GB2425658A

GB2425658A - Phase shifting arrangement

Info

Publication number: GB2425658A
Application number: GB0508316A
Authority: GB
Inventors: Christopher Davies
Original assignee: Alan Dick and Co Ltd
Current assignee: Alan Dick and Co Ltd
Priority date: 2005-04-25
Filing date: 2005-04-25
Publication date: 2006-11-01
Also published as: GB0508316D0

Abstract

An antenna array comprises a phase shifter arrangement with a plurality of discrete signal path components 24a - d that can be switched into or out of a signal path by a control system. The phase shifting arrangement may be used to vary the phase of a signal received by at least one antenna element of an antenna array such that it is out of phase with the signal supplied to at least one other antenna element of the said antenna array. A computer may be used to provide a digital control signal in which discrete signal path components 24a - d of different particular path lengths 25a - d may be switched into or out of a signal path by respective bits of the digital control signal. The phased antenna array arrangement may be used for horizontal and / or vertical scanning of an antenna beam. The phase shifters may be connected in series (figure 3). Each of the switches 26a - d may be an electronic device and comprise a PIN diode, MEM device, solenoid, hybrid ring, Lange coupler or loaded transmission line. Use of a hybrid ring or Lange coupler may provide continual operation even during adjustments to the phase shifter arrangement.

Description

I

CELLULAR WIRELESS COMMUNICATIONS ANTENNA ARRAY

Technical Field of the Invention

The invention relates to a cellular wireless communications antenna array including a digital phase shifting arrangement. The phase shifting arrangement may be used to control the antenna radiation pattern in the vertical (elevation) and/or horizontal (azimuth) planes.

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 emitting a horizontal beam, but in periods of peak capacity it is found that there is often interference or calls simply dropping off, with such an arrangement. In general, antennas are tilted downwards by a nominal amount, say 50 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-term 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. However, these have introduced their own mechanical and control complexities.

For example, in WO 01/03233 a phase shift system is described in which the phase is altered by altering the line length for any given antenna by varying the insertion or withdrawal of generally C-shaped conductor portions lying within, but not touching, folded conductors that form part of the line. This requires fabrication and assembly to a fine degree of tolerance and the mechanical arrangements for achieving continuous adjustment of the phase in different senses in different parts of the array in a co- ordinated manner are complex. Other approaches are to use moveable dielectric bodies such as described in US-A-2002/0003458 or a slidable T- junction arrangement as described in US-A-5801600. In each case the construction is complex and co- ordinated alteration of the phase shifts is difficult to obtain.

In addition, as the phase change is achieved by mechanically moving elements of the phase shifter, it is difficult to achieve a high level of reliability.

It is therefore an object of the invention to provide a phase shifting arrangement that overcomes these drawbacks.

mmarv of the Invention There is therefore provided a cellular wireless communications antenna array comprising a phase shifting arrangement, the phase shifting arrangement being suitable for connection between a signal connection point of the antenna array and a plurality of antenna elements of the antenna array, the phase shifting arrangement being adapted to vary the phase of a signal received at the signal connection point of the antenna array such that the signal supplied to at least one antenna element of the antenna array is out of phase with the signal supplied to the other antenna elements of the antenna array; wherein the phase shifting arrangement comprises a plurality of discrete signal path components that can be switched into or out of a signal path on the basis of respective bits in a digital control signal.

Brief Description of the Drawings

The invention will now be described, by way of example only, with reference to the following drawings, in which: Figure 1 is an illustration of an antenna mast with an array according to the invention; Figure 2 is a schematic view of an antenna array; Figure 3 is a more detailed view of a phase shifting arrangement in an antenna array according to a preferred embodiment of the invention; Figure 4 shows a phase shifter in a preferred embodiment of the invention; and Figure 5 shows a phase shifter in an alternative embodiment of the invention.

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 array 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 beam, 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 is nominally preset (for example electrically by means of phased cable lengths, or mechanically) at a 50 downtilt, and the downtilt can be adjusted between 00 and +100.

Figure 2 shows an antenna array 2 in accordance with the invention. The antenna array 2 has a signal connection point 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 signal connection point 3 of the antenna array 2 for supply to the antenna elements 4 in order to adjust the tilt of the antenna array 2.

However, in accordance with the invention, the phase shifting arrangement 5 is adapted to vary the phase of the signal electronically, i.e. without requiring any continuously variable mechanical moving parts.

Figure 3 shows in more detail the antenna array 2 according to the invention. This antenna array 2 has ten 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 the same phase. 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, antenna elements 13 and 14 are shifted in the negative sense by one phase unit (-6), whilst elements 11 and 12 are shifted negatively by two phase units (-26). Conversely, elements 17 and 18 are positively shifted by one phase unit (--6) and elements 19 and 20 are positively shifted by two phase units (+26).

In this embodiment of the invention, the arrangement of the phase shifting devices 23a, 23b and 23c, 23d in series means that the phase shifting devices 23a and 23d introduce a further phase shift of 6 into the phase-shifted signal provided by phase shifting devices 23b and 23c respectively. Therefore, as each of the phase shifting devices 23 are introducing a phase shift of 6, they can be identical to each other, and moreover can be controlled using a single control signal. This means that the complexity of the control circuitry for the array can be reduced.

The control circuitry may receive instructions for the tilt of the antenna beam over the air interface (perhaps via Bluetooth or infra-red), or alternatively the instructions can be provided from a remote location via cable, or could be produced by a software program running in an intelligent antenna. An intelligent antenna is an antenna that reacts to the real-time environment, perhaps by sensing the direction in which the majority of signals are being transmitted or received and adjusting the direction of the antenna beam accordingly.

Although this phase shifting arrangement is preferred, it will be appreciated that other phase shifting arrangements are possible in which the phase shifting devices 23 are arranged in series. In addition, phase shifting arrangements are possible in which the phase shifting devices 23 are not arranged in series.

The phase shifting devices 23 may vary the phase of the signal received at their respective inputs by any means known in the art. In the preferred embodiment of the invention, the phase of the signal from the signal connection point 3 is varied by switching a plurality of discrete signal path components into or out of the signal path on the basis of a digital control signal. In a preferred embodiment of the invention, the signal path components are switched into and out of the signal path by an electronic switch. The electronic switch may be any suitable electronic component, for example a PIN diode, micro-electromechanical system (MEMS) or a pseudo MEMS (such as a solenoid). Other means could be a reflective circuit such as a 3dB hybrid, Lange coupler or a loaded transmission line.

An exemplary phase shifter 23 is shown in Figure 4. In this embodiment, the phase shifting device 23 is made up of multiple elements 24a, 24b, 24c and 24d, with each element having a shorter signal path and a switchable signal path component having a longer path (25a, 25b, 25c, 25d) , controlled by a respective electronic switch 26a, 26b, 26c, 26d.

If the switchable delay (phase) of the first element 24a is n, then the switchable delay of the second element 24b will be 2n, the switchable delay of the third element 24c will be 3n and the switchable delay of the fourth element 24d will be 4n. Thus the resolution of the phase shifting device 23 will be n, and it will be a 4 bit device, with each digital bit controlling a respective one of the electronic switches 26a, 26b, 26c or 26d. The summation of the 4 bits gives n + 2n + 3n + 4n = iOn, which means that the maximum phase shift attainable by the phase shifting device 23 is IOn with a resolution of n.

Each of the phase shifting devices 23a, 23b, 23c and 23d will have the same configuration.

For example, if the delay introduced by path 25a is chosen such that n = 11 of phase delay, this would result in switchable delays of between 00 and 1100 with a resolution of 110, i.e. delays of 00, 110, 22 , 330, 440, 55 , 66 , 77 , 88 , 99 , 1100.

Therefore, referring to Figure 3, with the above range of phase delays available in each of the phase shifting devices 23a, 23b, 23c and 23d, it can be seen that electronically controlled digital phase shifters can be employed in this manner to effect a variable beam control antenna. For a ten element antenna array as shown in Figure 3 and using 4 bits with a phase delay resolution of 11 a switchable beam tilt range of 0 to 10 is possible at approximately 1 intervals.

It will be appreciated that other architectures with more or less than 4 bits are possible with resolutions other than 11 degrees.

Another exemplary phase shifter 23 is shown in Figure 5. In this embodiment, the phase shifting device 23 is made up of multiple elements 34a, 34b, 34c and 34d, with each element having, for example, a respective 3dB hybrid ring (90 or 180 ) or Lange coupler (35a, 35b, 35c or 35d).

Each element 34a, 34b, 34c or 34d has a pair of electronic switches 36a, 36b, 36c and 36d respectively, each switch being located between the hybrid ring or Lange coupler (35a, 35b, 35c, 35d) and ground. Each switch has one end connected directly to ground. The length of the signal path component between each switch 36a, 36b, 36c and 36d and the hybrid ring or Lange coupler 35a, 35b, 35c and 35d is L. The lengths of the signal path components between each switch 36a, 36b, 36c and 36d and ground are L2, L3, L4 and L5 for elements 34a, 34b, 34c, and 34d respectively.

When all of the electronic switches 36a, 36b, 36c and 36d are closed, a reference phase delay is present in the signal at Rf0 (compared with the signal at Rf).

Opening electronic switches 36a switches in the signal path component having length L2, which results in a phase delay equal to the reference phase delay plus a further delay n being observed at RF0 when compared to the signal at RF.

Similarly, opening electronic switches 36b switches in the signal path component having length L3, which results in a phase delay equal to the reference phase delay plus a further delay 2n being observed at RF0 when compared to the signal at RF.

Similarly, opening electronic switches 36c switches in the signal path component having length L4, which results in a phase delay equal to the reference phase delay plus a further delay 3n being observed at RF0 when compared to the signal at RF.

Similarly, opening electronic switches 36d switches in the signal path component having length L5, which results in a phase delay equal to the reference phase delay plus a further delay 4n being observed at RF0 when compared to the signal at RF.

By opening and closing various ones and combinations of the electronic switches 36a, 36b, 36c and 36d, various phase shifts are achievable. For example, if the lengths L2, L3, L4 and L5 are chosen such that the phase delay n = 110, this would result in switchable delays of between 00 and 1100 with a resolution of 110, i.e. delays of 00, 110, 22 , 33 , 44 , 550, 66 , 77 , 88 , 99 , 1100.

One advantage of this embodiment of the invention is that, unlike the arrangement shown in Figure 4, the antenna array 2 can be maintained in an operational state when te beam tilt is being adjusted, thereby reducing the chance of disruption occurring to user services whilst the antenna array 2 is being reconfigured. It will be appreciated by a person skilled in the art that other arrangements are possible in which the phase shifter can adjust the phase shift without breaking the signal path between the input and output of the phase shifter.

It will also be appreciated that the invention is applicable to multiband antenna arrays.

In this case, the phase shifting arrangement 5 will be adapted to introduce a different phase difference for each frequency band.

Claims

Claims 1. A cellular wireless communications antenna array comprising a

phase shifting arrangement, the phase shifting arrangement being suitable for connection between a signal connection point of the antenna array and a plurality of antenna elements of the antenna array, the phase shifting arrangement being adapted to vary the phase of a signal received at the signal connection point of the antenna array such that the signal supplied to at least one antenna element of the antenna array is out of phase with the signal supplied to the other antenna elements of the antenna array; wherein the phase shifting arrangement comprises a plurality of discrete signal path components that can be switched into or out of a signal path on the basis of respective bits in a digital control signal.
2. A cellular wireless communications antenna array as claimed in claim 1, wherein the phase shifting arrangement comprises one or more phase shifting devices, each phase shifting device connected to a respective antenna element or elements, each phase shifting device being adapted to vary the phase of the signal received at the signal connection point of the antenna array such that the signal supplied to the respective antenna element or elements is out of phase with the signal supplied to the other antenna elements of the antenna array.
3. A cellular wireless communications antenna array as claimed in claim 2, wherein the phase shifting arrangement comprises a plurality of phase shifting devices, the phase shifting devices being arranged in series.
4. A cellular wireless communications antenna array as claimed in claim 3, wherein the signal supplied to a first antenna element has passed through one of said phase shifting devices, while the signal supplied to a second antenna element has passed through two of said phase shifting devices.
5. A cellular wireless communications antenna array as claimed in claims 3 or 4, wherein the phase shifting devices are controlled using a common control signal, such that they introduce equal phase shifts.
6. A cellular wireless communications antenna array as claimed in any of claims 2 to 5, wherein an electronic switch is provided to switch the plurality of discrete signal path components into or out of the signal path.
7. A cellular wireless communications antenna array as claimed in claim 6, wherein the electronic switch comprises a PIN diode.
8. A cellular wireless communications antenna array as claimed in claim 6, wherein the electronic switch comprises a micro-electromechanical system.
9. A cellular wireless communications antenna array as claimed in any of claims 6 to 8, wherein the phase shifting devices comprise a plurality of signal paths, each having a particular length, and wherein the electronic switch adjusts the phase of the signal received from the input of the antenna array by selecting a signal path from the plurality of signal paths.
10. A cellular wireless communications antenna array as claimed in any preceding claim, wherein the phase shifting arrangement provides a continuous signal to each of the antenna elements whilst the phase of the signal is being varied.
11. A cellular wireless communications antenna array as claimed in any preceding claim, wherein the antenna elements of the antenna array are arranged in a vertical array, and the phase shifting arrangement is provided to adjust an elevation of a beam radiated by the antenna elements.
12. A cellular wireless communications antenna array as claimed in any one of claims 1 to 10, wherein the antenna elements of the antenna array are arranged in a horizontal array, and the phase shifting arrangement is provided to adjust an azimuth of a beam radiated by the antenna elements.
13. A cellular wireless communications antenna array as claimed in any one of claims 1 to 10, wherein the antenna elements of the antenna array are arranged in a planar array, and the phase shifting arrangement is provided to adjust an elevation and azimuth of a beam radiated by the antenna elements.
14. A cellular wireless communications antenna array as claimed in any preceding claim, wherein the antenna array operates in two or more frequency bands, and the phase shifting arrangement is adapted to vary the phase of the signal by a different amount for each frequency band.
15. A cellular wireless communications antenna array as claimed in any preceding claim, further comprising a computer for providing the digital control signal for the phase shifting arrangement.
16. A cellular wireless communications antenna array as claimed in any one of claims 1 to 14, further comprising means for receiving the digital control signal for the phase shifting arrangement over an air interface.