[0001] This invention relates to a compact LTE (Long Term Evolution) antenna suitable for use in portable electronic devices, including mobile handsets, tablets and laptop computers.

BACKGROUND

[0002] Firstly, some of the terms used in the main Detailed Description will be explicitly defined so as to ensure that the reader is able fully to understand the concepts described therein.

[0003] 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.

[0004] 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.

[0005] A balun may be used to convert a balanced feed to an unbalanced feed and vice versa.

[0006] 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.

[0007] With the current advancement of technology in mobile telecommunications devices such as tablets, laptops and smartphones, the trend is towards supporting more wireless standards and being thinner and more aesthetically desirable. To this end wireless connectivity is being required in smaller and smaller locations in the ever populous real-estate inside the cases of powerful laptops, tablets, 360-degree flip devices and 2-in-1 portable computing devices.

[0008] All wireless devices, irrespective of size, require antennas capable of supporting the bands of communications standards necessary for their operation, and particularly, support for latest and fastest standards currently available in larger devices, such as LTE (4G).

[0009] Current wireless devices such as tablets, 2-in-1 devices, mobile telephones and laptops include the use of 4G LTE, a fast cellular data service for networking as WWAN (wireless wide area network). This is similar to WLAN (wireless local area network) operation but utilises fast cellular data protocols such as 4G LTE or even 5G, utilising LTE- LAA 5GHz sharing with WiFi as the data backhaul.

[0010] The desire for 4G and 5G implementation into smaller footprint devices raises some technical challenges that need to be overcome.

[0011] Firstly, most high-end equipment and newer consumer equipment makes use of all-metal casings, as this is fashionable and highly desirable due to aesthetics and robustness of the casing and chassis of the device. This leaves very few places in the casing and chassis where an RF signal can be radiated effectively to the outside. Some of the places that are typically still plastic include the very slim bezel area surrounding the screen of the device, or specific RF-opaque windows that are plastic and can be painted to mimic a metal finish, both of which are very small areas.

[0012] Secondly, there is a problem that the physical lengths of the monopole radiating elements forming the LTE antenna are normally required to be of particular lengths in order to create the necessary resonances in the low bands. It is a requirement that, as the frequency of resonance decreases, the length of the resonant radiating element must increase in order to maintain the response. Such increases in the lengths of radiating elements can cause problems in space-constrained environments. [0013] Techniques such as meandering or fractal type extensions of the monopole radiator allow increased lengths in confined spaces. However, these have disadvantages since they are low bandwidth (i.e. have a high Q in their resonances) and also low efficiency. In China, for example, the TDD (Time Division Duplex) low bands utilise 1.88- 1.92GHz. It would be challenging to fully cover these bands using a correct-length, resonant monopole radiating element, especially in a small form-factor device. Also, the LTE-LAA (Licence Assisted Access) band at 5GHz uses co-existence with existing WiFi to provide fast LTE in the unlicensed spectrum. Such aggregation of licensed and unlicensed bands can provide gigabit-class LTE speeds.

[0014] Fractal and folded meander line type radiators, due to their complicated designs, can be difficult to design and manufacture.

[0015] It is also known to change the properties of a monopole antenna using capacitive coupling of radiating elements nearby. However, such modifications need to be carefully considered in view of coupling distances, as well as whether they are grounded or floating, since these will affect the electrical length and the manner of coupling.

BRIEF SUMMARY OF THE DISCLOSURE

[0016] Certain embodiments of the present disclosure seek to provide a solution addressing the foregoing problems by way of an LTE antenna structure with a very small footprint capable of operating in LTE-LAA bands and 5GHz WiFi.

[0017] Viewed from one aspect, there is provided an antenna device comprising a planar dielectric substrate having a longitudinal axis and a transverse axis, a top edge and a bottom edge extending substantially parallel to the longitudinal axis of the substrate, and first and second opposed end portions, the antenna device further comprising a conductive ground plane strip extending along the bottom edge of the substrate, an elongate conductive radiating element extending along the top edge of the substrate towards the first end portion and provided with a conductive ground connection at the second end portion, a U- or J-shaped feed conductor formed on the substrate between the top and bottom edges, the feed conductor having a distal arm extending towards the first end portion of the substrate substantially parallel to the elongate conductive radiating element and a proximal arm for connection to an RF feed, and an L-shaped conductive radiating element having a first arm connected the ground plane strip and a second arm extending towards the first end portion of the substrate substantially parallel to the elongate conductive radiating element and the distal arm of the U- or J-shaped feed conductor. [0018] There may further be provided one or more additional L-shaped conductive radiating elements each having a first arm connected to the ground plane strip and a second arm extending towards the first end portion of the substrate substantially parallel to the elongate conductive radiating element and the distal arm of the U- or J-shaped feed conductor.

[0019] Where one or more additional L-shaped conductive radiating elements are provided, these may be arranged in a nested configuration with the L-shaped conductive radiating element.

[0020] The second arm of each L-shaped conductive radiating element may extend substantially parallel to the ground plane strip provided along the bottom edge of the substrate.

[0021] Each L-shaped conductive radiating element may be configured as an unbalanced radiating element. The L-shaped conductive radiating elements are located sufficiently close to the feed conductor so as electromagnetically to couple therewith. The L-shaped conductive radiating elements, being connected to the ground plane strip by way of their first arms, act as coupled grounded loops when excited by the feed conductor.

[0022] When two or more L-shaped conductive radiating elements are provided, they may electromagnetically couple with each other as well as with the feed conductor so as to provide appropriate modified frequency responses.

[0023] The lengths of the first and/or second arms of each L-shaped conductive radiating element are selected to support different frequency resonances when excited by the feed conductor.

[0024] The elongate conductive radiating element provided along the top edge of the substrate also couples electromagnetically with the feed conductor to support a desired resonance. The length of the elongate conductive radiating element may be selected to support a desired resonance when excited by the feed conductor. The elongate conductive radiating element has a conductive ground connection at the second end portion of the substrate. The conductive ground connection may be connected to the ground plane strip at bottom edge of the substrate, or may be configured for connection to a separate ground plane.

[0025] The elongate conductive radiating element and its conductive ground connection may, in some embodiments, be configured as a large L-shaped conductive radiating element, with the U- or J-shaped feed conductor and the at least one L-shaped conductive radiating element nested under the elongate conductive radiating element. [0026] The substrate may have a front surface and a rear surface. In some embodiments, the U- or J-shaped feed conductor, the at least one L-shaped conductive radiating element and the ground plane strip may all be formed on the front surface of the substrate. The elongate conductive radiating element may be formed on the front surface of the substrate in the same plane as the feed conductor and the at least one L-shaped conductive radiating element. Alternatively, the elongate conductive radiating element may be formed along a top edge portion of the substrate extending between the front and rear surfaces, and thus in a plane substantially perpendicular to the plane of the feed conductor and the at least one L-shaped conductive radiating element. Alternatively, the elongate conductive radiating element may be formed on the rear surface of the substrate. The conductive ground connection for the elongate conductive radiating element may be formed on the rear surface of the substrate at the second end portion. Alternatively, the conductive ground connection for the elongate conductive radiating element may be formed along a side edge portion of the substrate extending between the front and rear surfaces of the substrate, or on the front surface of the substrate if space permits.

[0027] The proximal arm of the U- or J-shaped feed conductor is configured for connection to an RF feed. The RF feed may be by way of a coaxial cable or other unbalanced transmission line. Preferably, the RF feed is routed along the ground plane strip, or an extension to the ground plane strip provided at the second end portion of the substrate. By routing the RF feed, e.g. a coaxial cable, along a grounded area, RF noise or interference can be reduced or minimised.

[0028] The various conductive radiating elements may be resonant antenna elements (i.e. they have a length that directly supports resonance at a frequency of operation), or they may be non-resonant antenna elements provided with appropriate matching circuitry for operation at desired frequencies. Both resonant and non-resonant elements may be used together.

[0029] The substrate may be made of an RF-transparent dielectric material. Examples include (but are not limited to) polycarbonate plastics and ceramic materials, or any other type of dielectric material in use in the industry. In some embodiments, the substrate may be formed as a substantially rectangular planar element. It will be appreciated that corner portions of the substrate, especially where no conductive elements are formed, may be rounded or cut off depending on spatial requirements (e.g. to fit into particular device casings). It is, however, desirable for the substrate to provide a surface for supporting the various conductive elements (including the ground plane strip) in a way that they are respectively parallel and/or perpendicular to each other so as to promote electromagnetic coupling where this is desired, and to minimise electromagnetic coupling where this is not desired.

[0030] The substrate may comprise a dielectric (e.g. plastics or ceramic) carrier with the various conductive elements formed on a flexible printed circuit board (FPCB) which is wrapped onto the carrier. Alternatively, the various conductive elements may be printed or coated directly onto the carrier, for example by way of laser direct structuring (LDS) techniques. In some embodiments, one or more of the conductive elements may be formed from stamped or pressed metal elements, or metal deposited onto ceramic for example by way of low temperature co-fired ceramic (LTCC) techniques. The substrate may also be printed-circuit board, such as FR4 or other, with the conductive elements produced via PCB processing techniques. Other techniques as known in the industry may be used.

[0031] The ground plane strip may comprise or be connected to a ground plane flap extending from the bottom edge of the substrate. The ground plane flap allows simple connection to a larger electronic device ground plane, for example a main PCB of the electronic device, or a metal chassis, or display screen or the like.

[0032] The close co-location of the feed conductor and the various radiating elements between the top edge and the bottom edge of the substrate (in some embodiments, the distance from top edge to bottom edge is no more than 10mm, and may be no more than 6mm) means that the antenna device may be located in a gap between a screen and a surrounding bezel of a portable electronic device, and thereby radiate effectively to the outside of the portable electronic device even when the device has a metal casing.

[0033] Certain embodiments comprise a first substantially U-shaped radiating unbalanced element acting as a feed arm. Two or more additional unbalanced L-shaped radiating elements are arranged in close proximity to the feed arm and configured to couple with the feed. The additional radiating elements are of differing lengths, depending on the resonance they support, and grounded, to form coupled grounded loops. The additional-shaped radiating elements couple with each other to create appropriate modified frequency responses.

[0034] Advantages of certain embodiments include:

i) Single feed point for low and mid/high band responses;

ii) Use of coupled grounded loop radiating elements to obtain required electrical lengths in a very compact form-factor;

iii) Responses for mid-high band tuned by nesting radiating elements to couple with each other, as well as with the feed arm; iv) 6mm bezel antenna is made possible, enabling market-leading screen sizes on laptops, tablets and other portables.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is a perspective view of an antenna device mounted in a bezel portion of casing of a portable electronic device;

Figure 2 shows a front elevation of the antenna device of Figure 1 ;

Figure 3 shows a rear elevation of the antenna device of Figure 1 ;

Figure 4 shows exemplary dimensions of the substrate of the antenna device of

Figure 1 ;

Figure 5 shows a simulated return loss plot for the antenna device of Figure 1 ; and

Figure 6 shows a simulated total efficiency plot for the antenna device of Figure 1.

DETAILED DESCRIPTION

[0036] The constraints of a small form factor and only a single port to serve low, mid and high LTE bands requires a solution based around capacitively coupled loops fed by a feed arm. This type of antenna allows for a compact design whilst allowing multiple coupled loop resonances to be fed via a single port. It should be noted that the antenna configuration can use resonant antenna elements or can use non-resonant elements with appropriate matching circuitry.

[0037] Certain embodiments comprise a first substantially U- or J-shaped radiating unbalanced element acting as a feed arm. Two or more additional unbalanced L-shaped radiating elements are arranged in close proximity to the feed arm and configured to couple with the feed. The additional radiating elements are of differing lengths, depending on the resonance they support, and grounded, to form capacitively-coupled grounded loops. The additional L-shaped radiating elements couple with each other to create appropriate modified frequency responses.

[0038] The antenna device comprises a rectangular carrier structure or substrate which is made from RF transparent material such a polycarbonate plastic or ceramic, or any other suitable material used in the industry having a first (front) side, and a second (rear side); a feed arm portion, which is substantially U- or J-shaped; a radiating element located along the top edge of the carrier which is grounded via a vertical conductive element on the rear-side of the carrier; and one or more additional L-shaped radiating elements on the front-side of the carrier, in close proximity to the feed arm and configured to couple with the feed to create coupled grounded loops.

[0039] It is not essential that the top element is perpendicular to the additional L-shaped radiating element, it could be formed on a side of the carrier (front or rear). However, due to the very constrained height of the bezel area, typically 6-6.5mm, it is optimally placed at such a location.

[0040] The feed arm is fed via an RF coaxial cable that is routed along a ground-plane extensions portion. All ground points at the bottom of the structure are connected to a ground-plane flap that forms part of the antenna device and subsequently connected to the larger ground-plane formed by the metal chassis or LCD screen encasing of the mobile device.

[0041] The antenna device can be made using a plastic carrier with an FPC (flexible printed circuit) to form the required radiating elements, or the radiating elements can be produced using LDS where metal is coated directly onto the carrier. The antenna device could also be formed from pressed or stamped metal elements, or metal deposited onto ceramic (LTCC), or by simple printed-circuit board processing techniques on a PCB, or any other method widely used to form conductive radiating elements onto a dielectric carrier in the industry.

[0042] With reference to Figures 1 to 3, there is shown an antenna device comprising a planar dielectric substrate 1 having a longitudinal axis and a transverse axis, a top edge 2 and a bottom edge 3 (best shown in Figures 2 and 3) extending substantially parallel to the longitudinal axis of the substrate 1 , and first and second opposed end portions 4, 5. The antenna device further comprises a conductive ground plane strip 6 extending along the bottom edge 3 of the substrate 1. An elongate conductive radiating element 7 extends along the top edge 2 of the substrate 1 towards the first end portion 4, and is provided with a conductive ground connection 8 at the second end portion 5. A U- or J-shaped feed conductor 9 is formed on the substrate 1 between the top and bottom edges 2, 3, the feed conductor 9 having a distal arm 10 extending towards the first end portion 4 of the substrate 1 substantially parallel to the elongate conductive radiating element 7 and a proximal arm 11 for connection to an RF feed 12. There are further provided two additional L-shaped conductive radiating elements 13, 13’ each having a first arm 14,14’ connected to the ground plane strip 6 and a second arm 15, 15’ extending towards the first end portion 4 of the substrate 1 substantially parallel to the elongate conductive radiating element 7 and the distal arm 10 of the U- or J-shaped feed conductor 9. The L-shaped conductive radiating elements 13, 13’ are in a nested configuration, with element 13’ being smaller than element 13 and contained within a footprint or envelope of element 13. Indeed, the elongate conductive radiating element 7 and its conductive ground connection 8 also form an L-shaped conductive radiating element defining a footprint or envelope within which the other L-shaped conductive radiating elements 13, 13’ and the feed conductor 9 are contained and/or nested.

[0043] In the illustrated embodiment, the elongate conductive radiating element 7 is formed along a top edge portion of the substrate 1 extending between front and rear surfaces of the substrate 1 , and thus in a plane substantially perpendicular to the plane of the feed conductor 9 and the L-shaped conductive radiating element 13, 13’. This helps to make the best use of the small space available, although the elongate conductive radiating element 7 could be formed on the front or rear surface of the substrate 1 along the top edge 2.

[0044] The proximal arm 11 of the U- or J-shaped feed conductor 9 is configured for connection to the RF feed 12. The RF feed 12 is by way of a coaxial cable or other unbalanced transmission line 16. The transmission line 16 is routed along the ground plane strip 6, or an extension 18 to the ground plane strip 6 provided at the second end portion 5 of the substrate 1. By routing the transmission line 16 along a grounded area, RF noise or interference can be reduced or minimised.

[0045] Also shown in Figure 1 is a bezel portion 20 of a casing of a portable electronic device, and a screen portion 21. It can be seen that the antenna device fits between the bezel portion 20 and the screen portion 21.

[0046] Figure 2 shows a front elevation of the embodiment of Figure 1 , and Figure 3 shows a rear elevation. The nested arrangement of the L-shaped conductive radiating elements 13, 13’ is clearly seen, as is the nesting or the L-shaped conductive radiating elements 13, 13’ under the elongate conductive radiating element 7. The distal arm 10 of the feed conductor 9 extends towards the first end portion 4 of the substrate 1 between the elongate conductive radiating element 7 and the second arms 15, 15’ of the L-shaped conductive radiating elements 13, 13’. In this way, the various radiating elements 7, 13, 13’ all couple with the feed conductor 9, and also to some extent with each other, so as to support different frequency resonances.

[0047] As seen in Figures 2 and 3, the conductive ground connection 8 connecting the elongate conductive radiating element 7 to ground at the second end portion 5 of the substrate 1 is provided on the rear surface of the substrate 1. This helps to avoid noise or interference from the RF feed 12 and transmission line 16 on the front surface of the substrate 1 , since shielding is provided by the ground plane strip 6 and its extension 18.

[0048] In this particular embodiment, the elongate conductive radiating element 7 on the top edge 2 of the substrate 1 is the longest, and when coupled with the feed conductor 9 generates a low and wideband resonance between 1.7 and 2.7GHz. The further grounded L-shaped radiating elements 13, 13’, being shorter, support high frequency resonances at 3.4 to 3.8GHz and 5.1 to 5.85GHz respectively.

[0049] The ground plane strip 6 at the bottom edge 3 of the substrate 1 conveniently extends across the whole width of the substrate 1. The ground plane strip 6 and the extension 18 serve two purposes: (i) to provide a base for attachment of a foil flap to ensure good connectivity into the main device grounding (in the case of tablets or laptops, this can be the screen enclosure or the chassis); and (ii) to provide a grounded area for routing of coaxial cables to minimise any noise or interference.

[0050] Figure 4 shows suitable dimensions for a substrate 1 of a particular embodiment. The substrate 1 has a width of 26mm, a height of 6mm, and a thickness of 0.8mm. Due to the very constrained area in the bezel section surrounding the screen in many tablets and laptops, the maximum height of the carrier substrate 1 should be no more than 6.0mm. The length is less of an issue, although there are other components that may need to be located the area in the bezel section. Therefore, the design provides a compromise between fitting all of the radiating elements in the 6.0mm height while still having enough electrical length to operate at the desired resonances within a reasonable physical length.

[0051] From a high-level aspect, the top elongate conductive radiating element 7 and the coupled loop it forms with the conductive feed 9 to produce the low band resonance can be considered separate and independent from the response of the other L-shaped conductive radiating elements 13, 13’.

[0052] The mid and high band resonances supported by the L-shaped conductive radiating elements 13, 13’ are more complex, and the responses in both the 3.4 to 3.8GHz and the 5.1 to 5.85GHz bands rely on both elements 13, 13’ being arranged appropriately and having the correct coupling both with the conductive feed 9 and with each other. For example, the top L-shaped element 13 provides a resonance at around 3.5GHz in isolation, as a simple grounded coupled loop with the conductive feed 9. But it also couples with the nested shorter L-shaped element 13’ to both broaden the bandwidth of the resonance and shift the centre slightly in order properly to cover the frequency range required. Conversely, the smaller L-shaped radiator 13’, which is responsible for the 5.5GHz resonance, couples with the other L-shaped radiator 13, in order both to widen the bandwidth and to position the centre of the frequency response appropriately to cover the required frequency band. This means that nested L-shaped radiating elements 13, 13’ are configured to produce resonances appropriate to their electrical length, but also such that they couple in order to adjust the properties of that resonance to cover the required frequency range accurately.

[0053] Figure 5 illustrates the simulated return loss for the antenna arrangement of Figures 1 to 3. It can be seen that there is a first, low band resonance between 1.7 and 2.7GHz. Additional resonances occur at 3.4 to 3.8GHz and at 5.1 to 5.85GHz.

[0054] Some of the resonances are not particularly deep, for example in the region from 1.8 to 2.8GHz. However, as shown in the simulated total efficiency plot of Figure 6, the arrangement is particularly efficient at radiating in the bands of interest. It can be seen that the antenna arrangement has an efficiency around -3dB in the lower band region (1.7 to 2.7GHz), which is around 50% efficiency, and this increases in the higher bands (3.4 to 3.8GHz and 5.1 to 5.85GHz) with efficiencies around -1.5 dB, which is around 70%. Therefore, although the low band appears marginal from the return loss, the reasonable efficiency means this is a useful antenna in that band.

[0055] 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.

[0056] 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.

[0057] 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.