Bandstop Frequency Selective Surface Based on Impedance Transformation and Its Synthesis Design Method

Abstract

The present invention discloses a band-stop frequency selective surface based on impedance transformation and its integrated design method. The band-stop frequency selective surface adopts a three-dimensional stacked slot line structure, which consists of a periodic array of multiple stacked slot line units. Each of the stacked slot line units is composed of two layers and / or three layers, including: the first layer is a metal layer A, the second layer is a dielectric substrate, and the third layer is optionally provided as a metal layer B parallel to the first layer. The first to second layers and / or the first to third layers are sequentially laminated together. In the present invention, the designed band-stop frequency selective surface can be mapped and modeled by two parts, an equivalent impedance transformation network and a band-stop network, and has the advantages of compact unit structure, high selectivity narrow stopband, good out-of-band passband performance, and integrated design, etc., and is applicable to fields such as radars, antenna systems, satellite communications, and electromagnetic shielding with narrowband band-stop requirements.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic field and microwave technology, in particular to a band-stop frequency selective surface based on impedance transformation and a comprehensive design method thereof. Background Art

[0002] Frequency selective surfaces are array structures composed of several units arranged in a periodic or quasi-periodic manner, and have the characteristics of selecting and regulating electromagnetic waves in space. With the rapid development of wireless communication and radio frequency technology, band-stop frequency selective surfaces have been widely used in radar, antenna systems, satellite communications, electromagnetic shielding and other fields. Band-stop frequency selective surfaces can effectively achieve frequency band isolation and interference suppression by suppressing the propagation of electromagnetic waves in a specific frequency band, thereby improving the signal quality of the system. However, existing design methods still face many technical difficulties in achieving high-performance band-stop response, mainly including poor stopband selectivity, difficulty in meeting narrowband requirements, and lack of comprehensive design methods.

[0003] The traditional two-dimensional frequency selective surface adopts patch structure design, and forms resonant units (such as open loop, ring resonator, cross resonator, etc.) by designing the geometric shapes of different metal iron sheets, and adjusting their size and layout parameters to control the resonant frequency, thereby achieving band-stop response. For example, slotted or periodic metal structures are loaded to introduce the resonance phenomenon of electromagnetic waves. However, this method has high accuracy in low frequency bands and is sensitive to changes in geometric dimensions, making it difficult to meet high-frequency and high-precision requirements.

[0004] The existing three-dimensional frequency selective surface can also achieve the band-stop effect by loading an open or short-circuited resonant structure in the stacked microstrip line structure. This frequency selective surface has the characteristics of good frequency selectivity and simple processing. However, the design of this method is relatively complex and it is difficult to meet the needs of comprehensive design.

[0005] In general, in the current design of two-dimensional and three-dimensional frequency selective surfaces, how to explore the comprehensively designed band-stop frequency selective surfaces while taking into account narrowband and high in-band selectivity is a technical problem that needs to be solved urgently. Summary of the invention

[0006] The present invention provides a band-stop frequency selective surface based on impedance transformation with high selectivity and good full-band passband and a comprehensive design method thereof, which can solve at least one of the above technical problems.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The band-stop frequency selective surface based on impedance transformation adopts a three-dimensional stacked slot-line structure and consists of a periodic array of multiple stacked slot-line units. Each of the stacked slot-line units is composed of two layers and / or three layers, including: the first layer is a metal layer A, the second layer is a dielectric substrate, and the third layer is optionally provided and is a metal layer B parallel to the first layer. The first to second layers and / or the first to third layers are laminated together in sequence.

[0009] Further, the metal layer A of the first layer is composed of cascaded metal slotted lines and series-connected short-circuit slotted lines;

[0010] For a third-order band-stop frequency selective surface, the metal slotted lines include a first metal slotted line, a second metal slotted line, a third metal slotted line, and a fourth metal slotted line, and the short-circuit slotted lines include a first short-circuit slotted line, a second short-circuit slotted line, and a third short-circuit slotted line;

[0011] The first metal slotted line and the second metal slotted line are symmetrically arranged and are respectively uniform transmission lines, and the two form an impedance transformation network;

[0012] The third metal slotted line and the fourth metal slotted line are symmetrically arranged and are respectively uniform transmission lines. The second short-circuit slotted line is in an inverted "T" shape. The first short-circuit slotted line and the third short-circuit slotted line respectively rotate towards the first metal slotted line and the second metal slotted line and are symmetrically arranged on both sides of the second short-circuit slotted line. The first short-circuit slotted line, the second short-circuit slotted line, and the third short-circuit slotted line are respectively series-connected short-circuit stubs. The third metal slotted line, the fourth metal slotted line, the first short-circuit slotted line, the second short-circuit slotted line, and the third short-circuit slotted line form a short-circuit stub type band-stop network.

[0013] Further, in the short-circuit stub type band-stop network, the physical structure of the short-circuit stub is realized by the short-circuit slotted line, and the impedance of the short-circuit slotted line increases as its width increases.

[0014] Further, the metal layer B of the third layer is optionally provided as needed and is parallel to the metal layer A of the first layer. It includes a first metal strip, a second metal strip, and a third metal strip. The first metal strip, the second metal strip, and the third metal strip are parallel in sequence and correspond to the first short-circuit slotted line, the second short-circuit slotted line, and the third short-circuit slotted line.

[0015] The comprehensive design method of the band-stop frequency selective surface based on impedance transformation is realized by using the band-stop frequency selective surface based on impedance transformation and includes the following steps:

[0016] S1. According to the stopband index requirements of the required band-stop frequency selective surface, select a short-circuit stub type band-stop network with an appropriate order and its port impedance;

[0017] S2. For a short - circuited stub - type band - stop network with a known order, the analytical relationship between the band - stop index and each component in the band - stop network can be established by using the band - stop transfer function or selecting an appropriate characteristic function, and then the parameters of each component can be solved;

[0018] S3. According to the impedance transformation theory, the port impedance of the selected band - stop network is impedance - transformed with the free - space wave impedance. When impedance matching is achieved within the stop - band frequency range, the parameters of each component in the impedance transformation network are determined;

[0019] S4. The selected band - stop network and the determined impedance transformation network are respectively mapped to form a three - dimensional stacked slot - line - type band - stop frequency - selective surface unit. Finally, the actual physical structure of the band - stop frequency - selective surface is determined, and a physical sample can be produced using printed circuit board technology.

[0020] Furthermore, the factors for the comprehensive design of the band - stop frequency response in the band - stop network at least include: the center frequency of the stop - band, the bandwidth of the stop - band, and the return loss in the pass - band.

[0021] Furthermore, the band - stop network adopts a short - circuited stub - type band - stop circuit topology, and the available characteristic functions at least include the optimal band - stop characteristic function.

[0022] Furthermore, the physical structure of the band - stop network is realized by a three - dimensional stacked slot - line structure. The band - stop network includes series - connected short - circuited stubs and cascaded uniform transmission lines. The short - circuited stubs serve as band - stop resonators, and the uniform transmission lines serve as coupling structures / resonators. Both operate at the center frequency of the stop - band;

[0023] In the three - dimensional stacked slot - line structure, the series - connected short - circuited slot - lines correspond to the series - connected short - circuited stubs in the band - stop network, and the cascaded metal - slotted lines correspond to the cascaded uniform transmission lines in the band - stop network.

[0024] Furthermore, as a spatial electromagnetic wave amplitude control device, the impedance transformation network at the input and output ports of the band - stop frequency - selective surface is used to realize the impedance transformation between the free - space wave and the band - stop network. While widely solving the problem of maintaining the band - stop performance within the band in the amplitude comprehensive design of spatial electromagnetic waves, it ensures good low - reflection band - pass performance outside the stop - band;

[0025] The impedance transformation network selects single - section or multi - section cascaded uniform transmission lines as single - section or multi - section impedance transformers, both of which operate at the center frequency of the stop - band;

[0026] In the three - dimensional stacked slot - line structure, the single - section or multi - section cascaded metal - slotted lines correspond to the single - section or multi - section cascaded uniform transmission lines in the impedance transformation network.

[0027] Furthermore, the three-dimensional stacked slot line type band-stop frequency selective surface has the ability to convert spatial electromagnetic waves into guided wave modes, converting complex spatial electromagnetic waves into guided waves that are easy to control. Thus, a comprehensive "field-circuit" conversion design is carried out from the perspective of "circuit", and the three-dimensional stacked slot line structure is directly mapped by the distributed transmission line model to improve the design efficiency and accuracy.

[0028] The beneficial effects of the present invention are as follows:

[0029] 1. The present invention realizes a comprehensive design method for band-stop response in a three-dimensional stacked slot line structure. The comprehensive design is carried out based on the center frequency of the stopband, the bandwidth of the stopband, and the return loss of the passband, providing an effective narrow-band band-stop frequency selective surface design scheme. A 3dB bandwidth of less than 10% can be achieved, including an effective impedance transformation network design scheme, enabling high selectivity within the stopband and good passband performance across the entire frequency band. At the same time, the profile thickness of the band-stop frequency selective surface is relatively small, approximately one wavelength of the center frequency.

[0030] 2. Compared with the design of traditional two-dimensional band-stop frequency selective surfaces, the three-dimensional band-stop frequency selective surface of the present invention has the ability to convert spatial electromagnetic waves into guided wave modes, which can convert complex spatial electromagnetic waves into guided waves that are easy to control. Thus, a comprehensive "field-circuit" conversion design is carried out from the perspective of "circuit", and the three-dimensional stacked slot line structure is directly mapped by the distributed transmission line model to improve its design efficiency and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application.

[0032] Figure 1 is a three-dimensional structure schematic diagram of the band-stop frequency selective surface of Embodiment 1 of the present invention.

[0033] Figure 2 is a unit structure schematic diagram of the band-stop frequency selective surface of Embodiment 1 of the present invention in a three-dimensional space coordinate system.

[0034] Figure 3 is a front view of the band-stop frequency selective surface of Embodiment 1 of the present invention.

[0035] Figure 4 is a dimension schematic diagram of the band-stop frequency selective surface of Embodiment 1 of the present invention.

[0036] Figure 5 is a front view of the band-stop frequency selective surface of Embodiment 2 of the present invention.

[0037] Figure 6 is a rear view of the band-stop frequency selective surface of Embodiment 2 of the present invention.

[0038] Figure 7 It is a schematic diagram of the front structural dimensions of the band-stop frequency selective surface in the second embodiment of the present invention.

[0039] Figure 8 It is a schematic diagram of the reverse structural dimensions of the band-stop frequency selective surface in the second embodiment of the present invention.

[0040] Figure 9 It is the overall flowchart of the comprehensive design method of the band-stop frequency selective surface in the embodiment of the present invention.

[0041] Figure 10 It is the circuit topology diagram of the comprehensive design method of the band-stop frequency selective surface in the embodiment of the present invention.

[0042] Figure 11 It is the typical S-parameter curve diagram in the embodiment of the present invention.

[0043] Figure 12 It is the S-parameter curve diagram of the full-wave electromagnetic simulation of the band-stop frequency selective surface in the first embodiment of the present invention.

[0044] Figure 13 It is the S-parameter curve diagram of the full-wave electromagnetic simulation of the band-stop frequency selective surface in the second embodiment of the present invention.

[0045] Figure 14 It is the structural block diagram of the computer device in the embodiment of the present invention.

[0046] The marks of each component in the drawings are as follows:

[0047] In the first embodiment:

[0048] 1. Dielectric substrate; 2. Metal layer A; 3. First metal slotted line; 4. Third metal slotted line; 5. Fourth metal slotted line; 6. Second metal slotted line; 7. First short-circuit slotted line; 8. Second short-circuit slotted line; 9. Third short-circuit slotted line;

[0049] In the second embodiment:

[0050] 10. Dielectric substrate; 11. First metal slotted line; 12. Third metal slotted line; 13. Fourth metal slotted line; 14. Second metal slotted line; 15. First short-circuit slotted line; 16. Second short-circuit slotted line; 17. Third short-circuit slotted line; 18. Metal layer A; 19. Metal layer B; 20. First metal strip; 21. Second metal strip; 22. Third metal strip. Detailed implementation manners

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] It should be noted that if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, such descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the meaning of "and / or" appearing throughout the text includes three parallel scenarios. Taking "A and / or B" as an example, it includes scenario A, or scenario B, or the scenario where both A and B are satisfied simultaneously. In addition, "a plurality of" means two or more.

[0053] Referring to Figures 1-4 , Embodiment 1 of the present invention provides a band-stop frequency selective surface based on impedance transformation. The band-stop frequency selective surface has a design index with a center frequency of 5 GHz and a 3 dB bandwidth of 4%. It adopts a three-dimensional stacked slot line structure, which consists of a periodic array formed by a plurality of stacked slot line units through equidistant air gaps. Each of the stacked slot line units is composed of two layers, including: the first layer is a metal layer A2, and the second layer is a dielectric substrate 1. The dielectric substrate 1 is closely attached to the metal layer A2.

[0054] In Embodiment 1, the provided band-stop frequency selective surface is of the third order. The first layer of the metal layer A2 is composed of cascaded metal slotted lines and series-connected short-circuit slotted lines, where:

[0055] The metal slotted lines include a first metal slotted line 3, a second metal slotted line 6, a third metal slotted line 4, and a fourth metal slotted line 5. The short-circuit slotted lines include a first short-circuit slotted line 7, a second short-circuit slotted line 8, and a third short-circuit slotted line 9;

[0056] The first metal slotted line 3 and the second metal slotted line 6 are symmetrically arranged and are respectively uniform transmission lines, and the two form an impedance transformation network;

[0057] The third metal slotted line 4 and the fourth metal slotted line 5 are symmetrically arranged and are respectively uniform transmission lines. The second short-circuit slotted line 8 has an inverted "T" structure. The first short-circuit slotted line 7 and the third short-circuit slotted line 9 are respectively rotated towards the first metal slotted line 3 and the second metal slotted line 6 and are symmetrically arranged on both sides of the second short-circuit slotted line 8. The first short-circuit slotted line 7, the second short-circuit slotted line 8 and the third short-circuit slotted line 9 are respectively series short-circuit stubs. The third metal slotted line 4, the fourth metal slotted line 5, the first short-circuit slotted line 7, the second short-circuit slotted line 8 and the third short-circuit slotted line 9 form a short-circuit stub type band-stop network.

[0058] Combined with Figure 2 and Figure 4 the physical size markings of the band-stop frequency selective surface in, the design parameters are as follows:

[0059] P x = 15 mm, P y = 15 mm, d 1 = 0.508 mm, d 2 = 7.246 mm, W 1 = 7.8 mm, W 2 = 6.7 mm, W 3 = 0.8 mm, W 4 = 0.6 mm, W 5 = 1 mm, L 1 = 14 mm, L 2 = 13.84 mm, L 3 = 10.31 mm, L 4 = 5 mm, L 5 = 5.9 mm.

[0060] In the first embodiment, in the short-circuit stub type band-stop network, the physical structure of the short-circuit stub is realized by the short-circuit slotted line, and the impedance of the short-circuit slotted line increases as its own width increases.

[0061] The short - circuit stub - type band - stop network is combined with the impedance transformation network to jointly form the band - stop frequency - selective surface of the present invention. The band - stop frequency - selective surface is designed to be left - right symmetric. The rotation of the first short - circuit slot line 7 and the third short - circuit slot line 9, as well as the bending of the second short - circuit slot line 8, aim to reduce y the width in the y direction, and at the same time reduce the coupling between adjacent series short - circuit stubs. At the same time, in order to avoid the grating lobe effect of the band - stop frequency - selective surface, in the three - dimensional space coordinate system, x the size of the stacked slot - line unit in the P y direction P x is less than or equal to one - quarter of the wavelength corresponding to the center frequency of 5 GHz. Usually, P y is equal to P x , and the two jointly affect the free - space wave impedance and the stacked slot - line impedance.

[0062] In summary, the band - stop frequency - selective surface of the first embodiment of the present invention adopts a three - dimensional stacked slot - line structure, which is mapped and modeled by two parts: an equivalent impedance transformation network and a band - stop network, achieving high selectivity in the stop - band operating frequency band and good pass - band performance outside the operating frequency band.

[0063] Referring to Figures 5-8 , the second embodiment of the present invention also provides a band - stop frequency - selective surface based on impedance transformation. The band - stop frequency - selective surface has a design index with a center frequency of 5 GHz and a 3 - dB bandwidth of 4%. It adopts a three - dimensional stacked slot - line structure, and a periodic array is composed of multiple stacked slot - line units through equidistant air gaps. Each of the stacked slot - line units consists of three layers, including: the first layer is the metal layer A18, the second layer is the dielectric substrate 10, and the third layer is the metal layer B19. The third layer is parallel and corresponding to the first layer, and the first to third layers are laminated together in sequence.

[0064] In the second embodiment, the provided band - stop frequency - selective surface is of the third order. The first - layer metal layer A18 is composed of cascaded metal slotted lines and series - connected short - circuit slot lines, where:

[0065] The metal slotted lines include the first metal slotted line 11, the second metal slotted line 14, the third metal slotted line 12, and the fourth metal slotted line 13, and the short - circuit slot lines include the first short - circuit slot line 15, the second short - circuit slot line 16, and the third short - circuit slot line 17;

[0066] The first metal slotted line 11 and the second metal slotted line 14 are symmetrically arranged and are respectively uniform transmission lines, and the two together form an impedance transformation network;

[0067] The third metal slotted line 12 and the fourth metal slotted line 13 are symmetrically arranged and are respectively uniform transmission lines. The second short - circuit slotted line 16 has an inverted "T" - shaped structure. The first short - circuit slotted line 15 and the third short - circuit slotted line 17 respectively rotate towards the first metal slotted line 11 and the second metal slotted line 14 and are symmetrically arranged on both sides of the second short - circuit slotted line 16. The first short - circuit slotted line 15, the second short - circuit slotted line 16, and the third short - circuit slotted line 17 are respectively series short - circuit stubs. The third metal slotted line 12, the fourth metal slotted line 13, the first short - circuit slotted line 15, the second short - circuit slotted line 16, and the third short - circuit slotted line 17 form a short - circuit stub type band - stop network.

[0068] In the second embodiment, in the short - circuit stub type band - stop network, the physical structure of the short - circuit stub is realized by the short - circuit slotted line, and the impedance of the short - circuit slotted line increases with the increase of its own width.

[0069] In the second embodiment, the third metal layer B19 is parallel to the first metal layer A18 and includes a first metal strip 20, a second metal strip 21, and a third metal strip 22. The first metal strip 20, the second metal strip 21, and the third metal strip 22 are parallel to each other in sequence and correspond to the first short - circuit slotted line 15, the second short - circuit slotted line 16, and the third short - circuit slotted line 17. The function of these three metal strips is to reduce the characteristic impedance of the first short - circuit slotted line 15, the second short - circuit slotted line 16, and the third short - circuit slotted line 17, thereby reducing the width of the slotted line short - circuit stub. In the second embodiment, the periodic size of the provided band - stop frequency - selective surface is the same as that in the first embodiment. Combining Figures 7-8 with the physical size markings of this band - stop frequency - selective surface, its design parameters are as follows:

[0070] P x = 15mm, P y = 15mm, d 1 = 0.508mm, d 2 = 7.246mm, W 6 = 7.8mm, W 7 = 6.7mm, W 8 = 0.4mm, W 9 = 0.5mm, W 10 = 0.4mm, W 11 = 0.6mm, W10 = 0.4 mm, L 6 = 14 mm, L 7 = 13.84 mm, L 8 = 10.06 mm, L 9 = 4.4 mm, L 10 = 6.9 mm, L 11 = 10.06 mm, L 12 = 4.4 mm, L 13 = 6.9 mm.

[0071] By covering a parallel metal strip parallel to the short - circuited slot line of the first layer on the third layer, the impedance of the slot line can be further reduced, so as to meet the small - impedance design requirements of the narrow - band band - stop response, and further achieve a narrower stop - band bandwidth.

[0072] The short - circuited stub - type band - stop network and the impedance transformation network are combined to jointly form the band - stop frequency - selective surface of the present invention. This band - stop frequency - selective surface is designed to be left - right symmetric. The rotation of the first short - circuited slot line 15 and the third short - circuited slot line 17, as well as the bending of the second short - circuited slot line 16, aim to reduce y the width in the y , x direction, and at the same time reduce the coupling between adjacent series - connected short - circuited stubs. At the same time, in order to avoid the grating lobe effect of the band - stop frequency - selective surface, in the three - dimensional space coordinate system, P y , P x the size of the stacked slot - line unit in the P y and P x direction is less than or equal to one - quarter of the wavelength corresponding to the center frequency of 5 GHz. Generally,

[0073] In summary, the band - stop frequency - selective surface of the second embodiment of the present invention still adopts a three - dimensional stacked slot - line structure, which is mapped and modeled by two parts: an equivalent impedance transformation network and a band - stop network. However, the difference from the first embodiment is that in the second embodiment, a metal strip parallel to the upper - layer metal slotting is added to the lower surface of the dielectric substrate to reduce the width of the slot - line short - circuited stub, and the high selectivity in the stop - band operating frequency band is also achieved, and at the same time, the pass - band performance is good outside the operating frequency band.

[0074] See Figure 9, an embodiment of the present invention also provides a comprehensive design method for a band-stop frequency selective surface based on impedance transformation, which is implemented by using the band-stop frequency selective surface based on impedance transformation, and includes the following steps:

[0075] S1. According to the stopband index requirements of the required band-stop frequency selective surface, select a band-stop network of a suitable order of short-circuited stubs and its port impedance;

[0076] S2. For a band-stop network of a known order of short-circuited stubs, an analytical relationship between the band-stop index and each component in the band-stop network can be established by using a band-stop transformation function or selecting an appropriate characteristic function, and the parameters of each component are solved;

[0077] S3. According to the impedance transformation theory, perform impedance transformation on the port impedance of the selected band-stop network and the free space wave impedance, and determine the parameters of each component in the impedance transformation network when impedance matching is achieved within the stopband frequency range;

[0078] S4. Map the selected band-stop network and the determined impedance transformation network respectively to form a three-dimensional stacked slot-line type band-stop frequency selective surface unit, and finally determine the actual physical structure of the band-stop frequency selective surface, and a physical sample can be produced by using printed circuit board technology.

[0079] The present invention designs a band-stop frequency selective surface with high selectivity within the stopband and good passband performance in the entire frequency band by comprehensively designing a band-stop network and an impedance transformation network. As Figure 10 shown, a general circuit topology of the present invention is given, which is divided into two parts: space electromagnetic wave and guided wave, where the guided wave part is a combination of a single-section or multi-section cascaded impedance transformation network and a short-circuited stub type band-stop network. As Figure 11 shown, a typical S-parameter curve of the present invention is given. Within the operating frequency band, a highly selective stopband is achieved, the passband performance in the entire frequency band is good, and the passband return loss is below 10 dB.

[0080] As Figure 12 shown, the S-parameter curve of the full-wave electromagnetic simulation of the band-stop frequency selective surface in Embodiment 1 is given. Its center frequency is 5.00 GHz, the 3 dB bandwidth is in the range of 4.90 - 5.10 GHz, the stopband has high selectivity, the passband is good outside the range of 4.87 - 5.14 GHz, and the return loss is less than 10 dB.

[0081] As Figure 13 shown, the S-parameter curve of the full-wave electromagnetic simulation of the band-stop frequency selective surface in Embodiment 2 is given. Its center frequency is 5.01 GHz, the 3 dB bandwidth is in the range of 4.91 - 5.11 GHz, the stopband has high selectivity, the passband is good outside the range of 4.88 - 5.15 GHz, and the return loss is less than 10 dB.

[0082] In this embodiment, the factors for the comprehensive design of the band-stop frequency response in the band-stop network at least include: the center frequency of the stopband, the bandwidth of the stopband, and the return loss of the passband. The band-stop network is combined with an impedance transformation network, so that the stopband has high selectivity, the passband of the entire frequency band is good, and it is easy to physically implement the frequency selective surface.

[0083] In this embodiment, the band-stop network adopts a short-circuit stub type band-stop circuit topology, and the available characteristic functions at least include the optimal band-stop characteristic function.

[0084] In the first and second embodiments of the present application, the characteristic function of the short-circuit stub type band-stop network of the band-stop frequency selective surface is selected as the optimal band-stop characteristic function. Compared with the Chebyshev characteristic function of the same order, the optimal band-stop characteristic function has a steeper attenuation characteristic in the stopband;

[0085] Specifically, the optimal band-stop characteristic function F N （f） is expressed as follows:

[0086]

[0087] Where:

[0088] t and t c are respectively:

[0089]

[0090] T n ( x ) and U n ( x ) are respectively n the first and second kind Chebyshev functions of order

[0091] In this embodiment, the physical structure of the band-stop network is realized by a three-dimensional stacked slot line structure. The band-stop network includes series-connected short-circuit stubs and cascaded uniform transmission lines. The short-circuit stubs serve as band-stop resonators, and the uniform transmission lines serve as coupling resonators. Both operate at the center frequency of the stopband;

[0092] In the circuit topology, the series-connected short-circuit stubs and the cascaded uniform transmission lines respectively correspond to the series-connected short-circuit slot lines and the cascaded metal slotted lines in the three-dimensional stacked slot line structure.

[0093] In this embodiment, the band-stop frequency selective surface serves as a spatial electromagnetic wave amplitude regulation device, and the impedance transformation network at its input and output ports is used to achieve the impedance transformation between the free space wave and the band-stop network, ensuring good out-of-band passband performance while keeping the in-band performance of the stopband unchanged;

[0094] The impedance transformation network selects a single-section or multi-section cascaded uniform transmission line. As a single-section or multi-section impedance transformer, it operates at the center frequency of the stopband;

[0095] In the circuit topology, the single-section or multi-section cascaded uniform transmission lines respectively correspond to the single-section or cascaded metal slotted lines in the three-dimensional stacked slot-line structure.

[0096] In this embodiment, impedance transformation can adopt multi-stage cascading technology, such as a Chebyshev multi-section matching transformer, to further expand the stopband width of the band-stop frequency selective surface while maintaining good in-band insertion loss characteristics, and all can be realized by multi-section cascaded metal slotted lines.

[0097] In this embodiment, the three-dimensional stacked slot-line type band-stop frequency selective surface has the ability to convert spatial electromagnetic waves into guided waves for easy regulation, so as to conduct a comprehensive "field-circuit" conversion design from the perspective of "circuit", and directly map the three-dimensional stacked slot-line structure through the distributed transmission line model, improving its design efficiency and accuracy.

[0098] The embodiment of the present invention also provides a computer-readable storage medium storing a computer program, which when executed by a processor causes the processor to execute the steps of the above method.

[0099] See Figure 14 , the embodiment of the present invention also provides a computer device including a memory and a processor, where the memory stores a computer program, and when the computer program is executed by the processor, it causes the processor to execute the steps of the above method.

[0100] The embodiment of the present invention also provides a computer program product containing instructions, which when running on a computer causes the computer to execute the steps of the above method.

[0101] It can be understood that the system, device and storage medium provided by the embodiment of the present invention correspond to the method provided by the embodiment of the present invention. The explanations, examples and beneficial effects of the relevant content can refer to the corresponding parts in the above method.

[0102] It should be noted that those of ordinary skill in the art can understand that all or part of the steps implemented in the embodiments of the present invention can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented using hardware, it can be implemented in whole or in part in the form of purchasing standard parts or modified parts. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the processes or functions described in the embodiments of the present application are generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that the computer can access or a data storage device such as a server, data center, etc. that contains one or more integrated available media. The available media can be magnetic media (such as floppy disks, hard disks, magnetic tapes), optical media (such as DVDs), or semiconductor media (such as solid state disks (SSDs)), etc.

[0103] In summary, the present invention proposes the idea of combining the design of a band-stop circuit with impedance transformation, realizes the comprehensive design of a band-stop frequency selective surface in a three-dimensional stacked slot-line structure, and corresponds the band-stop circuit prototype with the physical structure of the three-dimensional stacked slot-line type frequency selective surface, and designs a band-stop frequency selective surface with high selectivity in the stop band and good pass bands in the entire frequency band.

[0104] It should be understood that the examples and embodiments described herein are for illustrative purposes only and are not intended to limit the present invention. Those skilled in the art can make various modifications or changes based on it. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A band-stop frequency selective surface based on impedance transformation, characterized in that: A three-dimensional stacked slot line structure is adopted, and a plurality of stacked slot line units are formed into a periodic array through air gaps with equal distances, and each of the stacked slot line units is composed of two layers and / or three layers, including: the first layer is a metal layer A, the second layer is a dielectric substrate, and the third layer can be optionally set to be a metal layer B parallel to the first layer, and the first to second layers and / or the first to third layers are pressed together in sequence; The first metal layer A is composed of cascaded metal slotted lines and series-connected short-circuit slotted lines; For the third-order band-stop frequency selective surface, the metal slotted lines include a first metal slotted line, a second metal slotted line, a third metal slotted line and a fourth metal slotted line, and the short-circuit slot lines include a first short-circuit slot line, a second short-circuit slot line and a third short-circuit slot line; The first metal slotted line and the second metal slotted line are symmetrically arranged and are uniform transmission lines respectively, and the two form an impedance transformation network; The third metal slotted line and the fourth metal slotted line are symmetrically arranged, and are uniform transmission lines respectively; the second short-circuit slot line is in an inverted "T" structure; the first short-circuit slot line and the third short-circuit slot line are respectively rotated toward the first metal slotted line and the second metal slotted line, and are symmetrically arranged on both sides of the second short-circuit slot line; the first short-circuit slot line, the second short-circuit slot line and the third short-circuit slot line are respectively series short-circuit branches; the third metal slotted line, the fourth metal slotted line, the first short-circuit slot line, the second short-circuit slot line and the third short-circuit slot line form a short-circuit branch type band-stop network; The third metal layer B can be optionally set as needed, parallel to the first metal layer A, and includes a first metal strip, a second metal strip and a third metal strip. The first metal strip, the second metal strip and the third metal strip are parallel to each other and correspond to the first short-circuit slot line, the second short-circuit slot line and the third short-circuit slot line respectively.

2. The band-stop frequency selective surface based on impedance transformation according to claim 1, characterized in that: In the short-circuit branch type band-stop network, the physical structure of the short-circuit branch is realized by the short-circuit slot line, and the impedance of the short-circuit slot line increases with the increase of its own width.

3. A comprehensive design method of a band-stop frequency selective surface based on impedance transformation, which is implemented by using the band-stop frequency selective surface based on impedance transformation as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: S1. According to the stopband index requirements of the required stopband frequency selection surface, select the short-circuit branch type stopband network of appropriate order and its port impedance; S2. For a short-circuit branch-type band-stop network of known order, the band-stop transformation function or appropriate characteristic function can be used to establish the analytical relationship between the band-stop index and each component in the band-stop network, and solve the parameters of each component; S3. According to the impedance transformation theory, the port impedance of the selected band-stop network is transformed with the free space wave impedance to determine the parameters of each component in the impedance transformation network when the impedance matching is achieved within the stopband frequency range; S4. The selected band-stop network and the determined impedance transformation network are mapped respectively to form a three-dimensional stacked slot-line band-stop frequency selective surface unit, and finally the actual physical structure of the band-stop frequency selective surface is determined, and a physical sample can be produced using a printed circuit board process.

4. The comprehensive design method of the band-stop frequency selective surface based on impedance transformation as claimed in claim 3, characterized in that: The factors for the comprehensive design of the band-stop frequency response in the band-stop network at least include: stop-band center frequency, stop-band bandwidth and pass-band return loss.

5. The comprehensive design method of the band-stop frequency selective surface based on impedance transformation according to claim 3, characterized in that: The band-stop network adopts a short-circuit branch-type band-stop circuit topology, and the characteristic functions that can be used include at least an optimal band-stop characteristic function.

6. The comprehensive design method of the band-stop frequency selective surface based on impedance transformation according to claim 5, characterized in that: The physical structure of the band-stop network is realized by a three-dimensional stacked slot line structure, and the band-stop network includes series-connected short-circuit branches and cascaded uniform transmission lines, the short-circuit branches serve as band-stop resonators, and the uniform transmission lines serve as coupling structures / resonators, both of which work at the center frequency of the stop band; In the three-dimensional stacked slot line structure, the series short-circuit slot lines correspond to the series short-circuit branches in the band-stop network, and the cascaded metal slot lines correspond to the cascaded uniform transmission lines in the band-stop network.

7. The comprehensive design method of the band-stop frequency selective surface based on impedance transformation according to claim 3, characterized in that: The band-stop frequency selective surface is used as a spatial electromagnetic wave amplitude control device, and the impedance transformation network of its input and output ports is used to realize the impedance transformation between the free space wave and the band-stop network, which can widely solve the problem of the spatial electromagnetic wave keeping the stopband performance unchanged within the amplitude comprehensive design band, and ensure good low-reflection bandpass performance outside the stopband; The impedance transformation network uses a single-section or multi-section cascaded uniform transmission line as a single-section or multi-section impedance transformer, all of which work at the stopband center frequency; In the three-dimensional stacked slot line structure, a single section or multiple sections of cascaded metal slotted lines correspond to a single section or multiple sections of cascaded uniform transmission lines in an impedance transformation network.

8. The comprehensive design method of the band-stop frequency selective surface based on impedance transformation according to claim 3, characterized in that: The three-dimensional stacked slot-line type band-stop frequency selective surface has the ability to convert spatial electromagnetic waves and guided wave modes, converting complex spatial electromagnetic waves into guided waves that are easy to control, thereby performing a comprehensive design of "field-to-path" conversion from the perspective of "path", and directly mapping the distributed transmission line model to realize the three-dimensional stacked slot-line structure to improve design efficiency and accuracy.

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