WO2005004281A1

WO2005004281A1 - Improvements in and relating to antennas

Info

Publication number: WO2005004281A1
Application number: PCT/EP2004/006054
Authority: WO
Inventors: Fergal Joseph Lawlor; Niallo Donal Carroll
Original assignee: Finglas Technologies Limited
Priority date: 2003-06-26
Filing date: 2004-06-03
Publication date: 2005-01-13
Also published as: GB0314894D0; EP1639673A1

Abstract

Apparatus for use in the conveying of RF signals comprises one or more transmission elements (120,122) for conveying said signals and a moveable member (110) for interacting with the transmission elements to affect the RF signal, for example by affecting the time taking for the RF signal to travel along said one or more transmission elements. A sensor (36, 38, 56, 20, 22, 60, 62, 64 and 66) is responsive to movement said member and generates an output for use in determining the position of the member. The sensor comprises a transducer for converting an input effected by movement or position of the sensor intra-electrical output, wherein the transducer is remotely situated from the one or more transmission elements so that the transducer does not interfere with the RF signal. The apparatus may comprise a phase shifter for adjusting the orientation of a radiation of a radio antenna, and enables the position of the moveable member (and hence the state of the phase shifter) to be monitored without creating intermodulation products that can interfere with the RF signals being conveyed by the antenna.

Description

Title: Improvements in and Relating to Antennas

Field of the invention

This invention relates to apparatus for use in the conveying of RF signals, and to a drive mechanism for an antenna phase shifter.

Background to the invention

In certain situations, it is desirable to adjust the orientation of the radiation pattern of a radio antenna. For example, the beam pattern for a base station of a cellular mobile telecommunications system might need to be tilted downwards so that the associated cell does not in encroach on neighbouring cells. To that end it is known to use a phase shifter to alter the relative phase of signals in the elements of the antenna array.

One such phase shifter utilises a number of transmission lines, each in the signal path for a respective antenna element, and a dielectric slider member for altering the relative dielectric path lengths along the transmission lines, thereby to alter the relative times taken for signals to travel along the transmission lines, and hence to alter the relative phase of the antenna elements. The slider can be moved by a motor driven drive mechanism in which, for example, the slider is connected to an electric motor via a transmission comprising a screw threaded shaft, rotation of which moves the slider along the transmission lines.

In order to ensure that the slider is properly positioned, it is desirable to provide the mechanism with a control feedback loop which uses one or more sensors to determine the slider position and/or the extensor slider movement. Such sensors may comprise optical or electronic devices for detecting, for example, end positions of the slider or rotation of the drive shaft. However, these devices typically use non-linear electronic elements which can give rise to intermodulation products that can interfere with the RF signals being conveyed by the antenna. Intermodulation products are particularly problematic in modern antennas (for mobile telecommunication systems) because those antennas are designed to accommodate many carrier frequencies which can interact with each other through a non linear element and create responses in undesirable frequencies.

Summary of the invention

According to a first aspect of the invention, there is provided apparatus for use in the conveying of RF signals, the apparatus comprising one or more transmission elements for conveying said signals, a moveable member for interacting with said transmission elements to affect the RF signal, and a sensor responsive to movement of said member and operable to generate an output for use in determining the position of the member, the sensor comprising a transducer for converting an input affected by movement or position of the sensor into an electrical output, wherein the transducer is situated remotely from the element so that the transducer does not interfere with the RF signal.

It has been realised that the amplitude of any intermodulation products generated in the transducer falls off with the square of the distance from the transducer to the transmission element. Thus, if the transducer is positioned far enough away from the transmission element, there would be substantially no interference from intermodulation products. The minimum distance of the transducer from the transmission elements will depend on numerous factors relating to the nature of the RF signals to be conveyed, but one way of determining the minimum distance would be by experiment.

Preferably, the apparatus comprises a phase shifter for an antenna having an array of antenna elements, the moveable member being a dielectric member moveable to alter the relative phase of the RF signals fed to or received by the antenna elements, the transmission elements comprising transmission lines situated adjacent the dielectric member. Preferably, the moveable member comprises a dielectric slider, the sensor being responsive to sliding movement of the slider. Where the slider is linked to a screw threaded shaft drive mechanism, the sensor is preferably responsive to rotational movement of the shaft.

Preferably, the sensor is one of two such sensors, each being responsive respectively to said sliding movement and rotational movement of the shaft.

Preferably, the transducer is operable to convert electromagnetic energy incident thereon into said output, the sensor being so arranged that said movement of the member varies the incident electromagnetic energy, or that the incident electromagnetic energy is related to the sensor position.

Thus, the interaction of the moveable member (or something mechanically linked to it) with light can be used to derive an electrical signal representative of the movement or position of the member. The light can be in the form of a beam which can therefore extend over a relatively long distance, to enable said remote placing.

Preferably, the sensor further comprises light guide means for conducting light from the vicinity of said position of the member to the transducer to enable the latter to be remotely situated from the position. Preferably, the light guide means comprises a fibre optic cable.

Preferably, the sensor further comprises a light source for generating a beam of light to be directed towards the transducer, the arrangement being such that, in use, the beam traverses a gap in which it can be interrupted by the slidable member or a component linked thereto, as the member moves, the sensor further comprising a further fibre optic cable for conveying the beam of light from said source to said gap.

The further fibre optic cable enables the source to be a non linear device such an LED, since the source can also be situated sufficiently far from the transmission elements to avoid interference in the RF signal as the result of the generation of intermodulation products in the source.

Preferably, therefore, the light source comprises a LED.

Preferably, both the LED and the transducer are situated in a shielded housing. The shielding blocks RF signals, and therefore further reduces the problems of intermodulation products and can enable both the transducer and the LED to be situated closer to the transmission elements than would otherwise be possible.

The invention also lies in a drive mechanism for an antenna phase shifter having a moveable member for causing said phase shifting, the mechanism comprising linkage means for connecting the mechanism to the member so as to enable the mechanism to move the latter, and a sensor responsive to movements of least part of the linkage means and operable to generate an electrical output from which the position of the member can be determined, the sensor having a transducer for generating said electrical output, wherein said transducer is situated remotely from said part of the linkage means so that, in use, the transducer does not substantially interfere with the RF signal conveyed by the antenna.

Preferably, the mechanism creates drive means, such as a motor, connected to the linkage via a transmission such as a screw threaded shaft.

The linkage conveniently comprises a slidable drive plate attached, in use, to a dielectric slider which constitutes said member of the phase shifter, the plate having or carrying formations which engage the thread of the shaft so that the plate is driven by rotation of the shaft.

Brief description of the drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings in which; Figure 1 is an isometric view of a pair of antenna phase shifters fitted with a drive mechamsm, in accordance with the invention.

Figure 2 is an isometric view of the phase shifters, taken from a different angle from figure 1;

Figure 3 is a more detailed view of part of the drive mechanism;

Figure 4 shows the same part with a cover removed;

Figure 5 is a block diagram of the control electronics for the system.

Figures 6, 7 and 8 are respective plan, side and end elevational views of the transmission line and dielectric sliders forming part of the phase shifters;

Figure 9 is a partially exploded view of the phase shifters with the drive mechanism removed;

Figure 10 is an isometric view of transmission lines of one of the phase shifters; and

Figure 11 is a sectional side view of part of one of the phase shifters.

Detailed Description

With reference to figure 1 , a drive mechanism 3 for a pair of antenna phase shifters 5 has a copper support plate 1 on which a drive plate 2 is slidably mounted. The drive plate 2 carries on its underside formations for attaching it to dielectric sliders 7 of two micro strip antenna phase shifters of the kind in which there is provided an array of micro strip transmission lines over which the slider can slide so as to alter the relative time taken for a signal to travel along the transmission lines. A description of the structure and function of the phase shifters follows a description of the drive mechanism and its operation. The mechanism comprises a rectangular support plate 1 on which a drive plate 2 is slidebly mounted. The drive plate 2 is attached to the dielectric sliders 7 of the phase shifters 5 so that sliding movement of the plate 2 causes a corresponding movement of the dielectric sliders 7. The drive plate 2 is mounted on support plate 1 via a pair of end brackets 4 and 6 attached to the plate 1 at opposite ends of the range of allowable movement of the drive plate 2. A pair of spaced apart, parallel, cylindrical rails 8 and 10 are mounted at their end regions on the brackets 4 and 6 in a position spaced slightly above the plate 1. The plate 2 has a pair guides 12 and 14, each of which engages the respective one of the rails 8 and 10 to define the path of allowable movement of the plate 2, whilst the brackets 4 and 6 also define the end points of that path. The bracket 6 has a central support block 16 which incorporates a gap, and includes through bores through which fibre optic cables 20 and 22 extend in a direction parallel to the rails 8 and 10.

Situated under the blocks 16 is a socket 24 for receiving the end of a screw threaded shaft 26 which is free to rotate relative to the bracket 6. The shaft 26 extends in a direction parallel to the rails 8 and 10 to the other bracket 4, and passes through a channel 28 in the plate 2. The channel 28 is screw threaded and engages the screw thread on the shaft 26 so that rotation of the shaft 26 causes the plate 2 to move in either direction along the rails 8 and 10.

Immediately above the shaft 26 is a paddle 30 which, when the plate is at the end of its path of travel defined by the bracket 6, extends into the gap in block 16. The bracket 4 also carries a block 32 which is similar in form and function to the block 16. Thus the block 32 defines a gap, and includes passages for a pair of fibre optic cables 36 and 38. The bracket 4 also has a central passage 40 through which the shaft 26 extends. The end of the shaft protruding beyond the bracket 4 is coupled to a drive shaft 42 which, in turn, is connected to the output of a servo motor 44, the drive shaft 42 of which extends through a sensor block 46. Referring to figure 3, the block 46 has a U-shaped channel through which the shaft 42 extends, and includes a pair of through bores 52 and 53, one on each respective side of the U-shaped channel.

Referring to Figure 4 (in which the block 46 has been removed), the block 46 covers a paddle wheel 56 carried on shaft 42. There is a cavity in block 46 which accommodates the paddle wheel 56 and provides an air gap in the paths of the through bores 52 and 53.

The paddles of the paddle wheel 56 define two radial gaps, for example, the gap 58, and are so arranged that, as the paddle wheel rotates with the shaft 42, the paddles interrupt the pathways of the bores 52 and 58 in the block 46 periodically. Furthermore, the pathways are not diametrically opposed relative to the shaft 42 so that the order in which the pathways are interrupted by the paddle wheel 56 will depend upon the sense of rotation of the paddle wheel 56. As can be seen from Figure 4 the plate 1 includes a slot 57 into which the paddles can extend to prevent rotation of the wheel from being interrupted by the plate 1.

A respective one of four fibre optic cables 60, 62, 64 and 66 extends into each bore in the bracket block 46, but stops short of the air gap so as not to interrupt the movement of the paddle wheel 56.

The fibre optic cables 20, 22, 36, 38, 60, 62, 64 and 66 all terminate in a shielded housing 68. It will be appreciated that the fibre optic cables are all arranged in pairs, with the end of the pairs remote from the housing 68 being arranged in spaced apart opposed relationship so as to define a space into which a paddle of the paddle wheel 56 can pass. One member of each pair of cables is coupled to an LED in the housing 68, whilst the other member of the same pair is coupled to a phototransistor.

As can be seen from figure 5, the housing 68 also contains a microprocessor and control electronics 70 which governs supply of power to the LEDs and monitors the signals received from the phototransistor s. In use, each LED emits light which is conveyed back to the opposite end of its respective fibre optic cable. Since that end is at one edge of a gap, the light from the end of the fibre optic cable is projected across the gap towards the end of other fibre optic cable in the same pair. That fibre optic cable conveys any light received by it to its photo transistor which generates an electrical output signal representative of light incident thereon. Thus, for example, when the drive plate 2 reaches the extremity of travel defined by the bracket 6, the paddle 30 extends into the gap in the support block 16, thus interrupting the beam of light transmitted across that gap by the LED connected to the fibre optic cable 22. This correspondingly reduces the amount of light conveyed by the fibre optic cable 20 to its photo transistor, thus providing an electrical output signal which is representative of the drive plate having reached one end of its extremity of travel.

When the plate 2 is at the other extremity of its range of travel, the paddle 30 extends into the gap between the block 32 and 34, so that the beam conveyed by the fibre optic cable 38 towards the cable 36 is interrupted, and the output signal from the photo transistor connected to the cable 36 is correspondingly altered.

As the motor 44 operates, the shaft 42 rotates and the paddle wheel 56 periodically interrupts the beams projected by cables 60 and 66 to cables 62 and 64 respectively, thus, causing fluctuations in the signal detected by the photo transistors connected to cables 62 and 64. The outputs of those transducers are, when the shaft 42 is rotating, in the form of wave forms, the relative phase of which indicates the direction of rotation, whilst the number of cycles of which will indicate the angular travel of shaft 42. The angular position of the shaft 42 will be related to the position of the plate by virtue of the screw threaded engagement between the shaft 26 and the plate 2, so that the output from these sensors can be used to enable the position of the plate 2 between the two end positions to be deduced.

The micro processor and control electronics also control the operation of the motor, so that the fibre optic cables, the LEDs and photo transistors provide a feedback for the control of the motor to enable the plate 2 to be accurately positioned and/or moved. Since the LEDs and photo transistors are separated from the mechanical elements (i.e. the paddles) the movement of which is being detected, they are less prone to interference from the transmission lines of the phase shifter which underlies the support board 1. The intermodulation levels in the LEDs and photo transistors fall off with a square distance from the transmission lines. The housing 68 may include or incorporate shielding so as to eliminate intermodulation products. However, it has also been found that the need for shielding can, in some circumstances, be dispensed with altogether provided that the LEDs and photo transistors are positioned sufficiently far from the transmission lines.

The phase shifters 5 (one for each antenna polorisation), are situated between the copper support plate 1 and a bottom copper plate 80. Two cable clamps, 82 and 84 are bolted to the plates 1 and 80 at the end regions of the plates, and are sandwiched between the two plates. Each of the phase shifters has an input feed (86 and 88 respectively) and eleven output feeds such as the feed 90. Each of the outputs feeds one or more elements in a dipole antenna array (not shown), via a respective coaxial cable. Most of these cables have been omitted from the figures for the sake of clarity but some are shown (from end of the apparatus at 92-103) in figure 9.

In use the apparatus is mounted with the plates 1 and 80 vertical, and the inputs feeds 86 and 88 situated at the bottom of the device.

Each of the phase shifters includes a respective arrangement of transmission lines 106 and 108 which connect the input feeds 86 and 88 to the output feeds, and which are described in further detail below.

Each phase shifter also includes a respective one of a pair of dielectric sliders 7, individually referenced 110 and 112, connected to the common drive mechanism. With reference to Figures 6-10 the two arrangements of transmission lines 106 and 108 are substantially identical, and only the arrangement of transmission lines 106 will, therefore, be described in detail.

The transmission lines 106 comprise a PTFE board 114 on the upper surface of which an arrangement of copper tracks 118 has been etched. The tracks define two generally serpentine paths 120 and 122 across the width of the board 114. The serpentine paths 120 and 122 are connected at one end to the input feed 86 and run from that end to the output feeds 124 and 500 respectively. The path 126 is connected to the input terminal 86 at a Wilkinson divider which also connects the terminal 86 to a^' through track 126. The track 126 leads to a Wilkinson divider 128 which connects the track to the path 122 and to a branch track extending to a reference output 130. The tracks include a number of intermediate branches, each connecting a respective one of the other output feeds (referenced 131-138 and 500) to the serpentine paths through a respective Wilkinson Power Divider (139-147). The through track 126 provides a route for a signal between feed 130 and terminal 86 which does not pass through any runs of the paths 120 and 122. The opposite face of the PTFE board 114 is coated with a continuous layers of copper 150 (Figure 12) to provide the ground plane for transmission lines. The PFTE board has a thickness of .76mm, low loss characteristics and a dielectric constant of 2.5 The sides of the board 114 include lateral steps 152 and 154 which act as guide tracks (with end stops) for two end strips 156 and 158 projecting downwardly from the ends of the dielectric slider 112 (Figure 11). The slider has a dielectric constant of 4.5 and a loss tangent of .002, and its position along the tracks 152 and 154 affects the length of the path taken by a signal from the feed terminal 86 to the output feeds other than output 130 which passes under the slider 110 and during which the speed of transmission of the signal is therefore modified by the slider 110.

It will be appreciated that the length of the transmission path for signal from the terminal 86 to the output 130 extending under the slider 110 will be the same for all positions of the slider 110 along the tracks 152 and 154. However, the total length of each of the serpentine paths 120 and 122 under the slider 110 will be related to the linear position of the slider. Furthermore, the length of the portions of the transmission path from the feed terminal 86 to any of the outputs 131, 132, 133, 134, 124 and 135, 136, 137, 138, 500 passing under the slide 110 (and hence the total electric lengths of the paths) will differ from path to path by virtue of the fact that the branches for the outputs are connected to the paths 120 and 122 at differing distances therealong.

The following table illustrates the effect on the relative phase of signals between the feed terminal and each of outputs bays 124, 130, 131, 132, 133, 134 (top half) and 135| 136, 137, 137 and 500 (bottom half).

3 Output Slider moved (top) Centre Slider moved (bottom)

124 0°-5 0° 0°+5 134 0°-4 0° 0°+4 133 0°-3 0° 0°+3 132 0°-2 0° 0°+2 132 0°- 0° 0° + 124 (Fixed Ref) 0° 0° 0° 135 0°+ 0° 0°- 136 0°+2 0° 0°-2 137 0°+3 0° 0°-3 138 0°+4 0° 0°14 500 0°+5 0° 0°-5 Column 1 shows the eleven outputs of the phase shifter. The phases at ten of these outputs are variable and that at output 130 is fixed. The other columns each show the phase differences of signals at the outputs after a respective position of the slider 110. Column 3 shows the phase differences when the slider 110 is equally covering the serpentine paths 120 and 122. Column 2 in the table indicates the relative changes caused by the movement of the slider 110 towards the top end of the board 114. This movement increases the portion of the paths from the input feed 46 to the top outputs (131, 132, 133, 134, 124) under the sliding dielectric 110. This correspondingly increase the time taken for a signal to travel from input feed 86 to those outputs, and this introduces a phase delay (represented by - ). The movement of the slider 110 towards the top of board 110 also causes the reduction in the portion of the serpentine path 120 under the slider 110. Therefore, there is an equal but opposite phase change at output 135 when compared to the output 131. The phase shift to each of the remaining outputs is shown in the above table. For any position of the dielectric slider 110 the phase shift between outputs 132 and 136 is double that of outputs 131 and 135 and so on. The fourth column shows the relative phase changes when the sliding dielectric 110 is moved towards the bottom of board 114. It can be seen that this has the opposite effect on the relative phases.

The phase shifter, like an antenna is of a reciprocal nature. Thus the shifter can convey signals to be transmitted by the antenna from the input 86 to the output bays or can output signals received by the antenna through the terminal 86. In either case, the phase shifter allows the radiation pattern of antenna to adjusted.

With reference to figure 12, the transmission lines 108 of the second phase shifter are mounted in such a way that the conductive tracks (118) face downwards so that the ground planes 150 and 150 of the two sets of transmission lines face each other. The boards of the transmission lines 106 and 108 are separated by an insulator board 109. The dielectric slider 112 is bolted to the end pieces 156 and 158 attached to the slider 110.

Claims

1. Apparatus for use in the conveying of RF signals, the apparatus comprising one or more transmission elements for conveying said signals, a moveable member for interacting with said transmission elements to affect the RF signal, and a sensor responsive to movement of said member and operable to generate an output for use in determining the position of the member, the sensor comprising a transducer for converting an input affected by movement or position of the sensor into an electrical output, wherein the transducer is situated remotely from the one or more transmission elements so that the transducer does not interfere with the RF signal.

2. Apparatus according to claim 1, in which the apparatus comprises a phase shifter for an antenna having an array of antenna elements, the moveable member being a dielectric member moveable to alter the relative phase of the RF signals fed to or received by the antenna elements, the transmission elements comprising transmission lines situated adjacent the dielectric member.

3. Apparatus according to claim 1 or claim 2, in which the moveable member comprises a dielectric slider, the sensor being responsive to sliding movement thereof.

4. Apparatus according to claim 3, in which the slider is linked to a screw threaded shaft drive mechanism and in which the sensor is responsive to rotational movement of the shaft.

5. Apparatus according to claim 4 in which the sensor is one of two sensors, the other of the sensors being responsive directly to said sliding movement.

6. Apparatus according to any of the preceding claims, in which the transducer is operable to convert ' electronmagnetic energy incident thereon into said electrical output, the sensor being so arranged that said movement of the member varies the incident electromagnetic energy, or that the incident electromagnetic energy is related to the sensor position.

7. Apparatus according to claim 6, in which the sensor further comprises light guide means for conducting light from the vicinity of said position of the member to the transducer to enable the latter to be remotely situated from the position.

8. Apparatus according to claim 7, in which the light guide means comprises a fibre optic cable.

9. Apparatus according to claim 8, in which the sensor further comprises a light source for generating a beam of light to be directed towards the transducer, the arrangement being such that, in use, the beam traverses a gap in which it can be interrupted by the slideable member, or a component linked thereto, as the member moves, the sensor further comprising a further fibre optic cable for conveying the beam of light from said source to said gap.

10. Apparatus according to claim 9, in which the light source comprises a LED.

11. Apparatus according to claim 10, in which both the LED and the transducer are situated in a shielded housing

12. A drive mechanism for an antenna phase shifter having a moveable member for causing said phase shifting, the mechanism comprising linkage means for connecting the mechanism to the member so as to enable the mechanism to move the latter, and a sensor responsive to movements of least part of the linkage means and operable to generate an electrical output from which the position of the member can be determined, the sensor having a transducer for generating said electrical output, wherein said transducer is situated remotely from said part of the linkage means so that, in use, the transducer does not substantially interfere with the RF signal conveyed by the antenna.

13. A mechanism according to claim 12, in which the mechanism including drive means, such as a motor, connected to the linkage via a transmission includes comprising a screw threaded shaft drive.

14. A mechamsm according to claim 13, in which the linkage comprises a slidable drive plate attached, in use, to a dielectric slider which constitutes said member of the phase shifter, the plate having or carrying formations which engage the thread of the shaft so that the plate is driven by rotation of the shaft.

15. A base station of a radio telecommunication system, the base station having an antenna connected to a phase shifter in accordance with claim 2.