Electromagnetic lenses based on artificial dielectric materials

Abstract

The present invention discloses a cylindrical focusing lens, comprising a dielectric outer cover and an artificial dielectric material, wherein the artificial dielectric material comprises a plurality of multi-layered foamed dielectric material sheets arranged in layers and a plurality of short conductive tubes placed in the foamed dielectric material sheets; wherein the short conductive tubes placed in the foamed dielectric material sheets form a circle and a ring around the circle, and the ring formed by the foamed dielectric material without the short conductive tubes separates the circle formed by the short conductive tubes, the ring, and the dielectric outer cover from each other. The lens of the present invention overcomes the shortcomings of the known lenses made of lightweight artificial dielectric materials, can be well matched with free space, and is simpler to manufacture than known analogs.

Description

Technical Field

[0001] The present invention relates to an electromagnetic wave focusing lens made of artificial dielectric material. Background Art

[0002] The modern mobile communications market requires multi-beam antennas that can create narrow beams and operate in different frequency bands. The focusing dielectric lens is the main part of the multi-beam antenna. Usually the multi-beam antenna contains a Luneburg lens that matches the free space, because the dielectric constant ε of this lens decreases from the center to the outer contour according to the formula ε=2-(R / A)2, where R is the distance from the center of the lens to an inner point, and A is the outer radius of the lens. Patent WO 2019 / 003939 A1 describes that the thickness in the radial outer region of the Luneburg lens stacked by disc-shaped members is less than the thickness in the central region. The diameter of the focusing lens must be several wavelengths of the electromagnetic wave, and the propagation through the lens can produce a narrow beam, so the lens diameter of some multi-beam antennas for mobile communications exceeds 1m. This lens made of commonly used dielectric materials is too heavy, so many studies have been conducted in the industry to manufacture lightweight and low-loss lenses to provide ideal focusing characteristics.

[0003] Most lightweight artificial dielectric materials are made by randomly mixing small particles to provide isotropic properties of the final material. For example, U.S. Patent 9819094B2 describes a cylindrical lens made of a lightweight artificial isotropic dielectric material with a substantially homogeneous dielectric constant ε. When the diameter of the lens in free space at the nominal operating frequency is less than 3 wavelengths, the lens of this design provides greater gain than a Luneburg lens of the same diameter. Therefore, a relatively small lens made of an isotropic dielectric material with a substantially homogeneous dielectric constant ε is smaller than a Luneburg lens that provides the same gain, but has some disadvantages.

[0004] A cylindrical lens made of an isotropic artificial dielectric material depolarizes the electromagnetic waves generated by the lens, so an antenna including such a lens is subject to high cross-polarization levels. U.S. Patent US 9819094 B2 describes a multi-beam antenna that includes a special element called a compensator arranged around the lens. The compensator reduces the depolarization of the electromagnetic waves passing through the cylindrical lens, improves the cross-polarization ratio of the multi-beam antenna, but increases the manufacturing cost. Another drawback of lenses made of isotropic dielectric materials with a substantially homogeneous dielectric constant ε is the large reflection from the outer contour of the lens. U.S. Patent US 9780457 B2 describes a design for an improved matching free space lens. The lens includes a plurality of compartments for a lightweight isotropic dielectric material with a substantially homogeneous dielectric constant ε. The dielectric material-filled compartments arranged near the center of the lens have a larger dielectric constant ε than the dielectric material-filled compartments arranged near the outer contour of the lens. Lenses of this design are better matched to free space, but are more complex to manufacture and offer less directivity than lenses with a homogeneous dielectric constant ε.

[0005] A cylindrical lens made of anisotropic dielectric material can reduce the depolarization of electromagnetic waves passing through the cylindrical lens and improve the cross-polarization rate of a multi-beam antenna.

[0006] In New Zealand NZ patent 752904 and US patent US 10971823 B1, lightweight artificial dielectric materials with anisotropic properties and suitable for making cylindrical lenses are described. These materials consist of short conductive tubes with thin walls, which are layered inside a foamed dielectric material. One layer includes a sheet of foamed dielectric material containing a plurality of holes. The thin-walled short conductive tubes are placed in the holes made of lightweight dielectric material. The layer containing the tubes is separated by a layer of lightweight dielectric material without tubes. New Zealand patent 752904 describes a material in which the axes of all conductive tubes are facing away from the direction perpendicular to the layer. This structure can provide electromagnetic waves with a dielectric constant ε of up to 2.5 propagating along the tube axis, but the dielectric constant ε of electromagnetic waves propagating along the perpendicular direction is significantly reduced. The artificial dielectric material described in US patent US10971823 B1 contains tubes with perpendicular layers and axial directions parallel to the layers. Due to the different orientations of the tubes, this material has the desired anisotropic properties, thereby reducing the cross-polarization level of the antenna including the cylindrical lens.

[0007] Lenses that focus RF waves must be well matched to free space to improve return loss and isolation of multibeam antennas, so lenses made of new artificial dielectric materials need to be well matched to free space. Summary of the invention

[0008] The first object of the invention is to overcome the deficiencies of known lenses made of lightweight artificial dielectric materials and to develop a compact lens that is well matched to free space. The second object of the invention is to provide a lens that is well matched to free space and is simpler to manufacture than known analogues.

[0009] The present invention has developed a cylindrical focusing lens, which includes a dielectric cover and an artificial dielectric material, wherein the artificial dielectric material includes a foamed dielectric material sheet arranged in multiple layers and a plurality of short conductive tubes placed in the foamed dielectric material sheet. The cross section of the conductive tube can be circular or polygonal, such as square, hexagonal or octagonal. The short conductive tubes arranged in the dielectric sheet form a circle and a ring around the circle, and are separated from the circle and the antenna cover by a foamed dielectric material ring without short conductive tubes. The foamed dielectric material sheet containing short conductive tubes is separated by the foamed dielectric material sheet without short conductive tubes.

[0010] The circle containing the short conductive tubes forms a layer of focusing cylinder. The two rings of foamed dielectric material and the ring containing the short conductive tubes form a broadband transformer, matching the ring containing the short conductive tubes with free space. The conductive tubes forming the circle can be arranged in the shape of any lattice described in New Zealand Patent 752904 and US US10971823 B1. Lenses including tubes forming other shaped lattices can also be matched to free space by transformers containing rings of tubes and rings of foamed dielectric material. In some lenses with operating frequencies below 1 GHz and with large-sized rings of foamed dielectric material, voids can be used instead to make them lighter and save foamed dielectric material.

[0011] The axes of the short conductive tubes forming a layer of rings and loops may point in the same direction or in different directions.

[0012] The axes of the short conductive tubes placed in different layers may point in the same direction or in different directions.

[0013] The axis of the short conductive tube placed in a layer can be perpendicular to the layer or parallel to the layer.

[0014] The axis of the short conductive tube disposed in one layer and parallel to the layer may be perpendicular to the axis of the short conductive tube disposed in an adjacent layer and parallel to the layer.

[0015] The width of the ring forming the broadband transformer depends on the operating frequency band and the thickness of the dielectric radome which is the outer part of the broadband transformer.

[0016] The width of the ring of foamed dielectric material without short conductive tubes placed between the circle and the ring with short conductive tubes is 0.2-0.8 times the width of the ring with short conductive tubes. The width of the ring of foamed dielectric material without short conductive tubes placed between the dielectric radome and the ring with short conductive tubes is 1.0-4.0 times the width of the ring with short conductive tubes.

[0017] The tubes placed in adjacent layers can be placed on top of each other on the same axis or displaced from each other and have different axes.

[0018] The tubes are placed with different tube axis directions. Some tube axes are perpendicular to the layers and other tube axes are parallel to the layers. Tubes with axes parallel to the layers can be placed perpendicular to each other. In this way, the tube axes have three orthogonal directions, thereby providing a lightweight artificial dielectric material whose dielectric properties are less dependent on the direction and polarization of the electromagnetic waves passing through the material.

[0019] The tubes placed in one layer may have the same axial orientation or different axial orientations. The layers containing tubes placed on top of each other may have the same structure or different structures.

[0020] Lenses comprising said transformer do not contain additional components, and therefore their manufacture is simpler than known analogues. Such transformers can be used to match other types of focusing lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1a is a top view of the first layer of the cylindrical lens. Figure 1b is a cross-sectional view AA of the first layer of a cylindrical lens, in which the tubes forming a circle are placed in the shape of a hexagonal lattice and the axis of the tubes is perpendicular to the direction of the layer.

[0022] Figure 1c 1D is a cross-sectional view BB of the second layer of cylindrical lenses, wherein the tubes forming a circle are placed in a hexagonal lattice shape with the axis of the tube parallel to the layer and parallel to the cross section BB.

[0023] Figure 1e is a top view of the third cylindrical lens. Figure 1f It is the cross-sectional view CC of the third layer of cylindrical lenses. The circle formed by the tubes is placed in a hexagonal lattice shape, with the axis of the tubes parallel to the layer and perpendicular to the cross-sectional view CC of the layer.

[0024] Figure 1g Shown include Figures 1a to 1f Cross section AA of a 36-layer cylindrical lens shown. Separated by layers of foamed dielectric material without tubes. The lens is assembled from three different layers.

[0025] Figure 2a Description Figures 1a to 1g Reflection of a plane electromagnetic wave propagating through a lens as described in .

[0026] Figure 2bThe normalized impedance of the matching transformer formed by the radome, the ring of foamed dielectric material and the ring of tubes is shown. For other applications, the tubes placed in one layer can form other lattices and the lens can be composed of other numbers of different layers. For example, Figures 3a to 3e A cylindrical lens assembled from two different layers is shown, where each layer comprises a number of short tubes arranged in a circle and whose axes have two orthogonal orientations.

[0027] Figure 3a is a top view of the first layer of cylindrical lenses. Figure 3b is the cross-sectional view DD of the first layer of cylindrical lenses. The axes of the tubes forming the odd-numbered circles are oriented along one layer and along the circle. The axes of the tubes forming the even-numbered circles are perpendicular to the layer.

[0028] Figure 3c is a top view of the second cylindrical lens. Figure 3d is the cross-sectional view EE of the second layer of cylindrical lenses, the axis of the tubes forming the odd circles is oriented along one layer and perpendicular to the circle. The axis of the tubes forming the even circles is perpendicular to the layer.

[0029] Figure 3e It shows Figures 3a to 3d The 24 layers of cylindrical lenses shown in cross-section AA are separated by foamed dielectric material without tubes. DETAILED DESCRIPTION

[0030] For better understanding and implementation, the technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. The accompanying drawings show several typical embodiments of cylindrical lenses made of lightweight artificial dielectric materials containing short conductive tubes and the way in which the short conductive tubes can be matched with lenses in free space.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0032] Figure 1a-1g The lens of the first embodiment of the present invention is assembled from three different layers.

[0033] Figure 1a and 1bA top view and corresponding cross section AA of a first layer 1 of a cylindrical lens is shown, wherein the tubes 11a placed inside the circle 5 are arranged in the shape of a hexagonal lattice and the axis of the tubes is perpendicular to the layer and parallel to the cross section AA. The tubes 11b arranged between the rings 6 and 7 are arranged in two circles forming a ring 8 arranged between the ring 5 and the dielectric radome 9 and separated by rings 10 and 12 formed of a foamed dielectric material without tubes. The axis of the tubes 11b is perpendicular to the layer and parallel to the cross section AA. Thin dielectric rods 13 pass through all the layers and fix all the layers to each other to form a lens.

[0034] Figure 1c and 1d A top view and a cross section BB of the second layer 2 of the cylindrical lens are shown respectively, wherein the tubes 21a forming the circle 5 are arranged in the shape of a hexagonal lattice and the axis of the tubes is parallel to the layer and to the cross section BB. The tubes 21b arranged between the rings 6 and 7 are arranged in two rings forming a ring 8 placed between the circle and the dielectric radome 9 and separated by rings 10 and 12 formed of a foamed dielectric material without tubes. The axis of the tubes 21b is parallel to the layer and to the cross section BB.

[0035] Figure 1e and 1f A top view and a cross section CC of a third layer of a cylindrical lens are shown, respectively, in which the tubes 31a forming the ring 5 are arranged in the shape of a hexagonal lattice and the axis of the tubes is parallel to the layer and perpendicular to the cross section CC. The tubes 31b arranged between the rings 6 and 7 are arranged in two rings forming a ring 8 arranged between the ring 5 and the dielectric radome 9 and separated by rings 10 and 12 formed of a foamed dielectric material without tubes. The axis of the tubes 31b is parallel to the layer and perpendicular to the cross section CC.

[0036] Figure 1g shows a cross section AA of a cylindrical lens comprising a Figures 1a to 1f All layers with tubes are separated by layers of foamed dielectric material 4 without tubes. These layers are stacked together to form twelve modules 14, which have the desired anisotropic properties. Since the rings 8, 10 and 12 with different dielectric constant values ​​ε reflect the electromagnetic waves passing through the lens in an opposite way compared to the reflections from the radome 9 and circle 5, the lens improves the match with free space. The additional reflections from the rings 8, 10 and 12 suppress the reflections from the radome 9 and circle 5 that match the lens with free space. The width of the rings 8, 10 and 12 that provides the best match depends on the nominal operating frequency and the thickness of the radome 9 and the dielectric constant value ε.

[0037] Figure 2aThe multiple reflections of a plane electromagnetic wave passing through the radome 9 and the rings 8, 10 and 12 are illustrated, with different dielectric constant values ​​ε relative to the lens axis. The impedance normalized to the impedance of the dielectric material layer relative to the impedance of free space is the formula Z = 1 / squrt dielectric constant ε, therefore, the reflection of the plane electromagnetic wave from the dielectric material layer can be calculated as the reflection from the successively (closely) connected parts of the main line with different impedance Z and length. Figure 2b The impedance of the radome 9 and the rings 8, 10 and 12 with an outer radius R are shown.

[0038] Table 1 contains the width W and the dielectric constant ε of the ring of the transformer forming a lens of artificial dielectric material, with a dielectric constant ε=2.0, placed in ring 5. The outer radome of the transformer has a thickness of 3 mm and a dielectric constant ε=4.3.

[0039] Table 1

[0040]

[0041] Table 2 contains the electrical length L=Wsqurt of the closely (sequentially) connected parts of the transmission line simulating the matching transformer, the dielectric constant ε and the normalized impedance Z.

[0042] Table 2

[0043]

[0044] The calculated transformer provides VSWR=1.06 over a wide frequency band of 0.5-1.0 GHz, so this approach can be used to match different lenses for broadband multi-beam antennas, including antenna lenses used in modern mobile communication base stations.

[0045] like Figure 1g As shown, short conductive tubes fill the holes of the entire disc of foamed dielectric material formed by the rings 10, 8 and 12 together with the circle 5. The way provided to match the lens to free space does not require a complex radome with multiple compartments as described in patent US 9780457 B2, so the manufacturing cost of the matched lens is the same as that of a lens made of a lightweight artificial dielectric material with a substantially homogeneous dielectric constant ε. The rings 8, 10 and 12 together with the radome 9 form a broadband transformer, the length of which is less than that of a conventional transformer, consisting of a portion with a length equal to a quarter wavelength in free space at the nominal operating frequency and different impedance. As a result, according to the invention, the lens has a smaller diameter than a lens providing the same gain, wherein the dielectric constant ε decreases successively towards the outer contour of the lens.

[0046] Other embodiments of the application, the tubes displaced in the layers may form other structures and the lens may include other numbers of different layers. For example, Figures 3a to 3eThe cylindrical lens shown in FIG. 1 is assembled from two different layers, each layer comprising a plurality of short conductive tubes arranged in a circle and having their axes in two orthogonal orientations.

[0047] Figure 3a and 3b A top view and a corresponding cross section DD of a first layer 41 are shown, respectively, in which the tubes 40a and 43a placed inside the circle 45 are arranged in the shape of a sunflower (lattice). The axis of the tube 40a forming the odd-numbered circles is parallel to the layer and parallel to the circle 45. The axis of the tube 43a forming the even-numbered circles is perpendicular to the layer. The tube 40b placed between the circles 46 and 47 is placed in two circles, forming a ring 48 arranged between the circle 45 and the dielectric radome 49 and separated by rings 50 and 52 formed by a foamed dielectric material without tubes. The axis of the tube 40b is parallel to the layer and parallel to the circle 45. The axis of the tube 43b is perpendicular to the layer. Thin dielectric rods 53 pass through all the layers and are fixed to each other to form a lens.

[0048] Figure 3c and 3d 4 shows a top view and a corresponding cross section EE of the second layer, wherein the tubes 60a and 63a arranged inside the circle 45 are arranged in the shape of a sunflower (lattice). The axis of the tubes 60a forming the odd circles is parallel to the layer and perpendicular to the circle 45. The axis of the tubes 63a forming the even circles is perpendicular to the layer. The tubes 60b placed between the circles 46 and 47 are placed in two circles forming a ring 48 arranged between the circle 45 and the dielectric radome 49 and separated by rings 50 and 52 formed by the foamed dielectric material without tubes. The axis of the tube 60b is parallel to the layer and perpendicular to the circle 45. The axis of the tube 63b is perpendicular to the layer.

[0049] Figure 3e Shown include Figure 3a to Figure 3b , Figures 3c to 3d 4. The cross section AA of a cylindrical lens of layers shown in FIG. 4 is shown, the layers being separated by layers of foamed dielectric material 54 without tubes. The layers are stacked together to form twelve modules 44, having the desired anisotropic properties.

[0050] Since the rings 48 , 50 and 52 , having different dielectric constant values ​​ε, reflect electromagnetic waves passing through the lens in an opposite manner compared to the reflection from the radome 49 and circle 45 , the lens improves the match to free space.

[0051] Additional reflections from rings 48, 50 and 52 suppress reflections from radome 49 and circle 45 matching the lens with free space. The width of rings 48, 50 and 52 that provides the best match depends on the nominal operating frequency and the thickness of radome 49 and the dielectric constant value ε.

[0052] The focusing lens group can match the free space through but not limited to the above-mentioned implementation cases. The lens can also be composed of tubes with other structures. For example, the tubes forming the layers can have three orthogonal directions, and the ring of the matching transformer formed by the tubes can also include tubes with axes in three orthogonal directions. Such a lens can also contain only one layer.

[0053] It should be understood that, if any prior art publication is referred to herein, this citation does not constitute an admission that the publication is part of the common general knowledge in the art in any country.

Claims

1. A cylindrical focusing lens, characterized in that: The invention comprises a dielectric outer cover and an artificial dielectric material, wherein the artificial dielectric material comprises a plurality of foamed dielectric material sheets arranged in layers and a plurality of short conductive tubes placed in the foamed dielectric material sheets; wherein the short conductive tubes placed in the foamed dielectric material sheets form a circle and a ring surrounding the circle, and the ring formed by the foamed dielectric material without the short conductive tubes separates the circle formed by the short conductive tubes, the ring and the dielectric outer cover from each other; The width of the ring composed of the foamed dielectric material without the short conductive tube placed between the circle and the ring with the short conductive tube is 0.2-0.8 times the width of the ring composed of the foamed dielectric material with the short conductive tube; The width of the ring composed of the foamed dielectric material without the short conductive tube placed between the dielectric cover and the ring with the short conductive tube is 1.0-4.0 times the width of the ring composed of the foamed dielectric material with the short conductive tube; The ring formed by the short conductive tube, the ring formed by the foamed dielectric material without the short conductive tube separated by the ring formed by the short conductive tube, and the ring formed by the foamed dielectric material without the short conductive tube separated by the ring formed by the short conductive tube and the dielectric cover, having different dielectric constant values, reflect electromagnetic waves passing through the lens in an opposite manner compared to the reflection from the circle formed by the dielectric cover and the short conductive tube, and the additional reflection from the ring formed by the short conductive tube, the ring formed by the foamed dielectric material without the short conductive tube separated by the ring formed by the short conductive tube and the ring, and the ring formed by the foamed dielectric material without the short conductive tube separated by the ring formed by the short conductive tube and the dielectric cover suppresses the reflection from the dielectric cover and the circle formed by the short conductive tube matched with the lens with free space.

2. The cylindrical focusing lens according to claim 1, characterized in that: The sheets of foamed dielectric material containing the short conductive tubes are separated by sheets of foamed dielectric material without the short conductive tubes.

3. The cylindrical focusing lens according to claim 1, characterized in that: The cross section of the short conductive tube is circular or polygonal.

4. The cylindrical focusing lens according to claim 1, characterized in that: The axes of the short conductive tubes forming a ring and a circle point in the same direction.

5. The cylindrical focusing lens according to claim 1, characterized in that: The axes of the short conductive tubes in different layers point in different directions.

6. The cylindrical focusing lens according to claim 1, characterized in that: The axis of the short conductive tube placed in one layer is perpendicular to the layer.

7. The cylindrical focusing lens according to claim 1, characterized in that: The axis of the short conductive tube placed in one layer is parallel to the layer.

8. The cylindrical focusing lens according to claim 1, characterized in that: The axes of the short conductive tubes placed in one layer are parallel to the layer, perpendicular to the axes of the short conductive tubes placed in other layers, and parallel to the other layers.

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