Dual antenna structure having circular polarisation characteristics

Abstract

There is disclosed an antenna device made up of at least first, second and third conductive metal plates arranged in a parallelepiped configuration. The third plate defines a lower plane and the first and second plates together define an upper plane substantially parallel to the lower plane. The first and second plates are separated by a slot in the upper plane, and the second and third plates are connected to each other by a grounding connection. The first plate comprises a first, active antenna arm that is provided with a feed connection, and the second plate comprises a second antenna arm that may be passive or active. The antenna device generates a circularly polarized radiation pattern that is good for personal navigation devices, while being significantly more compact than existing ceramic patch antennas that are typically used in these devices.

Claims

1. An antenna assembly comprising: a first conductive plate and a second conductive plate both co-planar in a first plane; and a third conductive plate positioned in a second plane substantially parallel to the first plane, the three conductive plates being assembled to form a parallelepiped antenna configuration that transmits or receives circularly polarized signals, the parallelepiped antenna configuration having a first side in the first plane, a second side in the second plane and four inter-plane sides intersecting the first and second sides, each of the first conductive plate and the second conductive plate having one or more conductive connections to the third conductive plate, at least one of the conductive connections of each of the first conductive plate and the second conductive plate being formed along a different one of the four inter-plane sides of the parallelepiped antenna configuration, each of the four inter-plane sides having no more than one conductive connection formed along the same inter-plane side.

2. The antenna assembly of claim 1 wherein the first conductive plate, the second conductive plate, and the third conductive plate are formed from a continuous piece of metal.

3. The antenna assembly of claim 1 wherein the first conductive plate, the second conductive plate, and the third conductive plate are formed from a flexible printed circuit wrapped around a non-conductive support.

4. The antenna assembly of claim 1 wherein the first conductive plate includes an active antenna arm and a conductive feed connection.

5. The antenna assembly of claim 4 wherein the first conductive plate further includes a conductive grounding connection to the third conductive plate.

6. The antenna assembly of claim 4 wherein the conductive feed connection of the first conductive plate is formed along one of the inter-plane sides of the parallelepiped antenna configuration.

7. The antenna assembly of claim 4 wherein the conductive feed connection of the first conductive plate extends within the interior of the parallelepiped antenna configuration and not along one of the inter-plane sides of the parallelepiped antenna configuration.

8. The antenna assembly of claim 7 wherein the conductive feed connection of the first conductive plate passes extends substantially orthogonally from the first conductive plate through a hole in the third conductive plate.

9. The antenna assembly of claim 1 wherein the second conductive plate includes a passive antenna arm and a conductive grounding connection to the third conductive plate.

10. The antenna assembly of claim 1 wherein the first conductive plate includes an active antenna arm and a conductive feed connection and the second conductive plate includes a passive antenna arm and a conductive grounding connection to the third conductive plate.

11. The antenna assembly of claim 10 wherein the conductive feed connection and the conductive grounding connection are formed along opposing inter-plane sides of the parallelepiped antenna configuration.

12. The antenna assembly of claim 11 wherein the first conductive plate further comprises a conductive grounding connection to the third conductive plate formed along an inter-plane side of the parallelepiped antenna configuration that is adjacent to the opposing inter-plane sides of the parallelepiped antenna configuration.

13. The antenna assembly of claim 1 wherein the first conductive plate includes a first conductive grounding connection to the third conductive plate and the second conductive plate includes a second grounding conductive connection to the third conductive plate.

14. The antenna assembly of claim 13 wherein the first conductive grounding connection and the second conductive grounding connection are formed along opposing inter-plane sides of the parallelepiped antenna configuration.

15. The antenna assembly of claim 14 wherein the first conductive plate further comprises a conductive feed connection formed along an inter-plane side of the parallelepiped antenna configuration that is adjacent to the opposing inter-plane sides of the parallelepiped antenna configuration.

16. The antenna assembly of claim 1 wherein the first conductive plate and the second conductive plate are separated by a slot in the first plane.

17. The antenna assembly of claim 16 wherein an electromagnetic field radiated by the slot and an electromagnetic field radiated by a radio-frequency current circulating around a loop-like path formed by the three conductive plates combine to create radiation having circular polarization emanating from the antenna assembly.

18. The antenna assembly of claim 1 wherein the antenna assembly is configured to generate right handed circular polarization radiation when the first conductive plate is fed and to generate left handed circular polarization radiation when the second conductive plate is fed.

19. The antenna assembly of claim 1 wherein the first conductive plate includes an active antenna arm, a conductive feed connection, and a conductive grounding connection to the third conductive plate, the second conductive plate includes an active antenna arm, a conductive feed connection, and a conductive grounding connection to the third conductive plate, and the first conductive plate is fed with a signal that is out of phase with a signal that is fed to the second conductive plate to form a differential feeding arrangement.

20. A method comprising: forming an antenna assembly including a first conductive plate and a second conductive plate both co-planar in a first plane and a third conductive plate positioned in a second plane substantially parallel to the first plane, the three conductive plates being assembled to form a parallelepiped antenna configuration that transmits or receives circularly polarized signals, the parallelepiped antenna configuration having a first side in the first plane, a second side in the second plane and four inter-plane sides intersecting the first and second sides, each of the first conductive plate and the second conductive plate having one or more conductive connections to the third conductive plate, at least one of the conductive connections of each of the first conductive plate and the second conductive plane being formed along a different one of the four inter-plane sides of the parallelepiped antenna configuration, each of the four inter-plane sides having no more than one conductive connection formed along the same inter-plane side.

21. A method comprising: generating radiation having circular polarization from an antenna assembly having a first conductive plate and a second conductive plate both positioned co-planar in a first plane and a third conductive plate positioned in a second plane substantially parallel to the first plane, the three conductive plates being assembled to form a parallelepiped antenna configuration that transmits or receives circularly polarized signals, the parallelepiped antenna configuration having a first side in the first plane, a second side in the second plane and four inter-plane sides intersecting the first and second sides, each of the first conductive plate and the second conductive plate having one or more conductive connections to the third conductive plate, at least one of the conductive connections of the first conductive plate and the second conductive plate being formed along a different one of the four inter-plane sides of the parallelepiped antenna configuration, each of the four inter-plane sides having no more than one conductive connection formed along the same inter-plane side.

22. The method of claim 21 wherein the circular polarization radiation is generated by a combination of an electromagnetic field radiated by a slot separating the first conductive plate and second conductive plate in the first plane and an electromagnetic field radiated by a radio-frequency current circulating around a loop-like path formed by the three conductive plates.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the present invention and to show how it may be carried info effect, reference shall now be made by way of example to the accompanying drawings, in which:

(2) FIGS. 1a and 1b show a prior art ceramic patch enabled GPS receiving device;

(3) FIG. 2 shows a first embodiment of the present invention;

(4) FIG. 3 shows a second embodiment of the present invention;

(5) FIG. 4 shows a third embodiment of the present invention;

(6) FIG. 5 shows a fourth embodiment of the present invention;

(7) FIGS. 6a and 6b show the radiation patterns of an antenna of the present invention when used without connection to a groundplane;

(8) FIGS. 7a, 7b and 7c show an embodiment of the present invention connected to the PCB of a consumer navigation device;

(9) FIGS. 8a and 8b show the radiation patterns of the antenna of FIGS. 7a to 7c when connected to the groundplane of the consumer navigation device; and

(10) FIG. 9 shows the impedance of an antenna of the present invention across a frequency band of interest both before and after matching;

(11) FIG. 10 shows a variation of the embodiment of FIG. 2 configured to generate LHCP;

(12) FIGS. 11 and 12 show an embodiment comprising an antenna with an integrated radio circuit;

(13) FIGS. 13 and 14 show an embodiment comprising an antenna with an integrated radio circuit and a screening can made from an extension of the ground plate; and

(14) FIG. 15 shows an alternative mounting arrangement on a PCB substrate.

DETAILED DESCRIPTION

(15) FIG. 2 shows a first embodiment of the present invention, comprising an antenna device 5 consisting of first 6, second 7 and third 8 conductive metal plates arranged in a substantially parallelepiped configuration. The third plate 8 defines a lower plane and the first 6 and second 7 plates together define an upper plane substantially parallel to the lower plane. The first 6 and second 7 plates are separated by a slot 9 in the upper plane.

(16) The first plate 6 comprises an active antenna arm that is provided with a feed connection or pin 10 that passes through a hole 11 provided in the third plate 8. The first plate 6 also has a grounding connection or pin 12 that connects to the third plate 8.

(17) The second plate 7 comprises a passive antenna arm that is provided with a ground connection or pin 13 that connects to the third plate 8 at an opposite end thereof to the ground connection or pin 12 of the first plate 6.

(18) It can be seen that the overall envelope of the antenna device 5 is that of a rectangular parallelepiped, with the area of the first and second plates 6, 7 and their intermediate slot 9 being substantially the same in size and shape as the area of the third plate 8, and substantially parallel thereto.

(19) Tabs 18, 19 are created in the third plate 8 so as to allow the antenna device 5 to be soldered along the edge of a host PCB (not shown). The tabs 18, 19 provide both a mechanical support and a ground connection. The tabs 18, 19 are preferably disposed in the same plane as the feed connection or pin 10 so that soldering can be done on a single side of the host device. Alternatively, tabs 18, 19 and the feed 10 can be arranged so that they are connected to different sides of the host PCB.

(20) FIG. 3 shows a second, alternative embodiment which is substantially the same as the first embodiment, except in that the feed connection or pin 10 and the ground connection or pin 12 of the first plate 6 are swapped around. The feed connection or pin 10 extends through the third plate 8 by way of a slot or cut-out 100 formed in the third plate 8.

(21) In a third embodiment, shown in FIG. 4, the first plate 6 is not provided with a ground connection or pin, but instead has only a feed connection or pin 10. In this embodiment, the first plate 6 is not physically connected to the third plate 8, and comprises a separate sheet of metal. In order to provide structural integrity, it is necessary for a non-conductive mechanical support 14 to be provided between the third plate 8 and the first plate 6.

(22) In a fourth embodiment, shown in FIG. 5, both arms (i.e. both the first plate 6 and the second plate 7) are fed and grounded. This arrangement is similar to the arrangement of FIG. 2, with the addition of a feed connection or pin 15 for the second plate 7 and an additional hole 11′ in the third plate 8 through which the feed connection or pin 15 may be passed. In this embodiment, the second plate 7 is fed with a signal that is out of phase with a signal that is fed to the first plate 6 so as to form a differential feeding arrangement.

(23) In one exemplary embodiment (FIG. 2) the antenna 5 is used without connection to a groundplane. The radiation patterns are shown in FIGS. 6a (z-x plane of the antenna pattern) and 6b (y-z plane of the antenna pattern) and they can be seen to be the same as those of a dipole, except that the patterns exhibit strong RHCP. The RHCP response is better than the LHCP response by a factor of 10 dB or more. This is very good for an electrically small device.

(24) In another exemplary embodiment (FIG. 2) the antenna 5 is connected to the PCB 2 of a consumer navigation device or other GPS-enabled device, as illustrated in FIGS. 7a, 7b and 7c. It can be seen in FIG. 7b that the antenna 5 is easily soldered or reflowed onto the edge of the PCB 2. FIG. 7c shows that the minimum device thickness is no longer dictated by the antenna 5, but rather by the PCB 2, an LCD screen 1, electronic circuitry 16 and a power supply 17.

(25) Despite the perturbing influence of the groundplane, the antenna 5 still exhibits a preference for RHCP, as can be seen in FIGS. 8a (y-z plane of the antenna pattern) and 8b (z-x plane of the antenna pattern). Furthermore, the antenna 5 shows excellent upward radiation characteristics, as required for most navigation applications. In this respect the radiation pattern of the present invention is similar to that of a ceramic patch antenna, but the present invention is much thinner in profile and cheaper to manufacture.

(26) An important advantage of embodiments of the present invention is that they have a wider impedance bandwidth than the sharp resonance of a ceramic patch antenna. This wider bandwidth makes it much easier to use in different applications. Furthermore, the antenna 5 is easily matched to the 50 ohm impedance typical of many RF systems using a simple LC matching circuit having typically one or two components. In different applications, the resonant frequency of the antenna 5 can therefore be adjusted simply by changing the matching circuit, at least within a reasonable frequency range. This is considered advantageous in the integration and manufacturing process, as the same antenna 5 can be easily re-used in many different devices without any physical or mechanical change. Only the matching circuit needs to be changed. An example of matching the antenna in a typical application is shown in FIG. 9.

(27) In the exemplary embodiments shown so far the antenna 5 has been used for GPS applications where RHCP response and an upward radiation pattern response is preferred. However, in other applications, LHCP may be preferred. RHCP and LHCP are easily swapped by symmetry operations. FIG. 10 shows a variation of the embodiment of FIG. 2, using the same labelling of parts, that is configured to generate LHCP. Other radiation patterns may be created by disposing the antenna 5 in different locations on the PCB 2.

(28) In the exemplary embodiments shown so far the antenna has been described as a stand-alone component separate from the radio. However, as shown in FIGS. 11 and 12, the presence of the bottom ground plate 8 allows the possibility of attaching a small PCB 20 mounted with the components required for a RF front end (Low Noise Amplifier plus a Surface Acoustic Wave filter) or a complete a radio receiver. In this way, an active antenna or complete radio-antenna module is created. The input to the LNA or radio receiver may be connected to the feed 10 of the antenna 5 and the ground of the LNA or radio would be connected to the bottom ground plate 8 of the antenna 5. The output of the radio/LNA is connected to the host PCB using a commercially available connector 21, coaxial cable or via soldering pins. A conductive shielding can 22 is provided to shield the LNA or radio receiver components.

(29) In a further embodiment, shown in FIGS. 13 and 14, the stamping, cutting and bending process used to create the antenna from a sheet of metal is also used to create a screened volume 23 beneath the ground plate suitable for locating the radio. The radio-antenna module is thus created with an integral screening can 23 for the radio.

(30) Instead of mounting the antenna device 5 on a top edge of a PCB substrate 2 as shown in, for example, FIGS. 7a to 7c, it is also possible for the antenna device 5 to be mounted on a flat surface of a PCB substrate 2 as shown in FIG. 15. In this arrangement, there is no requirement for tabs 18, 19, and the bottom ground plate 8 may be soldered directly to a flat surface of the host PCB 2 as shown.

(31) 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.

(32) 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.

(33) 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.