Spur line structure based artificial surface plasmon polariton low-pass filter with steep transition

Abstract

The application discloses a steep transition type artificial surface plasmon low-pass filter based on a spur line structure and belongs to the technical field of low-pass filters. The low-pass filter comprises a dielectric substrate, the upper surface of the dielectric substrate is provided with a coplanar waveguide, and the lower surface of the dielectric substrate is provided with a spur line unit array. The coplanar waveguide comprises a center conductor strip and ground strips symmetrically distributed on both sides of the center conductor strip. An L-shaped slot unit array is etched on the ground strips. The L-shaped slot unit array is distributed along the length direction of the coplanar waveguide. The low-pass filter comprises a filter unit and transition units symmetrically arranged at both ends of the filter unit. The projection of the spur line unit array on a plane perpendicular to the wave propagation direction is aligned with the center of the filter unit. The low-pass filter based on the spur line structure can realize adjustable dispersion cutoff frequency and sharp transition from a passband to a stopband, and has simple structure and miniaturization.

Description

Technical Field

[0001] This invention relates to the field of artificial surface plasmon low-pass filter technology, and in particular to a steep transition artificial surface plasmon low-pass filter based on a spur line structure. Background Technology

[0002] Artificial surface plasmon polaritons (SSPPs) refer to a class of surface electromagnetic wave modes supported by artificially designed structural materials. They simulate the characteristics of natural surface plasmons by etching periodic subwavelength structures on a metal surface, overcoming the limitation that natural surface plasmons behave as ideal conductors rather than plasmons in the microwave and terahertz frequency bands. SSPPs exhibit strong field confinement, low transmission loss, and their dispersion characteristics and cutoff frequencies can be achieved by altering the structural parameters of the metal, greatly facilitating device design and demonstrating broad application prospects.

[0003] Transmission lines based on artificial surface plasmons (ASPs) inherently possess low-pass filtering characteristics, achieving filtering functionality without the need for additional resonant units, thus offering significant practical advantages. Currently, numerous ASP-based low-pass filter schemes have been proposed, achieving performance goals such as miniaturization, bandwidth extension, or adjustable cutoff frequency. For example, some schemes lower the asymptotic frequency by altering the slot shape or adding capacitor structures; others introduce defect structures into the coplanar waveguide grounding band or transmission line to improve stopband suppression. While these methods improve filtering performance to some extent, they generally suffer from a wide transition region between the passband and stopband and insufficient filter selectivity.

[0004] Typically, to achieve a steeper transition characteristic, one can increase the filter order or cascade more SSPP units. However, this approach significantly increases the overall size and insertion loss, and the structural design is complex and sensitive to manufacturing tolerances. Furthermore, the asymptotic frequency and transition steepness of traditional SSPP units are often coupled, making it difficult to independently control them using a single geometric parameter.

[0005] Therefore, how to achieve both asymptotic frequency controllability and a steeper transition from the passband to the stopband without increasing structural complexity has become an important problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a steep transition artificial surface plasmon low-pass filter based on a spur line structure, which solves the problems of wide transition region between passband and stopband, insufficient filter selectivity and complex structure of existing SSPP structure filters. By introducing a spur line structure at the bottom layer, a steep transition artificial surface plasmon low-pass filter based on a spur line structure is proposed to achieve an adjustable dispersion cutoff frequency and a sharp transition from passband to stopband, while also being simple and miniaturized.

[0007] To achieve the above objectives, the present invention provides a steep transition type artificial surface plasmon low-pass filter based on a spur line structure, comprising a dielectric substrate, a coplanar waveguide disposed on the upper surface of the dielectric substrate, and a spur line unit array disposed on the lower surface. The coplanar waveguide includes a central conductor strip and ground strips symmetrically distributed on both sides of the central conductor strip. An L-shaped slot unit array is etched on the ground strip. The L-shaped slot unit array is distributed along the length direction of the coplanar waveguide and includes a filter unit and transition units symmetrically disposed at both ends of the filter unit. The spur line unit array is aligned with the center of the filter unit on a projection plane perpendicular to the wave propagation direction.

[0008] Preferably, the spur line unit array is composed of periodically arranged spur line units, and each spur line unit is composed of folded branches;

[0009] The spur line unit is symmetrically distributed with respect to its vertical axis of symmetry, and consists of a main branch and a parallel branch extending from the main branch to both sides.

[0010] Preferably, the spur line unit array includes a transmission region and transition regions symmetrically arranged at both ends of the transmission region. The spur line units in the transition region have a smaller branch length and width than the spur line units in the transmission region, while the spur line units in the transmission region have the same size.

[0011] Preferably, the size of the L-shaped slot unit of the transition unit increases from both sides to the middle in the coplanar waveguide length direction, and the size of the L-shaped slot unit of the filter unit is the same.

[0012] Preferably, the dielectric substrate is FR4 material with a relative permittivity of 4.4 and a loss tangent of 0.02.

[0013] Therefore, the present invention employs the steep transition type artificial surface plasmon low-pass filter based on the spur line structure described above, which has the following beneficial effects:

[0014] (1) By introducing a bottom spur line structure and coupling it with the top SSPP unit, the attenuation pole is brought closer to the asymptotic frequency, thereby achieving a steeper transition between the passband and the stopband and improving the selectivity of the filter.

[0015] (2) The dispersion characteristics and the steepness of the stopband edge can be controlled simultaneously by rationally designing the geometric parameters of the spur line unit array;

[0016] (3) Excellent out-of-band suppression, stable performance, can effectively suppress high-order harmonics and spurious signals, while maintaining low insertion loss in the passband and providing high attenuation in the stopband, with overall stable and reliable performance;

[0017] (4) The introduction of the spur line structure not only effectively controls the size of the filter, but also reduces the manufacturing complexity; based on standard PCB process and FR4 material, it is easy to process and further improves the cost-effectiveness of production, making it suitable for large-scale production in modern integrated circuits.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the unit structure based on SSPP of the present invention;

[0020] Figure 2 The figures show a comparison of the dispersion curves and attenuation curves of the transition steep artificial surface plasmon unit based on the spur line structure and the unit without the spur line structure in this invention. (a) is a comparison of the dispersion curves, and (b) is a comparison of the attenuation curves.

[0021] Figure 3 The graphs show the changes in the dispersion cutoff frequency and attenuation poles of the plasmonic unit of the transition steep artificial surface based on the spur line structure in this invention, with different branch lengths. (a) shows the changes in the dispersion cutoff frequency and attenuation poles. The graph shows the variation of the dispersion cutoff frequency and attenuation poles of the length, (b) for changing... The curves showing the changes in the dispersion cutoff frequency and attenuation poles of the length;

[0022] Figure 4 This is a schematic diagram of the overall structure of a specific embodiment of the present invention;

[0023] Figure 5 This is a schematic diagram of the back of a specific embodiment of the present invention;

[0024] Figure 6 The above are simulation and measurement curves of the S-parameters in an embodiment of the present invention.

[0025] Figure Labels

[0026] 1. Dielectric substrate; 2. Coplanar waveguide; 21. Center conductor strip; 22. Ground strip; 3. Transition unit; 31. First L-shaped slot unit; 32. Second L-shaped slot unit; 33. Third L-shaped slot unit; 4. Filtering unit; 5. Transition region; 6. Transmission region. Detailed Implementation

[0027] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0028] Please see Figures 1-6 A steep transition artificial surface plasmon low-pass filter based on a spur line structure includes a dielectric substrate 1. A coplanar waveguide 2 is disposed on the upper surface of the dielectric substrate 1, and a spur line unit array is disposed on the lower surface. The coplanar waveguide 2 includes a central conductor strip 21 and ground strips 22 symmetrically distributed on both sides of the central conductor strip 21. An L-shaped slot unit array is etched on the ground strip 22. The L-shaped slot unit array is distributed along the length direction of the coplanar waveguide 2 and includes a filter unit 4 and transition units 3 symmetrically disposed at both ends of the filter unit 4. The spur line unit array is aligned with the center of the filter unit 4 on the projection plane perpendicular to the wave propagation direction.

[0029] The spur line unit array is composed of periodically arranged spur line units, each of which is made up of folded branches;

[0030] The spur line unit is symmetrically distributed with respect to its vertical axis of symmetry, and consists of a main branch and a parallel branch extending from the main branch to both sides.

[0031] The spur line unit array includes a transmission region 6 and transition regions 5 symmetrically arranged at both ends of the transmission region 6. The spur line unit in the transition region 5 has a smaller spur line unit length and width than the spur line unit in the transmission region 6, while the spur line units in the transmission region 6 have the same size.

[0032] Transition unit 3 and filter unit 4 are symmetrical about the center guide band. The size of the L-shaped slot element of transition unit 3 increases uniformly from both sides to the middle along the coplanar waveguide length direction, and the size of the L-shaped slot element of filter unit 4 is the same. The size of the L-shaped slot element of filter unit 4 is equal to that of its closest transition unit 3.

[0033] The dielectric substrate 1 is made of FR4 material with a relative permittivity of 4.4 and a loss tangent of 0.02.

[0034] The structure of this embodiment is based on a coplanar waveguide 2. Two metal grounding strips 22 are etched with L-shaped slot unit arrays periodically distributed along the length (y-direction) of the coplanar waveguide 2. At the bottom, there is also a spur line unit array along the length of the coplanar waveguide 2. Both arrays are symmetrical about the central conductor strip 21. The dimensions of the L-shaped slot units (i.e., their lengths in the x and y directions) and the spur line unit branch lengths (i.e....) are... and In the x-direction, the pattern matching segment is formed by increasing from both sides towards the middle, while the unit structure in the middle remains unchanged to form the SSPPs filtering segment.

[0035] The dielectric substrate 1 of the filter is FR4 (dielectric constant 4.4, thickness 0.76mm). Figure 1 The periodic dispersive unit structure in this embodiment has a periodic distribution of units. Vertical groove length Vertical groove width Vertical groove length Horizontal slot width The Spurs' line parameters are as follows: , , , , , .

[0036] The unit structure was simulated using electromagnetic simulation software, and compared with the unit without the barbed wire structure, resulting in... Figure 2 A comparison of the dispersion and attenuation curves of the two is shown in the figure. It can be seen from the figure that adding the spur line structure not only lowers the dispersion cutoff frequency of the element, but also makes the attenuation slope from the propagation mode to the cutoff region steeper. Simultaneously, the length of the spur line element branches (…) are changed... and )get Figure 3 The curve showing the relationship between the dispersion cutoff frequency and the attenuation pole as a function of length shows that increasing the stub length of the folded stub unit can bring the attenuation pole closer to the dispersion cutoff frequency, which is beneficial for the steep transition from the passband to the stopband of the cascaded SSPP low-pass filter.

[0037] In a specific embodiment of the present invention, the overall structure of the low-pass filter is shown in the figure below. Figure 4 As shown in the diagram, the back side is as follows. Figure 5 The length of the structure is Width is Thickness of dielectric substrate 1 Metal layer thickness Coplanar waveguide 2 signal linewidth The distance between the signal line and ground .

[0038] Transition unit 3 includes a first L-shaped slot unit 31, a second L-shaped slot unit 32, and a third L-shaped slot unit 33. The corresponding dimensions of the first L-shaped slot unit 31, the second L-shaped slot unit 32, and the third L-shaped slot unit 33 increase uniformly in sequence along the length of the coplanar waveguide 2. Filter unit 4 includes several fourth L-shaped slot units with dimensions equal to those of the third L-shaped slot unit 33. The dimensions of each L-shaped slot unit and the spur wire unit are as follows:

[0039] First L-shaped slot unit 31: , .

[0040] Second L-shaped slot unit 32: , .

[0041] Third L-shaped slot unit 33: , .

[0042] Spurs line unit in the transition zone: , , .

[0043] Spur line unit in the transmission area: , , .

[0044] The simulation and measured S-parameter results of this embodiment are as follows: Figure 6 As shown, electromagnetic waves can propagate efficiently between 0 and 1.027 GHz, forming an effective cutoff at 1.27 GHz. Out-of-band S21 is below -25 dB, and in-band S11 is essentially below -10 dB. Furthermore, this example exhibits a steep transition from the passband to the stopband, with a rectangularity factor of 1.067.

[0045] Therefore, this invention adopts the steep transition artificial surface plasmon low-pass filter based on the above-mentioned spur line structure to solve the problems of wide transition region between passband and stopband, insufficient filter selectivity and complex structure of existing SSPP structure filters. By introducing a spur line structure at the bottom layer, an adjustable dispersion cutoff frequency and a sharp transition from passband to stopband can be achieved, while the structure is simple and miniaturized.

[0046] Finally, 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A steep transition type artificial surface plasmon polariton low-pass filter based on a spur structure, comprising a dielectric substrate, characterized in that: The upper surface of the medium substrate is provided with a coplanar waveguide, and the lower surface is provided with a protruding line unit array, the coplanar waveguide comprises a center conductor strip and a ground strip symmetrically distributed on both sides of the center conductor strip, and a L-shaped slot unit array is etched on the ground strip, the L-shaped slot unit array is distributed along the length direction of the coplanar waveguide, and comprises a filter unit and a transition unit symmetrically arranged at both ends of the filter unit, and the protruding line unit array is vertically aligned with the center of the filter unit in the projection plane perpendicular to the wave propagation direction. The transition unit comprises a first L-shaped slot unit, a second L-shaped slot unit and a third L-shaped slot unit, the corresponding sizes of the first L-shaped slot unit, the second L-shaped slot unit and the third L-shaped slot unit are uniformly increased in the length direction of the coplanar waveguide in turn; the filter unit comprises a plurality of fourth L-shaped slot units with the same size as the third L-shaped slot unit.

2. The plasmonic low-pass filter based on a sharp wire structure artificial surface plasmon, according to claim 1, wherein: The protruding line unit array is composed of periodically arranged protruding line units, and each protruding line unit is composed of a folded branch. The protruding line unit and its vertical symmetry axis are distributed in left-right symmetry, and are composed of a main branch and a parallel branch extending to both sides from the main branch.

3. The plasmonic low-pass filter based on a sharp wire structure artificial surface plasmon, according to claim 2, wherein: The protruding line unit array comprises a transmission area and a transition area symmetrically arranged at both ends of the transmission area, the branch length and width of the protruding line unit of the transition area are smaller than those of the protruding line unit of the transmission area, and the sizes of the protruding line units of the transmission area are equal.

4. The plasmonic low-pass filter based on sharp wire structure artificial surface plasmons according to claim 1, wherein: The transition unit and the filter unit are symmetric about the center conductor strip, the size of the L-shaped slot unit of the transition unit increases from both sides to the middle in the length direction of the coplanar waveguide, and the size of the L-shaped slot unit of the filter unit is the same.

5. The plasmonic low-pass filter based on sharp wire structure artificial surface plasmons according to claim 1, wherein: The medium substrate is an FR4 plate material, the relative dielectric constant is 4.4, and the loss tangent is 0.02.

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