Patent Description:
Portable devices such as smartphones and laptops need a number of antennas to be positioned close together while avoiding coupling between them. A variety of isolation means are known in the art, including resonators positioned between a first and a second antenna to increase the isolation between the two antennas. The resonators typically comprise a conductor having a length tuned to the frequency band in which isolation is required, which may take a variety of forms, such an inverted L shape, grounded at the end of one of the arms, such as the free end of the longer arm, positioned between the first and the second antennas. Further structures are known, such as ground planes that, when positioned between a first and second antennas, will provide isolation between them. Typically, however, such structures operate well only in a limited frequency band, outside which isolation is significantly reduced. This is a significant obstacle in the design of compact multi-frequency band antenna systems, such as MIMO antenna systems to cover multi global wireless standards.

The use of metal monocoque ('unibody') chassis for portable devices such as laptop computers restricts the positioning of antennas to regions behind non-metallic components, such as polymer inserts into the chassis, or polymer components used as part of the hinge between the keyboard and screen part of the chassis. Multi-band MIMO antenna systems for laptops operating in the LTE low band, mid band and WLAN band comprising radiators placed in the hinge region of the laptop are known, as disclosed for example in <CIT>). These prior art designs are limited in the need for a conductive coupling between the two parts of the chassis formed by the hinges, which is an undesirable design constraint, and by the positioning of the hinges, which sensitively affects the operation of the antenna system. Such design constraints render the prior art designs too narrow in scope to accommodate the range of design concepts required by manufacturers. Additionally, the feed ports in the prior art design require a first connection to the keyboard part of the chassis, and a second connection to the screen part of the chassis, which requires a cumbersome RF electrical connection between the two parts.

A further challenge is to provide a multi-band MIMO antenna system that is compact enough to fit within the hinge region of a laptop, comprising two WLAN antennas and two LTE cellular antennas, each capable of independent operation in different frequency bands, with sufficient isolation between the antennas. In particular, the hinge presents a constrained length, and the antennas need to be disposed within the length while being isolated one from another. Conventionally, isolation is achieved by providing a first WLAN antenna and a first LTE antenna within the hinge region, and a second WLAN antenna and a second LTE antenna within either the keyboard or the screen part of the chassis. The use of metallic monocoque chassis however means that all four antennas need to be provided within the hinge region.

Accordingly, embodiments of the present disclosure seek to provide improved antenna systems comprising multiple antennas and one or more isolation structures to provide isolation between the antennas. Certain embodiments of the disclosure provide an improved <NUM> port or <NUM> port multi-band MIMO antenna system for use in laptops, in which the radiating elements are provided within the hinge region of the laptop, without the need for electrical connection between the two parts of the laptop chassis.

Additionally, present reconfigurable antenna systems suffer from losses in the matching network used to couple an RF port, for example a combined transmit/receive RF port, to the antenna, such as parasitic losses in the switches typically used in prior art matching networks. It is a further aim of certain embodiments of the present disclosure to provide an improved reconfigurable antenna system that reduces or avoids such drawbacks.

<CIT> discloses an isolator assembly configured to provide isolation in each of multiple non-overlapping frequency bands and including a selection network to select one of the multiple non-overlapping frequency bands for an isolation operation. During the isolation operation, the isolator assembly prevents signal coupling between antennas that are positioned on opposite sides of the isolator assembly.

<CIT> discloses an antenna system comprising a first antenna element mutually coupled with a second antenna element, the mutual coupling between the first and second antenna elements causing a first current in the second antenna element, and a coupling element disposed at least partially between the first and second antenna elements, wherein the coupling element is mutually coupled to each of the first and second antenna elements, and wherein the coupling element is configured to induce a second current in the second antenna element that at least partially cancels the first current.

<CIT> discloses an antenna device including an antenna ground portion and first and second antenna units. The first antenna unit includes a first feed point, a first feed element connected to the first feed point, and a first parasitic element which operates upon electrically coupling to the first feed element. The second antenna unit includes a second feed point, a second feed element connected to the second feed point, and a second parasitic element which operates upon electrically coupling to the first parasitic element and the second feed element.

<CIT> discloses a multi-input multi-output (MIMO) antenna system including multiple antennas, a ground part and an isolating part. The isolating part is disposed between each two adjacent antennas. The isolating part is electrically connected to the ground part. A distance exists between an end of the antenna and an end of the isolating part. A circuit board applying the MIMO antenna system is also disclosed. Since the isolating part is disposed between each two adjacent antennas, signal interference between the antennas can be prevented, and the MIMO antenna system and the circuit board applying the same have better isolation.

<CIT> discloses an antenna system including a first antenna, a second antenna, a first isolation element, and a second isolation element. The first antenna is excited by a first signal source. The second antenna is excited by a second signal source. A first end of the first isolation element is coupled to a ground region, and a second end of the first isolation element is open. A first end of the second isolation element is coupled to the ground region, and a second end of the second isolation element is open. The first isolation element and the second isolation element are both disposed between the first antenna and the second antenna, and are configured to enhance the isolation of the antenna system.

<CIT> discloses a MIMO/diversity antenna high isolation including a printed circuit board, a plurality of antenna elements, a current conversion element connected with a common ground of the printed circuit board apart from the antenna elements at a predetermined distance, wherein the current conversion element is coupled with the antenna elements to induce an electric current from the antenna elements into the antenna elements again via the common ground.

<CIT> discloses an antenna system including a first antenna, a second antenna, and a bridge element. The first antenna is excited by a first signal source. The second antenna is excited by a second signal source. The bridge element is disposed between the first antenna and the second antenna. Both ends of the bridge element are coupled to a ground region.

Viewed from a first aspect there is provided an antenna system comprising first and second antennas as defined in claim <NUM> of the appended claims.

In some embodiments, components of the antenna system may be disposed or arranged on an elongate substrate comprising a dielectric material, the elongate substrate defining the longitudinal axis and a lateral extent or direction. The substrate may be generally rail- or bar-like in shape, and be adapted or configured for incorporation into a hinge mechanism between a screen and a keyboard of a laptop computer.

Herein for clarity a lateral direction is between the left and right sides along the longer length of the substrate, and a vertical direction is substantially perpendicular to the lateral direction. The substrate may be substantially planar and may have a thickness, or may be a three dimensional body having front and rear faces joined by an upper and a lower surface. The antennas and resonator elements may be disposed on one of both of the front and rear faces and may extend over the upper or lower faces, according to the embodiment.

In other embodiments, at least one of the first and second antennas and the isolation structure may be self-supporting, for example being cut or stamped from a metal sheet. Alternatively or in addition, at least one of the first and second antennas may be formed on a casing or frame of a mobile handset or other communications device, for example on an inner surface of the casing, or forming part of a metal frame.

The first arm of the first resonator element may be connected to ground via a short circuit. Alternatively, the first arm may be connected to ground via an impedance, optionally via a selectable impedance. The selectable impedance may be one or more of: an open circuit, a short circuit, a series capacitance, a series inductance, a series LC impedance and a parallel LC impedance.

The arms of the resonator element may be generally rectilinear, or may have other shapes, for example being tapered.

Preferably a portion of the said second arm is located adjacent to a portion of the first antenna and spaced apart therefrom, such that the coupling is achieved between the said portion of the second arm and the said portion of the first antenna. The portion of the second arm adjacent to the portion of the first antenna may be widened or flared outwardly towards the first antenna so as to enhance the coupling. In some embodiments, an end portion of the second arm may be substantially parallel to the portion of the first antenna; in other embodiments, the end portion of the second arm may be angled relative to the portion of the first antenna.

In some embodiments the first resonator element comprises a third arm connected to the lateral second arm at the end of the lateral second arm distal from the first arm and oriented at an angle (for example a right angle) to the second arm, at least a portion of the third arm being aligned substantially parallel to a portion of the first antenna and spaced apart therefrom, such that coupling is achieved between the said portion of the third arm and the said portion of the first antenna. In other embodiments, the third arm may be angled relative to the portion of the first antenna. The third arm may be arranged to extend in either or both directions alongside the portion of the first antenna.

In some embodiments the antenna system is configured to be mounted adjacent to a ground plane such that the second arm of the resonator structure is aligned with and spaced apart from an edge of the ground plane. In some embodiments the antenna system comprises a ground plane, the substrate (where provided) being mounted adjacent to the edge of the ground plane. In a typical embodiment, the ground plane may be part of a portable device, such as a ground plane on a main PCB of the device or a conducting chassis component, such as a monocoque chassis. The ground plane may take any suitable shape or configuration, and in some embodiments may be split into two or more separate ground plane components.

Strong coupling between first and second elements, such as between an antenna and a resonator element or between first and second resonator elements, has the sense herein that an electrical excitation in a first element creates an electrical excitation in a second element, such that the position and configuration of the first element relative to the second influences the strength of the excitation, as known in the art. Means to achieve strong coupling will be known to the skilled person, but in a range of embodiments strong coupling may be said to exist when one or more of the following are true: the first element is close to the second element, such as having a separation less than <NUM>; a portion of the boundary of the first element is adjacent to, and spaced apart from a portion of the boundary of the second element, for example the boundary portions being parallel; the first and second elements have a similar geometrical layout on a surface, such as comprising one or more linear portions adjacent to and spaced apart from one another; the first and second elements are separated by a distance through a material, such as a substrate, such as being on a first and second opposing faces of a common substrate; the first and second elements are spaced apart on from another on two separate substrates, the elements facing one another across a gap between the substrates.

Strong coupling may be said to exist if a resonant condition may be excited between the first and second elements. The strength of the resonance may be indicative of the strength of the coupling. A first and a second element may be coupled strongly in a first frequency band and less strongly, or coupled weakly, in a different frequency band.

A first element being adjacent to a second means herein that no further element lies between them and the distance between the two portions is less than a distance selected in order to achieve strong coupling between the first resonator element and the antenna. The distance may be selected to be <NUM> or less, such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or less. The distance will typically by greater than a minimum distance defined by the fabrication process for providing the elements, or the maximum degree of coupling required in a given design, such as greater than <NUM> or greater than <NUM>.

In some embodiments a portion of the first resonator element is located adjacent to a portion of the first antenna. In some embodiments a portion of the first resonator element has a boundary substantially parallel to a portion of the antenna, such as of a radiating element forming part of the antenna, the two parallel portions being adjacent, that is separated by a distance selected as above. The degree of coupling may be increased by increasing the length of the adjacent portions, and decreasing the distance between them.

In this way the antenna system of certain embodiments provides an effective isolation structure located between the first and second antennas, which is strongly coupled to the antenna, so providing a path to ground for radiated energy that would otherwise excite an undesirable current in the second antenna.

The specific lengths and shapes of the resonator elements can be used to optimise the coupling so that the resonator element influences the properties of the antenna, achieving improved characteristics at certain frequencies. This property uses the coupling effect between the antenna and the resonator element(s) to create other paths for the surface currents. For example, a quasi-loop antenna can be formed through appropriate coupling, with surface currents following a path from the antenna, through the resonator element(s), and back to the ground-plane. This contrasts with configurations where the surface currents simply reside in the antenna, or affect other antenna elements located nearby. This principle of the simultaneous resonator coupling and isolating property, derived from the optimisation of lengths and positions of the resonator element(s), is an important feature of embodiments.

It will be appreciated that, while in some embodiments a resonator element may be located adjacent to its associated antenna element on the same face of a substrate, other embodiments may locate the resonator element on one face of a substrate and the associated antenna on an opposed face of the substrate, or even on a separate substrate, or with one of both of the resonator element and the antenna being self-supporting. What is important is that the resonator element and the associated antenna are mutually arranged in such a way that effective coupling can take place.

The first isolation structure further comprises a second resonator element comprising a lateral elongated element located between the first antenna and the first arm of the first resonator element.

The antenna system may further comprise a second isolation structure having the same or similar features as the first, located between the first isolation structure and the second antenna. In a preferred embodiment the first and second isolation structures are substantially mirror images of each other.

In an embodiment, the antenna system further comprises a second isolation structure located between the first isolation structure and the second antenna, the second isolation structure comprising:.

Preferably the first and second isolation structures are substantially mirror images of each other.

The first and second resonator elements are located adjacent one to another, and/or adjacent to the first antenna, in order to achieve strong coupling between the said resonator elements or between a resonator element and the antenna.

The second resonator element is connected to ground. In some embodiments the fourth element is connected to ground. In some embodiments the second and/or the fourth resonator are connected via an impedance to ground, such as a fixed or a variable impedance.

In some embodiments the antenna system further comprises a matching network connected to the second resonator element, the matching network being configured to provide a selectable impedance between the second resonator element and ground. In such embodiments the impedance may be selectable between an open circuit, a short circuit to ground, a series capacitance, a series inductance, a series LC impedance and a parallel LC impedance. The matching network may be configured to be controllable using switches or a data input to select the said impedance.

In embodiments comprising a second isolation structure, the antenna system may comprise a second matching network connected to the fourth resonator element, the second matching network being configured to provide a second selectable impedance between the fourth resonator element and ground. In such embodiments the second impedance may be selectable between an open circuit, a short circuit to ground, a series capacitance, a series inductance, a series LC impedance and a parallel LC impedance. The second matching network may be configured to be controllable using switches or a data input to select the said impedance.

The first and second matching networks may be substantially identical and may form part of a common matching network, configured such that the first and second impedances are controllable to be the same, to be different, to be controlled together or to be controlled independently, by means of switches or a data input.

The second resonator element is disposed such that the second resonator element is strongly coupled to the first resonator element. For example, at least a portion of the said second resonator element may be located adjacent to a portion of the first resonator element and spaced apart from it, such that the said strong coupling is primarily between the said portion of the second resonator element and the said portion of the first resonator element. The said portion of the second resonator element may be located within a distance of <NUM> of the said portion of the first resonator element, or within a distance such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or less.

In this way, certain embodiments may provide one or more actively matched isolation structures between the first and second antennas, in which the isolation structures may be tuned to isolate the antennas in a selected frequency band when the antennas are operating in the said frequency band. Tuning may be achieved by means of selecting the impedance between the second and/or, where present, the fourth resonator elements, and ground, by means of the first and, where present, the second matching network, the impedance being selected by a control setting of a switch forming part of the matching network or a data signal received by the matching network, which may operate a switch electronically. This active impedance matching allows certain embodiments to provide a reconfigurable antenna system.

The antennas may be monopole antennas, dipole antennas, PIFAs, IFAs, PILAs, chassis antennas, loop antennas or other antennas as known in the art.

In some embodiments the first and second antennas are LTE antennas, so operating in one or more frequency bands in which the spacing of the LTE antennas is close enough to cause coupling between them. The isolation structure isolates the two LTE antennas even though they are closely spaced together. The selectable impedance between the second resonator element and ground allows the isolation structure to be tuned to isolate the two antennas in the selected frequency band(s).

The second and/or fourth resonators may comprise a connection point adjacent to the feed point of the first and/or second antennas respectively. The feed point of the first and/or second antennas may be towards the bottom side of the substrate (where provided), and the connection point(s) of the second and/or fourth resonators may similarly be located towards the bottom side of the substrate (where provided), spaced a distance apart from the said feed point(s).

In some embodiments the first resonator element comprises a third arm connected to the lateral second arm at the end of the lateral second arm distal from the first arm, the third arm being aligned substantially parallel to the first arm and spaced apart from it.

In some embodiments the end of the said third arm is adjacent to the centre of the second resonator element.

In such embodiments the first resonator element forms an inverted L-shaped resonator with a third arm extending back from the second, lateral arm of the L, parallel to the first arm. The presence of the third arm on the L shaped resonator so formed allows the length of the first resonator element to be adjusted within the spatial constraints of the system so as to allow isolation at one or a number of operating frequency bands while maintaining a narrow footprint in a direction perpendicular to the longitudinal axis. The presence of the second resonator element in proximity to the first allows the first resonator to be coupled to ground via a selectable impedance. The end of the third arm of the first resonator is separated from the second resonator by a gap dimensioned to provide a selected degree of coupling. The said end of the third arm is preferably located adjacent to a centre of the lateral extent of the second resonator element.

In some embodiments the first resonator element comprises a fourth lateral arm connected to the base of the first arm, the first resonator element being grounded at the end of the fourth arm distal from the first arm. This may provide space for a third antenna, for example a WLAN antenna, to be located above the fourth arm (for example, on an opposed surface of a main substrate), while the fourth arm allows the first resonator element to be long enough to isolate in the LTE frequency band. In this way the length of the first resonator element may be selected to provide isolation in the selected frequency band of operation of the antennas, while disposing the first resonator element conveniently to allow the third antenna to be disposed close to the isolation structure, while the fourth arm of the first resonator is tracked past the third antenna to a central ground point. The advantage of this arrangement will be seen in the embodiments described below.

The preferred configurations of the various resonators help to promote different radiation directionality for each antenna, thus promoting isolation between the antennas.

In some embodiments the antenna system further comprises a third antenna located such that the first isolation structure is disposed between the first and third antennas. A third antenna may be located between the first isolation structure and the second isolation structure.

In some embodiments the antenna system comprises the first and second antennas, first and second isolation structures disposed between the first and second antennas, and third and fourth antennas located between the first and the second isolation structures.

The antenna system may further comprise a third isolation structure, at least a portion of the third isolation structure being disposed between the third and fourth antennas. The said third isolation structure may comprise a ground plane, a portion of the ground plane being disposed between the third and fourth antennas. The third isolation structure may comprise a protrusion from a main ground plane that extends between the third and fourth antennas. The protrusion may be a protrusion, or may comprise two (or more) protrusions. In embodiments where two, substantially symmetrically arranged ground plane protrusions are disposed between the third and fourth antennas, the protrusions can be relatively thin. In particular, the total area of the two ground plane protrusions may be less than the area of a single, centrally-disposed ground plane protrusion that provides the same isolation. This can help to reduce material costs and reduce the size of the antenna system. In other embodiments, the ground plane may be configured as two (or more) separate ground planes.

In some embodiments the third and fourth antennas are WLAN antennas, operating in the <NUM> and/or <NUM> frequency bands, and so being effectively isolated from the first and second antennas (which may operate in different frequency bands) but requiring isolation from each other. This is provided by the third isolation structure and the ground plane forming part thereof.

The third isolation structure may further comprise a grounded meander resonator structure, comprising:.

The third isolation structure may comprise first and second grounded meander resonator structures, the first adjacent to the third antenna and between the third antenna and the ground plane, and the second adjacent to the fourth antenna and between the fourth antenna and the ground plane.

The antenna system of certain embodiments may be provided as part of a device adapted to be used for communication by a portable device such as a laptop computer or a tablet computer or mobile handset. Accordingly, the antenna system may form part of an antenna device comprising the antenna system and one or more further antennas. The antenna system may form part of an antenna device comprising two or more antenna systems as described herein, disposed on a common substrate or on a separate substrates mounted together on the portable device.

In a preferred embodiment, the antenna system comprises, disposed from left to right on a common substrate, the first antenna, being a first LTE antenna; the first isolation structure; the third antenna, being a first WLAN antenna; the third isolation structure, comprising a ground plane with a grounded meander resonator structure provided to either side thereof and connected thereto; the fourth antenna, being a second WLAN antenna; the second isolation structure; and the second antenna, being a second LTE antenna.

The antenna system as above may be substantially or wholly symmetrical about a vertical centre line of the substrate.

In this way, first and second LTE antennas are isolated from each other by means of the first and second isolation structures, and the third and fourth WLAN antennas are located between the first and second isolation structures and isolated from each other by the third isolation structure. This embodiment therefore provides a compact four port antenna system having two LTE antennas, isolated from each other, and two WLAN antennas, also isolated from each other.

The antennas and isolation structures may be formed as self-supporting metal components or as conductive tracks on the surface of a substrate as known in the art. The substrate may comprise a single contiguous insulating material element on which all the conductive resonator and antenna elements are formed, or may comprise an assembly of a plurality of sub-components, each having one or more of the antennas, isolation structures, or resonator elements formed or mounted thereon. It is envisaged that in typical embodiments the antennas and isolation structures may be formed on a common substrate by a metal deposition process such as printing, electroplating or electroless plating, though embodiments are not limited to the method of fabrication, and antenna systems in which one or more free standing conductive elements are disposed to form the features of the inventive system are included in the scope of the present invention as defined by the appended claims. The substrate may be a 3D substrate with the antennas and isolator structure elements formed on the 3D surface such that they are adjacent to and spaced apart from each other. In this way coupling can be provided between portions of the antennas and isolator structure elements, and between multiple isolator structure elements, so as to provide the desired isolation between the antennas. Such coupling and isolation may be derived from the 3D structure using methods known in the art, allowing the 3D structure to be designed and optimised.

The antenna system may be formed on a 3D substrate comprising a first vertical face, a second vertical face and an upper face joining the two vertical faces, wherein the first and second antennas and the one or more isolation structures are provided on the first vertical face and the third and fourth antennas and at least a portion of the ground plane between them are provided on the second vertical face. The ground plane and meander isolation structure may extend from the first vertical face over the upper face to the second vertical face.

In some embodiments the antenna system comprises a first conductive sheet component located adjacent to the top side of the substrate and a second conductive sheet component located adjacent to the bottom side of the substrate, the conductive sheet components being for example part of a case of a portable device such as a laptop. The antenna system is preferably designed and optimised for operation when mounted in the vicinity of the first and second sheet components.

The antenna system may form part of a portable device having a conductive first and second case components hinged together, the antenna system being located in a gap between the first and second case components, such as in the hinge region. The antenna system may form part of a hinge component that attaches the two case components.

The first and second resonator elements together form a resonator structure, portions of which are strongly coupled to the antenna.

Strong coupling between the first resonator element and the antenna, and between the first resonator element and the second resonator element, is defined as described above and may be achieved by means of features as described above.

The said portion of the first resonator element may be located adjacent to the said portion of the first antenna, such as within a distance of <NUM> of it, thereby achieving strong coupling between the resonator element and the antenna.

The said portion of the second resonator element may be located adjacent to a portion of the first resonator element, such as within a distance of <NUM> of it, thereby achieving strong coupling between the resonator elements.

At least a portion of the second resonator element may be substantially parallel to and spaced apart from a portion of the first resonator element.

In some embodiments the second resonator element comprises an elongated element aligned substantially parallel to the second arm of the first resonator element, and is located between the first antenna and the first arm of the first resonator element.

In some embodiments the first resonator element comprises a third arm connected to its second arm, and the end of the said third arm is adjacent to the centre of the second resonator element to achieve strong coupling between the said third arm and the central portion of the second resonator element.

In some embodiments the antenna system comprises an antenna matching network and the antenna is connected via the matching network to a port, for example a port for one or both of transmitting and receiving functions.

In some embodiments the first antenna is connected directly to a port without an intervening matching network.

The said selectable impedance may be selectable between an open circuit, a short circuit, a series capacitance, a series inductance, a series LC impedance and a parallel LC impedance.

In this way, certain embodiments provide a reconfigurable antenna operable over a wide frequency band or in a range of frequency bands that may be selected by means of the matching network connected to the second resonator element, which determines the frequency band in which strong coupling occurs between the antenna and the resonator structure comprising the first and second resonator elements, in which the antenna may be coupled directly to a port and hence to one of a receiver, a transmitter or a combined transmitter/receiver, without passing through an antenna matching network as is typical in the prior art. Antenna matching networks are known to have losses, such as due to parasitic capacitance from the switches that are connected to the antenna to control the matching characteristics of the network. Certain embodiments avoid these losses by allowing direct coupling to the port without an intervening matching network. Additionally, prior art matching networks typically comprise a first multi-way switch connected to the antenna, and a second multiway switch connected to the port, to provide a plurality of signal pathways through the network. The matching network coupled to the second resonator element needs only one multi-way switch, so reducing component count and cost.

In some embodiments the antenna system comprises:.

Preferably the first and second resonator structures are substantially mirror images of each other.

In some embodiments the antenna system comprises a first matching network connected to the second resonator element, the matching network being configured to provide a selectable impedance between the second resonator element and ground, and a second matching network connected to the fourth resonator element, the second matching network being configured to provide a second selectable impedance between the fourth resonator element and ground.

The first and second matching networks may be identical and may form part of a common matching network, configured such that the first and second impedance are controllable to be the same, to be different, to be controlled together or to be controlled independently, by means of switches or a data input.

In some embodiments the antenna is a monopole antenna. In other embodiments, the antenna may be a dipole antenna, a PIFA, IFA, PILA, chassis antenna, loop antenna or other suitable antenna. The antenna may be an LTE antenna or a WLAN antenna.

In some embodiments the antenna system forms part of a hinge component for a portable device having a conductive first and second case components hinged together, the antenna system being located in the gap between the first and second case components.

In some embodiments, first and second antenna systems may be implemented together, one at each end of a main PCB of a mobile handset or tablet. The first and second antenna systems may have substantially the same configuration as each other such that the PCB with attached antennas will display <NUM>nd order rotational symmetry, at least with respect to the antennas. In other words, if the main PCB is rotated in its plane about <NUM>°, the arrangement of the antennas and resonator elements will look the same. The main PCB may include a groundplane and the matching networks may be located on the main PCB. The antenna or antennas may be formed on or as part of a casing or frame of the mobile handset or tablet, or may be configured as self-supporting structures, or may be formed on a substrate. The first and/or second resonators may be self-supporting or formed on a substrate. In some embodiments, at least a portion of the first and/or second resonator remote from an end connected to ground (for example to the groundplane of the main PCB) may be formed on or as part of the casing or frame of the mobile handset or tablet.

It has been found for some embodiments that good isolation between the antenna(s) of the first antenna system and the antenna(s) of the second antenna system is obtained when there is strong coupling between the first and second resonator elements in each respective antenna system, and strong coupling between the first antenna and the first resonator element in each respective antenna system. It has surprisingly been found that the antenna system still works well even if there is little or no coupling between the first antenna and the second resonator element.

In further embodiments, the antenna system may further be provided with an additional antenna configured to operate in a <NUM> frequency band.

The <NUM> band is used by the <NUM>. 11ad or WiGig® communications standard. WiGig® antennas may make use of directional beam steering capabilities, and are ideally suited for very fast data transfer over short distances.

The additional <NUM> antenna may be located substantially centrally on the elongate substrate. In embodiments comprising, for example, first and second LTE antennas and optionally third and fourth WLAN antennas, the additional <NUM> antenna is disposed centrally on the substrate between the first and second LTE antennas and, where provided, the third and fourth WLAN antennas.

The additional <NUM> antenna may be provided with its own substrate, which may be conformed to or disposed on the substrate of the antenna system as a whole. The additional <NUM> antenna may be driven against a groundplane, for example the same groundplane as used by the other antennas.

Advantageously, first and second additional isolation structures or resonator elements are provided, one on either side of the <NUM> antenna, for example between the <NUM> antenna and the first and second LTE antennas. The additional isolation structures or resonator elements may be inverted-L type elements, connected to the groundplane.

In embodiments comprising first and second LTE antennas and third and fourth WLAN antennas, the first and second additional isolation structures or resonator elements may respectively be located between the first and third antennas and the fourth and second antennas.

There may be provided a portable device comprising an antenna system as described hereinabove. The portable device may further comprise first and second conductive case components hinged together, the antenna system being disposed in the hinge region between the adjacent edges of the first and second case components. Alternatively, the portable device may comprise a mobile handset or tablet.

Referring to <FIG>, a reconfigurable antenna system comprises:.

The first and second antennas have feed points <NUM>, <NUM>, and may be mounted adjacent to a ground plane <NUM>, such as forming part of a portable device.

The examples shown in <FIG> and <FIG> are not within the scope of the claims. In the embodiments of <FIG> and <FIG>, the first resonator element <NUM> comprises a third arm <NUM> connected to the lateral second arm at the end of the lateral second arm distal from the vertical first arm and oriented at a right angle to it, at least a portion of the third arm being arranged alongside a portion <NUM> of the first antenna and spaced apart from it, such that the coupling is primarily between the said portion of the third arm and the said portion of the first antenna, as indicated by the region <NUM>. The third arm <NUM> may be directed upwardly away from the edge of the groundplane <NUM>, or may be directed downwardly as shown, towards the edge of the groundplane <NUM>. The third arm <NUM> may be aligned substantially parallel to at least a portion <NUM> of the first antenna <NUM>, or may be angled relative thereto.

In some embodiments the third arm <NUM> is omitted and a portion of the second arm <NUM> is located adjacent to and parallel to a portion of the first antenna and spaced apart from it, such that the coupling is primarily between the said portion of the second arm and the said portion of the first antenna. The second arm <NUM> may be widened or flared outwardly towards the portion <NUM> of the first antenna <NUM>.

The first resonator element <NUM> may include additional meanders or sections angled relative to each other, for example to allow the first resonator element <NUM> to take a desired pathway across the substrate without interfering with other structures on the substrate.

The distance between the coupling portion of the first resonator element and the antenna may be selected according to the frequency band and the electrical properties of the materials used to form the antenna system, and may be <NUM> or less, such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or less.

Referring to the example of <FIG> (not claimed), the antenna system further comprises a second isolation structure <NUM> having the same features as the first, located between the first isolation structure <NUM> and the second antenna <NUM>, the first and second isolation structures being substantially mirror images of each other.

Referring to <FIG>, an embodiment of a reconfigurable antenna system comprises:.

In this embodiment the first resonator element <NUM> is strongly coupled to the first antenna as before, and also strongly coupled to the second resonator element <NUM> in the region <NUM> and also, optionally, in the region <NUM> also. The degree of coupling between the first and second resonator elements may be chosen by selecting the spacing of the first and second resonator elements in these regions.

The antenna system may further comprise a second isolation structure <NUM> located between the first isolation structure and the second antenna, the second isolation structure comprising:.

In this embodiment the first <NUM> and second <NUM> isolation structures are substantially mirror images of each other.

The second and fourth resonator elements are each connected via an impedance Z1, Z2 to ground, by means of a first and second matching networks <NUM>, <NUM> connected to the second and fourth resonator elements <NUM>, <NUM> and configured to provide a selectable impedance between the respective resonator elements and ground. The selectable impedance may comprise two or more capacitors selectable by way of an RF switch, for example an SP4T switch. Optionally, one switch position may consist of an "open" position, or direct connection to ground. In one exemplary embodiment, an SP4T switch may be used to switch between three capacitors: 68pF, <NUM>. 4pF and <NUM>. 5pF, as well as to a direct connection to ground. This allows switching between four modes, and enables the antenna to cover a low-band LTE frequency range of <NUM> to <NUM>. The matching networks are described in more detail in reference to <FIG> below.

The isolation structures <NUM>, <NUM> together with matching networks <NUM>, <NUM> each form an isolation system <NUM>. The first antenna <NUM> may be connected via an antenna matching network <NUM> to a first TX and/or RX port <NUM>. The second antenna <NUM> may be connected via an antenna matching network <NUM> to a second TX and/or RX port <NUM>.

In these embodiments, the electrical length of the respective antenna <NUM>, <NUM> and the tuning is being changed by the coupling with the respective second resonator <NUM>, <NUM> so as to optimise or at least improve performance in the LTE low band (or other bands as appropriate). As such, the isolation structures <NUM>, <NUM> act both as isolators and also as antenna elements.

Referring to <FIG>, a further embodiment comprises features as described for <FIG>, in which the first and second antennas are monopole antennas each having a first arm <NUM> and second arm <NUM> on each side of a feed point <NUM>. The first resonator element is disposed adjacent to the arm <NUM> of the antenna to achieve strong coupling in the region <NUM>, and close to the centre of the second resonator element <NUM> to achieve strong coupling in the region adjacent to the said centre, indicated by <NUM>. Further, one end of the second resonator element may optionally be disposed adjacent to the first arm of the first resonator element, to achieve coupling as indicated by <NUM>. The other end of the second resonator element may be disposed adjacent to the antenna <NUM>, to achieve coupling at that end region also.

Referring to <FIG>, a schematic diagram is shown of the placement of multiple antennas and isolation structures between two ground planes <NUM>, <NUM>, in which the antennas are isolated from each other by the isolation structures <NUM>, <NUM>. First and second antennas <NUM>, <NUM> are isolated from each other by isolation structures <NUM> and <NUM>, which are tuned by means of matching networks <NUM>, <NUM>. The antenna system comprises a third <NUM> and a fourth <NUM> antennas located between the first and second isolation structures, and a third isolation structure <NUM>, located between the third and fourth antennas, the third isolation structure comprising a ground plane.

Referring to <FIG>, an embodiment of a reconfigurable antenna system comprises.

Strong coupling between the first resonator element and the antenna, and between the first resonator element and the second resonator element, is defined as described above and may be achieved by means of the dimensions of the resonator elements and their disposition adjacent to one another and spaced a suitable distance from one another.

The said portion of the first resonator element is located within a distance of <NUM> of the said portion of the first antenna, or a lesser distance, as described above.

The said portion of the second resonator element is located within a distance of <NUM> of a portion of the first resonator element, thereby achieving strong coupling between the resonator elements.

Referring to <FIG>, in these embodiments the second resonator element comprises an elongated element aligned substantially parallel to the second arm <NUM> of the first resonator element, and is located between the first antenna and the first arm <NUM> of the first resonator element.

Referring to <FIG> and <FIG>, in these embodiments the first resonator element comprises a third arm <NUM> connected to its second arm, and the end of the said third arm is adjacent to the centre of the second resonator element <NUM> to achieve strong coupling between the said third arm and the central portion of the second resonator element. The coupling may be defined by the distance between the end of the third arm and the second resonator element. This distance may be made smaller than the width of the third arm, as shown in <FIG> and <FIG>.

Referring to <FIG>, in a further embodiment at least a portion of the second resonator element <NUM> is substantially parallel to and spaced apart from a portion of the first resonator element <NUM>, and further is substantially parallel to and spaced apart from a portion of the antenna <NUM>. The arrangement in <FIG> promotes strong coupling between the arm <NUM> of the antenna and both of the first and the second resonators. The total length along the conductive portion of the antenna, that along the first resonator element and that along the second resonator element may each be selected to suit the frequency band in which the antenna is configured to operate.

Referring to <FIG>, in some embodiments the antenna system comprises an antenna matching network <NUM> and the antenna is connected via the matching network to a port <NUM>, for example a port for one or both of transmitting and receiving functions.

Referring to <FIG>, in some embodiments the first antenna is connected directly to a port without an intervening matching network.

The said selectable impedance in the matching network <NUM> may be selectable between an open circuit, a short circuit, a series capacitance, a series inductance, a series LC impedance and a parallel LC impedance. An example of a matching network is described with reference to <FIG>.

In this way the embodiments in <FIG> provide a reconfigurable antenna operable over a wide frequency band or in a range of frequency bands that may be selected by means of the matching network <NUM> connected to the second resonator element <NUM>, which determines the frequency band in which strong coupling occurs between the antenna and the resonator structure comprising the first and second resonator elements, in which the antenna may be coupled directly to a port and hence to one of a receiver, a transmitter or a combined transmitter/receiver, without passing through an antenna matching network as is typical in the prior art.

It will be noted that the embodiments of <FIG> comprise first and second antennas (<NUM>, <NUM>), although the second antenna (<NUM>) is not shown in the Figures. The second antenna is disposed such that the first and second resonator elements are located between the first and the second antennas, the antennas and first and second resonator elements being as shown in the embodiments in <FIG>.

In some embodiments the said antenna system comprises:.

In this way the configurable antenna systems of the invention may be combined together to provide MIMO functionality with tuneable frequency band for each antenna, together with isolation between the first and second antennas.

Referring to <FIG>, an embodiment of a reconfigurable antenna system <NUM> is disposed on an elongated substrate <NUM> having a first face <NUM>, a second face <NUM>, elongated top <NUM> and bottom <NUM> sides, and left <NUM> and right sides <NUM>, the antenna system comprising:.

In this embodiment, the antenna system further comprises a second isolation structure <NUM> located between the first isolation structure and the second antenna, the second isolation structure comprising:.

Referring to <FIG>, the second resonator elements is connected via an impedance to ground, by means of a first matching network <NUM> connected to the second resonator element <NUM> and configured to provide a selectable impedance between the respective second resonator element and ground. The matching network <NUM> comprises a switch <NUM> operable to connect the second resonator to ground via four circuits 74a-74d, each comprising an impedance, such as an open circuit, a short circuit, a series capacitance, a series inductance, a series LC impedance or a parallel LC impedance. Preferably each of the four circuits 74a-74d comprises a different impedance. The circuits each comprise a first port, connected to the switch <NUM> as shown, and a second port, connected to ground. The switch <NUM> is configured to be operated by a digital input from a digital interface <NUM> forming part of, and/or controlled by, the portable device. The first antenna <NUM> may be connected via an antenna matching network <NUM> to a first port <NUM>.

Where present, the fourth resonator element <NUM> forming part of the second isolation structure <NUM> may be connected to a second matching network <NUM> having the same configuration as the first matching network <NUM>. Preferably the second matching network <NUM> comprises a switch <NUM> and circuits 174a-174d as for the first matching network, the impedance in each circuit 174a-174d being the same as that in the corresponding circuit 74a-74d, the switches <NUM>, <NUM> being operable together by the digital interface <NUM> to select the same impedance between the second resonator element <NUM> and ground as between the fourth resonator elements <NUM> and ground. The second antenna <NUM> may be connected via an antenna matching network <NUM> to a second port <NUM>.

In this embodiment the first matching network <NUM> is connected to the second resonator element <NUM> at a connection point <NUM> adjacent to the first antenna <NUM>, and the second matching network <NUM> is connected to the fourth resonator element <NUM> at a connection point <NUM> adjacent to the second antenna <NUM>.

In this embodiment the first resonator element <NUM> comprises a third arm <NUM> connected to the lateral second arm <NUM> at the end of the lateral arm distal from the vertical arm <NUM>, the third arm <NUM> being aligned substantially parallel to the vertical arm and spaced apart from it, and the end <NUM> of the said third arm <NUM> is adjacent to the centre of the second resonator element <NUM>.

In this embodiment the first resonator element <NUM> comprises a fourth lateral arm <NUM> connected to the base <NUM> of the vertical arm <NUM>, the first resonator element being grounded at the end <NUM> of the fourth arm distal from the vertical arm. It will be noted that the shape of the first resonator element <NUM> allows a WLAN antenna, for example, to be placed on the substrate above the fourth arm, while the fourth arm allows the first resonator element to be long enough to isolate in, for example, the LTE frequency band>>.

In this embodiment the antenna system comprises third <NUM> and a fourth <NUM> antennas located between the first <NUM> and second <NUM> isolation structures, and a third isolation structure <NUM>, located between the third and fourth antennas, the third isolation structure comprising a ground plane <NUM>, at least a portion of the ground plane being located between the third and fourth antennas. The said third isolation structure further comprises meander isolation structures <NUM> located between the third and fourth antennas <NUM>, <NUM> and the ground plane <NUM>. Instead of a single, wide ground plane <NUM> as shown in <FIG>, the third isolation structure may be formed as two relatively narrow ground plane strips 90a, 90b extending upwardly and generally parallel to each other between the third <NUM> and fourth <NUM> antennas. This is shown in <FIG>. The ground plane strips 90a, 90b may extend from a common ground plane <NUM>, or the ground plane <NUM> may be split into two (or more) separate ground plane components.

In this embodiment the first and second antennas are configured as LTE antennas, operable to transmit and/or receive in frequency bands between <NUM> and <NUM>. The antennas may be substantially identical and may be mirror images of each other, or they have minor differences, which may help to improve bandwidth. The first antenna <NUM> comprises a first arm <NUM>, and a second arm <NUM>, extending to either side of a feed point <NUM>. The second antenna <NUM> comprises a first arm <NUM>, a second arm <NUM>, extending to either side of a feed point <NUM>, and a slot <NUM> formed in the first arm.

In this embodiment the third and/or fourth antennas are WLAN antennas configured to operate in the WiFi frequency bands of <NUM> and <NUM>. Each antenna comprises an inverted L, having a vertical arm <NUM>, a lateral arm <NUM>, and a feed point <NUM> at the base of the vertical arm.

The antenna system may comprise further antennas, for example first and second GPS antennas <NUM>, <NUM>, having a folded shape and feed points <NUM>, <NUM>.

As seen most clearly in <FIG>, the embodiment is formed on a 3D substrate <NUM> comprising a first vertical face <NUM>, a second vertical face <NUM> and an upper face <NUM> joining the two vertical faces, wherein the first and second antennas <NUM>, <NUM> and the one or more isolation structures <NUM>, <NUM> are provided on the first vertical face <NUM> and the third and fourth antennas <NUM>, <NUM> are provided on the second vertical face <NUM>. The first and second antennas are wrapped over the top surface <NUM> to provide the correct dimensions on a limited height of the first face. The isolation structures are also wrapped from the first face, over the top face, to the second face. In particular, the first and second resonator elements, <NUM>, <NUM> are wrapped such that the second arm <NUM>, <NUM> is located on the upper face <NUM>. The third isolation structure <NUM> extends over both the first and second faces, and the upper face.

<FIG> show the disposition of the antenna system in the hinge region <NUM> of a laptop computer that comprises a first conductive sheet component <NUM> (a metallic screen case) located adjacent to the top side of the substrate and a second conductive sheet component <NUM> (a metallic base) located adjacent to the bottom side of the substrate.

The antenna system may form part of a portable device having a conductive first and second case components hinged together, the antenna system being located in the gap between the first and second case components, such as in the hinge region. The antenna system may form part of a hinge component that attaches the two case components.

It is a feature of the antenna system of the invention that no conductive connections are needed between the screen and base parts of the mobile device cover, and hence the hinges do not have to be conductive. Further, no electrical connections need to be made to the mobile device cover. The electrical connections to the antenna system <NUM> are made by RF coaxial cables <NUM>, which may be routed conveniently from the side of the substrate as shown in <FIG>. This is a great advantage of the antenna system of the invention over the prior art, and allows the system to be mounted between two hinges placed close to the edges of the mobile device, as shown in <FIG>.

<FIG> show the radiation characteristics of the antennas in certain embodiments, showing radiative efficiency in desired frequency bands and good isolation between them, in particular between the first and second LTE antennas and the third and fourth WLAN antennas. The good isolation is in part owing to a degree of directionality of the radiation pattern caused by the isolation structures: the left hand LTE antenna (the first antenna) having a degree of directionality to the left and the right hand LTE antenna to the right, and the left hand WLAN antenna (the third antenna) having a more pronounced degree of directionality to the left and the right hand WLAN antenna (the fourth antenna) to the right, as directed by the efficient isolation structures between them.

<FIG> shows the radiation characteristics of the first and second LTE antennas at <NUM>; <FIG> shows the radiation characteristics of the first and second LTE antennas at <NUM>; <FIG> shows the radiation characteristics of the first and second LTE antennas at <NUM>; <FIG> shows the radiation characteristics of the first and second LTE antennas at <NUM>, <FIG> shows the radiation characteristics of the first and second LTE antennas at <NUM>, <FIG> shows the radiation characteristics of the first and second WLAN antennas at <NUM> and <FIG> shows the radiation characteristics of the first and second WLAN antennas at <NUM>.

<FIG> shows a further development of the embodiment of <FIG>, with an additional <NUM> WiGig® antenna <NUM> mounted on its own substrate <NUM> which is conformed to the surface of the main substrate <NUM> and located at a central part of the main substrate <NUM> between WLAN antennas <NUM> and <NUM>. The <NUM> antenna <NUM> has a feed point <NUM>, and is driven against the groundplane <NUM>. Also shown in <FIG> are GPS antennas <NUM>, <NUM>.

<FIG> shows a variation of the <FIG> embodiment in which the GPS antennas <NUM>, <NUM> are replaced by additional isolation structures <NUM>, <NUM> in the form of L or inverted-L shaped resonators connected to the groundplane <NUM>. The additional isolation structures <NUM>, <NUM> help to isolate the <NUM> antenna <NUM> from the first and second LTE antennas which are not visible in <FIG> and <FIG>, being disposed on the other side of the substrate <NUM>.

<FIG> shows the simulated return loss and isolation characteristics in terms of S-parameters for the embodiment of <FIG>. It can be seen that the embodiment of <FIG> is in effect a five port antenna system, with ports <NUM> and <NUM> for the first and second LTE antennas, ports <NUM> and <NUM> for the first and second WLAN antennas, and port <NUM> for the <NUM> WiGig® antenna.

<FIG> is a plot showing the total efficiency of the <NUM> WiGig® antenna of the embodiment of <FIG>.

<FIG> shows a main PCB <NUM> of a mobile handset. The main PCB <NUM> includes a groundplane (not shown) and serves as a platform for various electronic components of the handset. The main PCB <NUM> is of generally rectangular shape, and has first and second opposed ends <NUM>, <NUM>. A first antenna system (not within the scope of the claims) comprises a first antenna <NUM>, a first resonator element <NUM> and a second resonator element <NUM> is arranged at the first end <NUM> of the PCB <NUM>. In this particular example, the first antenna <NUM> is configured as a monopole antenna, but other types of antennas may be employed. The first antenna <NUM> is driven against the groundplane of the PCB <NUM> by a feed <NUM>. In this example, the first antenna <NUM> is shown as a self-supporting structure, for example stamped or cut from a sheet of metal. The first antenna <NUM> is positioned generally at the left of the first end <NUM> of the PCB <NUM>, and extends laterally generally parallel to the edge of the first end <NUM>. The first antenna <NUM> includes a lateral portion <NUM> that extends towards the right of the first end <NUM> of the PCB <NUM>. The first resonator element <NUM> comprises a generally L shaped self-supporting conductive component with a first arm <NUM> connected to the groundplane on the right hand side of the PCB <NUM>, and a second arm <NUM> extending generally parallel to the edge of the first end <NUM> of the PCB <NUM>. The distal end of the second arm <NUM> is located parallel to and adjacent to the lateral portion <NUM> of the first antenna <NUM> so as to allow strong coupling therebetween. The second resonator element <NUM> is located between the first antenna <NUM> and the first resonator element <NUM> on the first end of the PCB <NUM>. The second resonator element is connected to ground, for example by way of a selectable impedance, such as a short circuit, an open circuit, a fixed or variable capacitance, or a fixed or variable impedance. The second resonator element <NUM> is a self-supporting conductive component shaped so that its distal end portion <NUM> is located adjacent and generally parallel to the second arm <NUM> of the first resonator element <NUM> so as to couple strongly therewith.

A second antenna system, essentially similar or identical to the first antenna system, is arranged at the second end <NUM> of the main PCB <NUM>, with like parts being labelled as for the first antenna system with the addition of a prime. It can be seen that the first and second antenna systems are arranged about the main PCB <NUM> with <NUM>nd order rotational symmetry - the main PCB <NUM> can be rotated through <NUM>° in its plane and the first and second antenna systems will be swapped and look similar or identical.

<FIG> shows the first antenna system at the first end <NUM> of the main PCB <NUM> in close-up. It can be seen how the components are arranged to promote strong coupling between the lateral portion <NUM> of the first antenna <NUM> and the distal end of the second arm <NUM> of the first resonator element <NUM>, and between the distal end portion <NUM> of the second resonator element <NUM> and the distal end of the second arm <NUM> of the first resonator element <NUM>.

<FIG> show an alternative configuration of the general example of <FIG> and <FIG>. In this example, a frame <NUM> surrounds the main PCB <NUM>. The frame <NUM> may be a part of the casing or housing of a mobile handset, and conveniently serves as a substrate for the first resonator element <NUM>.

A further variation is shown in <FIG>. Here, the frame <NUM> serves as a substrate not just for the first resonator element <NUM>, but also for the antenna <NUM> and for the distal end portion <NUM> of the second resonator element <NUM>. In the particular example shown in <FIG>, the antenna <NUM> is configured as a PIFA, with a feed pin <NUM> connected to the feed <NUM> and a shorting pin <NUM> connected to ground. The antenna <NUM> and the second arm <NUM> of the first resonator element <NUM> may be disposed in different planes on the frame <NUM>, for example being parallel to each other but spaced apart by a thin dielectric separation layer <NUM>. This allows strong coupling to be maintained between the antenna <NUM> and the first resonator element <NUM>. The distal end portion <NUM> of the second resonator element <NUM> runs parallel to the second arm <NUM> of the first resonator element <NUM> on the frame <NUM>, allowing strong coupling therebetween.

<FIG> is an S-parameter plot for the example of <FIG>, showing the S11 return loss for both an open circuit and a short circuit connection of the first resonator element to ground, as well as the S21 isolation between antennas <NUM> and <NUM>' for both the open circuit and short circuit configurations.

<FIG> show a comparative example where the second arm <NUM> of the first resonator element <NUM> is shortened so that it does not couple strongly with the lateral portion <NUM> of the antenna <NUM>. The S11 return loss plot in <FIG> shows that the antenna system no longer works effectively.

<FIG> show a comparative example where the second resonator element <NUM> is configured so that it still couples strongly with the first resonator element <NUM>, but less strongly (or even negligibly) with the first antenna <NUM>. The S11 return loss plot in <FIG> shows that the antenna system surprisingly still works reasonably well.

<FIG> show a comparative example where the second resonator element <NUM> is configured so that it does not couple strongly with the first resonator element <NUM>. The S11 return loss plot in <FIG> shows that the antenna system cannot be tuned effectively.

<FIG> show an example corresponding to the embodiment of <FIG> and <FIG>, mounted in a hinge region of a laptop computer, with a first antenna <NUM>, a first resonator element <NUM> and a second resonator element <NUM>. The S-parameter plot in <FIG> shows good performance, with the low frequency band being tuneable from <NUM> to <NUM>.

<FIG> show a comparative example similar to that of <FIG>, except with the second resonator element <NUM> removed. While tuning is still possible by adjusting the connection of the first resonator element <NUM> to ground by using an RF switch, for example an SP4T (single pole <NUM>-throw) switch, isolation between antennas <NUM> and <NUM> is not good.

<FIG> show a comparative example similar to that of <FIG>, except with the second resonator element <NUM> configured so as to couple less strongly with the antenna <NUM>. The S-parameter plot in <FIG> shows that the antenna system is still effective, and that the operational frequency band is shifted to higher frequencies.

<FIG> show a comparative example similar to that of <FIG>, except with the first resonator element <NUM> configured so as to couple less strongly with the antenna <NUM>. The S-parameter plot in <FIG> shows that the antenna system is still effective, and that the operational frequency band is shifted to higher frequencies.

<FIG> shows an S-parameter plot for the variations shown in <FIG> is similar to the example of <FIG> and <FIG>, except that the second resonator element <NUM> has been removed. The first arm <NUM> of the first resonator element <NUM> is connected to ground by a short circuit at <NUM>. <FIG> shows the same general arrangement, except that the first arm <NUM> of the first resonator element <NUM> is connected to ground by a variable impedance at <NUM>. An equivalent antenna system is provided at the bottom end <NUM> of the main PCB <NUM> as in <FIG>. <FIG> shows the S11 return loss for the antenna <NUM> in both short circuit <NUM> and variable impedance <NUM> configurations, as well as the S21 isolation between the antennas <NUM> and <NUM>'. Even without the second resonator element <NUM>, the antenna system can be made to work, with tuning being possible by adjusting the variable impedance <NUM>. It will be noted, however, that the isolation between antennas <NUM> and <NUM>' is not as good as for the example of <FIG> and <FIG>.

Claim 1:
An antenna system comprising first and second antennas (<NUM>, <NUM>), the second antenna (<NUM>) being disposed laterally from the first antenna (<NUM>) along a longitudinal axis, and further comprising a first isolation structure (<NUM>) disposed between the first and second antennas (<NUM>, <NUM>), the first isolation structure (<NUM>) comprising a first resonator element (<NUM>) having a first arm (<NUM>) with first (<NUM>) and second ends, the first arm (<NUM>) connected to ground at its first end (<NUM>) and extending across the longitudinal axis, and a lateral second arm (<NUM>) connected to the second end of the first arm (<NUM>), wherein at least a portion of the first resonator element (<NUM>) is disposed adjacent to a portion of the first antenna (<NUM>) such that the first resonator element (<NUM>) is strongly coupled to the first antenna (<NUM>) such that a resonant condition is created when the first antenna (<NUM>) is excited in a first frequency band, wherein the first isolation structure (<NUM>) further comprises a second resonator element (<NUM>) disposed relative to the first resonator element (<NUM>) so as to couple strongly to the first resonator element (<NUM>), and wherein the first (<NUM>) and second (<NUM>) resonator elements are not directly connected to each other, but are each separately connected to ground, and wherein the second resonator element (<NUM>) comprises a lateral elongated element located between the first antenna (<NUM>) and the first arm (<NUM>) of the first resonator element (<NUM>).