GB2439761A

GB2439761A - Phase shifting unit using mutually movable sections to vary path length

Info

Publication number: GB2439761A
Application number: GB0613407A
Authority: GB
Inventors: Andrew John Fox; Christopher Davies
Original assignee: Deltenna Ltd
Current assignee: Deltenna Ltd
Priority date: 2006-07-05
Filing date: 2006-07-05
Publication date: 2008-01-09
Also published as: GB0613407D0

Abstract

A phase shifting device has, mounted on a first unit, a signal input point and first and second signal output points. Mounted on a second unit, there is a conductive path having first, second and third end points, and including at least one impedance matching region. The second unit is held adjacent to the first unit such that a first signal path is established between the signal input, the first and second end points on the second unit, and the first signal output point, and a second signal path is established between the signal input, the first and third end points on the second unit, and the second signal output point. The second unit is movable relative to the first unit in order to vary the relative lengths of the first signal path and the second signal path. Multiple phase shifting devices can be connected together, such that the respective second units of the phase shifting devices move relative to the respective first units in different ways, such that the relative variations in the first and second signal path lengths differ between the phase shifting devices. This is achieved using a rod which has threaded sections of different coarsenesses.

Description

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PHASE SHIFTER

This invention relates to a phase shifting device, and in particular to a phase shifting device that can be inserted in a feed arrangement for an antenna in a wireless communications system.

It is known that, in order to adjust the directionality of a beam of radio waves transmitted from an antenna array, relative phase changes can be induced in the electrical signals sent to the antenna array elements. Specifically, by including a device that can adjust the lengths of the electrical paths to the antenna array elements by different amounts, the relative phases of the signals when they reach the antenna array elements can be adjusted. The result is that the direction of the transmitted radio signal is adjusted.

For example, when the array includes multiple elements arranged vertically above each other, such a change in the relative phases of the electrical signals results in an upwards or downwards tilt in the direction of the transmitted radio signal. This can be useful, for example, in a cellular mobile communications system, where the tilt of the transmitted radio signal determines the area over which that antenna array can communicate. For example, depending on the cell usage pattern, it may be desirable to increase or decrease this area.

W02004/004059 discloses a phase shifting device, having feed lines with open parts.

Slidable relative thereto is a circuit containing generally c-shaped conductive strips, which form connections at the open parts of the feed lines. Movement of the circuit will cause changes in the effective lengths of the feed lines, and hence in the relative phases of the electrical signals at the antenna array elements connected to those feed lines.

According to a first aspect of the present invention, there is provided a phase shifting device, comprising: mounted on a first unit, a signal input point and first and second signal output points; and, mounted on a second unit, a conductive path having first, second and third end points, and including at least one impedance matching region; wherein the second unit is held adjacent the first unit such that a first signal path is established between the signal input, the first and second end points on the second unit, and the first signal output point, and a second signal path is established between the signal input, the first and third end points on the second unit, and the second signal output point, and wherein the second unit is movable relative to the first unit in order to vary the relative lengths of the first signal path and the second signal path.

Preferably, the first, second and third end points of the conductive path on the second unit are each connected to a connection point.

Preferably, the conductive path has first and second impedance matching regions adjacent the connection point, with the first impedance matching region being between the connection point and the second end point and the second impedance matching region being between the connection point and the third end point.

Preferably, the conductive path is narrower in the first and second impedance matching regions than elsewhere.

Preferably, the first.and second impedance matching regions each have lengths of approximately one quarter of a wavelength, at an intended operating frequency of the device.

According to a second aspect of the present invention, there is provided a phase shifting unit, the phase shifting unit comprising a plurality of phase shifting devices, wherein each phase shifting device comprises: mounted on a respective first unit, a respective signal input point and respective first and second signal output points; and, mounted on a respective second unit, a conductive path having respective first, second and third end points; wherein the second unit is held adjacent the first unit such that a first signal path is established between the signal input, the first and second end points on the second unit, and the first signal output point, and a second signal path is established between the signal input, the first and third end points on the second unit, and the second signal output point, and wherein the second unit is movable relative to the first unit in order to vary the relative lengths of the first signal path and the second signal path, and wherein the phase shifting unit further comprises means for moving the respective second units of the phase shifting devices relative to the respective first units, such that the relative variations in the first and second signal path lengths differ between the phase shifting devices.

Preferably, the means for moving the respective second units of the phase shifting devices relative to the respective first units comprises a rod, having first and second threaded sections, and having a first threaded element interconnecting the first threaded section of the rod and a first of the phase shifting devices, and having a second threaded element interconnecting the second threaded section of the rod and a second of the phase shifting devices.

Preferably, the first threaded element interconnects the first threaded section of the rod and the second unit of the first phase shifting devices, and the second threaded element interconnects the second threaded section of the rod and the second unit of the second phase shifting device.

Preferably, the first and second threaded sections, and the first and second threaded elements, are such that rotation of the rod causes movement of the second unit of the first phase shifting device relative to the first unit thereof, and a different movement of the second unit of the second phase shifting device relative to the first unit thereof.

For example, the movement of the second unit of the first phase shifting device relative to the first unit thereof may be in a different direction to the movement of the second unit of the second phase shifting device relative to the first unit thereof.

For example, the movement of the second unit of the first phase shifting device relative to the first unit thereof may be by a different amount to the movement of the second unit of the second phase shifting device relative to the first unit thereof.

Preferably, the conductive path mounted on each Second unit includes at least one impedance matching region.

For a better understanding of the present invention, and to show how it may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic representation of a feed circuit for an antenna array, in accordance with the invention.

Figure 2 is a cross-sectional view through a phase shifting device in accordance with the invention.

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Figure 3 is a plan view of a first unit of the phase shifting device of Figure 2.

Figure 4 is a plan view of a second unit of the phase shifting device of Figure 2.

Figure 5 is a schematic plan view showing the first and second units of the phase shifting device of Figure 2.

Figure 6 is a schematic representation of a further phase shifting device in accordance with the invention.

Figure 1 shows the feed circuit for an antenna array 10. In the illustrated array shown in Figure 1, there are four antenna elements 12, 14, 16, 18, although it will be appreciated by the person skilled in the art that the array can have any number of antenna elements.

Figure 1 also schematically shows radio frequency processing circuitry 20, for generating a radio frequency signal for transmission by way of the antenna array 10.

The output signal from the radio frequency processing circuitry 20 is passed to a phase shifter unit 22, which splits the radio frequency signal for passing to the antenna elements 12, 14, 16, 18 of the antenna array 10, and can introduce relative phase shifts into the signals passing to the antenna elements 12, 14, 16, 18.

Figure 2 is a cross-sectional view through a phase shifter unit 22. For ease of illustration in Figure 2, the input signal is split to form two output signals, and different phase shifts can be applied to these two output signals. It will be apparent that a phase shifter unit 22 as shown in Figure 2 can simply be extended to produce any desired number of output signals.

As shown in Figure 2, the phase shifter unit 22 has a housing, having a lower part 24 and an upper part 26, held together by fixing means such as screws 28, 30. The housing preferably has a clam shell design, such that lower part 24 and upper part 26 are pivotably connected together.

A first substrate 32, for example in the form of a circuit board, is mounted to the lower part 24 of the housing on supports 32, 34, 36. An input RF track 38 and output RE tracks 40 are formed on the first substrate 32.

A second substrate 42 is mounted in a plane parallel to the plane of the first substrate 32, and is held, for example by springs 44, 46, in engagement with the first substrate 32. A non-stick coating 48 is provided between the first substrate 32 and the second substrate 42 to allow a relative sliding motion without significant friction. RF tracks 50, 52 are provided on the underside of the second substrate 42, such that they can make contact with the RF tracks 38, 40 on the upper side of the first substrate 32.

The tracks 38, 40 may be formed on the first substrate 32 in a suspended stnpline structure. Similarly, the tracks 50, 52 may be formed on the second substrate 42 in a suspended stripline structure, such that they are incontact with the tracks 38, 40.

An anchor point 54 is provided on the second substrate 42, accessible from the outside of the housing.

Figure 3 is a plan view showing the positions of the RF tracks formed on the first substrate 32. Specifically, the input RF track 38 is provided extending from a first edge 56 of the substrate 32, a first output RF track 40 is provided extending to a second edge 58 of the substrate 32 opposite the first edge 56, and a second output RF track is provided extending to the first edge 56. The input RF track 38, the first output RF track 40, and the second output RF track 60 each have an impedance of 50Q.

Parallel first and second slots 62, 64 are cut in the substrate 32.

Figure 4 is a plan view showing the positions of the RF tracks formed on the second substrate 42. Specifically, an RF track section 66 connects a first end point 68 to a connection point 70, while an RF track section 72 connects the connection point 70 to a second end point 74, and an RF track section 76 connects the connection point 70 to a third end point 78.

The RF track sections 66, 72, 76 each have an impedance of 500. However, in an impedance matching section 80 of the RF track section 72, and in an impedance matching section 82 of the RF track section 76, the RF tracks are narrowed, such that their impedances are increased. Specifically, their impedances are doubled to 1000 in these regions. This allows the combined impedance of the RF track section 72 and the RF track section 76 to be matched to the 500 impedance of the RF track section 66.

The impedance matching sections 80, 82 have lengths which are approximately equal to one quarter of the wavelength of the signal, at the intended operating frequency.

Parallel first and second slots 84, 86 are cut in the second substrate 42, matching the first and second slots 62, 64 cut in the first substrate 32.

Figure 5 is a schematic representation, showing the relative positions of the first and second substrates 32, 42 when they are mounted together in operation. Specifically, the first end point 68 on the RF track section 66 on the second substrate 42 overlaps the input RF track 38 on the first substrate 32; the second end point 74 on the RF track section 72 on the second substrate 42 overlaps the second output RF track 60 on the first substrate 32; and the third end point 78 on the RE track section 76 overlaps the first output RF track 40 on the first substrate 32.

The slots 84, 86 in the second substrate 42 are positioned overlapping the slots 62, 64 in the first substrate 32, and guide pegs 88, 90, 92, 94 are located in the slots to maintain the desired alignment, while allowing the second substrate 42 to move relative to the first substrate 32 in the directions shown by the arrow A, but also act as end stops to limit such movement. The anchor points 54, 96 can be used to cause such relative movement. As mentioned above the guide pegs 88, 90, 92, 94 can be spring loaded, in order to maintain electrical contact between the RF track section 66 and the input RF track 38; between the RE track section 72 and the second output RE track 60; and between the RF track section 76 and the first output RF track 40.

Thus, there are established connections between the input RF track 38 and the first and second output RF tracks 40, 60, through the RF track sections on the second substrate 42. Further, movement of the second substrate 42 relative to the first substrate 32 causes the relative lengths of these connections to change. Specifically, while the second substrate is at the upper end of its movement (as shown in Figure 5), the length of the path between the input RF track 38 and the second output RF track 60 is a minimum, and, while the second substrate is at the lower end of its movement (as shown in Figure 5), the length of the path between the input RF track 38 and the second output RF track 60 is a maximum.

Figure 6 is a schematic representation of a phase shifter 100, in which an input signal is supplied to four outputs, for connection to four antenna array elements. Specifically, an input path 102 splits into a first intermediate input path 104 and a second intermediate input path 106. In the region of their connection to the input path 102, the first intermediate input path 104 and the second intermediate input path 106 are narrower than the input path 102 in order to provide impedance matching.

The first intermediate input path 104 is an input to a first phase shifter device 108, which can be the same as the phase shifter device shown in Figures 2-5. and which provides output signals on output paths 110, 112. The second intermediate input path 106 is an input to a second phase shifter device 114, which again can be the same as the phase shifter device shown in Figures 2-5, and which provides output signals on output paths 116, 118.

The movable units of the first and second phase shifter devices 108, 114 can be moved by an adjustment device 120, including a partially threaded rod 122. A first mechanical interconnect device 124 has a first threaded end 126 in contact with a first threaded section 128 of the partially threaded rod 122, and a second end 130 in fixed contact with the movable unit of the first phase shifter device 108. A second mechanical interconnect device 132 has a first threaded end 134 in contact with a second threaded section 136 of the partially threaded rod 122, and a second end 138 in fixed contact with the movable unit of the second phase shifter device 114.

If the partially threaded rod 122 is held in position vertically, then rotating it causes the movable units of the first and second phase shifter devices 108, 114 to be moved vertically. However, in this case, the first threaded section 128 of the partially threaded rod 122, and the second threaded section 136 of the partially threaded rod 122 are oppositely threaded, such that the movable units of the first and second phase shifter devices move in opposite directions. For example, if the movable unit of the first phase shifter device 108 moves in the direction of the arrow B, then the movable unit of the second phase shifter device 114 moves in the direction of the arrow C. Moreover, the first threaded section 128 of the partially threaded rod 122 is more coarsely threaded than the second threaded section 136 of the partially threaded rod 122, such that the movable units of the first and second phase shifter devices move different distances. For example, if the movable unit of the first phase shifter device 108 moves a distance d, then the movable unit of the second phase shifter device 114 may only move a distance d/2.

It will be noted that the mechanism described herein imparts a linear movement to the movable units, in order to cause changes in the relative lengths of the paths to the two antenna elements. However, it will be appreciated that a mechanism can be selected that imparts a pivoting movement to the movable unit (in the embodiment of Figures 2- 5) or to each movable unit (in the embodiment of Figure 6). With a suitable design of the stationary unit or units, this can again cause changes in the relative lengths of the paths to the two antenna elements.

There is thus provided a mechanism that, in certain embodiments, allows adjustment of the phase of signals supplied to an antenna array, while maintaining appropriate impedance matching, and allowing appropriate relative movements to be achieved.

Claims

CLAIMS

1. A phase shifting unit, the phase shifting unit comprising a plurality of phase shifting devices, wherein each phase shifting device comprises: mounted on a respective first unit, a respective signal input point and respective first and second signal output points; and, mounted on a respective second unit, a conductive path having respective first, second and third end points; wherein the second unit is held adjacent the first unit such that a first signal path is established between the signal input, the first and second end points on the second unit, and the first signal output point, and a second signal path is established between the signal input, the first and third end points on the second unit, and the second signal output point, and wherein the second unit is movable relative to the first unit in order to vary the relative lengths of the first signal path and the second signal path, and wherein the phase shifting unit further comprises means for moving the respective second units of the phase shifting devices relative to the respective first units, such that the relative variations in the first and second signal path lengths differ between the phase shifting devices.

2. A phase shifting unit as claimed in claim 1, wherein the means for moving the respective second units of the phase shifting devices relative to the respective first units comprises a rod, having first and second threaded sections, and having a first threaded element interconnecting the first threaded section of the rod and a first of the phase shifting devices, and having a second threaded element interconnecting the second threaded section of the rod and a second of the phase shifting devices.

3. A phase shifting unit as claimed in claim 2, wherein the first threaded element interconnects the first threaded section of the rod and the second unit of the first phase shifting devices, and the second threaded element interconnects the second threaded section of the rod and the second unit of the second phase shifting device.

4. A phase shifting unit as claimed in claim 2 or 3, wherein the first and second threaded sections, and the first and second threaded elements, are such that rotation of the rod causes movement of the second unit of the first phase shifting device relative to the first unit thereof, and a different movement of the second unit of the second phase shifting device relative to the first unit thereof.

5. A phase shifting unit as daimed in claim 4, wherein the movement of the second unit of the first phase shifting device relative to the first unit thereof is in a different direction to the movement of the second unit of the second phase shifting device relative to the first unit thereof.

6. A phase shifting unit as claimed in claim 4, wherein the movement of the second unit of the first phase shifting device relative to the first unit thereof is by a different amount to the movement of the second unit of the second phase shifting device relative to the first unit thereof.

7. A phase shifting unit as daimed in any preceding claim, wherein the conductive path mounted on each second unit includes at least one impedance matching region.

8. A phase shifting device, comprising: mounted on a first unit, a signal input point and first and second signal output points; and, mounted on a second unit, a conductive path having first, second and third end points, and including at least one impedance matching region; wherein the second unit is held adjacent the first unit such that a first signal path is established between the signal input, the first and second end points on the second unit, and the first signal output point, and a second signal path is established between the signal input, the first and third end points on the second unit, and the second signal output point, and wherein the second unit is movable relative to the first unit in order to vary the relative lengths of the first signal path and the second signal path.

9. A phase shifting device as claimed in claim 8, wherein the first, second and third end points of the conductive path on the second unit are each connected to a connection point.

10. A phase shifting device as claimed in claim 9, wherein the conductive path has first and second impedance matching regions adjacent the connection point, with the first impedance matching region being between the connection point and the second end point and the second impedance matching region being between the connection point and the third end point.

11 A phase shifting device as claimed in claim 10, wherein the conductive path is narrower in the first and second impedance matching regions than elsewhere.

12. A phase shifting device as claimed in claim 10 or 11, wherein the first and second impedance matching regions each have lengths of approximately one quarter of a wavelength, at an intended operating frequency of the device.

13. A phase shifting device as claimed in claim 9, wherein the conductive path on the second unit is formed as a stripline structure, and further comprising suspended stnpline structures connected to the signal input point and the first and second signal output points on the first unit.