A high aspect ratio single parabolic cylinder compact range system based on linear array feed source

Abstract

This invention discloses a high aspect ratio single parabolic cylindrical compact field system based on a linear array feed, belonging to the field of antenna measurement and compact field technology. The system comprises a high aspect ratio single parabolic cylindrical reflector and a linear array feed located at its focal line. Thanks to the combination of the linear array feed and the single parabolic cylinder, the system avoids complex beamforming designs for high aspect ratio apertures and significantly suppresses the high cross-polarization problem commonly found in offset point source feeds. To address the low-frequency diffraction enhancement problem caused by vertical size limitations, this invention introduces a geometric phase delay design at the reflector edge, i.e., bending the serrated edge backward to introduce phase taper. In the design implementation, the optimal geometric setback at the edge was determined using a numerical optimization method based on the target quiet zone performance. This design, while maintaining the advantages of low cost and ease of fabrication, significantly suppresses edge diffraction, effectively extends the low-frequency operating bandwidth of the compact field, and greatly improves the quiet zone utilization.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic field measurement technology, and specifically to a high aspect ratio single parabolic cylindrical compact field system based on a linear array feed source. Background Technology

[0002] Compact-field technology utilizes reflectors to collimate spherical waves into plane waves, thereby achieving far-field measurement conditions at close range. Traditional compact-field reflectors, such as parabolic radii, typically have an aspect ratio close to 1:1. However, with the development of radar technology, targets such as synthetic aperture radar antennas exhibit high aspect ratios. If conventional square or circular aperture compact-field reflectors are used to test such targets, it will lead to redundancy in the quiet zone in the vertical direction, resulting in high manufacturing costs and wasted system space. To solve this problem, using a single parabolic cylindrical reflector in conjunction with a linear array feed has become a trend. The linear array synthesizes plane waves in the horizontal direction, and the single parabolic cylindrical reflector collimates the plane waves in the vertical direction. This architecture allows for a compressed reflector height. However, the compressed height leads to a reduction in the electrical dimension in the vertical direction. According to diffraction theory, the smaller the electrical dimension, the stronger the edge diffraction effect, which will severely disrupt the uniformity of the quiet zone, especially in the low-frequency band. Traditional sawtooth reflectors can only provide amplitude weighting and cannot provide phase control, thus offering limited improvement to the quiet zone. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention proposes a high aspect ratio single parabolic cylindrical compact field system based on a linear array feed. This method, through a special phase delay design of the reflector edge structure, can suppress edge diffraction under a limited vertical aperture, achieving a highly utilized and uniform quiet zone environment.

[0004] This invention comprises a high aspect ratio single parabolic cylindrical reflector, a linear array feed, and edge sawtooth structures with phase delay characteristics. The linear array feed generates a quasi-cylindrical wave in the horizontal dimension to illuminate the reflector. The single parabolic cylindrical reflector performs beam collimation in the vertical dimension, and the backward-curving sawtooth structure distributed along the upper and lower edges of the reflector introduces phase delay, effectively reducing ripple in the quiet zone.

[0005] The technical solution adopted in this invention is as follows:

[0006] A high aspect ratio single parabolic cylindrical compact field system based on a linear array feed includes: a single parabolic cylindrical reflector having a parabolic vertical cross-section and a straight horizontal cross-section; a linear array feed placed along the focal line of the single parabolic cylindrical reflector for radiating cylindrical waves to the reflector; the aspect ratio of the single parabolic cylindrical reflector is greater than 1, and the height of the reflector is compressed to adapt to the high aspect ratio target; the edge region of the single parabolic cylindrical reflector has a sawtooth structure, and the geometric contour of the edge region has a backward physical offset relative to the standard parabolic cylinder, the physical offset constituting a phase delay structure for introducing phase taper into the edge reflected waves.

[0007] Furthermore, the physical offset of the edge region is achieved by bending the serrated structure away from the focal line, and its surface profile equation satisfies:

[0008] ;

[0009] in, To introduce the phase-delayed surface coordinates of the reflecting surface, For standard parabolic cylindrical coordinates, The geometric offset is determined by the phase delay function, and The value increases nonlinearly with increasing vertical distance from the center of the reflecting surface.

[0010] Furthermore, each element of the linear array feed has independent amplitude and phase control capabilities, which are used to generate quasi-plane waves in the horizontal direction of the quiet zone through complex coefficient excitation and to compensate for field distribution errors in the horizontal direction.

[0011] Furthermore, this includes the following steps:

[0012] Step S1: Construct the basic geometric model of a single parabolic cylindrical reflector and set the aspect ratio and focal length of the reflector to adapt to targets with high aspect ratios;

[0013] Step S2: Establish a parameterized model of the edge phase delay, including the geometric receding amount of the reflecting surface edge relative to the standard parabolic cylinder. Defined as about the vertical coordinate The function is selected, and the set of parameters controlling the function is chosen as the optimization variables;

[0014] Step S3: Construct an optimization objective function based on the performance of the quiet zone, calculate the electric field distribution in the quiet zone under the current geometric parameters using an electromagnetic calculation algorithm, and calculate the amplitude and phase fluctuation values ​​in the quiet zone;

[0015] Step S4: Iteratively adjust the optimization variables in step S2 using a numerical optimization algorithm until the static zone amplitude fluctuation calculated in step S3 meets the preset index, thereby determining the optimal edge geometric backoff amount and generating the final reflective surface processing model.

[0016] Furthermore, in step S1, the constructed single parabolic cylindrical reflector has a free aspect ratio design;

[0017] Furthermore, in step S2, the geometric backoff amount The mapping relationship with the required edge phase delay distribution is as follows:

[0018] ;

[0019] in, The vertical coordinates on the reflecting surface (with the center of the reflecting surface as 0). For the height of the reflecting surface, These are optimizable parameters that control the width, rate of change, and maximum phase delay of the phase delay region. The equation for the reflecting surface is expressed as:

[0020] ;

[0021] in, Indicates the phase delay on the reflector coordinate, This indicates the focal length of the reflector.

[0022] Furthermore, in step S4, the numerical optimization algorithm used includes particle swarm optimization algorithm, genetic algorithm, neural network algorithm, and other algorithms.

[0023] Furthermore, in step S3, the electromagnetic calculation algorithm directly calculates the scattering field of the reflecting surface using the physical optics method or the multilayer fast multipole algorithm.

[0024] The advantages of this invention compared to the prior art are:

[0025] This invention employs a specific reflective surface architecture for targets with high aspect ratios, eliminating redundancy in the vertical static zone and significantly reducing the system's manufacturing cost and space requirements.

[0026] This invention, through the phase delay design at the edge of the reflective surface, adds phase taper to the aperture radiation field compared to the traditional compact field, which helps to improve the uniformity of the quiet zone;

[0027] This invention only requires geometric bending of the traditional sawtooth structure to achieve phase control, without the need to introduce complex edge-rolling processes or new materials, and without increasing additional processing costs. Attached Figure Description

[0028] Figure 1 Schematic diagram of a high aspect ratio single parabolic cylindrical compact field of a linear array feed;

[0029] Figure 2 This is a schematic diagram of the orthographic projection of the reflecting surface;

[0030] Figure 3 This is a schematic diagram of the phase delay of a single parabolic cylindrical reflector.

[0031] Figure 4 This is a flowchart of the design method of the present invention;

[0032] The meanings of the labels in the figure are as follows: 1 is a single parabolic cylindrical reflector; 2 is a linear array feed source; 3 is a cylindrical wave; 4 is a quiet zone. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] This invention provides a high aspect ratio single parabolic cylindrical compact field system based on a linear array feed, such as... Figure 1 As shown, it includes: a single parabolic cylindrical reflector 1, having a parabolic vertical cross-section and a straight horizontal cross-section; a linear array feed 2, positioned along the focal line of the single parabolic cylindrical reflector 1, used to radiate cylindrical waves 3 to the reflector; wherein, the single parabolic cylindrical reflector 1 has a high aspect ratio aperture, and the height of the single parabolic cylindrical reflector 1 is compressed to adapt to the high aspect ratio of the target being measured; the edge region of the single parabolic cylindrical reflector 1 has a serrated structure, and the geometric contour of the edge region has a backward physical offset relative to the standard parabolic cylinder, the physical offset constituting a phase delay structure, used to introduce a phase taper to the edge reflected wave. The single parabolic cylindrical reflector 1 is 5m wide and 1m high, with an aspect ratio of 5:1. The focal length of the single parabolic cylindrical reflector 1 is 1m, the linear array feed 2 is placed at the focal line position, the linear array feed 2 illuminates the center of the reflector at a 32° angle, and the lower edge of the single parabolic cylindrical reflector 1 is 0.07m from the ground. The single parabolic cylindrical reflecting surface 1 has right-angled triangular serrations distributed around its perimeter. The height of the top and bottom serrations is 0.2m, and the height of the left and right serrations is 0.5m. The projected structure of the reflecting surface is as follows: Figure 2 As shown. The amplitude and phase excitation of each unit of the linear array feed 2 are independently controllable, and it is responsible for synthesizing the quiet zone 4 in the horizontal direction. The quiet zone 4 in the height direction is provided by the collimation of the reflecting surface. The quasi-plane wave quiet zone 4 can be realized at a distance of 2 to 4 times the focal length from the reflecting surface.

[0035] The physical offset of the edge region is achieved by bending the serrated structure away from the focal line, and its surface profile equation satisfies:

[0036] ;

[0037] in, To introduce the phase-delayed surface coordinates of the reflecting surface, For standard parabolic cylindrical coordinates, The geometric offset is determined by the phase delay function, and The value increases nonlinearly with increasing vertical distance from the center of the reflecting surface.

[0038] Each element of the linear array feed 2 has independent amplitude and phase control capabilities, which are used to generate quasi-plane waves in the horizontal direction of the quiet zone 4 through complex coefficient excitation and to compensate for the field distribution error in the horizontal direction.

[0039] The phase delay structure design includes the following steps:

[0040] Step S1: Construct the geometric model of the single parabolic cylindrical reflector 1, and set the aspect ratio and focal length of the reflector to adapt to the target with a high aspect ratio.

[0041] Step S2: Establish a parameterized model of the edge phase delay, including the geometric receding amount of the reflecting surface edge relative to the standard parabolic cylinder. Defined as about the vertical coordinate The function is selected, and the set of parameters controlling the function is chosen as the optimization variables;

[0042] Step S3: Construct an optimization objective function based on the performance of quiet zone 4, calculate the electric field distribution in quiet zone 4 under the current geometric parameters using an electromagnetic calculation algorithm, and calculate the amplitude and phase fluctuation values ​​in quiet zone 4;

[0043] Step S4: Iteratively adjust the optimization variables in step S2 using a numerical optimization algorithm until the static zone 4-phase fluctuation calculated in step S3 meets the preset index, thereby determining the optimal edge geometric backoff amount and generating the final reflective surface processing model.

[0044] In step S1, the constructed single parabolic cylindrical reflector 1 has a free aspect ratio design.

[0045] In step S2, the geometric backoff amount The mapping relationship with the required edge phase delay distribution is as follows:

[0046] ;

[0047] in, The vertical coordinates on the reflecting surface (with the center of the reflecting surface as 0). For the height of the reflecting surface, These are optimizable parameters that control the width, rate of change, and maximum phase delay of the phase delay region. The equation for the reflecting surface is expressed as:

[0048] ;

[0049] in, Indicates the phase delay on the reflector coordinate, This indicates the focal length of the reflector.

[0050] In step S4, the numerical optimization algorithms used include particle swarm optimization algorithm, genetic algorithm, and neural network algorithm.

[0051] In step S3, the electromagnetic calculation algorithm directly calculates the scattering field of the reflecting surface using the physical optics method or the multilayer fast multipole algorithm.

[0052] The specific implementation method is as follows:

[0053] Before the phase retardation structure is loaded, the central principal surface of the reflecting surface follows the standard parabolic cylindrical equation:

[0054] ;

[0055] in, Represents the surface coordinates of the reflecting surface of a standard parabolic cylinder.

[0056] When vertical height is limited, relying solely on the amplitude taper provided by serrations is insufficient to synthesize a high-quality still zone. Existing edge-rolling techniques, while offering superior performance, rely on large radii of curvature to guide diffracted waves, resulting in complex processing and high costs. This invention introduces phase weighting by altering the physical path length of the edge. Unlike edge-rolling, which primarily utilizes curvature to guide rays, this invention employs geometrical physical displacement to introduce specific phase delays. For example... Figure 2 As shown, the reflecting surface has a backward displacement relative to the standard parabolic surface. Based on the principle of electromagnetic wave propagation, this geometric displacement generates a path difference, thereby introducing additional phase weighting. This design simultaneously achieves dual control of amplitude and phase, while retaining the low-cost advantage of easy manufacturing of the sawtooth structure.

[0057] To enable precise control of the phase delay distribution through optimization algorithms, this invention defines a phase delay function with optimizable parameters based on a taper function in its implementation. The geometric backoff amount in the vertical direction is defined. With vertical coordinates The pattern of change is as follows:

[0058] ;

[0059] in, The vertical coordinates on the reflecting surface (with the center of the reflecting surface as 0). For the height of the reflecting surface, These are optimizable parameters that control the width of the phase delay region, the rate of change, and the maximum phase delay.

[0060] Superimposing the aforementioned phase delay onto the standard parabolic cylindrical equation yields the final surface equation of the reflecting surface:

[0061] ;

[0062] This equation shows that the final reflecting surface approximates a standard parabola in the solid portion of the reflecting surface, while gradually shifting backward in the edge region to form the desired phase delay structure, such as... Figure 3 As shown.

[0063] To determine the parameter set in the above formula, a multi-objective optimization approach is adopted based on the particle swarm optimization algorithm to optimize the parameter values. The parameter optimization process is as follows: Figure 4 As shown.

[0064] Step A: Determine the set of geometric parameters to be optimized, set the search space boundary for each parameter, and randomly generate the initial population parameters;

[0065] Step B: Based on the current parameter set, calculate the geometric receding amount of the reflector edge using the phase delay function, and construct a physical model of a single parabolic cylindrical reflector with specific phase delay characteristics.

[0066] Step C: Call electromagnetic simulation software to establish a model of the linear array-fed reflector system and calculate the electric field distribution data on multiple quiet zone 4 sampling sections within the target frequency band.

[0067] Step D: Construct an evaluation function based on the peak-to-peak values ​​of amplitude and phase in quiet zone 4, and calculate the performance evaluation index of quiet zone 4 corresponding to the current parameter group based on simulation data.

[0068] ;

[0069] in, It is the maximum amplitude within quiet zone 4. It is the minimum amplitude within quiet zone 4. It is the maximum phase value within the quiet zone 4. It is the minimum phase value within the quiet zone 4.

[0070] Step E: Record the current optimal evaluation index value; if the convergence criterion is not met (e.g., the index does not improve significantly after 100 consecutive iterations), update the parameter group and return to step B; if the convergence criterion is met, terminate the iteration and output the optimal geometric parameter value.

Claims

1. A high aspect ratio single parabolic cylindrical compact field system based on a linear array feed, characterized in that, include: A single parabolic cylindrical reflecting surface, having a parabolic vertical cross section and a straight horizontal cross section; A linear array feed is positioned along the focal line of the single parabolic cylindrical reflector to radiate cylindrical waves onto the reflector. The single parabolic cylindrical reflector has a high aspect ratio aperture, and its height is compressed to accommodate a high aspect ratio target. The edge region of the single parabolic cylindrical reflector has a serrated structure, and the geometric contour of the edge region is physically offset backward relative to the standard parabolic cylinder. This physical offset constitutes a phase delay structure, which is used to introduce a phase taper into the edge reflected wave.

2. The system according to claim 1, characterized in that, The physical offset of the edge region is achieved by bending the serrated structure away from the focal line, and its surface profile equation satisfies: ； in, To introduce the phase-delayed surface coordinates of the reflecting surface, For standard parabolic cylindrical coordinates, The geometric offset is determined by the phase delay function, and The value increases nonlinearly with increasing vertical distance from the center of the reflecting surface.

3. The system according to claim 1, characterized in that, Each element of the linear array feed has independent amplitude and phase control capabilities, which are used to generate quasi-plane waves in the horizontal direction of the quiet zone through complex coefficient excitation and to compensate for field distribution errors in the horizontal direction.

4. The system according to claim 1, characterized in that, The phase delay structure design includes the following steps: Step S1: Construct the basic geometric model of a single parabolic cylindrical reflector and set the aspect ratio and focal length of the reflector to adapt to targets with high aspect ratios; Step S2: Establish a parameterized model of the edge phase delay, including the geometric receding amount of the reflecting surface edge relative to the standard parabolic cylinder. Defined as about the vertical coordinate The function is selected, and the set of parameters controlling the function is chosen as the optimization variables; Step S3: Construct an optimization objective function based on the performance of the quiet zone, calculate the electric field distribution in the quiet zone under the current geometric parameters using an electromagnetic calculation algorithm, and calculate the amplitude and phase fluctuation values ​​in the quiet zone; Step S4: Iteratively adjust the optimization variables in step S2 using a numerical optimization algorithm until the static zone amplitude fluctuation calculated in step S3 meets the preset index, thereby determining the optimal edge geometric backoff amount and generating the final reflective surface processing model.

5. The system according to claim 4, characterized in that, In step S1, the constructed single parabolic cylindrical reflector has a free aspect ratio design.

6. The system according to claim 4, characterized in that, In step S2, the geometric backoff amount The mapping relationship with the required edge phase delay distribution is as follows: ； in The vertical coordinates on the reflecting surface (with the center of the reflecting surface as 0). For the height of the reflecting surface, These are optimizable parameters that control the width of the phase delay region, the rate of change, and the maximum phase delay. Used to control the delay distance; the equation for the reflective surface is expressed as: ； in, Indicates the phase delay on the reflector coordinate, This indicates the focal length of the reflector.

7. The system according to claim 4, characterized in that, In step S4, the numerical optimization algorithms used include particle swarm optimization algorithm, genetic algorithm, and neural network algorithm.

8. The system according to claim 4, characterized in that, In step S3, the electromagnetic calculation algorithm directly calculates the scattering field of the reflecting surface using the physical optics method or the multilayer fast multipole algorithm.

9. The system according to claim 1, characterized in that, The single parabolic cylindrical reflector is 5m wide and 1m high, with a width-to-height ratio of 5:

1. The bottom edge of the reflector is 0.07m from the ground. Right-angled triangular serrations are distributed around the reflector, with the top and bottom serrations being 0.2m high and the left and right serrations being 0.5m high.

10. The system according to claim 1, characterized in that, The reflector has a focal length of 1m, and the linear array is placed at the focal line position. The linear array feed illuminates the center of the single parabolic cylindrical reflector at a 32° angle.

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