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1. WO2016097712 - ANTENNE MULTI-FONCTION MULTI-BANDE RECONFIGURABLE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

RECONFIGURABLE MULTI-BAND MULTI-FUNCTION ANTENNA

[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 laptop or tablet computer, although it may also find application in mobile phone handsets, femtocells, wireless routers or other radio communications devices.

BACKGROUND

[0002] Multiple-input multiple-output (MIMO) 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. This problem is exacerbated when attempting to combine many different wireless protocols, such as 4G LTE, WiFi, GPS, Bluetooth etc. into a device with limited space.

[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 PCB. 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 2014/020302 (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.

BRIEF SUMMARY OF THE DISCLOSURE

[0005] Viewed from a first aspect, there is provided a reconfigurable antenna device comprising a substrate incorporating a groundplane, a chassis antenna mounted at an end of the groundplane and configured to excite first radiating modes in the groundplane, and a balanced loop antenna mounted at the end of the groundplane adjacent to the chassis antenna and configured to excite second radiating modes, wherein the first and second radiating modes are substantially orthogonal to each other.

[0006] In the context of the present application, a "balanced antenna" is an antenna that has a pair of radiating arms extending in different, for example opposed or orthogonal, directions away from a central feed point. Examples of balanced antennas include dipole antennas and loop antennas. In a balanced antenna, the radiating arms are fed against each other, and not against a groundplane. In many balanced antennas, the two radiating arms are substantially symmetrical with respect to each other, although some balanced antennas may have one arm that is longer, wider or otherwise differently configured to the other arm. A balanced antenna is usually fed by way of a balanced feed. A balanced loop antenna may be understood to be a loop antenna with a balanced feed

[0007] In contrast, an "unbalanced antenna" is an antenna that is fed against a groundplane, which serves as a counterpoise. An unbalanced antenna may take the form of a monopole antenna fed at one end, or may be configured as a centre fed monopole or otherwise. An unbalanced antenna may be configured as a chassis antenna, in which the antenna generates currents in the chassis of the device to which the antenna is attached, typically a groundplane of the device. The currents generated in the chassis or groundplane give rise to radiation patterns that participate in the transmission/reception of RF signals. An unbalanced antenna is usually fed by way of an unbalanced feed.

[0008] A balun may be used to convert a balanced feed to an unbalanced feed and vice versa.

[0009] A reconfigurable antenna is an antenna capable of modifying dynamically its frequency and radiation properties in a controlled and reversible manner. In order to provide a dynamical response, reconfigurable antennas integrate an inner mechanism (such as RF switches, varactors, mechanical actuators or tuneable materials) that enable the intentional redistribution of the RF currents over the antenna surface and produce reversible modifications over its properties. Reconfigurable antennas differ from smart antennas because the reconfiguration mechanism lies inside the antenna rather than in an external beamforming network. The reconfiguration capability of reconfigurable antennas is used to maximize the antenna performance in a changing scenario or to satisfy changing operating requirements.

[0010] A chassis antenna may be understood to be an antenna that uses the groundplane as a counterpoise and excites particular radiating modes in the groundplane.

[0011] An active coaxial feed may be integrated into one side of the balanced loop antenna, and a dummy coaxial feed may be integrated into the other side of the balanced loop antenna so as to preserve symmetry of the balanced loop antenna.

[0012] The second radiating modes may be balanced radiating modes. Because the chassis antenna and the loop antenna are arranged so as to excite substantially orthogonal radiating modes, the isolation between the antennas will remain high, even with the antennas located close to each other. Indeed, the chassis antenna and the loop antenna may be integrated with each other.

[0013] Each of the chassis antenna and the balanced loop antenna has a feeding point, and the feeding points may be co-located or located very close to each other. If the geometry of the groundplane is symmetric about an axis in the plane, the antennas may be arranged to be substantially symmetric about the axis. The feeding point of each antenna may be located at the centre of the respective antenna, on the axis. Alternatively, one or both of the feeding points may be shifted slightly off-axis so as to tune the antennas for improved mutual isolation.

[0014] In some embodiments, the balanced loop antenna is fed by way of a balun.

[0015] Alternatively or in addition, if the balanced loop antenna has a substantially perfectly symmetrical geometry about the axis, it is possible to feed the balanced loop without a balun and still excite a balanced radiating mode.

[0016] In preferred embodiments, the balanced loop antenna and its feeding point are configured such that the balanced loop antenna can be fed by way of a balun at some

frequencies or frequency bands and without a balun at other frequencies or frequency bands.

[0017] The chassis antenna may comprise an elongate conductive strip with the feeding point substantially at the centre of the strip. Each end of the chassis antenna may be capacitively and/or inductively loaded so as to obtain a high input impedance at low frequencies.

[0018] The chassis antenna and the loop antenna are both mounted at an end edge of the groundplane, preferably generally parallel thereto. The end edge of the groundplane may be provided with a first groundplane extension in the form of a small, conductive metal sheet projecting from the edge of the groundplane and electrically connected thereto. The first groundplane extension may serve as the feeding point for the chassis antenna, and may be disposed substantially centrally on the end edge of the groundplane. A matching circuit for the chassis antenna, for example in the form of a monolithic microwave integrated circuit (MMIC) chip, may be mounted on the first groundplane extension. If a balun is used for feeding the balanced loop antenna, the first groundplane extension may also act as the ground for the balanced loop antenna.

[0019] Optionally, second and third groundplane extensions, also in the form of small, conductive metal sheets electrically connected to the groundplane, may be provided. The second and third groundplane extensions may be located in a plane parallel to but slightly above or below the plane of the groundplane and/or the plane of the first groundplane extension. The second and third groundplane extensions may overlap the first groundplane extension, and may be disposed symmetrically about the symmetry axis of the groundplane. The second and third groundplane extensions may serve at the feeding points for the balanced loop antenna. If no balun is used for feeding the balanced loop antenna, a matching circuit for the balanced loop antenna may be mounted on the second and/or third groundplane extensions.

[0020] The balanced loop antenna may be fed by a coaxial cable. It will be appreciated that the balanced loop antenna has two ends that need to be connected to the feeding point. In order to preserve the symmetry of the balanced loop antenna as much as possible, a first coaxial cable may be connected to or be incorporated in one end of the balanced loop antenna and a second, dummy coaxial cable may be connected to or incorporated in the other end of the balanced loop antenna. The provision of a substantially symmetric feeding cable arrangement can significantly reduce the unbalanced current on the feeding cable.

[0021] Matching circuitry is provided so as to match the impedances of the chassis antenna and the balanced loop antenna. The antennas may each be connected to a respective signal port by way of respective matching circuitry.

[0022] In some embodiments, the matching circuitry comprises an impedance transformer connected in series with a matching circuit between the respective antenna and signal port. In certain embodiments, the matching circuit may comprise first and second matching circuits connected in parallel, with an inductor connected in series with the first matching circuit (to act as a low pass filter to allow passage of RF signals below a predetermined frequency) and a capacitor connected in series with the second matching circuit (to act as a high pass filter to allow passage of RF signals above a predetermined frequency). In further embodiments, the matching circuitry may have two (or more) branches between the respective antenna and its signal port, each branch comprising an impedance transformer and a pair of matching circuits connected in parallel and provided with high and low pass filters as described above. Switches may be provided so as to isolate one or other of the branches.

[0023] The impedance transformers and matching circuits making up the matching circuitry may be selected so as to be optimised for operation at different frequencies. For example, one branch may be optimised for the LTE low band and LTE middle band (signals in the low band passing through the low pass inductor and signals in the middle band passing through the high pass capacitor). The other branch may be optimised for the LTE low band and LTE high band.

[0024] A particular advantage of certain embodiments is illustrated by the following consideration. The 4G LTE frequency spectrum typically extends from 700MHz to 2.69GHz. However, a typical balun can only cover the range from 700MHz to around 1 GHz. There are currently no small size baluns on the market that can cover the whole 700MHz to 2.69GHz frequency spectrum while still having a low insertion loss. The problem is that most balanced antennas such as dipoles and loop antennas need to be fed by way of a balun, but when a balun is used, the antenna cannot work at both the LTE low band and the LTE middle band simultaneously, because the balun is narrowband. As a result, the isolation between the chassis antenna and the balanced loop antenna will be lost because the balanced mode cannot be fully excited without a balun. However, this problem can be overcome by incorporating the feed cable for the balanced loop antenna as part of the loop, and then providing a dummy feed cable on the other half of the loop symmetrically to the active feed cable. By incorporating the feed as part of the loop antenna structure in this way, and providing a dummy feed in order to preserve symmetry, the loop antenna can be fully excited in the balanced mode without a balun, based on the symmetry properties of the loop antenna. This allows the loop antenna to operate in both the LTE low band and the LTE middle band simultaneously.

[0025] Alternatively or in addition, a balun structure may be used to feed the balanced loop antenna. In this case, the matching circuitry between the balanced loop antenna and its signal port comprises at least one impedance transformer connected in series with a matching circuit and a balun, optionally with switches to allow the components to be isolated. Advantageously, the matching circuitry comprises two or more parallel branches, each branch comprising an impedance transformer, a matching circuit and a balun connected in series. The impedance transformer and matching circuit in each branch is optimised for a different frequency band (for example, with three branches, LTE low, middle and high bands can be accommodated), and the required branch or branches can be actively switched in or out as required so as to switch the working frequency band.

[0026] Lumped elements, such as capacitors and inductors, can be integrated into the antenna device. The working frequency band(s) and performance of the antenna device can be tuned by changing the values of one or more of the lumped elements. In order to adapt the antenna device for integration into different platforms, the value(s) of the lumped element(s) can be tuned to meet the requirements of the matching circuit. Lumped elements may be incorporated in the chassis antenna, in the balanced loop antenna, and/or may provide an RF connection between the chassis antenna and the balanced loop antenna.

[0027] In some embodiments, one or more of the chassis antenna, balanced loop antenna and the groundplane is or are provided with one or more respective tuning branches, which may be integrated with the antenna device. The tuning branches can be adjusted so as to tune the resonance frequency of one or other or both of the chassis antenna and the balanced loop antenna, or to tune the isolation between the antennas and optionally to tune isolation between additional antennas, such as WiFi antennas, that may further be provided on either side of the antenna device at the edge of the groundplane. A tuning branch may take the form of a conductive strip or line parallel coupled to a portion of the respective antenna structure by way of a loaded capacitor at each end of the tuning branch. The resonant frequency of the respective antenna structure can be adjusted by adjusting the values of the loaded capacitors, and/or by adjusting the length of the tuning branch. The lower the capacitance and/or the shorter the tuning branch, the higher the resonant frequency.

[0028] In some embodiments, there may further be provided first and second additional antennas configured for other protocols, such as WiFi, GPS, Bluetooth etc. The first and second additional antennas may be disposed one to the left and one to the right of the

antenna device at the edge of the groundplane, typically arranged substantially symmetrically about the symmetry axis. In order to improve isolation between the first and second additional antennas, a band notch structure may be incorporated into the balanced loop antenna between the additional antennas. The band notch structure may, for example, comprise a quarter wavelength short circuit or parallel line, loaded-capacitor bandstop resonators. The band notch structure may be located on the edge of the groundplane, or possibly in the middle of the balanced loop antenna. In some embodiments, one band notch structure is provided on each side of the balanced loop antenna.

[0029] It is possible to operate in two bands (for example 2.4GHz and 5GHz WiFi bands) simultaneously by providing appropriate matching circuitry for each additional antenna. The matching circuitry may comprise first and second matching circuits connected in parallel. The first matching circuit is optimised for the lower-frequency band and is provided with a low pass filter in the form of an inductor. The second matching circuit is optimised for the higher-frequency band and is provided with a high pass filter in the form of a capacitor. This allows the low band and high band to be matched separately, and thus allows simultaneous matching of both bands. The first and second additional antennas may be connected to respective signal ports by way of their matching circuitry, and may be provided with switches to allow the antennas to be isolated.

[0030] In a further development, the first and second additional antennas may be integrated with the chassis antenna and the balanced loop antenna. In this embodiment, the first and second additional antennas may be located within the perimeter of the balanced loop antenna. A T-shaped groundplane extension may be provided at the centre of the edge of the groundplane, with the first and second additional antennas formed around the arms of the groundplane extension, for example as first and second U-shaped monopoles. The balanced loop antenna may be formed with a folded or meandering configuration at its left and right ends where it connects to the edge of the groundplane. This can help to improve the isolation between the first and second additional antennas. The T-shaped groundplane extension can serve as a main ground for the matching circuitry of the integrated antenna, which in this embodiment may have four ports (one for each additional antenna, one for the chassis antenna and one for the balanced loop antenna). RF components such as MMICs or LTCCs may be mounted on the T-shaped groundplane extension. The T-shaped groundplane extension also helps to isolate the first and second additional antennas from each other, for example at 2.4GHz.

[0031] Lumped elements such as capacitors and inductors may be integrated into this antenna as previously described, for example within the chassis antenna or the balanced loop antenna, and/or between the chassis antenna and the balanced loop antenna. The working frequency bands and performance of the integrated antenna can be tuned by changing or adjusting the values of the lumped elements. The values of the lumped elements can also be tuned to allow the integrated antenna to be fitted to different platforms and to meet the requirements of associated matching circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 shows a first embodiment;

Figure 2 shows the simulation results for the embodiment of Figure 1 in an LTE low band;

Figure 3 shows the simulation results for the embodiment of Figure 1 in an LTE middle band;

Figure 4 shows the simulation results for the embodiment of Figure 1 in an LTE high band;

Figure 5 shows a dual band matching circuit for the embodiment of Figure 1 ;

Figure 6 shows the simulation results for the embodiment of Figure 1 with the matching circuit of Figure 5;

Figure 7 shows a matching circuit for the balanced loop antenna of the embodiment of Figure 1 when fed by way of a balun;

Figure 8 shows the embodiment of Figure 1 provided with lumped loaded elements;

Figure 9 shows an alternative embodiment provided with tuning branches;

Figure 10 shows an exemplary tuning branch of the Figure 9 embodiment;

Figure 11 shows a further embodiment provided with first and second additional antennas;

Figure 12 shows a matching circuit for the first and second additional antennas of the Figure 1 1 embodiment;

Figure 13 shows the simulation results for the embodiment of Figure 1 1 with the matching circuit of Figure 12;

Figure 14 shows the isolation between first and second additional antennas and the chassis and the loop antennas of the Figure 11 embodiment;

Figure 15 shows a further alternative embodiment provided with first and second additional antennas;

Figure 16 shows the simulation results for the embodiment of Figure 15;

Figure 17 shows the isolation between first and second additional antennas and the chassis and the loop antennas of the Figure 16 embodiment; and

Figure 18 shows the embodiment of Figure 15 provided with lumped loaded elements.

DETAILED DESCRIPTION

[0033] A first embodiment is shown in Figure 1. There is shown a dielectric substrate 1 which is provided with is provided with a conductive groundplane 2 over a major portion of its surface. The substrate 1 with its groundplane 2 may comprise a printed circuit board or the like. Two main antennas are provided, namely a chassis antenna 3 and a loop antenna 4, the antennas 3 and 4 being integrated. By "chassis antenna" is meant an element that excites particular radiating modes in the main groundplane 3. The chassis antenna 3 may take the form of a conductive strip printed, etched or otherwise formed at one end of the substrate 1 , substantially parallel to an edge 20 of the main groundplane 2. The loop antenna 4 may take the form of a conductive loop incorporating an active coaxial feed on one side and a dummy coaxial feed on the other side so as to preserve symmetry about a symmetry plane bisecting and orthogonal to the substrate 1. The loop antenna 4 may include the edge 20 of the groundplane 2 as part of the loop, or may comprise a self-contained loop. In embodiments where the loop antenna 4 does contact the main groundplane, the point of contact may be at a centre of the edge 20 of the groundplane 2, or may be distributed symmetrically on both sides along the edge 20 of the groundplane 2. In embodiments where the loop antenna 4 is self-contained and does not contact the main groundplane 2, the loop antenna 4 can be configured as a floating antenna. The feeding points 5, 6 of the chassis antenna 1 and the loop antenna 2 are very close to each other. If the geometry of the main groundplane 3 is symmetric, the feeding points 5, 6 of the chassis antenna 3 and the loop antenna 4 will be exactly at the centre of each antenna 3, 4. The positions of the feeding points 5, 6 can be tuned slightly to get high isolation between the two antennas 3, 4. The chassis antenna 3 excites a chassis mode and the loop antenna 4 excites a balanced mode. The two modes are orthogonal, which means that isolation between the antennas 3, 4 is still quite high even when the two antennas 3, 4 are very close to each other. The loop antenna 4 in this embodiment may be a typical balanced antenna. Normally, a balun is required to excite a perfect balun mode. However, the balun mode still can be achieved without a balun if the geometry of the loop antenna 4 is perfectly symmetric.

[0034] The chassis antenna 3 is capacitively and/or inductively loaded at each end 7, 8 to obtain a high input impedance at low frequency band. Three conductive metal sheets 9, 10, 1 1 are provided at the feeding points 5, 6. The metal sheets 9, 10, 1 1 are electrically connected to the main groundplane 2 and serve as groundplane extensions. The larger, central metal sheet 9 is used to feed the chassis antenna 3. An MMIC chip (not shown) may be mounted on the metal sheet 9 and can provide an integrated matching circuit for the antenna. If a balun structure (not shown) is used to feed the loop antenna 4, the metal sheet 9 will also be the ground of the loop antenna 4. In addition, two smaller metal sheets 10, 1 1 are connected to the loop antenna 4. These two smaller groundplane extensions 10, 11 are used to connect the matching circuit (not shown) for the loop antenna 4 if no balun is used.

[0035] The loop antenna 4 is fed by a coaxial cable (not shown). The cable is integrated as part of one side of the loop antenna 4. An additional dummy cable (not shown) is symmetrically integrated as part of the other side of the loop antenna 4. The dummy cable is used to maintain the symmetry of the loop antenna 4.

[0036] Matching circuitry (not shown) is provided to match the chassis antenna 3 and the loop antenna 4. The antennas are designed to operate in the 4G LTE frequency bands.

[0037] Figure 2 gives the simulation results in terms of the S parameters at a low LTE frequency band, showing that the two antennas 3, 4 can be matched at an LTE low frequency band. The insertion loss is more than 6dB and the isolation between the two antennas is better than 15dB. The two antennas can also be tuned to work in an LTE middle band, with an insertion loss more than 10dB and an isolation better than 20dB as shown in Figure 3. The LTE high band performance is shown in Figure 4. The bandwidth at the LTE high frequency band is wider than 200MHz, the insertion loss is more than 10dB and the isolation is better than 20dB.

[0038] The chassis antenna 3 and the loop antenna 4 can also be configured to operate simultaneously at two different frequency bands. This can be achieved by way of the matching circuitry shown in Figure 5 connecting each antenna 3, 4 to a respective signal port 12, 13. The matching circuitry for each antenna 3, 4 comprises two electrically parallel branches, each branch comprising an impedance transformer 14 connected in series with a pair of matching circuits 15, 16 which are connected in parallel with each other. Matching circuit 15 is provided with an inductor 17 to act as a low pass filter, while matching circuit 16 is provided with a capacitor 18 to act as a high pass filter. Switches 19 are provided in the matching circuitry and are used to switch between different states. The impedance transformers 14, matching circuits 15, 16, inductors 17 and capacitors 18 are all independently selected so as to provide the necessary impedance matching for the frequency bands of interest. For example, one branch may be configured for LTE low band and LTE middle band operation, and the other branch may be configured for LTE low band and LTE high band operation. Due to the symmetrical arrangement of the loop antenna 4, it can be used without a balun to work at two frequency bands simultaneously.

[0039] The simulation results are shown in Figure 6, which shows the S parameters for the chassis antenna 3 and the loop antenna 4. The LTE low frequency band and LTE middle band can be used simultaneously. The insertion loss is more than 6dB in both frequency bands and the isolation is better than 20dB.

[0040] A balun structure can also be used to feed the loop antenna 4. The matching circuitry for this embodiment is shown in Figure 7. The matching circuitry between the loop antenna 4 and its signal port 13 comprises three parallel branches, each with an impedance transformer 14', 14", 14"' connected in series with a matching circuit 15', 15", 15"' and a balun 21. Switches 19 are provided to allow the branches to be individually selected for different frequency bands. The transformer 14', 14", 14"' and matching circuit 15', 15", 15"' in each branch is optimised for a different frequency band; for example the LTE low, middle and high bands.

[0041] Figure 8 shows how lumped elements 22 such as capacitors and inductors can be integrated into the antenna device. Lumped elements 22 may be integrated into either of the chassis antenna 3 or the loop antenna 4, or may be used to connect the chassis antenna to the loop antenna. The working frequency band and performance of the antenna device can be tuned by changing the values of the lumped elements 22. When the antennas are integrated into different platforms, the value of the lumped element(s) 22 can be tuned to meet the requirement of the matching circuit.

[0042] Turning now to Figure 9, different tuning branches 23 can be integrated into the chassis antenna 3, loop antenna 4 and the groundplane 2. The tuning branches 23 can be used to tune the resonant frequency of the two LTE antennas 3, 4 and/or to provide isolation between two additional antennas (not shown) such as WiFi antennas. The isolation between the two LTE antennas 3, 4 can also be tuned by the tuning branches 23.

[0043] Figure 10 shows an exemplary tuning branch 23 of the Figure 9 embodiment in more detail. The tuning branch 23 comprises a conductive strip 40 disposed generally parallel to a section of one or other of the chassis antenna 3 or loop antenna 4. The conductive strip 40 is connected at each end to the section of the antenna 3 or 4 by way of capacitors 41 , 42, which may be loaded capacitors. The resonant frequency of the antenna 3 or 4 can be adjusted by adjusting the length of the conductive strep 40 and/or by adjusting the value of the capacitors 41 , 42. Adjusting the tuning branches 23 can also tune the isolation between the antennas 3, 4.

[0044] As shown in Figure 11 , two additional antennas 24, 25 can be integrated with the two 4G LTE antennas 3, 4. The additional antennas 24, 25 may be configured as WiFi, GPS, Bluetooth or other protocol antennas. The additional antennas 24, 25 may be driven against groundplane extensions 26, 27 on either side of the LTE antennas 3, 4. The additional antennas 24, 25 are spaced apart to help improve their mutual isolation. Additional isolation may be provided by introducing two band notch structures 28 on the loop antenna 4 which will improve the isolation between the two additional antennas 24, 25. The band notch structures 28 may be a quarter wavelength short circuits. Alternatively, the band notch structure 28 could be a parallel line, loaded capacitor bandstop resonator similar in structure to the tuning branches 23 of Figures 9 and 10. The band notch structure 28 may be located at the bottom of the loop antenna 4 adjacent to the edge 20 of the groundplane 2, or in the middle of the loop antenna 4.

[0045] Figure 12 shows a suitable matching circuitry arrangement to connect the two additional antennas 24, 25 to respective signal ports 29, 30. The matching circuitry comprises first and second matching circuits 31 , 32 connected in parallel. The first matching circuit 31 is provided with an inductor 33 to act as a low pass filter, and the second matching circuit 32 is provided with a capacitor 34 to act as a high pass filter. This allows two different bands (for example, the 2.4GHz and 5GHz WiFi bands) to be matched simultaneously. Switches 19 allow the matching circuitry to be switched in and out as required.

[0046] Figure 13 shows the simulation results in terms of the S parameters for the two additional antennas 24, 25 provided with the matching circuitry of Figure 12. The insertion loss at WiFi bands 2.4GHz and 5.5GHz is more than 10dB, and the isolation is better than 20dB.

[0047] Figure 14 shows the isolation between the two WFi antennas 24, 25 and the LTE antennas 3, 4 to be more than 15dB in the low band. The isolation in the LTE middle band and high band is more than 10dB.

[0048] Figure 15 shows an alternative embodiment in which the two additional antennas 24, 25 are located within the loop antenna 4 and configured as U-shaped monopoles formed around a T-shaped groundplane extension 35. In this embodiment, opposite sides of the loop antenna 4 are provided with a meandered or folded geometry 36. This folded line geometry helps to improve the isolation of the two WiFi antennas 24, 25. The T-

shaped groundplane extension 35 is disposed at the centre of the four port antenna device and is used as the main ground of the matching circuitry for the 4 port antenna device. RF chips (not shown) such as MMICs or LTCCs can be seated on the T-shaped groundplane extension 35. The T-shaped groundplane extension 35 also provides isolation between the two WiFi antennas 24, 25 at 2.4GHz.

[0049] Figure 16 shows the simulation results for the embodiment of Figure 15 in terms of the S parameters of the two additional WiFi antennas 24, 25 with the matching circuitry of Figure 12. The insertion loss at WiFi bands 2.4GHz and 5.5GHz is less than 6dB, and the isolation is better than 20dB.

[0050] Figure 17 shows the isolation between the two WiFi antennas 24, 25 and the LTE antennas 3, 4 to be more than 15dB in the low band. The isolation in the LTE middle band and high band is more than 10dB.

[0051] Figure 18 shows how lumped elements 22 such as capacitors and inductors can be integrated into the antenna device of Figure 15. Lumped elements 22 may be integrated into either of the chassis antenna 3 or the loop antenna 4, or may be used to connect the chassis antenna to the loop antenna. The working frequency band and performance of the antenna device can be tuned by changing the values of the lumped elements 22. When the antennas are integrated into different platforms, the value of the lumped element(s) 22 can be tuned to meet the requirement of the matching circuit.

[0052] 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.

[0053] 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.

[0054] 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.