Antenna assembly for electronic device

Abstract

An antenna assembly for an electronic device, the antenna assembly comprising a conductive structure for housing at least a circuit board of the electronic device, an antenna formed as a slot in the conductive structure, a feeding element for feeding the antenna by electromagnetic coupling, the feeding element being positioned between the conductive structure and the circuit board and orientated to extend across said slot, the feeding element being connected to a feed line on the circuit board.

Claims

1. An antenna assembly for an electronic device, the antenna assembly, comprising: a conductive structure for housing at least a printed circuit board of the electronic device, the conductive structure including a base plate, a front plate and a side plate, the front plate and side plate extending perpendicularly from the base plate, an antenna including a radiating part formed as a slot in the front plate and an excitation part formed as a linear slot in the base plate connected to and extending from the radiating part where the front and base plate meet, wherein the radiating part has a tapered shape tapering towards the excitation part and divides the front plate, a feeding element for feeding the antenna by electromagnetic coupling, the feeding element being positioned between the base plate and the circuit board, and orientated to extend across said excitation part and wherein the excitation part being configured to electromagnetically couple with the feeding element, the feeding element being connected to a feed line on the circuit board, wherein the printed circuit board lies on the base plate and comrises a ground plane positioned at a predetermined distance from the front plate, the ground plane being provided with openings positioned in alignment with the feeding element and the excitation part of the slot.

2. The antenna assembly according to claim 1, wherein the feeding element is orientated to extend across the excitation part of the slot.

3. The antenna assembly according to claim 1, wherein the excitation part of the slot and the feeding element are positioned over corresponding openings in the ground plane of the circuit board.

4. The antenna assembly according to claim 1, wherein the feed element is positioned at a predetermined distance from the base plate and the circuit board, respectively.

5. The antenna assembly according to claim 1, wherein the feed element is held in position by a spacer made of insulating material.

6. The antenna assembly according to claim 1, wherein the conductive structure forms a ground reference plate for electronic components of the electronic device.

7. An electronic communication device comprising an antenna assembly according to claim 1, and a printed circuit board provided with a feed line for feeding the antenna assembly.

8. The electronic communication device according to claim 7 wherein the electronic device is a gateway device or a set top box.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which:

(2) FIG. 1 is a perspective view of a housing fitted with an antenna in accordance with the present invention.

(3) FIG. 2A is a perspective view of an antenna assembly and a printed circuit board in accordance with an embodiment the present invention;

(4) FIG. 2B is a top view of an antenna assembly and a printed circuit board in accordance with an embodiment the present invention;

(5) FIG. 3 is a vertical cross-section view of an antenna assembly and a printed circuit board in accordance with an embodiment the present invention

(6) FIG. 4 and FIG. 5 graphically illustrate curves as a function of frequency giving the performances obtained by simulating an antenna in accordance with embodiments of the present invention.

(7) FIG. 6A is a schematic representation of an antenna in accordance with an embodiment the present invention

(8) FIGS. 6B and 6C graphically illustrate radiation patterns of the antenna of FIG. 6A.

DETAILED DESCRIPTION OF THE INVENTION

(9) An embodiment of the present invention will be described by referring to an electronic device for a domestic network operating in the 2.4 GHz band. It will be appreciated that the invention is not limited to this specific type of device and may be applied to any wireless communication device. In the exemplary electronic device, a metal plate structure may be typically used as shielding and/or as a ground reference plate. The role of this metal plate structure is to obtain the electromagnetic compatibility of the electronic device that includes multiple electronic components, connectors and other circuits. The metal plate structure is used as ground reference for the elements and can reduce interfering signals. Embodiments of the present invention use this metal plate structure to produce a slot-antenna and supply this antenna by means of a contact-free interface.

(10) FIG. 1 is a perspective view of a conductive structure 1, forming a housing or ground reference structure for an electronic device in accordance with an embodiment of the invention. The conductive structure 1 is composed of metallic material and comprises a first lower metal plate 1a, forming a base plate 1a, and side plates 1b, 1c extending perpendicularly from the base plate 1a to form a front plate 1b and a side plate 1c. The metal plates form an open housing structure 1 in conductive material providing the function of a ground reference plate structure. In some embodiments of the invention the conductive structure acts as shielding. A slot-antenna 2 is formed in the conductive structure 1 and comprises a radiating part 2a and an excitation part 2b. The radiating part comprises an open slot 2a formed in the front plate 1b. The open slot 2a has a tapered form tapering inwards from the edge of the side plate 1b towards the base plate 1a and is extended by a linear slot 2b in the base plate 1a, forming the excitation part 2b. The linear slot 2b is used to feed the slot antenna 2 by electromagnetic coupling with a feeding strip 4 orientated to extend across the linear slot 2b. The linear slot 2b terminates in a short-circuit.

(11) FIGS. 2A and 2B schematically illustrate an antenna assembly comprising the conductive structure 1 of FIG. 1 and a printed circuit board PCB 3 of an electronic device disposed in the conductive structure 1. The PCB 3 is formed in a known manner, from at least one substrate in a dielectric material, featuring on one face a layer of conductive material forming a ground plane and on the opposite face a layer of conductive material that is printed, for providing a microstrip feed line 3c.

(12) The ground plane of the PCB 3 is provided with openings 3a, 3b located in correspondence respectively with the excitation slot 2b and the feeding strip 4.

(13) FIG. 3 is a schematic side view of the antenna assembly illustrating the elements enabling the supply of the slot-antenna 2 realised in the conductive housing structure 1. Feeding strip 4 is disposed between the PCB 3 and the base plate 1a of the conductive housing construction 1. A spacer 5 in insulating material, for example plastic, is mounted between the base plate 1a of the conductive housing structure 1 and the printed circuit board 3. In the illustrated embodiment the spacer 5 is provided by an insulating ring around the feeding strip 4. This spacer maintains the required distance between the feeding strip 4 and the base plate 1a and the printed circuit board 3, respectively. In the embodiment shown in FIG. 3, the feeding strip 4 has an L-shaped form so as to be positioned perpendicularly to and across the linear slot 2b and to pass through a via realised in the printed circuit board 3 for connection to the microstrip feed line 3c realised on the upper face of the printed circuit 3 for feeding the antenna 2. The ground plane 3d of the printed circuit board 3 has an opening 3a realised in the ground plane 3d and positioned to correspond to the linear slot 2b. Feeding of the slot antenna 2 is provided by electromagnetic coupling between the linear slot 2b, acting as an excitation part of the slot antenna 2 and the feeding strip 4 connected to the feed line 3c. To do this, the slot 2b and the strip 4 have a length equal to around λ/4 where λ is the guided wavelength at the operating frequency of the environment, the value of λ depending on the environment and the propagation mode.

(14) The simulation of an antenna in accordance with the described embodiments was realised in the Wi-Fi band of frequency 2.4 GHz. For this simulation the 3D electromagnetic tool HFSS™ (for High Frequency Structural Simulator) was used. The following parameters were taken for the simulation.

Simulation Parameters

(15) TABLE-US-00001 Printed Substrate = FR4, dielectric constant = DK = 4.4, circuit board dissipation factor = Df = 0.02 or PCB Surface = 114 × 90 mm2 Thickness = 0.2 mm width of the impedance microstrip line, characteristic 50 Ohm = 0.36 mm Strip square cross-section = 0.6 × 0.6 mm2 horizontal length of the slot at the open end = 14.5 mm horizontal length of the slot at the vertical point = 2 mm air thickness: strip at the PCB = strip at the plate = 0.6 mm horizontal slot width = 1.5 mm shielding length of the slot of the strip at short-circuit = 16.4 mm plate length of the slot of the strip in the vertical plane of the antenna = 4 mm Vertical Height = 35 mm shielding Width = 52 mm plate Distance of the PCB to the vertical plate = 3 mm width of the slot of the open end = 9.75 mm width of the slot of the plate end = 1.5 mm Plate T = 1 mm thickness Grounding metal posts are added in simulation between the shielding plate and the ground plane of the printed circuit board, providing a common grounding

(16) After optimization of the loss level by adding a parallel inductance of value Lp=3.5 nH and a series capacitor of value Cs=2.7 pF in parallel on the input, the results provided in FIGS. 4 and 5 were obtained. FIG. 4 shows the response of the return losses, this curve shows a level of loss close to −15 dB in the frequency band between 2.4 and 2.5 GHz.

(17) FIG. 5 shows responses for the efficiency of the antenna and efficiency of the radiation as a function of the frequency, respectively. These two curves show an efficiency greater than 95% for the radiation and for the antenna. Moreover in FIG. 6, the radiation patterns of an antenna in accordance with the present invention are shown diagrammatically in 3D. These diagrams show that the slot-antenna in accordance with the invention shown diagrammatically in (A) radiates mainly to the front (B) and on the right-hand side (C) of the electronic device in which the antenna is integrated.

(18) Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention.

(19) For instance, while the foregoing examples have been described with respect to an open slot antenna the antenna may be provided in other shapes.

(20) For example, the antenna may be formed by a closed slot, or by an open slot such as a tapered slot antenna or by a tapered open slot providing a Vivaldi type antenna. The conductive construction used to realise the antenna can be a plate of conductive material other than a ground reference plate or a shielding plate. The conductive feeding strip can have a meandering shape to reduce its size. Likewise, the feed strip and excitation slot can be oriented differently. They should simply cross each other to create an electromagnetic coupling enabling the supply of the antenna. Moreover, in some embodiments of the invention the radiating slot can be realised on the same plane as the excitation slot.

(21) Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.