An electromagnetic isolator and a combined dipole antenna array unit

Abstract

This invention discloses an electromagnetic isolator and a combined dipole antenna array unit, comprising a dielectric layer, a support layer, and a metal backplate. A loss layer is laid on the upper surface of the dielectric layer, and the support layer is sandwiched between the dielectric layer and the metal backplate. The loss layer is designed using a series multi-loss resonant structure to achieve low-frequency broadband absorption characteristics for electromagnetic waves. This invention can still achieve low-frequency broadband absorption even at large incident angles. When the incident angle of TM waves is 60°, the electromagnetic isolator can still maintain an absorption rate of over 90% in the 0.85-3.03GHz frequency band; when the incident angle of TE waves is 60°, the electromagnetic isolator can still maintain an absorption rate of over 90% in the 0.96-3.13GHz frequency band, effectively solving the problem of poor isolation between combined dipole antenna array units in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to an electromagnetic isolator and a combined dipole antenna array unit. Background Technology

[0002] Microwave-absorbing materials, due to their excellent attenuation properties for electromagnetic waves in space, easily achieve low-reflection absorption effects and are widely used in wireless communication, electromagnetic shielding, microwave anechoic chambers, electromagnetic compatibility, and stealth technologies. Traditional microwave-absorbing materials utilize the physical properties of their high dielectric constant and imaginary part of permeability to achieve electromagnetic wave loss characteristics, thus achieving efficient electromagnetic absorption. However, due to the limitations of the material properties themselves, the use of wedge-shaped absorbers and natural traditional absorbing materials such as ferrites or carbon powder suffers from problems such as complex three-dimensional structures and large volume and weight. Electromagnetic metamaterials, on the other hand, can realize special electromagnetic properties not found in natural materials, such as perfect absorbers, bringing new revolutions to the design and application of microwave-absorbing materials.

[0003] Electromagnetic metamaterials are artificial composite structures or materials composed of periodically arranged unit cells. The size of these unit cells is typically much smaller than the designed operating wavelength, allowing them to be analogous to the unit cells that make up natural materials, and their material properties can be analyzed using equivalent medium theory. Therefore, by rationally designing the structure of the unit cells, metamaterials can exhibit extraordinary electromagnetic properties. Compared to traditional absorbing materials, the absorption performance of electromagnetic metamaterials is no longer solely determined by the material's inherent electromagnetic loss characteristics; the periodic unit cell structure and its arrangement also influence the material's absorption performance.

[0004] In existing high-power ultra-wideband radiating systems, combined dipole antenna arrays are typically used as radiating antennas, with operating bandwidths ranging from 0.3 to 3 GHz. However, the compact antenna spacing easily leads to mutual coupling interference between adjacent antenna elements. When the array antenna is divided into multiple modules that operate independently, the electromagnetic wave signals radiated by the operating combined dipole antenna module will couple onto the antennas of adjacent modules, generating echoes. This can adversely affect the electronic components in the front-end of the radiating system, and the isolation between the combined dipole antenna array elements is poor. Summary of the Invention

[0005] The purpose of this invention is to provide an electromagnetic isolator and a combined dipole antenna array unit to overcome the shortcomings of the prior art.

[0006] An electromagnetic isolator includes a dielectric layer, a support layer, and a metal backplate. A loss layer is laid on the upper surface of the dielectric layer, and the support layer is sandwiched between the dielectric layer and the metal backplate.

[0007] Preferably, the dielectric layer is made of FR4 glass fiber epoxy resin substrate with a thickness of 1 mm.

[0008] Preferably, the relative permittivity ε of the dielectric layer r The value is 4.3, and the dielectric loss tangent is 0.025.

[0009] Preferably, the support layer is made of PMI foam substrate with a thickness of 28mm.

[0010] Preferably, the relative permittivity ε of the support layer r The value is 1.03 to 1.13, and the dielectric loss tangent is 0.018.

[0011] Preferably, the loss layer includes a metal thin film and a chip resistor. The metal thin film includes an outer ring stub, an inner ring stub, and a metal square ring. The metal square ring has a rectangular structure. The outer ring stub is arrayed on the outer ring of the metal square ring and is parallel to the rectangular border of the metal square ring. The outer ring stub and the metal square ring are connected through the chip resistor. The inner ring stub is arrayed on the inner ring of the metal square ring.

[0012] Preferably, the inner ring branch includes an inner ring elongated edge and a cross-shaped branch. One side of the inner ring elongated edge is connected to one end of the cross-shaped branch. The length of the inner ring elongated edge is greater than the cross length of the cross-shaped branch. The inner ring elongated edge is close to the inner edge of the metal square ring and parallel to the inner edge of the metal square ring it is close to.

[0013] Preferably, the surface mount resistor is a 120Ω surface mount resistor.

[0014] A combined dipole antenna array unit based on electromagnetic isolators includes two sets of electromagnetic isolators with metal backplates arranged close together, and a set of dipole antennas is arranged at each end of the two sets of electromagnetic isolators.

[0015] Preferably, the two sets of electromagnetic isolators are spaced apart with a spacing of 70mm.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects:

[0017] This invention discloses an electromagnetic isolator comprising a dielectric layer, a support layer, and a metal backplate. A loss layer is deposited on the upper surface of the dielectric layer, and the support layer is sandwiched between the dielectric layer and the metal backplate. The loss layer is designed using a series multi-loss resonant structure to achieve low-frequency broadband absorption characteristics for electromagnetic waves. This invention can still achieve low-frequency broadband absorption even at large incident angles. When the incident angle of TM waves is 60°, the electromagnetic isolator can still maintain an absorption rate of over 90% in the 0.85-3.03GHz frequency band; when the incident angle of TE waves is 60°, the electromagnetic isolator can still maintain an absorption rate of over 90% in the 0.96-3.13GHz frequency band, effectively solving the problem of poor isolation between combined dipole antenna array elements in the prior art.

[0018] This invention can stably achieve an absorption rate of over 90% in the 1.0-3.0 GHz frequency band, covering most of the radiation frequency band of the combined dipole antenna, effectively reducing the coupling effect between array antenna elements, which is beneficial to the stable operation of the radiation system.

[0019] Preferably, the present invention uses a metal thin film and a chip resistor as the loss layer structure, which increases the equivalent capacitance between the internal structures, reduces the resonant Q value, and achieves the purpose of improving the low-frequency absorption characteristics.

[0020] This invention discloses a combined dipole antenna array unit based on electromagnetic isolators, comprising two sets of electromagnetic isolators arranged close together with metal back plates, and a set of dipole antennas arranged at both ends of the two sets of electromagnetic isolators. The structure is simple, and the electromagnetic wave signals radiated by the combined dipole antenna module are effectively isolated by the electromagnetic isolators, thereby reducing the adverse effects of radiation on the electronic devices in the front end of the system. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the electromagnetic isolator structure in an embodiment of the present invention;

[0022] Figure 2 This is a planar schematic diagram of the loss layer in an embodiment of the present invention;

[0023] Figure 3 The following is an equivalent circuit diagram of the loss layer in an embodiment of the present invention; wherein 3(a) is a schematic diagram of the connection between the outer ring stub and the metal square ring, 3(b) is an equivalent circuit diagram of the connection between the outer ring stub and the metal square ring, 3(c) is an equivalent circuit diagram of the connection between the loss layer, the dielectric layer and the support layer, and 3(d) is an equivalent circuit diagram of the electromagnetic isolator.

[0024] Figure 4 This is a flowchart illustrating the design process of the loss layer in an embodiment of the present invention;

[0025] Figure 5 The simulation parameter curves for the two loss resonant structures are shown in the embodiments of the present invention.

[0026] Figure 6 This is a simulated curve of the absorption rate of electromagnetic waves under TM wave incident angle in an embodiment of the present invention.

[0027] Figure 7 This is a simulated curve of the absorption rate of electromagnetic waves under TE wave incident angle in an embodiment of the present invention.

[0028] Figure 8 This is a schematic diagram of a combined dipole array antenna structure containing an electromagnetic isolator in an embodiment of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0030] See Figure 1 An electromagnetic isolator includes a dielectric layer 100, a support layer 200 and a metal backplate 300 stacked sequentially, and a loss layer 400 is applied to the upper surface of the dielectric layer 100.

[0031] In this embodiment, the dielectric layer 100 is made of FR4 glass fiber epoxy resin substrate with a thickness of 1 mm and a relative permittivity ε. r The value is 4.3, and the dielectric loss tangent is 0.025.

[0032] The support layer 200 uses a PMI foam substrate with a thickness of 28mm and a relative permittivity ε. r The value is 1.03 to 1.13, and the dielectric loss tangent is 0.018.

[0033] The thickness of the metal backplate 300 is 1mm; the area of ​​one unit is 50mm×50mm.

[0034] See Figure 2 The loss layer 400 of the present invention includes a metal thin film and a chip resistor 404. The metal thin film includes an outer ring branch 401, a metal square ring 402 and an inner ring branch 403. The outer ring branches 401 are arranged parallel to the four sides of the metal square ring 402. The metal square ring 402 is a rectangular structure. The outer edge of the metal square ring 402 is parallel to the outer ring branches 401 arranged on its edge. The outer ring branches 401 are elongated structures. The outer ring branches 401 are connected to the edge of the nearest metal square ring 402 through the chip resistor 404.

[0035] The inner edge of the metal square ring 402 is parallel to the bottom edge of the inner ring branch 403. The inner ring branch 403 includes an inner ring long strip edge 403' and a cross-shaped structure branch. The inner ring long strip edge 403' and the cross-shaped structure branch form a "soil" character structure. The length of the inner ring long strip edge 403' is greater than the cross length of the cross-shaped structure branch. One side of the inner ring long strip edge 403' of the inner ring branch 403 is close to the inner edge of the metal square ring 402 and is parallel to the inner edge of the metal square ring 402; the inner ring branches 403 are arranged head-to-head and point to the center. There are gaps between the outer ring branch 401 and the metal square ring 402, and between the metal square ring 402 and the inner ring branch 403. The metal square ring 402 and the inner ring long strip edge 403' on the inner ring branch 403 are connected by a chip resistor 404; the entire loss layer structure is arranged in central symmetry.

[0036] In this embodiment, the length and width of the outer ring branch 401 are 30 mm × 2 mm; the length and width of the metal square ring 402 are 36 mm × 3 mm; the inner ring branch 403 is composed of an outer ring branch with a length and width of 16 mm × 2 mm and a cross-shaped metal branch with a length and width of 6 mm × 2 mm; the metal thin film is a copper thin film with a thickness of 0.017 mm.

[0037] In this embodiment, the chip resistor 404 uses a chip resistor with a resistance value of 120 Ω.

[0038] See Figure 3 (a) to Figure 3 (b), the surface metal thin film and the chip resistor of the present invention can be equivalent to a lossy resonant structure. Figure 3 (a) is a schematic diagram of two metal branches with a loaded resistor. The metal long strip can be equivalent to an inductor with a certain value, the gap between the two metal sheets can be equivalent to a capacitor, and the two metal sheets are connected by a lumped resistor. Therefore, the equivalent circuit model of this structure can be Figure 3 (b) represents. By designing metal long strips with different lengths and widths, different equivalent inductance values L can be obtained; by designing different metal gap widths, different equivalent capacitance values C can be obtained; the resistance value R of the chip resistor between the metal gaps can be selected according to requirements. Finally, an equivalent circuit in which the resistor R is connected in series with the equivalent inductance L and then in parallel with the equivalent capacitance C is obtained. <着

[0039] The formulas for calculating the equivalent inductance and equivalent capacitance are: <着

[0040] <着 <着 <着

[0041] <着 <着 <着

[0042] <着 <着 <着

[0043] Among them, d is the length of the metal strip, w is the width of the metal strip, s is the metal gap width, ε ris the relative permittivity of the medium. It should be noted that the equivalent circuit model extracted by the above formula is applicable to the case of perpendicular incidence of electromagnetic waves. This is because when electromagnetic waves are obliquely incident, especially for TM-mode waves, while the horizontal component of the electric field changes, the longitudinal component also continuously increases, resulting in a change in the equivalent capacitance.

[0044] See Figure 3 (c) to Figure 3 (d). For Figure 1 the unit structure of the present invention shown, the loss layer, the dielectric layer, and the support layer (equivalent to two dielectric layers), as well as the metal backplane, constitute a Salisbury screen, and its schematic diagram is as shown in Figure 3 (c). For the dielectric material, it can be equivalent to a transmission line model with corresponding parameters. On the one hand, the loss layer is laid on the surface of the dielectric layer, which is equivalent to connecting a branch in parallel at the port where the electromagnetic wave is incident. On the other hand, since the wave impedance of the metal backplane is 0, it is regarded as grounded in the equivalent circuit. Therefore, the calculation formula for the reflection coefficient can be obtained:

[0045]

[0046]

[0047] where, Z in is the input impedance, Z is the impedance of the loss layer branch, Z1 is the characteristic impedance in the dielectric, Z0 is the free space wave impedance, and β is the propagation constant of the lossless dielectric. For the designed absorption frequency band, it is required that the calculation result of the reflection coefficient obtained through the equivalent model is as small as possible. Generally, it is required that the S11 parameter of the equivalent circuit is less than -10 dB. Similarly, this equivalent circuit model is only applicable to the case of perpendicular incidence of electromagnetic waves, for qualitative analysis of transmission characteristics and helping to understand the working mechanism of the structure.

[0048] In this embodiment, according to the above theory, the equivalent circuit of the present invention can be obtained, as shown in Figure 3 (d). Among them, R1, L1, and C1 represent the external branch structure composed of Figure 2 the outer ring branch 401, the metal square ring 402, and the patch resistor 404. R2, L2, and C2 represent the internal branch structure composed of Figure 2 the inner ring branch 403, the metal square ring 402, and the patch resistor 404. C3 represents the equivalent capacitance between the internal "soil"-shaped metal branches 403. Z0 is the wave impedance in free space, Z1 is the wave impedance in the FR4 dielectric plate, d1 is the thickness of the FR4 dielectric plate, Z2 is the wave impedance in the foam board, d2 is the thickness of the foam board, and the metal backplane in the structure is equivalent to a terminal short circuit in the circuit model.

[0049] Refer to Figures 4 to 5To design an absorbing structure that absorbs electromagnetic waves in the 1.0-3.0 GHz band, multiple closely spaced resonant points need to be designed to achieve broadband absorption characteristics. For example... Figure 4 The diagram illustrates the design process of the loss layer in this invention. Through calculations using equations (1) to (5), an external stub structure consisting of an outer ring stub 401, a metal square ring 402, and a chip resistor 404 is first designed to form a loss resonant structure (a) at the lower limit frequency. The calculated resonant absorption frequency of this structure is 0.87 GHz. Then, an internal stub structure consisting of an inner ring long strip 403', a metal square ring 402, and a chip resistor 404 is designed to form a loss resonant structure (b) at the upper limit frequency. The calculated resonant absorption frequency of this structure is 3.42 GHz. For example... Figure 5 As shown, the two loss resonant structures were simulated using CST software. The results show that structures (a) and (b) generate strong resonances near 1.0 GHz and 3.6 GHz, respectively, forming two narrowband absorption peaks, which are similar to the calculated results.

[0050] In this embodiment, compared to the prior art which uses multiple loss layers to achieve broadband absorption characteristics at multiple resonant points, the loss layer 400 of the present invention adopts a three-combination structure of outer ring stub 401, inner ring stub 403, and metal square ring 402, forming two loss-type resonant structures connected in series. Figure 4 (c) and Figure 5 Simulation results show that a single loss layer is sufficient to achieve good absorption in the 1.0-3.0 GHz frequency band, but the absorption effect is poor in the middle frequency band (S11>-10dB). Therefore, by improving the internal strip metal 403' into an inner ring stub 403, as shown... Figure 4 As shown in (d), the equivalent capacitance C3 between the internal structures was increased, reducing the resonant Q value and achieving the goal of improving the low-frequency absorption characteristics. Figure 5 As shown.

[0051] See Figures 6 to 7 The figures show the simulated absorption rates of the absorbing structure for electromagnetic waves under TM and TE wave incident angles, respectively. As the incident angle increases, the absorption rate of the structure for low-frequency electromagnetic waves gradually decreases. However, overall, it still maintains efficient absorption (absorption rate >90%) for the 1.0-3.0 GHz electromagnetic wave band at large oblique incident angles of 60° or less, meeting the design requirements.

[0052] The absorption rate of an absorbing structure is defined as:

[0053] A(ω)=1-R(ω)-T(ω)=1-S 11 2 -S 21 2 (6)

[0054] Where A(ω), R(ω), and T(ω) represent absorptivity, reflectivity, and transmittance, respectively. In this embodiment, the absorbing structure has a metal plate at its bottom to prevent the transmission of incident electromagnetic waves; therefore, T(ω) = 0, and the absorptivity can be calculated using the following formula:

[0055] A(ω)=1-S 11 2 (7)

[0056] See Figure 8 To evaluate the performance of the electromagnetic absorbing isolator, two 4×4 element models (200mm×200mm) were designed and placed back-to-back between two combined dipole antennas 500 with a spacing of 70mm. One antenna was fed with a pulse signal of 3.12kV and a pulse width of 1ns, and the coupling signal and far-field radiation signal of the other antenna were measured. Simulation results show that, compared with no absorbing structure between the antennas, the coupling voltage amplitude on adjacent antennas decreased from 132.60V to 4.26V, and the far-field radiation potential changed from 3.58kV to 3.31kV. This indicates that the designed absorbing structure can effectively solve the coupling problem between adjacent antennas, while having a small attenuation effect (<8%) on the radiation field of the original combined dipole antenna. This absorbing structure is beneficial to the stability of the radiation system.

Claims

1. An electromagnetic isolator, characterized in that, The device includes a dielectric layer (100), a support layer (200), and a metal backplate (300). A loss layer (400) is deposited on the upper surface of the dielectric layer (100). The support layer (200) is sandwiched between the dielectric layer (100) and the metal backplate (300). The loss layer (400) includes a metal thin film and a chip resistor (404). The metal thin film includes an outer ring stub (401), an inner ring stub (403), and a metal square ring (402). The metal square ring (402) has a rectangular structure. The outer ring stub (401) is arrayed around the outer ring of the metal square ring (402). The outer ring stub (401) and the metal... The rectangular border of the square ring (402) is parallel, and the outer ring stub (401) is connected to the metal square ring (402) through a chip resistor (404); the inner ring stub (403) is arrayed in the inner circle of the metal square ring (402). The inner ring stub (403) includes an inner ring long strip (403') and a cross structure stub. One side of the inner ring long strip (403') is connected to one end of the cross structure. The length of the inner ring long strip (403') is greater than the cross length of the cross structure stub. The inner ring long strip (403') is close to the inner edge of the metal square ring (402) and parallel to the inner edge of the metal square ring (402) it is close to.

2. An electromagnetic isolator according to claim 1, characterized in that, The dielectric layer (100) is made of FR4 glass fiber epoxy resin substrate with a thickness of 1 mm.

3. An electromagnetic isolator according to claim 1 or 2, characterized in that, The relative permittivity α of the dielectric layer (100) r The value is 4.3, and the dielectric loss tangent is 0.

025.

4. An electromagnetic isolator according to claim 1, characterized in that, The support layer (200) is made of PMI foam substrate with a thickness of 28 mm.

5. An electromagnetic isolator according to claim 1 or 4, characterized in that, The relative permittivity α of the support layer (200) r The value is 1.03~1.13, and the dielectric loss tangent is 0.

018.

6. An electromagnetic isolator according to claim 1, characterized in that, The chip resistor (404) uses a chip resistor with a resistance of 120 Ω.

7. A combined dipole antenna array unit based on the electromagnetic isolator of claim 1, characterized in that, It includes two sets of metal backplates (300) with electromagnetic isolators placed close together, and a set of vibrating antennas (500) is set at each end of the two sets of electromagnetic isolators.

8. The combined dipole antenna array unit according to claim 7, characterized in that, Two sets of electromagnetic isolators are installed at intervals of 70 mm.

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