A method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus

Abstract

A method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed source focus, determining the focal length of the compact field reflection surface, the reflection surface offset direction, the quiet zone size and the quiet zone position; projecting the quiet zone onto the reflection surface, determining the lowest point and the highest point of the projection in the offset direction of the reflection surface; calculating the feed source focus route that makes the difference in the distance from the phase center of the feed source to the lowest point and the highest point in the offset direction of the reflection surface before and after the focus offset the same; obtaining the phase distribution of the front, middle and back three positions of the compact field quiet zone at each frequency point before the feed source focus offset, and judging the overall distribution form of the quiet zone phase; sampling on the feed source focus route, obtaining the phase data of the front, middle and back three positions of the quiet zone when the feed source is located at each sample point position; comparing the phase data of the front, middle and back three positions of the quiet zone when the feed source is located at each sample point position to obtain the feed source focus position that makes the quiet zone phase distribution optimal. The present invention can improve the low-frequency quiet zone performance of a compact field without changing the compact field reflection surface, the feed source and the darkroom structure.

Description

Technical Field

[0001] The invention belongs to the field of measurement technology, and in particular relates to a method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed source focus. Background Art

[0002] The compact range can obtain quasi-plane waves with excellent performance at close distances indoors, thus meeting the far-field conditions for antenna measurement and RCS measurement. The single-reflector compact range is currently the most widely used compact range measurement system due to its simple structure and low processing cost. It converts the spherical electromagnetic waves radiated by the feed source into plane waves through the reflector, forming a quiet zone that meets the far-field test requirements within a certain distance from the reflector.

[0003] When a single reflector compact field works at low frequency, the edge diffraction field will cause great interference to the quiet zone, resulting in uneven distribution of the amplitude and phase of the quiet zone. When the distance from the quiet zone to the reflector is large compared to the aperture of the reflector, the diffraction field has a particularly significant impact on the quiet zone due to the aperture diffusion effect. This impact is reflected in the phase characteristics as a large phase taper in the quiet zone, and a concave or convex distribution. Sawtooth or curling loading on the edge of the reflector can reduce the interference of the diffraction field at the edge of the reflector on the quiet zone and improve the performance of the compact field quiet zone. When the edge of the reflector has been processed, the only way to improve the low-frequency quiet zone performance of the compact field is to increase the size of the reflector so that the position where the diffraction field has a greater impact is moved to the rear of the quiet zone. However, this method will greatly increase the construction cost of the compact field. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for improving the low-frequency quiet zone performance of a compact range by adjusting the feed source focus, so as to solve the problem that the prior art requires redesigning the original compact range to improve the quiet zone performance of the compact range, resulting in increased costs.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus, comprising the following steps:

[0007] Step 1, determining the focal length of the reflection surface, the offset direction of the reflection surface, the size of the quiet zone and the position of the quiet zone of the compact field;

[0008] Step 2: Project the quiet zone onto the reflective surface, and determine the positions of the lowest point P and the highest point Q projected on the reflective surface in the offset direction of the reflective surface;

[0009] Step 3: Move the feed source on the offset plane of the reflective surface, calculate the position where the difference in distance from the phase center of the feed source to the lowest point P and the highest point Q in the offset direction of the reflective surface before and after the defocus is the same, and obtain the defocus path of the feed source;

[0010] Step 4: obtain the phase distribution of the front, middle and rear positions of the compact field quiet zone of each frequency point before the feed source is defocused by simulation or measurement, and determine whether its overall distribution shape is concave or convex;

[0011] Step 5: According to the phase distribution of the compact field quiet zone before the feed source is defocused in step 4, corresponding sampling is performed on the feed source defocus route obtained in step 3, the feed source is moved to each sampling point position, and the situation where the feed source is located at each sampling point position is simulated or measured to obtain the phase data of the front, middle and rear positions of the quiet zone of each frequency point when the feed source is located at each sampling point position;

[0012] Step 6: By comparing the phase flatness of the front, middle and rear positions of the quiet zone within the frequency band, the defocus position that optimizes the phase distribution of the quiet zone is obtained. The quiet zone phase flatness is the phase peak-to-peak value on the static curve surface at the corresponding position of the corresponding frequency.

[0013] In one embodiment, the compact field in step 1 is a single-reflecting-surface compact field.

[0014] In one embodiment, the compact quiet zone in step 1 is cylindrical.

[0015] In one embodiment, the quiet zone in step 2 is projected onto the reflecting surface, and the projection direction is from the quiet zone to the reflecting surface along the rotation axis of the parabolic portion of the reflecting surface.

[0016] In one embodiment, in step 3, the offset plane is a plane determined by the rotation axis of the parabola portion of the reflector and the offset direction of the reflector; and when center-fed, the offset plane is any plane passing through the parabola rotation axis.

[0017] In one embodiment, the phase center of the feed source before focusing is located at the focus F, and the phase center of the feed source after focusing is located at the point M.

[0018] In one embodiment, in step 3, the feed source focus deviation path is determined by the following distance relationship:

[0019] PF-PM=QF-QM

[0020] Wherein, PF refers to the distance from the phase center of the defocused forward feed source to the lowest point P in the bias direction of the reflecting surface, PM refers to the distance from the phase center of the defocused backward feed source to the lowest point P in the bias direction of the reflecting surface, QF refers to the distance from the phase center of the defocused forward feed source to the highest point Q in the bias direction of the reflecting surface, and QM refers to the distance from the phase center of the defocused backward feed source to the highest point Q in the bias direction of the reflecting surface.

[0021] Under the above distance relationship, the phase size after the feed source is defocused is equal on the boundary of the quiet zone, thereby avoiding the quiet zone position offset caused by conventional feed source defocusing, and at the same time ensuring that the phase distribution of the quiet zone is more uniform after compensating for the diffraction field interference by using the feed source defocusing.

[0022] In one embodiment, in step 4, the overall distribution form of the phase in the compact quiet zone is judged from two aspects: the operating frequency and the quiet zone position. The phase distribution form of each frequency point and each quiet zone position is judged, and the number of concave phase distributions and convex phase distributions is counted. If the number of concave phase distributions is large, the overall distribution form of the phase in the compact quiet zone is a concave distribution; if the number of convex phase distributions is large, the overall distribution form of the phase in the compact quiet zone is a convex distribution.

[0023] In one embodiment, in step 5, the sample point position on the feed source defocus path is The sampling is determined by is the phase difference between the edge of the quiet zone and the maximum defocus position with the working frequency f as the reference after defocusing, and is calculated using the geometric optics method. The calculation formula is as follows:

[0024]

[0025] Where c is the speed of light in free space, MF is the distance from the phase center of the defocused feed source to the focal point F;

[0026] The sampling of is similar to the scanning parameter. When the phase of the compact field quiet zone is overall concave distribution, Sampling is performed in the interval [-180°, 0°]; when the phase of the compact field quiet zone is overall convexly distributed, Sampling is performed in the interval [0°, 180°].

[0027] In one embodiment, in step 6, the focus position that minimizes phase_max is found from the maximum values ​​of phase flatness at the front, middle and rear positions of the quiet zone in the entire working frequency band when the feed source is located at each sample point, that is, the focus position that optimizes the quiet zone phase distribution.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The method for improving the low-frequency quiet zone performance of a compact range by adjusting the feed source focus provided by the present invention can be directly applied to the existing compact range without redesigning the compact range reflection surface, feed source and darkroom. For a compact range with a relatively obvious concave or convex phase distribution in the quiet zone, the feed source is defocused to produce a phase distribution opposite to that in the quiet zone to compensate for the diffraction field irradiated to the quiet zone, thereby improving the low-frequency quiet zone performance of the compact range without increasing the construction cost of the compact range. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of the method of the present invention.

[0031] Figure 2 It is a schematic diagram of feed source focus adjustment in an embodiment of the method of the present invention.

[0032] Figure 3 It is a main polarization phase distribution diagram of different positions in the quiet zone when the feed source of the method embodiment of the present invention is not defocused.

[0033] Figure 4 It is a main polarization phase distribution diagram behind the quiet zone of different frequencies when the feed source of the embodiment of the method of the present invention is not defocused.

[0034] Figure 5 It is a main polarization phase distribution diagram of the quiet zone caused by feed source defocus adjustment calculated by the geometric optics method of the method embodiment of the present invention.

[0035] Figure 6 It is a simulation result diagram of the main polarization phase distribution behind the quiet zone before and after the feed source focus adjustment of the method embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] Reference Figure 1 , the method of the present invention is further described in detail. The method of the present invention for improving the low-frequency quiet zone performance of a compact field by adjusting the feed source focus, the steps are as follows:

[0038] Step 1: Determine the focal length of the reflector surface, the reflector surface offset direction, the quiet zone size, and the quiet zone position of the compact field for which feed angle adjustment is required.

[0039] Figure 2 It is a schematic diagram of a compact field structure on a cross section (xoy plane) formed by the rotation axis of the parabolic portion of the reflecting surface and the offset direction of the reflecting surface in one embodiment of the present invention. In the figure, the feed source is placed at the focus F of the reflecting surface, the y-axis direction refers to the offset direction of the reflecting surface, and the x-axis is the rotation axis of the parabolic portion of the reflecting surface.

[0040] For example, the compact field in step 1 is a single reflector compact field, and the compact field quiet zone is cylindrical. To better illustrate the effect of the method of the present invention on improving the low-frequency quiet zone performance of the compact field, the reflector in this embodiment adopts mixed curling edge processing and is offset in the vertical direction.

[0041] Step 2: Project the quiet zone onto the reflective surface and determine the positions of the lowest point P and the highest point Q projected on the reflective surface in the offset direction of the reflective surface. Figure 2 As shown, the solid line portion of the parabola is the projection of the quiet zone on the reflecting surface, and the lowest and highest points of the projection are point P and point Q respectively.

[0042] For example, the projection direction of the quiet zone in step 2 is from the quiet zone to the direction of the reflecting surface along the rotation axis of the parabolic portion of the reflecting surface (see Figure 2 -x direction).

[0043] Step 3: Move the feed source on the offset plane of the reflector, calculate the position where the difference in distance from the phase center of the feed source to the lowest point P and the highest point Q in the offset direction of the reflector is the same before and after the offset, and obtain the feed source offset path.

[0044] For example, the bias plane of the present invention is a plane determined by the parabola rotation axis and the bias direction of the reflection surface, and when center-feeding is performed, the bias plane is an arbitrary plane passing through the parabola rotation axis.

[0045] In one embodiment, the phase center of the feed source before defocusing is located at the focal point F, and the phase center of the feed source after defocusing is located at the point M. The defocusing route of the feed source is determined by the following distance relationship:

[0046] PF-PM=QF-QM

[0047] Under the above distance relationship, the phase size after the feed source is defocused is equal on the boundary of the quiet zone, thereby avoiding the quiet zone position offset caused by conventional feed source defocusing, and at the same time ensuring that the phase distribution of the quiet zone is more uniform after compensating for the diffraction field interference by using the feed source defocusing.

[0048] Step 4: Obtain the phase distribution of the front, middle and rear positions of the compact field quiet zone of each frequency point before the feed source is defocused through simulation or measurement, and determine whether its overall distribution shape is concave or convex.

[0049] For example, the overall distribution form of the phase in the compact quiet zone is judged from two aspects: the operating frequency and the quiet zone position. The phase distribution form of each frequency point and each quiet zone position is judged, and the number of concave phase distributions and convex phase distributions is counted. If the number of concave phase distributions is large, and the number of convex phase distributions is small, then the overall distribution form of the phase in the compact quiet zone is a concave distribution; conversely, if the number of convex phase distributions is large, and the number of concave phase distributions is small, then the overall distribution form of the phase in the compact quiet zone is a convex distribution.

[0050] Step 5: According to the phase distribution of the quiet zone in the compressed field before the feed source is defocused in step 4, corresponding sampling is performed on the feed source defocusing route obtained in step 3, the feed source is moved to each sampling point position, and the situation where the feed source is located at each sampling point position is simulated or measured to obtain the phase data of the front, middle and rear positions of the quiet zone of each frequency point when the feed source is located at each sampling point position.

[0051] For example, in this step, the sample point position on the feed source defocus path is the phase difference between the edge of the quiet zone with the working frequency f as the reference and the maximum defocus position after defocusing. The sampling is determined. The geometric optics method is used for calculation, and the calculation formula is as follows:

[0052]

[0053] Where c is the speed of light in free space, and MF is the distance from the phase center of the defocused feed source to the focus F. When the phase of the compact field quiet zone is overall concave, Sampling is performed in the interval [-180°, 0°]; when the phase of the compact field quiet zone is overall convexly distributed, Sampling is performed in the interval [0,180°].

[0054] when After the sampling is completed, the corresponding off-focus sample point position can be calculated. Figure 2 For example, according to the concave distribution characteristics of the phase in the compact field quiet zone before the feed source is defocused, Sampling can be performed in the interval [-20°, 0°] with 8.2 GHz as the reference frequency, and the corresponding off-focus sample point position can be calculated.

[0055] Step 6: By comparing the phase flatness of the front, middle and rear positions of the quiet zone within the frequency band, the focus offset position that optimizes the phase distribution of the quiet zone is obtained.

[0056] For example, the quiet zone phase flatness in this step is the phase peak-to-peak value on the quiet curve surface at the corresponding position of the corresponding frequency. From the maximum phase flatness values ​​of the three positions of the front, middle and rear of the quiet zone in the entire working frequency band when the feed source is located at each sample point, find the defocus position that minimizes phase_max, that is, the defocus position with the best quiet zone phase distribution.

[0057] Figure 3 and Figure 4 Phase distribution diagrams of different positions of the quiet zone and phase distribution diagrams of the rear of the quiet zone at different frequencies in a specific implementation manner are respectively shown when the feed source is not defocused. Figure 3 The phase distribution diagram at different positions in the quiet zone when the feed source is not biased is the main polarization phase distribution curve at the front, middle and rear positions of the quiet zone at 8.2GHz frequency point on the 45° section (with the horizontal section as 0° as a reference). The size of the quiet zone is 300mm. It can be seen that the main polarization phase is concavely distributed in the entire depth of the quiet zone. Figure 4 The phase distribution diagram behind the quiet zone at different frequencies when the feed source is not defocused is the main polarization phase distribution curve at the 45° section (with the horizontal section as 0° as a reference) behind the quiet zone at 8.2GHz, 10.3GHz and 12.4GHz. It can be seen that the main polarization phase is concavely distributed in the entire working frequency band. Figure 3 and Figure 4 From the curve characteristics, it can be seen that the main polarization phase is generally concavely distributed in the front, middle and back positions of the quiet zone in the entire working frequency band.

[0058] Figure 5 The main polarization phase distribution diagram of the quiet zone calculated by the geometric optics method with 8.2 GHz frequency as reference in a specific embodiment is shown. Figure 5 As you can see, The main polarization phase of the quiet zone after defocusing is convexly distributed and the phases at both ends are consistent, which is opposite to the shape of the main polarization phase distribution curve of the quiet zone before defocusing when the diffraction field is considered. In this way, the interference caused by the diffraction field can be compensated by feed source defocusing.

[0059] Figure 6A simulation result diagram of the main polarization phase distribution at the 45° section (with the horizontal section as 0° as a reference) behind the quiet zone at the 8.2 GHz frequency point before and after the feed source is defocused in a specific embodiment is shown. It can be seen that the phase flatness on the 45° section behind the quiet zone is reduced from 14.65° to 3.99° after the feed source is defocused. In a specific embodiment, when the feed source is not defocused, the maximum value of the quiet zone phase flatness at the front, middle, and rear positions of the quiet zone in the 8.2 GHz to 12.4 GHz frequency band is 14.74°; after the feed source is defocused, the maximum value of the quiet zone phase flatness at the front, middle, and rear positions of the quiet zone in the 8.2 GHz to 12.4 GHz frequency band is 6.6°, which is 55.2% lower than before the defocusing, and the phase distribution of the quiet zone is more uniform, thereby significantly improving the performance of the quiet zone.

[0060] In summary, the present invention can improve the low-frequency quiet zone performance of the compact range without changing the compact range reflection surface, feed source and darkroom structure.

[0061] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus, characterized in that: The steps include: Step 1, determining the focal length of the reflection surface, the offset direction of the reflection surface, the size of the quiet zone and the position of the quiet zone of the compact field, wherein the compact field is a single reflection surface compact field; Step 2: Project the quiet zone onto the reflective surface, and determine the positions of the lowest point P and the highest point Q projected on the reflective surface in the offset direction of the reflective surface; Step 3: Move the feed source on the offset plane of the reflective surface, calculate the position where the difference in distance from the phase center of the feed source to the lowest point P and the highest point Q in the offset direction of the reflective surface before and after the defocus is the same, and obtain the defocus path of the feed source; Step 4: obtain the phase distribution of the front, middle and rear positions of the compact field quiet zone of each frequency point before the feed source is defocused by simulation or measurement, and determine whether its overall distribution shape is concave or convex; Step 5: According to the phase distribution of the compact field quiet zone before the feed source is defocused in step 4, corresponding sampling is performed on the feed source defocus route obtained in step 3, the feed source is moved to each sampling point position, and the situation where the feed source is located at each sampling point position is simulated or measured to obtain the phase data of the front, middle and rear positions of the quiet zone of each frequency point when the feed source is located at each sampling point position; Step 6: By comparing the phase flatness of the front, middle and rear positions of the quiet zone within the frequency band, the defocus position that optimizes the phase distribution of the quiet zone is obtained. The quiet zone phase flatness is the phase peak-to-peak value on the quiet zone aperture at the corresponding position of the corresponding frequency.

2. The method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus according to claim 1, characterized in that: The compact field quiet zone in step 1 is cylindrical.

3. The method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus according to claim 1, characterized in that: The quiet zone in step 2 is projected onto the reflecting surface, and the projection direction is from the quiet zone to the reflecting surface along the rotation axis of the parabolic portion of the reflecting surface.

4. The method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus according to claim 1, characterized in that: In the step 3, the bias plane is a plane determined by the rotation axis of the parabola portion of the reflector and the bias direction of the reflector; and when center-fed, the bias plane is any plane passing through the parabola rotation axis.

5. The method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus according to claim 1, characterized in that: In step 3, the feed source defocus path is determined by the following distance relationship: PF-PM=QF-QM In the formula, PF refers to the distance from the phase center of the defocused front feed source to the lowest point P in the offset direction of the reflecting surface, PM refers to the distance from the phase center of the defocused rear feed source to the lowest point P in the offset direction of the reflecting surface, QF refers to the distance from the phase center of the defocused front feed source to the highest point Q in the offset direction of the reflecting surface, and QM refers to the distance from the phase center of the defocused rear feed source to the highest point Q in the offset direction of the reflecting surface; under the above distance relationship, the phase size of the feed source after focusing is equal on the boundary of the quiet zone.

6. The method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus according to claim 1, characterized in that: In the step 4, the overall distribution form of the phase in the quiet zone of the compact field is judged from two aspects: the operating frequency and the quiet zone position. The phase distribution form of each frequency point and each quiet zone position is judged, and the number of concave phase distributions and convex phase distributions are counted; wherein, if the number of concave phase distributions is large, the overall distribution form of the phase in the quiet zone of the compact field is a concave distribution; if the number of convex phase distributions is large, the overall distribution form of the phase in the quiet zone of the compact field is a convex distribution.

7. The method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus according to claim 1, characterized in that: In step 5, the sample point position on the feed source defocus path is The sampling is determined by is the phase difference between the edge of the quiet zone and the maximum defocus position after defocusing with the working frequency f as the reference, and is calculated using the geometric optics method. The calculation formula is as follows: Where c is the speed of light in free space, PF refers to the distance from the focus F to the lowest point P in the offset direction of the reflector, PM refers to the distance from the phase center of the defocused feed source to the lowest point P in the offset direction of the reflector, and MF is the distance from the phase center of the defocused feed source to the focus F; When the phase of the compact field quiet zone is overall concave distribution, Sampling is performed in the interval [0, -180°]; when the phase of the compact field quiet zone is overall convexly distributed, Sampling is performed in the interval [0,180°].

8. The method for improving the low-frequency quiet zone performance of a compact field by adjusting the feed focus according to claim 1, characterized in that: In step 6, the focus position that minimizes phase_max is found from the maximum phase flatness values ​​of the three positions before, in the middle and after the quiet zone in the entire working frequency band when the feed source is located at each sample point, that is, the focus position that optimizes the quiet zone phase distribution.

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