Patent Document

FIELD OF THE INVENTION 
       [0001]    The present invention relates to an antenna array for phased array antennas, and construction thereof. 
       BACKGROUND 
       [0002]    Phased array antennas are used, by vehicles for example, for a wide range of functions including communications, target location and tracking, electronic sensing measure (ESM), electronic counter measures (ECM) and long range all-weather remote sensing. These functions require a range of different frequencies in the microwave and radio frequency bands of the electromagnetic spectrum. 
         [0003]    Conventionally, each function is usually performed by one or more dedicated antenna apertures. 
         [0004]    A phased array antenna intended to cover a wider range of frequencies and assembled using conventional techniques would face many manufacturing and operational obstacles. 
         [0005]    An antenna feed module is described in WO2009/077791 A1. 
       SUMMARY OF THE INVENTION 
       [0006]    In a first aspect, the present invention provides an antenna assembly, comprising: a layered structure comprising a planar array of antenna elements; and a feed arrangement provided in a plane that is at an angle to the plane of the antenna elements; wherein the layered structure further comprises one or more layers over the planar array of antenna elements, and wherein holes are provided through the one or more layers to allow the feed arrangement to be connected to contacts for the planar array of antenna elements. 
         [0007]    The feed arrangement may be provided in a plane that is substantially perpendicular to the plane of the antenna elements. 
         [0008]    The layered structure may further comprise vias provided such that heat may be applied remotely to the contacts for the array of antenna elements via the vias to connect the contacts electrically to the feed arrangement. 
         [0009]    The vias may be adapted for applying heat for soldering. 
         [0010]    The antenna assembly may further comprise a fixture securing the planar array of antenna elements and the feed arrangement, wherein the fixture comprises a ground plane box comprising a ground plane and sides. 
         [0011]    The ground plane may comprise grooves for positioning therein parts of the feed arrangement. 
         [0012]    The ground plane may comprise holes for parts of the feed arrangement to pass through. 
         [0013]    The ground plane box may be made of aluminium. 
         [0014]    The ground plane and the planar array of antenna elements may be separated by a distance approximately equal to one tenth of the wavelength of the intended lowest frequency of operation. 
         [0015]    The ground plane and the planar array of antenna elements may be separated by a distance approximately equal to 11.7 mm. 
         [0016]    The antenna assembly may further comprise electrical connector blocks connected to parts of the feed arrangement, the electrical connector blocks providing transmission connection into and/or away from the antenna assembly and the electrical connector blocks further providing mechanical fixing of the parts of feed arrangement relative to the ground plane box. 
         [0017]    The connector blocks may comprise apertures for connections that are positioned offset relative to each other. 
         [0018]    The feed arrangement may comprise one or more multilayer printed circuit boards. 
         [0019]    One or more baluns may be integrated in the feed arrangement. 
         [0020]    In a further aspect, the present invention provides an antenna assembly, comprising: a planar array of antenna elements; and vias provided such that heat may be applied remotely to contacts for the array of antenna elements via the vias to connect the contacts electrically to a feed arrangement. 
         [0021]    In a further aspect, the present invention provides an antenna assembly, comprising: a planar array of antenna elements; and a ground plane box comprising a ground plane and sides. 
         [0022]    The antenna assembly may further comprise a feed arrangement and electrical connector blocks connected to parts of the feed arrangement, the electrical connector blocks providing transmission connection into and/or away from the antenna assembly and the electrical connector blocks further providing mechanical fixing of the parts of feed arrangement relative to the ground plane box. 
         [0023]    In a further aspect, the present invention provides an antenna assembly, comprising: a planar array of antenna elements; and a ground plane separated from the planar array of antenna elements by a distance approximately equal to one tenth of the wavelength of the intended lowest frequency of operation. 
         [0024]    The ground plane and the planar array of antenna elements may be separated by a distance approximately equal to 11.7 mm. 
         [0025]    In any of the above aspects, the antenna elements may be substantially approximately triangular shaped, such that a point of a triangle of a first pole of a dipole is adjacent a point of the triangle of a second pole of the same dipole, whereas the side of the triangle of the first pole opposite the point of the triangle of the first pole provides an edge that is adjacent to a side of a triangle of a pole of a different dipole. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a schematic illustration of a plan view of a dipole array which is used to form a multi-octave phased array aperture; 
           [0027]      FIG. 2  is a schematic illustration of a plan view of a second dipole element and a certain portion of a first dipole element that is directly adjacent to the second dipole element; 
           [0028]      FIG. 3  shows in a magnified schematic (not to scale) form an area of  FIG. 2 ; 
           [0029]      FIG. 4  is a process flow chart of an example method of fabrication for fabricating the dipole array; 
           [0030]      FIG. 5  is a schematic illustration of the assembly produced by performing step s 2  of the method of fabrication; 
           [0031]      FIG. 6  is a schematic illustration of the assembly produced by performing steps s 2 -s 4  of the method of fabrication; 
           [0032]      FIG. 7  is a schematic illustration of the assembly produced by performing steps s 2 -s 6  of the method of fabrication; 
           [0033]      FIG. 8  is a schematic illustration of the assembly produced by performing steps s 2 -s 8  of the method of fabrication; 
           [0034]      FIG. 9  is a schematic illustration of the assembly produced by performing steps s 2 -s 10  of the method of fabrication; 
           [0035]      FIG. 10  shows schematically a shape of a reworking hole; 
           [0036]      FIG. 11  is a schematic illustration of the assembly produced by performing steps s 2 -s 16  of the method of fabrication; 
           [0037]      FIG. 12  is a schematic illustration of an exploded view of a feed structure via which signals are sent between the dipole array and transmit-receive module; 
           [0038]      FIG. 13  is a schematic illustration of a bottom view of the tip of a second protrusion of a pillar board; 
           [0039]      FIG. 14  is a schematic illustration of a perspective view of an assembled antenna array; and 
           [0040]      FIG. 15  shows schematically (not to scale) apertures as positioned on the top surface of a connector block. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]      FIG. 1  is a schematic illustration of a plan view of a dipole array  100  which is used in an active electronically scanned array (AESA) antenna. 
         [0042]    In this embodiment, the dipole array  100  is formed by photolithographically patterning a copper layer that is attached to a Liquid Crystal Polymer (LCP) layer. 
         [0043]    In this embodiment, each dipole element comprises four substantially triangular shaped elements patterned on to a top surface of the dipole array  1 . The dipole elements will be described in more detail later below with reference to  FIG. 2 . 
         [0044]    In this embodiment, the dipole array  100  comprises sixteen dipole elements arranged in a four rows by four column grid. The four rows are hereinafter referred to as the first row  10 , the second row  20 , the third row  30 , and the fourth row  40 . The four columns are hereinafter referred to the first column  11 , the second column  21 , the third column  31 , and the fourth column  41 . 
         [0045]    The structure of the dipole array  100  will be described with reference to the four dipole elements in the first row  10 . These four elements are hereinafter referred to as the first dipole element  1 , the second dipole element  2 , the third dipole element  3 , and the fourth dipole element  4 . 
         [0046]    The first dipole element  1  is in the first row  10  and the first column  11 . The second dipole element  2  is in the first row  10  and the second column  21 . The third dipole element  3  is in the first row  10  and the third column  31 . The fourth dipole element  4  is in the first row  10  and the fourth column  41 . 
         [0047]      FIG. 2  is a schematic illustration of a plan view of the second dipole element  2  and a certain portion of the first dipole element  1  that is directly adjacent to the second dipole element  2 . 
         [0048]    The second dipole element  2  comprises a horizontally polarised dipole and a vertically polarised dipole. 
         [0049]    The horizontally polarised dipole comprises a first and a second pole, hereinafter referred to as the “first horizontal pole  22 ” and the “second horizontal pole  23 ” respectively. 
         [0050]    In this embodiment, the first horizontal pole  22  and the second horizontal pole  23  are each substantially triangular in shape. The first horizontal pole  22  and the second horizontal pole  23  are positioned substantially opposite each other such that they form a ‘bow-tie’ shape, each triangular pole  22 ,  23  having a vertex at the middle of the bow-tie shape, said vertices being proximate to the centre of the second dipole element  2 . 
         [0051]    The vertex of the first horizontal pole  22  proximate to the centre of the second dipole element  2 , is hereinafter referred to as the “first vertex”, and is indicated in  FIG. 2  by the reference numeral  200 . The edge of the first horizontal pole  22  that does not form the first vertex  200 , i.e. the edge of the first horizontal pole  22  which is the furthest edge of the first horizontal pole  22  from the centre of the second dipole element  2 , is hereinafter referred to as the “first outside edge” and is indicated in  FIG. 2  by the reference numeral  202 . 
         [0052]    The vertex of the second horizontal pole  23  proximate to the centre of the second dipole element  2 , is hereinafter referred to as the “second vertex”, and is indicated in  FIG. 2  by the reference numeral  210 . The edge of the second horizontal pole  23  that does not form the second vertex  210 , i.e. the edge of the second horizontal pole  23  which is the furthest edge of the second horizontal pole  23  from the centre of the second dipole element  2 , is hereinafter referred to as the “second outside edge” and is indicated in  FIG. 2  by the reference numeral  212 . 
         [0053]    In this embodiment, the first outside edge  202  is 4.8 mm long. In this embodiment, the second outside edge  212  is 4.8 mm long. Also, the first and second outside edges  202 ,  212  are substantially parallel. 
         [0054]    In this embodiment, the first vertex  200  and the second vertex  210  are separated by a distance of 0.4 mm. 
         [0055]    The vertically polarised dipole comprises a first and a second pole, hereinafter referred to as the “first vertical pole  24 ” and the “second vertical pole  25 ” respectively. 
         [0056]    In this embodiment, the first vertical pole  24  and the second vertical pole  25  are each substantially triangular in shape. The first vertical pole  24  and the second vertical pole  25  are positioned substantially opposite each other such that they form a ‘bow-tie’ shape, each triangular pole  24 ,  25  having a vertex at the middle of the bow-tie shape, said vertices being proximate to the centre of the second dipole element  2 . 
         [0057]    The vertex of the first vertical pole  24  proximate to the centre of the second dipole element  2 , is hereinafter referred to as the “third vertex”, and is indicated in  FIG. 2  by the reference numeral  240 . The edge of the first vertical pole  24  that does not form the third vertex  240 , i.e. the edge of the first vertical pole  24  which is the furthest edge of the first vertical pole  24  from the centre of the second dipole element  2 , is hereinafter referred to as the “third outside edge” and is indicated in  FIG. 2  by the reference numeral  242 . 
         [0058]    The vertex of the second vertical pole  25  proximate to the centre of the second dipole element  2 , is hereinafter referred to as the “fourth vertex”, and is indicated in  FIG. 2  by the reference numeral  250 . The edge of the second vertical pole  25  that does not form the fourth vertex  250 , i.e. the edge of the second vertical pole  25  which is the furthest edge of the second vertical pole  25  from the centre of the second dipole element  2 , is hereinafter referred to as the “fourth outside edge” and is indicated in  FIG. 2  by the reference numeral  252 . 
         [0059]    In this embodiment, the third outside edge  242  is 4.8 mm long. In this embodiment, the fourth outside edge  252  is 4.8 mm long. Also, the third and fourth outside edges  242 ,  252  are substantially parallel. Moreover, the third and fourth outside edges  242 ,  252  are substantially perpendicular to the first and second outside edges  202 ,  212 . 
         [0060]    In this embodiment, the third vertex  240  and the fourth vertex  250  are separated by a distance of 0.4 mm. 
         [0061]    Each of the poles  22 ,  23 ,  24 ,  25  has a respective contact pad, which will now be described in more detail with reference to  FIG. 3 .  FIG. 3  shows in a magnified schematic (not to scale) form the area of  FIG. 2  indicated by reference numeral  28 , i.e. the vertexes of the poles. As such, in  FIG. 3 , only the end portions of the poles  22 ,  23 ,  24 ,  25  are shown. 
         [0062]    The first horizontal pole  22  comprises a contact pad, hereinafter referred to as the “first contact  32 ”, via which the first horizontal pole  22  is supplied with a signal, or forwards a received signal, as described in more detail later below. The first contact  32  is positioned adjacent, or substantially near to, the first vertex  200 . 
         [0063]    The second horizontal pole  23  comprises a contact pad, hereinafter referred to as the “second contact  33 ”, via which the second horizontal pole  23  is supplied with a signal, or forwards a received signal, as described in more detail later below. The second contact  33  is positioned adjacent, or substantially near to, the second vertex  210 , and is in contact with the second horizontal pole  23 . 
         [0064]    The first vertical pole  24  comprises a contact pad, hereinafter referred to as the “third contact  34 ”, via which the first vertical pole  24  is supplied with a signal, or forwards a received signal, as described in more detail later below. The third contact  34  is positioned adjacent, or substantially near to, the third vertex  240 , and is in contact with the first vertical pole  24 . 
         [0065]    The second vertical pole  25  comprises a contact pad, hereinafter referred to as the “fourth contact  35 ”, via which the second vertical pole  25  is supplied with a signal, or forwards a received signal, as described in more detail later below. The fourth contact  35  is positioned adjacent, or substantially near to, the fourth vertex  250 , and is in contact with the second vertical pole  25 . 
         [0066]    For each of the above described contacts, the contact and the pole are respective joined up areas of the patterned copper layer. 
         [0067]    Thus, the second dipole element  2  comprises four contacts  32 ,  33 ,  34 ,  35  substantially near the middle of the second dipole element  2 . 
         [0068]    Each of the other dipole elements in the dipole array  100 , for example the first dipole element  1 , the third dipole element  3 , and the fourth dipole element  4 , comprise horizontal and vertical dipoles, comprising poles and contacts corresponding to those described above for the second dipole element  2 . 
         [0069]      FIG. 2  further shows a pole of the horizontal dipole of the first dipole element. This pole, hereinafter referred to as the “third horizontal pole  27 ”, corresponds to the second horizontal pole  23  of the second dipole element  2 . Similarly to the second horizontal pole  23 , the third horizontal pole comprises an outside edge, hereinafter referred to as the “fifth outside edge  272 ”, and, in the vicinity of the vertex, a contact, hereinafter referred to as the “fifth contact” (not shown). 
         [0070]    The first horizontal pole  22  is adjacent to the third horizontal pole  27 . The first horizontal pole  22  and the third horizontal pole  27  are positioned such that the first outside edge  202  and the fifth outside edge  272  are substantially parallel. Also, in this embodiment the first horizontal pole  22  and the third horizontal pole  27  are positioned such that the first horizontal pole  22  and the third horizontal pole  27  are 0.4 mm apart. In other words, first outside edge  202  and the fifth outside edge  272  are 0.4 mm apart. 
         [0071]    The relatively small separation between the first horizontal pole  22  and the third horizontal pole  27 , i.e. the relatively small separation between the first outside edge  202  and the fifth outside edge  272 , and the relatively large size of the first horizontal pole  22  and the third horizontal pole  27  at the first outside edge  202  and the fifth outside edge  272  respectively, advantageously tend to provide that the horizontal diode of the first dipole element  1  and the horizontal diode of the second dipole element  2  are highly coupled. In other words, the relatively small spacing between the horizontal dipoles of the first and second dipole elements  1 ,  2 , together with the relatively large sizes of the surfaces of the horizontal dipoles of the first and second dipole elements  1 ,  2  that are directly adjacent, tend to provide for a relatively large capacitance between the horizontal dipoles of the first and second dipole elements  1 ,  2 . 
         [0072]    In a corresponding way to the way that the horizontal dipoles of the first and second dipole elements  1 ,  2 , are highly coupled together (as described above), each horizontal dipole of each element is highly coupled to the horizontal dipole of the element that is horizontally and directly adjacent to it. For example, in the first row  10  of the dipole array  100  the horizontal dipole of the first element  1  is highly coupled to the horizontal dipole of the second element  2 . Also, the horizontal dipole of the second element  2  is highly coupled to both the horizontal dipole of the first element  1  and the horizontal dipole of the third element  3 . Also, the horizontal dipole of the third element  3  is highly coupled to both the horizontal dipole of the second element  2  and the horizontal dipole of the fourth element  4 . Also, the horizontal dipole of the fourth element  4  is highly coupled to the horizontal dipole of the third element  3 . 
         [0073]    Furthermore, in a corresponding way to the way that the horizontal dipoles of the first and second dipole elements  1 ,  2 , are highly coupled together (as described above), each vertical dipole of each element is highly coupled to the vertical dipole of the element that is vertically and directly adjacent to it. For example, in the first column  11  of the dipole array  100  the vertical dipole of the first element  1  is highly coupled to the vertical dipole of the dipole element in the second row  20  and first column  10 . Also, the vertical dipole of the dipole element in the second row  20  and first column  10  is highly coupled to both the vertical dipole of the first element  1  and the vertical dipole of the dipole element in the third row  30  and first column  11 . Also, the vertical dipole of the dipole element in the third row  30  and first column  11  is highly coupled to both the vertical dipole of the dipole element in the second row  20  and first column  11  and the vertical dipole of the dipole element in the fourth row  40  and first column  11 . Also, the vertical dipole of the dipole element in the fourth row  40  and first column  11  is highly coupled to the vertical dipole of the dipole element in the third row  30  and first column  11 . 
         [0074]    Furthermore, due to the above described arrangement, advantageously some coupling tends to occur between elements in the array that are not the nearest neighbours, i.e. coupling tends to occur between all dipole elements in the array. 
         [0075]    Thus, the dipole array  100  may be considered as comprising highly coupled dipoles. 
         [0076]    Moreover, by virtue of the substantially orthogonal nature of the relative positioning/alignment of each vertical dipole with its corresponding horizontal dipole (e.g. the orthogonal positional relationship between the vertical dipole comprising the first vertical pole  24  and the second vertical pole  25  and the horizontal dipole comprising the first horizontal pole  22  and the second horizontal pole  23 ), independent dual polarisation operation is provided, i.e. the two polarisations (vertical and horizontal) may be operated independently. This advantageously allows, for example, the two polarisations to be driven with different phases. The overall substantially triangular form of the individual poles, with the triangles fitted in the above described interlaced manner, advantageously allows such substantial orthogonal positional relationship to be achieved whilst also achieving the high coupling effects described above. 
         [0077]    It will be appreciated that the above described substantially triangular shaped form of the individual poles provides a preferred layout in which the adjacent edges of adjacent poles where the adjacent poles are from different respective nearest neighbour dipole elements (e.g. the first edge  202  which is adjacent to the fifth edge  272  where these two edges are from neighbouring dipole elements, i.e. the pole whose distal edge is edge  202  forms a dipole with the pole whose distal edge is edge  212 , not with the pole with the adjacent edge  272 ) have a small separation between them compared to the dimensions of the poles and are of relatively large lengths compared to the dimensions of the poles such as to give highly couple dipoles as described above. As such it will be appreciated that, although true triangular shape represents a preferred implementation, nevertheless the substantially triangular shape may vary from absolute triangular shape in a variety of ways whilst still achieving some or all of the above described advantageous effects. For example, the overall shape of a pole may appear as an absolute triangle, but with the three sides thereof in detail being or comprising jagged, partly curved or some other deviations from straight. Another possibility is that the overall shape may be only approximately triangular, e.g. assessed as more like a triangle than any other simple geometric shape, even though not truly a triangle. Thus it will be appreciated that in other embodiments any substantially approximately triangular shaped poles may be provided. More generally, in other embodiments, yet further shapes may be provided that provide some or all of the advantageous effects provided by the above described substantially approximate triangular shaped poles. For example, irregular or more interlaced shapes may be provided, as long as such shapes provide a form of interlacing or relative positioning between the four separate poles of a given dipole pair such that a high degree of coupling is achieved between neighbouring dipoles by respective adjacent distal edges from neighbouring poles that are from respective neighbouring dipoles) being relatively long and relatively close to each other compared to the dimensions of the poles. 
         [0078]      FIG. 4  is a process flow chart of an example method of fabrication for fabricating the dipole array  100 . 
         [0079]    At step s 2 , two copper coated Liquid Crystal Polymer (LCP) layers are bonded together such that a copper film is on each of the outer surfaces of the bonded structure. 
         [0080]      FIG. 5  is a schematic illustration of the assembly produced by performing step s 2 . The material stack comprises a first copper film  52 , a first LCP layer  53 , a first bond layer  54 , a second LCP layer  55 , and a second copper film  56 . In this embodiment, each LCP layer and copper film is provided in the form of 50 μm thick Rogers Corporation Ultralam™ 3850 LCP, originally with 0.5 oz/sq.ft (17.5 μm) copper cladding on both faces but which then has the copper removed from one of its faces. In this embodiment, the first bond layer  54  is made from Ultralam™ 3908 bonding film. (In other embodiments, a single layer of LCP with the copper left on both faces may be used instead of the bonded stack shown in  FIG. 5 , if such a single layer of LCP is of sufficient thickness for a particular implementation.) 
         [0081]    At step s 4 , the first and second copper films  52 ,  56  are photolithographically patterned to remove portions of the first and second copper films  52 ,  56 . The first copper film  52 , on completion, contains pads, hereinafter referred to for convenience as “thermal pads”, which are later used to apply heat which is then conducted to the lower layer through ‘via’ structures subsequently described, to the lower second copper film layer  56 . The thermal pads are provided in the first copper film pattern such as to correspond to the earlier described contact pads provided in the second copper film  56 . The second copper film  56  is patterned to form the above described dipole element parts and contact pads, such as the poles  22 ,  23 ,  24 ,  25  and the contact pads  32 ,  33 ,  34 ,  35 .  FIG. 6  is a schematic illustration of the assembly produced by performing steps s 2 -s 4 . By way of example, in  FIG. 6 , as part of the remaining patterned second copper film  56 , a part of the first horizontal pole  22  and the first contact  32  are shown schematically (not to scale) in cross-section. Furthermore, in  FIG. 6 , as part of the remaining patterned first copper film  52 , a part of a corresponding thermal pad  532  is shown schematically (not to scale) in cross-section. 
         [0082]    At step s 6 , vias are formed. Holes are drilled through the assembly at points on a surface of the assembly corresponding to the positions of the contacts, for example the first, second, third and fourth contacts  32 ,  33 ,  34 ,  35  and the fifth contact, such as to also pass through the corresponding thermal pads such as thermal pad  532 . These holes are plated with copper to produce through-vias, which thus thermally couple a respective contact with its corresponding thermal pad. These vias are advantageous in a process of assembling an antenna from the dipole array  100  for reasons described later below with reference to  FIG. 14 . 
         [0083]      FIG. 7  is a schematic illustration of the assembly produced by performing steps s 2 -s 6 . In addition to those elements shown in  FIGS. 5 and 6 ,  FIG. 8  shows an example of the vias, namely a via  110 . The via  110  is positioned to pass through the contact  32  and the thermal pad  532 , thereby thermally coupling the contact  32  and the thermal pad  532 . 
         [0084]    At step s 8 , a third LCP layer is bonded to the exposed bottom surface of the second LCP layer  55 /the remaining patterned parts of second copper film  56 . 
         [0085]      FIG. 8  is a schematic illustration of the assembly produced by performing steps s 2 -s 8 , further showing the third LCP layer  114  bonded to the second LCP layer  55 /the remaining patterned parts of second copper film  56  by a second bond layer  116 . In this embodiment, the second bond layer  116  is Ultralam™ 3908 bonding film. 
         [0086]    At step s 10 , portions of the third LCP layer  114  and the second bond layer  116  are removed, or skived, to expose the contacts, such as the contacts  32 ,  33 ,  34 ,  35 . In this embodiment, this removal, or skiving, is performed using laser ablation. 
         [0087]      FIG. 9  is a schematic illustration of the assembly produced by performing steps s 2 -s 10 .  FIG. 9  shows, by way of example, a skived region  117  which has exposed the contact  32 . 
         [0088]    The exposed contacts such as contact  32  are then preferably plated with gold for corrosion protection purposes. 
         [0089]    At step s 12 , alignment holes (not shown) are then provided by drilling though the whole assembly. Such alignment holes are provided away from any functional areas, and are used for later alignment of the whole assembly of  FIG. 9  to other parts of the array. Such alignment holes are not essential, and other alignment techniques may be used instead. 
         [0090]    At step s 14 , further holes are provided through the whole assembly. In this embodiment such holes will be used for reworking purposes after a main soldering step, and as such may be conveniently termed reworking holes. However, the term reworking is not limiting, and in other embodiments some or all of these holes may be used for a main soldering process, or for particular first steps of soldering particular contacts with others of the contacts soldered by different means. More generally, if other soldering processes are adequate such that reworking is not envisaged or required, then these reworking holes may instead be omitted. The reworking holes are provided in the vicinity of the contacts such as the contacts  32 ,  33 ,  34 ,  35 . The holes are preferably shaped so that they are as close as possible to the contacts, but do not remove any of the copper film forming the contact or any of the copper film forming the poles, such as the poles  22 ,  23 ,  24 ,  25 . Preferably the reworking holes are provided of a shape that enables one reworking hole to provide access to all four of the contacts of a given dipole element. 
         [0091]      FIG. 10  shows one such shaped reworking hole  118 , shown schematically (not to scale) and of approximate shape as a shaded area  118  around the components previously shown in, and described with reference to,  FIG. 3 . The shape may conveniently be termed substantially swastika-like. 
         [0092]      FIG. 11  shows schematically (not to scale), a part of the cross-section of the reworking hole in the context of the cross-sectional representation of the assembly. It is noted that in  FIG. 11  the reworking hole is merely shown at a nominal position to enable the figure to indicate the hole in principle for improved understanding, and that its position as shown may not necessarily be consistent with regard to the true shape or location of the reworking hole compared to the contact and pole. 
         [0093]    At step s 16 , solder is applied to the contacts such as the contacts  32 ,  33 ,  34 ,  35 . By way of example, in  FIG. 11  a solder wetting  119  is shown applied to the exposed contact  32 . However, it is not essential to apply this solder at this time, and in other embodiments the solder may be applied at a later stage, or even not at all, since for example in other embodiments solder may instead be applied to the element that the contact  32  is to be soldered to, or in yet further embodiments other techniques, e.g. thermal adhesives, may be used instead if soldering. In the latter case, thermal adhesive may be applied to the contacts such as contact  32  at step s 16 , or may be applied at another stage. 
         [0094]    Thus, an example method of fabricating the dipole array  100  is provided. 
         [0095]    The dipole array  100  forms an antenna suitable for transmitting and/or receiving signals. Signals to be transmitted (or signals received by) the antenna are sent from (or to) an array of transmit-receive modules via a feed structure incorporating integrated baluns in order to achieve broad impedance matching of the elements with the transmission line fed inputs. The horizontal and vertical dipoles in the dipole elements of the dipole array  100  are connected to the feed structure via the contacts such as the contacts  32 ,  33 ,  34 ,  35  that are substantially in the middle of each of the dipole elements, as described above with reference to  FIG. 2 . The feed structure will be described below with reference to  FIG. 12 . 
         [0096]    The dipole array  100  tends to be capable of functioning at a range of different frequencies in the microwave and radio frequency bands of the electromagnetic spectrum. These performance characteristics tend to provide that a number of functions may be performed by the dipole array  100 . Thus, reductions in weight, cost and size of an antenna comprising such a dipole array  100  tend to result. 
         [0097]      FIG. 12  is a schematic illustration (not to scale) of an exploded view of the feed structure  44  via which signals are sent between the dipole array  100  and the antenna input/output via integrated baluns. The feed network is not shown in  FIG. 12 . Connection of the dipole array  100  to the feed will be described later below with reference to  FIG. 13 . 
         [0098]    In this embodiment, the feed structure  44  comprises four pillar boards. For clarity and ease of understanding on one such pillar board is depicted in  FIG. 5 . This pillar board is indicated by the reference numeral  152  and will hereinafter be referred to as the “first pillar board”. The feed structure  144  further comprises a ground plane box  154 , and a foam layer  156 . 
         [0099]    The purpose of each respective pillar board is to connect the antenna inputs, via integrated baluns (not shown in  FIG. 12 ) to the four contacts of each of the four dipole elements in a respective row of the dipole array  100 . How a pillar board makes contact with the four contacts of a dipole element is described later below with reference to  FIG. 13  after the description of the shapes and configuration of the pillar boards, the ground plane box  154 , and the foam layer  156 . 
         [0100]    The first pillar board  152  is connected to transmit-receive modules (not shown) via a connection arrangement  58  that is indicated merely conceptually in  FIG. 12 . Any suitable connection arrangement may be employed. The particular connection arrangement  58  employed in this embodiment will be described in more detail later below with reference to  FIG. 14 . 
         [0101]    The shape of the first pillar board  152  is a block having four protrusions (which may also be termed pillars), hereinafter referred to as the “first protrusion  62 ”, the “second protrusion  64 ”, the “third protrusion  66 ”, and “the fourth protrusion  68 ”. 
         [0102]    Each respective protrusion has a free end, or tip. The tip of the first protrusion will hereinafter be referred to as the “first tip  63 ”. The tip of the second protrusion will hereinafter be referred to as the “second tip  65 ”. The tip of the third protrusion will hereinafter be referred to as the “third tip  67 ”. The tip of the fourth protrusion will hereinafter be referred to as the “fourth tip  69 ”. 
         [0103]    Each respective protrusion is positioned through a respective hole in the ground plane box  154  and through a respective hole in the foam layer  156  such that the respective tip makes contact with the four contacts of a respective pair of dipole elements (one in each of two polarisations), as described in more detail below with reference to  FIG. 13 . 
         [0104]    The ground plane box  154  is an open-topped, substantially square, box made of aluminium. In this embodiment, the ground plane box  154  is fabricated by machining a single ingot of aluminium. 
         [0105]    The ground plane box  154  comprises four grooves, hereinafter referred to as the “first groove  72 ”, the “second groove  74 ”, the “third groove  76 ”, and “the fourth groove  78 ”. Each respective groove is adapted to hold in place a respective pillar board. For example, the first groove  72  is adapted to house the first pillar board  152 . 
         [0106]    The ground plane box  154  further comprises sixteen holes through a bottom surface of the ground plane box  154 . Four holes are positioned in each of the four grooves  72 ,  74 ,  76 ,  78 . The four holes through the ground plane box  154  on the first groove  72  are hereinafter referred to as the “first ground plane hole  82 ”, the “second ground plane hole  84 ”, the “third ground plane hole  86 ”, and the “fourth ground plane hole  88 ”. 
         [0107]    The ground plane box  154  advantageously tends to provide dimensional stability to the overall arrangement, thereby providing dimensional stability to the dipole elements, which tends to improve their operation in terms of correct phase and so on. Moreover, the grooves in ground plane box  154  advantageously provide a reduced thickness at the locations where the protrusions of the pillar board are, which tends to provide a first advantage in that the protrusion length may be reduced and/or a second advantage that the height of the overall assembly may be reduced. Moreover, by providing the grooves only where required (e.g. compared to making the whole bottom part of the ground box thinner) these advantages tend to be obtained whilst maintaining a substantial part of the physical strength of the ground box, and hence its ability to provide the above described dimensional stability etc. The ground plane box further allows the pillar bards, in particular the protrusions, to be held perpendicular to the dipole elements. 
         [0108]    The foam layer  156  is a layer of foam of substantially uniform thickness. In this embodiment, the foam layer  156  is approximately 11.7 mm thick. 
         [0109]    In this embodiment, the foam layer comprises sixteen holes arranged such that when the ground plane box  154  is positioned on top of the layer of foam layer  156 , the sixteen holes in ground plane box  154  align with the sixteen holes in the foam layer  156 . In other words, the holes in the foam layer are arranged in the four rows of four holes and are spaced substantially the same way as the holes in the ground plane box  154 . In this embodiment, a row of holes in the foam layer  156  comprises a first foam layer hole  92 , a second foam layer hole  94 , a third foam layer hole  96 , and a fourth foam layer hole  98 . When the ground plane box  154  is positioned on top of the foam layer  156 , the first ground plane hole  82  is aligned with the first foam layer hole  92 , the second ground plane hole  84  is aligned with the second foam layer hole  94 , the third ground plane hole  86  is aligned with the third foam layer hole  96 , and the fourth ground plane hole  88  is aligned with the fourth foam layer hole  98 . 
         [0110]    In this embodiment, the first pillar board  152 , the ground plane box  154  and the foam layer  156  are positioned relative to each other such that the first pillar board  152  lies along the first groove  72  in the ground plane box  154 . Also, the first protrusion  62  passes through the first ground plane hole  82  and the first foam layer hole  92  such that the first tip  63  makes contact with the four contacts of the first dipole element  1 . Also, the second protrusion  64  passes through the second ground plane hole  84  and the second foam layer hole  94  such that the second tip  65  makes contact with the four contacts of the second dipole element  2 . Also, the third protrusion  66  passes through the third ground plane hole  86  and the third foam layer hole  96  such that the third tip  67  makes contact with the four contacts of the third dipole element  3 . Also, the fourth protrusion  68  passes through the fourth ground plane hole  88  and the fourth foam layer hole  98  such that the fourth tip  69  makes contact with the four contacts of the fourth dipole element  4 . 
         [0111]    Similarly, a second pillar board (not shown) comprising four protrusions, and connected to the transmit-receive modules by a corresponding microwave connector, is positioned along the second groove  74  such that the respective protrusions of the pillar board pass through holes in the ground plane box  154  and the foam layer  156  to contact the four contacts on a respective different dipole element on the second row  20 . 
         [0112]    Similarly, a third pillar board (not shown) comprising four protrusions, and connected to the transmit-receive modules by a corresponding microwave connector, is positioned along the third groove  76  such that the respective protrusions of the pillar board pass through holes in the ground plane box  154  and the foam layer  156  to contact the four contacts on a respective different dipole element on the third row  30 . 
         [0113]    Similarly, a fourth pillar board (not shown) comprising four protrusions, and connected to the transmit-receive modules by a corresponding microwave connector, is positioned along the fourth groove  78  such that the respective protrusions of the pillar board pass through holes in the ground plane box  154  and the foam layer  156  to contact the four contacts on a respective different dipole element on the fourth row  40 . 
         [0114]    How a pillar board makes contact with the four contacts of a dipole element (i.e. a pair of dipoles) will now be described by way of example with reference to the second tip  65  and the second dipole element  2  described above with reference to  FIG. 2 . 
         [0115]      FIG. 13  is a schematic illustration of a bottom view of the second tip  65 . 
         [0116]    The second tip  65  is approximately a 3 mm square situated at the end of the second protrusion  64 . The second tip  65  comprises electrical contact pads, hereinafter referred to as the “first pad  102 ”, the “second pad  104 ”, the “third pad  106 ”, and the fourth pad  108 ”. 
         [0117]    In this embodiment, the pads are formed from first plating an outer surface of the first pillar board  152 , then laser stencilling the second tip  65  to the required pattern, and then peeling off the excess metallisation with a scalpel blade. Each pad is substantially rectangular having a width of approximately 0.5 mm, and a length of approximately 1.25 mm. 
         [0118]    During assembly, the protrusions are inserted through the holes in the ground plane box  54  and the foam layer  56  and positioned in the skived regions, such as the skived region  117 , in the dipole array  100 . For example, the second protrusion  64  is positioned through the second ground plane hole  84  and the second foam layer hole  94 . Consequently the second tip  65  makes contact with the middle portion of the second dipole element  2 . Accordingly, and in more detail, each of the pads  102 ,  104 ,  106 ,  108  on the second tip  65  is positioned in contact with a respective one of the contacts of a given dipole element, for example the contacts  32 ,  33 ,  34 ,  35 . This positional contact is then converted into a full electrical contact by soldering the pads  102 ,  104 ,  106 ,  108  to their respective contact of the four contacts e.g. the contacts  32 ,  33 ,  34 ,  35 . In this embodiment this soldering is done by applying heat to the thermal pads provided in the first copper film  52 , e.g. the thermal pad  532  described earlier above. The applied heat is thermally conducted by the respective via, i.e. the via  110  in the case of the thermal pad  532 , to the respective contact, i.e. the contact  32  in the case of the thermal pad  532 . The conducted heat acts to heat the contact  32 , and in this embodiment the solder wetting  119 , such that the solder wetting  119  flows and then forms a full electrical contact between the contact  32  of the dipole array  100  and the respective pad of the second tip  65  of the second protrusion  64  of the pillar board  152 . In this embodiment, if any of the soldered joints are found to be imperfect, or e.g. any short-circuiting due to solder is found to have occurred, e.g. during testing, then the relevant contacts can be reworked manually by accessing the contacts from the outer side of the overall assembly using the reworking holes such as reworking hole  118  described earlier above. 
         [0119]    In this embodiment, the first pad  102  and the second pad  104  are connected to a first Marchand balun (not shown), integrated into the first pillar board  152 , via a first and second conducting layer of the first pillar board  152  respectively. 
         [0120]    During operation, signals are sent between the first Marchand balun and the first horizontal pole  22  via the first conducting layer of the first pillar board  152 , and between the first Marchand balun and the second horizontal pole  23  via the second conducting layer of the first pillar board  152 . In other words, the first and second conducting layers of the pillar board  152  conduct signals between the first Marchand balun and the horizontal dipole of the second dipole element  2 . 
         [0121]    During operation, the first and second conducting layers conduct equal currents in opposite directions, i.e. the signals in the first and second conducting layers are equal in magnitude and opposite in phase (balanced). The first Marchand balun joins the balanced line formed by the first and second conducting layers to an unbalanced line, hereinafter referred to as the “first unbalanced line”. The first unbalanced line comprises a first terminal connected to electrical ground (the ground plane box  154 ), and a further terminal carrying an unbalanced signal corresponding to signals in the first and second conducting layers, i.e. a signal of twice the magnitude of the corresponding signal carried by either the first or second conducting layer. 
         [0122]    In this embodiment, part or all of the first unbalanced line is a first component of the connection arrangement  58 . Thus, the first Marchand balun is connected to the transmit-receive module (not shown). 
         [0123]    In other words balanced signals are sent between the first Marchand balun and the two arms of the horizontal dipole of the second dipole element  2 . These signals are transformed into unbalanced signals with respect to ground (i.e. the first unbalanced signal). The unbalanced signals are sent between the first Marchand balun and the transmit-receive module (not shown) via the connection arrangement  58 ). 
         [0124]    Also in this embodiment, the third pad  106  and the fourth pad  108  are connected to a second Marchand balun, integrated into the first pillar board  152 , via a third and fourth conducting layer of the first pillar board  152  respectively. 
         [0125]    During operation, signals are sent between the second Marchand balun and the first vertical pole  24  via the third conducting layer of the first pillar board  152 , and between the second Marchand balun and the second vertical pole  25  via the fourth conducting layer of the first pillar board  152 . In other words, the third and fourth conducting layers of the pillar board  152  conduct signals between the second Marchand balun and the vertical dipole of the second dipole element  2 . 
         [0126]    During operation, the third and fourth conducting layers conduct equal currents in opposite directions, i.e. the signals in the third and fourth conducting layers are equal in magnitude and opposite in phase. The second Marchand balun joins the balanced line formed by the third and fourth conducting layers to an unbalanced line, hereinafter referred to as the “second unbalanced line”. The second unbalanced line comprises a first terminal connected to electrical ground (the ground plane box  154 ), and a further terminal carrying an unbalanced signal corresponding signals in the third and fourth conducting layers, i.e. a signal of twice the magnitude of the corresponding signal carried by either the third and fourth conducting layer. 
         [0127]    In this embodiment, part or all of the second unbalanced line is a second component of the connection arrangement  58 . Thus, the second Marchand balun is connected to the transmit-receive module (not shown). 
         [0128]    In other words balanced signals are sent between the second Marchand balun and the two arms of the vertical dipole of the second dipole element  2 . These signals are transformed into unbalanced signals with respect to ground (i.e. the first unbalanced signal). The unbalanced signals are sent between the second Marchand balun and the transmit-receive module (not shown) via the connection arrangement  58 . 
         [0129]    Each pillar board, and each protrusion thereof, is arranged in substantially the same way as that described above for the second protrusion  65  of the first pillar board  152 . In this embodiment each board is manufactured from Rogers Corp.  4350  woven glass reinforced ceramic filled thermosetting pre-impregnated (“prepreg”) material. 
         [0130]    In this embodiment, each pillar board comprises feeds for each pole of the relevant dipole elements, and integrated Marchand baluns which effectively transform microwave input signals such that the output to opposite pairs of dipole arms are fed in anti-phase over a wide range of frequencies. However, in other embodiments, second order baluns may be used which limit the bandwidth of the balun to around 3:1 (less than the element with a 4:1 bandwidth). Higher order baluns tend to advantageously provide greater bandwidth but add additional manufacturing complexity and tend to require more board space. It is not essential to use Marchand baluns, nevertheless the Marchand balun tends to be advantageous over other types of balun, such as the Y-Y balun, which tend to be too sensitive to manufacturing variations to deliver consistent microwave performance. 
         [0131]    Thus, a feed structure  44  comprising multilayer microwave printed circuit board (PCB) pillar board, incorporating dual integrated Marchand baluns, for the purpose of driving a wide band array antenna (the dipole array  100 ) is provided. The feed structure  44  is suitable for sending signals from a transmit-receive module (not shown) to the dipole array  100  for onward transmission into free space by the dipole array  100 . Also, the feed structure  44  is suitable for sending signals that are received at the dipole array  100  from the dipole array  100  to the transmit-receive module (not shown). The overall arrangement thus provides what is referred to as “reciprocal device” from an electrical perspective. 
         [0132]    Any appropriate structure, in particular internal structure, of the pillar boards, including the details of the baluns integrated therein, may be used. In this embodiment, the internal structure and functionality is preferably as described in International Patent Application No. PCT/GB2008/051196 (International Publication Number WO2009/077791 A1), the contents of which are incorporated herein by reference. 
         [0133]    The particular form used in this embodiment for the above mentioned connection arrangement  58  will now be described with reference to  FIGS. 14 and 15 .  FIG. 14  is a schematic illustration of a perspective view of an electrically scanned antenna  301  comprising the elements described above. The antenna  301  comprises the first pillar board  152 , a second pillar board  302 , a third pillar board  303 , a fourth pillar board  304 , the ground plane box  154 , the foam layer  156 , and the dipole array  100 . 
         [0134]    The first pillar board  152  is positioned in the first groove  72  of the ground plane box such that the each protrusion of the first pillar board passes through a respective hole in the ground plane box  154  as described above with reference to  FIG. 12 . Also, each protrusion of the first pillar board passes through a respective hole in the foam layer  156  such that each protrusion contacts the middle portion of a respective dipole element in the first row  10  of the dipole array  100  as described above. 
         [0135]    The other pillar boards are arranged in a corresponding fashion, i.e. the second, third and fourth pillar boards  302 ,  303 ,  304  are positioned in the respective second, third and fourth grooves  74 ,  76 ,  78  such that the protrusions of the respective pillar board passes through the holes in the ground plane box  154  that lie along the along the respective groove. Also, the protrusions of the respective pillar boards pass through a respective set of holes in the foam layer  156  such that each protrusion of the second pillar board  302  contacts the middle portion of a respective dipole element in the second row  20  of the dipole array  100 , each protrusion of the third pillar board  303  contacts the middle portion of a respective dipole element in the third row  30  of the dipole array  100 , and each protrusion of the fourth pillar board  304  contacts the middle portion of a respective dipole element in the fourth row  20  of the dipole array  100 . 
         [0136]    In this embodiment, the edge of each pillar board that is opposite the edge having the protrusions is physically and electrically connected to a respective connector block  311 ,  312 ,  313 ,  314 , i.e. the first pillar board  152  is attached to and electrically connected to a first connector block  311 , the second pillar board  302  is attached to and electrically connected to a second connector block  312 , the third pillar board  303  is attached to and electrically connected to a third connector block  313 , and the fourth pillar board  304  is attached to and electrically connected to a fourth connector block  314 . The connector blocks  311 ,  312 ,  313 ,  314  are made of gold plated aluminium. 
         [0137]    In this embodiment, each pillar board is held in place with screws at the ends of the connector blocks and by a conductive epoxy applied between the protrusions of the pillar boards in order to permanently bond them to the box itself. 
         [0138]    In this embodiment, apertures (not shown in  FIG. 14 ) are machined into the connector blocks  311 ,  312 ,  313 ,  314 . The apertures align with the conductor layers in the pillar boards leading to the Marchand balun inputs in order to allow the dipoles to be fed with (or send back) microwave radiation. In this embodiment, an “SMP” connector (Sub-Miniature Version P, where “P” stands for “push-fit”) is fitted in each aperture  320  to provide the above described electrical connection to the connector block. In operation, an external transmit-receive module (not shown) is coupled to the SMP connectors by co-axial cables. 
         [0139]    A pair of apertures (i.e. a pair of SMP connectors) is provided for each protrusion (being one cable for each polarisation). In this embodiment the conductive layers for the different polarisations exist on opposite sides of each board. Advantageously, in this embodiment the apertures (and hence the SMP connectors) are positioned offset relative to each other.  FIG. 15  shows schematically (not to scale) such apertures  320  as positioned on the top surface of, for example, the connector block  311 . In terms of the plane defined by the top surface of the connector block  311 , consecutive apertures  320  are positioned offset to each other in the width direction of the top surface (indicated by reference numeral  322 ), such that overall the (in this example) eight apertures may be fitted into a shorter length in the length direction (indicated by reference numeral  322 ) of the top surface than would be the case if the layout was not staggered. This advantageously provides that the pillar boards may be closer together, which tends to allow for high frequency operation. In other words, in this embodiment microwave connectors (e.g. SMP connectors) are staggered to allow array elements to be brought closer together. This tends to facilitate high frequency operation and also allows signals to be taken from both sides of a microwave PCB pillar board for dual polar function from a single board. 
         [0140]    Thus, in this embodiment, the connection arrangement  58  comprises the above described connector blocks  311 ,  312 ,  313 ,  314 , along with their SMP connectors, and co-axial connections from the SMP connectors to e.g. an external transmit-receive module. 
         [0141]    In this embodiment, the foam layer  156  comprises a layer of Rohacell HF31 foam. This layer incorporates ‘floating posts’ which advantageously tend to provide for common mode current suppression between elements. These prevent the formation of significant surface currents in apertures which effectively remove energy which might otherwise radiate. Thus, the active match, i.e. the impedance match of the antenna to free-space when powered, tends to be improved. 
         [0142]    Also, as described above with reference to  FIG. 12 , the foam layer  156  is approximately 11.7 mm thick. Thus, in the assembled transceiver  301 , the dipole array  100  is separated from the ground plane box  154  by a distance of approximately 11.7 mm. This distance corresponds to about one tenth of a wavelength at the lowest frequency of operation, this being designed so as to tend to maximise the operational frequency bandwidth. Thus, more generally, in other embodiments, the foam layer thickness may be selected in response to the intended frequency of operation. 
         [0143]    The pillar boards are bonded such that any poorly performing elements are placed around the periphery. This advantageously tends to provide that the contribution of the poorly performing elements to the overall performance of the antenna is reduced. 
         [0144]    In this embodiment, a layer of Technibond™ 235 supported acrylic film adhesive is used to bond the foam layer  156  to the ground plane box  154 , and to bond the foam layer  156  to the dipole array  100 . 
         [0145]    In addition to the dipole array  100  being bonded to the foam layer, each pad of each pillar board is soldered to the corresponding contact in a dipole element. This advantageously provides a good electrical connection between the dipole elements and the feed structure  44 . 
         [0146]    The above mentioned through-vias, for example the via  110 , advantageously provide for effective heat transfer through a material with a low thermal conductivity (the LCP layers of the dipole array  100 ). This tends to allow solder applied to the contacts of the dipole array  100  prior to the bonding of the foam layer  156  to the dipole array  100 , to be re-melted after the bonding of the foam layer  156  to the dipole array  100 , by the application of heat to an underside of the contact, i.e. by indirect heating. This allows the solder to flow and form an electrically conductive bond between the contact and the corresponding pad. This advantageous soldering technique allows soldering, including use of automatic soldering techniques, to be carried out even though the dipole contacts are remote from the soldering heat source. 
         [0147]    In this embodiment, a protective layer (not shown) is bonded to the outer surface of the dipole array  100 , i.e. the surface of the dipole array not bonded to the foam layer  156 . In this embodiment, the protective layer comprises a 4 mm thick layer of Rohacell IG71 foam, and a 0.5 mm thick layer of Taconic RF-45. This advantageously tends to provide environmental and impact protection to the dipole array  100 , as well as further impedance matching between the assembly  301  and free space. 
         [0148]    Thus, a microwave array antenna containing a dual polarised feed structure  44  is provided. The feed structure  44  uses protrusions of a PCB pillar board as a mechanism to convey microwave radiation to antenna elements (dipole elements) which are perpendicular to the feed. 
         [0149]    In the above embodiment, the transceiver comprises a ground plane box, a foam layer, a dipole array comprising sixteen dipole elements arranged in four rows of four elements, four pillar boards, and four connector blocks. However, in other embodiments the transceiver may contain other numbers of dipole array elements, ground plane boxes, foam layers, pillar boards, connector blocks, and so on. For example, in a preferred embodiment, the array may comprise a few thousand dual polarised elements, with the number of pillar boards and connector boxes determined such as to accommodate such an array size, in a layout suitable for the particular application under consideration. 
         [0150]    In the above embodiment, the dipole array, the ground plane box, the foam layer, the pillar boards and the connector blocks are made from the materials specified above. However, in other embodiments some, or all, of the dipole array, the ground plane box, the foam layer, the pillar boards and the connector blocks are made from different appropriate materials. 
         [0151]    In the above embodiment, the dipole array, the ground plane box, the foam layer, the pillar boards are of the shapes and dimensions specified above. However, in other embodiments some, or all, of the dipole array, the ground plane box, the foam layer, the pillar boards and the connector blocks are of different appropriate shapes, with different appropriate dimensions, such that the same functionality is achieved. 
         [0152]    Also, in other embodiments the ground plane box and the foam layer comprise any number of holes, appropriately spaced such that some, or all, of the any number of dipole elements may be accessed through these holes. 
         [0153]    Furthermore, in other embodiments any number of pillar boards, each comprising any number of protrusions for contacting the any number of dipole elements, is used. In other embodiments, a plurality of pillar boards may be joined together joined together using, for example by clamping the pillar boards together using a connector board the length of sum of the lengths of the individual pillar boards being joined. An assembly jig may be used to facilitate this joining of pillar boards. 
         [0154]    In the above embodiment, the copper films are patterned photolithographically. However, this need not be the case, and in other embodiments, other patterning techniques may be used. 
         [0155]    In the above embodiment, the pads on the tips of the protrusions of the pillar boards are electrically connected to the contacts of the dipole elements by soldering. However, this need not be the case, and in other embodiments, other techniques may be used, for example using conductive adhesives. Such conductive adhesives may be activated by heating, in which case such heating may be applied remote from the adhesive by applying the heat using the above described vias, as was the case in the soldering example above. However, in other embodiments where the conducting adhesive, or other appropriate method, does not require heat, then the vias and thermal pads described above may be omitted. Another possibility where the vias and the thermal pads described above may be omitted is if all of the soldering (or other heat applying technique) is done using the earlier described reworking holes. 
         [0156]    In the above embodiment, the dipole array is fabricated using the process described above. However, in other embodiments the dipole array is fabricated using a different appropriate method, for example may be simplified to a monolithic structure with conductors deposited on either or just a single side. In other embodiments, the fabrication method for comprising the dipole array comprises some, all or none of the above described method steps. 
         [0157]    In the above embodiment, the dipole array was fabricated using layers of Liquid Crystal Polymer (LCP). However, in other embodiments a different appropriate material is used. For example, in other embodiments a material with a similar thickness and complex relative permittivity, such as Taconic HyRelex TF290, is used and may provide improved performance. The dimensional stability in this layer tends to be important since small variations from element to element sum over the dipole array surface to potentially produce large inaccuracies such that dipole elements do not line up with the corresponding tips of the pillar boards. The use of the materials specified tends to avoid this problem. Furthermore, it tends to be particularly advantageous to match the coefficient of thermal expansion of these layers to those of other materials, in particular that of the ground plane box. Doing this tends to minimise the internal stresses within the transceiver resulting from operating at varying temperatures. The use of the materials specified tends to avoid this problem. 
         [0158]    In the above description the various embodiments of feed arrangement, fixture, and the like, have been described in conjunction with a dipole array of substantially triangular poles (or other shapes providing highly coupled dipole effects as described earlier above). However, it will be appreciated that such dipole shapes are not essential, and in other embodiments other types of planar arrays of antenna elements may be used instead of the highly coupled ones described above, including conventional planar arrays of antenna elements with conventionally shaped antenna elements.

Technology Category: 5