BACKGROUND OF THE INVENTION Radio wave wireless communication is known and utilizes electromagnetic radiation having an associated carrier frequency included within a range of 20 Hz to 300 GHz, more usually in a contemporary range of 100 MHz to 5 GHz when pertaining to radio networked devices such as mobile telephones, wireless-linked computer apparatus and radio frequency tags.

At this contemporary range, muitipath radio propagation has earlier been a technical problem. More recently, it has been appreciated that such multipath radio radiation propagation is susceptible to providing benefits in specific types radio network configurations, for example as described in a scientific publication"Layered space-time architecture for wireless communication in a fading environment when using multiple antennas", G. J. Foschini, Bell Labs Technical Journal, Vol. 1, no. 2, pp. 41-59,1996 pertaining to radio network configurations characterised in practice. Such multipath configurations have been demonstrated to be capable of providing a high degree of spectral efficiency, as measured in bits/s/Hz, by utilizing a wide angular spread of incoming radio radiation reflected and scattered from many objects.

By utilizing such multipath reflected and scattered radiation, it is feasible to establish a vector channel between two locations. Each location includes several antennae thereat coupled to associated electronic signal processing hardware arranged to process signals output from the antennae for supplying signals thereto, the hardware operable to apply suitable complex scaling and phase shifting control to the signals so as to establish a set of parallel communication channels between the two locations. These parallel communication channels collectively comprise the aforesaid vector channel. Application of such complex scaling and phase shifting control is often referred to in the art as"applying antenna weighting". The parallel channels are susceptible to conveying information.

In a situation where there is only one antenna at a first of the two locations and several antennae at a second of the locations, inclusion of the several antennae at the second location is still advantageous because a plurality of signals generated thereat may be combined to generate a final signal of greater quality which is less susceptible to fading

and time dispersion. Such enhanced signal quality is described in a publication"Microwave Mobile Communications", edited by W. C. Jakes, New York, published by Wiley 1974. In a situation where channels of communication are unknown at a transmitter in such an arrangement, different signals are sent via the several antennae using intelligent coding, namely space-time-coding; conversely, in a situation where channels are known at the transmitter of the arrangement as well as at its receiver, further communication benefits arise as described in a publication"Array Gain and Capacity for Known Random Channels with Multiple Element Arrays at Both Ends", IEEE Journal of Selected Areas in Communications, Vol. 18, no. 11, November 2000.

Recently, MIMO systems have evolved which rely on spatial diversity of antennae, wherein individual antennae are disposed in a substantially linear formation, the antennae being mutually spaced apart by a distance corresponding to a half wavelength of radiation to which the antennae are designed to be responsive. The antennae in the linear formation are capable of being disposed with similar polarization orientations in their polar reception/transmission characteristics. Alternatively, the polarization can be varied along the linear formation from relatively horizontal polarization to correspondingly vertical polarization. However, this linear formation has been found to suffer a problem in that it is bulky, for example it is 66 cm long where the formation includes twelve antennae operable at a nominal radiation frequency of 2.5 GHz.

A recent publication"Tripling the Capacity of Wireless Communication using Electromagnetic Polarization"Nature, Vol. 409, January 2001, pp. 316-318 discloses a co- location arrangement of three electric dipoles and three magnetic dipoles capable of providing in operation six independent communication channels in an indoor environment.

The co-location arrangement is relatively compact as the antennae are all included within a cubic volume having a side length of a half wavelength of radiation to which the arrangement is designed to be responsive.

In a United States patent no. US 6,380, 910B, such patent co-pending with patent applications for the present invention, there is described a wireless communication device comprising a signal processing device coupled to a cluster of spatially-disposed multiple port antennae. The antennae are capable of simultaneously transmitting an/or receiving radio wave bearing communication signals. The cluster of antennae is operable within a frequency band f. Moreover, at least a pair of antenna ports is placed in a spatial volume whose longest linear dimension is less than or equal to k/3, where ? is the wavelength for the radiation. During operation of the antenna cluster, the antennae give rise to polar response lobes, which are directed in dissimilar directions, the lobes having mutual correlations of 0.7 or less.

The inventor has appreciated that the aforementioned antennae formations and arrangements known in the prior art suffer practical operational problems, for example are bulky, too expensive and complex to manufacture and needs an iterative procedure for installation in an environment, and for the same volume exhibits only 8 channels.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide an improved radio antenna device capable of addressing one or more of the aforementioned problems associated with the prior art.

According to a first aspect of the present invention, there is provided a radio antenna device for at least one of receiving and emitting electromagnetic radio radiation, the device including a plurality of antennae spatially distributed within a volume, each antenna being operable to at least one of receive and emit a component of the radiation, the antennae being so arranged so as to combine spatial and polarisation diversity of the device with respect to the radiation.

The invention is of advantage in that it is capable of providing a better combination of spatial and polarization diversity in comparison to hitherto known radio antenna devices and therefore improving one or more of data communication capacity.

Preferably, the antennae are arranged so as to define the volume as a geometrical form, the antennae being disposed along peripheral edges of the form. Inclusion of the antennae along the edges enables radiation to be intercepted more efficiently at the device, thereby at least one of enhancing its gain characteristics, rendering it more compact and less bulky.

More preferably, the edges are of a length corresponding substantially to a half wavelength of the radiation. In this respect, the inventor has appreciated that advantages of half wavelength spacing, corresponding to radio radiation nodal separation, is feasible for more efficient multi-antennae radio devices.

Most preferably, the geometrical form is substantially cuboid with twelve peripheral edges, wherein a plurality of the edges have disposed thereat associated antennae. The inventor has appreciated that a cuboid form encloses a near maximal volume and the disposition of antennae along edges of the cuboid provides a high degree of radio radiation interception as well as relative optimal antenna orientation.

Although only a subset of the edges of the cuboid need be occupied by antennae, the device is most preferably arranged so that each of the twelve edges has an associated

antenna disposed thereat. Such an arrangement is capable of providing an optimal configuration whether device spatial and polarization diversity is maximized for the number of antennae employed, such maximization being a consequence of the inventor appreciating that certain types of antennae are preferably employed in the device.

Preferably, each antenna of the device is an electric dipole antenna. Utilization of an electric dipole is of benefit in that it provides a relatively simple polar gain characteristic of broad predictable angular extent, thereby assisting to provide a high degree of polarisation diversity in the device. Moreover, interaction characteristics of mutually neighbouring dipoles is susceptible to analysis and simulation ; moreover, electric dipoles are also readily disposable along edges and are also potentially inexpensive to manufacture using linear conductors. Patch antennae may be used but they will occupy more space and they will provide less freedom for choosing various design parameters.

More preferably, each dipole includes two conductive elements substantially spatially disposed along an associated mutually common axis, the axis of each antennae being arranged substantially mutually orthogonally to that of one or more neighbouring antennae thereto. Orthogonal disposition of the dipoles is of synergistic advantage in that mutual interaction between the antenna dipoles is greatly thereby reduced whilst providing a compact spatial arrangement for the antenna dipoles.

Most preferably, the spatial and polarisation diversity of the device is substantially optimized in respect of the geometrical form. Such optimized diversity is capable of achieving maximum device operation in respect of a number of communication channels supported, device gain, device physical size and device manufacturing cost.

A device according to any one of the preceding claims wherein spatial separation of extremities of neighbouring antennae is less than a spatial extent of each of the antennae.

Such a characteristic distinguishes the device of the invention because a conventional approach is to enhance mutual antenna isolation by increase spatial separation therebetween.

In order to render the device easier to assembly in manufacture and yet ensure a greater degree of device physical robustness, neighbouring antennae are preferably mutually mechanically coupled at their extremities.

According to a second aspect of the present invention, there is provided a radio antenna device for at least one of receiving and emitting electromagnetic radio radiation, the device including a plurality of antennae spatially distributed within a volume, each antenna being operable to at least one of receive and emit a component of the radiation, the antennae

being arranged so as to define the volume as a geometrical form, the antennae being disposed along peripheral edges of the form.

Preferably, the antennae are so arranged so as to combine spatial and polarisation diversity of the device with respect to the radiation. More preferably, the antennae are so arranged so as to optimize spatial and polarisation diversity of the device.

Advantageously, the geometrical form is substantially cuboid with twelve peripheral edges, wherein a plurality of the edges have disposed thereat associated antennae. It will be appreciated that the device of the invention need not be perfectly cuboid in order to function; for example, the form can be of cuboid and/or generally rectangular shape whose sides have aspect ratios diverging from unity, for example an aspect ratio in a range of 1: 1 to 2: 1.

Beneficially, each of the twelve edges has an associated antenna disposed thereat.

Preferably, each antenna is an electric dipole antenna.

Preferably, spatial separation of extremities of neighbouring antennae is less than a spatial extent of each of the antennae. More preferably, neighbouring antennae are mutually mechanically coupled at their extremities.

Preferably, the device is operable to function in Multiple Input Multiple Output (MIMO) mode, such MIMO mode being as elucidated in the foregoing.

Preferably, the device of the first and/or second aspect of the invention further includes interfacing means for at least one of supplying and receiving signals to the antennae, the interfacing means being arranged to route such signals through an interior region of the device to the antennae around which the antennae are spatially disposed. Providing signal routing through the interior region enables the device to be more compact and assists to reduce aberrations to polar response characteristics of the device which could otherwise compromise its performance.

BRIEF DESCRIPTION OF DRAWINGS Embodiments of the invention will now be described, by way of example only, with reference to the following drawings wherein: Figure 1 is a schematic illustration of a radio antenna device according to the invention, the device implemented as a plurality of antennae disposed along edges defining a substantially cubic volume,

Figure 2 is a diagram of an electric dipole antenna known in the art, Figure 3 is an illustration of a practical implementation of a radio antenna device according to the invention including twelve electric dipole antennae disposed along peripheral edges of a substantially cubic volume, Figure 4 is a more detailed illustration of a part of the device of Figure 3 wherein adjacent antennae dipoles are in relatively close spatial proximity, and with a preferred cabling indicated, optionally with signal processing devices positioned within the cubic volume, Figure 5 is a graph illustrating for a MIMO antenna device its capacity depending on antenna spacing, Figure 6 shows a graph illustrating a computed antenna gain that can be achieved for each of twelve independent channels with the twelve element antenna device, Figure 7 shows a graph with computed capacities that can be obtained at different signal- to-noise ratios, and Figure 8 shows a graph indicating, for a twelve element implementation, computed capacity, maximum antenna gain, and a number of channels as a function of size of cube.

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the invention will be described in the following with reference to a publication US 6,144, 711 (Raleigh et al.) pertaining to"Spatio-temporal Processing for Communication"and its associated citations which are hereby incorporated by reference.

Referring firstly to Figure 1, there is shown a radio antenna device indicated generally by 10. The device 10 includes twelve antennae, for example an antenna 20, spatially arranged so as to define a cuboid volume as denoted by 30. The volume 30 includes at each of its edges a corresponding antenna represented by a circular graphical symbol.

Each antenna is disposed so that its nominal centre is located substantially mid-way along its associated edge. Although each antenna is denoted by a circular symbol, it will be appreciated that each antenna can have a spatial extent which extends significantly away from the mid-points of the edges.

Neighbouring edges of the volume 30 are substantially orthogonal although some deviation of a few degrees, for example 15°, from orthogonality can be tolerated.

Figure 2 shows a sketch of a simple electrical dipole antenna 40 which may be used to form each edge of the antenna device 10 shown in Figure 1. The dipole antenna 40 may in

its simplest form consist of two single antenna elements each forming a line. The two line elements 41,42 may be two strings or wires of electrical conductive material. The conductive material may be a metal, such as copper or aluminium. Preferably the two line elements 41,42 each has a length being half the total length of the line. In a centre part 43 each of the two line elements 41,42 may be fixed by a dielectric material. The centre part 43 may also comprise a termination of the two single antenna elements.

In Figure 2 the dashed lines indicate the directivity pattern of the dipole antenna when used as a receiver, this pattern being essentially the same for the antenna being used as a transmitter. The figure-of-eight pattern indicates that the antenna has its maximum sensitivity at an axis perpendicular to its main axis. Along its main axis the sensitivity is almost zero.

Figure 3 shows an antenna device 50 formed by twelve electrical dipole elements, each being similar to the one sketched in Figure 2. As seen in Figure 3 each of the twelve dipole elements form an edge of a cube so that a length of each dipole element essentially forms an edge length of the cube. In each of the eight corners of the cube the antenna elements may be positioned close to each other, but preferably their ends do not touch each other since this would electrically connect the elements thus deteriorating performance of the antenna device. Preferably, the dipole elements are similar, however small deviations due to production tolerances are not important with respect to performance of the antenna device. An edge length of half a wavelength may be preferred, but an edge length in the interval between a quarter of a wavelength and half a wavelength may also be preferred.

As the skilled person will know a simple electrical dipole antenna element for the antenna device in Figure 3 may be implemented in many different ways. However, it is possible to implement it very simple, such as two pieces of wire, and therefore it is possible to implement an antenna device according to the invention easy and simple without the need for any optimisation of physical parameters, such as directivities etc. , after production.

Figure 4 sketches an embodiment of an antenna device 60 with twelve dipole antenna elements, e. g. a principle similar to the one in Figure 3. Cables from each antenna element are indicated with thin dashed lines. In Figure 4 shows a preferred position of cables between each of the twelve antenna elements and a signal processing unit positioned in the centre of the cube with a cable for external termination, indicated with a bold dashed line, leaving the cube via one of its openings, for instance its bottom part. In this way it is possible to have all cabling positioned within the cube volume thus saving space. If preferred, all twelve cables from the antenna elements may be collected in the centre part of the cube and leave the cube for connection with a signal processing device being

positioned external to the cube. Cabling of each dipole element is known to persons skilled in the art.

In Figure 4 the ends of the antenna elements are mechanically connected in the cube corners by small elements of dielectric material 80. In this way it is possible to produce an antenna device being self-supporting provided that the material of the antenna elements has a sufficient stiffness. It may also be preferred to build the antenna elements into a box, for example a plastic box, so as to protect the antenna elements which then may then be mechanically weak, such as thin wire.

In practice, for instance when forming part of an antenna device sketched in Figure 3 or Figure 4, a dipole antenna as sketched in Figure 2 will exhibit a sensitivity pattern that will deviate from the theoretical figure-of-eight pattern shown in Figure 2. This is due to the fact that each single dipole antenna mutually couple since they are positioned physically close to each other. The close coupling changes the sensitivity pattern, which again decreases a correlation leading to an increased capacity of the antenna device.

Figure 5 shows a graph from J. W. Wallace and M. A. Jensen'The capacity of MIMO wireless systems with mutual coupling', Vehicular Technology Conference, 2002-Fall, pp. 696-700.

From this graph it is seen that with respect to channel capacity mutual coupling of antenna elements forming part of a larger antenna device of several antennas actually increases the capacity of the antenna device. From the graph in Figure 5 it is seen that channel capacity actually may reach a maximum even at very closely spaced antenna elements having a distance of less than 0.2 times the wavelength.

Figure 6 shows a graph with ordered mean gain values in dB for an antenna device with 12 independent channels. The values in Figure 6 are computed values. As seen in Figure 6,8 channels exhibit a gain higher than 0 dB with the highest gain being approximately 17 dB.

The weakest channel has a gain of-17 dB thus requiring a substantial signal-to-noise ratio (SNR) in order to be practically applicable.

Figure 7 shows computed capacity in bit/s/Hz for the twelve dipole element antenna device as a function of the SNR in dB. For the full capacity case (unbroken line) it is seen that a capacity of more than 40 bit/s/Hz can be obtained at a SNR of 20 dB. A capacity of 20 bit/s/Hz can be obtained at a SNR of approximately 11 dB. Almost 30 bit/s/Hz can be obtained at a SNR of 20 dB using horizontal polarization only.

Figure 8 shows mean capacity over many realizations for the antenna device with twelve dipole elements, the mean capacity is shown as a function of cube size indicated as a fraction of a wavelength. The curve'Capacity b/s/Hz, SNR=20 dB'indicates a capacity in <BR> <BR> bit/s/Hz that can be obtained at a SNR of 20 dB. 'Nmean'indicates the number of active

channels that can be achieved. 'Gain dB'indicates a gain in dB obtained for the channel with the highest gain. As seen a maximum capacity is obtained at a cube side of more than approximately 0.35 of a wavelength. However, it should be noted that a maximum gain of approximately 20 dB can be obtained for a single channel even with a very compact cube of only 0.05 times the wavelength.

The shown embodiments are in principle capable of handling twelve independent channels, provided the SNR is sufficient, such as 20 dB. However, for certain applications it may be preferred to utilize one channel only but then achieving an antenna gain of 20 dB.

An antenna device 60 with twelve dipole antennae as sketched in Figure 4 may be implemented in a cubic box cast in a dielectric material and with the antenna elements cast into this material. Cabling and signal processing device may then be mounted within the box so as to form a very compact antenna device suited for easy production.

It will be appreciated that modifications can be made to embodiments of the invention described in the foregoing without departing from the scope of the invention.