WO1996027917A1

WO1996027917A1 - Aperture-coupled planar antenna

Info

Publication number: WO1996027917A1
Application number: PCT/SE1995/000899
Authority: WO
Inventors: Björn LINDMARK; John Pettersson
Original assignee: Allgon Ab
Priority date: 1995-03-07
Filing date: 1995-07-31
Publication date: 1996-09-12
Also published as: SE504422C2; AU3488595A; SE9500839L; SE9500839D0

Abstract

An improved aperture-coupled planar antenna is disclosed, comprising a ground plane (5), an elongated feeding conductor (4) arranged in parallel with the ground plane (5), a conductive layer (2) provided with an elongated aperture (3) , a dielectric layer (1) arranged in parallel with the ground plane (5) and having fixed thereto, on a first side thereof, the elongated feeding conductor (4), and, on a second side thereof, the conductive layer (2), the elongated feeding conductor (4) intersecting the elongated aperture (3), and a dielectric carrier plate (13) having fixed thereon a radiating patch (14) arranged above and spaced from the conductive layer (2). The conductive layer (2) is attached to the ground plane (5) by a first spacer (6) extending from the ground plane (5) to the conductive layer (2) on the second side of the dielectric layer (1), the first spacer (6) functioning as a first mechanical support for the dielectric layer (1), an electrical connection between the conductive layer (2) and the ground plane (5), and a holder for a transmission line connector (8).

Description

APERTURE-COUPLED PLANAR ANTENNA

The present invention relates to the construction of an aperture-coupled planar antenna according to the first part of claim 1. Specifically, the invention relates to the general construction of an antenna, including spacer means for components of the antenna that facilitates such a construction.

Aperture-coupled planar antennas are disclosed in, e.g., Electronic Letters, No. 2, pp. 49-50, and US 5,355,143. These documents disclose the concept of a (microstrip) aperture- coupled planar antenna with arrangements of conductive and non- conductive layers. The selection of materials for the respective layers affect the performance of the antenna and its production method. In each of the disclosed antennas there is provided a solid dielectric material between a feeding conductor and a ground plane. The above-mentioned documents are incorporated by reference.

In order to avoid unwanted resonances and generation of inter- modulation products, which will affect the antenna function adversely, the ground plane and a conductive layer, situated above and spaced from the ground plane, must have a sufficient electrical connection. Further, the conductive layer must be mechanically supported in relation the ground plane. This is achieved by different or separate means in the prior art antennas. Such separate means involve a drawback in terms of complicated structure and increased costs.

A transmission line should be connected to the antenna via a connector arranged on the antenna. It is advantageous to couple the connector directly to the antenna ground and to a feeding conductor, respectively. This is not attained in the prior art antennas.

It is an object of the present invention to overcome the above- mentioned drawbacks of the prior art. It is another object to provide an aperture-coupled planar antenna with such a design that its housing masks the entry of a connected transmission cable into a wall, on which the antenna is mounted. It is another object to provide such an antenna with a low profile as well as an attractive physical appearance.

These objects are attained through an antenna according to the appended claims.

The invention will be described in detail below with references to the appended drawings, wherein Fig. 1 shows, in a perspective view, a bottom part of an antenna of the invention;

Fig. 2 shows, in a side view, the detailed structure of a first spacer combining different functions;

Fig. 3 shows, in a sectional view through an aperture of the antenna, components of the antenna and its enclosing housing; and

Fig. 4 shows, in side view similar to fig. 2, an alternative embodiment of the antenna.

With reference to Figs. 1-3, the aperture-coupled planar antenna is located inside a housing 15 and comprises a ground plane 5, an elongated feeding conductor 4 arranged substantially in parallel with the ground plane 5, a conductive layer 2 provided with an elongated aperture or slot 3, and a dielectric layer 1 arranged in parallel with the ground plane 5. The feeding conductor 4, the conducting layer 2, and the dielectric layer 1 are made of a (microstrip) laminate material. The elongated feeding conductor 4 extends perpendicularly to the elongated aperture 3. A dielectric carrier plate 13, forming an upper or hood part of the housing 15 of the antenna, is provided with a radiating patch 14 centred above the aperture 3. The patch 14 is adhered to the inside surface of the carrier plate 13 at a distance from the conductive layer 2.

The conductive layer 2 is attached to the ground plane 5 by means of a first spacer 6, constituted by a bent metal member, extending from the ground plane 5 to the conductive layer 2 on the second side of the dielectric layer 1, and being fastened with screws 11, 10. The first spacer 6 functions as a first mechanical support for the dielectric layer 1, as an electrical connection between the conductive layer 2 and the ground plane 5, and as a holder for a transmission line connector 8, which is fastened with screws. The shield conductor of the connector is connected directly to ground via the first spacer and the centre conductor 9 is soldered directly to the feeding conductor 4 on the dielectric board 1.

Four second spacers 12, constituted by projections integrated with the ground plane 5, provide a second mechanical support for the dielectric board 1, which is adhered to the second spacers for stability of the antenna. Alternatively, the spacers and the board 1 may be joined by conductive or non- conductive fastening means, e.g. screws.

The antenna housing 15 also includes the ground plane 5, which serves as a reflector. Normally, the ground plane is constituted by a metal plate mounted on a wall. The dielectric carrier plate 13, also serving as the upper or hood part of the housing, is joined to the ground plane 5 at circumferential edges thereof. The first spacer 6 is positioned at a distance from the edge, adjacent to an edge portion 7 of the ground plane 5 which is retracted from the main edge. The transmission cable may thus be connected to the transmission line connector 8 without making it necessary to remove the carrier plate. Also, the transmission line may be led from the antenna into the wall without the cable being exposed outside the housing.

The radiating patch 14 is arranged on the inside of the carrier plate 13, centred above the intersection of the feeding conductor 4 and the aperture 3, substantially in parallel with the ground plane 5. It has been found that, without affecting the radiating properties adversely, the carrier plate 13 and the radiating patch 14 may be slightly rounded or convexly curved for obtaining a low profile and a more attractive appearance of the antenna unit.

The first spacer 6 could be made an integrated part of the ground plane 5 through cutting a tongue in the edge of the ground plane and bending it into a suitable shape for providing the first spacer.

Alternatively, the first spacer may include a combination of a spacer element and fastening means. As shown in Fig. 4, the spacer element comprises a sleeve portion 16, which is internally threaded and is secured to the ground plane by means of a screw 17. An axial projection 16' of the sleeve portion 16 is formed as a screw threaded portion with smaller diameter. The screw threaded portion 16' extends through a hole in the dielectric layer 1 and engages whith a block or plate member 18, which is urged into contact with the conductive layer 2, when the screw threaded portion 16' is tightened. Hereby, the dielectric layer 1 is mechanically supported and an electrical connection is established between the conductive layer 2 and the ground plane.

Of course, the sleeve portion 16 can be a separate member, in which case the screw 17 may extend all the way through the sleeve and dielectric layer into the block or plate member 18.

In the embodiment shown in Fig. 4, the transmission line connector 8' is attached to a vertical metallic plate 19, which is secured to the metallic block or plate member 18 by means of a screw 20, adjacent to an edge portion of the dielectric layer 1.

Finally, the dielectric carrier plate 13 may be disposed separately from the antenna housing. Thus, it may be constituted by at least one body of dielectric material fixed to the dielectric board 1 for carrying the radiating patch.

Claims

1. An aperture-coupled planar antenna comprising: a ground plane (5) ; - an elongated feeding conductor (4) arranged substantially in parallel with said ground plane (5) ; a conductive layer (2) provided with an elongated aperture (3) ; a dielectric layer (1) arranged substantially in parallel with said ground plane (5) and having fixed thereto, on a first side thereof, said elongated feeding conductor (4), and, on a second side thereof, said conductive layer (2), said elongated feeding conductor (4) intersecting said elongated aperture (3) ; - a dielectric carrier plate (13) having fixed thereon a radiating patch (14) arranged above and spaced from said conductive layer (2) , c h a r a c t e r i z e d i n that said conductive layer (2) is attached to said ground plane (5) by means of a first spacer (6, 6') extending from said ground plane (5) to said conductive layer (2) on said second side of said dielectric layer (1), said first spacer (6, 6') functioning as a first mechanical support for said dielectric layer(1); an electrical connection between said conductive layer (2) and said ground plane (5) .

2. An antenna according to claim 1, wherein said first spacer (6) holds a transmission line connector (8) .

3. An antenna according to any one of claims 1-2, wherein said first spacer (6) is a bent metal member connected to said ground plane (5) and provided with fastening means for said transmission line connector and said dielectric layer (1) with said conductive layer (2) .

4. An antenna according to any one of claims 1-3, wherein said first spacer (6) means is an integrated part of said ground plane (5) .

5. An aperture-coupled planar antenna according to claim 1 or 2, wherein said first spacer (6') comprises a spacer element

(16) located between said ground plane (5) and said dielectric layer (1), a metallic plate member (18) contacting said conductive layer (2) on said second side of said dielectric layer (1), and metallic fastening means (16', 17), securing said spacer element (16, 16') and said metallic plate member

(18) so as to provide said first mechanical support and said electrical connection.

6. An antenna according to claim 5, wherein said first spacer element comprises a sleeve portion (16).

7. An antenna according to claim 5 or 6, wherein said metallic fastening means comprise at least one screw (16', 17).

8. An antenna acccording to claim 2 in combination with any one of claims 5-7, wherein said transmission line connector (8¹) is located at a metallic holding plate (19), which is secured to said plate member (18), by means of a metallic fastener (20) .

9. An antenna according to any one of claims 1-8, wherein at least one second spacer (12) constituted by a projection integrated with said ground plane (5) provides a second mechanical support for said dielectric layer (1) .

10. An antenna according to any one of claims 1-9, provided with a housing (15) comprising two parts, whereof said dielectric carrier plate (13) forms a first part and said ground plane (5) forms a second part, said dielectric carrier plate (13) being joined to said ground plane (5) at joining edges thereof, said first spacer (6) being positioned adjacent to an edge portion (7) of said ground plane (5) which is retracted from said joining edges in order to allow a portion of a transmission line, connected to said transmission line connector (8) , to be accomodated within the housing (15) .

11. An antenna according to any one of claims 1-10, wherein said dielectric carrier plate is constituted by at least one body of dielectric material fixed to said dielectric layer (1) with said conductive layer (2) .

12. An antenna according to any one of claims 1-11, wherein said radiating patch (14) is arranged substantially in parallel with said ground plane (5) .

13. An antenna according to any one of claims 1-12, wherein said dielectric carrier plate (13) has a somewhat curved or cylindrical shape and said radiating patch (14) has a substantially corresponding shape.

14. An antenna according to any one of claims 1-13, wherein said dielectric layer (1) is made of a laminate material.