PHASED ARRAY ANTENNA HAVING REFLECTION PHASE SHIFTERS

introduction

This invention relates to an antenna comprising a casing having a reflector defining a slot, a plurality of radiating elements, a feed harness comprising a plurality of feed tracks, each feed track being associated with one of the radiating elements and electrically connecting the feed harness to the radiating elements, and a printed circuit board (PCB) carrying the radiating elements and the feed harness, the PCB being mounted in the casing and protruding outwardly therefrom through the slot so that the radiating elements are on one side of the reflector and the feed harness is substantially on the other side of the reflector.

One such type of antenna is that disclosed in the applicants own PCT patent application numbers PCT/IB2004/004455 and PCT/EP2006/067163, the entire disclosures of which and in particular the disclosure relating to the specific constructions of antenna are incorporated herein by way of reference. This type of antenna is seen as a particularly efficient, robust, lightweight, compact and cost effective to provide. The present invention relates to improvements to this type of antenna in particular.

Antennae are widely used in wireless communications networks. It is often necessary to introduce a new antenna into the network to replace an existing faulty antenna or to cater for an increase in traffic on the network. One major problem that is encountered when introducing a new antenna into the network is the interference caused by that new antenna on the existing antennae in the network. It is often necessary to carefully configure the new antenna and/or the existing antennae so that they do not significantly interfere with each other. Furthermore, it is often necessary to re-configure one or more antenna in a wireless communications network so that coverage in a particular area is improved. One of the most common ways of configuring an antenna is by tilting the antenna so that the coverage pattern of the antenna is modified.

One of the most efficient ways of altering the tilt of an antenna is electronically.

Heretofore, this has entailed modifying the signals emitted by the radiating elements of the antenna by altering the length of the tracks from the feed harness to the radiating elements, otherwise known as the dipoles. These methods typically operate using

altemative lengths of track that may be switched in and out of the feed tracks in order to lengthen or shorten the overall length of the feed track to the dipoles thereby adjusting the tilt angle of the antenna. The alternative lengths of track are switched in and out of the feed tracks using electronically controlled switches which open and close paths through the wiring harness of the antenna. However, there are problems with the known types of electronically tilting antenna. Most importantly, as the frequency of the system approaches 2 gigahertz (GHz) and above, the space within which to fit the devices becomes critical and the size of the antenna becomes too large for practical application. Furthermore there are often problems concerning reflections and high Voltage Standing Wave Ratio (VSWR) which make these approaches unattractive.

It is an object therefore of the present invention to provide an antenna that overcomes at least some of the problems with the known antennae that is relatively compact and efficient in operation.

Statements of Invention

According to the invention there is provided an antenna comprising: a casing having a reflector defining a slot; a plurality of radiating elements; a feed harness comprising a plurality of feed tracks, each feed track being associated with one of the radiating elements and electrically connecting the feed harness to the radiating elements; a printed circuit board (PCB) carrying the radiating elements and the feed harness, the PCB being mounted in the casing and protruding outwardly therefrom through the slot so that the radiating elements are on one side of the reflector and the feed harness is substantially on the other side of the reflector; characterised in that the antenna further comprises: a controller; and at least one of the feed tracks having a phase shifting device responsive to the controller to electronically tilt the antenna, the phase shifting device comprising a stub track and an isolation means to prevent reflections to the input connected in series in the feed track.

By having such an antenna, the tilt of the antenna may be altered in a relatively simple manner in a highly predictable way. There is no need to provide a plurality of separate sets of tracks which take up a significant amount of space and the construction of antenna will be more compact than is otherwise possible. This has knock on advantages

including reducing the cost of manufacture of the antenna as well as reducing the windage of the final construction of antenna thereby providing a more steady and robust antenna. Furthermore, this is seen as a more simple construction to manufacture than the existing solutions and requires the minimum of difficulty to reproduce. Each phase shifting device is individually adjustable, thus making the design much easier than might otherwise be the case. Preferably, the stub track is an open stub track.

In one embodiment of the invention the isolation means comprises a hybrid coupler. Preferably, the isolation means is a 90° hybrid coupler. Alternatively, the isolation means comprises one of a rat race hybrid, a 3 port isolator (planar or non-planar) and a 4 port isolator (planar or non-planar). It is envisaged that other isolation means known in the art could also be provided.

In another embodiment of the invention there is provided an antenna in which the stub track is adjustable in length. By having an adjustable length track, it will be possible to have greater control over the amount of tilt produced. This will allow for a range of tilt angles to be achieved. In one embodiment of the invention there is provided an antenna in which the stub track further comprises an stub trunk, an stub branch and a switching device operable to connect the stub branch to the stub trunk.

In a further embodiment of the invention there is provided an antenna in which there are provided a plurality of stub branches and a plurality of switching devices, each of the stub branches having a switching device associated therewith, each of the switching ^d evices being operable to connect one of the stub branches to the stub trunk at a given time. By having such an arrangement, each of the stub branches will be able to provide a different amount of electronic tilt to the antenna and therefore the antenna will be more adjustable than would otherwise be the case. Again, this is seen as a particularly useful construction of antenna that will permit a significant amount of adjustability without requiring complex circuitry and furthermore a number of open stub tracks of varying length may be catered for in a simple manner.

In another embodiment of the invention there is provided an antenna in which the stub trunk and the stub branches are arranged in an asterisk configuration with the plurality of stub branches extending radially away from one end of the stub trunk. This is seen as a

very compact configuration of antenna that will allow for the maximum amount of branches to be provided in the space provided.

In one embodiment of the invention there is provided an antenna in which the phase shifting device is mounted on a separate daughter PCB ₁ the daughter PCB in turn being mounted on the PCB carrying the radiating elements and the feed harness. This is seen as particularly preferred as the phase shifting device may be constructed separately from the antenna radiating elements and the feed harness, thereby simplifying construction.

In a further embodiment of the invention there is provided an antenna in which there are provided a plurality of daughter PCBs each having a phase shifting device to electronically tilt the antenna thereon.

In a further embodiment of the invention there is provided an antenna in which the stub track is an open stub track. By this what is meant is that the stub track is not provided by a track having a short to ground but rather is a track that is disconnected at one end.

In another embodiment of the invention there is provided an antenna in which the plane of the daughter PCB is substantially perpendicular to the plane of the PCB carrying the radiating elements and the feed harness. This is seen as a simple way of mounting the daughter PCB on the main PCB.

In one embodiment of the invention there is provided an antenna in which the plane of the daughter PCB is substantially parallel to the plane of the PCB carrying the radiating elements and the feed harness. This is seen as a very useful alternative way of mounting the daughter PCB that will allow for the daughter PCB to be mounted in the same casing as the remainder of the feed harness without requiring modification of the existing casing design. This will facilitate retrofitting of the antenna with phase shifting into existing antenna casings thereby obviating the need to obtain supplementary planning permission for mounting a different antenna casing on a mast or other mount.

In a further embodiment of the invention there is provided an antenna in which the daughter PCB is laminated on the PCB carrying the radiating elements and the feed harness. By having such an embodiment, the construction of the antenna is sped up and fi irthermore the overall cost of the antenna is reduced by obviating the need for co-axial

connectors. In another embodiment of the invention there is provided an antenna in which there are provided a plurality of vias in the daughter PCB for electrical connection of the phase shifting device to the feed harness and the radiating elements.

In one embodiment of the invention there is provided an antenna in which the PCB carrying the radiating elements and the feed harness is substantially U-shaped in cross- section and comprises a pair of legs bridged by a centre portion. By having a U-shaped PCB, it is possible to provide a dual polarised antenna pattern in the antenna with the existing casing. The daughter PCB mounted in parallel to the PCB legs will therefore also fit in the existing design of casing and will not require a different casing design to be : oed. In a further embodiment of the invention there is provided an antenna in which the daughter PCB is mounted on one of the pair of legs.

In another embodiment of the invention there is provided an antenna in which the phase shifting device comprises a hybrid coupler having a pair of open stub tracks connected to the 0° port and the θ° port of the hybrid coupler connected in series in the feed track. In one embodiment of the invention there is provided an antenna in which the phase shifting device further comprises a 90° hybrid coupler having a pair of open stub tracks connected to the 0° port and the 90° port of the hybrid coupler. This is seen as a particularly preferred embodiment of antenna. In a further embodiment of the invention there is provided an antenna in which the pair of open stub tracks further comprise an open stub trunk, a plurality of open stub branches and a plurality of switching devices, each of the open stub branches having a switching device operable to connect that open stub branch to the open stub trunk.

In another embodiment of the invention there is provided an antenna in which the switching devices are positioned in the open stub branches at predetermined intervals proportional to a designated frequency wavelength. In one embodiment of the invention there is provided an antenna in which there are provided a pair of switching devices connected in series in each stub branch.

In a further embodiment of the invention there is provided an antenna in which the πtrollable switching device comprises a diode. This is a particularly simple and inexpensive device to use for the switching device that may be operated at very high

frequencies. This has particular advantages as the antenna tilt angle may now be adjusted practically instantaneously and therefore a whole range of possibilities open up regarding the frequency and manner in which the tiltable antenna may be operated. As an alternative to the diodes, it is possible to use a Field Effect Transistor (FET) or other switching device.

Detailed Description of the Invention

The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings, in which:-

Figure 1 is a perspective view of one embodiment of antenna according to the present invention;

Figure 2 is a perspective view of an alternative embodiment of antenna according to the present invention;

Figure 3 is a diagrammatic representation of an antenna pattern having means to electronically tilt an antenna;

Figure 4 is a diagrammatic representation of a phase shifting device according to the present invention;

Figure 5 is an enlarged view of part of the phase shifting device shown in Figure

4;

Figure 6 is an alternative construction of a phase shifting device;

Figure 7 is an alternative construction of a phase shifting device;

Figure 8 is a diagrammatic representation of an antenna pattern ground plane printed on a PCB for use in an antenna according to the present invention;

Figure 9 is a diagrammatic representation of the reverse side of the antenna pattern shown in Figure 8;

Figure 10 is an enlarged view of portion of the antenna pattern of Figure 8 with phase shifting devices mounted on the PCB;

Figure 11 is an enlarged diagrammatic representation of a phase shifting device;

Figure 12 is a diagrammatic representation of a dual polarised antenna pattern for use in an antenna according to the present invention;

Figure 13 is a diagrammatic representation of the reverse side (ground plane) of the antenna pattern shown in Figure 12;

Figure 14 is a diagrammatic representation of a PCB having the phase shifting devices for an antenna according to the present invention;

Figure 15 is a diagrammatic representation of a reverse side of the PCB shown in Figure 14;

Figure 16 is a diagrammatic representation of a daughter PCB mounted on the antenna of Figure 1 ; and

Figure 17 is a diagrammatic representation of a daughter PCB mounted on the antenna of Figure 2.

Referring to the drawings and initially to Figure 1 thereof, there is shown a perspective view of an antenna, indicated generally by the reference numeral 1 comprising a casing 3 having a reflector 5 defining a slot 7. The antenna further comprises a PCB 9 carrying a plurality of radiating elements 11 and a feed harness (not shown) comprising a plurality Jϊ feed tracks (not shown). The PCB 9 is mounted in the casing 3 and protrudes outwardly therefrom through the slot 7 so that the radiating elements are located on one side of the reflector 5 and the feed harness is substantially located on the other side of the reflector. The slot is dimensioned to be spaced apart from the radiating elements.

Referring to Figure 2 there is shown a perspective view of an alternative embodiment of antenna, indicated generally by the reference numeral 21 , where like parts have been given the same reference numeral as before. The antenna 21 comprises a U-shaped PCB 9 comprising a pair of legs 23, 25 bridged by a centre portion 27. The antenna further comprises a signal reflective sheet 29 mounted on one side of the centre portion 27 and a signal amplifying patch 31 mounted on the other side of the centre portion. A plurality of radiating elements and a feed harness (not shown) are printed on the PCB 9. The U-shaped PCB is formed from a unitary sheet of PCB material by heating the PCB to of the order of 120° Celsius and thereafter bending the PCB about two fold lines 33, 35 parallel to the longitudinal axis of the unitary sheet. The fold lines each have a radius of curvature of the order of between 1 mm and 3mm to avoid cracking the ground plane surface 37 of the PCB.

Referring to Figure 3 of the drawings, there is shown a diagrammatic representation of a PCB antenna pattern incorporating the phase shifting device according to the invention. The PCB antenna pattern 41 comprises a feed harness 42 which in turn comprises a plurality of feed tracks 43. The feed tracks connect the input 44 to the radiating elements 45. A phase shifting device 47 is positioned in series in the feed tracks 43 intermediate the input 44 and the radiating elements 45.

Figure 4 is a diagrammatic representation of a phase shifting device according to the present invention, indicated generally by the reference numeral 51. The means to electronically tilt an antenna 51 comprises a hybrid coupler 53 having an input 55, an output 57 and a pair of splitter ports 58(a), 58(b). The hybrid coupler further comprises a pair of open stub tracks 59 (a) and 59(b) connected to the splitter ports 58(a), 58(b) respectively, each of which comprises an open stub trunk 61 and a plurality of open stub branches 63(a), 63(b), 63(c), 63(d) and 63(e). All of the plurality of open stub branches, 63(a), 63(b), 63(c), 63(d) and 63(e), are of different length with respect to each other. Each of the open stub branches has a pair of diodes 65 formed therein along their length. A control line 66 with an inductor 67 therein is fed to each of the open stub branches and a connection to a DC earth 69 for the open stub trunk 61 is provided via a further inductor 71. The first open stub track 59(a) is at 0° whereas the second open stub track 59(b) is at an angle of 90° offset with respect to the first open stub track 59(a).

In use, the input 55 and the output 57 are connected in series with the track (not shown) of the antenna en route to the dipole half, and the diodes 65 are open until a DC voltage (in this case 1.1.V) is applied to one of the branches 63(a), 63(b), 63(c), 63(d) and 63(e) which causes the diodes in that branch only to close and therefore the length of the open stub track is changed, thereby altering the phase of the antenna and accordingly altering the tilt of the antenna. When it is desired to alter the tilt once more, the voltage is removed from that branch 63(a), 63(b), 63(c), 63(d) and 63(e) and applied to another branch 63(a), 63(b), 63(c), 63(d) and 63(e) to achieve the desired tilt. Again, this will alter the length of the track and thereby alters the tilt of the antenna. Therefore, the open stubs are essentially adjustable in length and they are able to achieve a digital phase shift. The speed at which this may be achieved is limited primarily by the response times of the devices which are fast and therefore this opens up a number of possibilities to the application of the invention as it is conceivable that the phase and hence the tilt may be changed numerous times in quick succession in a relatively short period of time. The pair of open stub track lengths are the same for a hybrid coupler but alter in length for the different half dipoles. It can be seen that such a configuration provides six alternative tilt angles from which to choose, one of which being provided when none of the stub branches are connected to the trunk and the other five being created when each one of the branches is connected to the trunk individually. Preferably, four alternative tilt angle configurations will be provided comprising three stub branches.

Furthermore, each of the branches 63(a), 63(b), 63(c), 63(d) and 63(e) is provided with a pair of diodes as this provides better isolation to the branch when it is in an open configuration however this will be understood to be optional and may not be necessary. The provision of a pair of diodes is important when working at frequencies at 2.5 - 3 GHz and above. The present invention will typically be utilised in application ranging in frequency from 1GHz up to 6GHz. If both stubs are of equal length there will be an adjustment of the phase at the output port leading to the dipole but little or no other adjustment to the incoming RF (AC) signal at the input 55.

The organisation of the stubs is such that each may be connected to a single feed track, will in certain embodiments, produce an asterisk shaped structure terminating in a stub trunk 61. The stub trunk 61 is the common part of the stub commencing at the hybrid

coupler port. Each limb of the asterisk is a possible stub extension and becomes an active part of the stub when closed by a switch consisting at least one, but possibly two diodes connected in series. The structure has the advantage that it does not require an RF connection to ground as some other implementations may require which is difficult to achieve when working in the range of 2.5 GHz. It is simpler to provide an open than a short at 2 GHz and above. It is further not necessary to provide a capacitor for each stub, which causes dB loss, as may be the case with alternative implementations and therefore this is seen as a particularly useful implementation. Furthermore, using this particular construction, it is far easier to create a stub branch to a specific length with a great deal of accuracy.

Figure 5 is an enlarged view of part of the means to electronically tilt an antenna shown in Figure 4. It can be seen that the diodes 65 are positioned at the root of the branch 63(b), 63(c). In this example, only one diode is shown. The remaining open stub branches, 63(a), 63(d) and 63(e) have been removed for reasons of clarity. The control line 66 with an inductor 67 therein is led to the open stub branch 63(c) and on a voltage being applied to the control line 66 the open stub branch is effectively closed by closing tne diode 65 and this in turn makes the open stub branch 63(c) form part of the greater open stub track, increasing its length and therefore altering the phase and accordingly the tilt of the antenna.

Referring now to Figure 6 of the drawings there is shown an alternative embodiment where like parts have been given the same reference numerals as before. In this embodiment, there is once again a short circuit stub 81 in each track leading to a dipole (not shown). The stubs are adjustable in length by inserting a plurality of switches, in this case diodes 65, at defined intervals along the stub 81. The intervals are proportional to the designated frequency wavelength. Typically, there will be provided a pair of stubs 81, 82, each of which is at the splitter port of a 90° hybrid coupler (not shown). The second stub 82 is identical in structure and essentially a mirror image of the first stub 81. The _^ tub is increased in length by gradually introducing more and more stub sections 83 or removing stub sections 83 as the case may be by controlling the control voltage 85 delivered to the stub section 83 via an inductor 87. A capacitor 89 is provided intermediate each of the sections to remove any DC component from the branch. The capacitor blocks DC but permits passage of RF signals. Finally, each section 83 is

connected to ground 90 via a pair of diodes. The maximum possible phase shift is achieved by having the longest possible track. Referring to the drawing, if the rightmost stub section 83 has 1.1V applied to it, all the other stub sections 83 to the left of the rightmost stub section 83 intermediate the rightmost section and the stub 81 will essentially be switched in to the stub section. Similarly, if the stub section second from the right is connected to the 1.1V, the stub sections 83 to the left of it will be switched in also but the stub section to the right, the rightmost section, will not be switched in to the stub.

One difficulty with such an approach is that as the frequency gets higher, the length of the wave gets shorter, and to accurately divide the track by switches becomes more and more difficult. Consider the accuracy required to solder a diode switch accurately between two other diodes in a track of 5mm in length. When a diode is switched on it has capacitance. The track the diode sits on is of finite length and also has capacitance and inductance and the via to ground will have inductance. This presents performance difficulties as frequency increases. Another difficulty with the structure described is that it requires a substantial RF (AC) connection to ground which is a principal source of manufacturing and performance problems. A third difficulty with the embodiment described is that each division requires an extra capacitor and the capacitors are responsible for a cumulative loss in gain of the system. The hybrid coupler solves the problems of reflections and low VSWR to a great extent.

Referring to Figure 7 of the drawings there is shown an alternative construction of stub track, indicated generally by the reference numeral 91. The stub track 91 comprises a stub track 92 with a transistor 93, a capacitor 95 and a diode 97 forming a switching circuit. In this embodiment, the common length of the stub 91 is shorted at its end, and the DC power to the shorting diode switches 97 at intervals along its length is supplied via the transistor 93 and a very short grounded stub. This variation deals with the problem of accurate track splitting to an extent and reduces the capacitor problem discussed above but increases the RF grounding problems. A second stub 94 which has not been shown in its entirety may be identical in structure and essentially a mirror image of the first open stub 92.

Referring now to Figure 8, there is shown an antenna, indicated generally by the reference numeral 91 , comprising a mother printed circuit board (PCB) 93 on which there is mounted an input 95 and a plurality of radiating elements 97. The radiating elements 97 are mounted in pairs and each radiating element 97 forms part of a dipole pair with its nearest neighbouring radiating element 97, separated by a small spacing gap 98 therebetween. There is further provided a plurality of connectors 99, each of which is associated with a dipole pair. This side of the antenna 91 is referred to as the ground side and the radiating elements 97 are made from an electrically conducting material, in this case copper which is etched onto the mother PCB 93.

Referring now to Figure 9 of the drawings there is shown a front view of the antenna shown in figure 8 showing the input 95 and feed harness 101. The feed harness 101 comprises a plurality of feed tracks 103 which supply power from the input 95 to the ^■ κJiating elements (not shown). The feed harness is provided in a pattern that will provide a cosecant squared radiation pattern and by having the feed harness pattern implemented in copper or like material on a PCB it is simple to reproduce the cosecant squared pattern accurately over and over again. When one considers a dipole stack arranged vertically, the power varies from the top to the bottom, but is highest somewhere above the centre dipoles. This causes the side lobes to be minimised, both upper and lower symmetrically. The phase variations further reduce the upper lobe and increase the lower side lobe to approximate a cosecant squared pattern. Built into the phase variations are values designed to eliminate spikes in the upper side lobe. These values are arrived at by experiment. In general, the phase changes required to create a five degree downtilt are progressively greater, though not uniformly, than those needed to create a one degree downtilt. It will be understood that as an alternative it would be possible to reduce the strength of radiation from the lower side lobe or provide a standard null filled antenna by choice of appropriate track configurations on the feed harness.

A number of spacers (not shown) may be provided on both sides of the antenna mother board 93 in the case of having a slot in the reflector (not shown) uniformly larger than the width of the PCB. It can be seen that there are a number of gaps 105 in the feed tracks 103. These gaps correspond with the connectors 99 on the other side of the mother PCB 93. The feed tracks 103 terminate in a hook portion 107, otherwise referred to as a

quarter line stub. The quarter line stub comprises a return leg 109 which corresponds and runs parallel to the spacer gap 98 between the radiating elements 97 on the other Ciide of the mother PCB. This acts to balance the power in the radiating elements of a dipole pair.

Referring to Figure 10, there is shown a phase shifting means for use with the present invention. In the embodiment shown, the phase shifting means are mounted on a daughter PCB 111 which in turn may be mounted on the mother PCB 93 using the connectors 99. The daughter PCB 111(a) in fact contains a solid track 113 of copper material and no additional tracks are provided, therefore this dipole pair is in fact kept constant relative the remaining dipoles and the remaining dipoles are changed to provide tilt. The second daughter PCB 111(b) comprises a solid track, in this case a hybrid coupler 115 having a pair of open stubs 117 connected thereto. There is further provided a pair of switches 119 to switch the open stubs into the circuit which will have the effect of altering the phase to the associated dipole pair.

Referring to Figure 11 of the drawings, there is shown a daughter PCB 111 having a phase shifting means thereon. The phase shifting means comprises a pair of open stubs 117 which in turn comprise a pair of open stub trunks 118 and a plurality of open stub branches 121 , each of different lengths with respect to the other open stub branches associated with that particular open stub trunk 118. A plurality of switching devices 123, in this case diodes, are provided, at least one per open stub branch to allow the open stub branch to be selectively connected to the open stub stalk. The control lines have been omitted for clarity. It can be seen that by providing appropriate phase shifting means along the length of antenna, the phase of the entire antenna may be altered in a controlled manner.

Referring to Figures 12 and 13 of the drawings there is shown a typical antenna pattern for a dual polarised antenna pattern as commonly used in mobile telephony applications. the antenna pattern is shown in a flat state prior to being folded about fold lines. Figure

12 shows the antenna feed harness 125, radiating elements 126 and feed tracks 127 with gaps 128 in the feed tracks. These gaps accommodate connectors for reception of hase shifting device. Figure 13 shows the ground plane of the antenna pattern shown in Figure 12 with a plurality of holes 129 therein for mounting the signal reflective sheet

(not shown) and the signal directing patches (not shown) as well as a number of vias 130 for reception of connections to a phase shifting device.

Referring to Figures 14 and 15, there is shown a daughter PCB 140 for mounting flat on a mother PCB (not shown). The daughter PCB comprises a plurality of phase shifting devices 141 , each of which comprises a 90° hybrid coupler 143 having a pair of open stub trunks 145 and a plurality of open stub branches 147. Control lines 148 are each provided with a diode 149 therein in a similar fashion to that described above. It can be seen that all of the phase shifting devices for the plurality of radiating devices may be provided on a single PCB. Referring specifically to Figure 15, there are shown a number

^f vias 151 which cooperate with vias on the mother PCB to connect the phase shifting devices in series in the feed tracks (not shown) to the radiating elements.

Referring to Figure 16, there is shown one method of mounting the daughter PCB 111 on the mother PCB 9. The daughter PCB is mounted on connectors 99 (only one of which is shown) substantially perpendicular to the mother PCB. The phase shifting devices are on the daughter PCB 111 and the antenna pattern including radiating elements and feed tracks is printed on the mother PCB 9. A controller 161 is provided on the mother PCB to send signals to the phase shifting devices to determine the branch (if appropriate) to be switched into the circuit to provide a certain amount of tilt to the antenna. Similarly, the controller will preferably have means to communicate with a remote central controller which may be a base station connected via a coaxial cable or a remote control station in a distant location in which case the controller may communicate using radio or other wireless communication means with the central controller. The central controller or the base station may relay specific tilt angles to be implemented by the antenna and these are achieved by the controller 161 communicating with the phase shifting devices (not shown).

Referring to Figure 17 of the drawings, there is shown another method of mounting the daughter PCB 140 onto the mother PCB 9. The daughter PCB 140 is mounted flat on or narallel to the leg 23, 25 of the U-shaped PCB 9. The daughter PCB is laminated on to the U-shaped PCB and the electrical connection between the phase shifting devices on the daughter PCB 140 and the feed tracks on the mother PCB 9 are provided through vias through the PCB board. It can be seen that there are a pair of daughter PCB boards

due to the fact that with a dual polarised antenna there will essentially be double the number of antenna radiating elements and double the number of antenna feed tracks. Unce again, a controller 161 is provided for controlling the degree of tilt.

In this specification the terms "comprise, comprises, comprised and comprising" and the terms "include, includes, included and including" are deemed totally interchangeable and should be afforded the widest possible interpretation.

The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail within the scope of the claims.