A broadband circuit simulating absorber structure

Abstract

This invention provides a broadband circuit analog absorber structure, comprising a metal substrate on which a first dielectric layer, a first absorbing layer, a second dielectric layer, a second absorbing layer, a third dielectric layer, and a third absorbing layer are sequentially covered. The unit cell structures of the first and second absorbing layers are both hexagonal ring structures, while the unit cell structure of the third absorbing layer is a triple dipole structure. All layers are made of resistive materials. This invention exhibits excellent impedance matching characteristics, effectively solving the problem of balancing the absorption bandwidth and thickness of the circuit analog absorber, expanding the absorption bandwidth, and enhancing oblique incidence stability. The absorbing layer can be fabricated using screen printing, inkjet printing, and etching processes, offering advantages such as low processing cost and mass production capability.

Description

Technical Field

[0001] This invention relates to a wideband circuit analog absorber structure. Background Art

[0002] To enhance the survivability of targets such as aircraft on the battlefield, radar-absorbing materials are used on the targets to absorb incident electromagnetic waves, thereby reducing the detection sensitivity of friendly targets by enemy radar. Radar-absorbing materials include coating-type and structural-type absorbing materials. Coating-type absorbing materials are a type of coating applied to the target surface. Their operating frequency band is related to the coating thickness, and these materials have a very high bulk density, thus limiting their application in the low-frequency band. Structural-type absorbing materials have advantages such as light weight, wide absorption bandwidth, and ease of design, and are therefore widely used in the field of wide-band radar cross-section reduction. Dallenbach absorbers, Salisbury screens, Jaumann screens, and circuit-simulated absorbers are all types of structural absorbers. Among them, circuit-simulated absorbers are the optimal type of absorber for achieving a balance between absorption bandwidth and overall thickness.

[0003] A circuit-simulated absorber typically consists of a metal base plate (ground plane), a dielectric isolation layer, and one or more frequency-selective surfaces. The metal base plate reflects electromagnetic waves, preventing them from reaching the target surface. The dielectric isolation layer isolates the frequency-selective surfaces from each other and from the metal base plate, fixing and supporting the surfaces. The frequency-selective surfaces absorb incident electromagnetic energy, thus reducing echo signals. A circuit-simulated absorber can be equivalent to a transmission line circuit, with the ground plane equivalent to a short-circuited transmission line, and the frequency-selective surfaces equivalent to a complex impedance connected in parallel with the transmission line. The short-circuited transmission line equivalent to the ground plane is usually fixed; improvements to the absorber's performance primarily involve controlling the equivalent impedance of the frequency-selective surfaces.

[0004] Currently, the bandwidth of single-layer circuit analog absorbers has reached its limit. Therefore, a common approach is to use multi-layer circuit analog absorbers to broaden the absorbing frequency band and meet the practical application requirements of reducing the cross-section of broadband radar.

[0005] However, in the existing technology, multilayer circuit analog absorbers are generally quite thick due to their structural design, which is limited by the space of the installation location in actual use; and none of them take into account the requirements of absorption bandwidth and absorber thickness at the same time, resulting in the absorption bandwidth and thickness of the obtained circuit analog absorber not reaching the optimal balance point. The frequency selection surface has the problem of strong capacitance at low frequency and strong inductance at high frequency, which cannot ensure broadband absorption characteristics and oblique incidence stability. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a wideband circuit analog absorber structure. This structure exhibits excellent impedance matching characteristics, effectively solving the design problem of balancing the absorption bandwidth and thickness of the circuit analog absorber, thereby expanding the absorption bandwidth and enhancing oblique incidence stability.

[0007] The present invention is achieved through the following technical solutions.

[0008] The present invention provides a broadband circuit analog absorber structure, comprising a metal base plate, wherein a first dielectric layer, a first absorbing layer, a second dielectric layer, and a second absorbing layer are sequentially covered on the metal base plate, the dielectric constants of the first dielectric layer and the second dielectric layer are 1.0 to 1.3; the unit cell structure of the first absorbing layer and the second absorbing layer is a hexagonal ring structure; the material of the hexagonal ring structure is a resistive material.

[0009] The unit cell structure of the first absorbing layer is a hexagonal ring structure with nested double rings.

[0010] The unit cell structure of the second absorbing layer is a single-ring hexagonal ring structure.

[0011] The hexagonal ring structure is fabricated on an FR4 substrate by printing, and the dielectric constant of the FR4 substrate is 3.8 to 4.0.

[0012] A third dielectric layer and a third absorbing layer are also covered on top of the second absorbing layer.

[0013] The unit cell structure of the third absorbing layer is a triple dipole structure; the triple dipole structure is fabricated on an FR4 substrate by printing, and the dielectric constant of the FR4 substrate is 3.8 to 4.0; the radius of the tangent circle of the unit cell structure of the third absorbing layer is similar to that of the unit cell structure of the second absorbing layer.

[0014] The underlying metal base plate is made of a good conductor, with a resistivity of no more than 2.83 × 10⁻⁶ at 20°C. -8 .

[0015] The line width of the hexagonal ring structure is less than 1.2 mm.

[0016] The thickness of the first dielectric layer and the second dielectric layer is greater than 7 times the thickness of the first absorbing layer and the second absorbing layer.

[0017] The beneficial effects of this invention are as follows: it has good impedance matching characteristics, effectively solves the problem of balancing the absorption bandwidth and thickness of the circuit analog absorber, expands the absorption bandwidth and enhances the stability of oblique incidence; the absorbing layer can be prepared using screen printing, inkjet printing and etching processes, which have the advantages of low processing cost and mass production capability. Attached Figure Description

[0018] Figure 1 This is a structural schematic diagram of at least one embodiment of the present invention;

[0019] Figure 2 yes Figure 1 Schematic diagram of the first absorbing layer structure;

[0020] Figure 3 yes Figure 1 Schematic diagram of the second absorbing layer structure;

[0021] Figure 4 yes Figure 1 Schematic diagram of the third absorbing layer structure;

[0022] Figure 5 yes Figure 1 Equivalent circuit diagram;

[0023] Figure 6 This is a Smith chart of an implementation containing the first absorbing layer structure;

[0024] Figure 7 It is a reflection coefficient curve of an embodiment containing the first absorbing layer structure;

[0025] Figure 8 This is a Smith chart of an implementation containing the first and second absorbing layer structures;

[0026] Figure 9 It is a reflection coefficient curve of an embodiment containing the first and second absorbing layer structures;

[0027] Figure 10 This is a Smith chart of an implementation containing the first, second, and third absorbing layer structures;

[0028] Figure 11 It is a reflection coefficient curve of an implementation containing the first, second and third absorbing layer structures;

[0029] Figure 12 This is a graph of the TE polarization reflection coefficient under a certain angle of incidence, representing one embodiment of the present invention.

[0030] Figure 13 This is a graph of the TM polarization reflection coefficient under a certain angle of incidence, according to one embodiment of the present invention. Detailed Implementation

[0031] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0032] Example 1

[0033] like Figures 1 to 5The illustrated broadband circuit analog absorber structure includes a metal base plate, on which a first dielectric layer, a first absorbing layer, a second dielectric layer, and a second absorbing layer are sequentially covered. The dielectric constants of the first and second dielectric layers are 1.0 to 1.3. The unit cell structure of the first and second absorbing layers is a hexagonal ring structure. The material of the hexagonal ring structure is a resistive material.

[0034] Example 2

[0035] Based on Embodiment 1, the unit cell structure of the first absorbing layer is a hexagonal ring structure with nested double rings.

[0036] Example 3

[0037] Based on Example 1, the unit cell structure of the second absorbing layer is a single-ring hexagonal ring structure.

[0038] Example 4

[0039] Based on Example 1, the hexagonal ring structure was fabricated on an FR4 substrate by printing, and the dielectric constant of the FR4 substrate was 3.8 to 4.0.

[0040] Example 5

[0041] Based on Embodiment 1, a third dielectric layer and a third absorbing layer are further covered on top of the second absorbing layer.

[0042] Example 6

[0043] Based on Example 5, the unit cell structure of the third absorbing layer is a triple dipole structure; the triple dipole structure is fabricated on an FR4 substrate by printing, and the dielectric constant of the FR4 substrate is 3.8 to 4.0; the radius of the tangent circle of the unit cell structure of the third absorbing layer is equivalent to the radius of the tangent circle of the unit cell structure of the second absorbing layer.

[0044] Example 7

[0045] Based on Example 1, the bottom metal base plate is made of a good conductor, with a resistivity of no more than 2.83 × 10⁻⁶ at 20°C. -8 .

[0046] Example 8

[0047] Based on Example 1, the line width of the hexagonal ring structure is less than 1.2 mm.

[0048] Example 9

[0049] Based on Example 1, the thickness of the first dielectric layer and the second dielectric layer is greater than 7 times the thickness of the first absorbing layer and the second absorbing layer.

[0050] Example 10

[0051] Based on the above embodiments, the system includes a bottom metal base plate, a first dielectric layer, a first absorbing layer, a second dielectric layer, a second absorbing layer, a third dielectric layer, and a third absorbing layer, which are bonded together in sequence.

[0052] The bottom metal base plate is made of a good conductor, with a resistivity of no more than 2.83 × 10⁻⁶ at 20°C. -8 .

[0053] The dielectric constants of the first and second dielectric layers are approximately 1.0–1.3, and their thicknesses are 12–14 mm. The dielectric constant of the third dielectric layer is approximately 1.0–1.3, and its thickness is 8–11 mm.

[0054] The unit cell structure of the first absorbing layer consists of two nested hexagonal rings, placed in the same manner. The radii r1 and r2 of the circles tangent to the two hexagonal rings are 8–9 mm and 6–7 mm, respectively, and the linewidths W1 and W2 of the two hexagonal rings are 0.8–0.9 mm and 0.9–1.0 mm, respectively. Both hexagonal rings are made of resistive material and are fabricated on an FR4 substrate by printing. The dielectric constant of the FR4 substrate is 3.8–4.0, and the thickness is 0.7–1.0 mm. The unit cell period sizes u and v are both 12–16 mm, and the angle θ between u and v is 60°.

[0055] The second absorbing layer has a hexagonal ring structure as its unit cell. The radius r3 of the circle tangent to the hexagonal ring is 7.5–8.5 mm, and the linewidth W3 of the hexagonal ring is 0.9–1.0 mm. Both hexagonal rings are made of resistive material and are fabricated on an FR4 substrate by printing. The dielectric constant of the FR4 substrate is 3.8–4.0, and the thickness is 0.7–1.0 mm. The unit cell period sizes u and v are both 12–16 mm, and the angle θ between u and v is 60°.

[0056] The unit cell structure of the third absorbing layer is a loaded triple dipole structure. The radius r4 of the circle tangent to the triple dipole structure is 7.5–8.5 mm, the linewidth W3 of the hexagonal ring is 0.9–1.0 mm, and the length of the loaded edge structure is 5.0–7.0 mm. Both hexagonal rings are made of resistive material and are fabricated on an FR4 substrate by printing. The dielectric constant of the FR4 substrate is 3.8–4.0, and the thickness is 0.7–1.0 mm. The unit cell period sizes u and v are both 12–16 mm, and the angle θ between u and v is 60°.

[0057] Example 11

[0058] Based on the above embodiments, Figures 1 to 4As shown, the frequency selective surface consists of three layers of resistive film, with spacings of h1, h2, and h3. The distances between the layers u and v are 15 mm and 15.01 mm, respectively, and the angle θ between u and v is 60°. Other parameters are: r1 = 8.6 mm, r2 = 6.7 mm, r3 = 8.1 mm, r4 = 8 mm, W1 = 0.9 mm, W2 = W3 = W4 = 1.0 mm, and I = 6.0 mm. The sheet resistance of the first layer is 20 Ω / sq, and the sheet resistances of the second and third layers are both 50 Ω / sq. The choice of the structure type of the first-layer lossy frequency selective surface is crucial because it will cancel out most of the imaginary part of the ground-ground admittance at the specified frequency. Figure 6 As shown, this structure is a multimode structure, overcoming the shortcomings of single-mode structures where the equivalent impedance exhibits strong capacitiveness at low frequencies and strong inductiveness at high frequencies. Furthermore, the frequency corresponding to the mode interaction zero of the hexagonal ring array is the highest among all simple geometric structures, exhibiting only one resonant mode over a wide frequency range, with other higher-order modes far from the operating frequency band. The equivalent admittance Y1 of the hexagonal ring lossy frequency selective surface lies to the left of the -10dB circle. The imaginary modulus of the equivalent admittance at both the lowest and highest frequencies is above 1.0J, effectively canceling the ground plane admittance ①, resulting in a more concentrated final input admittance curve (see curve ②). Curve ③ shows the input admittance after transmission line transformation; it can be seen that the imaginary part of the input admittance is further reduced. Thanks to the resonant frequency of the lossy frequency selective surface being near the center frequency, curve ③ is almost symmetrical about the horizontal axis. The reflection coefficient of the single-layer absorber is shown in [reference needed]. Figure 7 As can be seen, the reflection coefficient decreases over a wide frequency range, indicating that the equivalent admittance of the lossy frequency-selective surface and the ground plane admittance partially cancel each other out over a wide frequency range.

[0059] Building upon the single-layer absorber, a second lossy frequency-selective surface was introduced to bring the absorber's input admittance closer to the center of the Smith chart. Referring to curve ③, the real part of the equivalent admittance of the second layer should be relatively small; therefore, a resistive film with a sheet resistance of 50 Ω / sq was used to fabricate the lossy frequency-selective surface. Figure 8 As shown in the Smith chart, Y2 is located near the right side of the Smith chart. Although its resonant frequency is near the center frequency, the distribution of points at low and high frequencies is not symmetrical. Therefore, the input admittance of the absorber is most effectively canceled at low frequencies (see curve ④). The corresponding reflection coefficient is shown in [reference needed]. Figure 9 By observing curve ④, it was found that the imaginary part of the input admittance was already very small. Therefore, the thickness of the third dielectric layer was reduced to d3 = 9.5 mm. As a result, after the transmission line transformation, the imaginary part of the input admittance at high frequencies was reduced to below 0.2 J. At the same time, the imaginary part of the input admittance at low frequencies was also further reduced to around -0.5 J, as shown in curve ⑤.

[0060] At this point, the input admittance is capacitive at most frequencies. Therefore, the selection of the third-layer lossy frequency selective surface cannot be the same as the first two layers. Its equivalent admittance Y3 should be inductive across the entire frequency band, meaning the equivalent admittance of the third functional layer should be in the lower half of the Smith chart. Figure 10 The input admittance corresponding to curve ⑤ is added to the equivalent admittance Y3 of the third layer to obtain the final input impedance, i.e., curve ⑥. It can be seen that all points on curve ⑥ fall within the -10dB circle. The corresponding reflection coefficient curve is shown below. Figure 11 The normal incident reflectivity of the absorber is less than -12dB in the frequency range of 1.0 to 10 GHz, achieving an absorption bandwidth of -12dB more than 10 times the frequency.

[0061] To verify the above design, the reflection coefficient of the three-layer circuit simulated absorber was calculated using full-wave simulation, as follows: Figure 12 and Figure 13 As shown, under normal incidence, the absorption bandwidth of the absorber ranges from 0.88 GHz to 10.82 GHz, reaching a 12.3 octave, covering the L (1.0–2.0 GHz), S (2.0–4.0 GHz), and C (4.0–8.0 GHz) bands, while also covering parts of the P-band (0.3–1.0 GHz) and X-band (8.0–12 GHz). The total thickness of the absorber is 36.7 mm. The calculation results also show that the reflection coefficient changes to varying degrees under different incidence angles. This is due to changes in the ground impedance and the matching state of the absorber. Even at incidence angles less than 45°, it still exhibits good absorption performance.

[0062] Therefore, the present invention:

[0063] 1) It has broadband absorption characteristics and oblique incidence stability, achieving an absorption rate of over 90% for vertically incident electromagnetic waves in L-band, S-band, C-band, part of P-band (0.88~1.0GHz) and part of X-band (8.0~10.82GHz), and still has good absorption performance when obliquely incident at 45°.

[0064] 2) The use of a multimode frequency selective surface composed of double hexagonal rings improves the problem of traditional frequency selective surfaces exhibiting strong capacitance at low frequencies and strong inductive properties at high frequencies, and expands the bandwidth of the absorber; in addition, the use of a capacitive surface reduces the thickness of the absorber.

[0065] 3) The thickness design tolerance of the first, second, and third dielectric layers is large, allowing for an error within 1 mm. Furthermore, the first, second, and third absorbing layers can all be fabricated using screen printing, inkjet printing, and etching processes, offering advantages such as low processing costs and mass production capability.

Claims

1. A broadband circuit analog absorber structure, characterized in that: The device includes a metal base plate, on which a first dielectric layer, a first absorbing layer, a second dielectric layer, and a second absorbing layer are sequentially covered. The dielectric constants of the first and second dielectric layers are 1.0 to 1.

3. The unit cell structure of the first and second absorbing layers is a hexagonal ring structure. The material of the hexagonal ring structure is a resistive material. The unit cell structure of the first absorbing layer is a hexagonal ring structure with nested double rings; The unit cell structure of the second absorbing layer is a single-ring hexagonal ring structure; A third dielectric layer and a third absorbing layer are also covered on the second absorbing layer. The unit cell structure of the third absorbing layer is a triple dipole structure.

2. The broadband circuit analog absorber structure as described in claim 1, characterized in that: The hexagonal ring structure is fabricated on an FR4 substrate by printing, and the dielectric constant of the FR4 substrate is 3.8~4.

0.

3. The broadband circuit analog absorber structure as described in claim 1, characterized in that: The triple dipole structure was fabricated on an FR4 substrate by printing. The dielectric constant of the FR4 substrate was 3.8 to 4.

0. The tangent circle radius of the unit cell structure of the third absorbing layer and the tangent circle radius of the unit cell structure of the second absorbing layer were both 7.5 to 8.5 mm.

4. The broadband circuit analog absorber structure as described in claim 1, characterized in that: The metal base plate is made of a good conductor, with a resistivity of no more than [value missing] at 20°C. .

5. The broadband circuit analog absorber structure as described in claim 1, characterized in that: The line width of the hexagonal ring structure is less than 1.2 mm.

6. The broadband circuit analog absorber structure as described in claim 1, characterized in that: The thickness of the first dielectric layer and the second dielectric layer is greater than 7 times the thickness of the first absorbing layer and the second absorbing layer.

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