An ideal invisible radome for dual-band operation

Abstract

The present invention discloses an ideal invisible radome operating in dual frequency bands. The radome is primarily composed of periodically arranged sub-wavelength resonant units, each of which is primarily composed of a first metal circuit layer, a first dielectric layer, a second metal circuit layer, a second dielectric layer, and a third metal circuit layer stacked in sequence; the first metal circuit layer and the third metal circuit layer are symmetrically arranged about the plane where the second metal circuit layer resides, and each includes five rectangular metal frames; the first dielectric layer and the second dielectric layer are symmetrically arranged about the plane where the second metal circuit layer resides. The present invention is thin, lightweight, and has a simple structure. Its electromagnetic properties are equivalent to those of air, and it exhibits excellent transmission effects for incident plane waves at all angles. The present invention can be widely used in fields such as electromagnetic transparent windows and radomes.

Description

Technical Field

[0001] The present invention provides a radome, in particular to an ideal invisible radome which is formed by periodically arranging sub-wavelength resonant units and operates in dual frequency bands. Background Art

[0002] Radomes, also known as electromagnetic windows, ensure the smooth transmission of specific frequency signals while protecting the electronic equipment within from external extreme weather conditions (such as rain, snow, sand, animals, and high temperatures). Common radomes include vehicle-mounted radar radomes, aircraft nose radar radomes, and communication base station radomes. Because radomes protect valuable electronic communication equipment from direct exposure to extreme weather conditions, effectively ensuring the lifespan and operational stability of the equipment, they are widely used in various antenna, radar, and other signal transmission and reception applications.

[0003] Electronic communications equipment often operates simultaneously in different frequency bands. In the military, electronic countermeasures equipment, such as those on ships and aircraft, typically uses one frequency band for electronic reconnaissance and another for electromagnetic interference against enemy weapons. In civilian applications, such as electronic communications and broadcasting, a single antenna often transmits and receives signals in two (or even more) different frequency bands to avoid interference from co-frequency and co-polarization signals. Therefore, to meet practical requirements, a radome must maintain good passband characteristics across two or more frequency bands.

[0004] Currently, dual-band radome design methods, both domestically and internationally, primarily utilize methods such as FSS metal structures. While these traditional approaches can achieve impedance matching (excellent transmission characteristics), they cannot avoid phase distortion introduced by the radome itself. This is because when electromagnetic waves enter the radome from different angles, the phase of the transmitted wave is distorted, and the isophase plane of the transmitted wave no longer corresponds to the isophase plane of the incident wave. The fundamental reason for this is that, despite impedance matching, the radome's refractive index is not unity. This phase distortion is unacceptable in cutting-edge fields (such as missile guidance). Therefore, developing a dual-band, refractive index-equal-to-one dual-band radome is crucial. Summary of the Invention

[0005] To address the problems in the prior art, the present invention provides an ideal dual-band invisible radome. It is thin, lightweight, and has electromagnetic properties equivalent to those of air (refractive index equal to 1), providing excellent transmission of plane waves incident at all angles.

[0006] The technical solution adopted in the present invention is:

[0007] The antenna cover of the present invention is mainly composed of square sub-wavelength resonant units arranged in a periodic manner, and each sub-wavelength resonant unit is mainly composed of a first metal circuit layer, a first dielectric layer, a second metal circuit layer, a second dielectric layer and a third metal circuit layer stacked in sequence;

[0008] The first metal circuit layer and the third metal circuit layer are arranged symmetrically in the plane where the second metal circuit layer is located. They have identical and symmetrical structures and each includes five rectangular metal frames, one of which is concentric with the end face of the dielectric layer where it is located, and the other four identical rectangular metal frames are symmetrically distributed at the four corners of the end face of the dielectric layer where it is located, and the center of each of the four identical rectangular metal frames is located on a diagonal line of the end face of the dielectric layer where it is located;

[0009] The first dielectric layer and the second dielectric layer are symmetrically arranged on the plane where the second metal circuit layer is located.

[0010] The second metal circuit layer includes a straight-arm cross-shaped metal sheet and a curved-arm cross-shaped metal sheet; the middle portions of the straight-arm cross-shaped metal sheet and the curved-arm cross-shaped metal sheet are respectively a larger cross-shaped metal sheet and a smaller cross-shaped metal sheet, and the length of the larger cross-shaped metal sheet is greater than the length of the smaller cross-shaped metal sheet;

[0011] The central intersection of the larger cross-shaped metal sheet and the smaller cross-shaped metal sheet coincides and is located at the center of the second metal circuit layer, and both are composed of four identical branches connected in a cross shape; the four branches of the larger cross-shaped metal sheet are arranged radially and are respectively perpendicular to the four sides of the dielectric layer they are facing; the four branches of the smaller cross-shaped metal sheet are arranged at a 45-degree angle to the four branches of the larger cross-shaped metal sheet, that is, the four branches of the smaller cross-shaped metal sheet are arranged along the diagonal of the dielectric layer.

[0012] The straight-arm cross-shaped metal sheet further includes four identical tangential strip-shaped metal segments, the midpoints of the four tangential strip-shaped metal segments being connected to the outer ends of the four branches of the larger cross-shaped metal sheet, and the four tangential strip-shaped metal segments being parallel to one side of the dielectric layer to which they are adjacent;

[0013] The curved cross-shaped metal sheet further comprises four identical tangentially bent strip-shaped metal segments, the midpoints of the four tangentially bent strip-shaped metal segments being respectively connected to the outer ends of the four branches of the smaller cross-shaped metal sheet.

[0014] The bending direction of the tangentially bent strip metal segments is radially outward, and the four tangentially bent strip metal segments are all located on the same circumference and do not intersect with the straight-arm cross-shaped metal sheet.

[0015] The rectangular metal frames are all square, and the four sides are parallel to the surrounding side edges of the end surface of the dielectric layer.

[0016] The first dielectric layer and the second dielectric layer are both made of F4BMX265 plate, with a relative dielectric constant of 2.65 and a loss tangent of 0.0014.

[0017] The first dielectric layer and the second dielectric layer have the same thickness.

[0018] The radome is formed by a plurality of sub-wavelength resonance units being closely arranged periodically on the same plane.

[0019] The beneficial effects of the present invention are:

[0020] The invention is designed to be thin, light and simple in structure; the electromagnetic performance of the invention is very close to that of air, and it has an excellent transmission effect on plane waves incident at various angles. The material also satisfies the requirements of high transmission coefficient and refractive index approximately 1.

[0021] The present invention can be widely used in fields such as electromagnetic transparent windows and radar covers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a visual diagram of the unit structure of the radome of the present invention;

[0023] Figure 2 1 is a schematic structural diagram of a unit structure of a radome of the present invention;

[0024] Figure 2 (a) is a front view of the unit structure of the radome of the present invention;

[0025] Figure 2 (b) is a schematic diagram of the second metal circuit layer of the unit structure of the antenna cover of the present invention;

[0026] Figure 2 (c) is a side view of the unit structure of the radome of the present invention;

[0027] Figure 3 Schematic diagram of return loss parameters of the radome of the present invention when a plane wave is incident at different incident angles;

[0028] Figure 4 is a constitutive parameter result diagram of the unit structure of the radome of the present invention;

[0029] Figure 4 (a) is a schematic diagram of the constitutive parameters of the radome at 8.54 GHz;

[0030] Figure 4 (b) is a schematic diagram of the constitutive parameters of the radome at 11.27 GHz;

[0031] Figure 5Comparison of the electric field distribution of the radome of the present invention (right) and air (left) at 8.54 GHz plane wave vertical incidence, 20-degree oblique incidence, 40-degree oblique incidence, and 60-degree oblique incidence, respectively;

[0032] Figure 6 Comparison of the electric field distribution of the radome of the present invention (right) and air (left) at 11.27 GHz plane wave vertical incidence, 20-degree oblique incidence, 40-degree oblique incidence, and 60-degree oblique incidence, respectively;

[0033] Figure 7 This is a comparison diagram of the phase delay between the radome of the present invention and air when an 8.54 GHz plane wave is incident at different angles;

[0034] Figure 8 This is a comparison diagram of the phase delay between the radome of the present invention and air when a plane wave of 11.27 GHz is incident at different angles;

[0035] In the figure: 1, first metal circuit layer, 2, first dielectric layer, 3, second metal circuit layer, 4, second dielectric layer, 5, third metal circuit layer. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] like Figure 1 As shown, the antenna cover is mainly composed of multiple square sub-wavelength resonant units arranged closely in a periodic manner on the same plane, and each sub-wavelength resonant unit is mainly composed of a first metal circuit layer 1, a first dielectric layer 2, a second metal circuit layer 3, a second dielectric layer 4 and a third metal circuit layer 5 stacked in sequence.

[0038] The first metal circuit layer 1 and the third metal circuit layer 5 are arranged symmetrically about the plane where the second metal circuit layer 3 is located. They have identical and symmetrical structures and each includes five rectangular metal frames. One of the rectangular metal frames is concentric with the end faces of the dielectric layers 2 and 4, and the other four identical rectangular metal frames are symmetrically distributed at the four corners of the end faces of the dielectric layers 2 and 4. The centers of the four identical rectangular metal frames are each located on the diagonal lines of the end faces of the dielectric layers 2 and 4. The rectangular metal frames are all square, and the four sides are parallel to the surrounding side edges of the end faces of the dielectric layers 2 and 4.

[0039] The first dielectric layer 2 and the second dielectric layer 4 are arranged symmetrically about the plane of the second metal circuit layer 3. Both the first dielectric layer 2 and the second dielectric layer 4 are made of F4BMX265 sheet material, which has a relative dielectric constant of 2.65 and a loss tangent of 0.0014. The first dielectric layer 2 and the second dielectric layer 4 have the same thickness.

[0040] The second metal circuit layer 3 includes a straight-arm cross-shaped metal sheet and a curved-arm cross-shaped metal sheet; the middle parts of the straight-arm cross-shaped metal sheet and the curved-arm cross-shaped metal sheet are respectively a larger cross-shaped metal sheet and a smaller cross-shaped metal sheet, and the length of the larger cross-shaped metal sheet is greater than that of the smaller cross-shaped metal sheet.

[0041] The central intersection of the larger cross-shaped metal sheet and the smaller cross-shaped metal sheet coincides and is located at the center of the second metal circuit layer 3. Both are composed of four identical branches connected in a cross-shaped arrangement. The four branches of the larger cross-shaped metal sheet are arranged radially and perpendicular to the four sides of the dielectric layers 2 and 4 they are facing. The four branches of the smaller cross-shaped metal sheet are arranged at a 45-degree angle to the four branches of the larger cross-shaped metal sheet, that is, the four branches of the smaller cross-shaped metal sheet are arranged along the diagonal lines of the dielectric layers 2 and 4.

[0042] The straight-arm cross-shaped metal sheet also includes four identical tangential strip metal segments, the midpoints of which are respectively connected to the outer ends of the four branches of the larger cross-shaped metal sheet, and the four tangential strip metal segments are respectively parallel to one side of the dielectric layers 2 and 4 to which they are close.

[0043] The curved cross-shaped metal sheet also includes four identical tangentially bent strip-shaped metal segments, the midpoints of which are connected to the outer ends of the four branches of the smaller cross-shaped metal sheet. The tangentially bent strip-shaped metal segments bend radially outward, are located on the same circumference, and do not intersect with the straight cross-shaped metal sheet.

[0044] The working principle and process of the present invention are:

[0045] Set one of the vertices on the surface of the first metal circuit layer 1 of the sub-wavelength resonant unit as the origin, the direction from the origin to a vertex on the surface adjacent to the origin is the x direction, the direction from the origin to another vertex on the surface adjacent to the origin is the y direction, and the direction from the origin to a vertex on the surface of the third metal circuit layer 5 adjacent to the origin is the z direction.

[0046] Constructing an omnidirectional perfectly transparent invisible material is essentially to construct an equivalent relative dielectric constant ε eff and magnetic permeability μ eff The present invention is an artificial electromagnetic material, the dielectric constant of which can be described by the Lorentz model, that is, the dielectric constant ε in the electric resonance region eff The value will change from positive (greater than 1) to negative. Therefore, the dielectric constant ε between the two electrical resonances eff It will change from a negative number to a positive number greater than 1, that is, the relative dielectric constant ε of the material at a certain operating frequency between the two electrical resonances eff The value is equal to 1.

[0047] The present invention designs the unit structure so that when the TE polarized plane wave is incident on the sub-wavelength resonant unit, the metal line layers 1, 3, and 5 of the sub-wavelength resonant unit will jointly generate three electrical resonances, so the relative dielectric constant ε eff The value must be equal to 1 at two working frequencies. By adjusting the size of each part of the structure, the relative dielectric constant ε can be eff and magnetic permeability μ eff The intersection value is adjusted to 1. In the present invention, the bent-arm cross-shaped metal sheet structure has a smaller overall size, that is, a smaller electrical length, and corresponds to a higher operating frequency; the straight-arm cross-shaped metal sheet has a larger overall size, that is, a larger electrical length, and corresponds to a lower operating frequency.

[0048] Adjusting the straight-arm cross-shaped metal sheet, increasing / decreasing the width of the straight-arm cross-shaped metal sheet can increase / decrease the corresponding low-frequency operating point, increasing / decreasing the length of the branch of the larger cross-shaped metal sheet can decrease / increase the corresponding low-frequency operating point, and increasing / decreasing the length of the tangential strip metal segment can decrease / increase the corresponding low-frequency operating point; adjusting the curved-arm cross-shaped metal sheet, increasing / decreasing the width of the curved-arm cross-shaped metal sheet can increase / decrease the corresponding high-frequency operating point, increasing / decreasing the length of the branch of the smaller cross-shaped metal sheet can decrease / increase the corresponding high-frequency operating point, and increasing / decreasing the length of the tangential curved strip metal segment can decrease / increase the high-frequency operating point; increasing / decreasing the area of the rectangular metal frame of the first metal circuit layer 1 and the third metal circuit layer 5 can decrease / increase the magnetic permeability μ in the z direction z .

[0049] The electromagnetic material proposed in the present invention is a dispersive material, that is, the relative dielectric constant and magnetic permeability will change with the change of frequency. By adjusting the size of the metal circuit layers 1, 3, 5 and the thickness of the dielectric layers 2, 4, the positions of the two operating frequencies can be adjusted to adjust the relative dielectric constant ε eff and magnetic permeability μ eff Both are 1, that is, equivalent to air, so that the TE polarized plane waves of the two working frequencies can be fully transmitted at any incident angle.

[0050] An example of a sub-wavelength resonant unit of a dual-frequency perfect invisible radome operating in the X-band of the present invention is as follows: Figure 2 (a) Figure 2 (b) and Figure 2 As shown in (c):

[0051] The dimensions of the various components of the subwavelength resonant unit structure are as follows: side length n of the subwavelength resonant unit = 7.4 mm; side length m of the outer edge of the central rectangular metal frame = 1.28 cm; side length g of the outer edge of the diagonal rectangular metal frame = 1.6 mm; distance s of the diagonal rectangular metal frame offset from the geometric center of the surface on which it is located = 2.1 mm; width d of the rectangular metal frame = 0.2 mm; width f of the branch of the larger cross-shaped metal sheet = 0.2 mm; length l of the branch of the larger cross-shaped metal sheet = 3.2 mm; width w of the tangential strip metal segment = 0.4 mm; length u of the tangential strip metal segment = 4.8 mm; inner diameter r of the tangential curved strip metal segment = 2.5 mm; width o of the tangential curved strip metal segment = 0.3 mm; distance k between two opposing inner edge vertices of two adjacent tangential curved strip metal segments = 0.8 mm; width c of the branch of the smaller cross-shaped metal sheet = 0.32 mm; thickness t of the first dielectric layer 2 and the second dielectric layer 4 = 0.8 mm.

[0052] The simulation results are as follows Figure 3 As shown, the present invention achieves omnidirectional perfect matching of transmission dielectric materials at two operating frequencies. At the 8.54 GHz operating frequency, the return loss of the incident TE-polarized plane wave is less than -33 dB when the incident angle increases from 0 to 80 degrees, and the transmission coefficient still reaches 98.5% when the incident angle is 80 degrees. At the 11.27 GHz operating frequency, the return loss of the incident TE-polarized plane wave is less than -22 dB when the incident angle increases from 0 to 80 degrees, and the transmission coefficient still reaches 92.8% when the incident angle is 80 degrees, with almost no operating frequency offset.

[0053] Will Figure 3 The obtained return loss parameters, combined with the transmission coefficient, are calculated as follows: Figure 4 As shown in the figure, this figure is the constitutive parameter diagram of the sub-wavelength resonant unit. Figure 4 It can be seen that the imaginary part of the dielectric constant Im(ε y ) is almost equal to 0 and can be ignored. At 8.54 GHz, the components of the relative permittivity and permeability almost converge to an intersection point, where Re(ε y )=ε eff =1.02, Re(μ z )=Re(μ x )=μ eff =0.99, the refractive index is approximately equal to 1.004. Similarly, at 11.27GHz, we can analyze and obtain Re(ε y )=ε eff =1.04, Re(μ z )=Re(μ x )=μ eff=0.97, and the refractive index is approximately equal to 1.004. Therefore, the sub-wavelength resonant unit is almost equivalent to the air dielectric material at two operating frequencies, and the refractive index is approximately equal to 1. Re represents the real part of the complex number, Re(ε y ) represents the real part of the dielectric constant in the y direction, Re(μ x ) represents the real part of the x-direction component of the magnetic permeability, Im represents the imaginary part of the complex number, Im(ε y ) represents the imaginary part of the dielectric constant in the y direction.

[0054] The comparison of the propagation of plane waves in the radome of the present invention and in the air is shown in the figure below: Figure 5 and Figure 6 As shown. In each sub-graph, the right side is the perfect transparent invisible radome proposed by the present invention, and the left side is the air layer of the same thickness. For the cases of vertical incidence (0 degrees) and oblique incidence (20 degrees, 40 degrees, 60 degrees) of the plane wave, it can be seen that the propagation of the two frequencies of plane waves in the radome of the present invention is highly consistent with that in the air. Figure 7 and Figure 8 In the quantitative phase delay comparison between the radome and air, the phase delay difference at low frequency is less than 0.5°, and the phase delay difference at high frequency is less than 0.9°, which proves that the electromagnetic properties of the radome of the present invention are almost the same as those of air.

[0055] The structure described in the present invention operates at frequencies of 8.54 GHz and 11.27 GHz. If the present invention is to operate at other frequencies, the dimensions of the sub-wavelength resonant unit structure components need to be adjusted according to the operating wavelength ratio.

[0056] The above description is only a preferred embodiment of the present invention at specific frequencies of 8.54 GHz and 11.27 GHz, and does not limit the present invention in any form. Any technician familiar with the present profession can use the technical content explained above to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. An ideal invisible radome for dual-band operation, characterized by: The radome is mainly composed of sub-wavelength resonant units arranged in a periodic manner, and each sub-wavelength resonant unit is mainly composed of a first metal circuit layer (1), a first dielectric layer (2), a second metal circuit layer (3), a second dielectric layer (4), and a third metal circuit layer (5) stacked in sequence; The first metal circuit layer (1) and the third metal circuit layer (5) are symmetrically arranged on the plane where the second metal circuit layer (3) is located, and each includes five rectangular metal frames, one of which is concentric with the end face of the dielectric layer (2, 4) where it is located, and the other four identical rectangular metal frames are symmetrically distributed at the four corners of the end face of the dielectric layer (2, 4) where it is located, and the center of each of the four identical rectangular metal frames is located on the diagonal line of the end face of the dielectric layer (2, 4) where it is located; the first dielectric layer (2) and the second dielectric layer (4) are symmetrically arranged on the plane where the second metal circuit layer (3) is located; The second metal circuit layer (3) comprises a straight-arm cross-shaped metal sheet and a curved-arm cross-shaped metal sheet; the middle parts of the straight-arm cross-shaped metal sheet and the curved-arm cross-shaped metal sheet are respectively a larger cross-shaped metal sheet and a smaller cross-shaped metal sheet, and the length of the larger cross-shaped metal sheet is greater than the length of the smaller cross-shaped metal sheet; The central intersection of the larger cross-shaped metal sheet and the smaller cross-shaped metal sheet coincides and is located at the center of the second metal circuit layer (3); the four branches of the larger cross-shaped metal sheet are arranged radially and are respectively perpendicular to the four sides of the dielectric layers (2, 4) they are facing; the four branches of the smaller cross-shaped metal sheet are arranged at a 45-degree angle to the four branches of the larger cross-shaped metal sheet; The straight-arm cross-shaped metal sheet further comprises four identical tangential strip metal segments, the midpoints of the four tangential strip metal segments being respectively connected to the outer ends of the four branches of the larger cross-shaped metal sheet, and the four tangential strip metal segments being respectively parallel to one side of the dielectric layer (2, 4) to which they are adjacent; The curved cross-shaped metal sheet further comprises four identical tangentially bent strip-shaped metal segments, the midpoints of the four tangentially bent strip-shaped metal segments being respectively connected to the outer ends of the four branches of the smaller cross-shaped metal sheet; The bending direction of the tangentially bent strip-shaped metal segment is radially outward, and the four tangentially bent strip-shaped metal segments are all located on the same circumference and do not intersect with the straight-arm cross-shaped metal sheet.

2. The ideal invisible radome for dual-band operation according to claim 1, characterized in that: The four sides of the rectangular metal frame are respectively parallel to the peripheral side edges of the end faces of the dielectric layers (2, 4) where they are located.

3. The ideal invisible radome for dual-band operation according to claim 1, characterized in that: The first dielectric layer (2) and the second dielectric layer (4) are both made of F4BMX265 plate material, with a relative dielectric constant of 2.65 and a loss tangent value of 0.0014.

4. The ideal invisible radome for dual-band operation according to claim 1, characterized in that: The first dielectric layer (2) and the second dielectric layer (4) have the same thickness.

5. The ideal invisible radome operating in dual frequency bands according to claim 1, characterized in that: The radome is formed by periodically arranging a plurality of sub-wavelength resonance units on the same plane.

Images