RECONFIGURABLE MULTI-BAND ANTENNA WITH FOUR TO TEN PORTS

Abstract

There is disclosed a reconfigurable antenna device having a substrate incorporating a first groundplane, a two-arm 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. The antenna device may be configured with four or five feed points, and may drive from four up to ten signal ports.

Claims

1: A reconfigurable antenna device comprising: a substrate incorporating a first groundplane, a two-arm 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, 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, wherein the respective antennas and the first groundplane are substantially coplanar or disposed in two or more substantially parallel planes, wherein each of the two-arm antenna and the first, second and third unbalanced antennas is provided with a respective matching circuit and at least one signal port, wherein the two-arm antenna and the first unbalanced antenna are provided with substantially centrally located feedlines, and wherein at least the first, second and third unbalanced antennas have feedpoints at a central portion of said edge of said first groundplane.

2: A device as claimed in claim 1, wherein the first and second arms of the two-arm antenna comprise a pair of generally L-shaped members.

3: A device as claimed in claim 2, wherein the L-shaped members are disposed in a substantially mirror-symmetrical arrangement about the longitudinal axis of the substrate.

4: A device as claimed in claim 1, wherein the second arm of the two-arm antenna is configured as a groundplane, and wherein the first arm is configured as an unbalanced antenna.

5: A device as claimed in claim 4, wherein a matching circuit for the unbalanced antenna comprising the first arm is disposed on the second arm.

6: A device as claimed in claim 4, further comprising RF front end circuitry on the second arm.

7: A device as claimed in claim 1, wherein the two-arm antenna is connected to a second groundplane configured as a conductive patch located on the substrate but separated from the first groundplane.

8: A device as claimed in claim 1, wherein the two-arm antenna is configured as a balanced antenna, the first and second arms being configured as a dipole.

9: A device as claimed in claim 1, wherein the first unbalanced antenna comprises an elongate conductive strip as a radiating element.

10: A device as claimed in claim 9, wherein the first unbalanced antenna has a length that is substantially parallel to the proximal portions of the arms of the two-arm antenna.

11: A device as claimed in claim 9, 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 two-arm antenna, with a second half being located generally adjacent and parallel to the proximal portion of the second arm.

12: A device as claimed in claim 1, wherein the first unbalanced antenna further comprises a central stub that extends towards but does not contact the first groundplane.

13: A device as claimed in claim 1, wherein the second and third unbalanced antennas each comprise a conductive strip as a radiating element.

14: A device as claimed in claim 11, 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 two-arm antenna.

15: A device as claimed in claim 12, wherein the second unbalanced antenna is located between the distal portion of the first arm of the two-arm antenna and the central stub of the first unbalanced antenna.

16: A device as claimed in claim 11, 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 two-arm antenna.

17: A device as claimed in claim 12, wherein the third unbalanced antenna is located between the distal portion of the second arm of the two-arm antenna and the central stub of the first unbalanced antenna.

18: A device as claimed in claim 1, wherein the two-arm antenna and the first, second and third unbalanced antennas are disposed in the same plane.

19: A device as claimed in claim 1, wherein at least one of the two-arm antenna and the first, second and third unbalanced antennas is mounted in a different plane to the other antennas.

20: A device as claimed in claim 1, 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.

21: A device as claimed in claim 1, 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 two-arm antenna.

22: A device as claimed in claim 1, wherein the first, second and third unbalanced antennas are connected to and driven against the first groundplane.

23: A device as claimed in claim 1, wherein at least one of the two-arm antenna and the first, second and third unbalanced antennas is provided with at least two signal ports.

24: A device as claimed in claim 1, wherein the second and third unbalanced antennas are disposed in a plane overlying a plane in which the two-arm antenna is disposed.

25: A device as claimed in claim 24, wherein the distal ends of the second and third unbalanced antennas are folded downwards through substantially 90 degrees towards the distal portions of the two-arm antenna.

26: A device as claimed in claim 1, wherein the second and third unbalanced antennas have respective distal ends that overlap but do not touch the respective distal portions of the first and second arms of the two-arm antenna, wherein the first and second opposed arms are connected together to at least one first signal port, the first unbalanced antenna is connected to at least one second signal port, the second unbalanced antenna is connected to at least one third signal port and the third unbalanced antenna is connected to at least one fourth signal port, wherein the second and third unbalanced antennas and consequently the third and fourth signal ports are configured to operate at substantially the same given frequency band or bands as each other, wherein the second unbalanced antenna and the distal portion of the first arm, during operation, electromagnetically couple with each other so as to act as a bandstop filter to reduce propagation of RF signals to the third unbalanced antenna from the second unbalanced antenna, thereby to reduce coupling between the third and fourth signal ports at the given frequency band or bands, and wherein the third unbalanced antenna and the distal portion of the second arm, during operation, electromagnetically couple with each other so as to act as a bandstop filter to reduce propagation of RF signals to the second unbalanced antenna from the third unbalanced antenna, thereby to reduce coupling between the fourth and third signal ports at the given frequency band or bands.

27: A reconfigurable antenna device comprising a substrate incorporating a first groundplane, a two-arm antenna having first and second opposed arms each having a proximal portion and a distal portion, a first unbalanced antenna located between the distal portions and adjacent to the proximal portions of the first and second arms, a second unbalanced antenna located adjacent to the first arm and a third unbalanced antenna located adjacent to the second arm, and the second and third unbalanced antennas being located in a plane that is substantially coplanar with or parallel to the substrate, wherein the second and third unbalanced antennas have respective distal ends that overlap but do not touch the respective distal portions of the first and second arms of the two-arm antenna, wherein the first and second opposed arms are connected together to at least one first signal port, the first unbalanced antenna is connected to at least one second signal port, the second unbalanced antenna is connected to at least one third signal port and the third unbalanced antenna is connected to at least one fourth signal port, wherein the second and third unbalanced antennas and consequently the third and fourth signal ports are configured to operate at substantially the same given frequency band or bands as each other, wherein the second unbalanced antenna and the distal portion of the first arm, during operation, electromagnetically couple with each other so as to act as a bandstop filter to reduce propagation of RF signals to the third unbalanced antenna from the second unbalanced antenna, thereby to reduce coupling between the third and fourth signal ports at the given frequency band or bands, and wherein the third unbalanced antenna and the distal portion of the second arm, during operation, electromagnetically couple with each other so as to act as a bandstop filter to reduce propagation of RF signals to the second unbalanced antenna from the third unbalanced antenna, thereby to reduce coupling between the fourth and third signal ports at the given frequency band or bands.

28: A device as claimed in claim 26, wherein the first unbalanced antenna is configured to act as a resonator at the given frequency band or bands, thereby to reduce coupling between the third and fourth signal ports at the given frequency band or bands.

29: A device as claimed in claim 1, further comprising at least one parasitic resonator in the form of a resonant circuit located between the second and third unbalanced antennas.

30: A device as claimed in claim 29, wherein the at least one parasitic resonator is not coplanar with the second and third unbalanced antennas.

31: A device as claimed in claim 29, wherein the at least one parasitic resonator is not coplanar with the first unbalanced antenna.

32: A device as claimed in claim 29, wherein the at least one parasitic resonator extends under or over at least a central portion of the first unbalanced antenna in a substantially parallel plane thereto.

33: A device as claimed in claim 29, wherein the at least one parasitic resonator acts as a bandstop filter at a predetermined frequency band.

34: A reconfigurable antenna device comprising a substrate incorporating a first groundplane, a two-arm antenna having first and second opposed arms each having a proximal portion and a distal portion, a first unbalanced antenna located between the distal portions and adjacent to the proximal portions of the first and second arms, a second unbalanced antenna located adjacent to the first arm and a third unbalanced antenna located adjacent to the second arm, and the second and third unbalanced antennas being located in a plane that is substantially coplanar with or parallel to the substrate, wherein the second and third unbalanced antennas have respective distal ends that are located adjacent to but do not touch the respective distal portions of the first and second arms of the two-arm antenna, wherein the first and second opposed arms are connected together to at least one first signal port, the first unbalanced antenna is connected to at least one second signal port, the second unbalanced antenna is connected to at least one third signal port and the third unbalanced antenna is connected to at least one fourth signal port, wherein the second and third unbalanced antennas and consequently the third and fourth signal ports are configured to operate at substantially the same given frequency band or bands as each other, and wherein a first resonant circuit configured to resonate in a first frequency band is located on the first unbalanced antenna between the first and second arms of the two-arm antenna; thereby to reduce coupling between the third and fourth signal ports in the first frequency band.

35: A device as claimed in claim 29, further comprising a second resonant circuit, configured to resonate in a second frequency band different to the first frequency band, located on the first unbalanced antenna between the first and second arms of the two-arm antenna; thereby to reduce coupling between the third and fourth signal ports in the second frequency band.

36: A device as claimed in claim 27, 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.

37. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

[0090] FIG. 1 shows a schematic plan view of a first embodiment;

[0091] FIG. 2 shows a schematic plan view of a second embodiment with an RF front end system placed on a floating ground plane;

[0092] FIG. 3 shows a system block illustrating an implementation of embodiments configured for 6 port simultaneous operation;

[0093] FIG. 4 shows a schematic perspective view of a third embodiment with a floating groundplane;

[0094] FIG. 5 shows a return loss plot for the embodiment of FIG. 4;

[0095] FIG. 6 shows a system block illustrating an implementation of embodiments configured for 8 port simultaneous operation;

[0096] FIG. 7 shows a schematic plan view of a fourth embodiment;

[0097] FIG. 8 shows a system block illustrating an implementation of the embodiment of FIG. 7 configured for 10 port simultaneous operation;

[0098] FIG. 9 shows a system block illustrating an implementation of embodiments configured for 4 port simultaneous operation;

[0099] FIG. 10 shows a view from above of a further embodiment;

[0100] FIG. 11 shows a view from below of the embodiment of FIG. 10;

[0101] FIG. 12 shows an underplan view of the radiating elements of the embodiment of FIGS. 10 and 11;

[0102] FIG. 13 shows a perspective view of the radiating elements of the embodiment of FIGS. 10 and 11;

[0103] FIG. 14 shows a system block illustrating an implementation of the embodiment of FIGS. 10 and 11;

[0104] FIG. 15 shows an exemplary circuit diagram for the matching networks of FIG. 14;

[0105] FIG. 16 is a plot showing the frequency response of the embodiment of FIGS. 10 and 11;

[0106] FIG. 17 shows the return loss for first and second ports of the embodiment of FIGS. 10 and 11;

[0107] FIG. 18 shows the return loss for second, third and fourth ports of the embodiment of FIGS. 10 and 11;

[0108] FIG. 19 shows the radiation pattern for the first port at 730 MHz;

[0109] FIG. 20 shows the surface current distribution on the groundplane for the first port at 730 MHz;

[0110] FIG. 21 shows the radiation pattern for the second port at 720 MHz;

[0111] FIG. 22 shows the surface current distribution on the groundplane for the second port at 720 MHz;

[0112] FIG. 23 shows the radiation pattern for the third port at 2430 MHz;

[0113] FIG. 24 shows the current distribution in the radiating elements for the third port at 2430 MHz;

[0114] FIG. 25 shows the radiation pattern for the fourth port at 2430 MHz;

[0115] FIG. 26 shows the current distribution in the radiating elements for the fourth port at 2430 MHz;

[0116] FIG. 27 shows the radiation pattern for the third port at 5542 MHz;

[0117] FIG. 28 shows the current distribution in the radiating elements for the third port at 5542 MHz;

[0118] FIG. 29 shows the radiation pattern for the fourth port at 5542 MHz;

[0119] FIG. 30 shows the current distribution in the radiating elements for the fourth port at 5542 MHz;

[0120] FIG. 31 shows the return loss for the first to fourth ports at various frequencies;

[0121] FIG. 32 shows a further embodiment configured for use with a large groundplane, for example in a laptop or tablet computer;

[0122] FIG. 33 shows the return loss for the first to fourth ports of the embodiment of FIG. 32 at various frequencies;

[0123] FIG. 34 shows a plan view of the radiating elements of a yet further embodiment;

[0124] FIG. 35 shows a top perspective view of the radiating elements of the embodiment of FIG. 34;

[0125] FIG. 36 shows a bottom perspective view of the radiating elements of the embodiment of FIG. 34;

[0126] FIG. 37 is a shadow outline showing the position of the first resonator of the embodiment of FIG. 34;

[0127] FIG. 38 is a shadow outline showing the position of the second resonator of the embodiment of FIG. 34;

[0128] FIG. 39 shows the return loss for the first to fourth ports of the embodiment of FIG. 34 at various frequencies; and

[0129] FIG. 40 shows various possible configurations for the resonators.

DETAILED DESCRIPTION

[0130] FIG. 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 two-arm 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. The first and second arms 6, 7 in this embodiment are substantially symmetrical in a mirror plane.

[0131] In this embodiment, the second arm 7 of the two-arm 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.

[0132] 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.

[0133] 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.

[0134] FIG. 2 shows a development of the embodiment of FIG. 1, where an RF 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).

[0135] FIG. 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 RF 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.

[0136] FIG. 4 shows an alternative configuration of the FIGS. 1 and 2 embodiments, with like parts being labelled as for FIGS. 1 and 2. In this embodiment, the substrate 1 has a generally rectangular shape, being configured as a PCB 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 two-arm 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.

[0137] FIG. 5 is a return loss plot for the antenna device of FIG. 4 configured for 6 port operation as shown in FIG. 3. FIG. 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 700 MHz to 6 GHz. With reference to FIG. 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 2.4 GHz WiFi band. Signal port 206 can operate in either the 5.5 GHz WiFi band, or the GNSS bands (1.16 to 1.3 GHz and 1.5 GHz). 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.

[0138] FIG. 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.

[0139] FIG. 7 shows an alternative embodiment that is generally similar to that of FIG. 1, but with the important difference that the second arm 7 of the two-arm 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 two-arm 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.

[0140] FIG. 8 is a system block showing how the five antenna feeds 8, 13, 19, 20 and 80 of the FIG. 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.

[0141] FIG. 9 is a system block showing how the five antenna feeds 8, 13, 19, 20 and 80 of the FIG. 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).

[0142] FIG. 10 shows a further embodiment of a reconfigurable antenna device. 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. Two recesses 103, 103′ are cut from the substrate 1 at one end thereof to provide a reduced width portion 104. A two-arm antenna 5 (here configured as a substantially symmetric balanced dipole antenna) having first and second radiating arms 6, 7 and a central feed 8 is formed about the reduced width portion 104 of the substrate. The first and second radiating arms 6, 7 may be formed from folded metal strips, for example copper strips. Each radiating 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 103, 103′.

[0143] 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 radiating arms 6, 7. The first unbalanced antenna 11 is formed as a conductive layer on the substrate 1 across the reduced width portion 104, generally parallel to an edge 14 of the first groundplane 2, and includes a central stub portion 12 connected to a feed 13.

[0144] There is further provided a second unbalanced antenna 15 located generally adjacent to the first radiating arm 6 and a third unbalanced antenna 16 located generally adjacent to the second radiating arm 7. The second and third unbalanced antennas 15, 16 each have a portion that extends along the substrate 1 between the first unbalanced antenna 11 and the edge 14 of the groundplane 2, and a portion that extends from the edge of the reduced width portion 4 of the substrate 1 and overhangs the respective distal portion 10, 10′ of the balanced antenna 5. The distal ends 17, 18 of the second and third unbalanced antennas 15, 16 may be folded down substantially through a right angle. It is to be noted that the distal ends 17, 18 do not contact the first and second radiating arms 6, 7, but are spaced therefrom by a distance ‘D’. The second and third unbalanced antennas 15, 16 are provided with respective feeds 19, 20. The feeds 13, 19, 20 are all co-located at a midpoint of the edge 14 of the groundplane 2. It can be seen that all of the antennas are fed from a central longitudinal zone that follows a general line of mirror symmetry along the substrate 1. This helps to promote antenna isolation, and also simplifies the feeding arrangement, since all of the matching circuits for the various antennas can conveniently be provided in a single integrated circuit or chip mounted in the central longitudinal zone.

[0145] As shown in FIG. 11, the underside of the substrate 1 is provided with a parasitic resonator 21 in the form of a pair of oppositely-directed C-shaped conductive tracks, one nested inside the other. The parasitic resonator 21 is located on the underside of the substrate 1 generally opposite to the location on the topside of the substrate 1 of the central stub portion 12 of the first unbalanced antenna 11, which is between proximal ends of the second and third unbalanced antennas 15, 16. In this example, the parasitic resonator 21 is located in a plane substantially parallel to but not coplanar with the plane in which the second and third unbalanced antennas 15, 16 are located. Moreover, the first unbalanced antenna 11 is coplanar with proximal portions of the second and third unbalanced antennas 15, 16.

[0146] FIGS. 12 and 13 show, respectively, an underplan and a perspective view of the radiating elements and parasitic resonator of the embodiment of FIGS. 10 and 11, with the substrate 1 being omitted for clarity.

[0147] FIG. 14 is a system block showing how the balanced antenna 5 (with radiating arms 6, 7), first unbalanced antenna 11, second unbalanced antenna 15 and third unbalanced antenna 16 can be connected to four signal ports 22, 23, 24 and 25 by way of four matching circuits or matching networks 26, 27, 28, 29.

[0148] FIG. 15 shows details of one possible arrangement of matching networks, each matching network comprising a suitable arrangement of capacitors and inductors, and each matching network being tuned to a predetermined frequency band. It will be apparent to those of ordinary skill that different arrangements of capacitors and inductors may be used.

[0149] FIG. 16 is a plot showing the frequency response of the embodiment of FIGS. 10 to 15, demonstrating that the antenna device can operates in several well-defined frequency bands.

[0150] FIG. 17 shows the return loss for the first and second ports 22 and 23 of this embodiment, the first port 22 being connected to the balanced antenna 5 and the second port 23 being connected to the first unbalanced antenna 11. The first port 22 shows a good response with good isolation at around 730 MHz, while the second port 23 shows a good response at around 720 MHz.

[0151] FIG. 18 shows the return loss for the second, third and fourth ports 23, 24, 25 of this embodiment, the second port 23 being connected to the first unbalanced antenna 11, the third port 24 being connected to the second unbalanced antenna 15 and the fourth port 25 being connected to the third unbalanced antenna 16 The third port 24 and fourth port each show a good response with good isolation at around 2430 MHz and 5542 MHz.

[0152] FIG. 19 shows the radiation pattern associated with the balanced antenna 5 and the first port 22 at 730 MHz, with FIG. 20 showing the associated surface current distribution on the groundplane and in the radiating elements.

[0153] FIG. 21 shows the radiation pattern associated with the first unbalanced antenna 11 and the second port 23 at 720 MHz, with FIG. 22 showing the associated surface current distribution on the groundplane and in the radiating elements.

[0154] FIG. 23 shows the radiation pattern associated with the second unbalanced antenna 15 and the third port 24 at 2430 MHz, with FIG. 24 showing the associated current distribution in the radiating elements.

[0155] FIG. 25 shows the radiation pattern associated with the third unbalanced antenna 16 and the fourth port 25 at 2430 MHz, with FIG. 26 showing the associated current distribution in the radiating elements.

[0156] FIG. 27 shows the radiation pattern associated with the second unbalanced antenna 15 and the third port 24 at 5542 MHz, with FIG. 28 showing the associated current distribution in the radiating elements.

[0157] FIG. 29 shows the radiation pattern associated with the third unbalanced antenna 16 and the fourth port 25 at 5542 MHz, with FIG. 30 showing the associated current distribution in the radiating elements.

[0158] As clearly demonstrated in FIGS. 23 to 30, the parasitic resonator 21 acts as a band-stop filter to improve isolation between the third and fourth ports 24, 25 at the higher frequencies, here 5542 MHz. Isolation is only at the higher frequencies because the resonator 21 is relatively short.

[0159] FIG. 31 shows the return loss for all four ports, with the first port 22 operating at 1550 MHz and 2690 MHz, the second port 23 at 2690 MHz, the third port 24 at 2400 MHz and 5200 MHz, and the fourth port 25 at 2400 MHz and 5200 MHz.

[0160] FIG. 32 shows an alternative embodiment, in which an antenna device as herein disclosed is mounted at an offset location on a longer edge of a large substrate 1′ with a large groundplane 2′. The large substrate 1′ may be a PCB of a tablet or laptop computer.

[0161] FIG. 33 shows the return loss for all four ports of the embodiment of FIG. 32, with the first port 22 operating at 720 MHz and 1490 MHz, the second port 23 at 720 MHz, the third port 24 at 2500 MHz and 5200 MHz, and the fourth port 25 at 2500 MHz and 5200 MHz.

[0162] FIGS. 34 to 38 show a yet further embodiment, with like parts being labelled as for the previous embodiments. The substrate 1 and groundplane 2 are omitted in the Figures for the sake of clarity. In this embodiment, the second and third unbalanced antennas 15, 16 do not have distal ends that are folded downwardly. Instead, the second and third unbalanced antennas 15, 16 have distal ends that are substantially coterminous with the ends of the first unbalanced antenna 11, and do not extend over the distal portions 10, 10′ of the balanced antenna 5. Moreover, first and second parasitic resonators 26, 27 are provided on the underside of the substrate (not shown). The first parasitic resonator 26 is a relatively small bracket-shaped element located under and substantially opposite to the central stub 12 of the first unbalanced antenna 11. The second parasitic resonator 27 comprises a pair of relatively large, nested C-shaped elements arranged facing in opposite directions under a central portion of the first unbalanced antenna 11 on the underside of the substrate. The first, smaller parasitic resonator 26 is the right electrical length to provide isolation between the third and fourth ports 24, 25 at 5120 MHz, while the second, larger parasitic resonator 27 is the right electrical length to provide isolation between the third and fourth ports 24, 25 at 2430 MHz.

[0163] FIG. 39 shows the return loss for all four ports of the embodiment of FIG. 38, with the first port 22 operating at 710 MHz and 1500 MHz, the second port 23 at 710 MHz, the third port 24 at 2430 MHz and 5120 MHz, and the fourth port 25 at 2430 MHz and 5120 MHz.

[0164] FIG. 40 shows various different configurations for the parasitic resonators 21, 26, 27, including C-shaped, U-shaped, H-shaped, O-shaped, T-shaped, L-shaped and I-shaped. Certain shapes of parasitic resonator, for example C-shapes and U-shapes, have a mouth portion that may be denoted as a gate, and a capacitor and/or inductor may be placed across the gate.

[0165] 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.

[0166] 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.

[0167] 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.