Microwave line wave-absorbing load and terahertz equipment

Abstract

The invention discloses a microwave line wave-absorbing load which comprises a transmission line. One end of the transmission line is an input end, and the other end of the transmission line is a terminal short-circuit surface; the artificial surface plasmon circuit is arranged between the input end of the transmission line and the terminal short circuit surface; the artificial surface plasmon circuit comprises a plurality of branches extending into the transmission line, the branches are symmetrically distributed on the two sides of the transmission line in the transmission direction of the transmission line, and the length of the branch extending into the transmission line on any side is gradually increased. Traveling wave type conversion and absorption from a TE main mode to an artificial surface plasmon mode in the transmission line can be directly achieved through the artificial surface plasmon line directly embedded in the transmission line, an additional intermediate transition mode is not needed, and therefore echo characteristic deterioration caused by the intermediate mode is avoided. Therefore, the structure can greatly improve the echo / reflection characteristics of the microwave line wave-absorbing load.

Description

Technical Field

[0001] The present invention relates to the field of terahertz technology, and in particular to a microwave line absorbing load and a terahertz device. Background Art

[0002] Absorbing loads play an extremely important role in radio electronics. For example, in microwave and millimeter wave wireless communications and radar imaging, the transmission characteristic parameters of the commonly used directional couplers, such as port isolation, are directly affected by the absorbing performance of the matching loads at the isolation ports. However, the existing absorbing loads have relatively large standing waves and high return losses. Therefore, the system applications in the terahertz frequency band still have an extremely urgent need for waveguide absorbing loads with high absorption rate, low return reflection, low process difficulty and high reliability. Summary of the invention

[0003] An object of the present invention is to provide a microwave line absorbing load with high absorptivity and low echo reflection; another object of the present invention is to provide a terahertz device with high absorptivity and low echo reflection.

[0004] In order to solve the above technical problems, the present invention provides a microwave line absorbing load, comprising:

[0005] Transmission line; one end of the transmission line is an input end, and the other end of the transmission line is a terminal short-circuit surface;

[0006] An artificial surface plasmon circuit is arranged between the input end and the terminal short-circuit surface in the transmission line; the artificial surface plasmon circuit includes a plurality of branches extending into the transmission line, and along the transmission direction of the transmission line, the branches are symmetrically distributed on both sides of the transmission line, and the length of the branches on either side extending into the transmission line gradually increases.

[0007] Optionally, the transmission line is a waveguide, and the artificial surface plasmon circuit is embedded in the waveguide.

[0008] Optionally, the artificial surface plasmon circuit includes a substrate and the branches arranged on the surface of the substrate, and the branches are arranged on at least one side surface of the substrate.

[0009] Optionally, the branches are provided on two opposite surfaces of the substrate, and along the transmission direction of the transmission line, the branches located on the same surface of the substrate are symmetrically distributed on both sides of the transmission line, and the length of the branches on either side extending into the transmission line gradually increases.

[0010] Optionally, projections of branches located on two opposite surfaces of the substrate along the thickness direction overlap with each other.

[0011] Optionally, a first end of the artificial surface plasmon circuit facing the input end of the transmission line is connected to the waveguide via an impedance matching structure.

[0012] Optionally, the impedance matching structure includes protrusions protruding from the waveguide on both sides of the waveguide along the width direction, and the first end of the artificial surface plasmon circuit is connected to the protrusions; the protrusions protrude from the waveguide on both sides of the waveguide by equal lengths.

[0013] Optionally, the substrate is a low-conductivity metal substrate.

[0014] Optionally, the transmission line is a slot line, and the artificial surface plasmon circuit and the slot line are an integrated structure.

[0015] The present invention also provides a terahertz device, comprising the microwave line absorbing load as described in any one of the above items.

[0016] A microwave line absorbing load provided by the present invention comprises: a transmission line; one end of the transmission line is an input end, and the other end of the transmission line is a terminal short-circuit surface; an artificial surface plasmon line arranged between the input end and the terminal short-circuit surface in the transmission line; the artificial surface plasmon line comprises a plurality of branches extending into the transmission line, and along the transmission direction of the transmission line, the branches are symmetrically distributed on both sides of the transmission line, and the length of the branches on either side extending into the transmission line gradually increases.

[0017] By directly embedding the artificial surface plasmon circuit in the transmission line, the traveling wave conversion and absorption of the TE main mode in the transmission line to the artificial surface plasmon mode can be directly realized without the need for additional intermediate transition modes, thereby avoiding the deterioration of the echo characteristics caused by the existence of intermediate modes, such as converting the TE mode to the TEM mode first. Therefore, this structure can greatly improve the echo / reflection characteristics of the microwave line absorbing load. In addition, the artificial surface plasmon circuit can be realized only by using mature terahertz thin film circuit technology, with the characteristics of high graphic accuracy, good consistency and low cost; at the same time, the corresponding waveguide cavity structure is simple, the cavity circuit has good machinability, and there is no need for the traditional wedge-shaped absorber material to process the narrow wedge-shaped waveguide terminal, so the overall circuit machining maturity is high and the cost is low.

[0018] The present invention also provides a terahertz device, which also has the above-mentioned beneficial effects, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] FIG1 is a schematic diagram of the structure of a waveguide absorbing load in the prior art;

[0021] FIG2 is a diagram showing echo characteristics of the wedge-shaped waveguide in FIG1 in an absorbing load;

[0022] FIG3 is a schematic structural diagram of a microwave line absorbing load provided by an embodiment of the present invention;

[0023] Figure 4 It is the structural principle diagram of Figure 3;

[0024] Figure 5 It is the electric field schematic diagram in Figure 3;

[0025] Figure 6 for Figure 5 Corresponding return loss characteristic diagram;

[0026] Figure 7 It is a partial structural schematic diagram of Figure 3.

[0027] In the figure: 1. Transmission line, 2. Artificial surface plasmon line, 3. Branch, 4. Terminal short-circuit board, 5. Impedance matching structure. DETAILED DESCRIPTION

[0028] The core of the present invention is to provide a microwave line absorbing load. Please refer to Figures 1 and 2. Figure 1 is a schematic diagram of the structure of a waveguide absorbing load in the prior art; Figure 2 is a diagram of the echo characteristics in the wedge-shaped waveguide absorbing load in Figure 1. Referring to Figures 1 and 2, in the prior art, the waveguide absorbing load applied to the millimeter wave and terahertz wave fields is usually implemented in the form of embedding a wedge-shaped broadband absorber material structure inside a rectangular waveguide, as shown in Figure 1. However, with the application and promotion of millimeter wave-terahertz wave technology in detection and communication and other fields, the corresponding system operating frequency has been continuously pushed up. With the increase of the operating frequency, the waveguide size is adjusted accordingly. The cross-sectional size of the WR4.3 standard waveguide (170GHz-260GHz) is 1.092mm*0.546mm. At this time, the production and assembly of the wedge-shaped broadband absorber material will become very difficult. On the other hand, the traditional absorption load structure uses epoxy resin material with carbonyl iron powder added, but in the frequency band above about 70GHz, the complex magnetic permeability of the material is close to 1+j0, showing a non-magnetic characteristic, and can only rely on dielectric loss to absorb the incident power. Therefore, in the frequency band above 100GHz, traditional absorbing materials have no advantages over pure dielectric loss materials. The simulated transmission characteristic parameters of traditional wedge-shaped absorbing materials in WR4.3 waveguide are shown in Figure 2, which shows that its standing wave is relatively large and the return loss is high.

[0029] The present invention provides a microwave line absorbing load, comprising: a transmission line; one end of the transmission line is an input end, and the other end of the transmission line is a terminal short-circuit surface; an artificial surface plasmon line is arranged between the input end and the terminal short-circuit surface in the transmission line; the artificial surface plasmon line includes a plurality of branches extending into the transmission line, along the transmission direction of the transmission line, the branches are symmetrically distributed on both sides of the transmission line, and the length of the branches on either side extending into the transmission line gradually increases.

[0030] By directly embedding the artificial surface plasmon circuit in the transmission line, the traveling wave conversion and absorption of the TE main mode in the transmission line to the artificial surface plasmon mode can be directly realized without the need for additional intermediate transition modes, thereby avoiding the deterioration of the echo characteristics caused by the existence of intermediate modes, such as converting the TE mode to the TEM mode first. Therefore, this structure can greatly improve the echo / reflection characteristics of the microwave line absorbing load. In addition, the artificial surface plasmon circuit can be realized only by using mature terahertz thin film circuit technology, with the characteristics of high graphic accuracy, good consistency and low cost; at the same time, the corresponding waveguide cavity structure is simple, the cavity circuit has good machinability, and there is no need for the traditional wedge-shaped absorber material to process the narrow wedge-shaped waveguide terminal, so the overall circuit machining maturity is high and the cost is low.

[0031] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] Embodiment 1

[0033] Please refer to Figures 3 to Figure 7 , FIG3 is a schematic structural diagram of a microwave line absorbing load provided in an embodiment of the present invention; Figure 4 It is the structural principle diagram of Figure 3; Figure 5 It is the electric field schematic diagram in Figure 3; Figure 6 for Figure 5 Corresponding return loss characteristic diagram; Figure 7 It is a partial structural schematic diagram of Figure 3.

[0034] Referring to Figure 3, in an embodiment of the present invention, the microwave line absorbing load includes: a transmission line 1; one end of the transmission line 1 is an input end, and the other end of the transmission line 1 is a terminal short-circuit surface 4; an artificial surface plasmon circuit 2 is arranged between the input end and the terminal short-circuit surface 4 in the transmission line 1; the artificial surface plasmon circuit 2 includes a plurality of branches 3 extending into the transmission line 1, and along the transmission direction of the transmission line 1, the branches 3 are symmetrically distributed on both sides of the transmission line 1, and the length of the branches 3 on either side extending into the transmission line 1 gradually increases.

[0035] The above-mentioned transmission line 1 is a line for transmitting signals, which can be a line of an isolation port formed by a directional coupler or a section of a line of other structures, and is not specifically limited here. In the present embodiment, the transmission line 1 has two opposite ends, one of which is an input end, and the other end is a terminal short-circuit surface 4. The above-mentioned artificial surface plasmon circuit 2 usually needs to be arranged at a position of the transmission line 1 near the terminal short-circuit surface 4 to absorb sound waves. In the present embodiment, the transmission line 1 is usually used to transmit TE mode signals, that is, the transmission line 1 works in TE mode. For example, in the present embodiment, the transmission line 1 can specifically be a rectangular waveguide, and the signal transmitted by the rectangular waveguide is usually TE. 10 The artificial surface plasmon circuit 2 converts the TE mode signal into a surface plasmon mode signal, thereby achieving the wave absorbing function.

[0036] The above-mentioned artificial surface plasmon (spoof surface plasmon polariton, SSPP) line usually needs to be arranged between the input end and the terminal short-circuit surface 4 in the transmission line 1, and is usually arranged at a position close to the terminal short-circuit surface 4. The artificial surface plasmon line 2 usually has a plurality of regularly arranged branches 3. In this embodiment, the branches 3 need to extend into the transmission line 1, so as to realize the function of converting the TE mode signal transmitted by the transmission line 1 into a surface plasmon mode signal.

[0037] For the transmission line 1, it has a transmission direction pointing from the input end to the terminal short-circuit surface 4, and the corresponding artificial surface plasmon circuit 2 also has this transmission direction. In this embodiment, along the direction of the transmission line 1, the above-mentioned branches 3 are symmetrically distributed on both sides of the transmission line 1, and the length of the branches 3 on either side extending in the transmission line 1 gradually increases. The transmission direction of the above-mentioned transmission line 1 is usually also the length direction of the transmission line 1. The direction perpendicular to the transmission direction in the horizontal plane is the width direction of the transmission line 1. The above-mentioned branches 3 usually extend in the width direction, extending from the side of the transmission line 1 to the center of the transmission line 1.

[0038] The above-mentioned branches 3 will be symmetrically distributed on both sides of the transmission line 1, that is, the above-mentioned branches 3 will be set on both sides of the transmission line 1 along the width direction, and the branches 3 on both sides are symmetrically distributed with the axis of the transmission line 1 as the center. For the multiple branches 3 on either side of the transmission line 1, the length extending into the transmission line 1 will gradually increase along the transmission direction of the transmission line 1, that is, the length of the branches 3 close to the input end of the transmission line 1 in the artificial surface plasmon circuit 2 is shorter, and the length of the branches 3 close to the terminal short-circuit surface 4 is longer. Generally speaking, the length difference of adjacent branches 3 along the transmission direction of the transmission line 1 is usually equal, and the spacing between adjacent branches 3 is usually equal, forming a progressive surface plasmon structure to realize the function of converting TE mode signals into surface plasmon mode signals, thereby realizing the function of traveling wave absorbing matching load.

[0039] See also Figure 4The microwave line absorbing load provided in this embodiment mainly solves the problem of achieving the function of traveling wave absorbing matching load while breaking through the echo deterioration caused by the transition from the waveguide TE mode to the quasi-TEM mode of the planar transmission line 1. The artificial surface plasmon circuit 2 provided in this embodiment can directly achieve the efficient transition from the waveguide TE mode to the surface plasmon mode, and achieve traveling wave absorption and filtering characteristics in the process of transition. For the entire artificial surface plasmon circuit 2, the area close to the input end of the transmission line 1 is the TE-surface plasmon mode transition zone, and the length of the branches 3 in this area is relatively short. In this area, the signal will gradually change from the TE mode to the surface plasmon mode. The outside of the TE-surface plasmon mode transition zone is the TE mode zone, which is usually located in the transmission line 1; and the area of ​​the artificial surface plasmon circuit 2 close to the terminal short-circuit surface 4 is the surface plasmon mode zone, and the length of the branches 3 in this area is relatively long. The signal transmitted in this area is the surface plasmon mode, realizing the traveling wave conversion and absorption of the signal. This embodiment can achieve traveling wave conversion and absorption of the waveguide TE mode by fine-tuning the circuit topology pattern of the artificial surface plasmon circuit 2, and achieve ultra-high electromagnetic wave absorption efficiency and echo characteristics.

[0040] See also Figure 5 as well as Figure 6 The progressive surface plasmon structure in the artificial surface plasmon circuit 2 can realize the progressive conversion and absorption of the TE mode, thereby realizing efficient impedance matching with the standard waveguide. At the same time, the artificial surface plasmon circuit 2 of this structure can also realize the blocking transmission of signals within the working frequency band, effectively suppressing the leakage of electromagnetic waves to the terminal short-circuit 4 of the transmission line 1, thereby ensuring an extremely low echo signal. Figure 5 as well as Figure 6 The structure shows that the input TE 10 The efficient conversion and absorption of the mode to the surface plasmon mode shows that the gradient surface plasmon can achieve higher electromagnetic wave stopband characteristics, and the realized return loss is as high as more than 60dB.

[0041] In this embodiment, two microwave line absorbing loads with different structures are specifically provided according to different types of transmission lines 1 .

[0042] The first type is that the transmission line 1 is a waveguide, and the artificial surface plasmon circuit 2 is embedded in the waveguide. In this structure, the transmission line 1 can be a waveguide cavity structure, such as a rectangular waveguide. Taking a rectangular waveguide as an example, the signal transmitted in the waveguide is TE 10 The artificial surface plasmon circuit 2 can be embedded in the waveguide so that the branch 3 can extend into the waveguide. Generally speaking, the artificial surface plasmon circuit 2 is embedded in the waveguide horizontally.

[0043] Specifically, in the present structure, the artificial surface plasmon circuit 2 includes a substrate and the branches 3 arranged on the surface of the substrate, and the branches 3 are arranged on at least one side of the surface of the substrate. The substrate is usually arranged in a horizontal direction, that is, in the present structure, the artificial surface plasmon circuit 2 can be specifically an artificial surface plasmon circuit 2 formed by arranging branches 3 on the surface of the substrate through a thin film circuit process. Specifically, in the present structure, the substrate is usually a low-conductivity metal substrate, which can be specifically realized by processing a low-conductivity metal layer with a thickness of hundreds of nanometers, such as a nickel metal layer. Its progressive surface plasmon structure can realize progressive conversion and absorption of the TE mode, thereby realizing efficient impedance matching of the standard waveguide.

[0044] Generally, the substrate is usually a composite laminate substrate, which usually includes a substrate and a metal layer covering the surface of the substrate. The substrate can be made of quartz, ALN, Al2O3 and other materials, and the metal layer can be made of high resistivity materials such as tantalum with a thickness of hundreds of nanometers in addition to the above-mentioned nickel metal. Figure 7 In this structure, the width of each branch 3 and the width of adjacent branches 3 can be 10 μm. Of course, the specific parameters of the branches 3 in the artificial surface plasmon circuit 2 can be set according to actual conditions and are not specifically limited here. The above transmission line 1 can be realized by standard high-precision machine tool processing, and the material can be aluminum or copper.

[0045] Furthermore, since the artificial surface plasmon circuit 2 will be specifically embedded in the waveguide in the present structure, in order to further improve the wave absorption efficiency, the branches 3 may be provided on both opposite surfaces of the substrate, and along the transmission direction of the transmission line 1, the branches 3 located on the same surface of the substrate are symmetrically distributed on both sides of the transmission line 1, and the length of the branches 3 on either side extending into the transmission line 1 gradually increases. The above-mentioned substrate usually has two opposite surfaces, and each surface is correspondingly provided with a portion of the waveguide. In order to improve the wave absorption efficiency, the above-mentioned branch 3 structure may be provided on both surfaces of the above-mentioned substrate, and the direct structure of each surface has been described in detail in the above content. The branches 3 on each side of the substrate need to be symmetrically distributed on both sides of the transmission line 1, and each branch 3 usually extends from the side of the transmission line 1 to the center line of the transmission line 1, and the length of the branches 3 on either side extending into the transmission line 1 gradually increases.

[0046] Specifically, in this structure, the projections of the branches 3 located on two opposite surfaces of the substrate along the thickness direction overlap each other. That is, the branches 3 located on different surfaces of the substrate are symmetrically arranged along the thickness direction, which is the direction perpendicular to the plane where the substrate is located. At this time, the artificial surface plasmon circuit 2 is usually embedded in the center of the waveguide.

[0047] Furthermore, in the present structure, the first end of the artificial surface plasmon circuit 2 facing the input end of the transmission line 1 is connected to the waveguide through an impedance matching structure 5. The impedance matching structure 5 is mainly used to achieve impedance matching between the waveguide and the artificial surface plasmon circuit 2, and is mainly arranged at the end of the artificial surface plasmon circuit 2 facing the input end of the transmission line 1, so that the signal of the TE mode can be smoothly transmitted to the artificial surface plasmon circuit 2 and then converted into a surface plasmon mode. The above-mentioned artificial surface plasmon circuit 2 usually has a first end and a second end, wherein the first end is the end of the artificial surface plasmon circuit 2 facing the input end of the transmission line 1, and the second end is the end of the artificial surface plasmon circuit 2 facing the terminal short-circuit 4. The above-mentioned impedance matching structure 5 needs to be arranged at least at the position of the transmission line 1 corresponding to the first end of the artificial surface plasmon circuit 2, so that the first end of the artificial surface plasmon circuit 2 is connected to the waveguide through the impedance matching structure 5. The position of the waveguide corresponding to the second end of the artificial surface plasmon circuit 2 may or may not be provided with the above-mentioned impedance matching structure 5, depending on the specific situation, and is not specifically limited here.

[0048] In the present structure, the impedance matching structure 5 may include a protrusion protruding from the waveguide on both sides of the waveguide in the width direction, and the first end of the artificial surface plasmon circuit 2 is connected to the protrusion; the length of the protrusion protruding from the waveguide on both sides of the waveguide is equal. That is, in the present structure, the impedance matching between the waveguide and the artificial surface plasmon circuit 2 can be achieved by widening the waveguide, and the length of the protrusions on both sides of the waveguide along the width direction of the waveguide is usually equal. In order to further ensure that the signal can better pass from the waveguide into the artificial surface plasmon circuit 2, the length of the protrusion may be gradually increased along the waveguide transmission direction, and the end contour of the entire protrusion toward the waveguide input end may be arc-shaped, etc. The specific morphology of the protrusion can be set according to the actual situation, and is not specifically limited here.

[0049] The second type is that the transmission line 1 is a slot line, and the artificial surface plasmon circuit 2 and the slot line are an integrated structure. When the transmission line 1 is a planar slot line structure, the artificial surface plasmon circuit 2 can be directly prepared based on the metal material that forms the slot line, and a branch 3 of the above-mentioned morphology is formed inside the slot line. At this time, the artificial surface plasmon circuit 2 and the slot line can be an integrated structure. The specific morphology of the branch 3 has been introduced in detail in the above content and will not be repeated here. The microwave line absorbing load provided by this structure can be applied in the field of planar circuit or chip design to expand its application field.

[0050] A microwave line absorbing load provided by an embodiment of the present invention can directly realize the traveling wave conversion and absorption of the TE main mode in the transmission line 1 to the artificial surface plasmon mode by directly embedding the artificial surface plasmon circuit 2 in the transmission line 1, without the need for an additional intermediate transition mode, thereby avoiding the deterioration of the echo characteristics caused by the existence of the intermediate mode, such as converting the TE mode to the TEM mode first. Therefore, the structure can greatly improve the echo / reflection characteristics of the microwave line absorbing load.

[0051] Moreover, the artificial surface plasmon circuit 2 can be realized by adopting mature terahertz thin film circuit technology, and has the characteristics of high graphic accuracy, good consistency and low cost; at the same time, the corresponding waveguide cavity structure is simple, the cavity circuit has good machinability, and there is no processing requirement for the traditional wedge-shaped absorber material for the narrow wedge-shaped waveguide terminal, so the overall circuit machining maturity is high and the cost is low.

[0052] Due to the mature thin film circuit technology and the reliability of hybrid integrated circuit assembly, the microwave line absorbing load structure proposed in this embodiment can be applicable to circuits and system applications with frequencies up to 1 THz, solving the operating frequency limitation of traditional wedge-shaped absorbing loads caused by the mechanical processing and assembly of wedge-shaped waveguide terminals.

[0053] Embodiment 2

[0054] A terahertz device provided in an embodiment of the present invention is introduced below. The terahertz device described below and the microwave line absorbing load described above can be referred to each other.

[0055] In this embodiment, the terahertz device includes a microwave line absorbing load provided by any of the above-mentioned invention embodiments. The specific structure of the microwave line absorbing load has been described in detail in the above-mentioned invention embodiments, and will not be described in detail here. The remaining structures of the terahertz device, such as the antenna, the housing, etc., can refer to the prior art, and will not be described in detail here.

[0056] Since the terahertz device provided in this embodiment specifically uses the microwave line absorbing load provided in the above embodiment, the terahertz device can greatly improve the echo / reflection characteristics of the microwave line absorbing load, thereby having more excellent performance.

[0057] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0058] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0059] The above is a detailed introduction to a microwave line absorbing load and terahertz device provided by the present invention. This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A microwave line absorbing load, characterized in that: include: Transmission line; one end of the transmission line is an input end, and the other end of the transmission line is a terminal short-circuit surface; An artificial surface plasmon circuit is arranged between the input end and the terminal short-circuit surface in the transmission line; the artificial surface plasmon circuit includes a plurality of branches extending into the transmission line, and along the transmission direction of the transmission line, the branches are symmetrically distributed on both sides of the transmission line, and the length of the branches on either side extending into the transmission line gradually increases.

2. The microwave line absorbing load according to claim 1, characterized in that: The transmission line is a waveguide, and the artificial surface plasmon circuit is embedded in the waveguide.

3. The microwave line absorbing load according to claim 2, characterized in that: The artificial surface plasmon circuit comprises a substrate and branches arranged on the surface of the substrate, and the branches are arranged on at least one side surface of the substrate.

4. The microwave line absorbing load according to claim 3, characterized in that: The branches are arranged on two opposite surfaces of the substrate. Along the transmission direction of the transmission line, the branches located on the same surface of the substrate are symmetrically distributed on both sides of the transmission line, and the length of the branches on either side extending into the transmission line gradually increases.

5. The microwave line absorbing load according to claim 4, characterized in that: The projections of the branches located on two opposite surfaces of the substrate along the thickness direction overlap with each other.

6. The microwave line absorbing load according to claim 2, characterized in that: A first end of the artificial surface plasmon circuit facing the input end of the transmission line is connected to the waveguide via an impedance matching structure.

7. The microwave line absorbing load according to claim 6, characterized in that: The impedance matching structure includes a protrusion protruding from the waveguide on both sides of the waveguide along the width direction, and the first end of the artificial surface plasmon circuit is connected to the protrusion; the protrusion protrudes from the waveguide on both sides of the waveguide by an equal length.

8. The microwave line absorbing load according to claim 3, characterized in that: The substrate is a low-conductivity metal substrate.

9. The microwave line absorbing load according to claim 1, characterized in that: The transmission line is a slot line, and the artificial surface plasmon circuit and the slot line are an integrated structure.

10. A terahertz device, characterized in that: It comprises the microwave line absorbing load as claimed in any one of claims 1 to 9.

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