GB2529886A

GB2529886A - Reconfigurable multi-band antenna with four to ten ports

Info

Publication number: GB2529886A
Application number: GB1415782.0A
Authority: GB
Inventors: Sampson Hu
Original assignee: Smart Antenna Technologies Ltd
Current assignee: Smart Antenna Technologies Ltd
Priority date: 2014-09-05
Filing date: 2014-09-05
Publication date: 2016-03-09
Also published as: GB201415782D0

Abstract

A MIMO antenna device has a substrate 1 incorporating a first ground plane 2, a symmetric conductive strip 5 having first and second arms 6, 7 each having a proximal portion and a distal portion, a first conductive strip 11 located generally between the distal portions and adjacent to the proximal portions of the first and second arms, a second conductive strip 15 located generally adjacent to the first arm and a third conductive strip 16 located generally adjacent to the second arm. The first to third conductive strips are configured to be unbalanced. The symmetrical conductive strip may be configured to be balanced or the first arm may be unbalanced and the second arm a ground plane. The antenna device may be configured with four or five feed points, and may drive from four up to ten signal ports. The device enables conductive strips to be located in close proximity whilst providing sufficient isolation between the ports.

Description

RECONFIGURABLE MULTI-BAND ANTENNA WITH FOUR TO TEN PORTS

[0001] This invention relates to a reconfigurable antenna. Particularly, but not exclusively, the invention relates to a reconfigurable multiple-input multiple-output (MIMO) antenna for use in a portable electronic device such as a mobile phone handset, laptop, tablet, femtocell, wireless router or other radio communications device.

BACKGROUND

[0002] Multiple-input multiple-output (M IMO) wireless systems exploiting multiple antennas as both transmitters and receivers have attracted increasing interest due to their potential for increased capacity in rich multipath environments. Such systems can be used to enable enhanced communication performance (i.e. improved signal quality and reliability) by use of multi-path propagation without additional spectrum requirements. This has been a well-known and well-used solution to achieve high data rate communications in relation to 2G and 3G communication standards. For indoor wireless applications such as router devices, external dipole and monopole antennas are widely used. In this instance, high-gain, omni-directional dipole arrays and collinear antennas are most popular.

However, very few portable devices with MIMO capability are available in the marketplace.

The main reason for this is that, when gathering several radiators in a portable device, the small allocated space for the antenna limits the ability to provide adequate isolation between each radiator.

[0003] A reconfigurable MIMO antenna is known from WO 2012/072969 (the content of which is incorporated into the present disclosure by reference). An embodiment is described in which the antenna comprises a balanced antenna located at a first end of a PCB and a two-port chassis-antenna located at an opposite second end of the FCB.

However, in certain applications this configuration may not be ideal or even practical since it requires two separate areas in which to locate each antenna. However, as mentioned above this spacing was chosen to provide adequate isolation between each antenna structure.

[0004] Another reconfigurable antenna is known from WO 201 4/020302 (the content of which is incorporated into the present disclosure by reference). This antenna comprises a balanced antenna and an unbalanced antenna mounted on a supporting PCB substrate, with both the balanced antenna and the unbalanced antenna located at the same end of the substrate. The antenna may be configured as a chassis antenna for use in a portable device and may be configured for MIMO applications. In one embodiment of the antenna of WO 2014/020302, there is provided a floating groundplane connected to the balanced antenna. The floating groundplane is constituted by a rectangular metal patch located on a first surface of the substrate, centrally below feed lines provided on the first surface to feed the balanced and unbalanced antennas. A first matching circuit configured to excite the arms of the balanced antenna is located on the floating groundplane. The unbalanced antenna is mounted on a second surface of the substrate, opposed to the first surface, and is connected to a second matching circuit mounted on the PCB substrate. In another embodiment, the floating groundplane may be incorporated in one arm of the balanced antenna, thereby saving space on the PCB substrate. Each matching circuit is coupled to a signal port, and the antenna as disclosed therefore provides only two ports.

[0005] Certain handset and other portable device manufacturers, however, require an antenna with more than two ports. A particular problem with multi-port antennas, particularly when there more than just two ports, is how to obtain sufficient isolation between the ports.

BRIEF SUMMARY OF THE DISCLOSURE

[0006] Viewed from a first aspect, there is provided a reconfigurable antenna device comprising a substrate incorporating a first groundplane, a substantially symmetric antenna having first and second arms each having a proximal portion and a distal portion, a first unbalanced antenna located generally between the distal portions and adjacent to the proximal portions of the first and second arms, a second unbalanced antenna located generally adjacent to the first arm and a third unbalanced antenna located generally adjacent to the second arm.

[0007] The substrate may comprise a printed circuit board substrate, and the first conductive groundplane may be a conductive layer on one surface of the substrate or disposed between upper and lower surfaces of the substrate.

[0008] In preferred embodiments, a region at one end of the substrate where the various antennas are mounted is free of the first groundplane, the groundplane having an edge facing the end of the substrate where the antennas are mounted.

[0009] The first unbalanced antenna may be coplanar with the second and third unbalanced antennas, or may be disposed in a substantially parallel plane.

[0010] The first and second radiating arms of the symmetric antenna may comprise a pair of generally L-shaped members, which may be disposed generally in the plane of the substrate. The L-shaped members may be disposed in a substantially mirror-symmetrical arrangement about a longitudinal axis of the substrate. Although in some embodiments, the first and second arms are of substantially the same dimensions (i.e. exhibit true mirror symmetry about the axis), other embodiments may comprise first and second arms of differing dimensions.

[0011] The symmetric antenna is provided with a feed that is connected to matching circuitry. Where appropriate, the feed may incorporate a balun.

[0012] In one embodiment, the symmetric antenna is configured as a balanced antenna, which may be fed with a balanced feed between the first and second arms, where necessary by way of a balun. The symmetric antenna then acts as a dipole, and does not need to be driven against a groundplane.

[0013] Alternatively, the second arm of the symmetric antenna may comprise or be provided with a second groundplane. In this embodiment, the first arm of the symmetric antenna acts as a monopole driven against the second arm, which serves as a groundplane, and no balun is required for feeding an unbalanced signal to the first radiating arm. Matching circuitry for the symmetric antenna may be disposed on the second arm, thus freeing up valuable real estate on the main substrate. The symmetric configuration of the two arms of the antenna helps to improve isolation from the other antennas.

[0014] Alternatively, the symmetric antenna may be connected to a second groundplane (or floating groundplane) configured as a conductive patch located on the substrate but separated from the first groundplane. For example, the second groundplane may be disposed on an opposed surface of the substrate to that on which the first groundplane is disposed. Matching circuitry for the symmetric antenna may be disposed on the second groundplane or floating groundplane.

[0015] The first unbalanced antenna is located between the distal portions of the symmetric antenna, generally adjacent to the proximal portions. The first unbalanced antenna may comprise an elongate conductive strip as a radiating element, having a length that is preferably substantially parallel to the proximal portions. A first half of the conductive strip of the first unbalanced antenna is located generally adjacent and parallel to the proximal portion of the first arm of the symmetric antenna, with a second half being located generally adjacent and parallel to the proximal portion of the second arm. The first unbalanced antenna may be located in the same plane as the symmetric antenna, for example on the same surface of the substrate, or may be in a parallel plane, for example on an opposed surface of the substrate. The first unbalanced antenna may further comprise a central stub that extends towards but does not contact the first groundplane.

The stub may provide a connection point for a feed to the first unbalanced antenna.

[0016] The second unbalanced antenna may also comprise a conductive strip as a radiating element, and may be located adjacent to and substantially parallel to the first half of the first unbalanced antenna, and thus also generally adjacent to the first arm of the symmetric antenna. The second unbalanced antenna may be located between the distal portion of the first arm of the symmetric antenna and the central stub of the first unbalanced antenna.

[0017] The third unbalanced antenna may also comprise a conductive strip as a radiating element, and may be located adjacent to and substantially parallel to the second half of the first unbalanced antenna, and thus also generally adjacent to the second arm of the symmetric antenna. The third unbalanced antenna may be located between the distal portion of the second arm of the symmetric antenna and the central stub of the first unbalanced antenna.

[0018] The second and/or the third unbalanced antennas may be mounted on the substrate in the same plane as the symmetric antenna, or in a different plane (for example on an opposed surface of the substrate, or sandwiched between opposed surfaces of the substrate). The second and third unbalanced antennas need not be mounted in the same plane. In some embodiments, the second and third unbalanced antennas have substantially the same dimensions, and may be disposed symmetrically about the longitudinal axis of the substrate. Alternatively, the second and third unbalanced antennas have different dimensions.

[0019] In certain embodiments, the second and third unbalanced antennas are located between the first unbalanced antenna and the edge of the first conductive groundplane facing the end of the substrate where the antennas are mounted.

[0020] Alternatively, the second and third unbalanced antennas may be located between the first unbalanced antenna and, respectively, the proximal portions of the first and second arms of the symmetric antenna.

[0021] The first, second and third unbalanced antennas may be connected to and driven against the first groundplane. Each of the first, second and third antennas is provided with a respective feed and respective matching circuitry.

[0022] The second and third unbalanced antennas may be driven together as a balanced pair with appropriate matching circuitry.

[0023] Preferred embodiments thus provide a reconfigurable antenna which can be located at one end of a supporting substrate (e.g. a PCB) and which is therefore easily integrated into small portable devices such as mobile phone handsets and tablets. The antenna device may have a small, low profile and be relatively cheap to manufacture.

Embodiments may offer good performance (high efficiency and gain), reduced specific absorption rate (SAR), a wide bandwidth or range of bandwidths and high isolation between each radiator.

[0024] Matching circuitry may be provided for each antenna element to tune the respective element to a desired operating frequency or band. For example, the antenna device may be configured to cover one or more of: DVB-H, GSM71O, GSM85O, GSM900, GSM1BOO, P051900, GPS1575, UMTS2100, WiFi (e.g. 2.4GHz and 5GHz), Bluetooth®, LTE, LTA and 4G frequency bands.

[0025] The symmetric antenna and the first unbalanced antenna may be provided with substantially centrally located feed lines.

[0026] The antenna elements may be formed as etched or metallised tracks on the substrate, or may be formed as metal plates that are adhered or otherwise attached to the substrate.

[0027] Multiple matching circuits may be provided for the various antenna elements, and different modes of operation may be selected by switching between the various matching circuits.

[0028] Each matching circuit may comprise at least one variable capacitor to tune the frequency of its associated antenna element over a desired frequency range. The variable capacitor may be constituted by multiple fixed capacitors with switches, or by varactors or MEMs capacitors. In addition, one or more of the matching circuits may further be provided with at least one inductor, which may be fixed or variable.

[0029] The symmetric antenna and its associated matching circuitry may be coupled to a first signal port.

[0030] The first unbalanced antenna and its associated matching circuitry may be coupled to a second signal port.

[0031] The second unbalanced antenna and its associated matching circuitry may be coupled to a third signal port.

[0032] The third unbalanced antenna and its associated matching circuitry may be coupled to a fourth signal port.

[0033] In embodiments where the symmetric antenna is configured as a pair of unbalanced antennas with separate feeds, each arm of the symmetric antenna may be provided with its own matching circuitry. In this way, in addition to the first signal port, the symmetric antenna can be coupled to a fifth signal port.

[0034] Moreover, using the splitter circuits and matching circuits disclosed in WO 2013/014458 (the content of which is incorporated into the present disclosure by reference), it is possible for each of the first to third unbalanced antennas to drive two signal ports, the signals at each pair of signal ports being tuneable independently of each other.

[0035] Moreover, when the symmetric antenna is configured with the second arm as a groundplane and the first arm as a monopole (i.e. the first arm is an unbalanced antenna), then the symmetric antenna can drive two signal ports.

[0036] When the symmetric antenna is configured as a balanced dipole antenna, the symmetric antenna requires a balun and will only drive one signal port.

[0037] Where the symmetric antenna is configured as a pair of unbalanced antennas, each arm of the symmetric antenna can drive two signal ports.

[0038] Accordingly, an antenna device as disclosed herein may be configured with 4, 5, 6, 7, 8, 9 or 10 ports, each port being independently tuneable.

[0039] Alternatively or in addition, using the multi-band configurations disclosed in the present Applicant's co-pending UK patent application no GB1415780.4 filed simultaneously with the present application, it is possible for each signal port to support two or more independently tuneable signals.

[0040] As such, a single, small antenna device with a relatively small footprint can be used to support operation over a wide range of frequencies, in many different frequency bands.

[0041] Embodiments of the present device may be used for Multiple-Input-Multiple-Output (MIMO) applications, and also for diversity applications, where two or more signals in the same frequency band are distinguished by other characteristics such as polarization.

[0042] Polarization diversity, for example making use of phase shifts, for example 90 degree phase shifts, between certain matching circuits and/or signal ports, can be used to help improve isolation between signal ports.

[0043] The reconfigurable antenna device disclosed herein may be configured in a number of different ways depending on the requirements of a manufacturer of portable radio devices.

[0044] The antenna device may further comprise a control system which is connected to each signal port and which comprises a control means for selecting a desired operating mode.

[0045] The antenna device may be configured as a chassis antenna for use in a portable device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 shows a schematic plan view of a first embodiment; Figure 2 shows a schematic plan view of a second embodiment with an SF front end system placed on a floating ground plane; Figure 3 shows a system block illustrating an implementation of embodiments configured for 6 port simultaneous operation; Figure 4 shows a schematic perspective view of a third embodiment with a floating groundplane; Figure 5 shows a return loss plot for the embodiment of Figure 4; Figure 6 shows a system block illustrating an implementation of embodiments configured for 8 port simultaneous operation; Figure 7 shows a schematic plan view of a fourth embodiment; Figure 8 shows a system block illustrating an implementation of the embodiment of Figure 7 configured for 10 port simultaneous operation; and Figure 9 shows a system block illustrating an implementation of embodiments configured for 4 port simultaneous operation.

DETAILED DESCRIPTION

[0001] Figure 1 shows a first embodiment of a reconfigurable antenna device in schematic form. There is provided a substrate 1 including a first conductive groundplane 2 formed across a major portion of the upper surface of the substrate 1. The substrate 1 may be a PCB, for example FR4® or Duroid®. The substrate 1 of this embodiment has a generally rectangular shape, being configured as a PCB for a mobile phone handset. A symmetric antenna 5 (here configured as an unbalanced antenna driven against a floating groundplane) having first and second arms 6, 7 and a feed 8 is formed at one end of the substrate 1. The first and second arms 6, 7 may be formed from folded metal strips, for example copper strips, or may be etched or printed or otherwise formed as conductive strips or layers on the substrate 1. Each arm 6, 7 has a proximal portion 9, 9' and a distal portion 10, 10'. The distal portions 10, 10' extend substantially at right angles to the proximal portions 9, 9' towards the groundplane 2.

[0002] In this embodiment, the second arm 7 of the symmetric antenna 5 is configured as a floating groundplane, and the first arm 6 is configured as an unbalanced antenna driven against the groundplane provided by the second arm 7.

[0047] There is further provided a first unbalanced antenna 11, located generally between the distal portions 10, 10' and adjacent to the proximal portions 9, 9' of the first and second arms 6, 7. The first unbalanced antenna 11 is formed as a conductive layer on the substrate 1 across the reduced width portion 4, generally parallel to an edge 14 of the first groundplane 2, and includes a central stub portion 12 connected to a feed 13.

[0048] There is further provided a second unbalanced antenna 15 located generally adjacent to the first arm 6 and a third unbalanced antenna 16 located generally adjacent to the second arm 7. The second and third unbalanced antennas 15, 16 each extend along the substrate 1 between the first unbalanced antenna 11 and the edge 14 of the groundplane 2. The second and third unbalanced antennas 15, 16 are provided with respective feeds 19, 20.

[0049] Figure 2 shows a development of the embodiment of Figure 1, where an RE front end system 3 is located on the floating groundplane provided by the second arm 7. By locating the RF front end system 3 on the second arm 7, there is no need to find space for it on the main groundplane 2, thus providing additional flexibility for configuring the other electronic components of a mobile handset (not shown).

[0050] Figure 3 is a system block showing how the four antenna feeds 8, 13, 19 and 20 be connected to six signal ports 201, 202, 203, 204, 205 and 206 by way of six matching circuits or matching networks 301, 302, 303, 304, 305 and 306. The RE signals for antenna feeds 8 and 13 are split into high frequency and low frequency bands by high pass filters 401, 402 and low pass filters 403, 404. This is described in more detail in the present Applicant's co-pending UK patent application no GB1415780.4 filed simultaneously with the present application.

[0051] Figure 4 shows an alternative configuration of the Figure 1 and 2 embodiments, with like parts being labelled as for Eigures 1 and 2. In this embodiment, the substrate 1 has a generally rectangular shape, being configured as a FCB for a mobile phone handset.

Two recesses 30, 30' are cut from the substrate 1 at one end thereof to provide a reduced width portion 4. The symmetric antenna 5 having first and second arms 6, 7 and a feed 8 is formed about the reduced width portion 4 of the substrate 1. The first and second arms 6, 7 are formed from folded metal strips, for example copper strips. Each arm 6, 7 has a proximal portion 9, 9' and a distal portion 10, 10'. The distal portions 10, 10' extend substantially at right angles to the proximal portions 9, 9' along the recesses 3, 3'. One arm 7 is configured as a floating groundplane against which the other arm 6 is driven as an unbalanced antenna. First, second and third unbalanced antennas 11, 15 and 16 are provided as previously described, and the antenna device as a whole has four feeds 8, 13, 19, 20.

[00521 Figure 5 is a return loss plot for the antenna device of Figure 4 configured for 6 port operation as shown in Figure 3. Figure 5 shows that a single antenna device of a present embodiment can provide 6 port, multi-band, dual-MIMO operation over a frequency range of 700MHz to 6GHz. With reference to Figure 3, signal ports 201 and 203, operating at the same frequency, as MIMO, can cover either the low-band or the mid-band for 4G LTE. Signal ports 202 and 204, operating at the same frequency, as MIMO, can cover either the mid-band or the high-band for 4G LTE. Signal ports 201 and 202, and signal ports 203 and 204, can together provide dual-MIMO simultaneous operation for 4G LTE. Signal port 205 is operating in the 2.4GHz WiFi band. Signal port 206 can operate in either the 5.5GHz WiFi band, or the GNSS bands (1.16 to 1.3GHz and 1.5GHz). Each signal port 201-206 is independently controllable. This means that if one port is tuned to a different frequency band, the other ports will continue to operate in the same frequency bands as before.

(0053] Figure 6 is a system block showing how the four antenna feeds 8, 13, 19 and 20 be connected to eight signal ports 201 to 208 by way of eight matching circuits or matching networks 301 to 308. The RF signals for antenna feeds 8, 13, 19 and 20 are split into high frequency and low frequency bands by high pass filters 401, 402, 405, 406 and low pass filters 403, 404, 407, 408.

(0054] Figure 7 shows an alternative embodiment that is generally similar to that of Figure 1, but with the important difference that the second arm 7 of the symmetric antenna 5, instead of being configured as a groundplane, is configured as an unbalanced antenna driven against the main groundplane 2. The first arm 6 of the symmetric antenna 5 is also configured as an unbalanced antenna, driven against the main groundplane 2. The first arm 6 and second arm 7 have separate feeds 8, 80. Accordingly, the antenna device as a whole has five feeds 8, 13, 19, 20 and 80.

(0055] Figure 8 is a system block showing how the five antenna feeds 8, 13, 19, 20 and of the Figure 7 embodiment can be connected to ten signal ports 201 to 210 by way of ten matching circuits or matching networks 301 to 310. The RF signals for antenna feeds 8, 13, 19, 20 and 80 are split into high frequency and low frequency bands by high pass filters 401, 402, 405, 406, 409 and low pass filters 403, 404, 407, 408, 410.

[00561 Figure 9 is a system block showing how the five antenna feeds 8, 13, 19, 20 and of the Figure 7 embodiment can be connected to four signal ports 201 to 204 by way of six matching circuits or matching networks 301 to 306. The RF signals for antenna feed 13 are split into high frequency and low frequency bands by high pass filter 401 and low pass filter 403. The RF signals for antenna feeds 8 and 80 can be converted by balun 500 (when the first and second arms 6, 7 operate together as a dipole in balanced mode).

Likewise, the RF signals for antenna feeds 19 and 20 can be converted by balun 501 (when the second and third unbalanced antennas 15, 16 operate together as a dipole in balanced mode).

[0057] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0058] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments.

The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0059] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS: 1. A reconfigurable antenna device comprising a substrate incorporating a first groundplane, a symmetric antenna having first and second arms each having a proximal portion and a distal portion, a first unbalanced antenna located generally between the distal portions and adjacent to the proximal portions of the first and second arms, a second unbalanced antenna located generally adjacent to the first arm and a third unbalanced antenna located generally adjacent to the second arm.
2. A device as claimed in claim 1, wherein a region at one end of the substrate where the antennas are mounted is free of the first groundplane, the groundplane having an edge facing the end of the substrate where the antennas are mounted.
3. A device as claimed in any preceding claim, wherein the first and second arms of the symmetric antenna comprise a pair of generally L-shaped members.
4. A device as claimed in claim 3, wherein the L-shaped members are disposed in a substantially mirror-symmetrical arrangement about a longitudinal axis of the substrate.
5. A device as claimed in any preceding claim, wherein the second arm of the balanced antenna is configured as a groundplane, and wherein the first arm is configured as an unbalanced antenna.
6. A device as claimed in claim 5, wherein a matching circuit for the unbalanced antenna comprising the first arm is disposed on the second arm.
7. A device as claimed in claim 5 or 6, further comprising RF front end circuitry on the second arm.
8. A device as claimed in any one of claims 1 to 4, wherein the symmetric antenna is connected to a second groundplane configured as a conductive patch located on the substrate but separated from the first groundplane.
9. A device as claimed in any one of claims 1 to 4 or 8, wherein the symmetric antenna is configured as a balanced antenna, the first and second arms being configured as a dipole.
10. A device as claimed in any preceding claim, wherein the first unbalanced antenna comprises an elongate conductive strip as a radiating element.
11. A device as claimed in claim 10, wherein the first unbalanced antenna has a length that is substantially parallel to the proximal portions of the arms of the symmetric antenna.
12. A device as claimed in claim 10 or 11, wherein a first half of the conductive strip of the first unbalanced antenna is located generally adjacent and parallel to the proximal portion of the first arm of the symmetric antenna, with a second half being located generally adjacent and parallel to the proximal portion of the second arm.
13. A device as claimed in any preceding claim, wherein the first unbalanced antenna further comprises a central stub that extends towards but does not contact the first groundplane.
14. A device as claimed in any preceding claim, wherein the second and third unbalanced antennas each comprise a conductive strip as a radiating element.
15. A device as claimed in claim 12 or any one of claims 13 or 14 depending from claim 12, wherein the second unbalanced antenna is located adjacent to and substantially parallel to the first half of the first unbalanced antenna, and thus also generally adjacent to the first arm of the symmetric antenna.
16. A device as claims in claim 13 or any one of claims 14 or 15 depending from claim 13, wherein the second unbalanced antenna is located between the distal portion of the first arm of the symmetric antenna and the central stub of the first unbalanced antenna.
17. A device as claimed in claim 12 or any one of claims 13 to 16 depending from claim 12, wherein the third unbalanced antenna is located adjacent to and substantially parallel to the second half of the first unbalanced antenna, and thus also generally adjacent to the second arm of the symmetric antenna.
18. A device as claimed in claim 13 or any one of claims 14 to 17 depending from claim 13, wherein the third unbalanced antenna is located between the distal portion of the second arm of the symmetric antenna and the central stub of the first unbalanced antenna.
19. A device as claimed in any preceding claim, wherein the symmetric antenna and the first, second and third unbalanced antennas are disposed in the same plane.
20. A device as claimed in any one of claims 1 to 18, wherein at least one of the symmetric antenna and the first, second and third unbalanced antennas is mounted in a different plane to the other antennas.
21. A device as claimed in claim 2 or any one of claims 3 to 20 depending from claim 2, wherein the second and third unbalanced antennas are located between the first unbalanced antenna and the edge of the first conductive groundplane facing the end of the substrate where the antennas are mounted.
22. A device as claimed in any one of claims 1 to 20, wherein the second and third unbalanced antennas are located between the first unbalanced antenna and, respectively, the proximal portions of the first and second arms of the symmetric antenna.
23. A device as claimed in any preceding claim, wherein the first, second and third unbalanced antennas are connected to and driven against the first groundplane.
24. A device as claimed in any preceding claim, wherein each of the symmetric antenna and the first, second and third unbalanced antennas is provided with a respective matching circuit and at least one signal port.
25. A device as claimed in claim 24, wherein at least one of the symmetric antenna and the first, second and third unbalanced antennas is provided with at least two signal ports.
26. A reconfigurable antenna device substantially as hereinbefore described with reference to or as shown in the accompanying drawings.