GB2426635A

GB2426635A - Phase shifting arrangement

Info

Publication number: GB2426635A
Application number: GB0510976A
Authority: GB
Inventors: Christopher Davies
Original assignee: Alan Dick and Co Ltd
Current assignee: Alan Dick and Co Ltd
Priority date: 2005-05-27
Filing date: 2005-05-27
Publication date: 2006-11-29
Also published as: GB0510976D0

Abstract

There is provided a phase shifting arrangement comprising at least one block 40, 41, each block comprising a first body 42 and a second body 43, wherein the first body comprises a first respective circuit 55, 56 on each of two opposing sides; the second body comprises a second respective circuit 53, 54 on each of two inner sides; the second body fits around the first body, such that each first circuit is in contact with a respective second circuit, forming respective closed circuits; wherein each respective closed circuit introduces a phase shift into a signal passing through the closed circuit, the magnitude of the phase shift depending on the length of the closed circuit; and wherein the first or second body is operable to move in relation to the other body such that each closed circuit is lengthened by movement in a first direction, and each closed circuit is shortened by movement in a second direction. The contact between the circuits may be capacitive, rather than conductive.

Description

PHASE SHIFTING ARRANGEMENT

Technical Field of the Invention The invention relates to a phase shifting arrangement for an array of antenna elements and in particular, but not exclusively, to a ground-tilting array including such an arrangement. The phase shifting arrangement may be used to control the antenna radiation pattern in the vertical (elevation) and/or horizontal (azimuth) planes. Control can be remote (electrical) or local (mechanical). Background to the Invention In various applications, it is desirable to induce and adjust the phase difference between signals emitted from a plurality of antenna elements in an antenna array. One particular example of this is when the array forms a ground-tilting antenna. It is well known by designers of wireless cellular networks, such as mobile phone networks, that there is a continuous compromise to be made between coverage, capacity and quality. Maximum coverage is achieved by a radiation pattern in which the boresight is parallel to the ground, but in periods of peak capacity it is found that co-channel interference can degrade the network performance substantially. In general, antennas are tilted downwards by a nominal amount, say 5[deg]. It has, however, been appreciated that even a fixed tilt is not ideal, because it does not allow for changes in usage within the cell, either on a short-tem basis or a long-term basis. Many antennas are therefore placed in the system that can mechanically alter the tilt of the antenna array, but these require an engineer to visit the site and they often require the antenna to be switched off during adjustment. Proposals have, accordingly, been made to alter the tilt of the radiating beam by inducing phase changes along the length of the array corresponding to tilts of various angles. For example, in WO 2004/004059, a phase shift system is described in which the phase is altered by sliding a flexi-circuit attached to a block and printed with C-shaped conductive strips, across a printed circuit board with antenna feed lines. The movement of the block causes changes in the effective lengths of the feed lines and hence the relative phases of antennas fed by these feed lines. This construction, however, is quite large and therefore tends to be mechanically unstable, as even a slight misalignment in the two bodies can result in a loss of connection between the conductive strips and the antenna feed lines. It is therefore an object of the invention to provide a phase shifting arrangement that overcomes these drawbacks.

Summary of the Invention According to one aspect of the present invention there is provided a phase shifting arrangement comprising at least one block, each block comprising a first body and a second body, wherein the first body comprises a first respective circuit on each of two opposing sides; the second body comprises a second respective circuit on each of two inner sides; the second body fits around the first body, such that each first circuit is in contact with a respective second circuit, forming respective closed circuits; wherein each respective closed circuit introduces a phase shift into a signal passing through the closed circuit, the magnitude of the phase shift depending on the length of the closed circuit;and wherein the first or second body is operable to move in relation to the other body such that each closed circuit is lengthened by movement in a first direction, and each closed circuit is shortened by movement in a second direction. Brief Description of the Drawings The invention will now be described, by way of example only, by reference to the following drawings, in which: Figure 1 is an illustration of an antenna mast with an array according to the present invention; Figure 2 is a schematic view of an antenna array; Figure 3 is a circuit diagram of a phase shifting arrangement in an antenna array according to an embodiment of the invention; Figure 4 is an illustration of a phase shifting arrangement with two blocks, according to an embodiment of the present invention; Figure 5 is an exploded view of one of the blocks in Figure 4; Figure 6 is a diagram showing the circuitry of one of the blocks in Figure 4; Figure 7 is a further diagram showing the circuitry of one of the blocks in Figure 4; Figure 8 is a diagram showing the circuitry of the two blocks in Figure 4;Figure 9 is a diagram showing the phase shifting arrangement of Figure 4 in a first position; and Figure 10 is a diagram showing the phase shifting arrangement of Figure 4 in a second position.

Detailed Description of the Preferred Embodiments In the following description it should be noted that antennas are reciprocal devices, in that they can transmit or receive. Even though the antenna will be described below with reference to the transmit case, it should be understood that it can also be described from a receive point of view. The receive and transmit radiation patterns are identical. Thus the term "input" for the transmit case would be "output" for the receive case. Also, although the following description is for a linear array in which the antenna elements are arranged in a vertical configuration so that the elevation of the beam is controlled, the phase shifting arrangement can also or alternatively be used to control the azimuth of the beam when the antenna elements are arranged in a horizontal array. In a planar array, the phase shifting arrangement can be used to control both the elevation and azimuth of the radiation pattern. Figure 1 shows an antenna mast 1 with an antenna array 2 mounted thereon. The antenna array 2 is adapted to radiate a signal in the form of a directional beam as shown. The direction of the peak of the main beam of the antenna pattern, otherwise known as the tilt of the beam, can be adjusted by an angle, in response to the requirements in the network at a particular time. In this illustrated embodiment of the invention, the antenna beam, shown by means of solid lines, is nominally preset (for example electrically by means of phased cable lengths) at a 5[deg] downtilt, and the downtilt can be adjusted between 0[deg] and +10[deg]. Figure 2 shows an antenna array 2 in accordance with the invention. The antenna array 2 has an input 3 for receiving a signal to be transmitted, a plurality of antenna elements 4 and a phase shifting arrangement 5 connected between the input 3 and the antenna elements 4. In Figure 2, four antenna elements 4 of the antenna array 2 are shown. However, it will be appreciated by a person skilled in the art that the invention is applicable to antenna arrays having more or less than four antenna elements. As is conventional, the phase shifting arrangement 5 is adapted to vary the phase of a signal received at the input 3 of the antenna array 2 for supply to the antenna elements 4 in order to adjust the tilt of the antenna array 2. Figure 3 shows in more detail the antenna array 2 according to the invention. This antenna array 2 hasten antenna elements 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20. The elements 11 to 20 are arranged in pairs, with the elements in each pair (e.g. 11 and 12; 13 and 14; 15 and 16; 17 and 18; 19 and 20) radiating a signal having a fixed phase difference depending on interconnecting feed lines. The antenna elements 11 to 20 are connected to the input 3 by the phase shifting arrangement 5. In accordance with this embodiment of the invention, the phase shifting arrangement 5 comprises four phase shifting devices 23a, 23b, 23c and 23d. The phase shifting devices 23a-23d are located in feed lines 22 so that a respective phase shift, with respect to the pair 15 and 16, can be induced in each other pair of antenna elements. Thus, in the arrangement indicated in Figure 3, if antenna elements 15 and 16 are taken to have zero phase change, antenna elements 13 and 14 are shifted in the positive sense by one phase change unit (+ ), whilst elements 11 and 12 are shifted positively by two phase change units (+2 ). Conversely, elements 17 and 18 are negatively shifted by one phase change unit (- ) and elements 19 and 20 are negatively shifted by two phase change units (-26). In the following, the invention will be described with reference to a dual polar array, although it will be appreciated that the invention is applicable to other types of array. Figure 4 shows phase shifting arrangement 5 according to an embodiment of the present invention in more detail. In this illustrated embodiment, the phase shifting arrangement 5 comprises a pair of blocks 40, 41. Each block 40, 41 comprises a first body 42 and a second body 43. The first body 42 has a first circuit on each of two opposing sides indicated by arrows 44 and 45, and the second body 43 has a second circuit on each of two inner sides indicated by arrows 46 and 47. The second body 43 fits around the first body 42 such that each first circuit is in contact with a respective second circuit and closed circuits are formed. Preferably, the first and second respective circuits are in close capacitive contact. This can be achieved by placing a dielectric coating over at least one of the first and second respective circuits, thereby preventing direct electrical contact between the circuits. This allows for excellent passive intermodulation performance, and is suitable for use with signals having a high frequency. The second body 43 is adapted to move relative to the first body 42 such that each closed circuit is lengthened by movement in a first direction and shortened by movement in a second direction. In this embodiment, the first body 42 is provided with a bracket 48 for allowing the block 40, 41 to be attached to the antenna housing or mast 1. In an alternative embodiment of the invention, the first body 42 can be adapted to move relative to the second body 43. In this case, the second body 43 can be provided with the bracket 48 or other attachment means for allowing the block 40, 41 to be attached to the antenna housing or mast 1. As mentioned above, the phase shifting arrangement 5 according to this embodiment of the invention comprises two blocks 40, 41. The second body 43 of block 40 is connected to the second body 43 of block 41 by a rigid connector 49 so that the second bodies 43 move relative to their respective first bodies 42 by the same amount. In this embodiment, the blocks 40, 41 are oriented relative to each other such that movement of the second bodies 43 in one direction lengthens the closed circuit in block 40 while correspondingly shortening the closed circuit in block 41. When the second bodies 43 are moved in the opposite direction, the closed circuits in block 40 are shortened and the closed circuits in block 41 are lengthened. Figures 5, 6 and 7 show the structure of a block in more detail. Figure 5 shows an exploded view of a block according to a preferred embodiment of the invention. The second body 43 comprises first and second slider frames 51 and 52, and first and second circuit components 53 and 54. The first circuit component 53 is connected to inner side 46 of the first slider frame, and the second circuit component 54 is connected to inner side 47 of the second slider frame 52. The first slider frame 51 and second slider frame 52 are connected to each other such that they form a casing with a space for receiving the first body 42. In this illustrated embodiment, the first circuit component 53 comprises two conductive strips 61, 62 and the second circuit component 54 comprises two conductive strips 63, 64. The conductive strips could, for example, be in the shape of an elongated "C". However, it will be appreciated that any shape could be used, provided that a closed circuit is formed with the respective printed circuit component on the first body 42, and that the closed circuit is shortened or lengthened when the second body 43 moves relative to the first body 42. The circuit components 53, 54 are attached to the slider frames 51, 52 such that the open ends of all four conductive strips face in the same direction. The first body 42 is situated in the space formed by the slider frames 51 and 52. The first body comprises a printed circuit 55 on its upper side 44 and a printed circuit 56 on its opposing side 45. Between the two printed circuits 55, 56 there is a support 57, which may be a sheet such as a copper sheet. Printed circuit 55 comprises two sets of antenna feed lines 65, 66, and printed circuit 56 also comprises two sets of antenna feed lines 67, 68. One set of antenna feed lines on each printed circuit 55, 56 handles the signal with one polarisation in a dual polar array. The other set of antenna feed lines handles the signal with the opposite polarisation. Each of the antenna feed lines 65-68 forms open circuits. The layout of these circuits can be, for example, the two long sides of a rectangle, with the input and output connections at one end, and the other end left open. Again, it will be appreciated that any circuit configuration can be used that allows a closed circuit to be formed with the respective conductive strip on the second body 43 and that allows the closed circuit to be shortened or lengthened when the second body 43 moves relative to the first body 42.All of the antenna feed lines face in the same direction. The first body 42 is situated between the first and second slider frames 51, 52. The first body 42 can be provided with bracket 48 as described above. The casing formed by the first slider frame 51 and the second slider frame 52 is located around the first body 42. When the bracket 48 holds the first body 42 of the block 40 stationary, the slider frames 51, 52, with the attached circuit components 53, 54, are able to move lengthways relative to the first body 42. As mentioned above, it should be appreciated that the apparatus could be arranged so that the second body is held fixed and the first body 42 is able to move relative to the second body. Figure 6 shows printed circuits 55 and 56, which are situated on opposing sides 44 and 45 of support 57 respectively, as described above. They are drawn next to each other in Figure 6 in order to make the circuit diagram clearer. Printed circuit 55 comprises open antenna feed lines 65 and 66, and printed circuit 56 comprises open antenna feed lines 67 and 68. As mentioned above, feed lines 66 and 68 handle a signal with a different polarisation to the signal in feed lines 65 and 67. The connections of lines 66 and 68 will not be described further below. A signal is provided at input 3 and is split and fed to antenna element 15 and to antenna feed line 67, which is an open circuit. Also shown in figure 6, is first circuit component 53 with conductive strips 61 and 62, and second circuit component 54 with conductive strips 63 and 64. Again, these are situated on the opposing inner sides 46, 47 of the second body 43 respectively, but are shown next to each other in the figure, in order to make the figure and the description clearer. When the first and second bodies 42 and 43 are connected as described above, the first circuit component 53 is in contact with printed circuit 55. Therefore, antenna feed lines 65 and 66 contact the conductive strips 61, 62 respectively, closing the circuit of the antenna feed lines. Likewise, second circuit component 54 is in contact with printed circuit 56. Therefore, antenna feed lines 67 and 68 contact the conductive strips 63 and 64, respectively, closing the circuit of the antenna feed lines. The resulting circuit is shown in figure 7. The path of the signal from the input 3 can be seen from this diagram. The signal is input to a primary splitter 80. The signal is fed to radiating element 15 and to antenna feed line 67 on printed circuit 56. The signal passes through a circuit comprising antenna feed line 67 and conductive strip 63. The signal then passes through splitter 82, where the signal is directed to two antenna elements 13 and 14, and to antenna feed line 65 on printed circuit 55. The signal passes through a circuit comprising antenna feed line 65 and conductive strip 61, and passes to antenna elements 11 and 12. Hence, in the first block 40, there are five associated antenna elements. Element 15 can be considered to receive the signal with zero phase difference. When the signal reaches elements 13 and 14, the signal has travelled a longer electrical path than the path to element 15. The phase change of the signal at elements 13 and 14 therefore corresponds to a phase change of +8. When the signal reaches elements 11 and 12, it has travelled an additional distance again, which can be taken to correspond to a phase change of +28. The path of a signal for the opposite polarisation is not described in detail, as it corresponds to the path of the signal from input 3. Furthermore, the antenna elements for the signal of the opposite polarisation are not shown. One block 40 therefore provides a signal with three phases as an output. In an antenna array as shown in Figure 3, there are five pairs of antenna elements radiating a signal at different phases. In order to obtain the required additional phase shifts, second block 41 is used. The second bodies 43 of each block 40, 41 are joined together by a rigid connector 49, as shown in figure 4, and both of the second bodies 43 are able to move in relation to their respective first body 42. As above, it should be appreciated that the apparatus could be arranged so that each of the first bodies 42 are able to move in relation to the respective second body 43, while the second bodies 43 are held in a fixed position. Figure 8 represents the circuit diagram of two blocks 40, 41 joined together as described above, and shows the signal path for both signals in a dual polar array. The top half of figure 8 corresponds to figure 7. The bottom half of figure 8 represents the circuitry in the second block 41 of the phase shifting arrangement 5. The two blocks 40 and 41 are each constructed as described in relation to figures 5-7; hence the two printed circuits of the second block 41, labelled "top" and "bottom", and shown side by side, are actually one on top of the other. The first and second blocks are connected together, with rigid connector 49. The second block 41 is orientated such that the complete circuit layout is a mirror image of that of the first block 40. In each block 40, 41, the conductive strips are mounted to the second body 43 which is able to move with respect to the first body 42 which comprises the antenna feed lines, as described in relation to figures 4 and 5. The second bodies 43 of the two blocks 40, 41 are rigidly connected together, and are able to move along the direction of the antenna feed lines with the connection between the conductive strips and the antenna feed lines remaining intact. This causes the electrical paths of each of the closed circuits to increase or decrease, depending on the direction of movement. For example, if the second bodies 43 were to move in a direction indicated by arrow 70, the electrical paths of the first block 40 would become longer, and the electrical paths of the second block 41 would become shorter. This is represented in figure 9. On the other hand, if the second bodies 43 were to move in a direction indicated by arrow 71 the electrical paths of the first block 40 would become shorter, and the electrical paths of the second block 41 would become longer. This is represented in figure 10. The signal path and antenna elements for the opposite polarisation are not shown in figures 9 and 10. The phase shifts introduced-into the signal at each of the antenna elements in Figure 9 can therefore be described as follows: Elements 15 and 16: zero phase change, Elements 13 and 14: shifted in the positive sense by one phase change unit, +5, Elements 17 and 18: shifted in the negative sense by one phase change unit, -8, Elements 11 and 12: shifted in the positive sense by two phase change units, +28, Elements 19 and 20: shifted in the negative sense by two phase change units, -28. The phase shifts introduced into the signal at each of the antenna elements in Figure 10 will be the opposite of those introduced in Figure 9. Although a phase shifting arrangement has been described in relation to an antenna array having ten antenna elements, it will be appreciated that using an appropriate number of blocks connected together as shown in Figure 4 can control any number of elements. Alternatively, the use of multiple blocks can be avoided if the printed circuits and circuit components are adapted to include the elements found in multiple blocks. This means that there will be one first body moving relative to one second body.

Claims

1. A phase shifting arrangement comprising at least one block, each block comprising a first body and a second body, wherein the first body comprises a first respective circuit on each of two opposing sides; the second body comprises a second respective circuit on each of two inner sides; the second body fits around the first body, such that each first circuit is in contact with a respective second circuit, forming respective closed circuits; wherein each respective closed circuit introduces a phase shift into a signal passing through the closed circuit, the magnitude of the phase shift depending on the length of the closed circuit; and wherein the first or second body is operable to move in relation to the other body such that each closed circuit is lengthened by movement in a first direction, and each closed circuit is shortened by movement in a second direction.

2. A phase shifting arrangement as claimed in claim 1, wherein the first or second respective circuits comprise at least one open antenna feed line.

3. A phase shifting arrangement as claimed in claim 2, wherein the other of the first or second respective circuits comprises at least one open conductive strip.

4. A phase shifting arrangement as claimed in claim 3, wherein the at least one open conductive strip is in the shape of an elongated C.

5. A phase shifting arrangement as claimed in any of the preceding claims, wherein one of the first or second body is fixed to an antenna housing.

6. A phase shifting arrangement as claimed in any preceding claims, wherein the respective closed circuits are connected in series.

7. A phase shifting arrangement as claimed in claim 6, wherein an input for a signal to a first one of the closed circuits is provided, and wherein the block is arranged such that a first phase difference is introduced to an input signal passing through the first closed circuit to produce a first phase-shifted signal and wherein an additional phase difference is introduced into the first phase shifted signal as it passes through the second closed circuit to produce a second phase shifted signal.

8. A phase shifting arrangement as claimed in claim 7, further comprising respective outputs for the input signal, first phase-shifted signal and second phase-shifted signal.

9. A phase shifting arrangement as claimed in any preceding claim, wherein the phase shifting arrangement comprises a first block and a second block, wherein one of the bodies of the first block is connected to one of the bodies of the second block for movement therewith.

10. A phase shifting arrangement as claimed in claim 9, wherein the first and second blocks are arranged such that movement of the connected bodies in one direction results in each closed circuit in the first block being lengthened, and each closed circuit in the second block being shortened; and wherein movement of the connected bodies in the opposite direction results in each closed circuit in the first block being shortened and each closed circuit in the second block being lengthened.

11. A phase shifting arrangement as claimed in any of the preceding claims, comprising more than two blocks.

12. A phase shifting arrangement as claimed in any of the preceding claims, wherein each first circuit is in capacitive contact with the respective second circuit.

13. A phase shifting arrangement as claimed in claim 12, wherein at least one of the first circuit and respective second circuits has a dielectric coating, such that direct contact between the first circuit and respective second circuits is prevented.

14. An antenna arrangement comprising a phase shifting arrangement as claimed in any of the preceding claims.