GB2532978A

GB2532978A - Antenna module

Info

Publication number: GB2532978A
Application number: GB1421572.7A
Authority: GB
Inventors: Koon Chung Lau Eddie
Original assignee: Frontier Silicon Ltd
Current assignee: Frontier Silicon Ltd
Priority date: 2014-12-04
Filing date: 2014-12-04
Publication date: 2016-06-08
Anticipated expiration: 2034-12-04
Also published as: GB2532978B; GB201421572D0

Abstract

An antenna module for transmitting and/or receiving radio frequency (RF) signals comprising a central antenna element perpendicular to a ground plane 5 and extending in a direction parallel to the ground plane a distance of at least 1/8 of the operating wavelength of the antenna. The antenna further comprises an antenna feed 3 within the ground plane 5 that tapers from a narrow end for coupling to a radio frequency transmission line to a wider end in contact with the base of the antenna element. The antenna module may extend to a quarter of the operating wavelength, and may further comprise two extension antenna elements 2a/2b also perpendicular to the ground plane, one on either side of the antenna module 1. Each extension element 2a/2b may extend at least 1/8 of the wavelength, and may be 2-3mm less than the height H1 of the central antenna.

Description

ANTENNA MODULE

Technical Field

The present invention relates to an antenna module and to an apparatus comprising an antenna module.

Background

Integrating an antenna module into an apparatus such as a wireless speaker box poses many challenges. Even when there is ample space for antenna placement within an enclosure, obstacles within the enclosure can cause deformation of the antenna radiation pattern. Internal reflections from obstacles within the enclosure give rise to constructive and destructive interference resulting in sharp, unpredictable nulls in the antenna radiation pattern. This can result in the reception of an externally transmitted signal by an antenna located within the enclosure being strongly dependent on the relative positions of the antenna enclosure and the external transmitter/receiver. This is undesirable since both devices may be portable and as such their positions may change frequently during normal use.

Wireless devices typically operate on a broad range of frequencies in the industrial, scientific and medical (ISM) radio bands, for example bands associated BluetoothTm, WiFi. Typically, "1/4 wave" monopole antennas, exhibiting negligible width are employed in such devices. [By way of example, antenna lengths of 31mm and 13mm may be employed for the 2.40Hz and 5.80Hz bands.] The monopole is typically disposed on a printed circuit board (PCB) having a ground plane and a transmission line for feeding the antenna. However, such monopole antennas are strongly susceptible to the deleterious effect of antenna radiation pattern deformation, set out above.

There exists a need for an improved antenna module that may be employed inside an enclosure such as a speaker box used in a wireless audio application and which exhibits a more uniform radiation pattern.

Summary

According to a first aspect of the present invention there is provided an antenna module for transmitting and/or receiving radio-frequency signals. The antenna module comprises a central antenna element which is disposed substantially perpendicular to a ground plane and has a substantially uniform extent (W1) in a direction parallel to the ground plane of at least substantially 1/8 of the wavelength of the electromagnetic radiation with which the antenna is to be excited. The antenna module further comprises a coplanar waveguide which is disposed within the ground plane and which tapers from a relatively narrow end for coupling to a radio-frequency transmission line to a relatively wide end in contact with the base of the central antenna element across at least the side regions of the base of the central antenna element.

The wavelength may correspond substantially to the central wavelength of either the 2.4 GHz or 5.8 GHz radio-frequency band.

The extent of the central antenna element in the direction parallel to the ground plane (W1) may be substantially 1/4 of the wavelength of the electromagnetic radiation with which the antenna is to be excited.

The antenna module may further comprise two extension antenna elements disposed substantially perpendicular to the ground plane, one on either side of the central antenna element and in electrical contact with the central antenna radiator. Each extension antenna element may have substantially uniform extent (W2) in a direction parallel to the ground plane of at least substantially 1/8 of said wavelength. Furthermore, the height (H2) of the extension antenna elements may be 2-3 mm less than the height (H1) of the central antenna element, where the height (H1) of the central antenna element may be substantially 1/4 of said wavelength or an integer multiple thereof.

The central antenna element and extension antenna elements may together form a curved surface. Alternatively, the central antenna element and the extension antenna elements may be individually substantially planar. In this case, the two extension antenna elements may be disposed at a common angle (3) to the central antenna element, where the common angle (6) is in the range 0 to 60 degrees.

The coplanar waveguide may have substantially straight sides, with a tapering angle (cp) preferably in the range 45 to 63 degrees. Alternatively, the coplanar waveguide may have flared sides. The central antenna element may be in contact with the coplanar waveguide across substantially the entire width of the base of the central antenna element or across only the side regions of the base of the central antenna element.

The antenna module may be disposed on a printed circuit board (PCB) and said ground plane and said coplanar waveguide may be provided by a layer or layers of the PCB. The PCB may also comprise a radio-frequency transmission line for coupling to the coplanar waveguide.

According to a second aspect of the invention there is provided a wireless loudspeaker which is configured to send and/or receive radio-frequency electromagnetic radiation. The loudspeaker has an outer casing within which is contained at least one antenna module according to the first aspect of the invention. The wireless loudspeaker may be configured to operate the antenna module on the 2.4 GHz and/or 5.8 GHz bands.

Brief Description of the Drawings

Figure 1 shows a prior art antenna;

Figure 2 shows an improved antenna; Figure 3 shows a plan view of the antenna of Figure 2; Figure 4 shows a plan view of an alternative, improved antenna; Figure 5 shows radiation patterns for the prior art antenna of Figure 1; Figure 6 shows radiation patterns for antennae located in free space; Figure 7 shows radiation patterns for the prior art antenna of Figure 1 in the presence of obstacles; Figure 8 shows radiation patterns for the improved antenna of Figure 2 in the presence of obstacles; and Figure 9 shows various alternative improved antennae.

Detailed Description

Antenna modules will now be described which aim to take advantage of the often relatively generous available space within a device enclosure in order to improve antenna performance over conventional monopole antennas, such as shown in Figure 1. By harnessing the available space, the antenna dimensions may be maximized, which results in improved performance of the antenna module, at least in terms of uniformity of the radiation pattern. The improved performance arises from increasing the antenna dimensions, which is counter-intuitive given recent and current trends which aim to miniaturize electronic components and devices.

An improved antenna module is illustrated schematically in Figures 2 and 3. This may be configured to connect to a source via, for example, BluetoothTM or WiFi. The improved antenna module comprises two main components: an antenna, comprising a central antenna element 1 and extension antenna elements 2a, 2b; and an antenna feeder 3 for feeding the antenna with a radio-frequency (RF) electromagnetic signal. The antenna elements are disposed substantially perpendicular to a ground plane 5, where the ground plane is provided by a layer of a printed circuit board (PCB) 10. The antenna feeder is disposed within the ground plane layer of the PCB. The central antenna element has a height H1 and the extension antenna elements each have a height H2. The height H1 is substantially commensurate with 1/4 of the wavelength at which the antenna module is to send/receive electromagnetic radiation, or integer multiples thereof. The height of the extension antenna elements H2 is typically 2-3 mm less than H1, such that there is a clearance between the base of the extension radiators and the ground plane of 2-3 mm. Those skilled in the art of antenna design will appreciate that the optimal clearance may be greater or smaller when operating the antenna module in different frequency bands. The antenna module may be designed for use in the 2.4 GHz industrial, scientific and medical (ISM) radio band and therefore have height H1 of approximately 30 mm (or multiples thereof). Other heights are contemplated, for example in order to operate the antenna in other radio-frequency bands.

Figure 2 illustrates by the dashed outline 8 a casing of a wireless loudspeaker box within which the antenna module may be mounted. Also shown in the Figure is a transceiver module 9 that is coupled to the antenna and to other components not shown in the Figure (including a loudspeaker and computer system).

As used here, the "width" of an antenna element is defined as the extent of the antenna element in the direction parallel to the ground plane, relative to which the antenna element is substantially perpendicularly disposed. The extent of the antenna elements in said direction is substantially uniform for the full height of the antenna elements. The central antenna element has a width W1 of at least 1/8 of the wavelength at which the antenna module is to send/receive electromagnetic radiation. Both extension antenna elements 2a, 2b have substantially the same width W2 as each other, which is at least substantially 1/8 of said wavelength. The extension antenna elements 2a, 2b are angled relative to the central antenna element 1 by a common angle 6, which is typically in the range 0 to 60 degrees, although other angles are contemplated. According to an embodiment, the width W1 is 30 mm which corresponds substantially to a 1/4 wavelength at 2.4 GHz.

According to the exemplary embodiment presented here, the antenna feeder 3 is a coplanar waveguide disposed within the ground plane layer of the PCB. A clearance region 7 exists in the horizontal plane between the ground plane area and the coplanar signal plane. The coplanar waveguide is tapered at a tapering angle cp of between approximately 45 and 63 degrees, although other angles are contemplated. According to an embodiment, the optimum tapering angle is 54 degrees. The tapering occurs from a smaller width W3, in the range 1 to 3 mm, to a larger width W1, the smaller width typically being commensurate with that of an extension transmission line 4 and the larger width being commensurate with that of the central antenna element W1. The length of the coplanar waveguide L1 is typically 10 mm, which is an optimal length for operation at 2.4 GHz. For the antenna module illustrated in Figures 2 and 3, the antenna feeder only contacts the central antenna element 1 of the antenna module and is not in direct contact with the extension antenna elements 2a, 2b.

The clearance width 7 between the co-planar signal plane and the ground plane may be limited by PCB fabrication techniques and may at minimum be on the order of 0.1 mm, for example. Furthermore, the clearance at the narrow end of the coplanar waveguide may be less than the clearance at the wide end of the coplanar waveguide. For example, the clearance may be on the order or 1-2 mm at the wide end. The clearance is an adjustable parameter in the design process, enabling improved matching between the antenna and the antenna feeder and thus optimizing the overall performance of the antenna module.

Figure 4 illustrates a modification to the antenna module of Figures 2 and 3 and in which the straight tapered coplanar waveguide 3 is replaced by a flared coplanar waveguide 6. The flared geometry enables the ground plane coverage to be maximized, possibly resulting in further improved performance of the antenna module.

Figure 5 shows the horizontal antenna radiation pattern of a conventional monopole antenna, such as that shown in Figure 1, when located in free space (solid line) and when located within an exemplary wireless speaker system (broken line). In free space the horizontal radiation pattern is substantially isotropic. When located within the speaker box, i.e. within an environment containing conducting objects of varying sizes disposed at varying proximities to the antenna, the radiation pattern is observed to become highly non-isotropic. Deep nulls of the order 10-20 dB are observed with respect to the free space radiation pattern. Such nulls may cause an undesirable reduction in the received signal strength when an external transmitter is located at certain positions relative to the antenna, for example at 50 degrees in the example of Figure 5.

Figure 6 shows the horizontal antenna radiation pattern of a conventional monopole antenna located in free space (solid line) and an antenna module as described with reference to Figures 2 and 3 also located in free space (broken line). It is observed that the horizontal radiation pattern of the improved antenna module is substantially isotropic, i.e. In free space the radiation pattern is as uniform as that of the conventional monopole antenna.

The superior performance of an improved antenna module as described with reference to Figures 2 and 3 is made evident when comparison is drawn between a conventional monopole antenna and the improved antenna module as described, where the environment surrounding the antenna module contains obstacles such as, but not limited to, other electronic components or pieces of metal. Such an environment may be encountered inside a speaker enclosure, for example, although other scenarios are contemplated which may present similar electrical characteristics to the antenna module. Figure 7 shows the horizontal radiation pattern of a conventional monopole antenna with six obstacles (metal blocking plates) distributed radially about the antenna where the distance from the obstacles to the centre of the antenna is 30 mm (solid line) and 50 mm (dotted line). It will be apparent that the horizontal radiation pattern becomes deformed by approximately 10 dB as the obstacles are brought closer.

Figure 8 shows results of the same test, but with the conventional monopole replaced with the improved antenna module of Figures 2 and 3. As the obstacles are brought closer to the antenna elements, the deformation of the radiation pattern is less significant. It can therefore be concluded that, with many such obstacles of varying sizes inside an enclosure, the improved antenna module will suffer far less from antenna radiation pattern deformation as compared with the monopole antenna.

Alternative improved antenna modules are shown in Figure 9. In Figure 9 a) and Figure 9 d), the extension antenna elements are arranged at different angles B relative to the central antenna element. In Figure 9 b), the extension antenna elements and central antenna element form a curved surface. In Figure 9 c), the height Hi is n x 4-2", where it is any integer and A is the wavelength of the electromagnetic radiation exciting the antenna module. In Figure 9 e) a rectangular notch is cut out of the central antenna element, where the notch extends from the bottom of the central antenna element to an intermediate position. It is contemplated that such a notch may improve the multi-band capabilities of the antenna module, for example enabling a single antenna module to be effective both on the 2.4 GHz and 5.8 GHz WiFiTM bands.

Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS1. An antenna module for transmitting and/or receiving radio-frequency signals and comprising: a central antenna element disposed substantially perpendicular to a ground plane and having a substantially uniform extent (W1) in a direction parallel to the ground plane of at least substantially 1/8 of the wavelength of the electromagnetic radiation with which the antenna is to be excited; and a coplanar waveguide disposed within the ground plane and tapering from a relatively narrow end for coupling to a radio-frequency transmission line to a relatively wide end in contact with the base of the central antenna element across at least the side regions of the base of the central antenna element.
2. The antenna module according to claim 1, wherein the extent of the central antenna element in the direction parallel to the ground plane (W1) is substantially 1/4 of the wavelength of the electromagnetic radiation with which the antenna is to be excited.
3. The antenna module according to claim 1 or 2 and further comprising two extension antenna elements disposed substantially perpendicular to the ground plane, one on either side of the central antenna element and being in electrical contact therewith.
4. The antenna module according to claim 3, wherein each extension antenna element has a substantially uniform extent (W2) in a direction parallel to the ground plane of at least substantially 1/8 of said wavelength.
5. The antenna module according to claim 3 or 4, wherein the height (H2) of the extension antenna elements is 2-3 mm less than the height (H1) of the central antenna element.
6. The antenna module according to any one of the preceding claims, wherein the height (H1) of the central antenna element is substantially 1/4 of said wavelength or an integer multiple thereof.
7. The antenna module according to any one of claims 3 to 6, wherein the central antenna element and extension antenna elements together form a curved surface.
B. The antenna module according to any one of claims 3 to 6, wherein the central antenna element and the extension antenna elements are individually substantially planar, and wherein the two extension antenna elements are disposed at a common angle (0) to the central antenna element, where the common angle (0) is in the range 0 to 60 degrees.
9. The antenna module according to any one of the preceding claims, wherein said wavelength corresponds substantially to the central wavelength of either the 2.4 GHz or 5.8 GHz radio-frequency band.
10. The antenna module according to any one of the preceding claims, wherein the coplanar waveguide has substantially straight sides, with a tapering angle (p) preferably in the range 45 to 63 degrees.
11. The antenna module according to any one of claims 1 to 9, wherein the coplanar waveguide has flared sides.
12. The antenna module according to any one of the preceding claims, wherein the central antenna element is in contact with the coplanar waveguide across substantially the entire width of the base of the central antenna element.
13. The antenna module according to any one of claims 1 to 11, wherein the central antenna element is in contact with the coplanar waveguide across only the side regions of the base of the central antenna element.
14. The antenna module according to any one of the preceding claims and comprising a printed circuit board (PCB) on which the antenna is disposed, said ground plane and said coplanar waveguide being provided by a layer or layers of the PCB.
15. The antenna module according to any one of the preceding claims and comprising said radio-frequency transmission line.
16. A wireless loudspeaker configured to send and/or receive radio-frequency electromagnetic radiation and having an outer casing within which is contained at least one antenna module according to any preceding claim.
17. A wireless loudspeaker according to claim 16 and being configured to operate the antenna module on the 2.4 GHz and/or 5.8 GHz bands Amendments to the claims have been filed as followsCLAIMS1. An antenna module for transmitting and/or receiving radio-frequency signals in a radio band centered on a wavelength (A) and comprising: a central antenna element disposed substantially perpendicular to a ground plane and having a substantially uniform width (W1) of at least substantially 1/8 of the wavelength (A); and a coplanar waveguide disposed within the ground plane and tapering from a relatively narrow end for coupling to a radio-frequency transmission line to a relatively wide end in contact with the base of the central antenna element across at least the side regions of the base of the central antenna element, wherein said width of the central antenna element extends in a direction parallel to the ground plane and transverse to the guiding axis of the coplanar waveguide.2. The antenna module according to claim 1, wherein the extent of the central antenna element in the direction parallel to the ground plane (W1) is substantially 1/4 of the wavelength of the electromagnetic radiation with which the antenna is to be excited.3. The antenna module according to claim 1 or 2 and further comprising two extension antenna elements disposed substantially perpendicular to the ground plane, one on either side of the central antenna element and being in electrical contact therewith. C\I 4. The antenna module according to claim 3, wherein each extension antenna element has a substantially uniform extent (W2) in a direction parallel to the ground plane of at least substantially 1/8 of said wavelength.5. The antenna module according to claim 3 or 4, wherein the height (H2) of the extension antenna elements is 2-3 mm less than the height (H1) of the central antenna element.6. The antenna module according to any one of the preceding claims, wherein the height (H1) of the central antenna element is substantially 1/4 of said wavelength or an integer multiple thereof.7. The antenna module according to any one of claims 3 to 6, wherein the central antenna element and extension antenna elements together form a curved surface.8. The antenna module according to any one of claims 3 to 6, wherein the central antenna element and the extension antenna elements are individually substantially planar, and wherein the two extension antenna elements are disposed at a common angle (0) to the central antenna element, where the common angle (8) is in the range 0 to 60 degrees.9. The antenna module according to any one of the preceding claims, wherein said wavelength corresponds substantially to the central wavelength of either the 2.4 GHz or 5.8 GHz radio-frequency band.10. The antenna module according to any one of the preceding claims, wherein the coplanar waveguide has substantially straight sides, with a tapering angle (p) in the range 45 to 63 degrees.11. The antenna module according to any one of claims 1 to 9, wherein the coplanar waveguide has flared sides.12. The antenna module according to any one of the preceding claims, wherein the central antenna element is in contact with the coplanar waveguide across substantially the I'-.,, entire width of the base of the central antenna element.13. The antenna module according to any one of claims 1 to 11, wherein the central CJ antenna element is in contact with the coplanar waveguide across only the side regions of the base of the central antenna element.14. The antenna module according to any one of the preceding claims and comprising a printed circuit board (PCB) on which the antenna is disposed, said ground plane and said coplanar waveguide being provided by a layer of the PCB.15. The antenna module according to any one of the preceding claims and comprising said radio-frequency transmission line.16. A wireless loudspeaker configured to send and/or receive radio-frequency electromagnetic radiation and having an outer casing within which is contained at least one antenna module according to any preceding claim.17. A wireless loudspeaker according to claim 16 and being configured to operate the antenna module on the 2.4 GHz and/or 5.8 GHz bands.