The disclosure relates to antennas, and in particular, to the configuration and application of a metasurface lens to modify the performance of an antenna.
The advent of cellular radio systems has seen a great demand for base station antennas able to operate over wide frequency bandwidths while maintaining parameters such as gain, beamwidth and voltage standing wave ratio (VSWR) within limits that are acceptable for their intended function. National and international radiocommunications administrations have continued to assign additional frequency bands for use by cellular mobile radio networks. As a consequence, mobile radio network operators desire base station antennas providing for operation over increased bandwidths.
According to a non-limiting embodiment, an antenna includes a radiating structure to radiate electromagnetic waves having a phase along a radiating path extending in an axial direction, and a lens disposed in the radiating path and configured to pass the electromagnetic waves therethrough. The lens includes at least one lamina having a first surface, a second surface, a center axis that is aligned with the axial direction, a lamina thickness between the first surface and the second surface in a direction parallel to the axial direction, and an axial region extending about the center axis. Conductive scattering elements are arranged on the first surface, the second surface or both the first surface and the second surface. The conductive scattering elements are configured to change a first phase of the electromagnetic waves passing through the plurality of conductive scattering elements with respect to a second phase of the electromagnetic waves passing through the axial region.
In additional embodiments, or as an alternative, an amount of back-scattered energy reflected by the axial region is less than an amount of back-scattered energy reflected by the non-axial region.
In additional embodiments, or as an alternative, the axial region of the lens includes an area devoid of the conductive scattering elements.
In additional embodiments, or as an alternative, the conductive scattering elements include at least one of planar conductive scattering elements shaped as unfilled polygons, planar conductive scattering elements shaped as filed polygons, planar conductive scattering elements shaped as circular closed lines, and planar conductive scattering elements shaped as filled circles.
In additional embodiments, or as an alternative, the conductive scattering elements have a profile of one or a combination of concentric circles, ellipses, and polygons.
In additional embodiments, or as an alternative, the conductive scattering elements are arranged in rows extending in a radial direction with respect to the axial direction.
In additional embodiments, or as an alternative, the conductive scattering elements are disposed in a rectilinear arrangement that forms a plurality of row and a plurality of columns.
In additional embodiments, or as an alternative, the at least one lamina includes at least one of a planar lamina or a curved lamina.
In additional embodiments, or as an alternative, at least one lamina includes a plurality of laminas arranged in series next to one another along the axial direction. Each of the laminas includes a first lamina including a first plurality of conductive scattering elements having a first arrangement, a first shape, and a first size, and a second lamina including a first plurality of conductive scattering elements having a second arrangement, a second shape, and a second size. The at least one of the second arrangement, the second shape, and the second size is different from the first arrangement, the first shape, and the first size, respectively.
In additional embodiments, or as an alternative, the at least one radiating structure operates at a frequency greater than or equal to 0.5 gigahertz (Ghz) and less than or equal to 100 GHz.
According to another non-limiting embodiment, a metasurface lens comprises at least one lamina configured to pass electromagnetic waves traveling along a radiating path that extends along an axial direction of at least one radiating structure. The at least one lamina includes a first surface extending to an opposing second surface in a direction parallel to the axial direction to define a lamina thickness, an axial region extending radially from a center axis of the at least one lamina and configured to align with the radiating structure along the axial direction, and a plurality of conductive scattering elements arranged on one or both of the first surface and the second surface. The plurality of conductive scattering elements are configured to change the phase of the electromagnetic waves passing therethrough with respect to the phase of the electromagnetic waves passing through the axial region.
According to yet another non-limiting embodiment, a method of transmitting electromagnetic waves from an antenna is provided. The method comprises radiating, from at least one radiating structure, electromagnetic waves having a first phase, directing the electromagnetic waves along a radiating path extending in an axial direction, and passing the electromagnetic waves through an axial region of a lens including at least one lamina and a plurality of conductive scattering elements. The plurality of conductive scattering elements change the first phase of the electromagnetic waves to a second phase, wherein the first phase is different from the second phase.
In additional embodiments, or as an alternative, the method further includes delivering the electromagnetic waves having a wavefront curvature to an outer portion of the at least one lamina located adjacent an outer perimeter of the at least one lamina and to an inner portion of the lamina located between the outer portion and the axis region, and reducing the wavefront curvature in response to passing the electromagnetic waves through the outer portion and the inner portion.
In additional embodiments, or as an alternative, reducing the wavefront curvature includes delivering a first portion of the electromagnetic waves to the inner portion which includes at least one inner conductive scattering element among the plurality of conductive scattering elements; delivering a second portion of the electromagnetic waves to the outer portion which includes at least one outer conductive scattering element among the plurality of conductive scattering elements disposed; effecting a first phase advance on the first portion of the electromagnetic waves passing through the at least one inner conductive scattering element; and effecting a second phase advance greater than the first phase advance on the second portion of the electromagnetic waves passing through the at least one outer conductive scattering element.
According to another non-limiting embodiment, a method of manufacturing an antenna is provided. The method comprises providing at least one radiating structure configured to radiate electromagnetic waves having a first phase along a radiating path extending in an axial direction, and providing a lens disposed in the radiating path and configured to pass the electromagnetic waves therethrough. The lens includes at least one lamina having a first surface, a second surface, a center axis that is aligned with the axial direction, a lamina thickness between the first surface and the second surface in a direction parallel to the axial direction, and an axial region extending about the center axis; and a plurality of conductive scattering elements arranged on the first surface, the second surface or both the first surface and the second surface. The conductive scattering elements are configured to change the first phase of the electromagnetic waves passing through the plurality of conductive scattering elements to a second phase.
According to still another non-limiting embodiment, a method of transmitting electromagnetic waves from an antenna is provided. The method comprises at least one of providing and identifying at least one radiating structure; radiating, from the at least one radiating structure, electromagnetic waves having a phase; and directing the electromagnetic waves along a radiating path extending in an axial direction. The method further comprises disposing a lens in the radiating path. The lens includes at least one lamina having an axial region aligned with respect to the axial direction and having a plurality of conductive scattering elements. The method further comprises passing the electromagnetic waves through the axial region and the plurality of conductive scattering elements. The plurality of conductive scattering elements change the phase of the electromagnetic waves with respect to the phase of the electromagnetic waves passing through the axial region.
Most modern mobile radio networks are planned using base station antennas having a directional azimuth radiation pattern with a nominal half-power azimuth beamwidth. Such beamwidth may be between 60 degrees and 65 degrees. A single base station antenna may include a vertical column of dual-polar radiating elements, transmitting and receiving signals with linear polarizations inclined ±45 degrees to the vertical. Antenna arrays may include a plurality of radiating structures such as crossed dipoles and patches, mounted in front of a reflector. According to a non-limiting embodiment, the configuration of radiating structures and the reflector geometry are chosen by design to provide the required azimuth beamwidth, optimized as far as possible such that the nominal beamwidth is maintained over the widest possible range of frequencies (often referred to as “bandwidth” of the antenna).
A modern base station antenna may include a plurality of independent dual-polar antenna arrays arranged in a single physical housing. These may operate in the same frequency band, or in different frequency bands that are assigned to cellular radio networks.
In an exemplary embodiment, design parameters that together provide the required azimuth beamwidth of an antenna array include the choice of the antenna elements, their spacing from a conductive reflector placed behind them, and the cross-sectional geometry of the reflector. For example, the reflector may be a flat plate of chosen width, or may be bent, curved, flanged or slotted. Conductive enclosures that surround each radiating element may be provided, along with parasitic elements that operate cooperatively with the radiating elements and reflector.
In an exemplary embodiment, one or more lenses may be placed in front of an antenna or radiating structure. Such lenses can be convex lenses, or equivalent, whose function is to focus the energy radiated from the element, reducing the beamwidth provided by the element itself, and increasing its gain. In an exemplary embodiment, lenses are made from dielectric materials, for example polyethylene, but they have the characteristic that while most of the energy impinging on the lens may be transmitted in a forward beam, some energy is reflected by the surfaces of the lens and the reflected power is then received by the radiating element. The effect of this reflected power is to change the impedance presented by the radiating element to its feed line. According to the feed arrangements for an array of elements, this may disrupt the elevation radiation pattern of a base station antenna, and is very likely to increase the voltage standing wave ratio (VSWR) presented by the array to its feed line. In both cases such effects may be undesirable and generally become more troublesome for an antenna requiring a wide operating bandwidth. This is because the distance between the element and the lens causes the phase of the reflected signal to change with frequency, making it difficult to compensate the undesirable effects of the reflected signal on the input impedance of the element over a wide bandwidth.
In another exemplary embodiment, antenna technology may include the use of (3-dimensional) metamaterials and (2-dimensional) metasurfaces. These include arrangements of conductive scattering elements (sometimes referred to as “lattice elements), each element being much smaller than the wavelength at the operating frequency. The conductive scattering elements may be disposed in 3-D space or in a 2-D plane and may be supported by a dielectric medium. For example, a 3-D arrangement, may be supported by a foam material with low loss and low relative permittivity, or a 2-D arrangement may be etched on a planar low-loss dielectric material such as is used for printed circuit laminas. Conductive scattering elements such as but not limited to resonant structures (for example split-ring resonators) and non-resonant structures (such as small rings, crosses, disks and squares) may be employed. Regular arrays of conductive scattering elements having constant shape, dimensions and spacing, or to allow one or more of these parameters to change (for example as a function of radius from the axis of the incident radiation) may also be employed.
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In an exemplary embodiment, the thickest portion of the conventional lens 1 and that portion of the metamaterial lens 5 which provides the largest phase shift are close to the axis of each lens. In the case of the conventional biconvex lens the phase shift is a phase delay, caused by the reduced velocity of propagation of the electromagnetic wave through a dielectric medium. The metasurface lens is similarly designed to create a phase delay, the delay diminishing as a function of radial distance from the axis of the lens.
In an exemplary embodiment, the azimuth beamwidth required from a cellular radio base station antenna is around 65 degrees. In response to the need for an aesthetically acceptable, low cost package, a base station antenna may have limited frontal dimensions. As a consequence the dimensions of a metasurface lens to adjust or correct the azimuth beamwidth may be correspondingly small in terms of the operating wavelength. Such a lens may accordingly be positioned relatively close to the radiating elements. Introduction of a metasurface lens close to the radiating elements of a base station antenna element may cause unwanted reflections, which may in turn increase the VSWR of the radiating elements at some frequencies in the operating frequency range to an undesirable extent. One or more non-limiting embodiments of the present disclosure provides a metasurface lens having a desirable focusing effect while overcoming this disadvantage.
According to one or more non-limiting embodiments of the present disclosure, there is provided a metasurface lens having an axial aperture and/or an axial region configured with sparse or absent conductive scattering elements (also referred to as “lattice elements”). According to a non-limiting embodiment, the lens is situated in front of a substantially unidirectional antenna to provide the effect of focusing electromagnetic energy radiated by the antenna while creating a low level of back-scattered radiation, thereby minimizing reduction of the impedance bandwidth of the antenna.
With reference to
The lamina 31 can be formed from various dielectric materials including, but not limited to, fiberglass, glass epoxy laminate, or any suitable dielectric lamina material. The metasurface lens 30 further includes a plurality of conductive scattering elements 32 (also referred to as “scattering elements” or “lattice elements”) formed on a surface of the lamina 31. The conductive scattering elements 32 can be formed of various metal materials including, for example, copper. According to a non-limiting embodiment, the conductive scattering elements 32 have a substantially square profile and are arranged in concentric circles 33, 34, 35 surrounding the axial region 28a. It should be appreciated that the profile of the conductive scattering elements 32 can have other shapes without departing from the scope of the disclosure.
According to a non-limiting embodiment, the axial region 28a defines a central aperture 36, which may be a physical aperture in the lamina 31 or may be regions of the lamina 31 wherein no conductive scattering elements 32 are present. That is, in some embodiments the aperture is excludes elements (e.g., scattering elements), while in other embodiments the aperture 36 can include elements (e.g., scattering elements). In one or more non-limiting embodiments, a void is formed in the axial region 28a to define the central aperture 36.
The lamina 38 can be formed from various dielectric materials including, but not limited to, fiberglass, glass epoxy laminate, or any suitable dielectric lamina material. The metasurface lens 30 further includes a plurality of conductive scattering elements 39 formed on a surface of the lamina 38. According to a non-limiting embodiment, the conductive scattering elements 39 have a substantially square profile and are arranged in concentric squares 40, 41 surrounding the axial region 43a. The central aperture 43 may be a physical aperture in the dielectric lamina or may be regions of the lamina wherein no conductive scattering elements are present. In one or more non-limiting embodiments, a void is formed in the axial region 43a to define a central aperture 50, which may be a physical aperture in the lamina 38 or may be regions of the lamina 38 wherein no conductive scattering elements 39 are present. In one or more non-limiting embodiments, a void is formed in the axial region 43a to define the central aperture 50.
While both examples described above are symmetrical, asymmetric arrangements are also possible and may be advantageous when the source antenna is asymmetric. For example, an antenna may include a plurality of radiating elements disposed in an asymmetric arrangement. In this case, the lens can include an asymmetric arrangement of conductive scattering elements arranged with respect to the asymmetric arrangement of radiating elements.
The arrangement of the conductive scattering elements in concentric circles and squares is by way of example and is not limiting. According to a non-limiting embodiment, the number of conductive scattering elements in each radial direction is chosen by design. For example, a lens having axial symmetry may be advantageous, in which case the conductive scattering elements may be arranged in concentric groups having any regular polygonal form. In another example embodiment, a lens may be required to focus energy in a single plane, in which case an asymmetric or substantially linear geometry may be more appropriate. In one or more non-limiting embodiments, the angles between adjacent radial rows of conductive scattering elements 32 shown in
According to one or more non-limiting elements, the conductive scattering elements 32, 39 have dimensions substantially smaller than the operating wavelength and may take many forms, for example squares, circles and crosses, these being realized either as filled shapes or outlines. The dimensions of the conductive scattering elements are chosen by design such that the phase shift caused to an electromagnetic wave passing through the lens varies as a function of the distance from the center axis of the lens. The rate of change of the phase shift with radial distance from the axial direction of the radiating path of the lens determines the effective focal length of the lens and is chosen by design to suit particular applications. In one implementation the scatterers were initially dimensioned as 0.05 wavelengths in diameter, arranged on two circles having diameters of 0.49 and 0.55 wavelengths. In the same implementation the central aperture is 0.43 wavelengths in diameter which is the size of the physical aperture of the radiating structure which typically range, for example, from about 0.4 to about 0.6 wavelengths.
According to one or more non-limiting embodiments of the present disclosure, the design of a lens can be accomplished by the use of an electronic computer program providing simulation of electromagnetic waves in the presence of conductive scattering elements, for example CST Studio Suite or REMCOM XFdtd, which provide facilities for the optimization of the shape and dimensions of individual scattering elements and their configuration on a dielectric lamina.
As described herein, the lamina includes an axial region 50 aligned with respect to the axial direction of the radiating structure such that energy radiated along the radiating path by antenna 10 passes through the lens 30, causing modification of the characteristics of the antenna 10. In such a configuration the lens is sometimes referred to as forming a ‘superstrate’ relative to the antenna.
Metasurface lens 44, configured according to one or more non-limiting embodiments of the present disclosure, includes a central aperture 45 surrounded by a plurality of conductive scattering elements 46, 46′, 47, 47′ arranged to provide a phase advance of the wavefront as it passes through the lens. According to a non-limiting embodiment, the central aperture 45 has a size that matches, or substantially matches, the size of the radiating surface 506. In other non-limiting embodiments, the aperture 45 is sized larger or smaller than the radiating surface 506. The outer regions 47, 47′ of lens 44 are configured to provide a larger degree of phase advance than the inner regions 46, 46′. By this means the wavefront 49 emerging after passing through the lens 44 is reduced in curvature, or in other words “flattened.”. This has the effect of reducing the beamwidth of the resultant radiation pattern, thereby increasing the directivity and gain of the source antenna. It will be understood that the number of rows or circles of scatterers is not limited to two as shown in
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In the example of
A lens according to one or more non-limiting embodiments of the present disclosure can be manufactured from low-loss copper-clad dielectric laminas using low-cost printed-circuit techniques. In one or more non-limiting embodiments, the conductive scatterers may be formed on or supported by two faces of a thick dielectric sheet, for example a sheet of rigid polystyrene foam.
While a lens according to one or more non-limiting embodiments of the present disclosure may be fabricated on at least one substantially planar substrate, other non-limiting embodiments allow for forming the lens on at least one curved substrate or on a combination of planar and curved substrates.
A lens according to one or more non-limiting embodiments of the present disclosure may conveniently be supported in position by means of a plurality of elongate dielectric members extending from the antenna. In one or more non-limiting embodiments, a lens may be supported by, or be integral with, a protective dielectric cover enclosing the antenna, often referred to as a radome.
The teachings described herein may be implemented as an apparatus and/or a method at any possible technical detail level of integration. Aspects of the disclosure may be described herein with reference to flowchart illustrations and/or block diagrams of one or more methods. In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures or the block diagrams may be oriented in other orientations. For example, two blocks shown in succession may, in fact, be performed substantially concurrently, or the blocks may sometimes be arranged in the reverse order.
The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments described. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments described herein.