Low-loss, arbitrary-bandwidth terahertz bandpass filter based on metasurface and its design method

Abstract

The present invention relates to the field of wireless communication technology, and is a low-loss, arbitrary bandwidth terahertz bandpass filter based on a metasurface and a design method thereof. The filter includes a wide-stopband metasurface band-stop filter structure and an ultra-wideband band-pass filter structure. The wide-stopband metasurface band-stop filter structure includes a low-frequency and high-frequency metasurface band-stop filter structure. The filter structure adopts a silicon-based integrated gap waveguide structure for feeding; the ultra-wideband band-pass filter structure includes a ring resonator loaded with multiple non-equiimpedance branches; the wide-stopband metasurface band-stop filter structure includes a low-frequency metasurface band-stop filter structure and a high-frequency metasurface band-stop filter structure. The low-frequency metasurface band-stop filter structure and the high-frequency metasurface band-stop filter structure both include a metasurface array and a stripline, and the multiple open resonant rings of the metasurface array are axially symmetrically distributed about the stripline. The present invention realizes the design of an arbitrary bandwidth terahertz filter while ensuring low loss and easy integration, and effectively reduces the complexity of the design of an arbitrary bandwidth terahertz filter.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a low-loss, arbitrary-bandwidth terahertz bandpass filter based on a metasurface and a design method thereof. Background Art

[0002] Terahertz technology is one of the key wireless communication technologies in the future and will be widely used in civil and military fields. As an indispensable component of terahertz communication systems, filters play a vital role in realizing efficient and low-loss terahertz communication systems. However, terahertz filters currently face multiple challenges, such as significant losses, integration complexity, and difficulty in achieving arbitrary bandwidth designs.

[0003] The current implementation of terahertz filters mainly relies on metamaterial design, which makes it challenging to integrate them into silicon-based front-end circuits. Some waveguide-based filter designs face problems such as surface waves and high interconnection losses. In addition, regarding filter design, it is usually targeted at specific frequency bands and ranges and has a fixed structure, which makes it difficult to achieve filter design with arbitrary bandwidth. At present, only a few filter research and design methods have solved this problem, and basically all of them adopt the principle of increasing the resonance point; these research and design methods face problems such as computational difficulties and complex design. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a low-loss, arbitrary-bandwidth terahertz bandpass filter based on a metasurface and a design method thereof, which can ensure low loss and easy integration while realizing the design of an arbitrary-bandwidth terahertz filter, and can effectively reduce the complexity of the design of an arbitrary-bandwidth terahertz filter.

[0005] In the first aspect, a low-loss, arbitrary-bandwidth terahertz bandpass filter based on a metasurface according to an embodiment of the present invention comprises a wide-stopband metasurface bandstop filter structure and an ultra-wideband bandpass filter structure, wherein the bandstop filter structure and the bandpass filter structure are fed by a silicon-based integrated gap waveguide structure;

[0006] The ultra-wideband bandpass filter structure includes a ring resonator loaded with a plurality of non-equiimpedance branches, the ring resonator includes a ring body, and the plurality of non-equiimpedance branches are located at multiple equally divided positions of the ring body; input branches and output branches are respectively led out from two adjacent non-equiimpedance branches, and the remaining non-equiimpedance branches are set as broadband matching branches;

[0007] The wide stopband metasurface band-stop filter structure includes a low-frequency metasurface band-stop filter structure and a high-frequency metasurface band-stop filter structure. Both the low-frequency metasurface band-stop filter structure and the high-frequency metasurface band-stop filter structure include a metasurface array and a strip line. The metasurface array is loaded on both sides of the strip line. The metasurface array includes multiple open resonant rings. The multiple open resonant rings of the metasurface array are axially symmetrically distributed about the strip line.

[0008] In a second aspect, a design method of a terahertz bandpass filter according to an embodiment of the present invention comprises the following steps:

[0009] Establish the SSIGW physical model;

[0010] On the SSIGW model, an ultra-wideband bandpass filter structure is established;

[0011] Based on the SSIGW model, a wide stopband metasurface bandstop filter structure is established;

[0012] The ultra-wideband bandpass filter structure is integrated with the metasurface bandstop filter structure; the operating frequency band of the terahertz bandpass filter is controlled by adjusting the size, quantity, and spacing between the low-frequency metasurface bandstop filter structure and the high-frequency metasurface bandstop filter structure.

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

[0014] The arbitrary bandwidth terahertz bandpass filter of the present invention includes a wide stopband metasurface bandstop filter structure, an ultra-wideband bandpass filter structure and SSIGW, the wide stopband metasurface bandstop filter structure includes a low-frequency metasurface bandstop structure and a high-frequency metasurface bandstop structure, and the metasurface is an open resonant ring; the ultra-wideband bandpass filter structure is an ultra-wideband filter loaded with non-equiimpedance branches. The results of simulation analysis show that the passband center frequency is 0.151THz, the relative bandwidth is 6.9%, the group delay is 0.119±0.048ns, the insertion loss is less than 0.68dB, and the upper and lower stopband ranges are greater than 20GHz, which is more suitable for terahertz low-latency communication. Compared with the traditional method of increasing resonance points, the present invention realizes the design of arbitrary bandwidth filters, and the design method is easier to implement. The use of metasurface design can achieve a higher degree of freedom. Combined with SSIGW, low loss and easy integration in the terahertz frequency band can be achieved, effectively reducing the complexity of terahertz filter design. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flowchart of a method for designing a low-loss, arbitrary-bandwidth terahertz bandpass filter based on a metasurface in an embodiment of the present invention;

[0016] Figure 2 Schematic diagram of the structure of a wide stopband, low-loss terahertz bandpass filter based on a metasurface in an embodiment of the present invention;

[0017] Figure 3 Schematic diagram of the structure of a silicon-based integrated gap waveguide in an embodiment of the present invention;

[0018] Figure 4 is a schematic diagram of a silicon-based electromagnetic bandgap structure in an embodiment of the present invention;

[0019] Figure 5 is a schematic diagram of an equivalent physical model of a silicon-based electromagnetic bandgap structure in an embodiment of the present invention;

[0020] Figure 6 is a schematic diagram of an equivalent circuit of a silicon-based electromagnetic bandgap structure in an embodiment of the present invention;

[0021] Figure 7 Schematic diagram of electric field simulation results of the low-frequency metasurface band-stop filter structure in an embodiment of the present invention, wherein (b) is a simulation schematic diagram within the stop band, and (a) and (c) are simulation schematic diagrams outside the stop band;

[0022] Figure 8 It is a schematic diagram of S parameter simulation results of a low-frequency metasurface band-stop filter structure in an embodiment of the present invention;

[0023] Fig. 9 It is a schematic diagram of S parameter simulation results of the high-frequency metasurface band-stop filter structure in an embodiment of the present invention;

[0024] Fig.10 It is a schematic diagram of S-parameter simulation results of a terahertz wide-stopband, low-loss bandpass filter based on a metasurface in an embodiment of the present invention;

[0025] Fig.11 It is a schematic diagram of group delay simulation results of a terahertz wide stopband and low-loss bandpass filter based on a metasurface in an embodiment of the present invention;

[0026] Figure numerals: 1-first silicon dielectric layer; 2-second silicon dielectric layer; 3-third silicon dielectric layer; 4-copper cladding layer; 5-silicon dioxide isolation layer; 6-metal cylinder; 7-metal disc; 8-ultra-wideband bandpass filter structure; 9-low-frequency super-surface band-stop filter structure; 10-high-frequency super-surface band-stop filter structure; 11-metal strip line. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] It should be noted that the step numbers in the text are only for the convenience of explaining the specific embodiments and are not used to limit the order in which the steps are executed.

[0029] like Figure 1 As shown, this embodiment provides a method for designing a low-loss, arbitrary-bandwidth bandpass filter based on a metasurface, comprising the following steps:

[0030] Step 1), establish SSIGW physical model;

[0031] Step 2), establish an ultra-wideband filtering structure;

[0032] Step 3), establishing a metasurface band-stop filter structure;

[0033] Step 4), load the metasurface band-stop filter structure obtained in step 3) into the ultra-wideband filter structure in step 2), control the working frequency band of the filter structure by adjusting the metasurface specifications, and design a low-loss, arbitrary-bandwidth terahertz filter that meets the requirements.

[0034] The arbitrary bandwidth terahertz bandpass filter designed through the above four steps has effectively improved performance and can better assist terahertz communication equipment. In the design process, the ultra-wideband bandpass filter structure design should make the bandwidth as wide as possible and easy to integrate; the metasurface band-stop filter structure design should make the metasurface degree of freedom as high as possible to meet the requirements of multi-parameter adjustment, realize controllable passband bandwidth and easy integration.

[0035] Accordingly, according to the above-mentioned low-loss, arbitrary bandwidth bandpass filter design method based on metasurface, this embodiment also provides a terahertz wide stopband, low-loss bandpass filter based on metasurface, such as Figure 2 As shown, the filter includes a wide-stopband supersurface band-stop filter structure and an ultra-wideband band-pass filter structure 8. The wide-stopband supersurface band-stop filter structure includes a low-frequency supersurface band-stop filter structure 9 and a high-frequency supersurface band-stop filter structure 10. The band-stop filter structure and the band-pass filter structure are fed by a silicon-based integrated gap waveguide structure.

[0036] Among them, silicon-based integrated gap waveguide structures such as Figure 3 As shown, it includes a first silicon dielectric layer 1, a second silicon dielectric layer 2 and a third silicon dielectric layer 3 arranged from bottom to top; a silicon dioxide isolation layer 5 is arranged between two adjacent silicon dielectric layers; the top and bottom layers of the silicon-based integrated gap waveguide structure are copper-clad layers 4; and the strip line 11 is etched on the silicon dioxide isolation layer 5 above the second silicon dielectric layer 2. The wide stopband supersurface band-stop filter structure and the ultra-wideband bandpass filter structure are both etched on the silicon dioxide isolation layer on the lower surface of the third silicon dielectric layer.

[0037] In this embodiment, silicon dioxide isolation layers 5 are provided on the upper and lower surfaces of the first silicon dielectric layer 1, and a plurality of metal sheets distributed in a periodic array are etched on the silicon dioxide isolation layer 5 on the upper surface of the first silicon dielectric layer 1, and the metal sheets are preferably metal round sheets 7; a metal copper layer is etched on the silicon dioxide isolation layer on the lower surface of the first silicon dielectric layer; a metal column is connected through each of the metal sheets and the metal copper layer, and the metal column is preferably a metal cylinder 6. The width of the metal sheet is greater than the cross-sectional width of the metal column, and a silicon dioxide isolation layer 5 is wrapped outside the metal column to form a silicon-based electromagnetic bandgap structure unit; wherein the metal column is sequentially embedded in the silicon dioxide isolation layer 5 on the upper surface of the first silicon dielectric layer 1, the first silicon dielectric layer 1, and the silicon dioxide isolation layer 5 on the lower surface of the first silicon dielectric layer.

[0038] Preferably, on the silicon-based integrated gap waveguide structure of the present embodiment, each metal disc and metal cylinder are arranged concentrically to form a plurality of mushroom-shaped silicon-based electromagnetic bandgap structures, and the plurality of silicon-based electromagnetic bandgap structure units form a silicon-based electromagnetic bandgap structure array.

[0039] In a preferred embodiment, the physical model of the silicon-based electromagnetic bandgap structure array is as follows: Figure 4 As shown, the equivalent physical model is as follows Figure 5 As shown, the equivalent circuit is Figure 6 As shown in Figure 2, the period of the silicon-based electromagnetic bandgap structure unit is p, and the spacing between the discs is g. Figure 5 The equivalent physical model includes two equivalent dielectric layers, which are the lower equivalent dielectric layer and the upper equivalent dielectric layer from bottom to top, with thicknesses of d1 and d2 respectively, and equivalent dielectric constants of ε eff1 , ε eff2 , and copper is coated on the top and bottom layers of the dielectric substrate. The gap capacitance between the metal discs of two adjacent silicon-based electromagnetic bandgap structural units is C2, the capacitance from the metal disc to the top copper coating is C1, and the inductance of the metal cylinder (optionally a metal copper cylinder) is L.

[0040] In a preferred embodiment, the calculation theory of the silicon-based electromagnetic bandgap structure is shown in the following formula.

[0041]

[0042] T>0.2um

[0043] C1=ε0ε eff2 πR 2 / d2

[0044] C2=4ε0ε eff1 πR / log(sec(π(p-2R) / 2p))

[0045] L=-μ0h(4+ln(p-2r)) / 2π

[0046]

[0047]

[0048] Where, T is the thickness of the silicon dioxide layer, Cox(f) is the maximum capacitance of the side wall of the silicon dioxide isolation layer wrapping the metal cylinder, d1 is the thickness of the lower equivalent dielectric layer, d2 is the thickness of the upper equivalent dielectric layer, ε0 is the dielectric constant of free space, p is the period of the silicon-based electromagnetic bandgap structure unit, R is the radius of the metal disc, r is the radius of the metal cylinder, and μ0 is the magnetic permeability of free space; η eff1 is the wave impedance of the lower equivalent dielectric layer, f0 is the electromagnetic bandgap center frequency of the silicon-based electromagnetic bandgap structure, and FBW is the electromagnetic bandgap bandwidth of the silicon-based electromagnetic bandgap structure.

[0049] ε eff1 is the relative dielectric constant of the lower equivalent dielectric layer, which can be calculated using the following formula:

[0050]

[0051] The relative dielectric constant of the upper equivalent dielectric layer is calculated as follows:

[0052]

[0053] Where h1, h2 and h3 are the thicknesses of the first silicon dielectric layer, the second silicon dielectric layer and the third silicon dielectric layer respectively, ε o is the relative dielectric constant of silicon medium, ε s is the relative dielectric constant of silicon dioxide.

[0054] In this embodiment, the ultra-wideband bandpass filter structure 8 is established as follows: Figure 2 As shown, it mainly includes a ring resonator loaded with multiple non-equal impedance branches, the ring resonator includes a main body in the shape of a ring, and multiple non-equal impedance branches are located at multiple equal positions of the main body in the shape of a ring; input branches and output branches are respectively led out from two adjacent non-equal impedance branches, and the remaining non-equal impedance branches are set as broadband matching branches, the impedance of the input branch is equal to the impedance of the output branch, and the impedance ratio of the input branch (or output branch) to the broadband matching branch is preferably 1:2. The return loss of the filtering structure can be reduced and the bandwidth can be improved by the non-equal impedance branches. Preferably, four non-equal impedance branches are provided, and the four non-equal impedance branches are located at four equal positions of the main body in the shape of a ring. Among the non-equal impedance branches, the impedance of the broadband matching branch is 100 ohms, and the impedance of the input branch and the output branch is 50 ohms. The impedance of the ring resonator is 50 ohms.

[0055] In this embodiment, the wide stopband metasurface band-stop filter structure established is as follows: Figure 2 As shown, it specifically includes a low-frequency supersurface band-stop filter structure 9 and a high-frequency supersurface band-stop filter structure 10. The low-frequency supersurface band-stop filter structure 9 and the high-frequency supersurface band-stop filter structure 10 both include a supersurface array and a strip line 11 mainly composed of a plurality of open resonant rings, and the supersurface array is loaded on both sides of the strip line. The multiple open resonant rings of the supersurface array are axially symmetrically distributed about the strip line, generating resonance, limiting the propagation of electromagnetic waves, and forming band-stop performance. The circumference of the open resonant ring is equal to half the wavelength of its operating frequency. Open resonant ring metasurfaces of different specifications can achieve wide stopband characteristics by superimposing.

[0056] Further, by adjusting the size, number, and spacing between the open resonant rings of the low-frequency supersurface band-stop filter structure and the high-frequency supersurface band-stop filter structure and the strip line, the operating frequency band of the supersurface band-stop filter structure can be changed. In a preferred embodiment, the size of the open resonant ring of the low-frequency supersurface band-stop filter structure 9 is larger than the size of the open resonant ring of the high-frequency supersurface band-stop filter structure 10. Preferably, the low-frequency supersurface band-stop filter structure is a supersurface structure of 8 large open resonant rings loaded on both sides of the strip line, and the high-frequency supersurface band-stop filter structure is a supersurface structure of 8 small open resonant rings loaded on both sides of the strip line.

[0057] like Figure 7 The figure shows the electric field simulation results of the low-frequency metasurface band-stop filter structure of an embodiment of the present invention, where (b) the energy in the stop band is restricted by the open resonant ring metasurface and cannot be transmitted; (a) and (c) show that outside the stop band, the energy can be transmitted smoothly.

[0058] Figure 8 The figure shows the S parameter simulation result of the low-frequency metasurface band-stop filter structure of this embodiment, and its resonance point is 0.161THz; Fig. 9 The figure shows the S parameter simulation result of the low-frequency metasurface band-stop filter structure of this embodiment, whose resonance point is 0.17 THz. By comparing the two, it can be seen that adjusting the size of the open resonant ring metasurface can change the resonance point, thereby adjusting the passband range of the filter.

[0059] Fig.10 The S parameter simulation results of the bandpass filter of this embodiment are shown. It can be seen that the passband center frequency of the bandpass filter of this embodiment is 0.151 THz, the relative bandwidth is 6.9%, the insertion loss is lower than 0.68 dB, and the upper and lower stopband ranges are greater than 20 GHz.

[0060] Fig.11 The figure shows the group delay simulation result of the bandpass filter of this embodiment. It can be seen that the group delay is 0.119±0.048ns.

[0061] It can be seen that this embodiment can realize any bandwidth filter by introducing a metasurface band-stop filter structure in an ultra-wideband filter and adjusting the working frequency of the metasurface. At the same time, a silicon-based integrated gap waveguide (SSIGW) is introduced to reduce the insertion loss of the filter while improving the integration. In order to verify the effectiveness and superiority of the proposed method, a terahertz wide-stopband, low-loss bandpass filter based on a metasurface is designed. The filter includes a wide-stopband metasurface band-stop filter structure, an ultra-wideband band-pass filter structure and SSIGW. The wide-stopband metasurface band-stop filter structure includes a low-frequency metasurface band-stop structure and a high-frequency metasurface band-stop structure. The metasurface is an open resonant ring; the ultra-wideband band-pass filter structure is a ring resonator loaded with non-equiimpedance branches. The results of the simulation analysis show that the passband center frequency is 0.151THz, the relative bandwidth is 6.9%, the group delay is 0.119±0.048ns, the insertion loss is less than 0.68dB, and the upper and lower stopband ranges are greater than 20GHz. Compared with the traditional arbitrary bandwidth filter design method, the design method proposed in the present invention has the advantages of simple design, small insertion loss, controllable stopband bandwidth, easy integration, etc., and can effectively reduce the complexity of terahertz filter design.

[0062] The above-mentioned embodiments only express several preferred implementation modes of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in the technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be regarded as the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be based on the protection scope of the claims.

Claims

1. A low-loss, arbitrary-bandwidth terahertz bandpass filter based on a metasurface, characterized in that: It includes a wide-stopband metasurface band-stop filter structure and an ultra-wideband band-pass filter structure, and the band-stop filter structure and the band-pass filter structure are fed by a silicon-based integrated gap waveguide structure; The ultra-wideband bandpass filter structure includes a ring resonator loaded with a plurality of non-equiimpedance branches, the ring resonator includes a ring body, and the plurality of non-equiimpedance branches are located at multiple equally divided positions of the ring body; input branches and output branches are respectively led out from two adjacent non-equiimpedance branches, and the remaining non-equiimpedance branches are set as broadband matching branches; The wide stopband metasurface band-stop filter structure includes a low-frequency metasurface band-stop filter structure and a high-frequency metasurface band-stop filter structure, both of which include a metasurface array and a strip line, and the metasurface array is loaded on both sides of the strip line; the metasurface array includes a plurality of open resonant rings, and the plurality of open resonant rings of the metasurface array are axially symmetrically distributed about the strip line; The silicon-based integrated gap waveguide structure comprises a first silicon dielectric layer, a second silicon dielectric layer and a third silicon dielectric layer arranged from bottom to top; a silicon dioxide isolation layer is arranged between two adjacent silicon dielectric layers; the topmost layer and the bottommost layer of the silicon-based integrated gap waveguide structure are copper-clad layers; the band line is etched in the silicon dioxide isolation layer above the second silicon dielectric layer; the wide stopband ultra-surface band-stop filter structure and the ultra-wideband bandpass filter structure are both etched in the silicon dioxide isolation layer on the lower surface of the third silicon dielectric layer.

2. The terahertz bandpass filter according to claim 1, characterized in that: The impedance of the input branch is equal to the impedance of the output branch.

3. The terahertz bandpass filter according to claim 1, characterized in that: The impedance ratio of the input branch or the output branch to the broadband matching branch is 1:

2.

4. The terahertz bandpass filter according to claim 1, characterized in that: There are four non-equiimpedance branches, which are located at four equally divided positions of the annular main body.

5. The terahertz bandpass filter according to claim 1, characterized in that: The ring body of the ring resonator is a body in the shape of a circular ring.

6. The terahertz bandpass filter according to claim 1, characterized in that: The circumference of the split ring resonator is equal to half the wavelength of its operating frequency.

7. The terahertz bandpass filter according to claim 1, characterized in that: The size of the open resonant ring of the low-frequency metasurface band-stop filter structure is greater than the size of the open resonant ring of the high-frequency metasurface band-stop filter structure.

8. The terahertz bandpass filter according to claim 1, characterized in that: A silicon dioxide isolation layer is provided on the upper and lower surfaces of the first silicon dielectric layer, and a plurality of metal sheets distributed in a periodic array are etched on the silicon dioxide isolation layer on the upper surface of the first silicon dielectric layer; a metal copper layer is etched on the silicon dioxide isolation layer on the lower surface of the first silicon dielectric layer; a metal column is connected through each of the metal sheets and the metal copper layer; the width of the metal sheet is greater than the cross-sectional width of the metal column, and a silicon dioxide isolation layer is wrapped outside the metal column to form a silicon-based electromagnetic bandgap structure unit; wherein the metal column is sequentially embedded in the silicon dioxide isolation layer on the upper surface of the first silicon dielectric layer, the first silicon dielectric layer, and the silicon dioxide isolation layer on the lower surface of the first silicon dielectric layer; A plurality of silicon-based electromagnetic bandgap structure units form a silicon-based electromagnetic bandgap structure array.

9. A method for designing a terahertz bandpass filter according to any one of claims 1 to 8, characterized in that: The steps include: Establish the SSIGW physical model; On the SSIGW model, an ultra-wideband bandpass filter structure is established; Based on the SSIGW model, a wide stopband metasurface bandstop filter structure is established; The ultra-wideband bandpass filter structure is integrated with the metasurface bandstop filter structure; the operating frequency band of the terahertz bandpass filter is controlled by adjusting the size, quantity, and spacing between the low-frequency metasurface bandstop filter structure and the high-frequency metasurface bandstop filter structure.

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