A compacted field reflecting surface with FSS loading

Abstract

This invention proposes a compacted field reflector with a frequency selective surface (FSS) around its edge to address the severe low-frequency edge scattering problem of existing reflectors. The reflector comprises a parabolic compacted field reflector body and a frequency selective surface (FSS) loaded along its edge. The parabolic compacted field reflector body has a sawtooth edge. The frequency selective surface (FSS) includes a dielectric substrate and a resistor patch printed thereon. The dielectric substrate and the parabolic compacted field reflector body form a nested structure, with periodically arranged triangular sawtooths around its perimeter. The resistor patch is etched with a plurality of periodically arranged first cross-shaped slits and a plurality of second cross-shaped slits. This invention loads a resistor-type frequency selective surface structure at the edge of the reflector, reducing reflection abrupt changes and edge currents, improving edge scattering, and enhancing quiet zone performance, making it suitable for compacted field measurement systems.

Description

Technical Field

[0001] This invention belongs to the field of compact field measurement technology and relates to a compact field reflecting surface, specifically a compact field reflecting surface surrounded by a frequency selection surface (FSS), which can be used in a compact field measurement system. Background Technology

[0002] An ideal antenna test field should provide a reflection-free plane wave test area to measure the radiation characteristics of the antenna under test, and the same applies to scattering measurements. In field measurements, the minimum test distance needs to meet far-field conditions. When the antenna under test is very large or the test frequency is very high, the minimum test distance may need to be several kilometers or even tens of kilometers, which is practically impossible. Furthermore, field testing also suffers from drawbacks such as significant susceptibility to weather conditions, poor confidentiality, and high background levels. A compact field measurement system can provide a relatively uniform plane wave test area (i.e., a quiet zone) at close range using a parabolic reflector. This can be installed in a microwave anechoic chamber, thus offering all-weather testing and good confidentiality. For traditional reflectors, since the reflector is not infinitely large, electromagnetic waves diffract at the reflector's edge, scattering energy in multiple directions, thus interfering with the plane wave in the quiet zone. This causes uneven amplitude and phase distribution in the compact field's quiet zone, affecting its performance. Generally, a quiet zone with a stable amplitude within 1 dB and a stable phase within 10 degrees is considered to have good performance. The lower the frequency, the greater the impact of edge scattering, making low-frequency edge scattering a more challenging problem.

[0003] To reduce clutter interference in the quiet zone, related technologies involve edge-rolling or sawing the edges of reflective surfaces. Rolled-edge reflective surfaces guide surface currents to the back side by rolling the edges, thus reducing scattering in the quiet zone. While offering good performance, their high cost, complex modeling and fabrication, and susceptibility to deformation limit their widespread adoption. Sawtooth reflective surfaces, on the other hand, are easier to fabricate and are one of the most popular reflective surface choices. Sawtooth patterns typically include isosceles triangular, right-angled triangular, and cosine-edged shapes. However, even with optimized sawtooth patterns, edge scattering and ripple remain significant at low frequencies, and the performance achievable in the quiet zone may not be sufficient in certain situations.

[0004] For example, the patent application with publication number "CN111208359A" entitled "A compact field reflective surface edge teeth and design method" discloses a sawtooth edge reflective surface. This invention designs a sawtooth reflective surface with shapes such as right-angle sawtooth and cosine edge teeth, which can reduce the influence of the reflective surface edge on the amplitude and phase of the quiet zone to a certain extent. However, the edge scattering at low frequencies is still relatively serious, resulting in poor amplitude and phase stability in the quiet zone. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a compact field reflecting surface with an FSS-loaded perimeter, which solves the technical problem of poor amplitude and phase stability in the quiet zone caused by severe low-frequency edge scattering in the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A parabolic compressible field reflector with a parabolic frequency selective surface (FSS) around its edge includes a parabolic compressible field reflector body 1 and a parabolic frequency selective surface (FSS) 2 loaded on its edge with the same curvature. The parabolic compressible field reflector body 1 is a metal plate structure with a rectangular unfolded shape and periodically arranged triangular serrations around its perimeter. The parabolic frequency selective surface (FSS) 2. The device includes a flexible dielectric substrate 21 with a rectangular unfolded shape and a hollowed-out center, and a resistor patch 22 printed on its upper surface. The shape and size of the hollowed-out portion of the flexible dielectric substrate 21 are adapted to the rectangular unfolded metal plate structure in the parabolic compact field reflector body 1, forming a nested structure with the parabolic compact field reflector body 1. The flexible dielectric substrate 21 has periodically arranged triangular serrations around its periphery, corresponding to the periphery of the metal plate structure. The resistor patch 22 has a plurality of first cross-shaped slits 23 periodically arranged along the inner serration line etched near the inner edge of the rectangular metal plate structure, and a plurality of second cross-shaped slits 24 periodically arranged along the outer serration line etched near the outer edge.

[0008] The above-mentioned compressed field reflective surface with FSS loading is described above. The main body 1 of the parabolic compressed field reflective surface is made of a good conductor.

[0009] In the aforementioned compact field reflective surface with FSS loading, the flexible dielectric substrate 21, which has a rectangular unfolded shape and a hollowed-out center, coincides with the center normal of the metal plate structure, which also has a rectangular unfolded shape.

[0010] The aforementioned compressed field reflective surface with FSS loading is characterized in that the parabolic compressed field reflective surface body 1 and the flexible dielectric substrate 21 have isosceles triangles arranged around their periphery.

[0011] In the aforementioned compact field reflective surface with an FSS-enclosed edge, the period of the plurality of first cross-shaped slits 23 etched near the inner edge of the rectangular metal plate structure of the resistive patch 22 is the same as the period of the plurality of second cross-shaped slits 24 etched near the outer edge.

[0012] The above-mentioned compact field reflective surface with FSS loading is characterized in that the size of the first cross-shaped slit 23 is smaller than the size of the second cross-shaped slit 24.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. In this invention, by loading an FSS (Free-Side Surface) around the compacted field reflecting surface, the periodically arranged multiple first cross-shaped slits and second cross-shaped slits contained in the frequency-selective surface can achieve a gradual transmission characteristic, reduce the abrupt reflection at the edge of the reflecting surface, reduce edge scattering, and effectively improve the stability of the amplitude and phase in the quiet zone.

[0015] 2. In this invention, the FSS is applied to the compacted field reflective surface. The first and second cross-shaped slots of the frequency-selective surface are etched on the resistive patch, which can absorb and dissipate the edge-induced current at the edge of the reflective surface body. This helps to reduce the secondary radiation of the edge current and further improve the quiet zone performance. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present invention;

[0017] Figure 2 This is a planar unfolded view of an embodiment of the present invention;

[0018] Figure 3 This is a partial view of the frequency-selective surface of the present invention;

[0019] Figure 4 This is a simulation diagram of the amplitude and phase of the quiet zone of the present invention. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Reference Figure 1 A parabolic compacted field reflector with a frequency selective surface (FSS) around its edge includes a parabolic compacted field reflector body 1 and a frequency selective surface (FSS) 2 loaded on its edge with the same curvature. The parabolic compacted field reflector body 1 is a metal plate structure with a rectangular unfolded shape and periodically arranged isosceles triangular serrations around its perimeter. The metal plate structure generally uses a good conductor; in this embodiment, aluminum alloy is used. The rectangle is 0.62m in both length and width, and the base of the periodically arranged isosceles triangular serrations is 50mm long, with a serration height of 60mm. The serration design allows the scattered rays to be directed away from the quiet zone, reducing edge scattering. The serrations in the reflector body include, but are not limited to, isosceles triangles and right triangles. The frequency selective surface (FSS) 2 includes a flexible dielectric substrate 21 with a rectangular unfolded shape and a hollowed-out center, and a resistor patch 22 printed on its upper surface; as well as a first cross-shaped slit 23 and a second cross-shaped slit 24 etched on the resistor patch.

[0022] Reference Figure 2The frequency-selective surface FSS 2 includes a flexible dielectric substrate 21 with a rectangular unfolded shape and a hollowed-out center, and a resistor patch 22 printed on its upper surface. The flexible dielectric substrate 21 is made of a 15mm thick material with a relative permittivity of 2.2. The shape and size of the hollowed-out part at its center are adapted to the rectangular unfolded metal plate structure in the parabolic compact field reflector body 1, forming a nested structure with the parabolic compact field reflector body 1. The flexible dielectric substrate 21 has periodically arranged triangular serrations around its periphery, corresponding to the periphery of the metal plate structure. The base of the triangular serrations is 50mm long, and the serration height is 60mm. The resistor patch 22 has a surface resistance of 300 ohms and can absorb and dissipate the induced current at the edge of the reflector body. A plurality of first cross-shaped slits 23 are etched along the inner edge of the rectangular metal plate structure, arranged periodically along the inner serration line, and a plurality of second cross-shaped slits 24 are etched along the outer serration line, arranged periodically along the outer serration line.

[0023] Reference Figure 3 The multiple first cross-shaped slits 23 and multiple second cross-shaped slits 24 are arranged in a triangular pattern, with a period 'a' of 25 mm. This period size avoids the appearance of grating lobes that could affect transmission characteristics. The inner edge of the rectangular metal plate structure is etched with multiple first cross-shaped slits 23 arranged periodically along an inner serrated line, with a side length L2 of 14.7 mm and a width W of 4 mm. This size of slit unit can achieve 45% transmission of electromagnetic waves in the X-band. Near the outer edge, multiple second cross-shaped slits 24 arranged periodically along an outer serrated line are etched, with a side length L1 of 14.7 mm and a width W of 4 mm. This size of slit unit can achieve 90% transmission of electromagnetic waves in the X-band. From the inner edge to the outer edge, the size of the first cross-shaped slits 23 is smaller than that of the second cross-shaped slits 24, forming a gradient transmission characteristic. The cross-shaped slit design can achieve good performance under both horizontal and vertical polarization.

[0024] The parabolic surface of this invention has a focal length of 0.62m, with the focal point located on the center normal of the lower edge of a rectangular metal plate. When used in a compact field measurement system, this invention employs an offset feed source placed at the focal point to emit electromagnetic waves. These waves are reflected as quasi-plane waves onto the compact field reflecting surface, creating a quiet zone within a short distance. This invention also incorporates a frequency-selective surface with gradient transmission characteristics around the edge of the sawtooth reflecting surface to reduce abrupt reflections and edge scattering, effectively improving quiet zone performance. Furthermore, the use of a resistive frequency-selective surface absorbs and dissipates the edge-induced current at the edge of the reflecting surface, thereby reducing secondary radiation from the edge current and further enhancing quiet zone performance.

[0025] The technical effects of the present invention are illustrated below through simulation experiments:

[0026] 1. Simulation conditions and content:

[0027] The amplitude and phase of the 8GHz quiet zone of this invention were simulated and calculated using the commercial simulation software FEKO, and the results are as follows: Figure 4 As shown.

[0028] 2. Simulation Result Analysis:

[0029] Figure 4 (a) is a simulation diagram of the amplitude of the 8GHz quiet zone of the present invention. Figure 4 (b) is a phase simulation diagram of the 8GHz quiet zone of the present invention.

[0030] Depend on Figure 4 (a) It can be seen that the peak-to-peak horizontal amplitude in the quiet zone is 0.82 dB, and the peak-to-peak vertical amplitude is 1.02 dB; Figure 4 (b) It can be seen that the peak-to-peak value of the horizontal phase in the quiet zone is 7.33 degrees, and the peak-to-peak value of the vertical phase is 9.07 degrees; from Figure 4 Simulation results show that the quiet zone of the present invention has good amplitude and phase stability, with amplitude fluctuations basically within 1dB and phase fluctuations within 10deg, indicating good quiet zone performance.

[0031] The above description and embodiments are merely preferred examples of the present invention and do not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and design principles of the present invention, may make various modifications and changes in form and detail based on the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the protection scope of the claims of the present invention.

Claims

1. A compact field reflector loaded with FSS skirt, comprising a parabolic compact field reflector body (1) formed by a metal plate structure with a rectangular shape in an unfolded state and a periodic arrangement of triangular serrations provided on the periphery; characterized in that, The edge of the parabolic tight-field reflector body (1) is loaded with a frequency selective surface (FSS) (2) with the same curvature; the frequency selective surface (FSS) (2) comprises a flexible dielectric substrate (21) with a rectangular shape and a hollow center, and a resistive patch (22) printed on its upper surface; the flexible dielectric substrate (21) has a hollow center with a shape and size that is adapted to the rectangular metal plate structure in the parabolic tight-field reflector body (1), and forms a nested structure with the parabolic tight-field reflector body (1); the flexible dielectric substrate (21) has a perimeter provided with a periodic arrangement of triangular sawteeth corresponding to the perimeter position of the metal plate structure; the resistive patch (22) has a plurality of first cross-shaped slits (23) etched along the inner sawtooth line, and a plurality of second cross-shaped slits (24) etched along the outer sawtooth line.

2. A compact range of claim 1, wherein, The parabolic tight-field reflector body (1) is made of a good conductor.

3. A compact range of claim 1, wherein, The flexible dielectric substrate (21) with a rectangular shape and a hollow center coincides with the central normal of the rectangular metal plate structure.

4. A compact range of claim 1, wherein, The triangular sawteeth provided on the perimeters of the parabolic tight-field reflector body (1) and the flexible dielectric substrate (21) are isosceles triangles.

5. A compact range of claim 1, wherein, The period of the plurality of first cross-shaped slits (23) etched near the inner edge of the resistive patch (22) is the same as the period of the plurality of second cross-shaped slits (24) etched near the outer edge.

6. A compact range of claim 5, wherein, The size of the first cross-shaped slits (23) is smaller than the size of the second cross-shaped slits (24).

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