[0001] This disclosure relates to a switching arrangement to drive closely-arranged radiating elements in differential (balanced) or common (unbalanced) mode in order to achieve beam-forming between the two orthogonal modes.

BACKGROUND

[0002] 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.

[0003] 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.

[0004] A balun may be used to convert a balanced feed to an unbalanced feed and vice versa.

[0005] 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. BRIEF SUMMARY OF THE DISCLOSURE

[0006] Viewed from a first aspect, there is provided an antenna arrangement comprising at least first and second radiating elements, each provided with an associated RF switch, wherein the associated RF switches are operable so as selectively to connect either the first or the second radiating element individually to an RF port such that the first or the second radiating element respectively operates in an unbalanced mode, or to connect the first and second radiating elements together to the RF port such that the first and second radiating elements operate together in a balanced mode, wherein the first and second radiating elements are electrically connected to each other by a link connection when either the first radiating element or the second radiating element is operating in the unbalanced mode.

[0007] The RF port may be provided with an associated RF switch operable so as selectively to connect the RF port to the first radiating element, or to the second radiating element, or to both first and second radiating elements together. The RF switch associated with the RF port is operated together with the RF switches associated with the first and second radiating elements so as to provide different switchable RF pathways between the RF port and one or other or both of the first and second radiating elements.

[0008] The RF switches may be operated and controlled by appropriate control circuitry.

[0009] The first and second radiating elements may be connected together to the RF port by way of a balanced mode matching circuit when operating together in the balanced mode. Where required, the balanced mode matching circuit may include a balun.

[0010] The first radiating element may be connected to the RF port by way of a first unbalanced mode matching circuit when operating in the unbalanced mode.

[0011] The second radiating element may be connected to the RF port by way of a second unbalanced mode matching circuit when operating in the unbalanced mode.

[0012] However, in some embodiments, for example where the first and second radiating elements are specifically tuned to predetermined frequencies, it may not be necessary to provide matching circuitry. In addition, the feed from the RF port may incorporate appropriate stripline elements so as to perform a balun function for a differential mode antenna arrangement.

[0013] The link connection may force an excitation voltage of the first and second radiating elements to be the same when either of the first and second radiating elements is operating in the unbalanced mode. The link connection may reduce coupling and produce an unbalanced mode (common-mode) radiation pattern that is suitably different from the balanced (differential) mode to be used for beam-forming techniques. The link connection may be configured to uncouple the radiating elements and make them act as one when driven in unbalanced mode.

[0014] The link connection may be directly between the first and second radiating elements. In other words, one end of the link connection may be directly connected to the first radiating element and the other end of the link connection may be directly connected to the second radiating element.

[0015] Alternatively, the link connection may be situated between the RF switches associated with the first and second radiating elements and the RF switch associated with the RF port. In these embodiments, one end of the link connection is directly connected to a part of the RF pathway between the RF port and the first radiating element at a position between the RF switch associated with the RF port and the RF switch associated with the first radiating element. The other end of the link connection is directly connected to a part of the RF pathway between the RF port and the second radiating element at a position between the RF switch associated with the RF port and the RF switch associated with the second radiating element.

[0016] The link connection may be situated between the radiating elements and the matching circuit(s).

[0017] In some embodiments, the link connection includes an RF switch operable selectively to connect the first radiating element to the second radiating element when one or other of the radiating elements is operating in the unbalanced mode, or to disconnect the first radiating element from the second radiating element when both radiating elements are operating together in the balanced mode. There may be provided control circuitry or a control unit to operate the RF switch in the link connection.

[0018] The link connection may be a direct galvanic connection, or may include at least one lumped component selected from the group consisting of: resistors, capacitors, and inductors. Appropriate selection of lumped components can help to shape the resulting radiation pattern as required.

[0019] The antenna arrangement may be configured such that an RF path from the RF port to the first radiating element is of a different length to an RF path from the RF port to the second radiating element when either the first or the second radiating element is operating in the unbalanced mode. This may help to promote two distinct unbalanced (or common chassis) modes depending on which of the first and second radiating elements is directly driven from the RF port. [0020] The first and second radiating elements may take any suitable configuration, including but not limited to folded monopoles and coupled loop monopoles.

[0021] The antenna arrangement may comprise multiple pairs of first and second radiating elements in a nested configuration. The multiple pairs of first and second radiating elements may be disposed in substantially the same plane. Alternatively, the multiple pairs of first and second radiating elements may be disposed in substantially orthogonal planes.

[0022] The antenna arrangement may comprise first and second substantially symmetrical pairs of first and second radiating elements. Such an antenna arrangement may be mounted at an edge of a groundplane of a mobile communications device, the first pair of radiating elements being located about one third of a distance along the edge, and the second pair of radiating elements being located about two thirds of the distance along the edge.

[0023] Embodiments of the present disclosure may be particularly suited for MIMO or beam-forming operations.

[0024] Embodiments of the present disclosure provide a switching arrangement to drive closely-arranged radiating elements in differential (balanced) or common (unbalanced) mode in order to achieve beam-forming between the two orthogonal modes. Embodiments may make use of an arrangement of switching and matching circuits to drive the radiating elements in the two modes: differential (balanced) and common (unbalanced) in order to achieve beam-forming functionality through different radiation patterns having main lobes in substantially different directions.

[0025] There is also disclosed the provision of a 'key connection' or link connection between radiating elements when driven in unbalanced mode in order to create similar voltages, reduce coupling and produce a common-mode radiation pattern that is suitably different from the differential mode to be used for beam-forming techniques. The link connection may be configured to uncouple the radiating elements and make them act as one when driven in unbalanced mode. The link connection can be permanent or switched.

[0026] Embodiments of the disclosure enable the generation of differential (balanced) and chassis (unbalanced) radiation patterns that are suitable for use in beam-switching.

[0027] Embodiments of the disclosure enable beam-switching without the need for complicated phase circuitry.

[0028] Embodiments of the disclosure provide a more cost-effective technique for beam- forming.

[0029] Many new implementations of wireless standards feature provisions for beam- steering or beam-forming. This enables a transmitter to guide data streams more accurately to a receiver node, and not broadcast over a widespread area. Such techniques help to support more users, enhance reliability, and re-use of frequency codes within a confined space.

[0030] A simple version of beam-steering can be achieved using the inherent differences in radiation patterns from different radiating modes or antenna types. For example, copending application WO 2016/097712 by the present applicant describes a multi-radiator antenna arrangement using a balanced and an unbalanced radiator. Isolation of the radiating elements, positioned in close-proximity, is achieved by the orthogonality of the radiating modes. Balanced antennas create specific radiating patterns through surface currents situated mainly on the opposing balanced radiating elements, whereas an unbalanced antenna typically uses a portion of the ground-plane as a counterpoise for radiating modes and therefore induces surface currents in this region. These modes are typically termed chassis modes.

[0031] The first balanced mode from the balanced antenna creates main lobes in substantially orthogonal directions to the unbalanced, or chassis-mode.

[0032] Examples of beam switching effects being utilised for steering can be found in copending application GB1701613.0 by the present applicant, describing a nested arrangement of balanced and unbalanced radiating elements. Such a compact arrangement utilises the inherent isolation of the orthogonal radiating patterns whilst enabling MIMO support in portable devices. Similarly, patent applications GB170161 1.4 and PCT/GB2018/050285, also by the present applicant, describe arrangements of radiator arrays, arranged in 3D space, and configured to be driven as either balanced or unbalanced elements, therefore enabling beam-forming.

[0033] In order to create an electrically-small antenna arrangement, capable of acceptable operating characteristics over a wide range of frequencies, for example the 2.4 and 5GHz bands in the case of WLAN, switching and, in some cases, matching networks are required. The configuration is preferably designed to be compact and to use only a small number of switches to perform the mode switching.

[0034] Certain embodiments of the present disclosure may provide a driving configuration that is compact, uses the least number of switches to perform the mode switching, and is compact enough to be used in hand portable wireless devices such as laptops, tablets and mobile telephone equipment.

BRIEF DESCRIPTION OF THE DRAWINGS [0035] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 shows a prior art antenna arrangement in schematic form;

Figure 2 shows an antenna arrangement of a first embodiment in schematic form; Figure 3 shows a bow-tie implementation of the first and second radiating elements of an embodiment in schematic form;

Figure 4 shows two antennas of the embodiment of Figure 3 mounted at opposite ends of an edge of a groundplane contained in a laptop computer screen panel;

Figure 5 shows a radiation pattern generated by the prior art antenna arrangement of Figure 1 operating in unbalanced or chassis mode;

Figure 6 shows a radiation pattern generated by the prior art antenna arrangement of Figure 1 operating in balanced or differential mode;

Figure 7 shows a radiation pattern generated by the antenna arrangement of Figure 2 operating in balanced or differential mode;

Figure 8 shows a radiation pattern generated by the antenna arrangement of Figure

2 operating in unbalanced or chassis mode;

Figure 9 shows a variation of the embodiment of Figure 2, with a lumped component included in the link connector;

Figure 10 shows a variation of the embodiment of Figure 2, with a switch provided in the link connector;

Figure 11 shows a variation of the embodiment of Figure 2, with the link connector directly connected between the first and second radiating elements;

Figure 12 is a schematic illustration of different ways in which the first and second radiating elements may be arranged in 3D space;

Figure 13 shows an antenna arrangement of a second embodiment in schematic form, with first and second pairs of first and second radiating elements nested in the same plane;

Figure 14 shows an antenna arrangement of a second embodiment in schematic form, with first and second pairs of first and second radiating elements nested in orthogonal planes;

Figure 15 shows a simulation of surface currents excited in the groundplane of the embodiment of Figure 4 for different operating modes of the antenna arrangement; Figure 16 shows an alternative positioning for two antennas on an edge of a groundplane contained in a laptop computer screen panel;

Figure 17 is a schematic front elevation of a third embodiment mounted at an edge of a groundplane;

Figure 18 is a schematic rear elevation of the embodiment of Figure 17;

Figure 19 is a feed circuit schematic for the embodiment of Figure 17;

Figures 20A, 20B and 20C shows radiation patterns generated by the antenna arrangement of Figure 17 operating respectively in left unbalanced, balanced, and right unbalanced modes at 2.45GHz;

Figures 21 A, 21 B and 21 C shows radiation patterns generated by the antenna arrangement of Figure 17 operating respectively in left unbalanced, balanced, and right unbalanced modes at 5.5GHz;

Figure 22 is a schematic front elevation of a fourth embodiment mounted at an edge of a groundplane;

Figures 23A, 23B and 23C shows radiation patterns generated by the antenna arrangement of Figure 22 operating respectively in left unbalanced, balanced, and right unbalanced modes at 2.45GHz; and

Figures 24A, 24B and 24C shows radiation patterns generated by the antenna arrangement of Figure 22 operating respectively in left unbalanced, balanced, and right unbalanced modes at 5.5GHz.

DETAILED DESCRIPTION

[0036] A prior art circuit arrangement to address an antenna arrangement comprising two radiating elements, capable of being driven in balanced (differential) or unbalanced (common or chassis) modes, is shown in Figure 1.

[0037] The antenna arrangement comprises first and second radiating elements 1 , 2. Each radiating element 1 , 2 is respectively addressed by a single-pole, double-throw RF switch 3, 4, allowing selective connection of the respective elements 1 , 2 to matching circuits M1 , M2 and M3. Matching circuit M3 includes a balun for supporting a balanced antenna mode. Each matching circuit is then addressed via a single-pole, 3-throw RF switch 5 to an RF port 6. This arrangement provides three modes of operation:

1) Switch 3 connected to M1 , switch 4 connected to M2, switch 5 connected to M1 - left radiator 1 operates in unbalanced mode (Chassis mode 1); 2) Switch 4 connected to M2, switch 3 to M 1 , switch 5 connected to M2 - right radiator 2 operates in unbalanced mode (Chassis mode 2);

3) Switch 3 connected to M3, switch 4 connected to M3, switch 5 connected to M3 - left and right radiators 1 , 2 operate together in a balanced radiating mode.

[0038] Although Figure 1 shows a particular arrangement having switching and matching circuitry and a balun for supplying the differential mode, such circuitry is not always required. For example, this may be the case for specifically tuned antennas and where the feed incorporates appropriate stripline elements to function as a balun for the differential mode antenna.

[0039] In the arrangement of Figure 1 , which uses RF switches 3, 4, 5 to connect various close-proximity radiating elements 1 , 2, there will still be some unwanted electrical communication, i.e. the isolation in the switches themselves will not be perfect. In addition, the close proximity of the radiating elements 1 , 2 will also create a degree of coupling when driven. When seeking to provide beam-forming, it is desirable to generate clean radiation modes that are differentiated. RF electrical communication across switches will tend to deteriorate the differentiated modes and lead to changed radiation patterns.

[0040] The radiating patterns produced by the arrangement of Figure 1 may be too similar to be used in beam-forming techniques. This can be due to coupling and poor switch isolation.

[0041] Figure 2 shows an embodiment of the present disclosure that seeks to address the problems caused by coupling and poor switch isolation. In Figure 2, each radiating element 1 , 2 is connected to the RF port 6 via RF switches 3, 4, through switching and matching circuits M1 , M2 and M3 and via mode selector switch 5. An important difference between this arrangement and that of Figure 1 is the provision of a link connection 7, which couples the M1 and M2 circuits prior to the RF switches 3, 4. This forces the excitation voltage of the two radiating elements 1 , 2 in the unbalanced modes (Chassis mode 1 and Chassis mode 2 above) to be the same.

[0042] It has been experimentally found that this link connection 7 may alleviate the coupling of the radiating elements 1 , 2 and the isolation problems of the switches 3, 4 enough to create a common-mode which forms a suitably different radiation pattern from the differential, or balanced mode (mode 3), to be useful for beam-forming techniques. In theory, the coupling between the radiating elements 1 , 2 that affects the radiation pattern is nulled by forcing both radiating elements 1 , 2 to the same voltage potential. This negates the effects of the coupling and effectively uses both radiating elements 1 , 2 for each of the unbalanced chassis modes.

[0043] Again, although switching and matching circuitry are shown in Figure 2, such circuitry may not always be required. This may be the case for specifically tuned antennas and where the feed incorporates a balun for the differential mode antenna, for example.

[0044] Figure 3 shows a specific embodiment used in the following simulation analysis. The embodiment of Figure 3 comprises two bow-tie shaped radiating elements 1 , 2 located at the end of a common ground-plane 8 leading to a feeding cable 9.

[0045] Two such antenna arrangements can form a pair of WLAN antennas located in the top of a laptop screen or lid arrangement 10, as shown in Figure 4.

[0046] Without the link connection 7, i.e. using the switching arrangement of Figure 1 to select the balanced and chassis modes, the simulated radiation patterns at 5.5GHz are illustrated in Figures 5 and 6. Both chassis (Figure 5) and balanced (Figure 6) radiating patterns are generally spherical in nature and have similar features and main lobes oriented in the same direction. This means that the switch between the two patterns cannot effectively be used for beam-forming techniques.

[0047] Using the switching circuit of Figure 2 with the link connection 7, the simulated radiation patterns at 5.5GHz are illustrated in Figures 7 and 8. The chassis mode pattern (Figure 7) and the balanced mode pattern (Figure 8) are now suitably dissimilar, with main lobes oriented in perpendicular directions, which is much more suitable for beam-forming techniques.

[0048] The link connection 7 need not be limited to a direct or galvanic electrical connection between the matching circuits M1 , M2. The link connection 7 may contain or include other passive components or lumped components 11 such as a resistor, capacitor or inductor, or combinations of these components to achieve the required radiation pattern. Such an arrangement is illustrated in Figure 9.

[0049] The link connection 7 can also be switched in and out of the circuit, for example, with the use of an RF switch 12. The connection 7, and therefore the forced common mode, can now be forced to be on, or remain off, depending on the radiation patterns required. This example is illustrated in Figure 10.

[0050] The link connection 7 is also not limited to the position between the main mode selector switches 3, 4 and the matching circuitry M1 , M2, M3. The link connection 7 could be made directly between the radiating elements 1 , 2 as shown in Figure 1 1. [0051] This specific example would need to include a switch 12 in the link connection 7, as otherwise the radiators 1 , 2 would be shorted together when operating in the balanced mode. More specifically, when switches 3 and 4 are switched to M1 and M2, the link connection switch 12 is closed in the common-mode operation. For differential mode operation, where the antenna elements 1 , 2 are balanced, switches 3 and 4 are positioned to connect to M3L and M3R, and the link connection switch 12 is open, in order for the radiating elements 1 , 2 to perform correctly.

[0052] It should also be noted that the shape of the radiating elements 1 , 2 shown in the exemplary embodiments is not limiting. The radiator shapes can be any shapes that are required by the antenna solution and particular operating characteristics.

[0053] It should additionally be noted that in this specific example the radiating elements 1 , 2 are arranged as two linearly-opposed L-shaped elements. However, there are many other ways to arrange such elements in 3D space, as shown in Figure 12.

[0054] Particular arrangements of radiating elements could be chosen in order to best reflect the beam directions required in the specific antenna solution being addressed.

[0055] Another embodiment of the present disclosure makes use of stacked arrangements of radiating elements 1 , 2; 1', 2'. In the case of linearly-opposed L-shaped radiators, as discussed above, such stacked arrangements could take the form shown in Figure 13 where the radiators 1 , 2; 1 ', 2' are nested in the same plane and can be driven in balanced and unbalanced mode by way of a link connection 7.

[0056] Similarly, the nested arrangement could take the form of a second set of radiating elements 1 ', 2' being arranged perpendicularly to a first set of radiating elements 1 , 2, as shown in Figure 14.

[0057] Such arrangements, shapes, or nesting of radiating elements would be dictated by the constraints of the device in which the antenna is to be located, and the beam-forming performance required.

[0058] It is commonplace when providing radiating elements at a top (or other) edge of a laptop computer screen 10 or tablet device to locate the radiating elements at opposite ends of the edge of the laptop screen 10, or tablet device, as traditionally this provides maximum isolation. An example is shown in Figure 4. However, it has been discovered that this particular arrangement can have a significant effect on the direction of the main radiation lobes.

[0059] An analysis of the resultant surface currents from various modes of driving, of the left-hand radiating elements 1 , 2 (both chassis and balanced modes) was performed and the results are summarised in Figure 15. Each picture shows the driven radiating elements 1 , 2 situated at the top-left edge of the device (ground-plane) and the simulated plot of surface currents generated on the ground-plane in that particular driven mode.

[0060] It is clear from each of the various radiating modes that there are major surface currents along the top edge and down the side edge. Such currents tend to skew any radiation patterns (main lobes) towards the diagonal, which in turn deteriorates well defined lobes emanating out of the ground plane and out from the side of the ground plane.

[0061] It was found that this effect could be reduced by relocating the radiating elements 1 , 2 away from the very corners of the top edge of the device 10 (and therefore away from the corners of the ground-plane) and moving them closer inwards. The optimum spacing in order to balance reduction of the skewing effects and maintaining isolation was found to be when the pairs of radiating elements 1 , 2 were placed at approximately the 1/3 width vertexes of the top edge of the ground-plane as shown in Figure 16.

[0062] The relatively simple radiating element 1 , 2 design of the Figure 3 embodiment requires matching circuitry in order to operate effectively in dual 2.4/5GHz bands. Incorporation of matching circuitry M1 , M2, M3 does have an impact on the overall efficiency of the antenna, as this is in addition to the switching for the common-mode and balanced operation. It may therefore be beneficial to change the design of the radiating elements 1 , 2 to reduce or remove the need for matching and to operate efficiently over the dual bands of 2.4/5GHz required by WLAN. Some further embodiments of the present disclosure do not require matching for the unbalanced chassis (common) modes, although matching for the balanced mode may still be required.

[0063] Figures 17 and 18 respectively show a front and a rear elevation of a further embodiment that does not require matching circuitry for the unbalanced chassis modes. The conductor design of the antenna arrangement comprises two substantially square or pentagonal elements 13, 14 spaced apart from each other either side of a centreline of a dielectric substrate 15. The substrate 15 may be mounted at an edge of a laptop screen 10 or tablet device that has a ground-plane 16. A narrow elongate ground-plane extension 17 may be provided so as to define a space for a coaxial feeding cable 9 (not shown in Figure 17 and 18) between the substrate 15 and the ground-plane 16. The elements 13, 14 are disposed on the substrate 15 such that they do not touch the top edge of the ground-plane 15 or the ground-plane extension 17. Each element 13, 14 is respectively provided with a folded monopole 18, 19 extending from a top corner of the element 13, 14, along a top edge of the substrate 15, down a side edge of the substrate 15, and then back towards (but not touching) the element 13, 14. The folded monopoles 18, 19 extend mutually away from each other. The design is substantially symmetrical about the centreline of the substrate 15. [0064] Figure 18 shows a rear elevation of the substrate 15 on which is formed a large ground-plane extension 20 which serves to act as a portion for the feeding circuitry (common-mode and balanced switching) to be situated. It can be seen that the ground-plane extension 20 is situated opposite a space between the elements 13, 14 on the opposed surface of the substrate 15. In the illustrated embodiment, the elements 13, 14 each have a cutaway corner and this shape is mirrored in the shape of the ground-plane extension 20.

[0065] Figure 19 is a schematic view of the feeding circuitry that is situated on the ground- plane extension 20. As discussed previously, there are three modes in which the antenna arrangement can be driven: (i) Chassis mode 1 (CA1), using the RF switches 3 and 5 to address the common chassis mode from the left, with the RF switch 4 connecting the link connection 7 to the radiating element 2 (ii) Chassis mode 2 (CA2) where the RF switches 4 and 5 address the common chassis mode from the right, with the RF switch 3 connecting the link connection 7 to the radiating element 1 , and (iii) Balanced mode (BA) with the RF switches 3, 4 and 5 connecting the RF port to the radiating elements 1 , 2 through the matching circuit M3. It is to be noted that no matching circuitry is required for driving the unbalanced chassis modes CA1 and CA2

[0066] Simulated far-field radiation patterns obtained from the embodiment of Figures 17 to 19 can be seen in Figures 20 and 21 , covering the responses at 2.45GHz and 5.5GHz respectively.

[0067] Figure 20A shows the CA1 radiation pattern at 2.45GHz, Figure 20B shows the BA mode radiation pattern at 2.45GHz, and Figure 20C shows the CA2 radiation pattern at 2.45GHz. The CA1 mode has a useful lobe facing in a south-easterly direction, while the CA2 mode has a lobe facing west (or left). The BA mode has a main lobe facing west (or left). Accordingly, beam-forming or beam-steering can be effected by switching between these different modes.

[0068] Figure 21A shows the CA1 radiation pattern at 5.5GHz, Figure 21 B shows the BA mode radiation pattern at 5.5GHz, and Figure 21 C shows the CA2 radiation pattern at 5.5GHz. The CA1 mode has a useful lobe facing east (or right), while the CA2 mode has a useful lobe facing west (or left). The BA mode has a main lobe facing upwards. Again, beam-forming or beam-steering can be effected by switching between these different modes.

[0069] An alternative design for the radiating elements is shown in Figure 22. Here, a pair of linear monopole radiating elements 1 , 2 are arranged facing away from each other on either side of a centreline of one surface of a dielectric substrate 15 which is mounted at an edge of a ground-plane 16. The radiating elements 1 , 2 are located near the top of the substrate 15. A pair of L-shaped grounded passive elements 21 , 22 extend across the substrate 15 from the edge of the ground-plane 16 towards the respective radiating elements 1 , 2, before turning inwardly and extending towards each other generally parallel to the radiating elements 1 , 2. Driving circuitry such as shown in Figure 19 is situated on a ground- plane extension provided on the rear surface (not shown) of the substrate 15. Matching circuitry is required only for the balanced mode of operation.

[0070] Figure 23A shows the CA1 radiation pattern at 2.45GHz, Figure 23B shows the BA mode radiation pattern at 2.45GHz, and Figure 23C shows the CA2 radiation pattern at 2.45GHz. The CA1 mode has a useful lobe facing west (or left), while the CA2 mode has a useful lobe facing east (or right). The BA mode has dual main lobes facing both east and west (right and left). Accordingly, beam-forming or beam-steering can be effected by switching between these different modes.

[0071] Figure 24A shows the CA1 radiation pattern at 5.5GHz, Figure 24B shows the BA mode radiation pattern at 5.5GHz, and Figure 24C shows the CA2 radiation pattern at 5.5GHz. The CA1 mode has a lobe facing south-east, while the CA2 mode has a lobe facing south-west. The BA mode has a main lobe facing north (or upwards). Again, beam-forming or beam-steering can be effected by switching between these different modes.

[0072] 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.

[0073] 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.

[0074] 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.