation scene shown in Figure 2 is still used. By modifying the matlab program, the number of array elements, the distance of the reflecting plate, the direct distance and the frequency are changed to determine the required minimum offset distance. The control variable method is used to analyze the influence of different factors on the offset distance, and finally the relationship between the offset distance and the interference angle and the antenna radius is obtained:

[0097]

[0098] Wherein, α is the interference offset angle, L is the antenna offset distance, and R is the antenna aperture radius.

[0099] In order to verify the correctness of the fitting formula, a simulation scene is constructed as shown in Figure 6As shown, using full-wave simulation, the antenna under test is a horn antenna with an aperture of 138 mm x 107 mm, a 200 mm x 200 mm metal plate is placed 1.5 m away from the center side of the aperture to simulate the reflection interference, the direct distance measurement is 3 m, the -90° to 90° pattern data at 10 GHz is collected as the original data, and the pattern data without the reflection plate under the same conditions is taken as the ideal data.

[0100] According to formula (15), the offset distance is 182.66 mm, the actual simulation uses an offset distance of 185 mm, and the spectral domain image obtained by data processing in the same way is as shown in Figure 7 As shown, it can be seen that most of the interference has been successfully separated, and the filtered pattern data is compared with the original pattern data and the ideal horn antenna pattern data as shown in Figure 8 As shown, it can be found that the pattern data after spectral domain analysis and filtering is ideally recovered, which shows that the conclusion obtained from the array antenna is still applicable to the horn antenna, and proves the correctness of formula (1).

[0101] The above examples are only exemplary embodiments of the present application and are not used to limit the present application, the protection scope of the present application is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present application within the spirit and protection scope of the present application, and such modifications or equivalent replacements shall also be considered to fall within the protection scope of the present application.

Claims

1. A method for off-center distance determination for far field spectral domain filtering, characterized in that, The method comprises the following calculation steps: Step 1, obtain the directional diagram data including environmental interference signals through far-field test; Step 2, perform spectral domain filtering processing on the directional diagram data obtained in step 1, and reconstruct the directional diagram by using the reserved main signal; Step 3, analyze the minimum offset distance required under different antenna sizes and different interference angles by using the control variable method; Step 4, obtain the relationship between the offset distance and the interference angle and the antenna size by fitting analysis, and determine the required offset distance; Step 5, bring the relationship obtained in step 4 into another scene to verify the accuracy of the obtained relationship.

2. The method for determining the off-center distance for far field spectral filtering according to claim 1, wherein, The relationship between the offset distance and the interference angle and the antenna size obtained in step 4 is as follows: ; Wherein, α is the interference offset angle, L is the antenna offset distance, and R is the antenna aperture radius.

3. The method for determining the off-center distance for far field spectral filtering according to claim 1, wherein, The spectral domain filtering processing in step 2 specifically comprises: Step 2.1, determine the offset according to the antenna aperture and the interference source angle; Step 2.2, input the single-frequency directional diagram data of the antenna after offset; Step 2.3, obtain the far-field directional diagram through near-far-field directional diagram transformation; Step 2.4, shift the antenna limit center to the rotation center through differential phase change; Step 2.5, obtain the spectral domain mode coefficient through inverse Fourier transform; Step 2.6, filter out the high-order mode coefficient to reserve the main signal; Step 2.7, reconstruct the far-field directional diagram through spectral domain data Fourier transform.

4. The method for determining the off-center distance for far field spectral filtering according to claim 3, wherein, The spectral domain data is obtained through the single-frequency directional diagram data by using the fast Fourier algorithm in step 2.

2.

5. The method for determining the off-center distance for far field spectral filtering according to claim 3, wherein, The specific process of obtaining the far-field pattern by the near-far-field pattern transformation in step 2.3 is as follows: according to the knowledge of the cylindrical near-far-field transformation, the calculation relationship of the mode coefficients a n , b n is as follows: ； ； ； ； wherein , represents a component of the far field test field strength, represents an intermediate quantity for a n , represents an intermediate quantity for b n , is the measurement radius, n represents the order, and j represents the imaginary unit, , represents the free space wave number, , , represents the cylindrical coordinate system component, is the second kind Bessel function, which in the far field has the following approximation: ； wherein ; The far-field directional diagram can be obtained through simple summation of the mode coefficients, and each component is as follows: ； ； ； where , r, denotes the spherical coordinate system component, , , denotes the far zone radiation field component; , The two calculation formulas are obtained by one-dimensional inverse Fourier transform, the maximum mode coefficient N is given by the following formula, and the sampling number is greater than N. ； denotes a function that rounds to the nearest integer toward positive infinity, denotes the free space wave number, denotes the smallest cylindrical radius enclosing the antenna, denotes a margin.

6. The method for determining the off-center distance for far field spectral filtering according to claim 3, wherein, The antenna phase center is shifted back to the rotation center in step 2.4 by using the following formula: ； wherein, is a vector pointing from the center of the measurement scan to the center of the antenna aperture, is a unit vector, denotes the far zone radiation field after differential phase change, denotes the far zone radiation field obtained by near-far field transformation.

7. The method for determining the off-center distance for far field spectral filtering according to claim 3, wherein, When filtering out the high-order mode coefficient in step 2.6, the high-order mode coefficient n to be filtered out is determined by the following formula: ； Wherein, r0 represents the minimum cylindrical radius surrounding the antenna.

8. The method for determining the off-center distance for far field spectral filtering of claim 3, wherein, The far-field directional diagram is reconstructed by using the following formula in step 2.7: ； ； ； wherein , r, denotes a spherical coordinate system component, , , denotes a far zone radiation field component, , denotes a filtered mode coefficient.

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