Super-small low-pass artificial surface plasmon polariton filter based on interdigital structure

Abstract

The application discloses an ultra-small low-pass artificial surface plasmon filter based on an interdigital structure, which comprises upper copper sheets and lower copper sheets which are correspondingly laid on the upper and lower surfaces of a base layer, the middle part of the upper copper sheet is provided with 3-5 groups of plasmon units connected in parallel, the input end and the output end at both ends are connected with the adjacent plasmon units through 1-3 groups of transition units; each group of plasmon units has an L-shaped structure, an inverted and mirrored F structure and a mirrored F-shaped structure located at the lower end side of the L-shaped structure; the upper end side of the L-shaped structure is connected with the inverted and mirrored F structure through a transverse copper sheet, and the inverted and mirrored F structure and the mirrored F-shaped structure form a channel with equal width; the transition unit is different from the plasmon unit in that the transverse size of the transition unit gradually increases and is smaller than the transverse size of the plasmon unit. The application has a simple and compact structure, can effectively reduce the asymptotic frequency, can reduce the overall size and is suitable for an ultra-small low-pass filter.

Description

Technical Field

[0001] This invention relates to filter technology, belonging to the field of communications, and specifically to an ultra-miniature low-pass artificial surface plasmon polariton filter based on an interdigital structure. Background Technology

[0002] Filters can effectively filter out specific frequencies or frequencies outside of a power line to obtain a power signal of a specific frequency or to eliminate a power signal of a specific frequency. They play a very important role in wireless signal processing.

[0003] The main components of existing filter structures include a substrate material and metal layers laid on the top and bottom surfaces of the substrate material. The interdigitated structure of the upper metal layer is a "U" or "S" shaped structure. In actual use, its asymptotic frequency reduction effect is poor, and the reduction of the cutoff frequency is mainly achieved through the large equivalent capacitance formed by the interdigitated structure. The equivalent capacitance is roughly proportional to the relative area of ​​the interdigitated metal sheets in the interdigitated structure. However, increasing the length of the interdigitated structure will increase the actual size of the device while reducing the cutoff frequency.

[0004] Chinese patent application number CN201720518185.4: Microstrip interdigitated hairpin filter, its structure consists of n resonators, with input terminal 24 and output terminal 27 arranged in a straight line, and adjacent resonators having opposite opening directions; the lack of a "transition region" between the resonators and input terminal 24 and output terminal 27 results in a low roll-off rate at the cutoff frequency; in addition, some existing technical solutions use SSPP low-pass and band-pass filters, which, although they have matching structures, basically use a gradient comb structure. This structure results in an excessively large overall length of the filter, making it unsuitable for ultra-small low-pass filters. Summary of the Invention

[0005] The purpose of this invention is to provide an ultra-miniature low-pass artificial surface plasmon polariton filter based on an interdigital structure. The filter has a simple and compact structure, which not only effectively reduces its asymptotic frequency, but also reduces the overall size, making it suitable for ultra-miniature low-pass filters.

[0006] To achieve the above objectives, a miniaturized low-pass artificial surface plasmon polariton filter based on an interdigital structure is provided, comprising:

[0007] grassroots level;

[0008] Upper and lower copper sheets are laid horizontally on the upper and lower surfaces of the base layer, respectively. The characteristic of this design is that...

[0009] The upper copper sheet has 3-5 groups of parallel-connected exciton units in the middle, with the two ends being the input and output terminals of the microstrip line, respectively; the input and output terminals are connected to the adjacent exciton units through 1-3 groups of transition units;

[0010] Each group of exciton units has an L-shaped structure, an inverted and mirrored F-shaped structure, and a mirrored F-shaped structure located at the lower end of the L-shaped structure.

[0011] The upper end of the L-shaped structure is connected to the inverted and mirrored F-shaped structure by a horizontal copper sheet. The inverted and mirrored F-shaped structure and the mirrored F-shaped structure form a channel of equal width.

[0012] The structure of the transition unit is the same as that of the exciton unit. The difference is that the transverse dimensions of the 1st to 3rd groups of transition units increase sequentially and are smaller than the transverse dimensions of the exciton unit, while the longitudinal dimensions are the same as those of the exciton unit.

[0013] Furthermore, the number of polariton units is 5, and the number of transition units is 2.

[0014] Furthermore, the copper sheets above the input and output terminals are arranged symmetrically in the middle.

[0015] The input structure is rectangular and has a 90° rotated isosceles trapezoid connected to it. The narrow end of the isosceles trapezoid is connected to the transition unit.

[0016] Furthermore, the lower copper sheet is provided with slot assembly that matches the polaron unit and the transition unit;

[0017] Each slot assembly has an external slot with an orifice structure and three transverse slots located inside the external slot. The external slot and the three transverse slots form four spaced copper strips.

[0018] The first and third copper strip ends are connected to the transverse ends of the mirrored F-structure in the upper copper sheet via copper rods passing through the base layer; the opposite ends of the second and fourth copper strips are connected to the transverse ends of the inverted and mirrored F-structure via copper rods passing through the base layer.

[0019] Furthermore, the maximum natural frequency f of the transition unit / polaron unit has the following functional relationship with p:

[0020]

[0021] Where p is the lateral width of the transition unit / exciton unit, in mm.

[0022] Compared with existing technologies, the input and output terminals of this ultra-miniature low-pass artificial surface plasmon polariton filter based on an interdigital structure are connected to adjacent polariton units via 1-3 sets of transition units, forming the matching and waveguide section of an ultra-compact low-pass filter. Each set of polariton units has an L-shaped structure, an inverted and mirrored F-shaped structure, and an interdigital structure with a mirrored F-shaped structure located at the lower end of the L-shaped structure. By setting transition units of gradually varying lengths, the signal can smoothly transition from the TEM mode to the SSPP mode, reducing signal reflection. Therefore, improper design of the transition units will lead to a decrease in signal reflection within the passband. 11 Increase, S 21 The use of transition units with gradually varying lengths not only ensures the ultrafast roll-off performance of the filter at the cutoff frequency and effectively reduces its asymptotic frequency, but also reduces the overall size, making it suitable for ultra-miniature low-pass filters. In addition, adjusting the number of polariton units to 5 groups and transition units to 2 groups determines the number of units in the waveguide section to improve out-of-band suppression.

[0023] Since the slot assembly at the lower copper sheet corresponds to the transition unit and exciton unit of the upper copper sheet, and the four spaced copper strips formed are connected to the end side of the corresponding unit, the interdigital structure is extended in three dimensions, so as to reduce the cutoff frequency without increasing the size of the interval, resulting in a smaller overall size. Attached Figure Description

[0024] Figure 1 This is an overall top view of the invention;

[0025] Figure 2 This is an overall bottom view of the present invention;

[0026] Figure 3 This is a partial front view of the entire invention;

[0027] Figure 4 yes Figure 1 Enlarged view of position B in the middle;

[0028] Figure 5 yes Figure 1 Dimensioning diagram of position A in the middle;

[0029] Figure 6 yes Figure 1 Diagram showing the location of vias at position A (pionocyte unit);

[0030] Figure 7 yes Figure 2 Diagram showing the location of through-holes in the slot assembly corresponding to the C position and the polariton unit;

[0031] Figure 8 It is a simulation curve of the maximum natural frequency f of the exciton unit in this invention as a function of parameter p;

[0032] Figure 9 These are the simulated dispersion curves of U1, U2, and U3 in this invention;

[0033] Figure 10 These are the simulation curves of insertion loss and return loss for different numbers of polariton units U1 in the third region 23 of this invention.

[0034] Figure 11 This is a simulated electric field distribution diagram of the present invention at 3.6 GHz;

[0035] Figure 12 This is a simulated electric field distribution diagram of the present invention at 4.0 GHz;

[0036] Figure 13 This is a simplified diagram of the structure decomposition of the exciton unit in this invention;

[0037] In the diagram: 10. Base layer; 20. Top copper sheet; 21. First area; 22. Second area; 23. Third area.

[0038] 24. Input terminal; 25. Pyramid unit; 26. Transition unit; 27. Output terminal;

[0039] 30. Lower copper sheet; 31. Slot assembly; 32. External slot; 33. Horizontal slot. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] like Figures 1 to 3 , Figure 5 , Figure 13 As shown, this ultra-miniature low-pass artificial surface plasmon polariton filter based on an interdigital structure includes:

[0042] 10 at the grassroots level;

[0043] Upper copper sheet 20 and lower copper sheet 30 are laid laterally on the upper and lower surfaces of the base layer 10, respectively. The characteristic of this design is that...

[0044] The upper copper sheet 20 has 3-5 groups of parallel-connected exciton units 25 in the middle, with the two ends being the input terminal 24 and the output terminal 27 of the microstrip line, respectively; the input terminal 24 and the output terminal 27 are connected to the adjacent exciton units 25 through 1-3 groups of transition units 26;

[0045] Each group of exciton units 25 has an L-shaped structure and a mirror F-shaped structure located at the lower end of the L-shaped structure;

[0046] The upper end of the L-shaped structure is connected to the inverted and mirrored F-shaped structure by a horizontal copper sheet. The inverted and mirrored F-shaped structure and the mirrored F-shaped structure form a channel of equal width.

[0047] The structure of the transition unit 26 is the same as that of the exciton unit 25. The difference is that the transverse dimensions of the 1st to 3rd groups of transition units 26 are successively increased and smaller than the transverse dimensions of the exciton unit 25, and the longitudinal dimensions are the same as the longitudinal dimensions of the exciton unit 25.

[0048] Specifically, the substrate material can be FR-4, which has a dielectric constant of 4.3, a loss tangent of 0.018, and a thickness of 0.508 mm;

[0049] The upper copper sheet 20 and the lower copper sheet 30 are laid horizontally, and their thickness can be 0.0018mm;

[0050] This filter can be divided into 5 regions: the first region 21, the second region 22, the third region 23, the fourth region, and the fifth region. The first region 21 and the fifth region, as well as the second region 22 and the fourth region, are symmetrically arranged with respect to the third region 23. This symmetry indicates that the structure and size of the divided regions are symmetrical.

[0051] In the first region 21, the microstrip line serves as the input terminal 24 of the filter, and in the fifth region, the microstrip line serves as the output terminal 27 of the filter. The upper copper sheet 20 in the second region 22 and the fourth region is divided into multiple sets of artificial surface plasmon resonance (ASPR) transition units 26, and the upper copper sheet 20 in the third region 23 is divided into multiple sets of ASPR exciton units 25. It should be noted that the input terminal 24, the output terminal 27, the multiple sets of transition units 26, and the exciton units 25 form a unified whole without any gaps. The transition units 26 in the second region 22 and the fourth region respectively achieve matching between the first region 21 and the third region 23, and between the third region 23 and the fifth region.

[0052] Each group of 25 exciton units is connected side by side. Its interdigital structure consists of an L-shaped structure, an inverted and mirrored F-shaped structure, and a mirrored F-shaped structure, forming channels of equal width to ensure the ultra-fast roll-off performance of the filter at the cutoff frequency.

[0053] The size of microwave devices is related to their operating frequency, and can be measured by their electrical dimensions (actual device size / wavelength). Therefore, by reducing the operating frequency of the device, the wavelength of the electromagnetic wave can be increased. With the actual device size remaining constant, the electrical dimensions will decrease, thus achieving the goal of reducing the overall size.

[0054] In the first region, the electromagnetic wave propagation mode at the input terminal 24 is TEM mode, while in the third region, the signal propagation mode at the exciton unit 25 is SSPP mode. By setting a transition unit 26 with a gradually changing length, the signal can smoothly transition from TEM mode to SSPP mode, reducing signal reflection. Therefore, the transition unit 26 has an impact on signal reflection, specifically manifested in the S... 11 Increase, S 21 The reduction and lack of transition units affect the transmission performance of the filter, where S 11 S 21 The reflection coefficient is used; too many transition units 26 will increase the device size, so it is possible to try to meet the performance indicators during the design.

[0055] like Figure 1 As shown, further, the exciton units 25 consist of 5 groups, and the transition units 26 consist of 2 groups;

[0056] like Figure 1 , Figure 4 As shown, the input terminal 24 and the output terminal 27 are symmetrically arranged in the middle of the copper sheet 20.

[0057] The input terminal 24 has a rectangular structure and a 90° rotated isosceles trapezoid that is connected to it. The narrow end of the isosceles trapezoid is connected to the transition unit 26.

[0058] like Figure 1 , Figure 2 , Figure 7 As shown, the lower copper sheet 30 is further provided with a slot assembly 31 that matches the polaron unit 25 and the transition unit 26;

[0059] Each slot assembly 31 has an external slot 32 with an orifice structure and three transverse slots 33 located inside the external slot 32. The external slot 32 and the three transverse slots 33 form four spaced copper strips.

[0060] The first and third copper strip ends are connected to the transverse ends of the mirrored F structure in the upper copper sheet 20 via copper rods passing through the base layer 10; the opposite ends of the second and fourth copper strips are connected to the transverse ends of the inverted and mirrored F structure via copper rods passing through the base layer 10.

[0061] Specifically, the matching of the slot assembly 31 with the exciton unit 25 and the transition unit 26 means that the quantity is the same and the size is changed accordingly. That is, the lateral dimension of the slot assembly 31 corresponding to the transition unit 26 increases sequentially and is smaller than the lateral dimension of the slot assembly 31 corresponding to the exciton unit 25, while the longitudinal dimension is the same as that of the slot assembly 31 corresponding to the exciton unit 25.

[0062] like Figure 6 , Figure 7 , Figure 13 As shown, the description is based on the exciton unit 25 and the matching slot assembly 31. The through holes at the lateral ends of the mirrored F structure are D and E, and the through holes at the ends of the inverted and mirrored F structure are E and N. Four copper strips are formed in the slot assembly 31 at intervals. The through holes at one end of the first and third copper strips are d and m, and the through holes at the opposite ends of the second and fourth copper strips are e and n. D and d, M and m, E and e, N and n are connected by copper rods passing through the base layer 10.

[0063] The mechanism by which the interdigital structure reduces the cutoff frequency of a filter is that the interdigital structure forms a large equivalent capacitance. The size of the capacitance is proportional to the length of the interdigital part. To reduce the cutoff frequency, the length of the interdigital part needs to be increased, which leads to an increase in the overall structure size. Therefore, the interdigital part of the upper copper sheet is connected to the lower copper sheet by a copper rod in a metal cylinder, so that the interdigital structure is extended in three dimensions, thereby achieving the goal of reducing the cutoff frequency without increasing the overall size.

[0064] Compared with traditional and T-shaped geometric structures, this filter incorporates a three-dimensional interdigitated structure in the artificial surface plasmon polariton unit 25, which can effectively reduce its asymptotic frequency and decrease the unit size. Furthermore, the input terminal 24 and the output terminal 27 are connected to the adjacent polariton unit 25 through multiple sets of transition units 26. The polariton unit 25 and the transition unit 26 have different maximum natural frequencies and similar asymptotic frequencies, forming the matching and waveguide parts of an ultra-compact low-pass filter. In addition, the number of polariton units 25 is adjusted to 5 sets and the number of transition units 26 is adjusted to 2 sets to determine the number of units in the waveguide part in order to improve out-of-band suppression.

[0065] Example

[0066] Select the appropriate size. The substrate material can be FR-4, with a dielectric constant of 4.3, a loss tangent of 0.018, and a thickness of 0.508mm. The thickness of the upper copper sheet 20 and the lower copper sheet 30 is 0.0018mm. The length and width of the longitudinal structure of the input terminal 24 / output terminal 27 are both 1mm, the height of the trapezoid is 2mm, and the trapezoid is rotated 90° and connected to the rectangle.

[0067] Taking the preferred scheme with 2 sets of transition units 26 and 5 sets of polariton units 25 as an example, the specific details are as follows: Figure 1 , Figure 5 As shown, the transition unit 26 closer to the input terminal 24 / output terminal 27 is U2, the transition unit 26 farther from the input terminal 24 / output terminal 27 is U3, and the exciton unit 25 is U1. The dimensions of the corresponding regions are shown in the table below.

[0068] Table 1. Dimensional parameters of transition unit 26 and polaron unit 25;

[0069]

[0070] In structures U1, U2, and U3, the values ​​of dimensional parameters h, d, g1, and w1 are 2 mm, 0.1 mm, 0.2 mm, and 0.1 mm, respectively. The overall difference lies in the change in the lateral dimension p. Under these conditions, the maximum natural frequency f (in GHz) of this type of unit structure has the following functional relationship with parameter p (in mm):

[0071]

[0072] The above formula was numerically fitted using Matlab, and the resulting curve of f as a function of p was shown below. Figure 8 As shown, the results are in good agreement with the simulation results in the electromagnetic simulation software Hfss.

[0073] like Figure 10 As shown, the insertion loss and return loss simulation curves were obtained by placing different numbers of U1s on the exciton unit U3 in the third region 23 of this filter; it can be seen that increasing the number of exciton units U3 does not directly lead to a change in the cutoff frequency.

[0074] like Figure 10 As shown, within the passband, when the number of polariton units 25 increases from 3 to 5, the insertion loss curve remains essentially unchanged, and the peak value of the return loss curve is also largely unaffected. Within the high-frequency stopband, as the number of polariton units 25 increases, the return loss curve does not change significantly, but the peak value of the insertion loss curve decreases. Therefore, preferably, the number of polariton units 25 in the third region 23 is 5 groups to achieve good out-of-band suppression exceeding 24 dB.

[0075] In the third region 23, when the exciton unit U1 is selected with a p of 2.5mm, the maximum natural frequency is 6.017GHz. Correspondingly, in the second region 22, when the transition units U2 and U3 are selected with p of 1.6mm and 2.3mm respectively, the corresponding maximum natural frequencies are 8.834GHz and 6.452GHz. Figure 9 As shown, the simulated dispersion curves for U1, U2, and U3 are presented, with the asymptotic frequency of all three being 6 GHz.

[0076] Additionally, the roll-off rate F of the filter can be defined to evaluate its roll-off characteristics:

[0077]

[0078] Among them, f L and f H S 21 The frequencies at -3 and -25 dB;

[0079] S 21 S is the forward transmission coefficient of the signal. 21The smaller the absolute value of S, the better the transmission performance of the frequency filter; 21 The larger the absolute value, the better the filter's filtering performance for that frequency signal;

[0080] The F value calculated based on simulation data is 105 dB / GHz, which can verify the ultrafast roll-off performance of the filter at the cutoff frequency.

[0081] like Figure 11 , Figure 12 As shown, the electric field of this ultra-small low-pass artificial surface plasmon polariton filter based on interdigital structure is simulated at 3.6 GHz (below the simulation cutoff frequency) and 4.0 GHz (above the simulation cutoff frequency).

[0082] At 3.6 GHz below the cutoff frequency, artificial surface plasmon polariton modes can be observed to be excited and propagate through all regions. Above the cutoff frequency at 4.0 GHz, artificial surface plasmon polariton modes are basically only present in the two polariton units 25 near the second region 22 in the second region 22 and the third region 23, and can hardly propagate to the output terminal 27, thus verifying the low-pass characteristics of the filter.

[0083] Simulations of this filter on the electromagnetic simulation software CST Microwave Studio show that it has efficient transmission in the 0-5.66 GHz passband, high out-of-band rejection (over 24 dB) in the 5.95-12 GHz stopband, and ultrafast roll-off at 5.74 GHz.

[0084] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

Claims

1. An ultra-miniature low-pass artificial surface plasmon polarimeter filter based on an interdigital structure, comprising: Grassroots (10); Upper copper sheet (20) and lower copper sheet (30) are laid laterally on the upper and lower surfaces of the base layer (10), respectively. The characteristic of this design is that... The upper copper sheet (20) has 3-5 groups of parallel-connected exciton units (25) in the middle, and the two ends are the input end (24) and output end (27) of the microstrip line, respectively; the input end (24) and output end (27) are connected to the adjacent exciton units (25) through 1-3 groups of transition units (26); Each group of exciton units (25) has an L-shaped structure, an inverted F-shaped structure, and a mirror F-shaped structure; The upper vertical open end of the L-shaped structure is connected to the vertical branch open end of the inverted F-shaped structure through a horizontal copper sheet, and the lower horizontal open end of the L-shaped structure is connected to the vertical branch open end of the mirrored F-shaped structure. The horizontal branches of the inverted F-shaped structure are opposite to and staggered with the horizontal branches of the mirrored F-shaped structure, forming a reciprocating channel of equal width. The structure of the transition unit (26) is the same as that of the exciton unit (25). The difference is that the transverse dimensions of the 1st to 3rd groups of transition units (26) increase sequentially and are smaller than the transverse dimensions of the exciton unit (25), while the longitudinal dimensions are the same as those of the exciton unit (25). The lower copper sheet (30) is provided with a slot assembly (31) that corresponds to and matches the transition unit (26) and the exciton unit (25). Four spaced copper strips are formed on the slot assembly (31) for connecting with the corresponding transition unit (26) and exciton unit (25).

2. The ultra-miniature low-pass artificial surface plasmon polariton filter based on an interdigital structure according to claim 1, characterized in that, The exciton units (25) consist of 5 groups, and the transition units (26) consist of 2 groups.

3. The ultra-miniature low-pass artificial surface plasmon polariton filter based on an interdigital structure according to claim 1, characterized in that, The copper sheets (20) above the input terminal (24) and output terminal (27) are arranged symmetrically in the middle. The input end (24) has a rectangular structure and a 90° rotated isosceles trapezoid that is connected to the mating part. The narrow end of the isosceles trapezoid is connected to the transition unit (26).

4. The ultra-miniature low-pass artificial surface plasmon polariton filter based on an interdigital structure according to any one of claims 1 to 3, characterized in that, Each slot assembly (31) has an external slot (32) with an orifice structure and three transverse slots (33) located inside the external slot (32). The external slot (32) and the three transverse slots (33) form four spaced copper strips. The four spaced copper strips are arranged vertically from top to bottom as the first copper strip, the second copper strip, the third copper strip and the fourth copper strip. The ends of the first and third copper strips are connected to the transverse ends of the mirrored F-shaped structure in the upper copper sheet (20) by copper rods passing through the base layer (10); the ends of the second and fourth copper strips are connected to the transverse ends of the inverted F-shaped structure by copper rods passing through the base layer (10).

5. The ultra-miniature low-pass artificial surface plasmon polariton filter based on an interdigital structure according to claim 4, characterized in that, The maximum natural frequencies f and p of the transition unit (26) and the polaron unit (25) have the following functional relationship: ； Where p is the lateral width of the transition unit (26) and the exciton unit (25), in mm.

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