Abstract:
Embodiments of the invention relate to a broadband antenna structure and an antenna arrangement comprising the antenna structure and an electronic device. In one aspect, the antenna employs an electrically conductive enclosure with a closed end, over which a non-electrically conductive cover is placed. A radiating portion of the antenna feed layer comprising a conductive patch antenna element is placed in between the enclosure and the cover. This patch antenna element design is inherently broader band than that of conventional cavity-backed slot-radiating antennas, which are constrained in bandwidth by the need to keep the cavity formed in the enclosure small, so that the column elements may be arranged in an array at substantially half-wavelength spacing. The new design suffers less compromise in terms of bandwidth in achieving the same size constraint. This is achieved in part by the dielectric constant of the dielectric material of the cover reducing the required size of the conductive antenna element, compared to the size that would be required if the radiating portion were covered with a material with the dielectric constant of air. In another aspect, this broadband antenna structure is connected with an electronic device to form an antenna arrangement, wherein a portion of the antenna feed layer extends outside of the antenna housing through an opening in a surface of the antenna housing, said portion being within the electronic device enclosure of the electronic device. Connecting the electronic device directly to the antenna according to embodiments of the invention reduces the amount of coaxial cables needed or eliminates the need for coaxial cables completely. As a result the usual costs associated with coaxial cables, the RF losses introduced by the cables which can compromise the system performance, possible failure of the cables, lease costs for the space the cables occupy and lease costs for large footprint of the building or cabinet housing the electronic device are substantially reduced or eliminated.

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to a broadband antenna structure and an antenna arrangement comprising the antenna structure and an electronic device, and is particularly, but not exclusively, suited to physically connecting an electronic device onto an exterior surface of an antenna and providing electrical coupling between the antenna and its associated control electronics. 
       BACKGROUND OF THE INVENTION  
       [0002]    Antennas are transducers designed to transmit or receive electromagnetic waves. Those used at cellular communications base stations are commonly located on top of buildings, towers or masts to maximise or control the geographic coverage area of the system. The antennas are typically connected with electronic devices such as amplifiers, filters, transceivers etc via one or more coaxial cables. To ease maintenance and historically because of their size, the electronic devices connected to the antennas are conventionally housed remotely from the antennas and are positioned on the ground or in a building. This arrangement has a number of drawbacks which include the high cost of coaxial cables of this type, the RF losses introduced by the cables which can compromise the system performance, possible failure of the cables or the connectors used to attach them to the antennas and equipment, passive inter-modulation distortion due to metal-to-metal contact in the connectors, lease costs associated with the space that the cables occupy, and lease costs associated with the large footprint of the building or of the cabinet housing the electronic device. 
         [0003]    As is known, antennas include a feed layer comprising a radiating portion and a feed network. The feed layer in conventional arrangements is located inside the housing or radome of the antenna so as to protect the feed layer from the effects of environmental exposure including rain, wind, sand, UV, ice, etc, and mechanical damage. Such an arrangement is known from the applicant&#39;s co-pending patent application U.S. patent application Ser. No. 11,966,501, which describes a cavity-backed, slot-radiating type antenna. In this arrangement, an electrically conducting enclosure has an open or partially open end and a cover. The cover is configured with a slot which is positioned over the resonant cavity formed by the enclosure. The resonance cavity is then excited by or excites the feed layer located in between the enclosure and the cover, such that the higher the volume of the cavity, the greater the bandwidth that can be achieved. This arrangement is however constrained in bandwidth by the need to keep the cavity in the enclosure small, so that the sub-arrays may be arranged in an array at substantially half-wavelength spacing that is required for multi-element array antennas. Furthermore, this slot antenna design requires separate slots for each polarisation. 
         [0004]    It would be desirable to provide a broadband antenna with reduced cost and weight that can be connected with (and removed from) an electronic device easily and preferably with the aim of avoiding at least some of the disadvantages associated with connecting an antenna with a remotely located electronic device as described above. 
       SUMMARY OF THE INVENTION  
       [0005]    In accordance with a first aspect of the present invention, there is provided an antenna arrangement comprising: 
         [0006]    an antenna, said antenna comprising an antenna housing and a feed layer, said antenna housing having a surface and said surface comprising an opening; and 
         [0007]    an electronic device, said electronic device comprising an electronic device housing, 
         [0008]    wherein a portion of the feed layer protrudes outside of the antenna housing through the opening, said outside portion being within the electronic device housing of the electronic device. 
         [0009]    Connecting the electronic device directly to the antenna according to embodiments of the invention reduces the amount of coaxial cables needed or eliminates the need for coaxial cables completely. As a result the costs associated with coaxial cables, the RF losses introduced by the cables which can compromise the system performance, possible failure of the cables, lease costs for the space the cables occupy and lease costs for large footprint of the building or cabinet housing the electronic device are substantially reduced or eliminated. 
         [0010]    Whilst, as described above, it is normally not desirable to extend a portion of the feed layer outside of the antenna enclosure housing, configuring the feed layer in this way has the advantage of facilitating direct coupling between the feed layer and the electronic device track. Embodiments of the invention ensure feed layer protection by locating the outside portion of the feed layer within the electronic device housing of the electronic device which is connected with the antenna. 
         [0011]    In embodiments of this aspect of the invention, the electronic device comprises an electrically conductive track, and the electronic device track is coupled to the feed layer of the antenna. In one arrangement, the electronic device track is coupled to the feed layer of the antenna by means of broadside coupling, preferably an overlay coupling. Using an overlay coupling instead of conventional connectors eliminates possible failure, losses and costs associated with the connectors and passive inter-modulation distortion due to metal-to-metal contact in the connectors. 
         [0012]    In a preferred arrangement, the overlay coupling comprises two dielectric substrates, the feed layer being printed on a surface of one dielectric substrate, and the electronic device track being printed on a surface of the other dielectric substrate, wherein said two substrates are positioned such that a section of the feed layer is in registration with a section of the electronic device track. 
         [0013]    Printing the feed layer and the electronic device track on two separate substrates means that the feed layer of the antenna and the electronic device track are not permanently connected and are thus easily separable, which simplifies maintenance and assembling of the antenna arrangement. 
         [0014]    The aforementioned coupling of the feed layer and the electronic device by means of overlay coupling requires bringing the feed layer of the antenna and the electronic device track close together. This can be difficult to achieve in practice. The first difficulty to overcome is that, since the electronic device is normally populated with electronic components, it is not naturally in close enough proximity to the antenna feed layer. Secondly, the antenna feed layer outside the antenna enclosure may be at right angles to that of the electronic device track. Thirdly the antenna may use a triplate structure whereas the electronic device track is likely to use microstrip structure in the coupling region. Further aspects of the present invention address these problems. 
         [0015]    The first problem is partly solved by extending only a portion of the feed layer outside of the antenna enclosure and bringing only this portion of the feed layer close to the electronic device track. 
         [0016]    In some embodiments of the invention, the electrically conductive enclosure is substantially U-shaped and the feed layer is formed around an outer surface of the enclosure. The enclosure has a closed end without an opening and, unlike the prior art, slots are not provided in the enclosure. The enclosure can therefore be made of a continuous sheet of material which can be formed using an extrusion process or a folding process from a continuous sheet of material, both of which are relatively cheap and easy compared to the moulding process used in the prior art. 
         [0017]    One advantage of the enclosure being substantially U-shaped is that it readily allows different track-to-ground-plane spacings to be used in the distribution network and microstrip patch antenna sections. Small ground plane spacings are advantageous for the distribution network as they allow narrow line widths to be used for the impedances typically required in such a network, while large ground plane spacings beneath the patch elements allow broadband element designs to be implemented. The transition from one type of spacing to another can conveniently occur at the corners of the U shaped enclosure. 
         [0018]    In a preferred arrangement, the feed layer is substantially U-shaped so as to wrap around the corresponding U-shaped electrically conductive enclosure. This is desirable, especially when multiple dual polarization sub-arrays are provided, because U-shaped feed layers facilitate a simple dual polarized sub-array construction and simplifies the alignment of a plurality of closely spaced sub-arrays. 
         [0019]    In one embodiment of the invention, the feed layer comprises a plurality of patch antenna elements, and is printed on a dielectric substrate. The use of patch antenna elements instead of a cavity-backed, slot-radiating type used in the prior art provides an increase in broadband performance. 
         [0020]    In embodiments of the invention, the antenna comprises a ground plane for the feed layer within the antenna housing, and the electronic device comprises a ground plane for the electronic device track. In this arrangement, part of the portion of the feed layer extending outside of the antenna has a ground plane, which is electrically coupled to both the ground plane of the antenna and the ground plane of the electronic device. This arrangement provides a continuous ground plane for the feed layer inside and outside the antenna housing thus allowing a continuous transmission line. This in part solves the problem that the antenna uses a triplate structure whereas the electronic device track uses microstrip structure in the coupling region. 
         [0021]    In accordance with another aspect of the present invention, there is provided a method for connecting an electronic device with an antenna according to the appended claims. 
         [0022]    In accordance with another aspect of the present invention, there is provided an antenna arrangement comprising: 
         [0023]    an electrically conductive enclosure and a feed layer thereon, wherein the feed layer comprises a first electrically conductive track; 
         [0024]    an electronic device, said electronic device comprising a second electrically conductive track; and 
         [0025]    a substrate arranged to secure a section of the first electrically conductive track in registration with a section of the second electrically conductive track so as to facilitate electromagnetic coupling therebetween. 
         [0026]    As mentioned above, using an overlay coupling instead of conventional connectors eliminates possible failure, losses and costs associated with the connectors and passive inter-modulation distortion due to metal-to-metal contact in the connectors. 
         [0027]    In accordance with another aspect of the present invention, there is provided an antenna comprising: 
         [0028]    an electrically conductive enclosure; 
         [0029]    an non-electrically conductive layer comprising a portion covering at least part of a closed end of the enclosure; and 
         [0030]    a feed layer located between the enclosure and said portion of the non-electrically conductive layer, the feed layer comprising a conductive antenna element and an electrically conductive track, 
         [0031]    wherein said radiating portion and said portion of the non-electrically conductive layer provide a radiating element, and said radiating element is at least part aligned with the closed end. 
         [0032]    In one arrangement, the conductive antenna element is a conductive patch antenna element. 
         [0033]    The advantage of embodiments of this aspect of the invention is that the radiating element is inherently broader band (approx 25% of centre frequency compared to approx 15%) than are prior art antennas. The design described in U.S. patent application having application number U.S. patent application Ser. No. 11/966,501 is constrained in bandwidth by the need to keep the cavity formed in the enclosure small, so that the column elements may be arranged in an array at substantially half-wavelength spacing. Antennas according to an embodiment of the invention suffer less compromise in terms of bandwidth in achieving the same size constraint. 
         [0034]    This is achieved in part by the dielectric constant of the dielectric material of the non-electrically conductive cover reducing the required size of the conductive antenna element, compared to the size that would be required if the radiating portion were covered with a material with the dielectric constant of air. Another factor that affects the achievable bandwidth is the spacing between the electrically conductive enclosure and the feed layer, together with the dielectric beneath the patch antenna elements. In embodiments of the invention, there is a relatively large ground plane spacing between the middle surface of the electrically conductive enclosure and the feed layer, and the region beneath the patch antenna elements comprises an essentially air dielectric. This configuration affords the antenna a greater bandwidth of operability. 
         [0035]    Unlike conventional arrangements, the bandwidth is not constrained by the volume occupied by the cavity formed by the enclosure because the resonance structure, which is excited by or excites the feed layer, is provided by the gap between the ground plane, i.e. the middle surface of the electrically conductive enclosure, and the feed layer, instead of a cavity in the present invention. In fact, using patch antenna elements as conductive antenna elements eliminates the need for a cavity completely, or enables the cavity to be filled, for example by an electronic device such as a beam former. 
         [0036]    Preferably, the feed layer comprises the electrically conductive track and the feed layer is printed on a single substrate. The use of a single substrate reduces the cost and complexity of the design. The integrated feed network technology is also designed to permit ready integration of other RF elements that might for example be part of an integrated masthead cellular base station design, within the antenna housing. 
         [0037]    Preferably, the enclosure comprises two closed sides, each side having two end portions, wherein one of said end portions of a first closed side is joined to one of the end portions of a second closed side by the closed end of the enclosure. Preferably, the enclosure also comprises two open sides and an open end. 
         [0038]    Preferably the antenna comprises an electrically conductive layer covering, or providing, at least part of a closed side of the enclosure in the form of a ground plane. This ground plane forms an enclosed triplate transmission region which results in a well controlled distribution circuit and minimizes radiated and received interference. In addition, this isolates adjacent feed networks of adjacent sub-arrays and thereby minimizes interference between adjacent feed networks of different sub-arrays. In one embodiment, the triplate region is substantially air space e.g. by means of foam spacers so as to reduce costs. 
         [0039]    In one embodiment, the antenna comprises a dielectric spacer between said closed end of the enclosure and the radiating portion. Preferably, the dielectric spacer is arranged to separate the feed layer from said closed end of the enclosure by a distance greater than a distance between said feed layer and a said closed side of the enclosure. 
         [0040]    In one arrangement, the closed end can be provided by two sides. 
         [0041]    In one embodiment a sub-array is implemented as a multi-antenna array, comprising: 
         [0042]    a further electrically conductive enclosure, the further electrically conductive enclosure and the electrically conductive enclosure being located on two opposite sides of the electrically conductive layer, wherein the electrically conductive layer covering at least part of a closed side of the further electrically conductive enclosure; 
         [0043]    a further non-electrically conductive layer comprising a portion covering at least part of a closed end of the further enclosure; and 
         [0044]    a further feed layer located between the further enclosure and said portion of the further non-electrically conductive layer, the further feed layer comprising a further radiating portion comprising a conductive antenna element, 
         [0045]    wherein said further radiating portion and said portion of the further non-electrically conductive layer provide a further radiating element, and at least part of said further radiating element is aligned with the closed end. 
         [0046]    In one arrangement, the conductive antenna element is a conductive patch antenna element. In another arrangement, the non-electrically conductive layer and the further non-electrically conductive layer are provided as a single non-electrically conductive layer. Preferably, the further feed layer is located between the further enclosure and the electrically conductive layer. 
         [0047]    In a dual polarized antenna embodiment, there is also provided: 
         [0048]    a further electrically conductive cover covering at least part of the second side of the enclosure, 
         [0049]    wherein the feed layer comprises two electrically conductive tracks, a first of the two tracks extending between the first side of the enclosure and the electrically conductive cover covering at least part of the first side, and a second of the two tracks extending between the second side of the enclosure and the further electrically conductive cover. 
         [0050]    Another advantage of embodiments of this aspect of the invention is that the conductive antenna elements combine two polarisation elements in one patch, as opposed to the previous slot antenna design that required separate slots for each polarisation. As a result, a dual polarised vertical column sub-array with a given number of elements may be somewhat shorter in length. Furthermore, each polarization element is allotted almost twice the length along the longitudinal axis of the sub-array that would be allocated in the previous slot antenna design, allowing greater design freedom. 
         [0051]    Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0052]      FIG. 1  is a schematic diagram showing an antenna arrangement comprising a single polarized stand-alone single sub-array antenna and an electronic device according to an embodiment of the invention; 
           [0053]      FIG. 2  is a schematic diagram showing a dual polarized feed layer printed on a film layer; 
           [0054]      FIG. 3  is a schematic diagram showing more detailed construction of an antenna arrangement of  FIG. 1 ; 
           [0055]      FIG. 4  is a schematic diagram showing a dual polarized embodiment of an antenna arrangement of  FIG. 3 ; 
           [0056]      FIG. 5  is a schematic diagram showing details regarding the ground planes of a dual polarized embodiment of an antenna arrangement of  FIG. 3 ; 
           [0057]      FIG. 6A  is a schematic diagram showing coupling between a feed layer of an antenna and an electronic device track of an electronic device inside the electronic device enclosure without folding the feed layer; 
           [0058]      FIG. 6B  is a schematic diagram showing coupling between a feed layer of an antenna and an electronic device track of an electronic device inside the electronic device enclosure after folding the feed layer; 
           [0059]      FIG. 7  is a schematic diagram showing two piece overlay coupling between a feed layer of a single polarized antenna and an electronic device track of an electronic device inside the electronic device enclosure; 
           [0060]      FIG. 8A  is a schematic diagram showing an antenna arrangement comprising a multi-element array antenna and an electronic device comprising a plurality of electronic device tracks according to an embodiment of the invention; 
           [0061]      FIG. 8B  is a schematic diagram showing an antenna arrangement comprising a multi-element array antenna and a plurality of electronic devices each comprising an electronic device track according to an embodiment of the invention; 
           [0062]      FIG. 8C  is a schematic diagram showing an antenna arrangement comprising a multi-element array antenna and an electronic device comprising an electronic device track according to an embodiment of the invention; 
           [0063]      FIG. 8D  is a schematic diagram showing an antenna arrangement comprising a multi-element array antenna and an electronic device comprising an electronic device track, wherein feed layers of the antenna are combined inside the electronic device enclosure before coupled with the electronic track, according to an embodiment of the invention; 
           [0064]      FIG. 9  is a flow diagram showing steps involved in assembling a novel dual polarized antenna structure according to an embodiment of the invention; 
           [0065]      FIG. 10  is a flow diagram showing steps involved in physically connecting an electronic device onto an exterior surface of an antenna according to an embodiment of the invention; 
           [0066]      FIG. 11  is a schematic diagram showing detailed components for assembling an antenna arrangement according to an embodiment of the invention; 
           [0067]      FIG. 12  is a schematic diagram showing structural details of a side surface of an electrically conductive layer used in assembling an antenna arrangement according to an embodiment of the invention; 
           [0068]      FIG. 13  is a schematic diagram showing alignment between a section of the film layer and an uncovered surface of the spacer outside the antenna housing according to an embodiment of the invention; 
           [0069]      FIG. 14  is a schematic diagram showing a printed circuit board arrangement inside an electronic device according to an embodiment of the invention; and 
           [0070]      FIG. 15  is a schematic diagram showing two piece overlay coupling between a feed layer of a dual polarized antenna and two electronic device tracks of an electronic device according to an embodiment of the invention. 
       
    
    
       [0071]    Several parts and components of the invention appear in more than one Figure; for the sake of clarity the same reference numeral will be used to refer to the same part and component in all of the Figures. In addition, certain parts are referenced by means of a number and one or more suffixes, indicating that the part comprises a sequence of elements (each suffix indicating an individual element in the sequence). For clarity, when there is a reference to the sequence per se the suffix is omitted, but when there is a reference to individual elements within the sequence the suffix is included. 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0072]    As described above, embodiments of the invention are concerned with physically connecting an electronic device with an antenna to overcome some or all of the disadvantages associated with connecting an antenna with a remotely located electronic device. Specifically, embodiments of the invention provide a novel arrangement of an antenna structure and electronic components which interface with the antenna structure so as to input and output signals transceived therefrom. 
         [0073]    In particular, embodiments of the invention are concerned with physically connecting an electronic device onto an exterior surface of an antenna and coupling an electrically conductive track of the electronic device with a feed layer of the antenna outside the antenna housing but inside the electronic device enclosure, preferably without metal-to-metal contact, thus minimizing passive inter-modulation distortion, reducing losses, increasing reliability and reducing cost. 
         [0074]    The antenna in embodiments of this invention can form either a sub-array within a multi-element array antenna, or a stand-alone single-element or single sub-array antenna. A single sub-array can be used to form an antenna in its own right, for example suitable for use as a conventional tri-sectored masthead cellular base station antenna. A multi-element array antenna may be desirable for higher capacity and higher coverage cellsite antenna systems. Examples of an electronic device which may be desirably connected to the antenna in accordance with embodiments of the invention include an azimuth beam former, an amplifier or a transceiver. 
         [0075]    Turning to  FIG. 1 , a first embodiment of the invention, hereinafter referred to as an antenna arrangement, will now be described. The antenna arrangement comprises an antenna  200  and an electronic device  100  connected thereto. 
         [0076]    The electronic device  100  comprises an electronic device enclosure  101  and an electrically conductive track  104  therein. The electronic device enclosure  101  is shown in  FIG. 1  to be rectangular, and whilst other shapes are possible, the enclosure  101  preferably has a substantially flat outer surface  110  in the region of physical connection to the antenna  200 . The electronic device track  104  may for example be embodied as part of an Application-specific integrated circuit (ASIC) or a discrete track  104  within an electronic device enclosure  101 , in which case it is printed on a surface of a dielectric substrate, e.g. a film or a solid substrate. A ground plane is preferably attached to another surface of the dielectric substrate. In this embodiment, the track  104  is carried by a printed circuit board (PCB). 
         [0077]    The antenna  200  comprises an antenna housing  206  and a feed layer  202 . The antenna housing has a surface  210  onto which the electronic device  100 , specifically the outer surface  110 , is connected. The surface  210  comprises an opening  212  through which a portion  201  of the feed layer extends outside of the antenna housing into the electronic device enclosure  101 . 
         [0078]    The antenna housing  206  such as a radome comprises a non-electrically conductive material, e.g. plastic or fiberglass. The material preferably allows a relatively unattenuated electromagnetic signal transmission between the antenna inside the antenna housing and outside equipment. The antenna housing  206  is shown to be rectangular; however other shapes are possible although the outer surface  210  onto which the electronic device is connected is preferably substantially flat. 
         [0079]    The opening  212  in the surface  210  is arranged such that is big enough to allow a portion  201  of the feed layer to extend through but is preferably small enough to prevent undesirable movement of the feed layer once extended into the electronic device enclosure  101 , to avoid weakening the carrier structure of the cover  220  unnecessarily, and to ensure that the cover  220  is as electrically continuous as possible to ensure a continuous ground plane structure. The opening  212  is preferably confined within the surface area  110  of the electronic device  100  which is connected to the surface  210  of the antenna  200 , so that the antenna  200  and the portion  201  of the feed layer  202  is sealed against water and other environmental conditions. 
         [0080]    The feed layer  202  is printed on a dielectric substrate which is preferably at least partly flexible. In this embodiment, the feed layer  202  is printed on a single film layer  215 . A film is chosen over a solid dielectric substrate since it is likely to reduce cost, simplify the mechanical design and have a better high frequency performance. 
         [0081]    The feed layer  202  comprises an array of conductive antenna elements  248  and one or more feed distribution networks  234   a ,  234   b , each feed distribution network comprising one or more feed lines for every conductive antenna element as shown in  FIG. 2 , each feed line being an electrically conductive track. The conductive antenna elements  248  of the feed layer  202  transceive electromagnetic waves and are fed by the common feed network  234   a ,  234   b . The feed distribution network  234   a ,  234   b  is preferably designed to exhibit a suitable characteristic impedance to match other parts of the feed network; typically 50 Ohms is used. 
         [0082]    The feed lines for all conductive antenna elements  248  are combined and a resulting track extends away from the feed network, orthogonal to the length of the feed layer  202 . As described above, a portion  201  of this resulting track then extends outside of the antenna housing  206 , and is coupled to a section  111  of an electrically conductive track  104  of the electronic device  100  as shown in  FIG. 15 . 
         [0083]    As shown in  FIG. 3  two ground planes  216 ,  221  are provided for at least the feed network regions of the feed layer along the side surfaces  216   a ,  216   b  of the enclosure  208  inside the antenna housing, thereby forming an enclosed triplate transmission region which results in a well controlled distribution circuit and minimizes radiated and received interference. 
         [0084]    The feed layer  202  may be located between the two ground planes by means of mechanical spacers (not shown) such that the dielectric surrounding the feed layer is air. Alternatively, as shown in  FIG. 3 , a dielectric material such as foam, preferably in the form of a sheet  222 ,  224 , can be positioned between the feed layer and the two ground planes  216 ,  221  respectively in order to locate the feed layer  202 . The function of the dielectric layer is to locate the feed layer relative to the ground planes, in particular so as to maintain the distance therebetween. In terms of radio frequency performance, the two approaches are similar since the dielectric properties of foam are typically very similar to those of air. 
         [0085]    In this embodiment, a first ground plane  216  is conveniently provided by an electrically conductive enclosure  208 , which also provides mechanical support for the feed layer and a second  221  by an electrically conductive cover  220 , which conveniently carries the enclosure  208  and the feed layer  202  wrapped around the enclosure  208 . In this embodiment, the enclosure  208  is substantially U-shaped. The U-shaped structure is preferably mounted on or otherwise attached to the same surface  210  which is connected to the electronic device  100  but from inside of the antenna housing  206 . The U-shaped enclosure  208 , around part or all of the outer surface of which the feed layer  202  is wrapped, comprises a middle surface and two side surfaces, the angle between the middle surface and either of the two side surfaces being preferably 90 degrees. Wrapping the feed layer around the electrically conductive enclosure  208  forms a substantially U-shaped feed layer as shown in  FIG. 4  comprising a corresponding middle portion  232  comprising the conductive antenna elements  248 , and two corresponding side portions  230   a ,  230   b  each comprising a feed network. Alternatively the feed layer can be wrapped around the middle surface of the electrically conductive enclosure  208  and only one side surface of the enclosure  208  forming a V-shaped feed layer as shown in  FIG. 3 . In either case, to ease the wrapping process, the feed layer substrate  215  is flexible at least around the corners of the enclosure  208  or is non flexible around the corners but is of a corresponding shape similar to that of the enclosure  208 . 
         [0086]    When supported in this manner by the enclosure  208 , the portion  201  of the feed layer  202  extends outside the antenna housing  206  and is coupled to the electronic device track  104  inside the electronic device enclosure  101 . 
         [0087]    The coupling might be achieved for example using a known radio frequency (RF) connector or any other suitable means. RF connectors introduce loss which degrades the receiver noise figure and reduces transmitted power. In the case of the receiver this impairs the system link budget; in the case of the transmitter it can either impact the link budget or require the transmitter to have a more powerful (and hence more expensive) power amplifier. Furthermore RF connectors and the associated jumper cables are expensive. It is therefore desirable to remove these from the system to reduce equipment costs. Since RF connectors and the associated jumper cables are a cause of system failures, it is desirable to remove these from the system to improve reliability and reduce operating expenses. 
         [0088]    Accordingly, in one arrangement, the electronic device track  104  is coupled to the feed layer  202  of the antenna by means of overlay coupling as shown in  FIGS. 6A and 6B . An overlay coupler is an example of a broadside coupler and it couples two tracks sections of approximately a quarter wavelength in length that run one above the other capacitively. The wavelength referred to here is that corresponding to approximately the centre frequency of the operating band of the antenna in the dielectric material separating the feed layer  202  from the electronic device track  104 . 
         [0089]    The configuration of the U-shaped enclosure  208  and the feed layer  202  is such that the portion  201  of the feed layer  202  extending outside of the antenna housing  206  is at 90 degrees to the surface  210  connected to the electronic device  100 . Furthermore, as shown in  FIGS. 1 and 3 , in this embodiment, the electronic device track  104  is parallel to the surface  110  of the electronic device enclosure  101  which is connected to the surface  201  of the antenna. Therefore the portion  201  of the feed layer  202  extending outside of the antenna housing  206  is at an angle of 90 degrees relative to the electronic device track  104 . In order to achieve an overlay coupling arrangement in the manner described above, the portion  201  of the feed layer  202  is positioned parallel to the device track  104 . 
         [0090]    In this embodiment, a spacer  300 , possibly in the form of a block of non-electrically conductive material as shown in  FIG. 3 , is secured to the outer surface  210  of the antenna housing  206  which is in turn connected to the electronic device  100 . The height of the spacer  300  is preferably determined by the expected component height on the electronic device substrate. The portion  201  of the feed layer  200  is folded around a spacer  300  to bring it parallel to the electronic device track  104 . Alternatively, the electronic device  100  can be connected to the antenna surface  210  as shown in  FIG. 6A , so that the electronic device track  104  is parallel to the portion  201  of the feed layer  202  without folding the portion  201 . 
         [0091]    Once the portion  201  is secured, parallel, to the electronic device track  104 , the combined arrangement forms an overlay coupler. The benefit of an overlay coupler is that it allows connection of two tracks without metal-to-metal contact, thus minimizing passive inter-modulation distortion reducing losses, increasing reliability and reducing cost. In order to achieve effective coupling, the feed layer section  211  and the electronic device track section  111  of the overlay coupling are both substantially a quarter wave length in the dielectric constant of the substrate in between them. The overlay coupling is preferably aligned with the longitudinal axis of the feed layer, and consequently, the portion  201  outside of the antenna housing  206  is bent around an axis perpendicular to both the longitudinal and the transverse axis of the feed layer by 90 degrees as shown in  FIG. 2 . A resulting end portion  209  of the feed layer  202  is substantially aligned with the antenna and at least part  211  of the end portion  209  is coupled to a section  306  of the electronic device track  104 . 
         [0092]    The overlay coupling can be achieved using known one piece overlay coupling e.g. known broadside coupling, wherein the feed layer  202  and the electronic device track  104  are printed on opposite sides of a dielectric substrate so that a section of the feed layer  202  is at least partially aligned with a section of the electronic device track  104 . However, use of such a one piece overlay coupling arrangement means that the feed layer  202  of the antenna and the electronic device track  104  are permanently connected, which can be impractical and undesirable for maintenance and assembling. 
         [0093]    In a preferred arrangement a two piece overlay coupling arrangement is used. In a general sense, a suitable overlay coupling  500  comprises two dielectric substrates, the feed layer  202  being printed on a surface of one dielectric substrate, and the electronic device track  104  being printed on a surface of the other dielectric substrate  103 ; the two substrates are positioned such that a section of the feed layer  202  is in registration with a section of the electronic device track  104 . A dielectric substrate is located between a section  203  of the portion  201  of the feed layer  202  and a section  111  of the electronic device track. Preferably at least one of the two dielectric substrates, i.e. either or both the two dielectric substrates is located between the two sections of tracks. It is appreciated that this coupling arrangement of an electrically conductive track carried by the feed layer and an electrically conductive track of the electronic device provides a novel antenna arrangement comprising an antenna and an electronic device. 
         [0094]    In a preferred arrangement of the overlay coupling, and as shown in  FIG. 3 , the feed layer  202  is printed on the inner surface  218  of the feed layer substrate  215  closest to the U-shaped enclosure  208 ; the portion of the feed layer substrate  215  carrying the feed layer outside the antenna housing  206  is then folded around a spacer  300  and is located between a section  203  of the feed layer and the electronic device track  104  as also shown in  FIG. 7 . Alternatively, a third dielectric substrate (not shown) can be provided in between a section  203  of the portion  201  of the feed layer  202  and a section  111  of the electronic device track  104 . Examples of a suitable dielectric substrate layer include air, a film layer and a solid dielectric substrate layer. In this arrangement, the section  203  of the feed layer  202  is at the end of the portion  201  and the section  111  of the electronic device track  104  is at one end of the track  104 ; however this is not necessary. For example, the sections can be in the middle of or at the other end of the two tracks respectively. 
         [0095]    A ground plane is required for the overlay coupling  500 . In this embodiment, the ground plane  105  for the electronic device track  104  acts as the ground plane for the overlay coupling forming a microstrip transmission line structure for the coupling  500  as shown in  FIG. 5 . As a result, part of the feed layer  202  is in a triplate structure, e.g. the region within the antenna housing  206  (as described above), and part of the feed layer  202 , e.g. the coupling region  500  and the parallel section  203  which is not coupled to the electronic device track  104 , comprises a microstrip. The feed layer  202  is preferably designed so that the impedance remains substantially constant along the entire length of the feed layer  202  (i.e. throughout the tri-plate region and the micro-strip region); this may be achieved by varying the width of the tracks in the respective portions. 
         [0096]    The ground planes  216 ,  221  of the feed layer  202  inside the antenna housing  206  need to be electrically coupled to the ground plane  105  of the electronic device track  104  to allow a continuous transmission line. Electronic coupling may be achieved by direct physical connection or through an intermediary e.g. via electrical wires. Direct physical coupling could be selected, for example, if the whole of the portion  201  of the feed layer  202  outside the antenna housing  206  is coupled to the electronic device track  104 , in which case the ground plane for the electronic device track  104  can act as the ground plane  105  for the entire portion  201  of feed layer  202 . 
         [0097]    However, when only a section  203  of the portion  201  of the feed layer is coupled to the electronic device track  104  as shown in  FIGS. 6A and 6B , at least one ground plane  404  needs to be provided for at least the part  205  of the portion  201  of feed layer  202  which is not coupled to the electronic device track  104  as shown in  FIG. 6A  or which is not parallel to the electronic device track  104  as shown in  FIG. 6B . Furthermore, as shown in  FIG. 3 , the ground plane  404  is arranged so that it is electrically coupled to both the ground planes  216 ,  221  of the antenna  200  and the ground plane  105  of the electronic device  100 . That is to say, the ground planes  216 ,  221  of the feed layer  202  are electrically coupled to the ground plane of the electronic device track  104  through the ground plane  404  for the part  203  of the feed layer  202 . 
         [0098]    In this embodiment, two ground planes, for example two blades of material, are provided for the part  203  of the feed layer  202 , one on each side of the part  203  of the portion  201  of the feed layer  202 . The part may be located between the two ground planes  400 ,  404  by means of mechanical spacers (not shown). Alternatively, two layers of dielectric material such as foam  450 ,  452 , similar to the arrangement for the triplate region of the feed layer inside the antenna housing  206  as discussed above. Alternatively one of the two ground planes can be provided by a side surface of a U-shaped metal layer comprising two side surfaces and a middle surface. The U-shaped metal layer is preferably wrapped around the spacer  300 , with the middle surface connected to the antenna housing  206 . 
         [0099]    Preferably the cover  220 , also acting as a carrier for the enclosure  208  as well as the second ground plane for the feed layer  202  inside the antenna housing, is V-shaped or T-shaped (shown as T-shaped in  FIG. 3 ) such that one section  221  of the cover  220  forms the second ground plane and a perpendicular section  223  forms part of the surface  210  of the antenna housing  206  which is connected to the electronic device  100 . The non-electrically conductive material covering the antenna housing  206  preferably discontinues for at least some of the part of the perpendicular section  223  which is covered by the surface  110  of the electronic device  100  which is connected to the antenna  200 . As a result the ground plane(s) inside the electronic device can be electrically coupled to the second ground plane of the feed layer  202  within the antenna housing easily, e.g. by mounting the ground plane(s) inside the electronic device onto, or otherwise attaching to, this section  223 . 
         [0100]    The conductive antenna elements  248  transceiving electromagnetic waves need to be protected by a non-electrically conductive material, which allows a relatively unattenuated electromagnetic signal transmission between the antenna inside the antenna housing  206  and outside equipment. Accordingly, in this embodiment, the conductive antenna elements are placed on top of the middle surface of the U-shaped enclosure  208 , surrounded by the non-electrically conductive material, and located away from the surface  201 , which is not covered by the non-electrically conductive material. 
         [0101]    The conductive antenna elements excited by the feed layer can for example be of a cavity-backed, slot-radiating type as discussed in the prior art. In another arrangement, the conductive antenna elements of the feed layer comprise an array of patch antenna elements  248 , as shown in  FIG. 2 . The patch antenna elements  248  are then fed by a common feed network, a portion of which extends outside of the antenna housing  206  as discussed above. 
         [0102]    Unlike the prior art, slots are not provided in the enclosure  208 . The enclosure  208  can therefore be made of a continuous sheet of material which can be formed using an extrusion process or a folding process from a continuous sheet of material, which is relatively cheap and easy compared to the moulding process used in the prior art. A flat sheet of material can be made then folded to form an enclosure  208  as described above. Alternatively a folded enclosure  208  can be formed using an extrusion process directly. Opening portions can be made on the side surfaces of the enclosure  208  if desirable. 
         [0103]    The middle and two side surfaces of the U-shaped enclosure  208  may form a cavity; unlike conventional arrangements, the bandwidth is not constrained by the volume occupied by the cavity because the resonant structure, that is excited by or excites the feed layer, is provided by the gap between the ground plane, i.e. the middle surface of the electrically conductive enclosure  208 , and the feed layer, instead of a cavity. In fact, using patch antenna elements  248  can eliminate the need for a cavity completely, or enables the cavity to be filled, for example by an electronic device such as a beam former. 
         [0104]    In another arrangement, the electronic device track  104  may be carried by a PCB  106 , said PCB being located within the antenna housing  206 , possibly within the cavity of the enclosure  208 . A section  111  of the electronic device track  104  can then be coupled to a section  203  of the feed layer  202  inside the antenna housing  206  as described above. In this arrangement, the electronic device  100  of the antenna arrangement can have an enclosure  101  as described above. Alternatively, the electronic device  100  might not have an enclosure  101 . 
         [0105]    In this embodiment, a second ground plane is not provided along the middle surface of the enclosure  208  above the middle portion  232  of the feed layer  202 , this comprising the patch antenna elements  248 . Instead, a non-electrically conductive cover  250  such as a polycarbonate sheet is provided on top of the middle portion  232  of the feed layer  202  to reduce the resonant frequency for the patch antenna elements as shown in  FIG. 3 . The non electrically conductive cover  250  and the middle surface of the enclosure  208 , with the feed layer  202  held there in between, is secured together by securing means, e.g. via screws and nuts or other suitable fixing means. In one arrangement, the non-electrically conductive cover  250  forms part of the antenna housing  206 . It will be appreciated that this arrangement of patch antenna elements  248  in conjunction with the electrically conductive enclosure  208  and the non-electrically conductive cover  250  provides a novel antenna. 
         [0106]    A foam layer  226 , or air with mechanical spacers, is provided between the middle surface of the enclosure  208  and the middle portion  232  of the feed layer  202 . Generally the greater the distance between the middle surface of the electrically conductive enclosure  208  and the conductive antenna elements of the feed layer is and the lower permittivity of any intervening dielectric material, the greater the bandwidth that can be achieved. It is desirable that the same radiation characteristics are obtained over the whole band of interest, so that the antenna pattern generated over the band of interest is substantially constant. The upper limit to the spacing may be considered to have been reached when different resonant modes are excited at different parts of the band, unwanted levels of surface wave radiation is generated or when the impendence characteristic varies excessively. A different dielectric substrate and more than one dielectric substrate layer may be used instead. However, an increase in broadband performance is achieved by the combination of a relatively large ground plane spacing between the middle surface of the electrically conductive enclosure  208  and the conductive antenna elements of the feed layer, an essentially air dielectric (i.e. with low permittivity) beneath the conductive antenna elements  248 , and using patch antenna elements as conductive antenna elements. 
         [0107]    As mentioned above, embodiments of the invention can also be used for a multi-element array antenna, e.g. a multi-beam antenna, addressing the problem of the interface between the individual sub-arrays and an electronic device such as an azimuth beam former in particular, because overlay coupling is used instead of connectors, metal to metal contact and cost are reduced. Furthermore, it is easier to assemble the electronic device with the antenna this way since cable connections are not used. This is particularly significant for multi-element array antennas where more than one feed layers are connected to electronic device track(s). The embodiments shown in  FIGS. 8A ,  8 B,  8 C and  8 D, for example, comprise a multi-element array antenna comprising a plurality of sub-arrays. Each sub-array comprises an enclosure  208  and a feed layer  202 , a portion  201  of which extends outside of the antenna housing  206  through an opening  212  in the surface  210  of antenna housing  206 . Each sub-array may be provided within a different antenna housing  206  or more than one sub-array may be contained in a single antenna housing  206 . As shown in all these embodiments, the longitudinal axis of the feed layer  202 , the longitudinal axis of the feed layer substrate, and the longitudinal axis of the enclosure  208  are preferably perpendicular to the direction of the multi-element array antenna formation. 
         [0108]    A second ground plane  221  may not be provided for the feed network regions of the feed layer  202  along the side surfaces  216   a ,  216   b  of the enclosure  208  inside the antenna housing  206 , thereby forming a microstrip transmission region. However, for multi-element array antennas, a second ground plane  220  is desirable because, together with the enclosure  208 , it forms an enclosed triplate transmission line structure which results in a well controlled distribution circuit; in addition it isolates adjacent feed networks along adjacent side surfaces  216   a ,  216   b  of the enclosures  208   a ,  208   b  of adjacent sub-arrays so as to minimize interference between adjacent feed networks of different sub-arrays. 
         [0109]    As mentioned above, it is desirable to space antenna elements  248  no more than approximately a half wavelength apart in azimuth at a given cover frequency to avoid generating grating lobes in the antenna pattern with associated unwanted nulls. Therefore the outer middle surface  217  of the enclosure  208  can be of any arbitrary length depending on the size and number of the conductive antenna elements but preferably only less than or equal to half the cover frequency wavelength. Limiting the width in this fashion allows closely spaced sub-arrays to be built by positioning multiple electrically conductive enclosures  208  each carrying a feed layer  202  side by side. Furthermore, individual electrically conductive enclosures  208  of different sub-arrays are preferably inter-connected allowing the continuity of the inner ground plane. As regards the respective feed layers, each feed layer  202   a ,  202   b  can be coupled to a different, and possibly separate, electronic device track  104   a ,  104   b , in which case all electronic device tracks  104   a ,  104   b  can be provided in a single electronic device  100  comprising one electronic device enclosure  101 , as shown in  FIGS. 8A . Each electronic device track  104   a ,  104   b  can be provided in a different electronic device  100   a ,  100   b , each comprising an electronic device enclosure  101   a ,  101   b , as shown in  FIG. 8B . Alternatively, two or more feed layers  202   a ,  202   b  can be coupled to a single electronic device track  104  in an electronic device  100  as shown in  FIG. 8C . Electronic devices  100  such as amplifiers and transceivers are preferably implemented using these methods. 
         [0110]    The feed layers  202   a ,  202   b  can be coupled with one another outside of the antenna housing  206  before coupling to an electronic device track  104 . The feed layers  202   a ,  202   b  can for example be coupled with one another by a conventional connector, one piece overlay coupling, or two piece overlay coupling described above. An electrically conductive track  207  resulting from, or connected to, the coupling can then be coupled to an electronic device track  104  in an electronic device  100  as shown in  FIG. 8D . Electronic devices  100  such as beam formers are preferably connected this way. 
         [0111]    The embodiments and corresponding figures relate to single-polarized antennas. However, it is to be understood that multi-polarized antennas are equally applicable for the purpose of this invention.  FIG. 4  illustrates a dual polarized antenna embodiment of the invention, in which two feed lines, preferably orthogonal to one another, are connected to each of the conductive antenna elements, resulting in two common feed networks one on each side of the conductive antenna elements as shown in  FIG. 2 . The two feed networks cover the two side surfaces of the electrically conductive enclosure  208  respectively. As discussed above and as shown in  FIG. 2 , each feed network is then combined and a portion  201  of the resulting track extends outside of the antenna housing through an opening  212   a ,  212   b  in the surface  210  of the antenna housing  206 . The two portions are then folded around two opposite sides of the same spacer  300  before ending up on the same surface of the spacer  300 , the surface being opposite the surface of the spacer which is mounted onto the antenna housing. Both portions  201   a ,  201   b  are therefore parallel to the PCB carrying the electronic tracks so that each portion can be coupled to a section of the same or a different electronic device track respectively. 
         [0112]    The V-shaped or T-shaped cover  220  also acting as a second ground plane as shown in  FIG. 5  is provided for each polarization along a side surface of the enclosure  208 . As mentioned above, the second ground plane  221   a ,  221   b  together with the enclosure  208  forms an enclosed triplate transmission line structure which results in a well controlled distribution circuit and isolates adjacent feed networks along adjacent side surfaces  216   a ,  216   b  of the enclosures  208   a ,  208   b  of adjacent sub-arrays. The covers  220  for different polarizations may be connected or form one single cover  220 . For a dual polarized antenna, such a single cover  220  may be of a U or TT shape. 
         [0113]    In some of the above embodiments, the feed layers  202   a ,  202   b  are substantially U-shaped. This is desirable especially when multiple dual polarization sub-arrays are provided, because substantially U-shaped feed layers  202  facilitate a simple dual polarized sub-array construction and simplifies the alignment of a plurality of closely spaced sub-arrays. 
         [0114]    The above embodiments show a single feed layer  202  per enclosure  208 ; however it will be appreciated that more than one feed layer may be provided and more than one feed layer may extend outside of the antenna housing. Furthermore, whilst the feed layer  202  is associated with one feed layer substrate, the skilled person will recognise that more than one feed layer substrate may be used, and that the feed layer substrate may be made of different materials in different regions. 
         [0115]    In the above embodiments, a non-electrically conductive cover  250  is located on top of the conductive antenna elements of the feed layer  202  to provide frequency control of the radiating properties of the patch antenna elements  248  by making the patch  248  electrically larger than its physical size in the absence of the dielectric cover  250 . Although the non-electrically conductive cover  250  is desirable, it is not necessary. For example, if the dielectric substrate  226  underneath the patch antenna elements  248  is other than foam/air (i.e. of higher permittivity), the substrate  226  will also have the effect of increasing the electrical size of the patches  248 , possibly removing the need for an upper cover  250 . Alternatively, since stand alone single sub-array antennas are not constrained to 0.5 wavelengths width, the patches  248  can be physically larger, avoiding the need for any additional dielectric substrates of higher permittivity than air above or below them. 
         [0116]    As described above, and will be appreciated from a review of the figures exemplifying embodiments of the invention, the angle between the middle surface  217  of the electrically conductive enclosure  208  and either of the two side surfaces  216   a ,  126   b  of the electrically conductive enclosure  208  is preferably 90 degrees; however, other angular arrangements are possible. In particular, angles less than or close to 90 degrees are more desirable than angles substantially more than 90 degrees especially for multi-element array antennas. 
         [0117]    Another aspect of this invention relates to a method of assembling the antenna arrangement comprising an antenna  200  and an electronic device  100  described above. For illustrative purposes the method is described with reference to  FIGS. 4 ,  5 ,  10 ,  11 ,  13 ,  14  and  15 , in relation to a dual polarized stand alone single sub-array antenna; however it is appreciated that the method can be used to assemble all possible antenna arrangements described above. 
         [0118]    An antenna structure is assembled and an electronic device built before the antenna and the electronic device are connected. Before an antenna structure can be assembled, various components need to be manufactured or otherwise provided. The electrically conductive enclosure  208  comprising a continuous sheet of material is manufactured using e.g. an extrusion or folding process. The enclosure  208  is preferably U-shaped comprising a middle surface  217  and two side surfaces  216   a ,  126   b  as shown in  FIG. 4 . The enclosure  208  provides physical support for the feed layer  202  inside the antenna housing  206  and also functions as a first ground plane for the feed layer  202  inside the antenna housing  206 , as described above. 
         [0119]    A dielectric substrate such as a film layer  215  is manufactured or otherwise provided. A feed layer  202  is printed on the film layer  215  with the middle portion  232  of the feed layer  202  on a middle portion  234  of the film layer  215  and the two side portions  230   a ,  230   b  of the feed layer  202  on two side portions  236   a ,  236   b  of the film layer  215 . 
         [0120]    A TT-shaped cover  220  is manufactured or otherwise provided; the cover  220  comprises two sections  221   a ,  221   b , preferably substantially parallel to one another, functioning as a second ground plane for the two side portions  230   a ,  230   b  of the feed layer  202  inside the antenna housing  206  and one perpendicular section  223  which carries the enclosure  208 . The perpendicular section  223  comprises two openings  212   a ,  212   b  through which the two portions of film layer extend outside of the antenna housing  206  at step  28 . 
         [0121]    An antenna housing  206  is manufactured using a non-electrically conductive material, which allows a relatively unattenuated electromagnetic signal transmission between the antenna inside the antenna housing  206  and outside equipment. Referring back to  FIG. 1 , the antenna housing  206  could be of any shape; however in this embodiment, it comprises a hollow tube with a substantially flat surface  210  and two end caps. The substantially flat surface  210  comprises a hole which is to be covered by the surface  110  of the electronic device  100  after the surface  110  is connected to the surface  210  of the antenna  200 . 
         [0122]      FIG. 9  is a flow diagram showing a method of assembling a dual polarized antenna structure. At step  12  a relatively thin foam layer  224   a ,  224   b  is attached to the two outer side surfaces  216   a ,  216   b  of the enclosure  208  respectively and a relatively thick foam layer  226  attached to the outer middle surface of the enclosure  208  as shown in  FIG. 4 . In one arrangement, the relatively thin foam layers are 1 to 2 mm thick, while the relatively thick foam layer is 10 to 15 mm thick. Some or all of the foam layers  224   a ,  224   b ,  226  may be self adhesive to aid the attachment. 
         [0123]    At step  14 , and referring to  FIG. 3 , one or more spacing means (not shown), preferably of a similar height to that of the relatively thick foam layer  226 , are fixed to the outer middle surface  217  of the enclosure  208  possibly from underneath the middle surface  217  of the enclosure  208 . The spacing means may run through the relatively thick foam layer  226 . 
         [0124]    The film layer  215  is then wrapped around the outer surface of the enclosure  208  at step  18 , with the feed layer  202  on the inner surface of the film layer  215  and adjacent to the foam layers  224   a ,  224   b ,  226  attached to the enclosure  208 . The film layer  215  preferably covers the outer surface of the enclosure  208 , with the middle portion  232  of the feed layer  202  on top of the middle surface of the enclosure  208  and the side portions of the feed layer  202  overlying the side surfaces of the enclosure  208 . However, a portion  238   a ,  238   b  of the film layer  215  carrying a portion  201   a ,  201   b  of the feed layer  202  extends beyond each of the two side surfaces of the enclosure  208  respectively in accordance with step  20  and later through the openings  212   a ,  212   b  in the surface  210  of the antenna housing  206  into the electronic device enclosure  101  at step  28 . The film layer  215  is secured to the foam layers  224   a ,  224   b ,  226  attached to the enclosure  208  using e.g. glue. Optionally, temporarily fastening means may be used to achieve better alignment between the film layer and the electrically conductive enclosure  208 . 
         [0125]    Then at step  22 , a second, possibly self adhesive, foam layer  222   a ,  222   b  is attached to each of the two outer side portions of the film layer respectively. 
         [0126]    As can be seen from  FIG. 4  and better from  FIG. 5  showing only the ground plane details, the enclosure  208  carrying the feed layer  202  and foam layers  222   a ,  222   b ,  224   a ,  224   b ,  226  is located within the TT-shaped cover  220 , via the two parallel sections  221   a ,  221   b  of the TT-shaped cover  220  at step  26 . The two portions  238   a ,  238   b  of the film layer  215  carrying the two portions  201   a ,  201   b  of the feed layer  202  then extend through the openings  212   a ,  212   b  in accordance with step  28 . The enclosure  208  and the cover  220  are secured together as so to prevent relative movement with respect to one another using e.g. fastening means. 
         [0127]    At step  30 , the enclosure  208  is electrically coupled to the cover  220  to connect the two ground planes. In one arrangement, this is achieved through one or more protrusions (not shown) provided by, or attached to, the middle surface of the enclosure  208 . The protrusions extend through corresponding holes in the film layer and rest on the parallel sections  221   a ,  221   b  of the cover  220  thereby electrically connecting the first ground plane, i.e. the cover  220 , and the second ground plane, i.e. the enclosure  208 , for the feed layer inside the antenna housing. The connection between the protrusions and the cover  220  may be secured using e.g. conductive fabric tapes. 
         [0128]    A non-electrically conductive cover  250  such as a polycarbonate sheet is then placed on top of the middle portion  234  of the film layer  215  at step  32  as shown in  FIG. 4 . The non-electrically conductive cover  250  is secured to the spacing means using e.g. a corresponding number of fastening means such as nails, staples, bolts or screws. 
         [0129]    The two portions  238   a ,  238   b  of the film layer  215  carrying the two portions  201   a ,  201   b  of the feed layer  202  extending beyond the side surfaces  216   a ,  216   b  of the enclosure  208  may be temporarily taped onto the cover  220 , before the cover  220  carrying the enclosure  208  is inserted into the antenna housing  206  at step  34 . After insertion, the two openings  212   a ,  212   b  in the perpendicular section  223  of the cover  220 , through which the portions  238   a ,  238   b  of the film layer  215  extend outside of the antenna housing  206 , are arranged so that they are within the antenna housing  206 . The tape is removed to release the two portions  238   a ,  238   b  of film layer  215 , enabling them to extend through the hole in the surface  210  of the antenna housing  206 . Part of the perpendicular section  223  of the cover  220 , once inserted into the antenna housing, forms part of the surface  210  of the antenna housing  206  where the hole in the surface  210  of the antenna housing  206  is provided. 
         [0130]    Two end caps are applied to the two opposite ends of the hollow tube to help secure the cover  220  and the enclosure  208  in position at step  38 . 
         [0131]    Turning now to aspects associated with assembly of the electronic device  100 , the device enclosure  101  is typically a cast or moulded structure within which a PCB  106  carrying two parallel electrically conductive tracks  104   a ,  104   b  are fixed. Referring to  FIGS. 11 and 14 , one or more guidance pins  344  are attached to the PCB  106  so that relative lateral movement with respect to one another is restricted, using for example clinch studs. In a preferred embodiment, the guidance pins  344  can be mounted onto the ground plane  105  of the PCB  106 . The guidance pins  344  preferably comprise non-electrically conductive material. As can be seen in  FIGS. 4 and 14 , two parallel blades of metal  404   a ,  404   b , each of which is preferably of a substantially similar size to that of a side surface of the U-shaped metal  400 , are mounted onto the ground plane  105  of the PCB  106 , preferably perpendicular to the PCB  106 , so as to be able to receive the spacer  300  with the U-shaped metal layer  400  surrounding the spacer  300 , the portions  238   a ,  238   b  of the film layer  215  wrapped around the metal layer  400  and the spacer  300  and the foam layers attached thereto. 
         [0132]    The assembly of the electronic device  100  with the antenna housing will now be described with reference to  FIG. 10 : at step  52 , the middle surface of the metal layer  400  is mounted onto the outer surface of the perpendicular section of the cover  220  in between the two openings  212   a ,  212   b  using for example conductive adhesive. The physical connection of this ground plane  400  with the cover  220  ensures a continuous ground plane for the feed layer  202  inside and outside the antenna housing  206 . 
         [0133]    At step  54 , the ground plane  105  is electrically coupled with the metal layer  400 . Referring also to  FIG. 12 , the ground plane  400  is in contact with the ground plane  105  of the PCB  106  through contacting means such as one or more protrusions  440   aa ,  440   ab ,  440   ac  provided at or attached to the end of each of the two side surfaces of the U-shaped metal layer  400 . The protrusions  440   aa ,  440   ab ,  440   ac  extend through corresponding holes in the feed layer  202 , through the dielectric substrate  103  of PCB, and contact the ground plane  105  of the PCB  106 , once the electronic device  100  is connected to the antenna  200 . Once mounted to the cover  220  and electrically coupled to the ground plane  105  of the PCB  106 , the metal layer  400  effectively electrically couples the ground planes  216 ,  221  for the feed layer  202  inside the antenna housing  206  with the ground plane  105  of the PCB  106  so as to ensure a continuous electrical connection between the antenna  200  and the electronic device  100 . 
         [0134]    At step  56 , a spacer  300  preferably comprising a block of non-electrically conductive material is inserted into the U-shaped metal layer  400 , as shown in  FIG. 11 . The spacer  300  is preferably of a corresponding size to fit within the cavity provided by the U-shaped metal layer  400 . The spacer  300  is secured to the metal layer  400  and to the outer surface  210  of the antenna housing  206  relatively loosely by e.g. inserting fastening means  352  through a hole  353  in the spacer  300 , a corresponding hole in the middle surface of the U-shaped metal layer  400 , a corresponding hole  351  in the surface  210  of the antenna housing, and locating means  350  inside the antenna housing  206 . The fastening means preferably comprise non-electrically conductive material. An example of the fastening means is one or more screws  353  (only one is shown). More than one fastening means may be provided. 
         [0135]    The surface of the spacer  300  opposite the middle surface of the metal layer  400  (hereinafter “the uncovered surface”) is substantially uncovered by the metal layer  400  to allow for microstrip coupling between the sections  203   a ,  203   b  of the feed layer parallel to the electronic device tracks  104   a ,  104   b  and the corresponding sections  111   a ,  111   b  of the electronic device tracks  104   a ,  104   b  as shown in  FIG. 15 . The ground plane  105  of the PCB  106  also serves as the ground plane for the parallel section  203  of the feed layer  202 . 
         [0136]    Then, at step  58 , foam layers  452   a ,  452   b  are attached for at least part of the film layer outside the antenna housing  206 . Referring back to  FIG. 4 , a foam layer  452   a ,  452   b  is located in between each of the two outer side surfaces of the U-shaped metal layer  400  and the portion of the film layer  215  next to that side surface of the metal layer  400  respectively. In each case the foam layers  452   a ,  452   b  are attached to either the outer side surface of the U-shaped metal layer  400  or the corresponding portion of the film layer or both. A second foam layer  450   a ,  450   b  is attached to the other side of each of the two portions of the film layer respectively. The foam layers may be self-adhesive to aid the attachment. 
         [0137]    As shown in  FIGS. 2 and 4 , the two portions  238   a ,  238   b  of the film layer  215  are folded around the spacer  300  along two opposite side surfaces of the U-shaped metal layer  400  surrounding the spacer  300  at step  60 , so that a section of portion  238   a ,  238   b  of the film layer  215  carrying a section  203   a ,  203   b  of the portion  201   a ,  201   b  of the feed layer  202  is substantially parallel to at least a section  111   a ,  111   b  of the electronic device track  104   a ,  104   b  respectively, which, in this embodiment, is parallel to the surface  110  of the electronic device enclosure  101  which is connected to the surface  201  of the antenna housing  206  as shown in  FIG. 14 . 
         [0138]    Referring also to  FIG. 13 , at step  62 , the side edges  260   a ,  262   a ,  260   b ,  262   b  of the two sections of the film layer carrying two sections  203   a ,  203   b  of the feed layer  202  respectively are aligned with the top  264  and bottom  266  edges of the spacer  300  and the end edges  268   a ,  268   b  with a central recess  270  provided in the uncovered surface of the spacer  300 . The two sections of the film layer  215  are attached to spacer  300  so as to achieve registration of the sections of the film layer with the spacer  300 . This may be achieved by securing registration means  330  of the spacer  300  with receiving means  332  of the feed layer  202  as shown in  FIGS. 11 and 12 . The registration means can be one or more buttons attached to or provided by the uncovered surface of the spacer  300  and the receiving means can a corresponding number of holes in the film layer. Alternatively, the sections of the film layer may be glued onto the spacer  300 . The uncovered surface of the spacer  300  may be self-adhesive to aid the attachment. 
         [0139]    The electronic device  100  and the antenna  200  are brought close together at step  74 . In particular, a surface  110  of the electronic device enclosure  101 , which is substantially uncovered by the electronic device enclosure  101 , is brought close to the perpendicular section  223  of the cover  220  through the hole in the surface  210  of the antenna housing  206  while the spacer  300  together with the U-shaped metal layer  400  surrounding the spacer  300 , the portions  238   a ,  238   b  of the film layer  215  wrapped around the metal layer  400  and the spacer  300  and the foam layers attached thereto is received by the two blades of metal  404   a ,  404   b  attached to the PCB  106 . 
         [0140]    Bringing the electronic device  200  close to the antenna  100  as described above also brings the PCB  106 , as shown in  FIG. 14 , close to the sections of film layer carrying the sections  203   a ,  203   b  of the feed layer  202  on the uncovered surface of the spacer  300 , as shown in  FIG. 13 , in accordance with step  76 . 
         [0141]    As shown in  FIGS. 11 and 12 , the guidance pins  344  attached to the PCB  106  are inserted through a corresponding number of holes  340  in the spacer  300  at step  78 , as the electronic device  100  and the antenna  200  are brought close together, thereby to secure the spacer  300  to the PCB  106  so that relative lateral movement with respect to each other is prevented. This effectively secures the sections  203   a ,  203   b  of the feed layer  202  to the electronic device tracks  104   a ,  104   b  respectively, because the sections of film layer  215  carrying the sections  203   a ,  203   b  of the feed layer  202  on the uncovered surface of the spacer  300  are secured to the spacer  300  and the electronic device tracks  104   a ,  104   b  are printed on the PCB  106 . The location of the guidance pins  344  ensures that the sections  203   a ,  203   b  of the feed layer  202  overlap with the corresponding sections  111   a ,  111   b  of the electronic device tracks  104   a ,  104   b  when the guidance pins  344  are inserted into the spacer  300 . As a result the sections  203   a ,  203   b  of the feed layer  202  are at least partially aligned with the sections  111   a ,  111   b  of electronic device tracks  104   a ,  104   b  respectively as shown in  FIG. 15 . 
         [0142]    Since the tolerance between antenna housing  206  and the electronic device enclosure  101  is relatively coarse, the spacer  300  is preferably secured relatively loosely to the outer surface  210  of the antenna housing  206  and the portions  201  of the feed layer  202  outside the antenna housing  206  are at least partly flexible so as to facilitate alignment of the tracks. 
         [0143]    At step  80 , the surface  101  of the electronic device enclosure  101  is mounted onto the outer surface  201  of the antenna housing  206  by e.g. applying connection means such as screws around the periphery of the overlapping surfaces. Conductive caulking compounds may also be applied around the edges of the overlapping surfaces for better shielding. 
         [0144]    Finally, at step  82 , the spacer  300  is located against the electronic device tracks  104   a ,  104   b  so as to control relative lateral movement between the sections  203   a ,  203   b  of the feed layer and the corresponding sections  111   a ,  111   b  of the electronic device tracks  104   a ,  104   b  respectively for overlay coupling  500 . Securing the two sections so as to restrict relative lateral movement therebetween ensures that the electrical coupling between the two sections remains stable. Referring again to  FIG. 11 , in this embodiment, this is facilitated by fixing means  326 , which are inserted from an exterior face of the electronic device  100 , through a hole  328  in the electronic device enclosure  101 , a corresponding hole in the PCB  106 , a corresponding hole in the film layer  215 , and a corresponding hole  320  in the spacer  300 . The fixing means  326  preferably comprise non-electrically conductive material. An example of the fixing means  326  is one or more screws (only one is shown), and silicon sealant may also be applied around the hole(s)  328  in the electronic device enclosure  101  through which fixing means  326  are inserted. 
         [0145]    In the above embodiment, a section  203   a ,  203   b  of each portion  201   a ,  201   b  of the feed layer  202  is coupled to a section  111   a ,  111   b  of a different electronic device track  104   a ,  104   b . However it is to be understood the two sections  111   a,    111   b  can alternatively be part of a single electronic device track  104 , as shown schematically in  FIG. 1 . 
         [0146]    In the above embodiment, a second foam layer  222   a ,  222   b  is attached to each of the two outer side portions of the film layer respectively at step  22 . Alternatively, a second foam layer  222   a ,  222   b  can be attached to the inner surface of each of the two blades of metal  450   a ,  450   b  respectively as shown in  FIG. 14 . Indeed, where a foam layer is secured in between the feed layer and a ground plane in the above embodiment, it can be secured to either the feed layer or the ground plane or both. 
         [0147]    As an alternative to foam layers for separating the film layer from the ground planes and hold the film layer in position, air and mechanical spacers may be used. 
         [0148]    The hole in the surface  210  of the antenna housing  206  is not necessary. Alternatively two openings can be provided in the surface  210 , the two openings corresponding to the two openings  212   a ,  212   b  in the surface of the perpendicular section of the cover  220 . In this case, the ground planes inside the electronic device enclosure  101  can be electrically coupled to the ground planes inside the antenna housing using alternative methods, for example, at least part of the surface  210  of the antenna housing  206  can be made of electrically conductive material and can be electrically coupled to the ground planes inside the antenna housing  206  by physical connection and coupled to the ground planes inside the electronic device enclosure  101  as described above. 
         [0149]    The above embodiment relates to dual-polarized antennas. However, it is to be understood that single-polarized and other multi-polarized antennas can also be assembled using the above method. For example, for a single-polarized antenna, one portion of the film layer carrying one portion  201  of the feed layer  202  extends outside of the antenna housing  206  through one opening  212  in the perpendicular section of the cover  220 . This portion  201  is then folded around the spacer  300  and coupled to one electronic device track  104  as described above. In this case, a blade of metal resembling one side surface of the U-shaped metal layer  400 , as shown in  FIG. 12 , can be provided instead of the U-shaped metal layer  400 . Furthermore, the U-shaped enclosure  208  may be V-shaped instead, supporting a middle portion of the film layer carrying the conductive antenna elements of the feed layer  202  and a side portion of the film layer carrying one feed network  230 . 
         [0150]    The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, the metal components referred to above such as the blades of metal  404   a ,  404   b  and U-shaped metal layer  400  etc can be made of other electrically conductive material instead. 
         [0151]    The two ground planes for the feed layer  202  within the antenna housing  206  may be provided by two blades of metal instead of the cover  220  and the enclosure  208  while the enclosure  208  and the cover  220  may be provided separately and may be made of non-electrically conductive material. 
         [0152]    The spacer  300  may not be necessary for the invention if for example the plane of the PCB  106 , and thus its corresponding ground plane  105 , is oriented perpendicular to the plane of the surface  210 . In such an arrangement the feed layer  202 , together with its external ground plane  400 , can extend outside of the antenna housing  206  and cooperate with the PCB ground plane  105  without being folded. 
         [0153]    The part  205  of the feed layer  202  may be microstrip instead of triplate, in which case only one of the U-shaped metal layer  400  and the blade of metal  404  is needed for each polarization. 
         [0154]    It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.