A frequency tunable wave absorber with consideration of tuning range and absorption efficiency

Abstract

The application discloses a broadband tunable wave absorber which takes into account tuning range and absorption efficiency. The wave absorber breaks the restrictive relationship between tuning range and absorption efficiency, and can maintain high-efficiency and dynamic adjustable absorption in the whole frequency tuning range. The basic unit metal layer of the wave absorber includes basic microstrip resonant structure, parallel resonant branch, DC bias line, electrically tunable variable capacitance diode, patch resistor, patch inductor, patch capacitor and the like. By introducing the parallel resonant branch, the impedance load of the wave absorber structure presents frequency-dependent characteristics, which can meet the impedance matching conditions at different frequencies. Through the DC bias line, an externally adjustable DC voltage can be applied to the electrically tunable variable capacitance diode, thereby realizing dynamic adjustment of electromagnetic wave absorption frequency. The application can maximize the tuning capability of the electrically tunable variable capacitance diode, effectively improve the frequency tuning range and absorption efficiency, and has many potential applications in radar stealth, electromagnetic compatibility and intelligent stealth system.

Description

Technical Field

[0001] This invention relates to a frequency-tunable absorber that balances tuning range and absorption efficiency, belonging to the field of novel artificial electromagnetic devices. Background Technology

[0002] An absorber is an electromagnetic device that effectively dissipates and absorbs incident electromagnetic waves. Through structural design, specific boundary conditions can be achieved to match the characteristic impedance of free space. Simultaneously, by introducing appropriate dielectric loss within the structure, the incident electromagnetic waves can be dissipated as heat, reducing the radar cross-section of an object and improving stealth performance. It has wide applications in radar stealth systems and electromagnetic compatibility. The frequency-tunable absorber involved in this invention can dynamically and in real-time tune the electromagnetic wave absorption frequency, achieving frequency control and low-frequency electromagnetic absorption coverage, and can be used in next-generation intelligent radar stealth systems. Summary of the Invention

[0003] The purpose of this invention is to realize a frequency-tunable absorber that can balance frequency tuning range and absorption efficiency. This absorber can achieve high-efficiency absorption of bilinearly polarized (TE polarization and TM polarization) incident electromagnetic waves, and when combined with an external adjustable DC voltage source, the absorption frequency of the electromagnetic waves can be dynamically tuned.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a frequency-tunable absorber that balances tuning range and absorption efficiency, comprising two orthogonally placed metal layers with identical basic unit structures. Each metal layer includes a basic microstrip resonant structure, a parallel resonant stub, a DC bias line, an electrically adjustable varactor diode, a first surface-mount resistor, a second surface-mount resistor, a surface-mount inductor, and a surface-mount capacitor. The basic microstrip resonant structure includes a metal microstrip line structure with bent ends, and a first surface-mount resistor and an electrically adjustable varactor diode welded in the middle of the metal microstrip line structure. The parallel resonant stub is connected in parallel with the first surface-mount resistor, and a second surface-mount resistor, a surface-mount inductor, and a surface-mount capacitor are welded in the middle to adjust the impedance load of the absorber structure. The two ends of the bent microstrip line structure serve as the positive and negative terminals of the DC feed, respectively, and are connected to the DC bias line on the other side of the dielectric substrate through metallized vias. The voltage across the electrically adjustable varactor diode is controlled by an external DC voltage source. By changing the voltage across the electrically adjustable varactor diode, the capacitance value is switched, thereby tuning the absorption frequency.

[0005] The frequency-adjustable absorber, which balances tuning range and absorption efficiency, resonates with the surface-mount inductor and capacitor when the electromagnetic wave frequency is within their resonant band. The imaginary part of the input impedance of the parallel resonant stub is zero. At this time, the first and second surface-mount resistors are connected in parallel, and the overall absorber structure's load resistance is equivalent to their parallel value. When the electromagnetic wave frequency is far from the resonant band of the surface-mount inductor and capacitor, the imaginary part of the input impedance of the parallel resonant stub approaches infinity. At this time, the parallel resonant stub is equivalent to an open circuit, and the overall absorber structure's load resistance is equivalent to the first surface-mount resistor.

[0006] Preferably, the second surface mount resistor is smaller than the first surface mount resistor, i.e., R 第一贴片电阻 :R 第二贴片电阻 ≥5:1.

[0007] Preferably, the second surface mount resistor, surface mount inductor, and surface mount capacitor are sequentially soldered into the parallel resonant stub. Due to the presence of the parallel resonant stub, the impedance load of the absorber structure changes with frequency, which can meet the impedance matching conditions at different frequencies, thereby maintaining high absorption efficiency over a wide tuning range and breaking the constraint between tuning range and absorption efficiency. At the same time, by reasonably designing and selecting the values ​​of the surface mount inductor and surface mount capacitor, the rate of change of impedance load with frequency can be controlled, which can meet the design requirements of different frequency bands and has the characteristic of frequency band transferability.

[0008] Preferably, the structural layer of the basic unit includes two metal layers and an intermediate dielectric substrate. The upper and lower metal layers have the same structure and are placed orthogonally. They are printed on both sides of the dielectric layer using PCB technology to achieve a polarization-insensitive design. This design can achieve wideband, high-efficiency, and dynamically adjustable absorption of bipolar polarized (TE polarization and TM polarization) electromagnetic waves. There is an air layer between the structural layer and the metal ground plane.

[0009] Preferably, the two ends of the basic microstrip resonant structure placed on the upper surface of the dielectric substrate along the x-direction are connected to the DC bias line placed along the y-direction at the edge of the back side through metallized vias; the two ends of the basic microstrip resonant structure placed on the back side along the y-direction are connected to the DC bias line placed along the x-direction at the edge of the upper surface through metallized vias; by changing the voltage difference between the DC bias lines, the capacitance of the electrically adjustable varactor diode can be adjusted, achieving broadband, efficient, and dynamically adjustable absorption in the bipolar polarization state.

[0010] Preferably, a surface-mount inductor is soldered into the DC bias line to suppress the induced current in the DC bias line, thereby reducing the impact of the DC bias line on the absorber performance.

[0011] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0012] 1. Polarization multiplexing: The frequency-tunable absorber described in this invention, which balances tuning range and absorption efficiency, can achieve high-efficiency, wide-band adjustable dynamic absorption of bipolar (TE polarization and TM polarization) incident electromagnetic waves.

[0013] 2. Wideband adjustable absorption frequency: The frequency-adjustable absorber described in this invention, which balances tuning range and absorption efficiency, can achieve wideband adjustable absorption frequency for electromagnetic waves.

[0014] 3. Overcoming the constraint between tuning range and absorption efficiency in the design of frequency-tunable absorbers: The frequency-tunable absorber described in this invention, which balances tuning range and absorption efficiency, overcomes the constraint between tuning range and absorption efficiency. It can maintain good impedance matching and high-efficiency absorption throughout the entire frequency tuning range.

[0015] 4. Fully exploiting the tuning capability of varactor diodes and improving their utilization efficiency: Compared with existing technologies, the frequency-tunable absorber proposed in this invention, which balances tuning range and absorption efficiency, significantly improves the utilization efficiency of varactor diodes. Attached Figure Description

[0016] Figure 1 This is a design diagram of a frequency-tunable absorber that balances tuning range and absorption efficiency, as described in this invention.

[0017] Figure 2 These are basic unit structure design drawings. (a) is a plan view of the first layer of metal structure, and (b) is a plan view of the second layer of metal structure. The metal floor is not shown.

[0018] Figure 3 This is a schematic diagram showing the variation of the reflection coefficient of the frequency-tunable absorber of the present invention under TE polarization state with different capacitance values.

[0019] Figure 4 This is a schematic diagram showing the variation of the reflection coefficient of the frequency-tunable absorber of the present invention under different capacitance values ​​in the TM polarization state.

[0020] Figure 2 In the diagram, 1-choke inductor; 2-DC bias line; 3-first surface mount resistor; 4-electrically adjustable varactor diode; 5-second surface mount resistor; 6-surface mount capacitor; 7-metallized via; 8-surface mount inductor; 9-bent microstrip line. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments and the accompanying drawings.

[0022] This invention discloses a frequency-tunable absorber that balances tuning range and absorption efficiency. The basic unit structure comprises two identical, orthogonally placed metal layers. Each metal layer includes a basic microstrip resonant structure, parallel resonant stubs, a DC bias line, an electrically adjustable varactor diode, a first surface-mount resistor, a second surface-mount resistor, a surface-mount inductor, and a surface-mount capacitor. An externally adjustable DC voltage can be applied to the electrically adjustable varactor diode via the DC bias line, thereby adjusting the electromagnetic wave absorption frequency. To reduce the impact of the DC bias line on absorber performance, the DC bias line structure is placed parallel to the microstrip resonant structure at the edge of the unit structure and connected to both ends of the basic microstrip resonant structure on the other side via metallized vias. Simultaneously, a choke inductor is loaded on the DC bias line to reduce the impact of induced current in the DC bias line on absorber performance. This invention fully utilizes the adjustment capability of the varactor diode, effectively extending the frequency tuning range of the frequency-tunable absorber while maintaining good impedance matching and excellent absorption performance throughout the entire tuning range. It has many potential applications in intelligent stealth radar systems.

[0023] like Figure 1 As shown, the basic unit structure of this invention mainly includes two metal layers and one dielectric substrate, such as... Figure 2 As shown. To more clearly examine the composition of each layer, Figure 2 The diagrams show the planar structures of the first and second metal layers. The upper metal layer is a microstrip structure with bent microstrip lines 9 at both ends. A 30-ohm first surface mount resistor 3 and an electrically adjustable varactor diode 4 are sequentially soldered in the middle of the metal microstrip structure. In order to adjust the load resistance at different frequencies, a parallel resonant stub is connected in parallel with the 30-ohm first surface mount resistor 3. A 4pF surface mount capacitor 6, a 10nH surface mount inductor 8, and a 4-ohm second surface mount resistor 5 are sequentially soldered on the parallel resonant stub.

[0024] The lower and upper metal layers have the same structure, and are orthogonally placed to achieve a dual-polarization (TE and TM) response. The two ends of the bent microstrip line 9 are connected to the DC bias line 2 via metallized vias 7, serving as the positive and negative terminals of the electrically adjustable varactor diode 4. The voltage across the electrically adjustable varactor diode 4 is controlled by an external DC voltage source. By changing the voltage difference across the diode, the capacitance value is tuned, thereby tuning the absorption frequency. The DC bias line 2 is placed parallel to the edge of the unit structure. Two 2uH surface-mount inductors 1 are soldered onto the bias line structure to suppress the induced current, thus reducing the impact of the bias line structure on the absorber performance.

[0025] The aforementioned frequency-tunable absorber, which balances tuning range and absorption efficiency, has a parallel resonant stub connected in parallel with the 30-ohm surface-mount resistor 3 loaded in the basic microstrip resonant structure. A 10nH surface-mount inductor 8, a 4pF surface-mount capacitor 6, and a 4-ohm surface-mount resistor 5 are sequentially soldered onto the parallel resonant stub. To achieve effective adjustment of the load resistance, the value of the 30-ohm surface-mount resistor 3 is significantly larger than that of the 4-ohm surface-mount resistor 5. The surface-mount inductor and capacitor soldered onto the parallel resonant stub can be selected according to actual design requirements. When the electromagnetic wave frequency is within the resonant frequency band of the surface mount inductor and capacitor, the surface mount inductor and capacitor resonate, and the imaginary part of the input impedance of the parallel resonant stub is zero. At this time, the 30-ohm surface mount resistor 3 and the 4-ohm surface mount resistor 5 are connected in parallel, and the load resistance of the overall absorbing structure can be equivalent to the parallel value of the two. When the electromagnetic wave frequency is far from the resonant frequency band of the surface mount inductor and capacitor, the imaginary part of the input impedance of the parallel stub approaches infinity. At this time, the parallel resonant stub can be equivalent to an open circuit, and the load resistance of the overall absorbing structure is equal to the 30-ohm surface mount resistor 3. Since the value of the 30-ohm surface mount resistor 3 is much larger than that of the 4-ohm surface mount resistor 5, the parallel value of the two is much smaller than 30 ohms, thus enabling effective adjustment of the load resistance in the frequency domain. The same applies to orthogonally polarized electromagnetic waves. In practical applications, the voltage across the varactor diode is controlled by an external DC voltage source. The capacitance value is tuned by changing the voltage difference across the varactor diode. Due to the frequency-varying load resistance mentioned above, good matching can be achieved throughout the entire tuning range, thus enabling high-efficiency wave absorption throughout the entire tuning range.

[0026] Based on the above unit design, we used the commercial full-wave simulation software CSTMicrowaveStudio (CST-MWS) to simulate the unit structure. Periodic boundary conditions were set around the unit structure, while the longitudinal direction was set as an open boundary. The electrically adjustable varactor diode 4 described in this invention is model SMV2020-079LF. When the voltage across the electrically adjustable varactor diode varies within the range of 0 to 20V, the capacitance value of the electrically adjustable varactor diode varies within the range of 0.35 to 3.2pF. Figure 2 The basic parameters of the element model shown are as follows: element period p = 16 mm, air layer thickness h = 10 mm, t = 0.5 mm, L s =3mm, w=0.5mm. The metal microstrip line structure uses an electrical conductivity of 5.8×10⁻⁶. 7 The copper has a dielectric constant of 4.3 and a loss tangent of 0.025. The dielectric layer is FR-4.

[0027] Figure 3 and Figure 4Full-wave simulation results of the absorber under TE and TM polarization states are presented. The simulation results show that when the capacitance of the varactor diode varies from 0.20 to 4.00 pF, under TE polarization, the frequency-tunable absorber described in this invention, which balances tuning range and absorption efficiency, can achieve continuously tunable absorption in the range of 0.53 to 1.90 GHz, with a reflection coefficient of less than -10 dB for each operating state throughout the entire adjustment range. Under TM polarization, the frequency-tunable absorber described in this invention, which balances tuning range and absorption efficiency, can achieve continuously tunable absorption in the range of 0.55 to 1.88 GHz, while ensuring that the reflection coefficient is less than -10 dB for each operating state. It should be noted that under the same operating conditions, there is a slight deviation between the absorber's response to TE-polarized and TM-polarized electromagnetic waves. This is mainly because the metal structures operating in TE-polarized and TM-polarized states are distributed on the upper and lower surfaces of the dielectric layer, respectively. Since the dielectric layer has a certain thickness, the metal structures operating in the two polarizations are not located on the same plane, so the resonant frequency will deviate. This deviation can be improved by fine-tuning the metal structure.

[0028] The above embodiments are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and equivalent substitutions without departing from the principle of the present invention. For example, migrating to other frequency bands for wideband tunable absorption design, or obtaining different tuning ranges by changing the type of capacitor diode and the values ​​of surface-mount components, etc. These technical solutions that improve and equivalently substitute the claims of the present invention all fall within the protection scope of the present invention.

Claims

1. A frequency-tunable absorber that balances tuning range and absorption efficiency, characterized in that, The basic unit structure comprises two identical, orthogonally placed metal layers. Each metal layer includes a basic microstrip resonant structure, a parallel resonant stub, a DC bias line, an electrically adjustable varactor diode, a first surface-mount resistor, a second surface-mount resistor, a surface-mount inductor, and a surface-mount capacitor. The basic microstrip resonant structure includes a metal microstrip line structure with bent ends, and a first surface-mount resistor and an electrically adjustable varactor diode welded in the middle of the metal microstrip line structure. The parallel resonant stub is connected in parallel with the first surface-mount resistor, and a second surface-mount resistor, a surface-mount inductor, and a surface-mount capacitor are welded in the middle to adjust the impedance load of the absorber structure. The two ends of the bent metal microstrip line structure serve as the positive and negative terminals of the DC power supply, respectively, and are connected to the DC bias line on the other side of the dielectric substrate through metallized vias. The voltage across the electrically adjustable varactor diode is controlled by an external DC voltage source. By changing the voltage across the electrically adjustable varactor diode, the capacitance value is switched, thereby tuning the absorption frequency.

2. The frequency-tunable absorber that balances tuning range and absorption efficiency according to claim 1, characterized in that, When the electromagnetic wave frequency is within the resonant frequency band of the surface mount inductor and capacitor, the surface mount inductor and capacitor resonate, and the imaginary part of the input impedance of the parallel resonant stub is zero. At this time, the first surface mount resistor and the second surface mount resistor are connected in parallel, and the load resistance of the overall absorber structure is equivalent to the parallel value of the two. When the electromagnetic wave frequency is far away from the resonant frequency band of the surface mount inductor and capacitor, the imaginary part of the input impedance of the parallel resonant stub approaches infinity. At this time, the parallel resonant stub is equivalent to an open circuit, and the load resistance of the overall absorber structure is equivalent to the first surface mount resistor.

3. The frequency-tunable absorber that balances tuning range and absorption efficiency according to claim 1, characterized in that, the second... The surface mount resistor is smaller than the first surface mount resistor, R 第一贴片电阻 :R 第二贴片电阻 ≥5:

1.

4. The frequency-tunable absorber that balances tuning range and absorption efficiency according to claim 1, characterized in that, The second surface mount resistor, surface mount inductor, and surface mount capacitor are sequentially soldered into the parallel resonant stub. Due to the presence of the parallel resonant stub, the impedance load of the absorber structure changes with frequency, which can meet the impedance matching conditions at different frequencies. At the same time, by selecting the values ​​of the surface mount inductor and surface mount capacitor, the rate of change of the impedance load with frequency can be adjusted, which can meet the design requirements of different frequency bands.

5. The frequency-tunable absorber that balances tuning range and absorption efficiency according to claim 1, characterized in that, The basic unit's structural layer includes two metal layers and an intermediate dielectric substrate, with an air layer between the structural layer and the metal floor.

6. The frequency-tunable absorber that balances tuning range and absorption efficiency according to claim 5, characterized in that, The two ends of the basic microstrip resonant structure placed along the x-direction on the upper surface of the dielectric substrate are connected to the DC bias line placed along the y-direction at the edge of the back side through metallized vias; the two ends of the basic microstrip resonant structure placed along the y-direction on the back side are connected to the DC bias line placed along the x-direction at the edge of the upper surface through metallized vias; by changing the voltage difference between the DC bias lines, the capacitance of the electrically adjustable varactor diode can be adjusted, and dynamic adjustable absorption can be achieved in the bilinear polarization state.

7. The frequency-tunable absorber that balances tuning range and absorption efficiency according to claim 1, characterized in that, A surface-mount inductor is soldered into the DC bias line to suppress the induced current in the DC bias line.

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