Abstract:
A device for feeding signals between a common line and two or more ports. The device including a branched network of feedlines coupling the common line with the ports. The feedlines have transformer portions of varying width for reducing reflection of signals passing through the network. A dielectric member is mounted adjacent to the network and can be moved to synchronously adjust the phase relationship between the common line and one or more of the ports. The dielectric member also has transformer portions for reducing reflection of signals passing through the network. At least one of the junctions of the network does not overlap with the dielectric member, or overlaps a region of reduced permittivity.

Description:
FIELD OF INVENTION 
     The invention relates to a device for feeding signals between a common line and two or more ports. The invention also relates to a dielectric phase shifter and a method of manufacturing a dielectric phase shifter. 
     BACKGROUND OF THE INVENTION 
     Traditionally tuneable antenna elements consist of power splitters, transformers, and phase shifters cascaded in the antenna arrangement. In high performance antennas these components strongly interact with each other, sometimes making a desirable beam shape unrealisable. 
     A number of canonical beam-forming networks have been proposed in the past, to address these problems. 
       FIG. 1  is a plan view of part of a phase shifter described in U.S. Pat. No. 5,949,303. An input terminal  100  is coupled to an input feedline  101 . A feedline  102  branches off from junction  103  and leads to a first output terminal  104 . A second output terminal  105  is coupled to feedline  102  at junction  110  by a meander-shaped loop  106 . A dielectric slab  107  partially covers feedline  102  and loop  106  and is movable along the length of the feedline  102  and over loop  106 . 
     The leading edge  108  of the slab  107  is formed with a step-like recess  109 , as shown in  FIG. 2 . The step-like recess  109  is dimensioned to minimize reflection of the radio wave energy propagating along the feedlines. 
     This arrangement suffers from several shortcomings. 
     Firstly, recess  109  of the moveable dielectric body  107  operates like a transformer increasing wave impedance in the direction from input terminal  100  to the output terminals. In order to have equal impedance at the input and all outputs, the device shown in U.S. Pat. No. 5,949,303 requires additional transformers between junction  110  and output terminal  104 . 
     Secondly, all feedlines apart from  101 , which is the first from input terminal  100 , cross the edge of the dielectric plate twice. Therefore the reflection at two recesses can add up to double the reflection at one recess depending on the position of the dielectric plate. 
     Thirdly, the relative positions of the output terminals impose constraints on the layout, which may be incompatible with physical realisations of beam-forming networks for some applications. 
     Fourthly, it can be difficult to accurately and consistently fabricate the recess  109  in slab  107 . 
     Fifthly, this approach is not suitable for a linear array containing an odd number of output ports. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to address one or more of these shortcomings of the prior art, or at least to provide a useful alternative. 
     A first aspect of the invention provides a device for feeding signals between a common line and two or more ports, the device including a branched network of feedlines coupling the common line with the ports, at least one of the feedlines having a transformer portion of varying width for reducing reflection of signals passing through the network; and a dielectric member mounted adjacent to the network which can be moved along the length of at least one of the feedlines to synchronously adjust the phase relationship between the common line and one or more of the ports, the dielectric member having one or more transformer portions for reducing reflection of signals passing through the network. 
     The first aspect of the invention provides a means for integrating two types of transformer into the same device. As a result the wave impedance at the common line can be better matched to the wave impedance at the ports, whilst maintaining a relatively compact design. 
     Typically the feedline transformer portion includes a step change in the width of the feedline. 
     The transformer portion in the dielectric member may be provided by a recess in the edge of the member, as shown in  FIG. 2 . However, in the preferred embodiments described below, the transformer portion is provided in the form of a space or region of reduced permittivity. 
     A second aspect of the invention provides a device for feeding signals between a common line and two or more ports, the device including a branched network of feedlines coupling the common line with the ports via one or more junctions; the one or more junctions including a main junction which includes the common line; and a dielectric member mounted adjacent to the network which can be moved along the length of at least one of the feedlines to synchronously adjust the phase relationship between the common line and one or more of the ports, wherein the main junction does not overlap with the dielectric member 
     The second aspect of the invention provides an alternative arrangement to the arrangement of  FIG. 1 . In contrast to the system of  FIG. 1  (in which the dielectric member overlaps the junction  103 ), the dielectric member does not overlap with the junction. This may be achieved by forming a space in the dielectric member. 
     A third aspect of the invention provides a device for feeding signals between a common line and two or more ports, the device including a branched network of feedlines coupling the common line with the ports via one or more junctions; and a dielectric member mounted adjacent to the network which can be moved to synchronously adjust the phase relationship between the common line and one or more of the ports, wherein the dielectric member has a first region of relatively high permittivity, and a second region of relatively low permittivity which overlaps with at least one of the junctions. 
     The third aspect provides similar advantages to the second aspect. 
     Typically the dielectric member is formed with a transformer portion for reducing reflection of signals passing the leading or trailing edge of the space or region of reduced permittivity. In contrast to the arrangement of  FIG. 1 , the wave impedance at the transformer portion can decrease in the direction of the ports. 
     A variety of transformer portions may be used. For instance the leading and/or trailing edges of the space or region of reduced permittivity may be formed as shown in  FIG. 2 . However in a preferred embodiment the dielectric member is formed with at least one second space or region of relatively low permittivity adjacent to an edge of the first space or region, wherein the or each second space or region is relatively short compared to the first space or region in the direction of movement of the dielectric member, and wherein the position and size of the or each second space or region are selected such that the or each second space or region acts as an impedance transformer. 
     A fourth aspect of the invention provides a device for feeding signals between a common line and two or more ports, the device including a branched network of feedlines coupling the common line with the ports; and a dielectric member mounted adjacent to the network which can be moved to adjust the phase relationship between the common line and one or more of the ports, wherein the dielectric member is formed with a first space or region of relatively low permittivity, and at least one second space or region of relatively low permittivity adjacent to and spaced from an edge of the first space or region, wherein the or each second space or region is relatively short compared to the first space or region in the direction of movement of the dielectric member, and wherein the position and size of the or each second space or region are selected such that the or each second space or region acts as an impedance transformer. 
     The fourth aspect of the invention relates to a preferred form of transformer, which is easier to fabricate than the transformer of  FIG. 2 . The transformer is also easier to tune according to the requirements of the feed network (by selecting the position and size of the second space or region). 
     A fifth aspect of the invention provides a device for feeding signals between a common line and an array of ports, the array of ports including a central port and two or more phase shift ports, the device including a branched network of feedlines coupling the common line with the array of ports; and a dielectric member mounted adjacent to the network which can be moved to synchronously adjust the phase relationship between the common line and the two or more phase shift ports whilst maintaining a constant phase relationship between the common line and the central port. 
     The following comments relate to the devices according to the first, second, third, fourth and fifth aspects of the invention. 
     Typically the device includes a first ground plane positioned on one side of the network. More preferably the device also has a second ground plane positioned on an opposite side of the network. 
     Typically the feedlines are strip feedlines. 
     The dielectric member may be formed by joining together a number of dielectric bodies. However preferably the dielectric member is formed as a unitary piece. 
     Typically the dielectric member is elongate (for instance in the form of a rectangular bar) and movable along its length in a direction parallel to an adjacent feedline. 
     Typically the device has three or more ports arranged along a substantially straight line. 
     A variety of delay structures, such as meanders or stubs, may be formed in the feedlines. 
     A sixth aspect of the invention provides a method of manufacturing a dielectric phase shifter, the method including the step of removing material from an elongate dielectric member to form a space at an intermediate position along its length. 
     The sixth aspect of the invention provides a preferred method of manufacturing a dielectric member, which can be utilised in the device of the second, third or fourth aspects of the invention, or any other device in which such a design is useful. The space may be left free, or may be subsequently filled with a solid material having a different (typically lower) permittivity to the removed material. This provides a more rigid structure. 
     The space may be an open space (for instance in the form of a rectangular cut-out) formed in a side of the dielectric member. Alternatively the space may be a closed space (for instance in the form of a rectangular hole) formed in the interior of the dielectric member. 
     The member can then be mounted adjacent to a feedline with its length aligned with the feedline, whereby the dielectric member can be moved along the length of the feedline to adjust a degree of overlap between the feedline and the dielectric member. 
     Typically the feedline is part of a branched network of feedlines coupling a common line with two or more ports. Typically the space or region of relatively low permittivity overlaps with a junction of the branched network. 
     A seventh aspect of the invention provides a dielectric phase shifter comprising an elongate dielectric member formed with a space at an intermediate position along the length of the elongate member. 
     For instance a notch or recess may be formed in a side of the member, or a hole formed in the interior of the member. 
     An eighth aspect of the invention provides a dielectric phase shifter device including an elongate dielectric member formed with a space or region of relatively low permittivity at an intermediate position along the length of the elongate member, wherein the space or region is formed in a side of the dielectric member. 
     A ninth aspect of the invention provides a dielectric phase shifter device including an elongate dielectric member formed with a space or region of relatively low permittivity at an intermediate position along the length of the elongate member, wherein the space or region is formed in the interior of the dielectric member. 
     A tenth aspect of the invention provides a device for feeding signals between a common line and two or more ports. The device includes a branched network of feedlines coupling the common line with the ports via one or more junctions, the one or more junctions include a main junction, which includes the common line. Also included is a dielectric member mounted adjacent to the network having a region of relatively high permittivity and one or more transformer portions for reducing reflection of signals passing through the network. The dielectric member can be moved along the length of at least one of the feedlines to synchronously adjust the phase relationship between the common line and one or more of the ports. The dielectric member is formed with a second region having a space or region of relatively low permittivity, the second region overlapping the main junction. 
     A tenth aspect of the invention provides a method of manufacturing a dielectric phase shifter including the steps of forming a region of relatively low permittivity by removing material from an elongate dielectric member to form a space at an intermediate position along its length and filling the space with a solid material having a different permittivity relative to the removed material. 
     An eleventh aspect of the invention provides an elongate dielectric member formed with a space at an intermediate position along the length of the elongate member, the region of relatively low permittivity including a space filled with a solid material having a different permittivity relative to the removed material. 
     A twelfth aspect of the invention provides an elongate dielectric member having a first region of relatively low permittivity and at least one second region of relatively low permittivity adjacent to and spaced from an edge of the first region, where each region of relatively low permittivity is formed at an intermediate position along the length of the elongate dielectric member, the second region is relatively short compared to the first region, and each second region is positioned and dimensioned such that the second region acts as an impedance transformer. 
     The device can be used in a cellular base station panel antenna, or similar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description in conjunction with the accompanying drawings. Several embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic plan view of a prior art device; 
         FIG. 2  is side view of the edge of the prior art device shown in  FIG. 1 ; 
         FIGS. 3   a  to  3   c  are three plan views (width reduced ⅓ of length reduction) of a 10-port device for an antenna beam-forming network with integrated tuneable multi-channel phase shifter, with the movable dielectric bars in three different positions; 
         FIG. 4  is a cross-section taken along a line A—A in  FIG. 3   a;    
         FIG. 5  is a cross-section taken along a line B—B in  FIG. 3   b;    
         FIG. 6  is an enlarged plan view (width reduced ⅓ of length reduction) of the right hand side of the device of  FIG. 3   b;    
         FIG. 7  is a graph showing the variation in permittivity ∈ r , of the movable dielectric bars  47   a  and  47   b  taken along a portion of feedline  16 ; 
         FIG. 8  is a graph showing the variation in permittivity ∈ r  of the movable dielectric bars  47   a  and  47   b  taken along a portion of feedline  17 ; 
         FIG. 9  is a schematic plan view of a segment of an alternative movable dielectric bar; 
         FIGS. 10   a  to  10   c  are three plan views (width reduced ½ of length reduction) of a 5-port device for an antenna beam-forming network with integrated tuneable multi-channel phase shifter, with the movable dielectric bars in three different positions; 
         FIG. 11  is a cross-section taken along a line C—C in  FIG. 10   a;    
         FIG. 12  is a cross-section taken along a line D—D in  FIG. 10   c;    
         FIG. 13  is a schematic plan view (width reduced by ½ of length reduction) of the movable dielectric bar; 
         FIG. 14  is a schematic plan view of a 3-port device with a stripline formed with stubs; 
         FIG. 15  is a schematic plan view of a 3-port device with a stripline formed as meander line; and 
         FIG. 16  is a cross section of a device as shown in  FIG. 10  with an asymmetrical stripline arrangement. 
     
    
    
     DETAILED DESCRIPTION 
     In this written description, the use of the disjunctive is intended to include the conjunctive. The use of definite or indefinite articles is not intended to indicate cardinality. In particular, a reference to “the” object or thing or “an” object or “a” thing is intended to also describe a plurality of such objects or things. 
     The preferred arrangements described below provide a tuneable multi-channel phase shifter integrated with a beam-forming network for a linear antenna array. In order to control the beam direction and beam shape of this antenna array we need to provide certain phase relations between the radiating elements. For subsequent control and changing the beam direction these phase relations should be varied in a specific manner. The beam-forming network also includes circuit-matching elements to minimise signal reflection and maximise the emitted fields. 
     A 10-port feedline network with integrated phase shifter for a phased array antenna is shown in  FIGS. 3 to 6 . Conductor strips  1  to  18  form a feedline network (the dotted area in  FIG. 3 ). These conductor strips can be fabricated from conducting sheets (e.g. brass or copper) or PCB laminate by for example etching, stamping, or laser cutting. It should be noted that, for the purposes of clarity, the width dimension of the device has been reduced by ⅓ of the length reduction in the representation of  FIGS. 3   a – 3   c . As a result the view of the feedline is somewhat distorted in places. 
     As shown in  FIGS. 4 and 5 , the feedline network  1  to  18  is positioned between fixed dielectric blocks  43   a ,  43   b ,  46   a , and  46   b , and movable dielectric bars  47   a  and  47   b . The whole assembly is enclosed in a conducting case, made of metal blocks  48   a  and  48   b . The whole assembly forms a dielectric loaded strip-line arrangement. 
     The pair of sliding dielectric bars  47   a  and  47   b  is housed between the metal blocks  48   a  and  48   b , in the space between the fixed dielectric blocks  43   a ,  43   b ,  46   a , and  46   b . For clarity the contour of the upper bar  47   a  is outlined by a bold line in the three plan views of  FIG. 3 . The bar  47   a  is shown in three different positions in  FIGS. 3   a ,  3   b  and  3   c  . The lower bar  47   b  has an identical profile to the upper bar  47   a . The bar profiles are formed by cutting portions of material from a single piece of dielectric material. 
       FIG. 4  shows a cross section along line A—A in  FIG. 3   a , where the bars  47   a  and  47   b  have no off-cuts and entirely fill the space between the metal blocks  48   a ,  48   b  and the dielectric blocks  43   a ,  43   b ,  46   a , and  46   b .  FIG. 5  shows a cross section taken along line B—B in  FIG. 3   b , where the bars  47   a  and  47   b  have off-cuts  49   a  and  49   b  and partially fill the space between the metal blocks  48   a ,  48   b  and the dielectric blocks  43   a ,  43   b ,  46   a , and  46   b . All off-cuts in the bars  47   a  and  47   b  have well defined locations and dimensions, which depend on the desired phase and power relations at ports  20  to  28 . Simultaneously, the off-cuts serve as circuit-matching transformers for the feedline network. 
     The bars  47   a  and  47   b  can be continuously moved along their length to provide a desired phase shift. The movement of bars  47   a  and  47   b  provides simultaneous adjustment of the phase shift at all ports  20  to  28 . The locations and dimensions of the off-cuts are chosen so that the movement of bars  47   a  and  47   b  within certain limits alters the phase relations between the ports  20 – 28  in a specified manner without changing the impedance matching at the input port  19 . 
     To provide the desired division of power at each junction of the feedline network, circuit-matching transformers are integrated into the feedline network. An example of such circuit-matching elements is sections  11  and  12  near main junction  33  and section  29  in strip conductor  2 . Here the circuit matching is achieved by varying the width of the feedline section. The length and width of these circuit-matching sections  11  and  12  is selected to minimise signal reflection at the main junction  33 . In a preferred arrangement the sections  11  and  12  both have lengths of approximately λ\4 (where λ is the wavelength in the feedline corresponding to the centre of the intended frequency band). These types of circuit-matching transformers will be referred to below as fixed transformers. 
     Another example of a circuit-matching element in this device is shown in  FIG. 6 . Off-cut  52  and projection  51  on the moveable dielectric bar serve as an impedance matching transformer for the feedline segment  17  between junctions  37  and  38 . This transformer matches the wave impedances between the part of stripline  17  where it crosses the left edge of projection  51 , and the part of stripline  17  where it crosses the right edge of off-cut  52 . This type of circuit-matching transformer will be referred to below as a moveable transformer. The length of the feedline between junction  38  and the right edge of off-cut  52  as well as the length of the feedline between junction  37  and the left edge of projection  51  vary with movement of the bars  47   a ,  47   b . However the sum of the two lengths remains constant, regardless of the position of the bars  47   a  and  47   b  (within their working range), thus maintaining proper matching. 
     All of the movable and fixed transformers in the device decrease the wave impedance along the feedline network in the output direction. Therefore the steps in width-variation in the fixed transformers are smaller, and the lengths of the fixed transformers are shorter, when compared with a similar device having no moveable transformers. The reduced length of the fixed transformers enables greater movement of the moveable bars along a length of stripline with uniform width, thus allowing more phase shift. The smaller steps in width variation in the fixed transformers result in lower return loss. 
     An alternative type of moveable transformer is positioned between junctions  33  and  37  ( FIG. 6 ). The transformer is similar to the moveable transformer between junctions  37  and  38 , but in this case is formed by two projections  41 ,  42  and two off-cuts  44 ,  45 . 
     The moveable transformers act as cascaded impedance transformers as shown in  FIGS. 7 and 8  which illustrate variation of ∈ r  along the feedlines adjacent to the cut-outs/projections  41 ,  42 ,  44 ,  45 ,  51  and  52 . 
     The pattern of the strip conductors in  FIG. 3  serves as a power distribution network for antenna radiating/receiving elements (not shown) connected to ports  20  to  28 . The conductor pattern contains multiple splitters and circuit-matching elements. Thus the device can deliver an incoming signal from common port  19  to the ports  20  to  28  with specified phase and magnitude distribution (transmit mode). Also, the device can combine all incoming signals from ports  20  to  28  to the common port  19 , with a predefined phase and amplitude relationship between the incoming signals (receive mode). 
     An alternative topology for the movable dielectric bars  47   a  and  47   b  is shown in  FIG. 9 . In  FIG. 9 , the off-cuts of the bars  47   a  and  47   b  are filled with a dielectric material  80  of different permittivity to the bar material, for instance polymethacrylimite. 
     A 5-port feedline network with an integrated multi-channel phase shifter for a phased array antenna is shown in  FIGS. 10 to 13 . The cross section is in principle is similar to the one for the 10-port device, as shown in  FIGS. 4 and 5 . However, in contrast to the layout of the 10-port device, input port  60  is positioned in line with output ports  61  to  64 . 
     Conductor strips (shown as a dotted area in  FIG. 10 ) form the conductor pattern of the feedline network. These conductor strips can be fabricated from conducting sheets (e.g. brass or copper) or PCB laminate by for example etching, stamping, or laser cutting. As shown in  FIGS. 11 and 12 , the feedline network is positioned between fixed dielectric blocks  67   a , and  67   b , and movable dielectric bars  68   a  and  68   b . The whole assembly is enclosed in a conducting case, made of metal blocks  69   a  and  69   b . The whole assembly forms a dielectric loaded strip-line arrangement. For clarity, the contour of the upper bar  68   a  is outlined by a bold line in the three plan views of  FIG. 10 . The bar  68   a  is shown in three different positions in  FIGS. 10   a ,  10   b , and  10   c . The lower bar  68   b  has an identical profile to the upper bar  68   a . The bar profiles are formed by removing portions of bar material, as shown in  FIG. 13 . 
       FIG. 11  shows a cross section taken along line C—C in  FIG. 10   a  where the moveable bars  68   a ,  68   b  have off-cuts  92   a ,  92   b  and partially fill the space between the metal blocks  69   b ,  69   b  next to fixed dielectric blocks  67   a ,  67   b .  FIG. 12  shows a device cross section taken along line D—D in  FIG. 10   c  where the bars  68   a ,  68   b  have no off-cuts and entirely fill the space between the metal blocks  69   a ,  69   b  next to fixed dielectric blocks  67   a ,  67   b . All off-cuts in the bars  68   a  and  68   b  have well defined locations and dimensions, which depend on the desired phase and power distribution at ports  61  to  64 . Simultaneously, the off-cuts serve as matching transformers for the feedlines. 
     The bars  68   a  and  68   b  can be continuously moved along their length to provide a desired phase shift. The movement of bars  68   a  and  68   b  provides simultaneous adjustment of the phase shift at all ports  61  to  64 . The locations and dimensions of the off-cuts are chosen so that the movement of bars  68   a  and  68   b  within certain limits alters the phase relations between the ports  61  to  64  in a specified manner and provides suitable matching at the input port  60 . 
     Alternatively, the off-cuts  90  to  93  shown in  FIG. 13  could be filled with a dielectric material of different permittivity to the bar material. Alternative topologies for the bars  68   a  and  68   b  are described in the section with the 10-port device description. 
     To provide the desired division of power at each junction of the strip conductor, circuit-matching transformers are integrated into the distribution network formed by the strip conductors in  FIG. 10 . Examples of such fixed circuit-matching elements are sections  65  and  66  near junction  69 , sections  72  and  73  near junction  70 , and sections  74  and  75  near junction  71 . Here the circuit matching is achieved by varying the dimensions of the feedline section. The length and width of these circuit-matching sections  65 ,  66  and  72  to  75  is selected to minimise signal reflection at the junctions  69  to  71 . The off-cuts  90  to  93  in the dielectric bar  68   a  move only along a uniform portion of the feedline network. 
     The off-cuts  90  and  92  change the phase shift between outputs  61  to  64  when the dielectric bar  68   a  moves. The off-cuts  91  and  93  are the moveable transformers decreasing the wave impedance in the output direction from input  60  to outputs  61  to  64 . In order to have equal wave impedances at the input and all four outputs, the transformers of the 5-port device must decrease the wave impedance along the paths from the input to each output  61  to  64  by a factor of ¼. The fixed and moveable transformers of the 5-port device shown in  FIG. 10  facilitate this decrease in the following manner. The sections  65  and  66  decrease the wave impedance to ¾, the sections  72  and  73  to 10/16, the off-cuts  91  to ⅔, and the off-cuts  93  to ⅘ of the values at the beginning of each section. 
     It is possible to increase the phase shift per unit of bar-movement by changing the layout of the feedline network and creating a delay line. This delay line may be formed with short stubs (shown in  FIG. 14 ) or arranged in a meander pattern (shown in  FIG. 15 ). The arrangements shown in  FIGS. 14 and 15  result in a non-linear dependence of phase shift and bar position, still suitable for antennas with variable downtilt. 
     Thus the proposed device provides a beam-forming network for an antenna array with electrically controllable radiation pattern, beam shape and direction. The new arrangement integrates the adjustable multi-channel phase shifter and power distribution circuitry into a single stripline package. 
     The feedline network, as described above for the 5-port and 10-port device is symmetrical and contains two ground-planes  69   a  and  69   b  and two moveable dielectric bars  68   a  and  68   b . It is possible to use a different arrangement containing one ground plane and one dielectric moveable bar, as shown in  FIG. 16 , to realise a multi-channel phase shifter. This non-symmetrical arrangement provides a simpler design, although it yields less phase shift and higher insertion loss than in a symmetrical arrangement. 
     Principles of Operation 
     The operation of the feedline network  2  of the 10-port device will now be described with reference to the transmit mode of the antenna. However it will be appreciated that the antenna may also work in receive mode, or simultaneously in transmit mode and receive mode. 
     Phase Relationships: 
     An input signal on common line  10  ( FIG.3 ) propagates via impedance-matching transformers  11  and  12  to main junction  33 . At main junction  33  the signal is split and it propagates via subsequent feedlines and a series of splitters to nine ports  20  to  28 . Radiating elements (not shown) are connected, in use, to the nine ports  20  to  28 . The amplitude and phase relationships between the signals at the nine ports  20  to  28  determine the beam shape and direction in which the beam is emitted by the antenna. The angle between the beam direction and horizon is conventionally known as the angle of ‘downtilt’. The beam can be directed to the maximum ‘downtilt’ direction by creating the maximum phase shift ΔP between each pair of neighbouring ports. 
     Referring now to  FIG. 6 , feedline  5  leads from main junction  33  to central port  24 . Feedline  5 , branching off from splitter  33 , is formed by folded lengths of stripline with an impedance matching step  32 . Regardless of the position of the bars  47   a  and  47   b , there is no change in permittivity along the path of the strip conductor between junction  33  and port  24  (as can be seen in  FIGS. 3   a, b  and  c ). Therefore, the electrical length of the feedline between main junction  33  and central port  24  remains constant at all positions of the dielectric bars. 
     The dimensions of this device are chosen in a way that with the bars  47   a  and  47   b  set in the extreme left position shown in  FIG. 3   b , the ports  20  to  28  are in phase (that is, ΔP is zero). Moving the bars  47   a  and  47   b  to the right simultaneously changes the electrical length of certain parts of the feed network between the bars  47   a  and  47   b . For feedline  16  between junctions  33  and  37  in  FIG. 6 , moving the bars  47   a  and  47   b  to the right decreases the length of feedline  16  covered by projection  40  and simultaneously increases the open length of feedline  16  between main junction  33  and the left edge of projection  41 . With the permittivity ∈ r  of the projections being higher than the permittivity of the off-cuts, as shown in  FIG. 7 , moving bars  47   a  and  47   b  to the right will therefore decrease the length feedline  16  with higher ∈ r  and increase the length with lower ∈ r . As a result this will decrease the phase difference ΔP between junctions  33  and  37 . 
     For the feedline  17  between junctions  37  and  38 , moving the bars  47   a  and  47   b  to the right decreases the length of this feedline covered by projection  50 , and simultaneously increases the length of this feedline between junction  37  and the left edge of projection  51 . 
     The dimensions of the device are also chosen so that regardless of the positions of bars  47   a  and  47   b  (within their working range) there is a phase shift ΔP/2 between each pair of neighbouring ports. With the bars in the middle position ( FIG. 3   a ) the phase shift relative to port  24  is −2*ΔP degree at left-hand port  20 , and +2*ΔP degree at right-hand port  28 . With the bars in the extreme right position ( FIG. 3   c ) the phase shifts relative to port  24  are −4*ΔP degree at left-hand port  20 , and +4*ΔP degree at right-hand port  28 . 
     The amount of phase shift ΔP is determined by the permittivity of the material used for bars  47   a  and  47   b , and the off-cut shape. The permittivity of the dielectric materials used affects the phase velocity of the signals travelling in the feedline network. Specifically, the higher the permittivity, the lower the phase velocity or longer the electrical length of transmission line. Thus, by varying the length of dielectric bar sections that overlap (as viewed from the perspective of  FIG. 3 ) the strip conductors of the feedlines, it is possible to control the phase shift between the signal at the ports  20  to  28 . A dielectric material “Styrene” or polypropylene is used for fabricating the moveable dielectric bars  47   a ,  47   b.    
     The layout of the feedline network, and the locations and sizes of the off-cuts in bars  47   a  and  47   b  can be altered to obtain different phase relationships between the ports  20  to  28 . 
     The operation of the feedline network  2  of the 5-port device will now be described with reference to the transmit mode of the antenna. However it will be appreciated that the antenna may also work in receive mode, or simultaneously in transmit mode and receive mode. 
     An input signal on feedline  60  ( FIG. 10 ) propagates via impedance-matching transformers  65  and  66  to a junction  69 . From the junction  69  the signal is fed via junction  70  to ports  61  and  62 , and via junction  71  to ports  63  and  64 . Radiating elements (not shown) are connected, in use, to the four ports  61  to  64 . The phase relationship between the signals at the four ports  61  to  64  determines the beam shape and direction in which the beam is emitted by the antenna. 
     The position of the dielectric bars  68   a  and  68   b  controls the phase relationship between the ports  61  to  64 . The following refers to a device with the off cuts of bars  68   a  and  68   b  shaped as shown in  FIGS. 10 and 13 . The location and size of the off-cuts is chosen to obtain phase relationships as described below. 
     With the bars  68   a  and  68   b  set in the middle position, shown in  FIG. 10   b , the ports  61  to  64  have specified phase relationships. Moving for example the bars  68   a  and  68   b  to the left changes simultaneously the electrical length of certain parts of the feedline network between the bars  68   a  and  68   b . For example, when moving bars  68   a  and  68   b  from the middle position ( FIG. 10   b ) to the extreme left ( FIG. 10   a ) the length of the feedline between junction  69  and the left edge of off-cut  90  increases, and the length of the feedline between the left edge of  91  and junction  70  decreases simultaneously. The off-cuts  92  have a smaller width than off-cut  90  to change the variable phase shift between outputs  61  and  62  by only half the amount than between outputs  61  and  63 . With the moving bars  68   a  and  68   b  at the extreme left position ( FIG. 10   a ) the phase shift relative to port  61  is −ΔP at port  62 , −2*ΔP at port  63  and −3*ΔP at port  64 . 
     The amount of phase shift ΔP is determined by the permittivity of the material used for bars  68   a  and  68   b , and the off-cut shape. The permittivity of dielectric materials used affects the phase velocity of the signals travelling in the feedline network. Specifically, the higher the permittivity, the lower the phase velocity or longer electrical length of transmission line. Thus, by varying the length of dielectric bar sections that overlap (as viewed from the perspective of  FIG. 1 ) the strip conductors of the feedlines, it is possible to control the phase shift between the signal at the ports  20  to  28 . A dielectric material “Styrene” is used for fabricating moveable dielectric bars  68   a  and  68   b.    
     The offcuts in the dielectric bars may be removed by a stamping operation, or by directing a narrow high pressure stream of fluid onto the material to be removed. 
     Specific embodiments of an adjustable antenna feed network with integrated phase shifter according to the present invention have been described for the purpose of illustrating the manner in which the invention may be made and used. It should be understood that implementation of other variations and modifications of the invention and its various aspects will be apparent to those skilled in the art, and that the invention is not limited by the specific embodiments described. It is therefore contemplated to cover by the present invention any and all modifications, variations, or equivalents that fall within the true spirit and scope of the basic underlying principles disclosed and claimed herein.