Abstract
There is disclosed a multiband antenna device comprising a conductive elongate antenna element configured for electrical connection to a groundplane at a grounding point, and a conductive elongate feeding element configured for electrical connection to a radio transmitter/receiver at a feeding point. At least a major portion of the antenna element is configured to extend in a first direction and to double back on itself in a second, substantially counter-parallel direction forming a slot. The feeding point is adjacent to the grounding point, and the feeding element is configured to extend substantially parallel to the first and second directions of the major portion of the antenna element. The antenna device can operate in multiple frequency bands, and can be configured on a dielectric insulating former that fits compactly in a corner of a mobile communications handset housing.
Claims
1. A multiband antenna device comprising a conductive elongate antenna element configured for electrical connection to a ground plane at a grounding point, and a conductive elongate feeding element configured for electrical connection to a radio transmitter/receiver at a feeding point, wherein at least a major portion of the antenna element is configured to extend in a first direction along a first portion and to double back on itself forming a second portion that extends in a second direction substantially counter-parallel to the first direction prior to terminating at a first free end, the first portion and the second portion forming a first slot, wherein the feeding point is adjacent to the grounding point, and wherein the feeding element is configured to extend substantially parallel to the first and second directions of the major portion of the antenna element, wherein the antenna element is provided with a capacitive coupling branch separate from the second portion that extends from the first portion and runs substantially counter-parallel thereto prior to terminating at a second free end, thereby to define a second slot between the capacitive couple branch and the first portion, a portion of the feeding element positioned in the second slot and having opposing sides parallel to the first direction, the opposing sides being between and directly adjacent to the first portion and the capacitive coupling branch.
2. The device of claim 1, wherein the antenna element further includes a third portion that is for electrical connection to the ground plane at the grounding point and extends in a direction substantially perpendicular to an edge of the ground plane, wherein the first portion extends in the first direction substantially parallel to the edge of the ground plane, and wherein the second portion extends in the second direction substantially counter-parallel to the first direction.
3. The device of claim 1, wherein the feeding element is arranged to couple capacitively with the antenna element during operation of the antenna device.
4. The device of claim 1, wherein the antenna element is provided with a branch that extends from the first portion of the antenna element and away from the feeding element, the branch introducing an additional resonance having a higher frequency than a frequency of resonance provided by another portion of the antenna element.
5. The device of claim 1, wherein the feeding element comprises a first end for connection to the ground plane at the feeding, and a second end for connection to the ground plane at another position.
6. The device of claim 5, wherein the second end of the feeding element is provided with a complex impedance element for connection to the ground plane.
7. The device of claim 6, wherein the complex impedance element is an electronically controlled variable complex impedance element.
8. The device of claim 6, comprising an electronically controlled RF switch and a plurality of different complex impedance elements, the RF switch being controllable to commute between the different complex impedance elements.
9. The device of claim 1, wherein the antenna element is configured for electrical connection to the ground plane at the grounding point by way of a complex impedance element.
10. The device of claim 9, wherein the complex impedance element is an electronically controlled variable complex impedance element.
11. The device of claim 10, comprising an electronically controlled RF switch and a plurality of different complex impedance elements, the RF switch being controllable to commute between the different complex impedance elements.
12. The device of claim 1, wherein the antenna element and feeding element are formed as conductive tracks on a printed circuit board (PCB) having first and second opposed surfaces.
13. The device of claim 12, wherein the antenna element and the feeding element are formed on the same surface of the PCB.
14. The device of claim 12, wherein the antenna element is formed on the first surface of the PCB and the feeding element is formed on the second surface of the PCB.
15. The device of claim 12, wherein the PCB includes a conductive portion defining the ground plane.
16. The device of claim 12, wherein the PCB is configured as a separate daughterboard for connection to a motherboard including the ground plane.
17. The device of claim 1, wherein the antenna element and the feeding element are disposed on a dielectric former element configured for attachment to a PCB.
18. The device of claim 17, wherein antenna element and the feeding element are wrapped around the dielectric former element.
19. The device of claim 1, wherein the antenna element and optionally the feeding element have a bent or folded arrangement so as to conform around a corner of the ground plane.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:
(2) FIG. 1 shows a known capacitively fed antenna;
(3) FIG. 2 shows an antenna device with an elongated antenna element and an elongated capacitive feeding element;
(4) FIG. 3 shows a planar structure of the antenna device;
(5) FIG. 4 shows the antenna device on a printed circuit board (PCB);
(6) FIG. 5 shows an antenna device with the antenna element and feeding element formed on opposite sides of a PCB;
(7) FIG. 6 shows an alternative embodiment of the antenna device;
(8) FIG. 7 is an impedance matching plot for the antenna device of FIG. 4;
(9) FIG. 8 shows an embodiment with an auxiliary coupling branch;
(10) FIGS. 9 to 11 show alternative embodiments with an additional branch for improving bandwidth or introducing an additional resonance;
(11) FIG. 12 is an impedance matching plot for the antenna device of FIG. 9;
(12) FIG. 13 shows an antenna device with the groundplane extended on one side of the antenna device;
(13) FIG. 14 shows an antenna device arranged to fit around a corner of the groundplane;
(14) FIG. 15 shows an antenna device with an impedance element at the grounding point;
(15) FIG. 16 shows an antenna device with an electronically variable impedance element at the grounding point;
(16) FIG. 17 shows an antenna device with an electronically controlled RF switch at the grounding point;
(17) FIG. 18 shows an antenna device with the end of the feed element remote from the feeding point galvanically connected to the groundplane;
(18) FIG. 19 shows an antenna device with the end of the feed element remote from the feeding point connected to the groundplane through an impedance element;
(19) FIG. 20 shows an antenna device disposed perpendicularly to the groundplane;
(20) FIGS. 21 and 22 show an antenna device bent around the corner of the groundplane at one corner of a PCB;
(21) FIG. 23 shows a pair of antenna devices in a diversity arrangement bent around two corners of the groundplane at adjacent corners of a PCB; and
(22) FIGS. 24 to 29 illustrate an antenna device where the antenna is formed on an insulating carrier for positioning on a corner of a PCB.
DETAILED DESCRIPTION
(23) FIG. 2 illustrates a preferred embodiment of the present invention. It has been found that a particular arrangement of the more general capacitively fed antenna of FIG. 1 has several significant advantages in terms of the useable frequency bandwidth, the multiband behaviour and compactness of capacitively fed antennas.
(24) To realise the advantages noted above, the antenna element 202 is of the form of a conductive elongated strip connected to the groundplane 206, and is configured to lie in a plane parallel to the groundplane. Furthermore, the antenna element is folded on itself, approximately half way along its length at point B 201. The resultant U-shape maintains a long antenna and therefore the lowest resonance frequency available to the antenna. The U-shape may also be thought of as a slot 213 (shown in FIG. 3) within the antenna element formed by the two major portions of the antenna element. Folding the antenna element 202 also minimises the space required to accommodate the antenna device.
(25) The feeding element 204 is also an conductive elongated strip. A conductive elongated strip can be considered to be one in which the ratio of width to length is or smaller. The feeding element 204 is electrically connected to the groundplane 206 at a feeding point along the groundplane, in close proximity to the grounding point 208 of the antenna element 202 and is configured to run substantially parallel to a portion of the antenna in the same direction. The feeding element 204 must have sufficient length so as to provide a useable coupling capacitance. It should be noted that the total length of the feeding element must be shorter than the shortest resonant length at the lowest operation frequency, yet still be long enough to ensure that the coupling capacitance is effective.
(26) In FIG. 2, the antenna element 202 is shown having three portions. The first portion is connected to the groundplane at the grounding point 208 and runs to the first folding point, point A. The first portion 203 is positioned substantially perpendicular to the edge of the groundplane. The second portion 201 runs from point A, in a direction substantially parallel to the edge of the groundplane to folding point B. The antenna is then folded back on itself to form a U shape or slot, such that the free end portion (i.e. third portion) runs counter-parallel to the direction of the second portion.
(27) FIG. 3 illustrates a planar structure of the preferred embodiment of FIG. 2. The planar structure is formed by etching a printed circuit board (PCB), or by stamping metal or other method. The planar structure has several design parameters. For instance, the lowest resonant frequency of the antenna device 200 is determined by the overall length of the antenna element 202, the width of the first 203 and second 201 portions of the antenna element, especially in the region in close proximity to the grounding point 208, and the distance from the groundplane 206. The antenna device depicted in FIG. 3 provides a first and second resonance, and the second resonance is at a higher frequency than the first resonance frequency due to the fold in the antenna element 202 at point B. The frequency of the second resonance depends on the depth of the slot 213, the ratio of the length of the free end portion 202 to the length of the second portion 201, as well as other parameters. The same antenna element in an unfolded or straightened out arrangement exhibits just a single low band resonance. The value of the impedance of the antenna element at the resonance frequencies and the relative bandwidth of the antenna device may be optimized by adjusting the length of the elongated conductive feeding element 204 and the width of the capacitive gap 212 between the feeding element 204 and the antenna element 202.
(28) In a typical planar implementation the antenna element 202 and the feeding element 204 are created by etching the PCB which also includes the ground structure 207 (the ground plane in a planar arrangement is described as a ground structure), and therefore the antenna element 202 and the feeding element 204 are supported by the dielectric material 209 as shown in FIG. 4. It is also possible to etch the antenna element 202 on one side of the PCB, and etch the feeding element 204 on the other side of the PCB, as shown in FIG. 5. In general, the electronic circuitry constituting the radio transmitter/receiver 210, and other components (battery, LCD, speakers, etc.) are soldered or connected to the ground structure 207.
(29) The arrangement shown in FIG. 5 may be implemented as a stand-alone surface-mount antenna device in which the antenna element 202 and feeding element 204 are etched on separate PCBs and then soldered to the main PCB having the ground structure 207 and electronic components. In a typical embodiment the feeding element 204 is etched onto the lower surface of the PCB and the antenna element 202 is etched onto the upper surface of the PCB and connected to ground by means of a conductive strip. It should be noted that other configurations are possible.
(30) In the embodiments shown in FIGS. 3, 4 and 5, the feeding structure 208 is positioned between the antenna element 202 and the groundplane 206. In an alternative embodiment shown in FIG. 6, the feeding element 204 extends inside the slot 213 created by the fold in the antenna element 202.
(31) FIG. 7 shows a plot of the impedance matching of the antenna device shown in FIG. 4. FIG. 7 shows three characteristic troughs, each representing a corresponding frequency range.
(32) FIG. 8 illustrates a further preferred embodiment for an antenna able to operate at lower frequencies. An auxiliary coupling branch 205, electrically connected to the antenna 202, is positioned between the feeding element 204 and the ground structure 207, and increases the coupling between the antenna element 202 and the feeding element 204. Furthermore, by introducing an auxiliary coupling branch 205, the reduction in the width of the capacitive gap 212 between the antenna element 202 and the feeding element 204 does not change. If the capacitive gap 212 is too small, problems arise with manufacturing the antenna devices and with antenna tolerance.
(33) FIGS. 9, 10 and 11 illustrate preferred embodiments of the antenna device providing enhanced frequency bandwidth in the second resonant frequency band. This is achieved by adding a second branch 220 that stems from the second portion 201 of the antenna element 202 in close proximity to the grounding point 208. The second branch 220 may substantially follow the same direction as the antenna element 202 (see for example in FIG. 9) or alternatively may follow the opposite direction (see for example FIG. 10) of the antenna element 202. Furthermore, it is also possible to create a capacitive coupling between the second branch 220 and the end section of the antenna 202 by bringing them in close proximity to one another and thereby creating a small capacitive gap 222 (see for example FIG. 11).
(34) FIG. 12 shows the plot representing impedance matching for the antenna device shown in FIG. 9. The additional second branch 220 stemming from the second portion 201 of the antenna element 202 creates an additional resonance and widens the high band. The additional resonance is highlighted by a dashed circle 1202 on the plot.
(35) FIG. 13 illustrates an antenna device with the ground structure extended 207 on one side of the antenna element 202. One advantage of the embodiments of the antennas disclosed here is that they generally work well even when the ground structure 207 is extended 207 on one side of the antenna 202, making it convenient for many applications where the antenna cannot protrude completely outside the extended ground structure profile 207.
(36) FIG. 14 illustrates the antenna device arranged to fit around the corner of the ground structure 207. In this embodiment, the antenna maintains its advantageous properties while also minimising the space it occupies.
(37) A further advantage of the class of antennas disclosed here is that the frequency of the lowest resonance can be easily adjusted by connecting the antenna element 202 to the ground structure 207 through an impedance element 226, e.g. an inductor or a capacitor. FIG. 15 shows the antenna element 202, the feeding element 204, the ground structure 207 and an impedance element 226. The frequency of the lowest resonance is varied by the varying the properties of the impedance element. If the impedance element 226 is an inductor, then the frequency of the lowest resonance is lowered. Alternatively, if the impedance element is a capacitor then the frequency of the lowest resonance is increased.
(38) FIG. 16 illustrates a further advancement whereby the antenna device is electronically tuneable. Replacing the fixed impedance element 226 with an electronically controlled variable impedance element 227, such as a varicap diode, enables the variation of the frequency of the lowest resonance. Alternatively, as illustrated in FIG. 17, the antenna element 202 may be connected to an electronically controlled radio frequency (RF) switch 228 that commutes between two or more impedance elements 229, 229, 229 of different type or values (inductors and capacitors). Such an arrangement provides three different frequency states of the antenna device. For instance, in a first state the lowest resonance of the antenna device may cover the LTE700 frequency range (698-798 MHz) and in a second state the GSM850/900 range (824-960 MHz).
(39) In another embodiment of the invention, illustrated in FIG. 18, the feeding element, which is normally open ended, is instead connected to the ground structure at the feeding element grounding point 215. The closed end feeding element 214 arrangement improves the bandwidth in the upper resonance, at the expense of a slight reduction of the bandwidth in the lower resonance. The feeding element grounding point 215 connection to the ground structure 207 may be replaced by a connection through an impedance element 216, e.g. an inductor or a capacitor. Such an arrangement allows optimization of the feed point impedance by simply adjusting the value of the lumped inductor or the capacitor 216. This arrangement is illustrated in FIG. 19.
(40) FIG. 20 illustrates another embodiment of the invention, where the antenna element 202 is extended outside the plane containing the ground structure 207 to form a three dimensional structure. The antenna element 202 and the feeding element 204 are supported by a dielectric carrier 230. It should be understood that the dielectric carrier may be manufactured from plastic, resin, ceramic, or any other suitable material. The antenna element 202 and the feeding element 204 can be realized by many different manufacturing methods, for instance a conductor etched on a thin, flexible insulating layer (FPC) and attached to the dielectric carrier 230 using an adhesive layer; stamped metal parts or Laser Direct Structuring (LDS) techniques.
(41) In another embodiment the antenna device is bent around the corner of the ground structure 207 as illustrated in FIG. 21. As can be seen from the alternative view of FIG. 22, in such an embodiment it is generally necessary to add a clearance 232 between the ground structure 207 and the antenna element 202 and feeding element 204. This is in order to avoid the performance degradation that is common when an antenna element gets too close to the groundplane. This arrangement of the antenna device adapted to be arranged to fit around a corner is convenient in some devices where other components, such as a connector 234, occupy the straight edge of the ground structure. Moreover, the corner arrangement of FIGS. 21 and 22 enable the positioning of two antennas at opposite corners of the ground structure 207, thereby creating a symmetric diversity antenna pair or a symmetric multiple-input and multiple-output (MIMO) antenna pair, as shown in FIG. 23.
(42) FIGS. 24 and 25 show an alternative embodiment of the present invention. In this embodiment the antenna 302 is formed on an insulating carrier 330 in the corner of the ground structure 307. The antenna 302 is connected to a grounding point 308. The antenna 302 is folded so that it extends in three orthogonal planes to maximize the space utilization and create a very compact structure. In this case the elongated feed structure 304 (connected to the feeding point 309) and the part of the antenna 302 portion parallel to it are oriented so that they form an angle of approximately 45 with the edge of the ground structure 307. In the complex embodiment of FIGS. 24 and 25, a second branch element 320 is formed on the carrier 330 and extends from the antenna 302 providing a second branch capacitive gap 321 between the antenna 302 and the second branch element 320. Furthermore, an auxiliary coupling branch 305 is formed on the carrier 330 and extending from the antenna 302.
(43) FIGS. 26 to 28 show alternative views of the antenna device of FIGS. 24 and 25 and casing.
(44) FIG. 29 shows a variation of the antenna device of FIGS. 24 to 28, where an portion of the groundplane or ground structure 307 is cleared at the corner where the antenna 302 and carrier 330 are located. This results in a L-shaped strip 340 at the corner of the PCB where no conductive groundplane is present. The L-shaped strip 340 is located underneath the carrier 330 and antenna 302, and helps to increase the bandwidth of the antenna.
(45) It will be clear to a person skilled in the art that features described in relation to any of the embodiments described above can be applicable interchangeably between the different embodiments. The embodiments described above are examples to illustrate various features of the invention.
(46) 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.
(47) 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.
(48) 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.
(49) In the context of the present disclosure, the expression capacitively coupled is used to denote the electromagnetic effect that occurs between two conductors separated by an insulator, so that when time variable electric charge distributions and electric currents are present in one conductor, the electromagnetic fields generated by such charge distributions and currents induce corresponding charge distributions and currents on the second conductor.
