Antenna spherical near-field measurement method based on non-redundant uniform spherical sampling

Abstract

The invention discloses an antenna spherical near-field measurement method based on non-redundant uniform spherical sampling, and particularly relates to the field of antenna measurement. The method comprises the following steps: determining a minimum sampling distance; generating sampling point positions based on a spherical uniform point generation algorithm; measuring the positions of the sampling points, and measuring E theta and E phi of the radiation field of the antenna to be measured corresponding to signals received by the probe respectively; obtaining Ex, Ey and Ez components based on vector transformation; calculating E 'theta and E' phi at equal angle intervals corresponding to the Ex ', Ey' and Ez 'components at equal angle intervals based on a spherical harmonic function; and calculating far-field radiation parameters of the antenna according to equal-interval sampling. According to the technical scheme, the problems that when theta is close to 0 degree or 180 degrees, sampling measurement points in the phi direction are too many, redundant information is generated, and the measurement efficiency is affected are solved, and the measurement time is shortened.

Description

Technical Field

[0001] The invention relates to the field of antenna measurement, and in particular to an antenna spherical near-field measurement method based on non-redundant uniform spherical sampling. Background Art

[0002] In the development of antenna measurement technology, near-field measurement technology has gradually occupied an important position with its unique advantages. Especially in the context of complex electromagnetic environments and high-precision measurement requirements, near-field measurement technology has become a key means of antenna performance evaluation and optimization with its high security, strong anti-interference ability, and high measurement accuracy. Among them, spherical near-field measurement technology, as a measurement method that can fully cover the antenna radiation near-field area, has received widespread attention.

[0003] However, the traditional spherical near-field measurement method is to place the antenna to be tested in the measurement sphere, and the rotating motor drives the antenna to be tested or the probe to rotate, and the electromagnetic field emitted by the antenna to be tested is scanned at angles such as pitch angle θ and azimuth angle φ. When the pitch angle θ is close to 0° or 180°, the number of sampling measurement points in the azimuth angle φ direction is too large, generating redundant information and affecting the measurement efficiency. In order to overcome this problem, the antenna spherical near-field measurement algorithm based on non-redundant uniform spherical sampling came into being. Summary of the invention

[0004] The present invention aims to provide an antenna spherical near-field measurement method based on non-redundant uniform spherical sampling, which solves the problem in the traditional spherical near-field measurement method that when the pitch angle θ is close to 0° or 180°, the number of sampling measurement points in the azimuth angle φ direction is too large, which generates redundant information and affects the measurement efficiency.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows: a method for measuring the spherical near field of an antenna based on non-redundant uniform spherical sampling comprises the following steps:

[0006] S1. Determine the minimum sampling distance according to the antenna operating frequency and sampling radius;

[0007] S2, generating spherical sampling point position information based on an arbitrary spherical uniform point generation algorithm;

[0008] S3. Use the probe to measure the sampling point position, and measure the E of the radiation field of the antenna to be measured corresponding to the signal received by the probe. θ and E φ Quantity;

[0009] S4, based on vector transformation to obtain the sampling point position E x 、E y and E z The measurement signal corresponding to the component;

[0010] S5. Calculation of E′ at equal angle intervals based on spherical harmonics x , E′ y and E′ z E' corresponding to the equal angle intervals of the components θ and E′ φ ;

[0011] S6. Calculate the far-field radiation parameters of the antenna using a near-far-field transformation algorithm with equally spaced sampling.

[0012] Furthermore, in step S1, the method for confirming the number of sampling points is as follows:

[0013] S1.1. Determine the highest order N of the spherical wave mode according to the operating frequency and sampling radius:

[0014] N=[kr t ]+10;

[0015] Where k = 2π / λ is the wave number, λ is the wavelength, r t is the radius of the smallest sphere enclosing the measuring antenna;

[0016] S1.2. Determine the number of sampling points required. To ensure the calculation accuracy, the number of sampling points should be close to or greater than N1:

[0017] N 1 =2N(N+2).

[0018] Furthermore, in step S4, the near field measurement is usually performed in the radiation near field of the antenna, E r The distance attenuation of the component is much greater than E θ and E φ , so E is ignored r =0, the transformation matrix T is

[0019]

[0020] Further, the method of step S6 is as follows: Based on the spherical near-field and far-field transformation algorithm, the E′ at equal angle intervals is known. θ and E′ φ Components, corresponding to w′(χ=0°) and w′(χ=90°) in the formula, and then spherical wave analysis is performed to solve the spherical wave expansion coefficient T smn , and finally the far-field antenna parameters can be calculated:

[0021]

[0022] Compared with the prior art, this solution has the following beneficial effects:

[0023] Compared with the traditional equal-angle interval θ and φ sampling, the sampling points in this scheme are more evenly distributed and the number of sampling points is greatly reduced, thereby shortening the measurement time while ensuring the calculation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a sampling point position information diagram obtained by the non-redundant uniform sampling measurement method in the embodiment;

[0025] Figure 2 is a spherical sampling point position information diagram obtained by the equal-angle interval sampling measurement method in the embodiment;

[0026] Figure 3 is a structural diagram of a K-band standard gain antenna in an embodiment;

[0027] Figure 4 is the sampling angle E in the embodiment θ and E φ Amplitude and phase distribution diagrams of components;

[0028] Figure 5 is the non-redundant uniform sampling in the embodiment. θ and E φ Amplitude and phase distribution of the components.

[0029] Figure 6 is a comparison diagram of antenna far-field directions calculated by different sampling methods in the embodiment;

[0030] Figure 7 is the antenna pattern obtained by sampling at equal angle intervals in the embodiment. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below through specific embodiments:

[0032] Example

[0033] The antenna spherical near-field measurement method based on non-redundant uniform spherical sampling includes the following steps:

[0034] S1. Determine the number of sampling points according to the antenna operating frequency and sampling radius A.

[0035] In step S1, the method for confirming the number of sampling points is as follows:

[0036] S1.1. Determine the highest order N of the spherical wave mode according to the operating frequency and sampling radius:

[0037] N=[kr t ]+10;

[0038] Where k = 2π / λ is the wave number, λ is the wavelength, r tis the radius of the smallest sphere enclosing the measurement antenna.

[0039] S1.2, to solve the spherical wave decomposition coefficient T in the formula w′(A, χ, θ, φ) smn , determine the number of sampling points required. To ensure the calculation accuracy, the number of sampling points should be close to or greater than N 1 :

[0040] N 1 =2N(N+2).

[0041] When sampling at equal angle intervals, the sampling measurements in the azimuth angle φ are redundant when the elevation angle θ is close to 0° or 180°. smn , the actual number of sampling points is 2(2N+1)(N+1), which is much larger than the number of sampling points N required for uniform sampling. 1 .

[0042] In this embodiment, it is assumed that at the spherical coordinate (A, θ, φ), the instrument measurement value is w(A, χ, θ, φ), χ is the rotation direction of the probe, usually χ = 0° corresponds to E θ , χ=90°corresponds to E φ .

[0043] S2, such as Figure 1 As shown, based on any spherical uniform point generation algorithm (for example, using a particle-based sampling method to generate spherical uniform points), N is calculated and generated. 1 The spherical coordinate position information of the spherical sampling points.

[0044] S3, through the vector network analyzer N 1 The measurement is carried out at the sampling point position to obtain the received signals w(A, 0°, θ, φ) and w(A, 90°, θ, φ), which correspond to the E of the radiation field of the antenna to be measured. θ and E φ Component, thus achieving E θ and E φ Obtaining the quantity.

[0045] S4, N obtained based on vector transformation 1 E at the sampling point x , E y and E z The measured signal corresponding to the component:

[0046]

[0047] Among them, E θ and E φ is the measurement result of the spherical coordinates θ and φ, w r(A, θ, φ) is the signal corresponding to the normal component of the sampling point (A, θ, φ); E r is the normal component; near-field measurements are usually performed in the radiation near field of the antenna, E r The distance attenuation of the component is much greater than E θ and E φ , so ignore it and let E r =0 (i.e. w r (A, θ, φ) = 0), the transformation matrix T is:

[0048]

[0049] S5. Since the spherical near-field and far-field transformation algorithm requires data at equal angle intervals as input, the spherical harmonic function (i.e. where f lm is the expansion coefficient, which can be calculated by the function value on the sphere and the orthogonality of the spherical harmonic function) After calculation, the E′ with equal angle intervals is obtained x , E′ y and E′ z The received signal w′ corresponding to the component x (A,θ,φ),w′ y (A, θ, φ) and w′ z (A, θ, φ), and transform to obtain E′ with equal angle intervals θ and E′ φ ,Right now Where E′ x , E′ y , E′ z Components refer to the electric field components along the x, y, and z axes in the rectangular coordinate system. is the spherical coordinate electric field component.

[0050] S6, based on the spherical near-field and far-field transformation algorithm, the E′ at equal angle intervals is known θ and E′ φ Components, corresponding to w′(χ=0°) and w′(χ=90°) in the formula, and then spherical wave analysis is performed to solve the spherical wave expansion coefficient T smn , and finally the far-field antenna parameters can be calculated:

[0051]

[0052] Where A is the radius of the measuring sphere. v is the transmitting signal of the antenna under test. X is the rotation angle of the probe. represents the rotation coefficient of the spherical basis function. smnis the antenna transmission coefficient. The parameters (s, m, n) are constrained to be s = 1, 2, m = -N, ..., 0, ..., N, and n = |m|, ..., N, where N is the number of spherical basis functions used, given by N = [kr t ]+10, where [x] represents the nearest integer to x, r t is the radius of the smallest sphere of the antenna, P sμn (kA) is the response coefficient of the probe to spherical waves of mode (s, μ, n).

[0053] Case display:

[0054] In this case, a simulated K-band rectangular standard gain horn antenna is used, the operating frequency is 18GHz, and the waveguide model is WR-42. The geometric parameters of the antenna are as follows Figure 3 and Table 1 below:

[0055] Table 1:

[0056] parameter Dimensions (mm) W 104.6 H 79.2 L1 190.0

[0057] Equal angle interval sampling measurement method:

[0058] like Figure 2 As shown in the figure, it can be seen that near the upper and lower poles of the sphere, the sampling points are dense and there is a lot of redundancy. In the spherical near-field sampling, for the rotation angle χ of the probe, χ=0° and χ=90° are usually selected, corresponding to the θ and φ components of the radiation field of the antenna to be measured, that is, for the electric field probe, χ=0° usually corresponds to E θ , χ=90°corresponds to E φ . This means that the entire sphere needs to be scanned twice. The value range of n in the mode (s, m, n) is 1, 2, ..., n. Therefore, θ angle sampling covering 0°≤θ≤180° requires at least N+1 sampling points, and φ angle sampling covering 0°≤φ<360° requires at least 2N+1 sampling points. Therefore, using equal-angle interval θ and φ sampling requires 2(2N+1)(N+1) sampling points, which is about twice the number of sampling points actually required, 2N(N+2). The main reason is: for equal-angle interval sampling, the sampling points in the φ direction are the same for all angles. When θ is close to 0° and 180°, the φ angle is sampled too much. In these areas, the area on the sphere is very small. Even if the number of sampling points is large, their sampling data contributes little to the overall radiation pattern.

[0059] Perform equal angle sampling on the spherical surface with an outer radius of 300mm. According to the formula N = [kr t ]+10, the maximum number of patterns required for calculation is 53. Therefore, the number of sampling points in the θ direction is 54, the number of sampling points in the φ direction is 107, and the total number of sampling points is 2×54×107=11556.

[0060] like Figure 4 As shown, it shows that when sampling at equal angles, E θ and E φ The amplitude and phase distribution of the components. θ and E φ The components are sent to the near-far field transformation algorithm as measurement signal data to calculate the antenna far-field radiation parameters (i.e. directivity and radiation pattern) and compared with the results of the non-redundant uniform sampling measurement method.

[0061] 1. Case 1

[0062] Non-redundant uniform sampling measurement method (using Particle-based sampling method to generate spherical uniform points):

[0063] like Figure 1 As shown in (a), it can be seen that the sampling points on the spherical surface are evenly distributed, and there is no problem of large redundancy. 3402 evenly distributed sampling point position information is generated on the spherical surface with an outer radius of 300mm (considering E θ and E φ Component, the amount of sampling data is 6804), according to the method described in the steps of the above embodiment, the equi-angle sampling point data is restored. Figure 5 As shown in the figure, it can be seen that the restored electric field distribution on the spherical surface is very consistent with the equi-angle sampling result. Then the near-field to far-field transformation is performed to obtain the far-field radiation parameters of the antenna.

[0064] Comparison between the equi-angle interval sampling measurement method and the non-redundant uniform sampling measurement method:

[0065] 1. Comparison of the number of sampling points:

[0066] Determine the highest order N of the spherical wave mode to be 54;

[0067] Equal angle interval sampling measurement method: 2×(2×54+1)×(54+1)=11900;

[0068] Non-redundant uniform sampling measurement method: 2×(54×56)=6804;

[0069] Compared with the two, the number of sampling points is reduced by more than 40%, which greatly reduces the sampling volume.

[0070] 2. Comparison of directional calculation results:

[0071] Equal angle interval sampling measurement method: 22.985dBi;

[0072] Non-redundant uniform sampling measurement method: 22.779dBi;

[0073] The difference between the two is less than 0.3dB.

[0074] 3. Comparison of directional pattern calculation results:

[0075] Figure 7 a is the antenna pattern obtained by sampling at equal angle intervals; Figure 7 b is the antenna pattern obtained by uniform sampling (Particle-based sampling). It can be seen that the patterns obtained by the two sampling measurement methods are very close, and the main lobe width, side lobe level, first zero point position, etc. are all very close.

[0076] 2. Case 2

[0077] Non-redundant uniform sampling measurement method (using spiral-based sampling method to generate spherical uniform points):

[0078] like Figure 1 As shown in (b), it can be seen that the sampling points on the spherical surface are evenly distributed, and there is no problem of large redundancy. 3402 evenly distributed sampling point position information is generated on the spherical surface with an outer radius of 300mm (considering E θ and E φ Component, the amount of sampling data is 6804), according to the method described in the steps of the above embodiment, the equi-angle sampling point data is restored. Figure 6 As shown in the figure, it can be seen that the restored electric field distribution on the spherical surface is very consistent with the equi-angle sampling result. Then the near-field to far-field transformation is performed to obtain the far-field radiation parameters of the antenna.

[0079] Comparison between the equi-angle interval sampling measurement method and the non-redundant uniform sampling measurement method:

[0080] 1. Comparison of the number of sampling points:

[0081] Determine the highest order N of the spherical wave mode to be 54;

[0082] Equal angle interval sampling measurement method: 2×(2×54+1)×(54+1)=11900;

[0083] Non-redundant uniform sampling measurement method: 2×(54×56)=6804;

[0084] Compared with the two, the number of sampling points is reduced by more than 40%, which greatly reduces the sampling volume.

[0085] 2. Comparison of directional calculation results:

[0086] Equal angle interval sampling measurement method: 22.985dBi;

[0087] Non-redundant uniform sampling measurement method: 22.653dBi;

[0088] The difference between the two is less than 0.35dB.

[0089] 3. Comparison of directional pattern calculation results:

[0090] Figure 7 a is the antenna pattern obtained by sampling at equal angle intervals; Figure 7 c is the antenna pattern obtained by uniform sampling (spiral-based sampling). It can be seen that the patterns obtained by the two sampling measurement methods are very close, and the main lobe width, side lobe level, first zero point position, etc. are all very close.

[0091] The above are only embodiments of the present invention, and the common knowledge such as the known specific structures and / or characteristics in the scheme are not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. An antenna spherical near-field measurement method based on non-redundant uniform spherical sampling is characterized by: The steps include: S1. Determine the minimum sampling distance according to the antenna operating frequency and sampling radius; S2, generating spherical sampling point position information based on an arbitrary spherical uniform point generation algorithm; S3. Use the probe to measure the sampling point position, and measure the E of the radiation field of the antenna to be tested corresponding to the signal received by the probe. θ and E φ Quantity; S4, based on vector transformation to obtain the sampling point position E x 、E y and E z The measurement signal corresponding to the component; S5. Calculate the E at equal angle intervals based on spherical harmonics x ′,E y ′ and E z The equiangularly spaced E corresponding to the ′ component θ ′ and E′ φ ; S6. Calculate the far-field radiation parameters of the antenna using a near-far-field transformation algorithm with equally spaced sampling.

2. The antenna spherical near-field measurement method based on non-redundant uniform spherical sampling according to claim 1 is characterized in that: In step S1, the number of sampling points is calculated as follows: S1.

1. Determine the highest order N of the spherical wave mode according to the operating frequency and sampling radius: N=[kr t ]+10; Where k = 2π / λ is the wave number, λ is the wavelength, r t is the radius of the smallest sphere enclosing the measuring antenna; S1.

2. Determine the number of sampling points required. To ensure the calculation accuracy, the number of sampling points should be close to or greater than N1: N1=2N(N+2).

3. The antenna spherical near-field measurement method based on non-redundant uniform spherical sampling according to claim 1 is characterized in that: In step S4, the near field measurement is usually performed in the radiation near field of the antenna, E r The distance attenuation of the component is much greater than E θ and E φ , so E is ignored r =0, the transformation matrix T is:

4. The antenna spherical near-field measurement method based on non-redundant uniform spherical sampling according to claim 1 is characterized in that: The method of step S6 is as follows: Based on the spherical near-field and far-field transformation algorithm, the E′ at equal angle intervals is known. θ and E′ φ Components, corresponding to w′(χ=0°) and w′(χ=90°) in the formula, and then spherical wave analysis is performed to solve the spherical wave expansion coefficient T smn , and finally the far-field antenna parameters can be calculated:

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