WO2010016799A1

WO2010016799A1 - Antenna for omni directional, multi-beam, high gain communication

Info

Publication number: WO2010016799A1
Application number: PCT/SG2008/000292
Authority: WO
Inventors: Serguei Matitsine
Original assignee: Em Technologies Group Pte Ltd
Priority date: 2008-08-07
Filing date: 2008-08-07
Publication date: 2010-02-11

Abstract

An antenna comprising a spherical lens and a plurality of feeds arranged in a circular orbit around the spherical lens such that the beams associated with respective feeds provide a substantially omni directional angular coverage of 360 degrees.

Description

Antenna for Omni Directional, Multi-Beam, High Gain Communication

FIELD OF INVENTION

The present invention relates broadly to an antenna, to a method of fabricating a spherical lens for an antenna and to a wireless communication system.

BACKGROUND

One of the main challenges in communications is providing long distance connectivity with angular coverage of 360 degrees (for example, wireless internet or any other mobile applications). Currently, the standard solution available is to use a sector of an antenna which can cover an azimuth angle of 40 to 60 degrees and has short distance of connectivity. In order to cover an azimuth angle of 360 degrees, 6-9 antennas would be combined to achieve wider area coverage. However, the main drawback with the above-mentioned antenna configuration is that an antenna with a high sector azimuth angle of coverage generally does not have a high gain. Gain parameter is defined as inversely proportional to the azimuth angle. Thus, in order to increase the distance for communications, it is essential to increase the gain. Moreover, coverage of a whole angular sector of 360 degrees would require a large number of antennas.

As an example, let us consider a standard dish antenna (diameter 30 cm) for operation at a frequency of 2.4 GHz, with a gain of 16 dBi and an azimuth sector coverage of 24 degrees. There are two approaches that can be adopted to increase the distance of connectivity to three times. The first approach is to increase the output power by approximately 10 dB (where the range is proportional to the square root of power). However, this approach is not very practical as the output power is limited by environmental requirements. Also, the power required for commercial applications cannot be increased to such levels. Another approach is to increase the gain of the antenna by approximately 10 dB, (where the range is proportional to the square root of gain). In practise, a standard dish antenna with a gain of 16 dBi has a diameter of about 30 cm and angular sector coverage of about 24 degrees. A dish antenna with a gain of 26 dBi has a diameter of about 100 cm and angular sector coverage of 7 degrees. Therefore, in order to increase the distance of connectivity (range) to three times with the same output power, a 100 cm dish antenna has to be used in place of a 30 cm dish antenna. Moreover, in order to provide coverage for 360 degrees, 51 large dish antennas, each with a diameter of 100 cm, are required, rendering this approach impractical.

Another solution for long distance connectivity with angular coverage of 360 degrees is to use multi-beam antennas where these antennas can simultaneously support different directions. This can be done by using, for example, a Rotman lens antenna. The downside of this solution is the need for the development of big size antennas which would require complex technology and incur high implementation cost.

An alternative example of a multi-beam communication antenna is based on a Luneburg lens antenna or a spherical lens antenna, as shown in FIGURE 1. This antenna can provide multiple beams for different directions simultaneously (known as the multi-beam feature). In practice, the antenna comprises a small number of feeds (typically 2, 3), thereby providing a limited area of angular coverage. Furthermore, it is not known if spherical lens can be used for the purpose of providing omni directional coverage.

A need therefore exist to provide an antenna that seeks to address at least one of the abovementioned problems.

SUMMARY

According to a first aspect of the present invention there is provided an antenna comprising a spherical lens; and a plurality of feeds arranged in a circular orbit around the spherical lens such that the beams associated with respective feeds provide a substantially omni directional angular coverage of 360 degrees.

The spherical lens may comprise a plurality of concentric layers of dielectric material with respective different dielectric constants. The plurality of feeds may be arranged in an equatorial plane of the spherical lens.

The plurality of feeds may be arranged a horizontal distance away from an equatorial plane of the spherical lens such that the beams associated with the respective feeds are angled with respect to the equatorial plane.

The antenna according to any one of the preceding claims, wherein for each pair of diametrically opposite feeds respective polarisations of the feeds of the pair are perpendicular to each other.

The feeds may be dipole feeds.

The dipole feeds may be aligned at an angle of about 45 degrees.

The artificial dielectric material for the spherical lens may comprise a plurality of particles adhered together, the plurality of particles comprising a dielectric material; and at least one conductive fibre embedded in each particle of the plurality of particles.

The plurality of particles may be adhered together using a rubber adhesive or an adhesive comprising of a material in a group consisting of polyurethane; and epoxy.

The plurality of particles may be randomly distributed in the artificial dielectric material.

The dielectric material may have a density in the range of 0.005 to 0.1g/cm³.

The dielectric material may be a foam polymer.

The foam polymer may be made of one or more materials in a group consisting of polyethylene; polyestyrene; polytetrafluoroethylene (PTEF); polypropylene; polyurethane; and silicon. The average end-to-end measurement of each particle of the plurality of particles may be in the range of 0.5 to 20 mm.

The antenna may further comprise one or more additional feeds arranged away from the circular orbit.

The one or more of said additional feeds may be disposed for communication with a satellite.

The one or more of said additional feeds may be disposed for communication with another terrestrial antenna.

The plurality of feeds may comprises feeds operating at different frequencies such that the antenna can function as a multi-band antenna.

According to a second aspect of the present invention there is provided a method of fabricating a spherical lens for an antenna, the method comprising the use of an artificial dielectric material comprising a plurality of particles adhered together, the plurality of particles comprising a dielectric material; and at least one conductive fibre embedded in each particle of the plurality of particles.

According to a third aspect of the present invention there is provided a wireless communication system comprising a plurality of terrestrial antennas, each antenna comprising a spherical lens; and a plurality of feeds arranged in a circular orbit around the spherical lens such that the beams associated with respective feeds provide a substantially omni directional angular coverage of 360 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which: FIGURE 1 shows a cross-sectional top view of a multi-beam spherical Luneburg lens communication antenna of a prior art.

FIGURE 2 shows a cross-sectional top view of a multi-beam, high gain spherical lens communication antenna according to one embodiment of the present invention.

FIGURE 3 illustrates random orientation of a plurality of particles with embedded conductive fibres in an artificial dielectric material for the construction of a multi-beam, high gain spherical lens communication antenna according to one embodiment of the present invention.

FIGURES 4(a), 4(b), 4(c) and 4(d) illustrate possible configurations of a particle with embedded conductive fibres in an artificial dielectric material for the construction of a multi-beam, high gain spherical lens communication antenna according to one embodiment of the present invention.

FIGURES 5(a) and 5(b) illustrate the operation of an omni directional, multi- beam and high gain spherical lens communication antenna for receiving and transmitting electromagnetic wave, respectively, according to one embodiment of the present invention.

FIGURES 6(a) and 6(b) show perspective views of an omni directional, multi- beam and high gain communication antenna and antenna dipole feeds respectively, according to one embodiment of the present invention.

FIGURE 7 shows an overview of a communication system for direct line-of-sight, wireless, mobile and satellite communications using omni directional, multi-beam and high gain spherical lens communication antennas according to one embodiment of the present invention.

DETAILED DESCRIPTION A Luneburg lens is a spherical lens where its property of dielectric constant changes with the lens radius. Starting from the centre of the lens, the dielectric constant decreases as the radius increases towards the spherical surface of the lens. Perfect Luneburg lens are practically difficult to manufacture to achieve a smooth variation of dielectric constant with radius. However, approximations can be achieved by providing step-wise changes in the dielectric constant by forming concentric layers of dielectric material with relatively different dielectric constant.

The Luneburg lens is known to have a focal point on one side of its spherical surface and a corresponding second focal point at infinity in a direction away from the diametrically opposite side of the sphere to the first focal point. This allows an electromagnetic wave radiated by a source on one side of the spherical lens to propagate though the lens and emerge as a plane wave on the diametrically opposite side of the lens. Therefore, a Luneburg lens can be used as part of an antenna comprising a plurality of feeds to receive or transmit electromagnetic energies. The focal points of a Luneburg lens are generally located on the surface of the lens. However, for antenna design, it is appropriate that the focal points are located at some distance away from the surface of the lens. This can be achieved by providing variations in the dielectric constant of the concentric layers of dielectric material making up the lens, in this case, the lens is generally referred to as an electromagnetic (EM) spherical lens.

FIGURE 2 shows an omni directional, multi-beam and high gain communication antenna 200 based on a lens 202 designed and developed in accordance with example embodiments of the present invention. The antenna 200 comprises a lens 202 which has a substantially spherical surface 212. The lens 202 comprises concentric layers of dielectric material e.g. 220 and 224 with their physical sizes defined by radius R₁ 222 and R₂ 226 respectively determined from the centre, C 214, of the lens 202. The physical size of the lens 202 will be determined by the outer surface 212 of the lens 202 defined by the radius, R 208 depending on the number of concentric layers e.g. 220 and 224.

The antenna 200 further comprises a plurality of feeds e.g. 204 on a feed support 206 arranged symmetrically in a circular orbit around the lens 202. The feeds e.g. 204 are arranged with their centres substantially close to the focussing points of the lens 202 on different predetermined positions along the circular orbit to provide a plurality of radiation beams, each radiation beam having defined angular directions. Such an arrangement for the antenna 200 can offer the capability of providing angular coverage, φ 218, of 360 degrees with high gain for use as a communication antenna. As a result of the symmetrical placement of the feeds e.g. 204 on the feed support 206, each feed e.g. 204 acts as a receiver or radiator of electromagnetic wave propagating through the lens 202. The corresponding radiation beams of the electromagnetic waves will have their maximum gains in an angular direction away from the lens 202 defined by a line passing through the centres of the feeds e.g. 204 and the lens 202.

In an example embodiment, the spherical dielectric lens 202 comprising concentric layers e.g. 220 and 224 of dielectric material has a diameter of about 2R=106cm. The spherical lens 202 has a focusing distance, F 210, of about 1.5R. The plurality of feeds e.g. 204 arranged on the feed support 206 is positioned in a circular orbit around the lens 202 at a distance coinciding with the focusing distance 210 of the lens 202 in order to radiate or receive electromagnetic energy via the lens 202. Effectively, the feeds e.g. 204 are arranged in a circular orbit on the feed support 206 at a distance, D 216, of about 0.5R from the outer spherical surface 212 of the dielectric lens 202.

In an example embodiment, the lens 202 as shown in FIGURE 2 can comprises 8 concentric layers e.g. 220 and 224 (only 6 layers schematically shown in Figure 2 for better clarity) of dielectric material with different dielectric constant properties but it should be appreciated that the lens 202 could in effect comprise any number of concentric layers e.g. 220 and 224. Further in an example embodiment, 51 feeds e.g. 204 are arranged in a circular orbit around the lens 202 for angular coverage 218 of 360 degrees, wherein each individual feed e.g. 204 has an angular coverage 218 of about 7 degrees. It should be appreciated that any number of feeds e.g. 204 can be arranged on the feed support 206 for angular coverage 218 of 360 degrees depending on the angular coverage 218 of each individual feed e.g. 204. The plurality of feeds e.g. 204 are arranged in a circular orbit in the equatorial plane of the lens 202, where the equatorial plane is defined as a virtual plane cutting through the centre of the lens 202 parallel to the surface of the earth. Such a configuration can allow electromagnetic energy to be received or transmitted along the equatorial plane of the iens 202 in the angular coverage 218 of 360 degrees. However, a person skilled in the art will readily recognise that the plurality of feeds e.g. 204 can be arranged on the feed support 206 in any plane above or below the equatorial plane of the lens 202 to receive or transmit electromagnetic energy along a plane other than the equatorial plane or at an angle to the equatorial plane.

In example embodiments of the present invention, the spherical lens 202 is made from low-density meta-materials and has a total weight of about 30 kg. The low-density meta-material is an artificial dielectric material that is lightweight, irrespective of its dielectric constant, and has low dielectric losses. The artificial dielectric material can be made by adhering together a plurality of randomly distributed particles made of a lightweight dielectric material with relatively low densities of about 0.005-0.1 g/cm³. The plurality of randomly distributed particles may be adhered together using a rubber adhesive or other adhesives such as polyurethane and epoxy. At least one needle-like conductive fibre is embedded within each particle of lightweight dielectric material. Where there are at least two conductive fibres embedded within each particle, the at least two conductive fibres are in an array like arrangement, i.e. having one or more rows that include the conductive fibres. All the conductive fibres embedded within each particle are not in contact with one another.

FIGURE 3 illustrates a random orientation of a plurality of identical particles 302 with embedded conductive fibres 304 in an artificial dielectric material 300 typically used for the construction of the multi-beam, high gain spherical lens communication antenna according to embodiments of the present invention. For illustrative purposes, each particle 302 is represented as a cube. However, it should be appreciated that the shape may vary in the actual implementation for the construction of the spherical lens 202 as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. As an example, there are 4 identical conductive fibres 304 embedded in each particle 302 in the artificial dielectric material 300 in a non- contact array-like arrangement. The array arrangement of the 4 conductive fibres 304 is two by two, i.e. 2 rows and 2 columns of 4 evenly spaced conductive fibres 304 in parallel arrangement with one another. The conductive fibres in array-like arrangement in one particle may be randomly oriented with respect to the conductive fibres in array- like arrangement in another particle. In example embodiments, the length of each conductive fibre 304 is about 1.5 mm and the size of each particle 302 is about 1.5x1.5x1.5 mm. The particles 302 can be made of a low-density polyethylene foam with a typical density of about 0.01-0.02 g/cm³. Other foam polymers made of materials, such as polystyrene, polytetrafluoroethylene (PTEF), polypropylene, polyurethane, silicon, or the like, may also be used to make the particles 302. The conductive fibres 304 embedded in the particles 302 can be made from highly conductive materials, for instance, copper, silver, gold, aluminium, nickel or the like.

The size of each of the particle 302 may be set at about 1/20 of the wavelength of the selected operating frequency. As an example, at an operating frequency of 10GHz (equivalent to a wavelength of about 30 mm), particles 302 with the size of about 1.5x1.5x1.5 mm may be used. It should be appreciated that the average end-to-end measurement of the particle size, for any shape the particle 302 may take, can be in the range of about 0.5-5.0 mm.

It should be appreciated that the length of each conductive fibre 304 may be in the range of about 0.5-5.0 mm depending on the operating frequency, and the diameter of each conductive fibre 304 may be in the range of about 0.005-1.0 mm. In order to further reduce the weight of the dielectric material 300, conductive fibres 304 with smaller diameter may be used, subject to the limitation that the skin depth at the operating frequency must be much smaller than the fibre diameter.

Advantageously, the distribution of the conductive fibres 304 is uniform as every particle 302 making up the artificial dielectric material 300 is substantially identical, that is, they include the same number of conductive fibre(s) 304. Furthermore, as each particle 302 embeds the conductive fibres 304 in an array-like arrangement without allowing any contact between the conductive fibres 304, conductive clusters are prevented from occurring. This advantageously results in a reduction of dielectric losses. The array-like arrangement can be a 1 , 2, or 3 dimensional array.

It should be appreciated that the conductive fibres 304 in each particle 302 may be fully embedded within the particle 302 to prevent any exposed tips of conductive fibres 304 in one particle from contacting any exposed tips of conductive fibres within the other particles. However, it is also acceptable even if the tips are exposed. While, it is possible to have tip to tip contact in this case, the probability of such contact is relatively small.

FIGURES 4(a), 4(b), 4(c) and 4(d) illustrate possible configurations of a particle with embedded conductive fibres in an artificial dielectric material for the construction of a multi-beam, high gain spherical lens communication antenna according to example embodiments of the present invention.

FIGURE 4(a) illustrates a particle 400 made of a foam-type expanded polyethylene with a density of about 20 kg/m³ having a size of about 1.5x1.5x1.5 mm. The number of rows 402 in the particle 400 is 1 while the number of columns 404 is 2. Hence, the number of conductive fibres 406 in the particle 400 is 2. The distance between adjacent conductive fibres 406 is about 1 mm. The length of each conductive fibre 406 is about 1.5 mm and the diameter of each conductive fibre 406 is about 0.025 mm. The material used for the conductive fibres 406 is copper. An artificial dielectric material created by randomly mixing together a plurality of particles 400 has a density of about 51 kg/m³.

FIGURE 4(b) illustrates a second possible configuration of a particle with embedded conductive fibres in an artificial dielectric material particle. The particle 408 includes an array of three conductive fibres 414 arranged in a single row 410 and three columns 412.

FIGURE 4(c) illustrates a particle 416 made of a foam-type expanded polyethylene with a density of about 20 kg/m³ having a size of about 1.5x1.5x1.5 mm. The number of array rows 418 in the particle 416 is 2 while the number of columns 420 is 4. Hence, the number of conductive fibres 422 in the particle 416 is 8. The distance between adjacent conductive fibres 422 is about 0.3 mm. The length of each conductive fibre 422 is about 1.5 mm and the diameter of each conductive fibre 422 is about 0.025 mm. The material used for the conductive fibres is copper. An artificial dielectric material created by randomly mixing together a plurality of particles 416 has a density of about 68 kg/m³. FIGURE 4(d) illustrates a particle 424 that includes four rows of fibres 426, 428,

430 and 432. In the particle 424, each row can include two evenly spaced conductive fibres 434 in a parallel arrangement. The second row 428 and the fourth row 432 are oriented such that their conductive fibres 434 are substantially perpendicular to the first row 426 and the third row 430.

It should be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the configurations of the particles, such as the dimension and shape of the particles, the dimension and orientation of the conductive fibres and the number of conductive fibres as shown in FIGURES 4(a), 4(b), 4(c) and 4(d) without departing from the spirit or scope of the invention as broadly described. The configurations shown in FIGURES 4(a), 4(b), 4(c) and 4(d) are, therefore, to be considered in all respects to be illustrative and not restrictive.

Different configurations of the array like arrangement of the conductive fibres in each particle can achieve different dielectric constants for the dielectric material. In order to achieve higher values of the dielectric constant, the number of fibres in each particle can be increased. Conversely, in order to achieve lower values of the dielectric constant, the number of fibres in each particle can be reduced.

In the array like arrangement, each row of the array may consist of a row of conductive fibres arranged in parallel to one another. Each row may include different number of fibres that are evenly or randomly spaced apart. The distance between the fibres in adjacent rows may also be evenly or randomly spaced apart. The fibres in different rows of the array may be oriented such that the fibres in one row are in parallel or transversely disposed (for instance, arranged perpendicularly) with respect to the fibres in another row.

Each column of the array may include a column of conductive fibres arranged in parallel to one another. Each column may include different number of fibres that are evenly or randomly spaced apart. The distance between the fibres in adjacent columns may also be evenly or randomly spaced apart. The fibres in different columns of the array may be oriented such that the fibres in one column are in parallel or transversely disposed (for instance, arranged perpendicularly) with respect to the fibres in another column.

It should be appreciated that the number of fibres in each row and column may range from 1 to 10 or beyond. As such, each particle may have a 10x10 array of conductive fibres having 10 rows and 10 columns.

A dielectric material incorporating any one of the particles with embedded conductive fibres as described previously can be used to construct the lens for the multi-beam, high gain spherical lens communication antenna according to example embodiments of the present invention. The spherical lens with concentric layers of dielectric material is generally constructed in stages, whereby approximately 1/8 component of the lens is made each time using a typical moulding process. During the moulding process, a raw state of the dielectric material is poured into a mould so that when hardened, the dielectric material will adopt a shape of about 1/8 of a sphere.

A metal guide attached to the mould is used to define the thickness of each concentric layer of the dielectric material to be formed. In order to form different concentric layers of dielectric material, the metal guide attached to the mould is first configured at an appropriate distance in the radial direction to define the thickness of the first concentric layer. A raw state of the appropriate first dielectric material for the first concentric layer is poured into the mould and guided by the metal guide so that when the raw state hardened, the first concentric layer of dielectric material will have a thickness as defined by the radial distance set by the metal guide. In order to form a second concentric layer of dielectric material, the metal guide attached to the mould is then increased radially outward to the appropriate distance to define the thickness of the second concentric layer. A raw state of the appropriate second dielectric material with a relatively different dielectric constant compared to the first dielectric material is then poured into the mould in the space between the hardened first concentric layer and the metal guide. The second concentric layer is then allowed to harden and set in the mould. Successive concentric layers of relatively different dielectric constant can be formed by repeating the moulding process as described above using different dielectric material and controlling the metal guide to define the thickness of each layer. The moulding process ends when the appropriate number of concentric layers of dielectric material with the desired step-wise changes in the dielectric constant has been achieved. When the 1/8 component of the lens comprising concentric layers of dielectric material has hardened and set, the lens component can be removed from the mould. Similar procedures are then applied to form the remaining 7 components of the lens. When all the 8 components of the lens are completed, the 8 individual components are then assembled to form the whole lens by applying the appropriate adhesives or other fastening means to bond the 8 individual components of the lens together.

FIGURE 5(a) illustrates the operation of an omni directional, multi-beam and high gain spherical lens communication antenna 500 configured to receive electromagnetic (EM) energy according to embodiments of the present invention. For ease of illustration, the operation of receiving electromagnetic energy in the form of an electromagnetic plane wave will now be described, by way of example, using the electromagnetic plane wave 504 arriving at the lens 502 and received by the feed 508. The electromagnetic plane wave 504 (represented as solid lines) arriving on one side 510 of the lens 502 interacts with the lens 502 and can be focussed (radiation beam represented as dotted lines with arrows 506) by the lens 502 towards the specific feed 508 positioned at a distance coinciding with the focusing distance, F 518 of the lens 502 on the diametrically opposing side 512 of the lens 502. The configuration of the antenna 500 according to embodiments of the present invention is such that only the single feed 508 receives the radiation beam 506 associated with the electromagnetic plane wave 504. An independent electromagnetic plane wave arriving in a specific angular direction on one side of the lens will have its associated radiation beam focussed towards a corresponding feed on the opposite side of the lens due to the specific angular coverage of each independent feed. A plurality of feeds arranged in a circular orbit around the lens 502 can allow the antenna 500 to provide angular coverage of 360 degrees to receive electromagnetic waves. Each individual feed will be able to receive independent radiation beams, thereby providing an omni directional and multi-beam communication antenna. For example, in addition to the electromagnetic plane wave 504, the antenna 500 may simultaneously receive the electromagnetic plane wave 514 with its associated radiation beam 520 propagating through the lens 502 towards the feed 516. FIGURE 5(b) illustrates the reciprocal operation of an omni directional, multi- beam, high gain spherical lens communication antenna 522 configured to transmit electromagnetic energy according to embodiments of the present invention. For ease of illustration, the operation of transmitting electromagnetic energy in the form of an electromagnetic plane wave will now be described, by way of example, using the feed 526 as the source providing a radiation beam to be transmitted as an electromagnetic plane wave 530 by the lens 524.

In order for the antenna 522 to transmit the electromagnetic wave 530, the source feed 526 on one side 532 of the lens 524 provides a radiation beam (represented as dotted lines with arrows 528) propagating through the lens 524. The lens 524 subsequently transmits the electromagnetic wave 530 out of the diametrically opposing side 534 of the lens 524. It should be appreciated that each individual feed arranged in a circular orbit around the lens 524 can act as independent sources providing multiple propagating radiation beams. Each individual feed will have an associated radiation beam. Accordingly, the plurality of feeds can act in combination with the dielectric lens to produce a corresponding plurality of independent radiation beams, thereby providing an omni directional transmission of the beams in the angular coverage of 360 degrees.

FIGURE 6(a) shows an omni directional, multi-beam and high gain communication antenna 600 developed according to example embodiments of the present invention. The communication antenna 600 includes a spherical lens 602 comprising concentric layers of dielectric material with relatively different dielectric constant as described above. The spherical dielectric lens 602 is supported by single pole 612 at the base and three horizontal guides 615 attached to the antenna support structure 610. A feed support 606 located in the equatorial plane of the lens 602 is also attached to the antenna support structure 610. A plurality of feeds e.g. 604, are attached to the feed support 606 in a circular orbit around the lens 602, providing angular coverage of 360 degrees. The feeds e.g. 604 attached to the feed support 606 are aligned at 45 degrees to the vertical axis. Two additional feeds 608 are attached near the bottom plane of the antenna support structure 610 to provide elevation angles coverage for satellite communication. As an example for the demonstration of the omni directional, multi-beam and high gain communication antenna 600, an electromagnetic wave with a frequency of about 2.4GHz is selected for the interaction with the antenna lens 602. This frequency is selected as it is the general operational frequency used for wireless internet applications.

The feeds e.g. 604 are antenna dipoles for receiving and transmitting electromagnetic waves at the frequency of 2.4 GHz.. Antenna dipoles are understood in the art and will not be described here in detail. The dipole feeds e.g. 604 are electrical conductors comprising two symmetrical terminals extending in opposite directions from a central feed point connected to a feed line. In order to radiate an electromagnetic wave, a current is provided to the terminals from the central feed line. The current flowing in the terminals and the associated voltage produced between the terminals subsequently causes an electromagnetic wave to be radiated around the feeds e.g. 604. In order to increase the efficiency of the radiation towards the lens in the example embodiment, metal reflector dipoles e.g. 614 are attached at a distance of about λ/4 (where λ is the wavelength of the EM wave) from the external side of the feeds e.g. 604, as shown in FIGURE 6(b). This will allow the radiation to be directed towards the lens 602. In a reciprocal manner, an electromagnetic wave arriving at a dipole feed e.g. 604 produces a voltage between its two terminals, thereby causing a current flow along the terminals to the central feed line. The dipole feeds have structures with defined cross-sectional shapes and dimensions for supporting the propagation of electromagnetic waves in defined frequency bands. The dipole feed 604 and the metal reflector 614 are connected by dielectric holder 615, which does not effect the dipole performance.

The dipole feeds e.g. 604 are selected for operation in the frequency band of about 2.4-2.6 GHz in an example embodiment. All the feeds e.g. 604 are attached to the feed support 606 in a circular orbit around the spherical lens 602 at a distance coinciding with the focussing distance of the lens, F=1.5R. The feed support 606 is positioned in the equatorial plane of the lens 602. Each feed e.g. 604 combined with the lens 602 can cover an angular sector of around 7 degrees with a gain of about 26dB. In order to provide angular coverage of 360 degrees, a total of 51 feeds are provided for the antenna 600. One of the challenges faced is the isolation between neighbouring feeds e.g. 604. In order to preferably address the isolation issue, the focusing distance of the lens 602 is selected based on the distance between neighbouring feeds It was found that for feeds e.g. 604 aligned to a vertical position (e.g. perpendicular to the feed support 606), the isolation between neighbouring feeds* is higher than 25 dB. For feeds e.g. 204 aligned at 45 degrees to the feed support 606, the isolation is higher than 35 dB and for feeds e.g. 204 aligned to a horizontal position (e.g. parallel to feed support 606), the isolation is higher than 30 dB.

Another challenge is the blockage by feeds from diametrically opposite sides of the lens 602. It was found that for feeds e.g. 604 aligned to either a vertical or a horizontal position, the blockage is about 1-1.5 dB and for feeds e.g. 604 aligned at 45 degrees to the vertical axis, the blockage is about 0.5 dB. Therefore, it was recognised by the inventor that an optimum result obtained is for feeds e.g. 604 aligned at about 45 degrees such that feeds from diametrically opposite sides of the lens 602 are perpendicular to each other and this significantly reduces blockage.

In example embodiments, 2 additional feeds 608 operating at a frequency of about 4-5 GHz are attached near the bottom plane of the antenna support structure 610 to provide additional channels for satellite communication. Each of the feeds 608 is operable to change the angular and elevation angles. The additional feeds 608 may be electromagnetic horns. Electromagnetic horns are understood in the art and will not be described here in detail. The feeds 608 are generally placed at a position coinciding to the focussing distance of the lens 602 to receive electromagnetic waves focussed by the lens 602 and channel the signals to an amplifier or guide radiation beams towards the lens 602 which subsequently transmits the associated electromagnetic waves.

Table 1 summarises the characteristics of an antenna in an example embodiment at frequencies of 2.4 GHz and 4 GHz, as provided below:

TABLE 1

FIGURE 7 shows an overview of a communication system for direct line-of-sight, wireless, mobile and satellite communications using the omni directional, rnulti-bearn and high gain spherical lens communication antennas developed according to example embodiments of the present invention. An omni directional, multi-beam and high gain spherical lens communication antenna 700 can be positioned on top of a building 702 to provide high gain angular coverage of 360 degrees. As the antenna 700 is omni directional with high gain, a single antenna 700 is sufficient to provide both short and long range omni directional angular coverage of 360 degrees from the top of the building 702 compared to an array of conventional communication antennas required for omni directional angular coverage of 360 degrees. Based on the positioning of the feed support 704, the antenna 700 can allow communication with another antenna located substantially on the same plane as the antenna 700 parallel to the surface of the Earth or at an angle for communication with antennas on ground level. Numerous communication signals can be provided by the antenna 700, such as signal 712 for mobile phone 710 applications, signal 716 for wireless communications with a computer 714 and signal 726 for communications with a terrestrial antenna 728. If a second omni directional, multi-beam and high gain spherical lens communication antenna 706 is positioned on top of a second building 708, there is the possibility of providing signal 722 through additional directional feeds for direct line-of-sight communications between the antenna 700 positioned on top of the building 702 and the antenna 706 positioned on top of the building 708, where the building 708 is located at a considerable distance from the building 702. Also, additional feeds provided for antenna 700 to change the angular and elevation angles can support signal 720 for communications with a satellite 718. Similarly, additional feeds provided for antenna 706 to change the angular and elevation angles can support signal 724 for communications with the satellite 718. It should be appreciated by a person skilled in the art that although the omni directional, multi-beam and high gain spherical lens antenna according to embodiments of the present invention has been described as a communication antenna for multiple communication applications, the antenna may also be used for other applications without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

The omni directional, multi-beam and high gain communication antenna according to example embodiments of the present invention can provide angular coverage of 360 degrees with high gain for both short and long range communication applications. The use of lightweight material with low density enables the construction of large size spherical lens for communication antennas with a diameter of about 1 m or more and weighing about 30 kg. The spherical lens comprising concentric layers of lightweight dielectric material is made from foam-type expanded polymer with conductive fibres embedded in array like arrangement within the polymer. The dielectric material has a dielectric permittivity, ε', typically in the range of about 1-2. In contrast, spherical lens made from conventional lens material such as composites of ceramic particle and polymer foam are about 5-8 times heavier.

Example embodiments can provide an antenna for relatively low frequency application with high gain using an antenna with a large size spherical lens. A large size spherical lens providing high gain is important as the aperture or the diameter of the lens typically has to be much higher than the wavelength of operation. As an example, for an operational frequency of about 2.4 GHz, being equivalent to a wavelength of about 12 cm, a lens with a diameter of about 1 m can provide a gain of about 26dBι.. Hence, the communication antenna according to example embodiments can be used at the frequency of 2.4 GHz as the use of lightweight dielectric material with low density enables the construction of large size spherical lens with a diameter of about 1 m or more and weighing about 30 kg for the antenna.

The omni directional, multi-beam and high gain communication antenna according to example embodiments can also be employed for use at other frequencies. Table 2 summarises the characteristics of an antenna with a spherical lens with a diameter of about 1 m at different frequencies.

TABLE 2

Moreover in some cases it is possible to employ different feeds operable at different frequencies around the lens of an antenna, thereby enabling the antenna to function as a multi-band communication antenna.

The ability to construct large size spherical lens allows the attachment of a relatively large number of independent feeds in a circular orbit around the lens to offer angular coverage of 360 degrees with high gain for both short and long range applications. Each individual feed around the lens can provide independent radiation beam (electromagnetic wave) irrespective of the other feeds. A further improvement for the omni directional, multi-beam and high gain communication antenna according to example embodiments is the alignment of the plurality of feeds around the lens at 45 degrees to the vertical axis. Alignment of the feeds at an angle of 45 degrees to the vertical axis can ensure a relatively high degree of isolation between neighbouring feeds. In addition, alignment of the feeds at 45 degrees reduces blockage of feeds on diametrically opposite sides of the lens as the feeds are aligned perpendicular to each other. The problem of blockage can be further alleviated by the large size lens which helps to reduce the probability of blockage between feeds on diametrically opposite sides of the lens. Conventional antennas constructed from conventional lens material have limitations of size and weight for feasible deployment as omni directional antennas. Therefore, small size conventional antennas are generally constructed to have low gain. Such conventional antennas are not able to operate as omni directional antennas because of isolation and blockage issues among the feeds due to the small size lens which cannot help in minimizing the blockage. Hence, these antennas are not able to provide high gain and omni directional characteristic.

The use of large size spherical lens and the plurality of feeds aligned at 45 degrees around the lens according to example embodiments can advantageously enable omni directional coverage of 360 degrees with high gain. The deployment of such omni directional communication antenna with high gain can reduce the number of communication antennas necessary to cover a relatively large area to a single antenna. In comparison, the cost and weight of spherical lens for communication antennas using conventional lens material limit the manufacturing of large size spherical lens for antennas. Also in comparison, current conventional antennas, e.g. dish antennas, can provide only a small angular angle of coverage, typically about 40-60 degrees and relatively low gain. Therefore, an array of separate small size conventional antennas will be required to provide the necessary radiation beams within the individual angular coverage of each antenna so that in combination, the array of antennas can provide the full angular coverage of 360 degrees with relatively low gain. The use of an array of conventional antennas takes up a significant amount of space and requires more base stations to cover the same area compared to a large size spherical lens with higher gain.

In a similar fashion, an array of directional parabolic antenna would be necessary to provide an angular coverage of 360 degrees as each parabolic antenna has limited angular angle of coverage. Hence, the implementation of a single omni directional, multi-beam and high gain communication antenna according to example embodiments can advantageously minimise the cost of setting up the antenna system compared to a system comprising an array of conventional spherical antennas or parabolic antennas. The cost and resources incurred in maintaining a single antenna is also significantly reduced, in addition to the decrease in power consumption to maintain a single antenna over an array of conventional antennas. The single omni directional, multi-beam and high gain communication antenna according to example embodiments can also be positioned on top of a building to provide omni directional coverage, thus freeing up large tracts of land areas, which would otherwise be required to accommodate more base stations, each with an array of conventional antennas.

Additional feeds operating at a frequency of about 4-5 GHz can be attached to the omni directional, multi-beam and high gain communication antenna according to example embodiments to change the angular and elevation angles to provide additional channels for satellite communication. This will allow a single communication antenna according to example embodiments to be deployed for communication with satellites in orbit as well as communication with terrestrial antennas in wireless communication applications.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims

1. An antenna comprising: a spherical lens; and a plurality of feeds arranged in a circular orbit around the spherical lens such that the beams associated with respective feeds provide a substantially omni directional angular coverage of 360 degrees.

2. The antenna according to claim 1. wherein the spherical lens comprises a plurality of concentric layers of dielectric material with respective different dielectric constants.

3. The antenna according to claim 1 or 2, wherein the plurality of feeds are arranged in an equatorial plane of the spherical lens.

4. The antenna according to claim 1 or 2, wherein the plurality of feeds are arranged a horizontal distance away from an equatorial plane of the spherical lens such that the beams associated with the respective feeds are angled with respect to the equatorial plane.

5. The antenna according to any one of the preceding claims, wherein for each pair of diametrically opposite feeds respective polarisations of the feeds of the pair are perpendicular to each other.

6. The antenna according to any one of the preceding claims, wherein the feeds are dipole feeds.

7. The antenna according to claim 6, wherein the dipole feeds are aligned at an angle of about 45 degrees.

8. The antenna according to any one of the preceding claims, wherein an artificial dielectric material for the spherical lens comprises: a plurality of particles adhered together, the plurality of particles comprising a dielectric material; and at least one conductive fibre embedded in each particle of the plurality of particles.

9. The antenna according to claim 8, wherein the plurality of particles are adhered together using a rubber adhesive or an adhesive comprising of a material in a group consisting of: polyurethane; and epoxy.

10. The antenna according to claims 8 or 9, wherein the plurality of particles is randomly distributed in the artificial dielectric material.

11. The antenna according to any one of claims 8 to 10, wherein the dielectric material has a density in the range of 0.005 to 0.1g/cm³.

12. The antenna according to any one of claims 8 to 11 , wherein the dielectric material is a foam polymer.

13. The antenna according to claim 12, wherein the foam polymer is made of one or more materials in a group consisting of: polyethylene; polyestyrene; polytetrafluoroethylene (PTEF); polypropylene; polyurethane; and silicon.

14. The antenna according to any one of claims 8 to 13, wherein an average end-to-end measurement of each particle of the plurality of particles is in the range of 0.5 to 20 mm.

15. The antenna according to any one of the preceding claims, further comprising one or more additional feeds arranged away from the circular orbit.

16. The antenna according to claim 15, wherein one or more of said additional feeds are disposed for communication with a satellite.

17. The antenna according to claims 15 or 16, wherein one or more of said additional feeds are disposed for communication with another terrestrial antenna.

18. The antenna according to any one of the preceding claims, wherein the plurality of feeds comprises feeds operating at different frequencies such that the antenna can function as a multi-band antenna.

19. A method of fabricating a spherical lens for an antenna, the method comprising the use of an artificial dielectric material comprising: a plurality of particles adhered together, the plurality of particles comprising a dielectric material; and at least one conductive fibre embedded in each particle of the plurality of particles.

20. A wireless communication system comprising a plurality of terrestrial antennas, each antenna comprising: a spherical lens; and a plurality of feeds arranged in a circular orbit around the spherical lens such that the beams associated with respective feeds provide a substantially omni directional angular coverage of 360 degrees.