Stopband-tunable hollow bowtie cell plasmon bandpass filter

Abstract

The present invention provides a stopband-tunable hollow bowtie cell plasmon bandpass filter. The filter comprises a metal ground layer, a dielectric plate layer, and a metal circuit top layer, arranged in order from bottom to top. The metal circuit top layer comprises a first coplanar waveguide transmission line, a first wave conversion transition region, a hollow bowtie cell group, a second wave conversion transition region, and a second coplanar waveguide transmission line, connected in sequence along an axis. The metal circuit top layer is rectangular, with arc-shaped metal conductors positioned at each of its four corners. Both the first and second wave conversion transition regions are constructed by connecting multiple gradient-cut solid cells in series. The hollow bowtie cell group consists of multiple hollow bowtie cells, each of which is formed by removing a bowtie-shaped through-hole from a solid cell. A set number of hollow bowtie cells in the middle of the hollow bowtie cell group have their upper and lower ends truncated and connected by capacitors. This filter achieves dynamic adjustment of the low-frequency cutoff frequency, stopband suppression level within the passband, bandwidth, and frequency.

Description

Technical Field

[0001] The present invention relates to the field of microwave transmission technology, and in particular to a hollow bowtie cell plasmon bandpass filter with tunable stopband. Background Art

[0002] In recent years, surface plasmon polaritons (SPPs) have attracted attention in many technical fields such as microwaves and photonics.

[0003] Surface plasmons are electromagnetic wave patterns caused by the interaction of photons with free electrons on a metal surface. In other words, they are excited by the coupling of photons and free electrons at the interface of two materials with opposite polarity. For example, the two materials with opposite polarity can be a metal and an insulating medium. Surface plasmons have both the speed of photonics and the scale of electronics, and therefore have attracted widespread attention and research.

[0004] In the optical frequency band, surface plasmons can propagate along the metal-dielectric interface, with the electric field tightly confined near the contact surface, and the propagation constant increases exponentially with increasing frequency. However, in the lower terahertz (THz) and microwave frequency bands, because metals exhibit ideal conductor properties, the necessary condition that the dielectric constants of the two materials have opposite signs cannot be met, which limits the application of surface plasmons. To this end, an artificial surface plasmon polaritons (SSPPs) transmission structure with a periodic structure has emerged. It breaks the limitation of the surface plasmon application frequency band, supports excitation and transmission in the terahertz and microwave frequency bands, and still has the advantages of low crosstalk, extremely high field confinement, and suppression of high-frequency harmonic signal interference.

[0005] To date, although a variety of microwave devices based on artificial surface plasmon transmission structures have been designed and proposed, most circuits do not have dynamic adjustment capabilities and cannot be adjusted and applied in complex circuit systems. This is also the main obstacle to the widespread application of artificial surface plasmon microwave devices in reconfigurable integrated microwave systems and electronically controlled antenna feeding networks. Summary of the Invention

[0006] In view of this, an embodiment of the present invention provides a hollow bowtie cell plasmon bandpass filter with tunable stopband to eliminate or improve one or more defects existing in the prior art and solve the problem that the prior art cannot dynamically adjust the low-frequency cutoff frequency, the bandwidth of the stopband within the passband, and the frequency.

[0007] The present invention provides a stopband-tunable hollow bowtie cell plasmon bandpass filter, comprising:

[0008] Metal ground plane;

[0009] a dielectric layer, arranged above the metal ground layer;

[0010] A top layer of the metal circuit is arranged above the dielectric board layer, and the top layer of the metal circuit includes a first coplanar waveguide transmission line, a first wave conversion transition region, a hollow bowtie cell group, a second wave conversion transition region, and a second coplanar waveguide transmission line connected in sequence along an axis; the top layer of the metal circuit is rectangular, and the four top corners of the top layer of the metal circuit are respectively provided with arc-shaped metal conductors, and the arc-shaped metal conductors are connected to the metal ground layer through metal vias; the first wave conversion transition region and the second wave conversion transition region are both composed of a plurality of gradient-cut solid cells connected in series; the hollow bowtie cell group is composed of a plurality of hollow bowtie cells, and each hollow bowtie cell is obtained by digging out a bowtie-shaped through hole from the solid cell; the upper and lower ends of a set number of hollow bowtie cells in the middle of the hollow bowtie cell group are truncated and capacitor connections are added.

[0011] In some embodiments of the present invention, a set number of hollow bowtie cells in the middle of the hollow bowtie cell group are cut off at the upper and lower ends, and a variable capacitor is added at one end and a fixed capacitor is added at the other end.

[0012] In some embodiments of the present invention, the upper and lower ends of a set number of hollow bow tie cells in the middle of the hollow bow tie cell group are truncated, and variable capacitors are added at both ends; in a single hollow bow tie cell, the capacitance values ​​of the variable capacitors at both ends are equal.

[0013] In some embodiments of the present invention, the height of each solid cell in the first wave conversion transition region gradually increases along the first coplanar waveguide transmission line toward the hollow bowtie cell group;

[0014] The height of each solid cell in the second wave conversion transition region gradually decreases along the direction of the hollow bow tie cell group toward the second coplanar waveguide transmission line.

[0015] In some embodiments of the present invention, the hollow bow tie cell group is composed of 7 hollow bow tie cells connected in series, wherein the upper and lower ends of the middle 3 hollow bow tie cells are truncated and capacitor connections are added; the first wave conversion transition region and the second wave conversion transition region each include 5 solid cells connected in series.

[0016] In some embodiments of the present invention, the method further includes: providing a DC bias circuit to provide power to the hollow bowtie cell with a variable capacitor, wherein the DC bias circuit is provided with a plurality of AC isolation inductors.

[0017] In some embodiments of the present invention, a first DC blocking capacitor is provided between the first coplanar waveguide transmission line and the first wave conversion transition region; and a second DC blocking capacitor is provided between the second wave conversion transition region and the second coplanar waveguide transmission line.

[0018] In some embodiments of the present invention, the arc-shaped metal conductor is a quarter ellipse.

[0019] In some embodiments of the present invention, the dielectric constant of the dielectric layer is 3.66, and the loss constant is 0.0037.

[0020] In some embodiments of the present invention, the unit length of the periodically repeated solid cells in the circuit is 6 mm.

[0021] The beneficial effects of the present invention are at least:

[0022] The present invention provides a stopband-tunable hollow bowtie cell plasmon bandpass filter. A first coplanar waveguide transmission line, a first wave conversion transition region, a hollow bowtie cell group, a second wave conversion transition region, and a second coplanar waveguide transmission line are sequentially arranged along the axis of a top layer of a metal circuit. Arc-shaped metal conductors are disposed at the four corners of the top layer of the metal circuit. The filter provided by the present invention has a simple structure and is easy to implement.

[0023] Furthermore, the upper and lower ends of a set number of hollow bow tie cells in the middle of the hollow bow tie cell group are cut off and capacitor connections are added. When a variable capacitor is added to one end of the hollow bow tie cell and a fixed capacitor is added to the other end, the filter of the present invention has the advantages of low crosstalk, high field binding and deep high-frequency harmonic suppression, while being able to achieve dynamic adjustment of the low-frequency cutoff frequency, the stopband suppression level in the passband, the bandwidth and the frequency. When variable capacitors are added to the upper and lower ends of the hollow bow tie cell respectively, the filter of the present invention has the advantages of low crosstalk, high field binding and deep high-frequency harmonic suppression, while being able to achieve dynamic adjustment of the low-frequency cutoff frequency, the passband bandwidth and the frequency. The present invention lays the foundation for the widespread application of artificial surface plasmon microwave devices in reconfigurable integrated microwave systems and electrically controlled antenna feeding networks.

[0024] Additional advantages, objects, and features of the present invention will be set forth in part in the following description and will become apparent to those skilled in the art upon examination of the following or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained by the structures particularly pointed out in the description and drawings.

[0025] Those skilled in the art will understand that the purposes and advantages that can be achieved by the present invention are not limited to the above specific descriptions, and the above and other purposes that can be achieved by the present invention will be more clearly understood based on the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute a limitation of the present invention. In the drawings:

[0027] Figure 1 FIG. 1 is an ideal simulation structure diagram of a hollow bowtie cell plasmon bandpass filter with tunable stopband in one embodiment of the present invention.

[0028] Figure 2 3D structural diagram of a solid cell and a hollow bowtie cell and near-field radiation diagram of the solid cell and the hollow bowtie cell in one embodiment of the present invention.

[0029] Figure 3 Graph showing dispersion curves of a solid cell and a hollow bowtie cell as various preset parameters vary in one embodiment of the present invention.

[0030] Figure 4 This is a three-dimensional structural diagram of a hollow bowtie cell after adding capacitors in one embodiment of the present invention.

[0031] Figure 5 This is a dispersion curve diagram of the hollow bowtie cell with added capacitance in the fundamental mode and the second-order mode as the capacitance value changes in one embodiment of the present invention.

[0032] Figure 6 This is a comparison diagram of ideal simulated S parameters and a near-field radiation distribution diagram of a hollow bowtie cell plasmon bandpass filter with tunable stopband in one embodiment of the present invention.

[0033] Figure 7 1 is a diagram showing the actual structure of a hollow bowtie cell plasmon bandpass filter with tunable stopband in one embodiment of the present invention.

[0034] Figure 8 This is a comparison chart of the measured S parameters of the hollow bowtie cell plasmon bandpass filter with tunable stopband in one embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0036] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, the accompanying drawings only show structures and / or processing steps closely related to the solutions according to the present invention, while other details that are not closely related to the present invention are omitted.

[0037] It should be emphasized that the term "include / comprises" when used herein refers to the existence of features, elements, steps or components, but does not exclude the existence or addition of one or more other features, elements, steps or components.

[0038] It should also be noted that, unless otherwise specified, the term "connection" herein may refer not only to a direct connection but also to an indirect connection involving an intermediate.

[0039] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0040] In order to solve the problem that the existing technology cannot dynamically adjust the low-frequency cutoff frequency, the bandwidth of the stopband within the passband, and the frequency, the present invention provides a hollow bowtie cell plasmon bandpass filter with tunable stopband, such as Figure 1 The figure shows an ideal simulation structure diagram of the filter of the present invention, which includes:

[0041] Metal ground plane.

[0042] The dielectric layer is arranged above the metal ground layer.

[0043] The metal circuit top layer is disposed above the dielectric board layer. The metal circuit top layer includes a first coplanar waveguide transmission line, a first wave conversion transition region, a hollow bowtie cell group, a second wave conversion transition region, and a second coplanar waveguide transmission line, connected sequentially along an axis. The metal circuit top layer is rectangular, with arc-shaped metal conductors disposed at each of the four corners. The arc-shaped metal conductors are connected to the metal ground layer via metal vias. Both the first and second wave conversion transition regions are composed of a plurality of gradient-cut solid cells connected in series. The hollow bowtie cell group is composed of a plurality of hollow bowtie cells, each of which is formed by removing a bowtie-shaped through-hole from a solid cell. A predetermined number of the hollow bowtie cells in the middle of the hollow bowtie cell group have their upper and lower ends truncated and connected with capacitors.

[0044] In some embodiments, the dielectric plate layer is a Rogers RO4350B dielectric plate with a thickness of 0.508 mm, wherein the dielectric constant ε of the dielectric plate is r is 3.66, and the loss constant tanδ is 0.0037.

[0045] A large area of ​​metal paving is provided on the lower surface of the dielectric plate to form a metal grounding layer.

[0046] In some embodiments, the thickness of the metal ground layer and the metal circuit top layer are both 0.035 mm.

[0047] In the top layer of the metal circuit, the first coplanar waveguide transmission line and the second coplanar waveguide transmission line serve as filter signal feed lines, respectively used to input and output microwave signals into and out of the filter. In some embodiments, the width w of the first coplanar waveguide transmission line and the second coplanar waveguide transmission line are both 1.08 mm.

[0048] Arc-shaped metal conductors are provided at the four corners of the top layer of the metal circuit. In some embodiments, each arc-shaped metal conductor is a quarter-ellipse. Multiple metal vias are provided on each arc-shaped metal conductor, connecting the metal ground layer through the metal vias for grounding. This reduces signal transmission insertion loss and improves signal transmission efficiency. Each arc-shaped metal conductor forms a coplanar waveguide with the first and second coplanar waveguide transmission lines.

[0049] In some embodiments, the distance s between the arc-shaped metal conductor and the first coplanar waveguide transmission line and the second coplanar waveguide transmission line is 0.81 mm.

[0050] Electromagnetic waves are transmitted along the first and second coplanar waveguide transmission lines as quasi-TEM waves (transverse electromagnetic waves), while transverse magnetic waves (TM waves) are polarized and excited in the artificial surface plasmon transmission structure. Therefore, first and second wave conversion transition regions are provided between the first and second coplanar waveguide transmission lines and the hollow bowtie cell group to achieve waveform transition and improve signal transmission efficiency. Simulation experiments have demonstrated that combining four arc-shaped metal conductors with gradient-cut solid cells connected in series within the first and second wave conversion transition regions effectively achieves waveform conversion from quasi-TEM waves to TM waves.

[0051] In some embodiments, as Figure 1 As shown, one side of the arc-shaped metal conductor is l r The length is 37.5 mm, and the other side is w r 13.65 mm long, near l r Eleven metal vias are set on one side of the edge.

[0052] In some embodiments, each solid cell in the first wave conversion transition region is gradient cut according to a preset angle, and the height of each solid cell gradually increases along the first coplanar waveguide transmission line toward the hollow bow tie cell group; each solid cell in the second wave conversion transition region is also gradient cut according to a preset angle, and the height of each solid cell gradually decreases along the hollow bow tie cell group toward the second coplanar waveguide transmission line.

[0053] In some embodiments, as Figure 1 As shown, the preset angles of cutting of each solid cell in the first wave conversion transition region and the second wave conversion transition region are based on w cut =3.1mm,l cut = calculated as 30mm.

[0054] In some embodiments, as Figure 1 As shown, the hollow bow tie cell group consists of seven hollow bow tie cells connected in series, where the upper and lower ends of the three middle hollow bow tie cells are truncated and connected with capacitors. The first wave conversion transition region and the second wave conversion transition region both contain five solid cells in series.

[0055] like Figure 2 As shown in (a), the left picture is the structural diagram of the solid cell, and the right picture is the structural diagram of the hollow bow tie cell.

[0056] A cell is a periodic structure with a certain shape made on a dielectric substrate by etching or laser engraving. Figure 2 As shown in (a), in the present invention, the unit length of each solid cell that repeats periodically in the circuit is represented by d. The hollow bow tie cell is obtained by cutting out a bow tie-shaped through hole in the middle of the solid cell. Therefore, the hollow bow tie cell has the same outer contour size as the solid cell. The specific shape is as follows: Figure 2 (a) As shown in the right figure, the hollow dimensions of the hollow bow tie cell are represented by h2, b2 and c2. The near-field radiation diagrams of the solid cell and the hollow bow tie cell are shown in Figure 2 (b) shown.

[0057] like Figure 3 Shown are dispersion curves for solid cells and hollow bowtie cells as the periodic length and hollowing size are varied. In an artificial surface plasmon transmission device implemented with a periodic arrangement of solid cells, the dispersion curve of a single solid cell falls within the slow-wave region, where the slow-wave region and the fast-wave region are separated by the dispersion curve of light. The figure shows that the propagation constant increases exponentially with increasing frequency, indicating that a single solid cell inherently has a high-frequency cutoff frequency.

[0058] like Figure 2 (b) As shown in the near-field radiation diagram of the solid cell and the hollow bow tie cell, the energy coupling at the center of the solid cell is weak, so after the metal at the center of the solid cell is hollowed out, as shown in Figure 3As shown, the resulting hollow bowtie cell is still in the slow-wave region and still has a high-frequency cutoff frequency, which remains almost unchanged. This high-frequency cutoff frequency enables the transmission device formed by the periodic arrangement of solid cells and / or hollow bowtie cells to suppress high-frequency harmonic signal interference, and this suppression performance increases with the number of constituent cells, while the transmission efficiency within the passband decreases with the increase in the number of constituent cells.

[0059] The periodic length d of the solid cell and the hollow dimensions h2, b2, c2 of the hollow bow tie cell are changed, such as Figure 3 As shown in the figure, as the periodic length d of the solid cell and its corresponding hollow bowtie cell increases, their high-frequency cutoff frequency decreases. When the periodic length d is equal, changing the hollow dimensions h2, b2, and c2 of the hollow bowtie cell maintains almost no change in its high-frequency cutoff frequency, indicating that changes in hollow dimensions do not affect the performance of the hollow cell. Therefore, the high-frequency cutoff frequency of solid cells and hollow bowtie cells with the same outer dimensions is equal.

[0060] In some embodiments, Figure 2 In (a), the unit length d = 6 mm of the solid cell and its corresponding hollow bow tie cell that are periodically repeated in the circuit, and the other outer contour dimensions are: w = 1.08 mm, b1 = 1.8 mm, c1 = 4.2 mm, h1 = 3.6 mm. The corresponding hollow dimensions of the hollow bow tie cell are: b2 = 0.53 mm, c2 = 2 mm, h2 = 2.2 mm.

[0061] In order to achieve tunability of the filter's low-frequency cutoff frequency, stopband width, and frequency, the present invention cuts off the upper and lower end paths of the hollow bowtie cell, and adds variable capacitors and / or fixed capacitors at the cutoff points to reconnect them.

[0062] When a capacitor is added to the hollow bowtie cell and turned on, its dispersion curve splits into two propagation modes: the fundamental mode and the second-order mode. Furthermore, the dispersion curves of the hollow bowtie cell with the added capacitor are different in mode 1 and mode 2. The fundamental mode is denoted as mode 1, and the second-order mode is denoted as mode 2.

[0063] In some embodiments, as Figure 4 As shown in (a), a variable capacitor C1 is added to one end of the hollow bowtie cell, and a fixed capacitor C2 is added to the other end. For example, C2 = 0.9pF. During implementation, the capacitance of C1 can be adjusted within the range of 0.3 to 1.8pF and is different from the capacitance of C2.

[0064] When a variable capacitor C1 is added to one end of the hollow bow tie cell and a fixed capacitor C2 is added to the other end, the dispersion curves under the two propagation modes are shown as follows: Figure 5 (a) and the following conclusions can be drawn:

[0065] 1. After adding capacitance to the hollow bowtie cell, the low-frequency portion of its dispersion curve coincides with the light dispersion curve in both propagation modes. As frequency increases, it deviates from the light dispersion curve after reaching its respective turning points, falling into the slow-wave region and gradually approaching its high-frequency cutoff frequency in both propagation modes. However, as the capacitance of variable capacitor C1 increases, the high-frequency cutoff frequency of the hollow bowtie cell with the added capacitance decreases in mode 1, while the high-frequency cutoff frequency in mode 2 remains unchanged at 5.81 GHz.

[0066] 2. When the dispersion curve of the hollow bowtie cell after adding capacitance coincides with the dispersion curve of light, it indicates that the electromagnetic wave is now completely radiated into the external light. The hollow bowtie cell does not support signal transmission on its surface. Therefore, in both propagation modes, the hollow bowtie cell after adding capacitance has a low-frequency cutoff frequency, and the frequency at each turning point corresponds to its respective low-frequency cutoff frequency.

[0067] 3. When C2 = 0.9pF and the capacitance of C1 is adjusted within the range of 0.3 to 1.8pF, regardless of how C1 is adjusted, the low-frequency cutoff frequency in mode 2 is always greater than the high-frequency cutoff frequency in mode 1, forming a stopband within the passband of the hollow bowtie cell of the present invention. As the variable capacitance C1 decreases, the frequency of the resulting stopband increases; the closer the capacitance of C1 is to C2 = 0.9pF, the narrower the stopband becomes; specifically, when C1 = C2 = 0.9pF, the stopband does not exist. This achieves tunable stopband.

[0068] 4. As the variable capacitance C1 increases, the turning points under mode 1 will shift slightly downward, that is, the low-frequency cutoff frequency of the hollow bowtie cell after adding the capacitance is slightly reduced, thus achieving tunable low-frequency cutoff frequency.

[0069] like Figure 1 In the ideal simulation structure diagram of the filter shown in FIG, the filter is simulated in the case where the tunable hollow bow tie cell adopts the method of adding a variable capacitor C1 at one end and a fixed capacitor C2 at the other end, as shown in FIG. Figure 6 The left half of (a) shows the ideal simulation result of the S parameters of the filter, where the S parameters include return loss |S 11 | and insertion loss |S 21 Return loss, also known as reflection loss, is the reflection caused by impedance mismatch in a link. Return loss is a parameter that indicates signal reflection performance, indicating that a portion of the incident power is reflected back to the signal source. It is usually specified at the input and output. Insertion loss refers to the loss of load power caused by the insertion of a component or device at a certain point in the transmission system. It is expressed as the ratio (in decibels) of the power received by the load before the component or device is inserted to the power received by the same load after insertion.

[0070] Specifically, according to Figure 6 (a) The S parameter comparison section shows that when a variable capacitor C1 is added to one end of the tunable hollow bowtie cell in the filter, and C1 is adjusted in the range of 0.3 to 1.8 pF, and a fixed capacitor C2 = 0.9 pF is added to the other end, a transmission stopband will be generated in the passband of the filter. The frequency of the stopband increases as C1 decreases, and the closer the capacitance value of the variable capacitor C1 is to the capacitance value of the fixed capacitor C2, the smaller the stopband bandwidth and the lower the suppression level. For example, when C1 = 0.7 pF, the stopband is the narrowest, only 0.08 GHz, and the insertion loss | S 21 |The suppression level is about 20dB; when C1=0.3pF, the stopband is the widest, reaching 0.47GHz, and the insertion loss |S 21 The suppression level exceeds 40dB. Meanwhile, as the variable capacitor C1 increases, the filter's low-frequency cutoff frequency gradually decreases from 2.56GHz to 1.62GHz, while the filter's high-frequency cutoff frequency remains at around 5.76GHz, unchanged by the adjustment of C1.

[0071] like Figure 6 (a) The right half shows the near-field radiation distribution of the filter circuit at seven frequencies: 1.0 GHz, 2.95 GHz, 3.1 GHz, 3.5 GHz, 3.8 GHz, 4.3 GHz, and 8.0 GHz. For the left half, the variable capacitor C1 is adjusted within the range of 0.3 to 1.8 pF, the fixed capacitor C2 = 0.9 pF, and C1 ≠ C2. Regardless of the value of capacitor C1, the circuit signal is interrupted at two frequencies: 1.0 GHz, which is below the low-frequency cutoff frequency, and 8.0 GHz, which is above the high-frequency cutoff frequency. At 1.0GHz, the hollow bowtie cell after adding capacitors in the filter does not support the transmission of low-frequency signals, that is, this frequency point is lower than the low-frequency cutoff frequency of the hollow bowtie cell after adding capacitors. Therefore, at 1.0GHz, the signal transmission is interrupted at the hollow bowtie cell after adding capacitors. The 8.0GHz frequency point exceeds the high-frequency cutoff frequencies of the solid cell, the hollow bowtie cell, and the hollow bowtie cell after adding capacitors. Therefore, the signal transmission is interrupted in the first wave conversion transition region of the solid cell. As the variable capacitor C1 is adjusted within the range of 0.3 to 1.8 pF, the filter will experience signal interruption within the corresponding stopband frequency: when C1 = 1.8 pF, it will be interrupted at 2.95 GHz; when C1 = 1.4 pF, it will be interrupted at 3.1 GHz; when C1 = 0.7 pF, it will be interrupted at 3.5 GHz; when C1 = 0.5 pF, it will be interrupted at 3.8 GHz; when C1 = 0.3 pF, it will be interrupted at 4.3 GHz. Figure 6As can be seen from the near-field distribution diagram on the right half of (a), the electromagnetic waves are tightly bound to the surfaces of each metal cell, with almost no energy leakage, indicating that the filter of the present invention has high field confinement. At the same time, this feature also means that the filter of the present invention hardly causes signal interference to other circuits that are relatively close, and has low circuit crosstalk performance.

[0072] In some embodiments, Figure 1 On the basis of the ideal simulation structure diagram, a DC bias circuit is set to stimulate the normal operation of the variable capacitor to verify the feasibility of the filter of the present invention. Figure 7 Shown is the complete block diagram of the filter when implemented.

[0073] A first DC blocking capacitor is provided between the first coplanar waveguide transmission line and the first wave conversion transition region; a second DC blocking capacitor is provided between the second wave conversion transition region and the second coplanar waveguide transmission line. The DC blocking capacitor is used to prevent DC signals loaded across the variable capacitor from entering the microwave signal input and output devices, potentially causing instrument malfunction.

[0074] A plurality of AC blocking inductors are provided in the DC bias circuit, wherein the AC blocking inductors are used to prevent microwave signals from flowing into the bias circuit and affecting the power supply of the DC voltage source.

[0075] For example, Figure 7 As shown, the variable capacitor C1 is SMV2019-097LF; the fixed capacitor C2 = 0.9pF; the DC blocking capacitor C bias =120 / / 680pF, where the symbol “ / / ” indicates capacitors in parallel; the first AC inductor L bias1 =390nH; Second AC isolation inductor L bia =180nH. According to the above values, the circuit is actually tested. Figure 8 Shown is a comparison diagram of the measured S parameters of the filter of the present invention in the frequency range of 0.5 to 16 GHz.

[0076] Specifically, as the DC voltage V cc As the capacitance of variable capacitor C1 increases and the capacitance of variable capacitor C1 decreases, the frequency range of the stopband increases, and the low-frequency cutoff frequency also increases accordingly. When the capacitance of variable capacitor C1 is closer to C2 = 0.9pF, the corresponding stopband bandwidth is narrower, that is, the suppression level is lower. For example, when C1 = 0.81pF, there is almost no stopband in the filter passband. This confirms the feasibility of the practical application of the filter of the present invention.

[0077] At the same time, no matter how the capacitance of the variable capacitor C1 changes, the filter has good |S in a wide frequency range exceeding the high frequency cutoff frequency. 21 | Harmonic suppression level. For example, in the frequency range of 6 to 16 GHz, |S 21| are all less than -30dB, therefore, the filter of the present invention has deep high frequency harmonic suppression performance.

[0078] In some embodiments, as Figure 4 As shown in (b), variable capacitors C1 are added at the upper and lower ends of the hollow bow tie cell. ′ and C2 ′ When implemented, C1 ′ and C2 ′ The capacitance value of the capacitor can be changed, and the capacitance value of the two is equal C1 ′ =C2 ′ .

[0079] The hollow bow tie cell is equipped with variable capacitors C1 at the upper and lower ends. ′ and C2 ′ In the case of , the dispersion curves under the two propagation modes are as follows Figure 5 (b) and the following conclusions can be drawn:

[0080] 1. After adding the capacitor, the low-frequency part of the dispersion curve of the hollow bow tie cell in both propagation modes coincides with the light dispersion curve. As the frequency increases, it deviates from the light dispersion curve after reaching its respective turning point and falls into the slow wave region, gradually approaching its high-frequency cutoff frequency in both propagation modes. However, as the variable capacitor C1 ′ and C2 ′ With the increase of capacitance value, the high-frequency cutoff frequency of the hollow bowtie cell equipped with capacitance in mode 1 becomes smaller, while the high-frequency cutoff frequency in mode 2 remains unchanged at 5.81 GHz.

[0081] 2. When the dispersion curve of the hollow bowtie cell after adding capacitance coincides with the dispersion curve of light, it indicates that the electromagnetic wave is now completely radiated into the external light. The hollow bowtie cell does not support signal transmission on its surface. Therefore, in both propagation modes, the hollow bowtie cell after adding capacitance has a low-frequency cutoff frequency, and the frequency at each turning point corresponds to its respective low-frequency cutoff frequency.

[0082] 3. When C1 ′ =C2 ′ And C1 ′ and C2 ′ When the capacitance value is adjusted within the range of 0.6 to 1.2 pF, no matter how the two variable capacitors are adjusted, the low-frequency cutoff frequency of the hollow bowtie cell after adding the capacitor in mode 2 is the same as the high-frequency cutoff frequency in mode 1, that is, there is an intersection in the two propagation modes, and no stopband is formed, which is a bandpass structure.

[0083] 4. With C1 ′ and C2 ′With the increase of capacitance, the turning points under mode 1 will shift slightly downward, that is, the low-frequency cutoff frequency of the hollow bowtie cell will be slightly reduced after adding capacitance, thus achieving the tunability of the low-frequency cutoff frequency and the tunability of the passband range.

[0084] like Figure 1 In the ideal simulation structure diagram of the filter shown in the figure, variable capacitors C1 are added to the upper and lower ends of the tunable hollow bow tie cell. ′ and C2 ′ And C1 ′ =C2 ′ In this way, the ideal filter is simulated, such as Figure 6 (b) shows the ideal simulation results of the S parameters of the filter.

[0085] Specifically, according to Figure 6 (b) It can be seen that when the variable capacitors added to the upper and lower ends of the tunable hollow bowtie cell in the filter have the same capacitance value, there is no transmission stopband within the passband of the cell dispersion curve. As the two variable capacitors increase in value, the low-frequency cutoff frequency of the passband gradually decreases from 2.75 GHz to 1.83 GHz; the high-frequency cutoff frequency of the passband remains at around 5.76 GHz and does not change with the adjustment of the two variable capacitors.

[0086] In summary, the present invention provides a stopband-tunable hollow bowtie cell plasmon bandpass filter. A first coplanar waveguide transmission line, a first wave conversion transition region, a hollow bowtie cell group, a second wave conversion transition region, and a second coplanar waveguide transmission line are sequentially arranged along the axis of a top layer of a metal circuit. Arc-shaped metal conductors are disposed at the four corners of the top layer of the metal circuit. The filter provided by the present invention has a simple structure and is easy to implement.

[0087] Furthermore, the upper and lower ends of a set number of hollow bow tie cells in the middle of the hollow bow tie cell group are cut off and capacitor connections are added. When a variable capacitor is added to one end of the hollow bow tie cell and a fixed capacitor is added to the other end, the filter of the present invention has the advantages of low crosstalk, high field binding and deep high-frequency harmonic suppression, while being able to achieve dynamic adjustment of the low-frequency cutoff frequency, the stopband suppression level in the passband, the bandwidth and the frequency. When variable capacitors are added to the upper and lower ends of the hollow bow tie cell respectively, the filter of the present invention has the advantages of low crosstalk, high field binding and deep high-frequency harmonic suppression, while being able to achieve dynamic adjustment of the low-frequency cutoff frequency, the passband bandwidth and the frequency. The present invention lays the foundation for the widespread application of artificial surface plasmon microwave devices in reconfigurable integrated microwave systems and electrically controlled antenna feeding networks.

[0088] It should be understood by those skilled in the art that the various exemplary components, systems and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software or a combination of the two. Whether it is specifically performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in, a function card, etc. When implemented in software, the elements of the present invention are programs or code segments that are used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted on a transmission medium or a communication link via a data signal carried in a carrier.

[0089] It should be understood that the present invention is not limited to the specific configurations and processes described above and illustrated in the figures. For the sake of brevity, a detailed description of known methods is omitted. In the above embodiments, several specific steps are described and illustrated as examples. However, the method of the present invention is not limited to the specific steps described and illustrated. Those skilled in the art may make various changes, modifications, and additions, or change the order of the steps after understanding the spirit of the present invention.

[0090] In the present invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or replace features of other embodiments.

[0091] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations to the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A stopband-tunable hollow bowtie cell plasmon bandpass filter, characterized in that: include: Metal ground plane; a dielectric layer, arranged above the metal ground layer; A metal circuit top layer is arranged above the dielectric plate layer, and the metal circuit top layer includes a first coplanar waveguide transmission line, a first wave conversion transition region, a hollow bowtie cell group, a second wave conversion transition region, and a second coplanar waveguide transmission line connected in sequence along an axis; the metal circuit top layer is rectangular, and the four vertex corners of the metal circuit top layer are respectively provided with arc-shaped metal conductors, and the arc-shaped metal conductors are connected to the metal ground layer through metal vias; the first wave conversion transition region and the second wave conversion transition region are both composed of a plurality of gradient-cut solid cells connected in series; the hollow bowtie cell group is composed of a plurality of hollow bowtie cells, and each hollow bowtie cell is obtained by digging out a bowtie-shaped through hole from the solid cell; the upper and lower ends of a set number of hollow bowtie cells in the middle of the hollow bowtie cell group are truncated and capacitive connections are added, including adding a variable capacitor at one end and a fixed capacitor at the other end, or adding variable capacitors with equal capacitance values ​​at both ends; A DC bias circuit is provided to provide power to the hollow bowtie cell with a variable capacitor, wherein a plurality of AC isolation inductors are provided in the DC bias circuit.

2. The stopband-tunable hollow bowtie cell plasmon bandpass filter according to claim 1, characterized in that: The height of each solid cell in the first wave conversion transition region gradually increases along the first coplanar waveguide transmission line toward the hollow bowtie cell group; The height of each solid cell in the second wave conversion transition region gradually decreases along the direction of the hollow bow tie cell group toward the second coplanar waveguide transmission line.

3. The stopband-tunable hollow bowtie cell plasmon bandpass filter according to claim 1, characterized in that: The hollow bow tie cell group is composed of 7 hollow bow tie cells connected in series, among which the upper and lower ends of the middle 3 hollow bow tie cells are truncated and capacitors are added for connection; the first wave conversion transition region and the second wave conversion transition region each contain 5 solid cells connected in series.

4. The stopband-tunable hollow bowtie cell plasmon bandpass filter according to claim 1, characterized in that: A first DC blocking capacitor is provided between the first coplanar waveguide transmission line and the first wave conversion transition region; and a second DC blocking capacitor is provided between the second wave conversion transition region and the second coplanar waveguide transmission line.

5. The stopband-tunable hollow bowtie cell plasmon bandpass filter according to claim 1, characterized in that: The arc-shaped metal conductor is in the shape of a quarter ellipse.

6. The stopband-tunable hollow bowtie cell plasmon bandpass filter according to claim 1, characterized in that: The dielectric constant of the dielectric layer is 3.66, and the loss constant is 0.0037.

7. The stopband-tunable hollow bowtie cell plasmon bandpass filter according to claim 1, characterized in that: The unit length of the solid cell periodically repeated in the circuit is 6 mm.

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