ANTENNA ARRANGEMENT FOR CEILING MOUNTED DEVICE

Abstract

An antenna is provided. The antenna comprises a dielectric lamina having a first face and a second face opposite the first face. The antenna further comprises a groundplane on the first face of the dielectric lamina, wherein the groundplane is a planar conductive groundplane comprising first and second L-shaped apertures. The antenna further comprises a microstrip transmission line on the second face of the dielectric lamina.

Claims

1. An antenna comprising: a dielectric lamina having a first face and a second face opposite the first face; a groundplane on the first face of the dielectric lamina, wherein the groundplane is a planar conductive groundplane comprising first and second L-shaped apertures; and a microstrip transmission line on the second face of the dielectric lamina.

2. The antenna of claim 1, wherein the groundplane comprises an edge and: wherein the first L-shaped aperture is adjacent to the edge of the groundplane so that a first conductive track is defined by a portion of the groundplane between the edge of the groundplane and the first L-shaped aperture; and/or wherein the second L-shaped aperture is adjacent to the edge of the groundplane so that a second conductive track is defined by a portion of the groundplane between the edge of the groundplane and the second L-shaped aperture.

3. The antenna of claim 1, wherein the first and second L-shaped apertures are adjacent each other so that a third conductive track is defined by the portion of the groundplane between the first and second L-shaped apertures.

4. The antenna of claim 1, wherein the first L-shaped aperture comprises: a first edge parallel to the edge of the groundplane so that a first conductive track is defined between the edge of the groundplane and the first edge of the first aperture, a second edge opposite the first edge of the first aperture, and a third edge extending between the first and second edges of the first aperture, and/or wherein the second L-shaped aperture comprises: a first edge parallel to the edge of the groundplane so that the second conductive track is defined by a portion of the groundplane between the edge of the groundplane and the first edge of the second aperture, and a second edge opposite the first edge of the second aperture and parallel to the first edge of the second aperture, and a third edge extending between the first and second edges of the second aperture wherein the third edge of the second aperture is adjacent the third edge of the first aperture so that a third conductive track is defined by a portion of the groundplane between the third edge of the first aperture and the third edge of the second aperture.

5. The antenna of claim 4, wherein the first L-shaped aperture comprises a fourth edge between the second edge of the first aperture and the first edge of the first aperture and opposite the third edge of the first aperture, wherein the fourth edge of the first L-shaped aperture is formed as a step.

6. The antenna of claim 4, wherein the second L-shaped aperture comprises a fourth edge between the second edge of the second aperture and the first edge of the second aperture and opposite the third edge of the second aperture, wherein the fourth edge of the second L-shaped aperture is formed as a step.

7. The antenna of claim 4, wherein the groundplane further comprises: a first gap between the first conductive track and the third conductive track; and/or a second gap between the second conductive track and the third conductive track.

8. The antenna of claim 7, wherein the groundplane further comprises: a fourth conductive track extending from an end of the first conductive track adjacent the first gap towards the second edge of the first aperture.

9. The antenna of claim 8, wherein the fourth conductive track extends at least 50% of the distance across the first aperture.

10. The antenna according to claim 7, further comprising a fifth conductive track that extends from an end of the second conductive track adjacent the second gap towards the second edge of the second aperture.

11. The antenna of claim 1, wherein the transmission line passes across first and second portions of the second face of the dielectric laminar that are opposite each of the first and second L-shaped apertures, respectively.

12. The antenna of claim 1, wherein the transmission line comprises a first conductive track on the second face of the dielectric lamina, wherein the first conductive track of the transmission line is substantially parallel to the edge of the groundplane wherein a distal end of the first conductive track of the transmission line is an open circuit, wherein a proximal end of the first conductive track opposite the distal end provides a feed for the antenna.

13. The antenna of claim 12, wherein the transmission line further comprises a second conductive track on the second face of the dielectric lamina perpendicular to the first conductive track of the transmission line and opposite the third conductive track of the groundplane.

14. The antenna of claim 12, wherein the transmission line further comprises a third conductive track on the second face of the dielectric lamina perpendicular to the first conductive track of the transmission line.

15. The antenna of claim 12, further comprising a RF connector, wherein an inner connection of the RF connector is conductively connected to the proximal end of the transmission line.

16. The antenna of claim 15, wherein a first ground area is provided on the second face of the dielectric lamina opposite a portion of the groundplane on the first face of the dielectric lamina and conductively connected therewith, wherein an outer connection of the RF connector is conductively connected to the ground area.

17. The antenna of claim 1, wherein the first aperture is dimensioned to provide operation on a first frequency band and/or the second aperture is dimensioned to provide operation on a second frequency band.

18. An antenna arrangement comprising a substantially planar conductive member having a first face and a second face opposite the first face, and one or more recesses in the first face, wherein each recess has a respective antenna according to claim 1 mounted therein, wherein each antenna is connectable with a respective cable, wherein each recess is dimensioned to accommodate the respective antenna and respective cable, wherein each recess corresponds with a respective opening in the second face of the substantially planar conductive member, wherein each opening is shaped to align with the first and second L-shaped apertures in the groundplane of the respective antenna mounted in the respective opening.

19. The antenna arrangement of claim 18, wherein each opening in the second face of the planar conductive member is dimensioned so that the boundary of the opening is at least a predetermined distance from the first and second L-shaped apertures of the respective antenna.

20. The antenna arrangement according to claim 18, wherein the planar conductive member is a flange outwardly extending from a substantially cylindrical body.

21. The antenna arrangement according to claim 18, wherein the groundplane of each antenna is proximate to a surface of the respective recess and is electrically insulated therefrom by a dielectric film.

22. The antenna arrangement according to claim 21, wherein the dielectric film is provided by: double-sided adhesive tape, solder resist, and/or anodising of an the proximate surface of the respective recess.

23. A lighting and/or loudspeaker device comprising an antenna arrangement according to claim 18.

24. The lighting and/or loudspeaker device according to claim 23, further comprising a housing having a front end from which light and/or sound is configured to project, wherein the antenna arrangement is provided in the form of a flange at the front end of the housing.

25. The lighting and/or loudspeaker device according to claim 24, wherein the lighting and/or loudspeaker device is suitable for mounting in a ceiling aperture in a ceiling, wherein the flange engages a front of the ceiling when the lighting and/or loudspeaker device is mounted in the ceiling aperture, wherein the lighting and/or loudspeaker device further comprises a biasing member mounted to the housing configured to engage and exert a force against a rear side of the ceiling when the lighting and/or loudspeaker device is mounted in the ceiling aperture to brace the lighting and/or loudspeaker device against the ceiling.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0087] FIG. 1(a) and FIG. 1(b) show external views of the ceiling mountable assembly.

[0088] FIG. 2 is a simplified cross section showing the device as mounted in a ceiling.

[0089] FIG. 3 is a view of a flange of the cylindrical device having four antennas positioned in openings therein.

[0090] FIG. 4 shows the groundplane side of an antenna.

[0091] FIG. 5 show the feed arrangements of an antenna.

[0092] FIG. 6 shows the antenna feed arrangement overlaid on the groundplane.

[0093] FIG. 7 is a detailed view of the accommodation for one antenna within a recess in a flange of the ceiling mounted device.

[0094] FIG. 8 is a graph showing the measured return loss of an antenna accommodated in the flange of the ceiling mounted device.

[0095] FIG. 9 is a graph showing the measured efficiency of an antenna accommodated in the flange of the ceiling mounted device.

[0096] FIG. 10 shows the radiation patterns of an antenna accommodated in the flange of the ceiling mounted device measured in the 2.4-GHz frequency band.

[0097] FIG. 11 shows the radiation patterns of an antenna accommodated in the flange of the ceiling mounted device measured in the 5-GHz frequency band.

[0098] FIG. 12 illustrates the sample P1.

[0099] FIG. 13 illustrates the impedance of P1

[0100] FIG. 14 shows Sample 2 as optimised for measurement.

[0101] FIG. 15 shows Sample 2 impedance.

[0102] FIG. 16 shows Sample 3 as optimised for measurement.

[0103] FIG. 17 shows Sample 3 impedance

[0104] FIG. 18 shows Return loss of sample 3 in free space and in sample ceiling materials.

[0105] FIG. 19 shows Sample 3a as optimised for measurement.

[0106] FIG. 20 shows return loss of sample 3a in free space and in the ceiling materials.

DETAILED DESCRIPTION

[0107] In the following description the antennas are described as physical entities distinct from the outwardly projecting flanges of the conductive housing of the host device. However it is to be understood that from a functional point of view the antennas and the host device form a single electromagnetic entity. By reason of the small dimensions of the antenna in terms of the operating wavelength it is necessary for the electromagnetic fields created within the structure of the antenna to excite radiating currents in the conductive host device. For this reason the conductive groundplane of the antenna is capacitively connected to the groundplane provided by the outwardly projecting conductive flange of the host device. Capacitive coupling is preferred to direct galvanic connection because it mitigates the possibility of intermetallic corrosion between the copper groundplane of a typical printed circuit laminate and the metallic flange onto which the antenna is mounted. An insulating layer may be provided between the groundplane of the antenna and the conductive flange by means of double-sided adhesive tape, solder resist on the groundplane or anodising of an aluminium flange.

[0108] The invention is further described by reference to the drawings.

[0109] FIG. 1 shows external views of the ceiling mountable assembly comprising a cylindrical body 1, a closure on an upper end of the cylindrical body 2, a mounting flange 3 on a lower end of the cylindrical body and spring retaining member 4. FIG. 1(a) shows the assembly in its orientation when mounted, while FIG. 1(b) shows it inverted.

[0110] FIG. 2 shows a simplified view of the mounted assembly in which an upper surface of the flange component 3 is in contact with a lower surface of a supporting planar member 6 and is held in place by at least two spring retaining members 4. The planar member 6 may form a ceiling or other structural component of a building and preferably comprises an electrically insulating material such as plasterboard, MDF or plywood. Planar member 6 may support a metallic foil 7 on its upper surface to enhance thermal insulation.

[0111] FIG. 3 shows an enlarged view of the flange component 3 seen obliquely from below in the configuration as mounted (FIG. 2), having recesses 11a, 11b, 11c, 11d and openings 10a, 10b, 10c, 10d, each of said recesses having a corresponding antenna 5a, 5b, 5c, 5d respectively mounted within it so that the antenna is aligned with the opening. The flange 3 may be in the form of a truncated circle, wherein the antennas are positioned in the regions having circular profile and maximum radial extent. The dimensions of the recesses 11a, 11b, 11c, 11d in the flange 3 are chosen together with those of the antennas 5 such that the antennas are entirely accommodated within the recesses. The dimensions of the openings 10 are chosen such that when the antennas 5 are each placed within a recess in the flange, the openings 21, 23 in the groundplane 20 of the antenna 5 closely match the openings 10 such that the edges of the openings lie between 0.5 mm and 1.0 mm within the groundplane in both radial and circumferential directions. This ensures that the conductive flange does not encroach on the functional area of the antenna while providing sufficient proximate area between the conductive groundplane of the antenna and the conductive flange to enable the flow of radio frequency currents by the capacitance thereby provided.

[0112] FIG. 4 shows a first surface of the antenna 5 comprising a first surface of a dielectric lamina 50 provided with a conductive foil groundplane 20 having a first opening 21 and a second opening 23 separated by a conductive region 25. The first opening 21 is arranged to be resonant in the 2.4-GHz frequency band and the second opening 23 is arranged to be resonant in the 5-GHz frequency band. The resonant frequency of the opening 21 is determined by its dimensions and also by the capacitance provided between conductive regions 24 and 25. In like manner the resonant frequency of the opening 23 is determined by its dimensions and also by the capacitance provided between conductive regions 26 and 25.

[0113] FIG. 5 shows a second surface of the antenna 5 comprising conductive foils on a second surface of the dielectric lamina 50. The image is oriented such that the corresponding features of the first and second surface are shown in the same relative position, that is as if seen through the dielectric lamina. A ground area of conductive foil 30 is provided at a first end of the second surface of the antenna and a ground area 31 is provided at a second end of the second surface of the antenna. Plated-through holes 32 (vias) are provided between the conductive foils 30, 31 and the groundplane 20 on the first surface of the antenna, such vias being positioned close to the periphery of conductive areas 30, 31 and typically spaced at intervals not exceeding 6 mm. An opening 33 is provided in the conductive area 31 to enable the placement of a subminiature coaxial connector, for example type W.FL. As shown in FIG. 5(a) the said connector is placed such that its body 36 may be connected by soldering to the conductive area 31 and its inner conductor 37 may be connected by soldering to the end 34 of microstrip transmission line 35.

[0114] The elongate microstrip transmission line 35 is preferably of arcuate form but may alternatively be of linear form. It extends from the coaxial connector 37 to an open circuit at its distal end 38 and has lateral branches 39, 40. Branch 39 preferably overlies the conductive member 25 formed in the groundplane foil on the first surface of the antenna.

[0115] The dimensions of openings 21, 23 may be determined by experiment or by simulation using suitable commercially available computer software. The width of the transmission line 35, the position of its distal open circuit end 38, and the length and width of each of the lateral branch lines 39, 40 are optimised by design together with the dimensions of the openings in the groundplane such that the input impedance of the antenna, when measured with the antenna placed within the recess 11 in the flange 3, is minimised across each of the operating frequency bands. By way of example the measured voltage standing wave ratio (VSWR) may be less than 3:1 across each of the frequency bands 2.4-2.485 and 4.9-5.8 GHz. This corresponds to a return loss exceeding 6 dB as shown in FIG. 8.

[0116] FIG. 6 shows overlaid views of the conductive foil on the first and second surfaces of the antenna. It will be seen that the microstrip line 35 passes across the openings 21, 23 in the underlying conductive foil 20.

[0117] FIG. 7 shows the antenna 5 positioned within recess 11 and proximate to opening 10 in the flange 3. A subminiature coaxial cable 44 positioned within a groove 45 in the flange 3 is connected by a coaxial plug 42 to the antenna connector 36. The distal end of coaxial cable 44 is connected to radio communications circuits. To protect the antenna 5 from damage, a second dielectric lamina 41 having no conductive foil on any surface is adherently connected to the antenna. Such connection may be provided by double-sided adhesive tape or by the use of a standard printed circuit board lamination process. The second dielectric lamina 41 is provided with an opening 43 to provide accommodation for the coaxial connectors 36, 42.

[0118] The depth of the recess 11 is chosen to be greater than the thickness of the antenna 5 together with the assembled height of the coaxial socket 36 and mating plug 42, such that no part of the antenna or the connected cable projects above the surface of the flange 3.

[0119] In a practical embodiment the printed circuit laminate accommodating the complete antenna had a radial dimension of 9.0 mm, an external circumferential dimension of 34 mm and was constructed on dielectric laminate 0.8-mm thick. The overall dimensions of the groundplane opening for the 2.4-GHz frequency band were 7 mm (radially)×9 mm (circumferentially), and those for the 5-GHz frequency band were 7 mm (radially)×4 mm (circumferentially). The antenna was constructed on glass-epoxy laminate having a relative permittivity of 4.0. The microstrip feed line 35 had a width of 1.0 mm and overlapped the groundplane 20 by 1.2 mm at its open circuit end. The larger branch conductor 39 was 1 mm wide×4.5 mm long and the shorter branch 40 was 1.0 mm wide×1.5 mm long and was positioned 7 mm from the input end of the coaxial socket.

[0120] The thickness of the dielectric lamina was 0.8 mm. The maximum assembled height of a coaxial plug and socket of type W.FL is 1.55 mm so the minimum required depth of the recess was 2.35 mm. W.FL2 is has a maximum assembled height of 1.3 mm so the minimum depth of the recess may be reduced to 2.10 mm with this connector. The cylindrical housing was 92.8 mm in diameter and 114 mm long, with a mounting flange extending 9.51 mm from the cylindrical housing (in some examples, the flange extends a maximum of 9.0 mm from the housing).

[0121] When optimally dimensioned the antenna requires no external matching network and no discrete internal tuning or matching components.

[0122] FIG. 8 shows the measured return loss of an antenna constructed according to the dimensions provided above and mounted in a plasterboard ceiling.

[0123] FIG. 9 shows the efficiency of the antenna, measured in a Satimo Stargate-64 chamber.

[0124] FIG. 10 shows radiation patterns and gain of the antenna in the 2.4-GHz frequency band measured in azimuth and elevation planes.

[0125] FIG. 11 shows radiation patterns and gain of the antenna in the 5-GHz frequency band measured in azimuth and elevation planes.

[0126] As would be expected from antennas mounted on a conducting platform, the radiation patterns are not omnidirectional in the azimuth plane. In order to optimise the use of the antenna configuration a first antenna and a second antenna having azimuth bearings separated by 180 degrees (with the device mounted as shown in FIG. 2) are preferably fed to two diversity inputs of a first radio device while a third antenna and a fourth antenna, mutually oriented at 90 degrees in the azimuth plane relative to the first and second antenna, are connected to two diversity inputs of a second radio device. This arrangement, when combined with the multipath propagation characteristics of a typical indoor environment provides a high level of data throughput and communications reliability.

[0127] The arrangement provides a mutual isolation between the antennas exceeding 25 dB in the 2.4-GHz frequency band and exceeding 28 dB in the 5-GHz frequency band, permitting their simultaneous use for different radio systems without suffering mutual interference.

[0128] In an alternative implementation the radio signals from each of the four antennas may be connected to radio circuits providing MIMO (multiple input multiple output) functionality.

EXPERIMENTAL NARRATIVE

[0129] A number of sample antennas were provided on 0.8-mm thick 370HR produced by a milling machine.

[0130] FIG. 12 illustrates the sample P1. FIG. 13 illustrates the impedance of P1

[0131] Sample 1 was fitted with via rivets and after adjustment produced the impedance shown in FIG. 13. The frequency of the two working bands is approximately correct. The impedance plot has a loop passing close to the chart centre at 2.4 GHz and curled round the centre at 5 GHz. This is the expected behaviour, but the impedance needs improving by getting a tighter curl at 5 GHz without degrading 2.4 GHz.

[0132] The impedance was measured with the antenna grounded to the chassis, separated by a thick card and also mounted using double sided tape. the results are slightly different in each case, but by much less than with the original version. The feed cable was wrapped three times through a ferrite ring to decouple the cable, but the effect of the cable is now much less than with the original breadboard models.

[0133] Sample 1 was set aside as a possible candidate for chamber testing. The objective of this first chamber test is to make sure that the efficiency of the antenna is sensibly consistent with the impedance plot, i.e. that losses are not significantly higher than would be expected from reflection loss. This creates confidence that when the impedance is further improved, efficiency will also be improved.

[0134] The ground area of sample 1 is more than it was hoped would be needed, so this should be reduced if at all possible.

[0135] Sample 2 was prepared, cutting the ground and the notches to the dimensions cut more approximately on sample 1. The edges of board were trimmed to make sure the copper would not contact the cylindrical surface of the chassis. The feed line was removed apart from a small tag to solder the connector inner, and replaced with a narrower track. After careful optimisation the results in FIG. 13 were obtained. This is much closer to what is needed. The difference in measured impedance with and without the ferrite choke on the cable is now negligible. The result does not change significantly with cable position at either band.

[0136] The radial trace on the ground side provides a capacitance which allows adjustment of the centre frequency of the 2.4-GHz response. The radial trace on the feed side helps to centre the impedance plot on the 5-GHz band. The lengths of the tuning line and the overlap of the main feed line with the ground side of the larger notch are both critical; trimming has been by the smallest increments possible with a sharp scalpel—probably less than 0.2 mm.

[0137] FIGS. 14 and 15 show the dimensions and impedance of this sample which will be kept as the default sample for measurements at the chamber.

[0138] FIG. 14 shows Sample 2 as optimised for measurement. The feedline here is copper tape; the provided track was removed apart from a 1.5-mm length close to the connector.

[0139] FIG. 15 shows Sample 2 impedance.

[0140] Sample 3: Reducing the width of the feed track from the connector moved the impedance plot to the right (larger R component). It would still be good to move further, so for sample 3 the width of the feed track will be reduced from 1.0 mm to 0.7 mm.

[0141] The extension of the larger notch was cut radially 2.2 mm wide and is 5.0 mm long; the extension of the small notch is 2.2 mm wide and 3.0 mm long. Both extensions are aligned with the outer edge of the existing notches. The tuning line is 0.6 mm wide and initially 7 mm long to allow for trimming to the correct frequency. It is aligned with the outer end of the large notch. The original feed line was trimmed straight (not curved) to 0.7 mm wide. The ground on each side of the feed was left in place.

[0142] Sample 4: The input feed line, as supplied, was trimmed to 0.7 mm wide. A slightly more complex arrangement used at the open circuit end of the feedline, but some improvement in return loss was achieved.

[0143] FIG. 16 shows Sample 3 as optimised for measurement. The feedline is as supplied but reduced in width. FIG. 17 shows Sample 3 impedance

[0144] The provided ceiling material samples were slightly modified by cutting a small radial groove to clear the U.FL connectors and cable, This was necessary because the present flange thickness assumes the use of a smaller connector. the groove was kept to a minimum size to avoid changing the antenna performance. The return loss of sample 3 in free space and in the samples is shown in FIG. 18.

[0145] FIG. 18 shows Return loss of sample 3 in free space and in sample ceiling materials. As expected, the least dense material (plywood) shows least effect at 2.4 GHz, but all the material had a similar effect at 5 GHz.

[0146] Sample 3 was modified by extending its low band notch by 2 mm. The feed was remade and adjusted to provide a bias towards the upper part of both bands in free space. The arrangement and return loss measurements are shown in FIG. 19.

[0147] FIG. 19 shows Sample 3a as optimised for measurement FIG. 20 shows return loss of sample 3a in free space and in the ceiling materials

[0148] Despite increasing the length of the small notch the frequency of best match has moved up. It will be interesting to see how the chamber results correlate with the return loss measurements. A second position for an antenna will now be prepared to allow measurement of the isolation between antennas in position on the chassis.