Radome and method of forming the same

Abstract

Various embodiments may relate to a radome. The radome may include a plurality of meta- material unit cells. The plurality of meta-material unit cells may be arranged such that one or more layers of meta-material unit cells of the plurality of meta-material unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of meta- material unit cells to form a honeycomb arrangement. The depths of the plurality of meta- material unit cells of at least a portion of the one or more layers may vary in a substantially parabolic manner with the layer of the one or more layers from the central meta-material unit cell.

Description

RADOME AND METHOD OF FORMING THE SAMECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore application No. 10202400785 Y filed March 20, 2024, the contents of it being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] Various embodiments of this disclosure may relate to a radome. Various embodiments of this disclosure may relate to a method of forming a radome.BACKGROUND

[0003] The term ‘radome’ comes from the combination of the terms “radar” and “dome”. As an integral part of the antenna system, the antenna radome protects the antenna from environmental conditions such as rain, snow, frost, and strong wind etc. The radome should have sufficient mechanical strength such that it would not be easily deformed under drastic environmental conditions. Furthermore, the radome should be transparent to the electromagnetic characteristics of the antenna, i.e., radiation pattern, and should have minimal attenuation to the signal passing through it. Various plastic materials such as polycarbonate, thermoplastics, polymer, polyimide and polyether ether ketone (PEEK) material are widely used in constructing conventional radomes. However, these materials are lossy to radiated radio wave signals, especially at very high frequencies, such as millimeter-wave (mmWave) frequencies. The reflection and absorption losses of such conventional radomes are very high and unpredictable for applications of mmWave imaging radar antenna (95 - 100 GHz) and sixth generation (6G) communication antenna (>100 GHz).

[0004] Tn recent years, meta-materials (MTM) or meta-surfaces and their applications have gotten tremendous attention among researchers in the field of microwaves and optics. It has been seen that extreme manipulation and control of incident electromagnetic waves, e g., beam shaping, cloaking, lens focusing etc., can be achieved with meta-material structures, which can be artificially engineered to attain desired values of dielectric permittivity and magnetic permeability.SUMMARY

[0005] Various embodiments may relate to a radome. The radome may include a plurality of meta-material unit cells. Each of the plurality of meta-material unit cells may include a side wall forming a hexagon and defining a hollow hexagonal cavity. Each of the plurality of metamaterial unit cells may also include an end wall extending from the side wall to cover a first end of the meta-material unit cell. A second end of each of the plurality of meta-material unit cells may be exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity. The plurality of meta-material unit cells may be arranged such that one or more layers of meta-material unit cells of the plurality of meta-material unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of meta-material unit cells to form a honeycomb arrangement. The depths of the plurality of meta-material unit cells of at least a portion of the one or more layers may vary in a substantially parabolic manner with the layer of the one or more layers from the central meta-material unit cell.

[0006] Various embodiments may relate to an antenna system including a radome and an antenna spaced from the radome. The radome may include a plurality of meta-material unit cells. Each of the plurality of meta-material unit cells may include a side wall forming a hexagon and defining a hollow hexagonal cavity. Each of the plurality of meta-material unit cells may also include an end wall extending from the side wall to cover a first end of the meta-materialunit cell. A second end of each of the plurality of meta-material unit cells may be exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity. The plurality of meta-material unit cells may be arranged such that one or more layers of meta-material unit cells of the plurality of meta-material unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of meta-material unit cells to form a honeycomb arrangement. The depths of the plurality of meta-material unit cells of at least a portion of the one or more layers may vary in a substantially parabolic manner with the layer of the one or more layers from the central meta-material unit cell.

[0007] Various embodiments may relate to a method of forming a radome. The method may include forming a plurality of meta-material unit cells. Each of the plurality of meta-material unit cells may include a side wall forming a hexagon and defining a hollow hexagonal cavity. Each of the plurality of meta-material unit cells may also include an end wall extending from the side wall to cover a first end of the meta-material unit cell. A second end of each of the plurality of meta-material unit cells may be exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity. The plurality of meta-material unit cells may be arranged such that one or more layers of meta-material unit cells of the plurality of meta-material unit cells are arranged in a concentric arrangement around a central metamaterial unit cell of the plurality of meta-material unit cells to form a honeycomb arrangement. The depths of the plurality of meta-material unit cells of at least a portion of the one or more layers may vary in a substantially parabolic manner with the layer of the one or more layers from the central meta-material unit cell.

[0008] Various embodiments may relate to a method of forming an antenna system. The method may include forming a radome. The radome may include a plurality of meta-material unit cells. Each of the plurality of meta-material unit cells may include a side wall forming a hexagon and defining a hollow hexagonal cavity. Each of the plurality of meta-material unitcells may also include an end wall extending from the side wall to cover a first end of the metamaterial unit cell. A second end of each of the plurality of meta-material unit cells may be exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity. The plurality of meta-material unit cells may be arranged such that one or more layers of meta-material unit cells of the plurality of meta-material unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of metamaterial unit cells to form a honeycomb arrangement. The depths of the plurality of metamaterial unit cells of at least a portion of the one or more layers may vary in a substantially parabolic manner with the layer of the one or more layers from the central meta-material unit cell. The method may also include providing an antenna spaced from the radome.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily drawn to scale, emphasis instead generally being placed upon illustrating the principles of various embodiments. In the following description, various embodiments of the invention are described with reference to the following drawings.FIG. 1 shows a general illustration of a radome according to various embodiments.FIG. 2 shows a general illustration of an antenna system according to various embodiments.FIG. 3 shows a general illustration of a method of forming the radome according to various embodimentsFIG. 4 shows a general illustration of a method of forming an antenna system according to various embodiments.FIG. 5A shows a perspective view of a unit cell according to various embodiments.FTG. 5B shows a cross-sectional perspective view of the unit cell according to various embodiments.FIG. 5C shows a traverse cross-sectional view of the unit cell according to various embodiments.FIG. 5D shows a simulation model of the unit cell according to various embodiments.FIG. 6A shows a plot of transmission coefficient S21 magnitude (in decibels or dB) as a function of cavity depth (in millimeters or mm) illustrating the S21 characteristics of unit cells with different cavity depths at 96 GHz according to various embodiments.FIG. 6B shows a plot of transmission coefficient S21 phase angle (in degrees) as a function of cavity depth (in millimeters or mm) illustrating the S21 characteristics of unit cells with different cavity depths at 96 GHz according to various embodiments.FIG. 7 shows a portion of a radome illustrating the concentric layering of unit cells according to various embodiments.FIG. 8 shows a schematic of a radome according to various embodiments.FIG. 9A shows a schematic of a 96 GHz square horn antenna according to various embodimentsFIG. 9B shows a schematic of a system including the horn antenna and the radome according to various embodiments.FIG. 9C shows a partial, three-dimensional view of the radome with 6 mm deep unit cells with the horn antenna according to various embodiments.FIG. 10 shows a plot of reflection coefficient S11 (in decibels or dB) as a function of frequency (in Giga-Hertz or GHz comparing the reflection coefficients Si l of a horn antenna, a system with a horn antenna and a solid radome, and a system with a horn antenna and a honeycomb meta-material radome of 6 mm cavity depth according to various embodiments.FTG. 1 1 shows simulated near-field electric field distributions at 96 GHz, taken on the YZ cutplane for (left) the antenna alone, (middle) a system including the antenna and the solid radome; and (right) a system including the antenna and the honeycomb meta-material radome according to various embodiments.FIG. 12A shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for the antenna alone according to various embodiments.FIG. 12B shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for a system including the antenna and the solid radome according to various embodiments.FIG. 12C shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for a system including the antenna and the honeycomb meta-material radome according to various embodimentsFIG. 13A shows a plot of gain (in decibels-isotropic or dBi) as a function of theta (in degrees) illustrating the two-dimensional (2D) cut plane (Phi-0 plane) results of the three-dimensional (3D) far-field gain patterns shown in FIGS. 12A-C for the various scenarios according to various embodiments.FIG. 13B shows a plot of gain (in decibels-isotropic or dBi) as a function of theta (in degrees) illustrating the two-dimensional (2D) cut plane (Phi-90 plane) results of the three-dimensional (3D) far-field gain patterns shown in FIGS 12A-C for the various scenarios according to various embodiments.FIG. 14 shows a partial, three-dimensional view of the distributed honeycomb meta-material radome with unit cells of different cavity depths and the horn antenna according to various embodiments.FIG. 15A shows a plot of cavity depth (in millimeters or mm) as a function of concentric layer illustrating the cavity depth profiles of a linearly distributed honeycomb meta-material radomeand a parabolic distributed honeycomb meta-material radome according to various embodiments.FIG. 15B shows a plot of S21 phase angle (in degrees) as a function of concentric layer illustrating the S21 phase profiles of a linearly distributed honeycomb meta-material radome and a parabolic distributed honeycomb meta-material radome according to various embodimentsFIG. 16 show s a plot of reflection coefficient S 11 (in decibels or dB) as a function of frequency (in Giga-Hertz or GHz) comparing the reflection coefficients Si l of the horn antenna alone, a system including the horn antenna and an uniform 6 mm depth honeycomb meta-material radome, a system including the horn antenna and a linearly distributed honeycomb metamaterial radome and a system including the horn antenna and a parabolic distributed honeycomb meta-material radome according to various embodiments.FIG. 17 shows simulated near-field electric field distributions at 96 GHz for (left) the antenna alone; (middle) a system including the antenna and the linearly distributed honeycomb metamaterial radome, and (right) a system including the antenna and the parabolic distributed honeycomb meta-material radome according to various embodiments.FIG. 18A shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for the antenna alone according to various embodiments.FIG. 18B shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for a system including the antenna and the linearly distributed radome honeycomb meta-material according to various embodiments.FIG. 18C shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for a system including the antenna and the parabolic distributed radome honeycomb meta-material according to various embodiments.FTG. 19A shows a plot of gain (in decibels-isotropic or dBi) as a function of theta (in degrees) illustrating the two-dimensional (2D) cut plane (Phi-0 plane) results of the three-dimensional (3D) far-field gain patterns shown in FIGS 18A-C for the various scenarios according to various embodiments.FIG. 19B shows a plot of gain (in decibels-isotropic or dBi) as a function of theta (in degrees) illustrating the two-dimensional (2D) cut plane (Phi-90 plane) results of the three-dimensional (3D) far-field gain patterns shown in FIGS. 18A-C for the various scenarios according to various embodiments.DESCRIPTION

[0010] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0011] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0012] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0013] Tn the context of various embodiments, the terms “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance, e g. within 10% of the specified value.

[0014] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0015] By “comprising” it is meant including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0016] By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0017] The design of MTM with unit-cells structure for radome application may have the advantages of being tunable and manipulable electromagnetic properties with unit-cells for desired parameters - high impedance matching, low dissipation factor, being able to influence and shape the radiation pattern and beamwidth of antennas for directivity and gain enhancement, as well as showing potential for mass production based on the engineering of the MTM radome structures.

[0018] FIG. 1 shows a general illustration of a radome according to various embodiments. The radome may include a plurality of meta-material unit cells 102. For the sake of clarity, only a few unit cells 102 in FIG. 1 have been labelled. Each of the plurality of meta-material (MTM) unit cells 102 may include a side wall 104 forming a hexagon and defining a hollow hexagonal cavity 106. Each of the plurality of meta-material unit cells 102 may also include an end wall (not shown in FIG. 1) extending from the side wall 104 to cover a first end of the meta-material unit cell 102. For the sake of clarity, the side wall 104 and cavity 106 of only one of the metamaterial unit cells 102 has been labelled. A second end of each of the plurality of meta-materialunit cells may be exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity 106. The plurality of meta-material unit cells 102 may be arranged such that one or more layers of meta-material unit cells 102 of the plurality of metamaterial unit cells 102 are arranged in a concentric arrangement around a central meta-material unit cell (shaded in a solid black in FIG. 1) of the plurality of meta-material unit cells 102 to form a honeycomb arrangement. While FIG 1 shows two layers of meta-material unit cells 102 (first layer being unshaded and second layer shaded by diagonal stripes), various embodiments may have any suitable number of layers. The depths of the plurality of meta-material unit cells 102 of at least a portion of the one or more layers may vary in a non-linear manner, e.g., a substantially parabolic manner with the layer of the one or more layers from the central metamaterial unit cell.

[0019] In other words, the radome may relate to a honeycomb arrangement of hexagonal meta-material unit cells 102. The depth of a unit cell 102 may be dependent on which layer of unit cells it is in from a central unit cell. All unit cells in the same layer may have substantially the same depth, while depths of unit cells in different layers may follow a non-linear relationship, e g., substantially parabolic relationship based on layer in which a particular unit cell is part of relative to a central unit cell.

[0020] For avoidance of doubt, FIG. 1 seeks to illustrate features of the radome according to various embodiments, and is not intended to limit features such as the number of layers (as mentioned above), the dimensions of the unit cells (unit cells may be of any suitable dimensions), orientation of the radome etc.

[0021] As mentioned above, the depths of some layers of the radome may vary in a substantially parabolic manner with the layer of the one or more layers from the central metamaterial unit cell. The phrase “parabolic manner" may mean that the depth y may vary with the layer x (in which the unit cell is part of) via the relationship y — Ax2+ Bx + C, where A, Band C are any suitable constants and The term “substantially” may mean a variance of tolerance of ±10%. The radome may alternatively be referred to as a parabolic distributed metamaterial radome or a parabolic distributed honeycomb meta-material radome.

[0022] In various embodiments, the depth of the cavity of the central meta-material unit cell may be the lowest or shortest, and the depth of the cavity of a particular meta-material unit cell may increase with the layer from the central meta-material unit cell. The depth of the cavity of a particular meta-material unit cell may increase at an increasing rate or a decreasing rate with the layer from the central meta-material unit cell.

[0023] In various other embodiments, the depth of the cavity of the central meta-material unit cell may be the highest or longest, and the depth of the cavity of a particular meta-material unit cell may decrease with the layer from the central meta-material unit cell The depth of the cavity of a particular meta-material unit cell may decrease at an increasing rate or a decreasing rate with the layer from the central meta-material unit cell.

[0024] In various embodiments, the plurality of meta-material unit cells may include a dielectric material. The dielectric material may be a plastic material, such as polycarbonate, thermoplastics, polymer, polyimide or polyether ether ketone (PEEK).

[0025] In various embodiments, the side wall 104 and the end wall of a unit cell 102 may be made of or include the same dielectric material. In various embodiments, all the unit cells 102 in the radome may be made of or include the same dielectric material.

[0026] In various embodiments, the radome may further include a frame surrounding the plurality of meta-material unit cells 102. The frame may be of any suitable shape, for instance, rectangular, square or circular shape.

[0027] In various embodiments, the frame and the plurality of meta-material unit cells 102 may be made of or include a same dielectric material. In various other embodiments, the frameand the plurality of meta-material unit cells 102 may be made of or include different dielectric materials.

[0028] In various embodiments, the radome may be configured to be substantially transparent to millimeter-waves. A millimeter-wave may be a high frequency wave having a frequency selected from a range from 30 GHz to 300 GHz, e.g., 96 GHz. The radome being “substantially transparent” to millimeter-waves may mean that the transmittance of millimeterwaves through the radome may be 80% or more, e.g., 90% or more, e.g., 95% or more.

[0029] In various embodiments, different layers of the one or more layers may contribute different S21 phase angles. A “S21 phase angle” may be defined as the phase difference between the phase of the wave transmitted through the radome, and the phase when the wave is incident onto the radome.

[0030] FIG. 2 shows a general illustration of an antenna system according to various embodiments. The antenna system may include a radome 200 as described herein and an antenna 202 spaced from the radome 200.

[0031] For avoidance of doubt, FIG. 2 is intended to illustrate some features of an antenna system according to various embodiments, and is not intended to limit, for instance, the shape, dimensions, arrangement etc. of the various features.

[0032] In various embodiments, the antenna 202 may be any suitable antenna. In various embodiments, the antenna 202 may be a square horn antenna.

[0033] In various embodiments, the end walls of the plurality of meta-material unit cells may face the antenna 202.

[0034] FIG. 3 shows a general illustration of a method of forming the radome according to various embodiments. The method may include, in 302, forming a plurality of meta-material unit cells. Each of the plurality of meta-material unit cells may include a side wall forming a hexagon and defining a hollow hexagonal cavity. Each of the plurality of meta-material unitcells may also include an end wall extending from the side wall to cover a first end of the metamaterial unit cell. A second end of each of the plurality of meta-material unit cells may be exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity. The plurality of meta-material unit cells may be arranged such that one or more layers of meta-material unit cells of the plurality of meta-material unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of metamaterial unit cells to form a honeycomb arrangement. The depths of the plurality of metamaterial unit cells of at least a portion of the one or more layers may vary in a non-linear manner, e.g., a substantially parabolic manner with the layer of the one or more layers from the central meta-material unit cell.

[0035] Tn other words, various embodiments may relate to a method of forming a radome including a plurality of unit cells.

[0036] In various embodiments, the plurality of meta-material unit cells may include a dielectric material. In various embodiments, the radome or the plurality of unit cells may be formed via three-dimensional (3D) printing. An ink containing the dielectric material may be used to print the radome including the plurality of unit cells. Tn various other embodiments, the radome may be formed by any other suitable means.

[0037] In various embodiments, the method may also include forming a frame surrounding the plurality of meta-material unit cells. In various embodiments, the frame may be formed integrally together with the plurality of meta-material unit cells, e.g., via 3D printing. In various other embodiments, the frame and the plurality of meta-material unit cells may be formed separately, and may be attached together via a suitable means, e.g., adhesive or via melting the dielectric material.

[0038] In various embodiments, the frame may be of any suitable shape, e g., rectangular, square or circular.

[0039] Tn various embodiments, the frame and the plurality of meta-material unit cells may be made of or may include a same dielectric material. In various other embodiments, the frame and the plurality of meta-material unit cells may be made of or include different dielectric materials.

[0040] In various embodiments, the radome may be configured to be substantially transparent to millimeter-waves.

[0041] In various embodiments, different layers of the one or more layers may contribute different S21 phase angles.

[0042] FIG. 4 shows a general illustration of a method of forming an antenna system according to various embodiments. The method may include, in 402, forming or providing a radome as described herein. The method may also include, in 404, forming or providing an antenna spaced from the radome.

[0043] For avoidance of doubt, FIG. 4 is intended to illustrate some steps of forming an antenna system and is not intended to be in sequence. Step 402 may occur before, after or at the same time as step 404.

[0044] In various embodiments, the antenna may be any suitable antenna, e g., a square horn antenna.

[0045] In various embodiments, the end walls of the plurality of meta-material unit cells may face the antenna.

[0046] Various embodiments may relate to a planar meta-material radome for millimeterwave (mmWave) antenna system that operates at 96GHz. The meta-material radome may be transparent to the radiating electromagnetic wave of the antenna system, and / or may enhance the antenna performance characteristics of the antenna system. The design of the meta-material radome may start with evaluating the performance characteristics of single unit-cell. The unitcell may be meant to be all-dielectric, meaning no conductive component is involved, so as notto introduce additional electric conductivity loss. One key feature of the unit-cell is the inclusion of a cavity, to tune the transmission coefficient (S21) characteristics while maintaining the overall external dimensions of the unit-cell. The unit-cell may take the form of a hexagon pillar, and may be populated in a concentric pattern, layer after layer, to form the meta-material radome. The concentric layering of the unit-cells may be meant to concentrate the radiating energy of the antenna to a narrower region, hence minimizing side interference. Such a meta-material radome may contribute towards aerospace communication applications, such as mmWave imaging radar, as well as future 6G communication applications.

[0047] As mentioned above, the radome may be made up of multiple hexagon sharped unitcells arranged in concentric layers to wholly cover the surface area of the radome. The unitcells may generate different phase angles

[0048] Hexagonal Unit Cell

[0049] FIG. 5A shows a perspective view of a unit cell 502 according to various embodiments. FIG. 5B shows a cross-sectional perspective view of the unit cell 502 according to various embodiments. FIG. 5C shows a traverse cross-sectional view of the unit cell 502 according to various embodiments. The unit-cell 502 may take the form of a hexagon pillar, with side-width of 0.75 mm (quarter of a wavelength at 96GHz) and height of 6.5 mm. A hexagon cavity 504 may be introduced in the hexagon unit-cell, with its opening on the top surface of the unit-cell 502 (i.e., exposed end). The cavity 504 may be defined by the side wall 506 and end wall 508 (i.e., at the bottom surface opposite the top surface). The cavity depth, as labelled in FIG. 5B, may be an important parameter of the unit-cell 502 as different cavity depths may result in different S-parameter characteristics. The hexagon unit-cell 502 may be an all-dielectric unit cell, made of three-dimensional (3D) printed plastic material with dielectric constant of 2.81 and electric tangent loss of 0.014. The unit-cell 502 may not have any conductive component so as not to introduce additional conductivity losses.

[0050] Computational electromagnetic simulations were carried out to study the influence of the cavity depth of the unit cell 502 on the S-parameter characteristics, in particular the Transmission Coefficient S21 magnitude and phase angle. FIG. 5D shows a simulation model of the unit cell 502 according to various embodiments. As shown in FIG. 5D, the simulation model may have a wave port (WavePort-1) setup as the transmitting source, below the bottom surface of the unit-cell 502, and a wave port (WavePort-2) setup as the receiving end, above the top surface of the unit-cell 502. Simulated data of the transmission coefficient (S21) between WavePort-1 and WavePort-2 may be captured for different cavity depths ranging from 0 to 6 mm. FIG. 6A shows a plot of transmission coefficient S21 magnitude (in decibels or dB) as a function of cavity depth (in millimeters or mm) illustrating the S21 characteristics of unit cells with different cavity depths at 96 GHz according to various embodiments. FIG. 6B shows a plot of transmission coefficient S21 phase angle (in degrees) as a function of cavity depth (in millimeters or mm) illustrating the S21 characteristics of unit cells with different cavity depths at 96 GHz according to various embodiments. As the application of the unit cell is on a radome, a reasonable S21 magnitude would be above -2 dB. From FIG. 6B, it can be observed that changing the cavity depth tends to shift the S21 phase angle. With cavity depths between 0 to 6 mm, the S21 phase angle can be seen shifting between -180° to 180°.

[0051] Honeycomb Meta-material Radome

[0052] To form the meta-material radome, the hexagon unit-cell as described above may be laid out in a concentric pattern to form a honeycomb structure as shown in FIG. 7. FIG. 7 shows a portion of a radome illustrating the concentric layering of unit cells according to various embodiments. The structure may share a common hexagon unit-cell (i.e., central meta-material unit cell or Centre-cell) which is labelled as “C”. The first concentric layer of hexagon unitcells (Layerl -cells) surrounding the Centre-cell is labelled as “a”. The second concentric layer of hexagon unit-cells (Layer2-cells) that encloses Layerl-cells is labelled as “b”, following withthe third concentric layer Layer3-cells (labelled as “c”) enclosing Layer2-cell s, the fourth concentric layer Lay er4-cells (labelled as “d”) enclosing Layer3-cells and so on. The concentric layering of unit-cells may be expanded until the honeycomb structure fills up the space within a 26 mm by 26 mm radome frame as illustrated in FIG. 8. FIG. 8 shows a schematic of a radome according to various embodiments. The radome frame 810 may be made of the same plastic material as that of the hexagon unit-cells 802, with dielectric constant of 2.81 and electric tangent loss of 0.014.

[0053] To evaluate the performance characteristics of the honeycomb meta-material radome in FIG. 8, the radome may be placed in front of a square horn antenna. FIG. 9A shows a schematic of a 96 GHz square horn antenna 902 according to various embodiments. The horn antenna 902 an aperture opening of 10.05 mm by 10.05 mm with a length of 20.09 mm, operating at 96GHz. In this evaluation, the meta-material radome 900 is placed half a wavelength (which is 1.5mm at 96GHz) in front of the horn antenna 902, with the antenna aperture opening facing the bottom surface of the radome as illustrated in FIGS. 9B - C. In other words, the end walls of the plurality of meta-material unit cells face the antenna 902. FIG. 9B shows a schematic of a system including the horn antenna 902 and the radome 900 according to various embodiments. FIG. 9C shows a partial, three-dimensional view of the radome 900 with 6 mm deep unit cells with the horn antenna 902 according to various embodiments. For better illustration, FIG. 9C shows only one-quarter of the honeycomb structure presented in FIG. 8. Each unit cell in the meta-material radome 900 has identical cavity depth at 6 mm, which may contribute towards a S21 phase angle of -1.46° (closest to 0°). This may be equivalent to a radome with uniform S21 phase angle throughout the radome surface dimensions

[0054] The evaluation of the meta-material radome was carried out using computational electromagnetic simulation to study the antenna performance characteristics in the form of itsreflection coefficient SI 1 , near-field distribution and far-field characteristics FIG. 10 shows a plot of reflection coefficient S I 1 (in decibels or dB) as a function of frequency (in Giga-Hertz or GHz comparing the reflection coefficients Si l of a horn antenna, a system with a horn antenna and a solid radome, and a system with a horn antenna and a honeycomb meta-material radome of 6 mm cavity depth according to various embodiments.

[0055] In the case of solid radome, it is a full block of radome with the same outer dimension of 26 mm by 26 mm by 6.5 mm, and same material properties (dielectric constant at 2.81 and electric tangent loss at 0.014) as the meta-material radome. From FIG. 10, it can be observed that the inclusion of either radome may cause an impedance mismatch towards the antenna, hence resulting in reduction of the SI 1 of the original horn antenna. A typical acceptable SI 1 is to maintain the level at below -10 dB within its operating frequency range. From the plots in FIG. 10, the solid radome has better Si l characteristics of less than -16 dB, while the honeycomb meta-material radome offers Si l of less than -10 dB at frequency between 95 GHz and 97 GHz.

[0056] FIG. 11 shows simulated near-field electric field distributions at 96 GHz, taken on the YZ cut-plane for (left) the antenna alone; (middle) a system including the antenna and the solid radome; and (right) a system including the antenna and the honeycomb meta-material radome according to various embodiments. It can be observed from FIG. 11 that the electric field strength is weakened after going through either radome.

[0057] FIG. 12A shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for the antenna alone according to various embodiments. FIG. 12B shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for a system including the antenna and the solid radome according to various embodiments. FIG 12C shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for a system including the antenna and the honeycomb metamaterial radome according to various embodiments. A slight change in the antenna gain patterncan be observed when a radome is added in front of the antenna, and its peak gain value can be seen dropping from 20 dBi to 18 dBi and 18.55 dBi for solid radome and meta-material radome respectively.

[0058] FIG. 13 A shows a plot of gain (in decibels-isotropic or dBi) as a function of theta (in degrees) illustrating the two-dimensional (2D) cut plane (Phi-0 plane) results of the three- dimensional (3D) far-field gain patterns shown in FIGS 12A-C for the various scenarios according to various embodiments. FIG. 13B shows a plot of gain (in decibels-isotropic or dBi) as a function of theta (in degrees) illustrating the two-dimensional (2D) cut plane (Phi-90 plane) results of the three-dimensional (3D) far-field gain patterns shown in FIGS. 12A-C for the various scenarios according to various embodiments. On the Phi-0 plane shown in FIG. 13 A, the difference in the 2D gain plot between the three different scenarios is minor. On the Phi- 90 plane shown in FIG. 13B, an increase in the back lobe can be seen taking place when either radome is added in front of the antenna. Table 1 below summarizes the far-field characteristics for the three different scenarios presented in FIGS. 12A-C and FIGS. 13A-B.0059] Table 1. Summary of far-field gain characteristics at 96GHz

[0060] Distributed Honeycomb Meta-Material Radome

[0061] The previous section presents a honeycomb meta-material radome that is built using hexagon unit-cells with uniform cavity depth, with all the unit-cells contributing identical S21 characteristics This section presents a honeycomb meta-material radome that is built using hexagon unit-cells of different cavity depths, and such a radome may be referred as a distributed honeycomb meta-material radome.

[0062] FIG. 14 shows a partial, three-dimensional view of the distributed honeycomb metamaterial radome 1400 with unit cells of different cavity depths and the horn antenna 1402 according to various embodiments. The distributed honeycomb meta-material radome may have each concentric layer of hexagon unit-cells contributing towards different S21 phase angles, meaning each concentric layer of unit-cells has different cavity depths. Two types of distributed honeycomb meta-material radomes may be a linearly distributed honeycomb metamaterial radome, and a parabolic distributed honeycomb meta-material radome.

[0063] Linearly Distributed Honeycomb Meta-Material Radome

[0064] In linearly distributed honeycomb meta-material radome, each concentric layer of hexagon unit-cells may be designed to contribute towards S21 phase angle that will result in a phase difference of 15° between each concentric layer. Ideally, the Centre-cell may contribute S21 phase angle of 0°, the Layer- 1 cells may contribute S21 phase angle of 15°, the Layer-2 cells may contribute S21 phase angle of 30°, the Layer-3 cells may contribute S21 phase angle of 45° and so on. Table 2 lists the cavity depths and the contributing S21 phase angles of the respective concentric layers of hexagon unit-cells on the linearly distributed honeycomb metamaterial radome.0065] Table 2. Linearly distributed concentric layer of unit-cells

[0066] The cavity depths may be selected in a way such that the respective unit-cell can contribute a S21 phase angle as close to the target phase angle listed in the last column of Table 2.

[0067] Parabolic Distributed Honeycomb Meta-Material Radome

[0068] In the parabolic distributed honeycomb meta-material radome, an algorithm may be developed and used to calculate the S21 phase angle that each concentric layer of hexagon unitcells is contributing. The fundamental idea of the developed algorithm, which is further developed from the phase-gradient refractive index metasurfaces for the applications in mmWave / sub-THz domain, is to enforce a mapping between any pre-defined phase distribution (parabolic, hyperbolic, etc.) on a plane right-above the meta-material (MTM) surface to the corresponding unit-cells, which have the S21 phase values approximately follow the ones in the distribution spatially. Indeed, the wave emitted from the horn antenna traveling througheach unit-cell may be slower or faster along the propagating direction depending on the unitcell medium’s characteristic, which is reflected in its phase profile.

[0069] Different optimization methods have been implemented to enforce the mapping based on the distribution required that can achieve either beam shaping or beam steering capabilities of the MTM.

[0070] The developed algorithm can also be formulated as an inverse design approach, where the objective function is defined to maximize gain, minimize 3dB beamwidth, and suppress the sidelobe to achieve the optimal distributed unit-cells (honeycomb or newly design ones).

[0071] Table 3 lists the cavity depths and the contributing S21 phase angles of the respective concentric layers of hexagon unit-cells on the parabolic distributed honeycomb meta-material radome.0072] Table 3. Parabolic distributed concentric layer of unit-cells

[0073] FIG. 15A shows a plot of cavity depth (in millimeters or mm) as a function of concentric layer illustrating the cavity depth profiles of a linearly distributed honeycomb metamaterial radome and a parabolic distributed honeycomb meta-material radome according to various embodiments. From FIG. 15A, the linearly distributed meta-material radome has a cavity depth profile that increases almost linearly from 0 to 3.7 mm, with increasing concentric layers of unit-cells (i.e., from layer 0 to layer 15). The parabolic distributed meta-material radome has a cavity depth profile that increases in a parabolic trend from 0 to 5.8 mm, with increasing concentric layers of unit-cells across a portion of the concentric layers (i.e., from layer 0 to layer 11). The cavity depth stays constant at 5.8 mm from layer 11 to layer 15.

[0074] FIG. 15B shows a plot of S21 phase angle (in degrees) as a function of concentric layer illustrating the S21 phase profiles of a linearly distributed honeycomb meta-material radome and a parabolic distributed honeycomb meta-material radome according to various embodiments A similar trend can be seen in FIG. 15B, the linearly distributed metal -material radome has a S21 phase angle profile that increases almost linearly from 4.3° to 222.15° (i.e., from layer 0 to layer 15) while the parabolic distributed meta-material radome has a S21 phase angle profile that increases in a parabolic trend from 4.3° to 348.81° (i.e., from layer 0 to layer 11). In other words, the S21 phase profile may be proportional to the cavity depth profile of a radome.

[0075] FIG. 16 shows a plot of reflection coefficient Si l (in decibels or dB) as a function of frequency (in Giga-Hertz or GHz) comparing the reflection coefficients Si l of the horn antenna alone, a system including the horn antenna and an uniform 6 mm depth honeycomb meta-material radome, a system including the horn antenna and a linearly distributed honeycomb meta-material radome, and a system including the horn antenna and a parabolic distributed honeycomb meta-material radome according to various embodiments. From FIG.16, it can be observed that the distributed honeycomb meta-material radomes may slightly improve the impedance matching towards the antenna as compared to the uniform honeycomb meta-material radome.

[0076] FIG. 17 shows simulated near-field electric field distributions at 96 GHz for (left) the antenna alone; (middle) a system including the antenna and the linearly distributed honeycomb meta-material radome; and (right) a system including the antenna and the parabolic distributed honeycomb meta-material radome according to various embodiments. The field distributions were taken on the YZ cut-plane. From the field distribution plot shown in FIG. 17, it can be observed that both distributed honeycomb meta-material radomes may help to strengthen the electric field strength by directing and focusing the electric field towards the center regions. This phenomenon may be stronger in the case of the parabolic distributed honeycomb meta-material radome.

[0077] FIG. 18A shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for the antenna alone according to various embodiments. FIG. 18B shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for a system including the antenna and the linearly distributed radome honeycomb meta-material according to various embodiments. FIG 18C shows a three-dimensional (3D) far-field antenna gain pattern at 96 GHz for a system including the antenna and the parabolic distributed radome honeycomb meta-material according to various embodiments. From the simulated gain patterns shown in FIGS. 18A - C, it can be observed that the distributed honeycomb meta-material radomes may help to sharpen the main- lobe radiation beam and reduce the sidelobe With the linearly distributed honeycomb metamaterial radome, the peak gain value can be seen increasing to 19.7 dBi, while the parabolic distributed honeycomb meta-material radome increases the peak gain to 20.7 dBi.

[0078] FIG. 19A shows a plot of gain (in decibels-isotropic or dBi) as a function of theta (in degrees) illustrating the two-dimensional (2D) cut plane (Phi-0 plane) results of the three-dimensional (3D) far-field gain patterns shown in FIGS 18A-C for the various scenarios according to various embodiments. FIG. 19B shows a plot of gain (in decibel s-isotropic or dBi) as a function of theta (in degrees) illustrating the two-dimensional (2D) cut plane (Phi-90 plane) results of the three-dimensional (3D) far-field gain patterns shown in FIGS. 18A-C for the various scenarios according to various embodiments. On both Phi-0 and Phi-90 planes shown in FIGS. 19A - B respectively, the gain pattern has sharpened main-lobe and reduced sidelobe when distributed honeycomb meta-material radome is added to the antenna. Table 4 below summarizes the far-field characteristics for the three far-field patterns presented in FIGS. 18A - C and FIGS. 19A - B. The simulated results show that the parabolic distributed meta-material radome may offer a better solution to improve the antenna performance in sharpening the radiating beam, increasing the peak gain as well as reducing the sidelobe of the antenna0079] Table 4. Summary of far-field gain characteristics at 96GHz

[0080] Various embodiments may relate to a meta-material radome for mmWave antenna system operating at 96GHz. The meta-material radome may be made up of hexagon unit-cells arranged in concentric layering, with each concentric layer of unit-cells contributing towards different transmission coefficient S21 phase angles. This arrangement of the unit-cells can modify the antenna radiation pattern such that its main radiating beam can be more focused and reduce side-lobe level to minimize side interference. The radome size may not be bound by the dimensions indicated herein, and may be extended infinitely to accommodate antenna systems of larger sizes. This radome may contribute towards aerospace communication applications such as mmWave imaging radar, as well as future 6G communication applications.

Claims

Claims1. A radome cornpri sing : a plurality of meta-material unit cells; wherein each of the plurality of meta-material unit cells comprises a side wall forming a hexagon and defining a hollow hexagonal cavity, each of the plurality of meta-material unit cells also comprising an end wall extending from the side wall to cover a first end of the meta-material unit cell; wherein a second end of each of the plurality of meta-material unit cells is exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity; wherein the plurality of meta-material unit cells is arranged such that one or more layers of meta-material unit cells of the plurality of meta-material unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of meta-material unit cells to form a honeycomb arrangement; and wherein the depths of the plurality of meta-material unit cells of at least a portion of the one or more layers vary in a substantially parabolic manner with the layer of the one or more layers from the central meta-material unit cell.

2. The radome according to claim 1, wherein the plurality of meta-material unit cells comprises a dielectric material.

3. The radome according to claim 1, further comprising: a frame surrounding the plurality of meta-material unit cells.

4. The radome according to claim 3, wherein the frame is rectangular, square or circular.

5. The radome according to claim 3, wherein the frame and the plurality of meta-material unit cells comprise a same dielectric material.

6. The radome according to claim 1, wherein the radome is configured to be substantially transparent to millimeterwaves.

7. The radome according to claim 1, wherein different layers of the one or more layers contribute different S21 phase angles.

8. An antenna system comprising: a radome comprising: a plurality of meta-material unit cells; wherein each of the plurality of meta-material unit cells comprises a side wall forming a hexagon and defining a hollow hexagonal cavity, each of the plurality of meta-material unit cells also comprises an end wall extending from the side wall to cover a first end of the meta-material unit cell; wherein a second end of each of the plurality of meta-material unit cells is exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity;wherein the plurality of meta-material unit cells is arranged such that one or more layers of meta-material unit cells of the plurality of metamaterial unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of meta-material unit cells to form a honeycomb arrangement; and wherein the depths of the plurality of meta-material unit cells of at least a portion of the one or more layers vary in a substantially parabolic manner with the layer of the one or more layers from the central metamaterial unit cell; and an antenna spaced from the radome.

9. The antenna system according to claim 8, wherein the antenna is a square horn antenna.

10. The antenna system according to claim 8, wherein the end walls of the plurality of meta-material unit cells face the antenna.

11. A method of forming a radome, the method comprising: forming a plurality of meta-material unit cells; wherein each of the plurality of meta-material unit cells comprises a side wall forming a hexagon and defining a hollow hexagonal cavity, each of the plurality of meta-material unit cells also comprising an end wall extending from the side wall to cover a first end of the meta-material unit cell; wherein a second end of each of the plurality of meta-material unit cells is exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity;wherein the plurality of meta-material unit cells is arranged such that one or more layers of meta-material unit cells of the plurality of meta-material unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of meta-material unit cells to form a honeycomb arrangement; and wherein the depths of the plurality of meta-material unit cells of at least a portion of the one or more layers vary in a substantially parabolic manner with the layer of the one or more layers from the central meta-material unit cell.

12. The method according to claim 11, wherein the plurality of meta-material unit cells comprises a dielectric material.

13. The method according to claim 11, further comprising: forming a frame surrounding the plurality of meta-material unit cells.

14. The method according to claim 13, wherein the frame is rectangular, square or circular.

15. The method according to claim 13, wherein the frame and the plurality of meta-material unit cells comprise a same dielectric material.

16. The method according to claim 11, wherein the radome is configured to be substantially transparent to millimeterwaves.

17. The method according to claim 11,wherein different layers of the one or more layers contribute different S21 phase angles.

18. A method of forming an antenna system, the method comprising: forming a radome comprising: a plurality of meta-material unit cells; wherein each of the plurality of meta-material unit cells comprises a side wall forming a hexagon and defining a hollow hexagonal cavity, each of the plurality of meta-material unit cells also comprises an end wall extending from the side wall to cover a first end of the meta-material unit cell; wherein a second end of each of the plurality of meta-material unit cells is exposed, a distance between the first end and the second end defining a depth of the hollow hexagonal cavity; wherein the plurality of meta-material unit cells is arranged such that one or more layers of meta-material unit cells of the plurality of metamaterial unit cells are arranged in a concentric arrangement around a central meta-material unit cell of the plurality of meta-material unit cells to form a honeycomb arrangement; and wherein the depths of the plurality of meta-material unit cells of at least a portion of the one or more layers vary in a substantially parabolic manner with the layer of the one or more layers from the central metamaterial unit cell; and providing an antenna spaced from the radome.

19. The method according to claim 18, wherein the antenna is a square horn antenna.

20. The method according to claim 18, wherein the end walls of the plurality of meta-material unit cells face the antenna.

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