A method for improving the performance of a compact range quiet zone by adjusting the feed source tilt

Abstract

The application discloses a method for improving the performance of a compact range quiet zone by adjusting the feed source deflection angle, and the method comprises the following steps: determining the focal length of a compact range reflecting surface, the deflection direction of the reflecting surface, the size of the quiet zone and the position of the quiet zone; projecting the quiet zone to the reflecting surface to determine the lowest point and the highest point projected on the deflection direction of the reflecting surface; obtaining the feed source directional diagram data through simulation or measurement; rotating the feed source from the lowest point to the highest point, and calculating the amplitude flatness of the quiet zone in the deflection direction of the reflecting surface at different deflection angles by using a geometric optics method; and finding the feed source deflection angle that makes the amplitude flatness minimum by comparison. The application can improve the performance of the compact range quiet zone without changing the compact range reflecting surface, the feed source and the darkroom structure.

Description

Technical Field

[0001] This invention belongs to the field of measurement technology, and specifically relates to a method for improving the static performance of a compact field by adjusting the feed angle. Background Technology

[0002] Compacted fields can obtain high-performance quasi-plane waves at close range indoors, thus meeting the far-field conditions for antenna measurement and RCS measurement. Single-reflector compacted fields are currently the most widely used compacted field measurement systems due to their simple structure and low manufacturing cost. They convert the spherical electromagnetic waves radiated by the feed source into plane waves through a reflecting surface, forming a quiet zone within a certain distance from the reflecting surface that meets the requirements for far-field testing.

[0003] In a compact field system, the feed source is often a Gaussian type feed source that points towards the center of the reflecting surface. In this case, when the feed source radiates onto the reflecting surface, on the one hand, the radiation pattern of the feed source in the angular domain of the parabolic part of the reflecting surface has a certain taper, and on the other hand, the electromagnetic waves radiated by the feed source have different spatial attenuations at different positions on the reflecting surface, resulting in inconsistent distribution of wavefront amplitude, which limits the performance of the quiet zone of the compact field. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for improving the performance of the quiet zone of the compact field by adjusting the feed angle, so as to reduce construction and design costs while improving the performance of the quiet zone of the compact field.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for improving the static performance of a compact field by adjusting the feed angle includes the following steps:

[0007] Step 1: Determine the focal length of the reflecting surface, the offset direction of the reflecting surface, the size of the quiet zone, and the location of the quiet zone for the compact field;

[0008] Step 2: Project the still area onto the reflecting surface and determine the positions of the lowest point P and the highest point Q of the still area projection on the reflecting surface in the offset direction of the reflecting surface;

[0009] Step 3: Obtain the radiation pattern data of the feed source used in this compacted area through simulation or measurement;

[0010] Step 4: Rotate the feed source from the center pointing to the lowest point P along the offset direction of the reflecting surface to the center pointing to the highest point Q. Calculate the flatness of the static area amplitude in the offset direction of the reflecting surface when the feed source is at different feed source offset angles α. The feed source offset angle α is the angle between the feed source center pointing to the rotation axis of the parabolic part of the reflecting surface.

[0011] Step 5: Find the feed offset angle α that minimizes the flatness of the still zone amplitude in the offset direction of the reflecting surface by comparison.best α best This refers to the adjusted feed angle.

[0012] In one embodiment, the compaction field in step 1 is an offset-feed single-reflector compaction field.

[0013] In one embodiment, the still area in step 2 is projected onto the reflecting surface, and the projection direction is from the still area to the reflecting surface along the rotation axis of the parabolic portion of the reflecting surface.

[0014] In one embodiment, the feed source in step 3 needs to illuminate the still zone projection on the reflective surface within its operating frequency band in the angular range. Figure 1 Good consistency.

[0015] In one embodiment, step 4 involves first determining the angle range [-φ0, φ0] of the feed pattern data used, where the feed center points to the 0° direction of the pattern; secondly, setting the accuracy σ of the feed deflection angle, which is used as the step value for feed angle rotation and the sample angle accuracy for calculating the amplitude flatness of the quiet zone in the reflector offset direction; and finally, using geometric optics to calculate the amplitude flatness of the quiet zone in the reflector offset direction when the feed is at different feed deflection angles α.

[0016] In one embodiment, the angle range [-φ0, φ0] is determined by the following method:

[0017] Connect the focal point F to the lowest point P and the highest point Q described in step 2. The angle between the line FP and the rotation axis of the parabolic part of the reflecting surface is ξ, and the angle between the line FQ and the rotation axis of the parabolic part of the reflecting surface is η. Then the angle ψ between the lines FP and FQ is η-ξ. The angle range of the feed pattern data used to calculate the amplitude flatness should be greater than 2ψ, that is, φ0 should be greater than ψ.

[0018] In one embodiment, the angular domain [ξ,η] included in the calculation of the static zone amplitude flatness in the offset direction of the reflector is sampled with a precision σ, and the feed pattern data is interpolated with a precision σ to be consistent with the sampling precision of the angular domain [ξ,η].

[0019] In one embodiment, the distribution of the still zone amplitude E1(θ,α) in the offset direction of the reflecting surface, calculated using geometric optics, is as follows:

[0020]

[0021] Where E1(θ,α) is in dB, E s (θ,α) represents the far-field electric field intensity of the feed when the feed deflection angle is α and the angle between the electromagnetic wave propagation direction and the rotation axis of the parabolic portion of the reflecting surface is θ, and r(θ) is the E s(θ,α) represents the distance the electromagnetic wave travels from the focal point to the reflecting surface, r min Let r(θ) be the minimum value of θ in the range [ξ,η].

[0022] The amplitude distribution E1(θ,α) of the still zone in the offset direction of the reflecting surface is transformed into an expression with respect to position y:

[0023]

[0024] Where position d is E s (θ,α) represents the distance from the point on the reflecting surface where the electromagnetic wave strikes to the axis of rotation of the parabolic portion of the reflecting surface, d1 is the distance from the lowest point P described in step 2 to the axis of rotation of the parabolic portion of the reflecting surface, and d2 is the distance from the highest point Q described in step 2 to the axis of rotation of the parabolic portion of the reflecting surface.

[0025] The formula for calculating the flatness E(α) of the static zone in the offset direction of the reflecting surface is:

[0026] E(α)=max(E2(y,α))-min(E2(y,α)),ξ≤α≤η

[0027] Where max(E2(y,α)) is the maximum value of E2 when the feed angle is α, and min(E2(y,α)) is the minimum value of E2 when the feed angle is α.

[0028] In one embodiment, the static area amplitude flatness in the reflector offset direction compared in step 5 is the static area amplitude flatness in the reflector offset direction of each sample angle within the range [ξ,η] obtained in step 4.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] The method for improving the quiet zone performance of a compact field by adjusting the feed angle provided by this invention can be directly applied to existing compact fields without redesigning the compact field reflector, feed, and anechoic chamber. It only requires adjusting the feed angle to compensate for the spatial attenuation of electromagnetic waves irradiated onto the reflector by the feed pattern tapering, thereby improving the quiet zone performance of the compact field without increasing the construction cost of the compact field. Attached Figure Description

[0031] Figure 1 This is a flowchart of the method of the present invention.

[0032] Figure 2 This is a schematic diagram of the feed angle adjustment in an embodiment of the method of the present invention.

[0033] Figure 3 This is a quiet zone amplitude distribution diagram considering only spatial attenuation in an embodiment of the method of the present invention.

[0034] Figure 4 This is a schematic diagram of a simulation result of the feed pattern of an embodiment of the method of the present invention.

[0035] Figure 5 This is a simulation result diagram of the static zone amplitude distribution before and after the feed angle adjustment in an embodiment of the method of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] Reference Figure 1 The present invention provides a further detailed description of the method for improving the static performance of a compact field by adjusting the feed angle, the steps of which are as follows:

[0038] Step 1: Determine the focal length of the reflecting surface, the offset direction of the reflecting surface, the size of the quiet zone, and the location of the quiet zone for the compact field that requires feed angle adjustment.

[0039] Figure 2 This is a schematic diagram of the compacted field structure in this embodiment on the cross section (yoz plane) formed by the offset direction of the reflecting surface and the rotation axis of the parabolic part of the reflecting surface. The feed source is placed at the focal point F of the reflecting surface. The y-axis direction refers to the offset direction of the reflecting surface, and the z-axis is the rotation axis of the parabolic part of the reflecting surface.

[0040] The feed angle α referred to in this invention is the angle between the feed center and the rotation axis of the parabolic portion of the reflecting surface.

[0041] For example, the compressed field described in step 1 is an offset-feed single-reflector compressed field. This type of compressed field is characterized by significant differences in spatial attenuation at different positions of the reflecting surface caused by the offset of the reflecting surface, and it lacks symmetry in the direction of the reflecting surface offset, thereby reducing the uniformity of the amplitude distribution in the quiet zone.

[0042] Step 2: Project the still area onto the reflecting surface, and determine the positions of the lowest point P and the highest point Q of the still area projection on the reflecting surface along the offset direction. For example... Figure 2 As shown, the solid line portion of the parabola is the projection of the static region onto the reflecting surface, with the lowest and highest points of this projection being point P and point Q, respectively.

[0043] For example, in step 2, the projection direction of the still zone is along the rotation axis of the parabolic portion of the reflecting surface, pointing from the still zone towards the reflecting surface (see appendix). Figure 2 (middle-z direction).

[0044] Step 3: Obtain the feed pattern data by simulating or measuring the feed used in the compressed field.

[0045] When obtaining feed pattern data in step 3, the measured or simulated pattern section is the section formed by the offset direction of the reflecting surface and the rotation axis of the parabolic portion of the reflecting surface when the feed is placed in a compact field. Figure 2 (Middle yoz noodles).

[0046] For example, the radiation pattern of the feed needs to be within the angular range of the projection of the quiet zone on the reflecting surface within its operating frequency band. Figure 1 Good consistency. Thus, the feed offset angle obtained through the method of this invention can achieve a good improvement in compact field performance across the entire operating frequency band. In this invention, the direction... Figure 1 Good consistency means that the radiation pattern remains basically unchanged. It can be evaluated by the error between the radiation pattern and the center frequency radiation pattern within the angle range of the quiet zone projection on the reflector surface at different frequency points within the feed's operating frequency band, which meets the general perception in this field.

[0047] Step 4: Rotate the feed source from the center pointing to the lowest point P along the offset direction of the reflecting surface to the center pointing to the highest point Q. Use the geometric optics method to calculate the flatness of the static zone amplitude in the offset direction of the reflecting surface when the feed source is at different offset angles.

[0048] For example, in step 4, it is necessary to determine the angle range [-φ0, φ0] of the feed pattern data used to calculate the amplitude flatness, with the feed center pointing in the 0° direction of the pattern. The method for determining this angle range is as follows: connect the focal point F to the lowest point P and the highest point Q mentioned in step 2 respectively. The angle between the connecting line FP and the rotation axis of the parabolic part of the reflecting surface is ξ, and the angle between the connecting line FQ and the rotation axis of the parabolic part of the reflecting surface is η. Then, the angle ψ between the connecting lines FP and FQ is η-ξ. In this embodiment, the angle range of the feed pattern data used to calculate the amplitude flatness should be greater than 2ψ, that is, φ0 should be greater than ψ, so as to ensure that the angle range of the feed pattern used to calculate the amplitude flatness of the static area in the offset direction of the reflecting surface can cover the projection of the static area on the reflecting surface during the process of the feed rotating from the center to the lowest point P along the offset direction of the reflecting surface to the center pointing to the highest point Q.

[0049] For example, in step 4, the accuracy σ of the feed angle needs to be set, which serves as the step value for the feed angle rotation and the sampling angle accuracy for calculating the amplitude flatness of the quiet zone in the reflector offset direction. Further, the angular domain [ξ,η] included in the calculation of the quiet zone amplitude flatness in the reflector offset direction is sampled according to accuracy σ. To ensure consistency with the sampling accuracy of the angular domain [ξ,η], the feed pattern data needs to be interpolated according to the angular accuracy σ.

[0050] For example, the still zone amplitude distribution (in dB) in the offset direction of the reflecting surface calculated by the geometric optics method in step 4 is as follows:

[0051]

[0052] Where E s (θ,α) represents the far-field electric field intensity of the feed when the feed deflection angle is α and the angle between the electromagnetic wave propagation direction and the rotation axis of the parabolic portion of the reflecting surface is θ, and r(θ) is the E s (θ,α) represents the distance the electromagnetic wave travels from the focal point to the reflecting surface, r min Let r(θ) be the minimum value of θ in the range [ξ,η].

[0053] The electric field distribution in the quiet zone is typically a function of position. Therefore, the amplitude distribution E1(θ,α) in the quiet zone along the bias direction of the reflecting surface can be transformed into an expression with respect to position y:

[0054]

[0055] Where position d is E s (θ, α) represents the distance from the point on the reflecting surface where the electromagnetic wave strikes to the axis of rotation of the parabolic portion of the reflecting surface, d1 is the distance from the lowest point P described in step 2 to the axis of rotation of the parabolic portion of the reflecting surface, and d2 is the distance from the highest point Q described in step 2 to the axis of rotation of the parabolic portion of the reflecting surface.

[0056] The formula for calculating the flatness of the still zone amplitude in the offset direction of the reflecting surface is:

[0057] E(α)=max(E2(y,α))-min(E2(y,α)),ξ≤α≤η

[0058] Where max(E2(y,α)) is the maximum value of E2 when the feed angle is α, and min(E2(y,α)) is the minimum value of E2 when the feed angle is α.

[0059] Step 5: Find the feed offset angle α that minimizes the flatness of the still zone amplitude in the offset direction of the reflecting surface by comparison. best α best This refers to the adjusted feed angle.

[0060] For example, the static area amplitude flatness in the reflector offset direction compared in step 5 is the static area amplitude flatness in the reflector offset direction of each sample angle within the range [ξ,η] obtained in step 4.

[0061] Figure 3 and Figure 4 The diagrams show simulation results for a quiet zone amplitude distribution map and a feed pattern considering only spatial attenuation in a specific embodiment. Figure 3 The amplitude distribution diagram of the quiet zone, which only considers spatial attenuation, is shown as the main polarization amplitude distribution curve of the cutoff line of the quiet zone in the direction of the reflecting surface. The size of the quiet zone is 300 mm. It can be seen that the main polarization amplitude is a monotonic curve that varies with position. Figure 4 The feed pattern shown is the pattern on the cross section formed by the offset direction of the reflecting surface and the rotation axis of the parabolic portion of the reflecting surface when the feed is placed in a compact field. It can be seen that the feed pattern has a certain taper and is symmetrical about the feed center. Figure 3 and Figure 4 As can be seen from the curve characteristics, the flatness of the static zone amplitude in the offset direction of the reflecting surface varies with the feed angle.

[0062] Figure 5 The diagram illustrates the distribution of the main polarization amplitude in the quiet zone along the reflector bias direction after adjusting the feed angle, with the feed pointing towards the center of the reflector in a specific embodiment (the feed angle in the traditional method). The simulation frequency is 25 GHz. It can be seen that after adjusting the feed angle, the flatness of the quiet zone amplitude along the reflector bias direction decreases from 0.91 dB to 0.69 dB, and the amplitude distribution in the quiet zone becomes more uniform, thereby significantly improving the performance of the quiet zone.

[0063] In summary, the present invention can improve the performance of the quiet zone of the compacted field without changing the compacted field reflector, feed source and anechoic chamber structure.

[0064] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of improving the performance of a compact range quiet zone by adjusting the feed source tilt angle, characterized by, The method comprises the following steps: Step 1: determining the focal length of the reflecting surface, the bias direction of the reflecting surface, the size of the quiet zone and the position of the quiet zone of the tight-field, wherein the tight-field is a single-reflector tight-field of bias feeding type; Step 2: projecting the quiet zone on the reflecting surface to determine the positions of the lowest point P and the highest point Q of the quiet zone projection on the reflecting surface in the bias direction of the reflecting surface; Step 3: obtaining the directional diagram data of the feed source used in the tight-field through simulation or measurement; Step 4: Rotate the feed from center pointing to the lowest point P along the reflector bias direction to center pointing to the highest point Q, calculate the quiet zone amplitude flatness when the feed is at different feed bias angles the feed bias angles the angle between the feed center pointing and the rotation axis of the parabolic section of the reflector Step 5: Find the feed tilt angle that minimizes the quiet zone amplitude flatness in the bias direction of the reflector by comparison , is the adjusted feed tilt angle.

2. The method of claim 1, wherein the method further comprises: In the step 2, the projection direction of the quiet zone on the reflecting surface is from the quiet zone to the reflecting surface along the rotation axis of the parabolic surface part of the reflecting surface.

3. The method of claim 1, wherein the method further comprises: In the step 3, the feed source needs to have good directional diagram consistency in the angle range of the quiet zone projection on the reflecting surface within the working frequency band of the feed source.

4. The method of claim 1, wherein the method further comprises: adjusting the feed angle of the feed source. The step 4 calculation, first determines the angular range of the feed pattern data used where the feed center pointing is the pattern 0° direction; second sets the accuracy of the feed squint angle , the step value used as the feed angle rotation and the calculated sample angle accuracy of the flatness of the quiet zone amplitude in the reflector squint direction; finally, the geometric optics method is used to calculate the flatness of the quiet zone amplitude in the reflector squint direction when the feed is at different feed squint angles .

5. The method of claim 4, wherein the method further comprises adjusting the feed angle of the feed source. the angular range is determined by the method: The angle between the line FP and the rotation axis of the parabolic part of the reflecting surface is The angle between the line FQ and the rotation axis of the parabolic part of the reflecting surface is The angle between the lines FP and FQ is The angle range of the feed pattern data used for calculating the amplitude flatness should be greater than 2 That is The value greater than is taken.

6. The method of claim 5, wherein the method further comprises adjusting the feed angle of the feed source. The included angle domain for the calculation of the quiet zone amplitude flatness in the direction of the reflector bias In terms of accuracy The feed pattern data is sampled in terms of accuracy Interpolation is performed to be consistent with the angle domain of the sampling accuracy.

7. The method of claim 5, wherein the method further comprises adjusting the feed angle of the feed source. The static zone amplitude in the bias direction of the reflecting surface calculated according to the geometrical optics method The distribution is: in, The unit is dB. The feed angle is The angle between the direction of electromagnetic wave propagation and the axis of rotation of the parabolic portion of the reflecting surface is... The far-field electric field strength of the feed source at that time for It represents the distance the electromagnetic wave travels from the focal point to the reflecting surface. for exist Within range The minimum value; Null amplitude distribution in the direction of the offset of the reflecting surface Converting to expressions in terms of position : wherein the position is the distance from the point on the reflecting surface where the electromagnetic wave is irradiated to the rotation axis of the parabolic portion of the reflecting surface, is the distance from the lowest point P described in step 2 to the rotation axis of the parabolic portion of the reflecting surface, is the distance from the highest point Q described in step 2 to the rotation axis of the parabolic portion of the reflecting surface; Null amplitude flatness in the direction of reflector bias The formula for calculating is: wherein is the maximum value of the feed tilt angle when is the minimum value of the feed tilt angle when is the minimum value of the feed tilt angle when 8. The method of claim 7, wherein the method further comprises adjusting the feed angle of the feed source. The quiet zone amplitude flatness in the reflector bias direction compared in step 5 is the quiet zone amplitude flatness in the reflector bias direction at each of the angles in the range from the feed bias angle obtained in step 4.

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