CN1393957A - planar antenna device - Google Patents

Abstract

A planar antenna comprising a rectangular conductive element formed by two square elements, the square elements being defined within the rectangle by a centrally located and bifurcated return conductor having two leads, each square element being connected at one end to a connector element and at the other end to said return conductor, wherein the dimensions of the square elements are selected so as to have maximum gain for a selected radio frequency, characterised in that the antenna further comprises one or more additional partial square elements, each additional partial square element terminating at one end adjacent a respective square element and being defined on one side by a lead of the return conductor.

Description

planar antenna device

technical field

The present invention relates to antennas intended to be fixed to a surface for radio frequency equipment, such as a cellular telephone, GPS positioning system, and other RF applications. The invention also relates to a method for producing conductive patterns on a substrate.

Background technique

An RF antenna is provided in many existing applications to enable communications, such as cellular telephones, GPS systems, wireless data networks, and the like. In some cases, the device is equipped with an antenna, such as a stub unit on a cellular phone. In other cases, however, an externally connected antenna needs to be provided. Additionally, for applications such as cellular phones used in automobiles, it is desirable to provide an additional antenna to enhance signal strength. Conventional antennas for this purpose are usually mounted externally on the vehicle. This increases wind noise, is prone to damage, and detracts from the appearance of the vehicle.

For any antenna application of this type, various issues need to be considered. Moving away from the problems indicated above, the antenna should provide the largest effective area while preferably being unobtrusive in appearance. Installation should be simple and electrically and structurally reliable.

It has been suggested to provide an antenna by adhering an array to the inside of a window of a car. US Patent No. 5,363,114 to Shoemaker describes a planar, helical antenna that is adhered to a carrier layer and then adhered to a suitable vehicle surface. The disclosed antenna has a helically patterned arrangement.

It is an object of the present invention to provide an improved antenna for mounting on a planar surface.

Summary of the invention

According to one aspect of the present invention, there is provided a planar antenna comprising a rectangular conducting element formed by two square elements, the square element being defined within the rectangle by a centrally positioned and bifurcated return wire having two leads, Each square element is connected on one end to a connector element and on the other end to said return wire, wherein the dimensions of the square elements are chosen so as to have maximum gain for the selected radio frequency, characterized in that the antenna further comprises One or more additional but partial square elements, each additional partial square element terminating at one end adjacent to a respective square element and bounded on one side by a lead of the return conductor.

It should be understood that the term planar means both flat surfaces and smoothly curved surfaces, such as the shape of a car windshield.

The antenna arrangement of the present invention has a number of advantages over existing designs. In the intended application, where the antenna is adhered to an existing surface (such as a window), the conductive element itself does not need to be structurally rigid, thus enabling the use of sparse geometries. Furthermore, this enables the antenna to have a relatively large effective area since it is mounted on a surface rather than being freestanding. In addition, with elements arranged horizontally and vertically, the antenna is good at receiving vertically or horizontally polarized signals, which is advantageous in applications where scattering occurs due to the presence of buildings and other structures.

Furthermore, the present invention provides a method for providing conductive elements on a substrate comprising the steps of:

printing a desired conductive pattern on a substrate using conductive ink; and

In an electroplating process, additional conductive material is electrodeposited on the conductive pattern using the pattern formed from the conductive ink as an electrode.

Conveniently, the conductive material may be copper. The parameters of the electroplating process will depend on the process chosen, but should provide a sufficient thickness of copper without depositing so much copper that the pattern becomes prone to mechanical failure. The inventors have found that in cellular telephone applications, a thickness of about 25 microns is suitable.

Graphics are adapted to be printed using a screen printing process. In practice, a large sheet of flexible material can be printed and cut using appropriate tooling to provide many antenna arrays.

After deposition, a double-sided adhesive film (preferably clear) is preferably applied to provide a mechanism for adhesion to the desired surface and to prevent corrosion of the copper.

The inventors have studied various methods for the actual manufacture of the antenna. Although the invention has been explained herein, it should be understood that the invention is equally applicable to the fabrication of other conductors on substrate devices. The use of conductive ink alone would not provide the proper resistive properties of the antenna, and adding electrodeposition to the printing method was only arrived at after a great deal of trial and error.

Brief description of the drawings

An embodiment of the invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a plan view of an embodiment of the apparatus of the present invention;

Figure 2 schematically shows the connections of another embodiment of the invention enabling multi-device connections; and

FIG. 3 is an exploded view of the connector arrangement of FIG. 2 .

Detailed description of the invention

The invention is primarily described with respect to devices designed to be adhered to a surface as an additional device. However, it should be clear that the inventive antenna design may be formed as part of an article, or formed within eg a part of a vehicle or the housing of an electronic device.

Figure 1 shows an embodiment of the present invention suitable for use as a multi-band antenna for use on the frequency bands of cellular telephone frequencies, global satellite positioning (GPS) frequencies and personal communication system (PCS) frequencies.

Antenna 10 is generally rectangular in shape and is formed of four elements 12 , 13 , 17 and 18 . The two elements 12 and 13 are square elements connected to connector elements 32 and 33 respectively. The adjacent sides of the elements 12 and 13 are formed by the leads 41 and 42 of a common return element which is also connected to the connector element 31 . The two elements 17 and 18 are part square elements and are provided inside the elements 12, 13 respectively. However, part of the square elements 17 and 18 are not (like the square elements 12 and 13 ) connected to the connector elements 32 and 33 but do not reach the leads 41 , 42 respectively. This bifurcated element with leads 41 and 42 forms a common side of the square (or part of a square) formed by each element 12 , 13 , 17 and 18 and is connected to the central connector 31 .

This design is based on the realization that for many applications, reception on multiple frequency bands is useful, and that multiple harmonics of the 900MHz band are close to other frequency bands, in this case the GPS band at 1575MHz , PCS frequency band in 1800-2000MHz. Elements 12 and 13 have dimensions suitable for 900MHz+/-50MHz. Central elements 17 and 18 allow proper resonance on the GPS and PCS frequency bands.

Antenna dimensions are shown in the figure. Tracks are expected to be about 1 mm across and about 30 microns thick, including conductive ink and copper. Although the corners are shown as right angles, they could be rounded if desired. The antenna elements are mounted on a sheet 11 (shown in dashed outline) of a suitable flexible material. This can be any suitable substrate, such as clear polyester, or any material used for flex PCBs. Preferably the material is transparent, especially when used in a vehicle, so that visual distraction is minimized. In the application in question, the film thickness is suitably between 75 and 300 microns.

The proper length of the antenna element can be determined according to the formula:

L=K/F

where L is the length, F is the frequency, and K is a constant that varies with the dielectric properties of the material surrounding the conductor. In the case of the described implementation, the dielectric properties of the substrate need to be taken into account. It will be appreciated that, in use, the dielectric properties of the surface being adhered (eg a windshield) will also be related to the constant K, and thus the length L.

For an antenna of the dimensions shown in Figure 1, the resonant frequencies on one glass substrate are 99MHz and 1800MHz, and the antenna has a VSWR of 1.08:1 in the 900MHz band and 2.8:1 in the 1575MHz band.

The transparent films used in the best implementations cannot tolerate the high temperatures involved, for example, in soldering. Figure 3 shows an exploded view of an arrangement developed by the inventors that enables the connection of the antenna to a transmission line.

In the embodiment of Figures 2 and 3, element 20 is a connecting portion of a copper trace. It should be understood that this is held between the substrate film 11 and the double-sided adhesive film (not shown), and thus the contacts are not exposed for simple connection. The spacer 21 is placed under the element 20 and the socket 22 is placed above the element 20 . Conductive rivets, such as brass, are inserted through the openings 24 , 25 , 26 , 27 in the spacers, through the element 20 , and through corresponding holes in the socket 22 . This provides an electrical connection between the body of the receptacle 22 and the exterior 16 of the element 20 . Another rivet passes through the central portion 15 of the element 20 and into the central portion of the socket 22 . The plug 23 is then easily connected by means of an illustrative press-fit mechanical connection to provide a cable link to the device for connection to the antenna.

Figure 2 shows a connection arrangement according to the invention for a device - in which multiple frequency bands are received and where it is desired to connect signals of these frequency bands to different devices. Exemplary, these devices are a cellular phone and a GPS receiver. Antenna 30 is connected to plug 23 on cable 24 via socket 22 . A cable 24 connects the antenna to an antenna power splitter unit 25 . This provides a connection 26 for a cell phone and a connection 27 for a GPS receiver.

Devices suitable for use as antenna power splitter 25 are commercially available. The function of this device is to isolate the output ports 26, 27 from each other so that the respective devices do not interfere with each other. In this particular case, the concern will be to ensure that the cellular phone's transmitted energy reaches the GPS receiver. Desirably, the antenna power splitter should have an isolation factor of at least -25dB in this application. It should be clear that the required isolation will depend on the equipment intended to be connected to antenna 30 .

It should be appreciated that although the invention has been primarily described in the context of a vehicle antenna adhered to the inside of a window, many other applications exist. The inventive antenna can be adhered to an interior or exterior building wall, or used to implement a wireless LAN or other data network. It can be easily used, modified to adapt to frequency band changes, for mobile or fixed data recording and transmission.

The method of the present invention can be applied wherever a highly conductive pattern is required, especially when transparent substrates are used.

Claims (9)

1. A planar antenna comprising a rectangular conductive element formed by two square elements defined within the rectangle by a centrally positioned and bifurcated return wire having two leads, each square element at one end is connected to a connector element on the other end and to said return wire on the other end, wherein the dimensions of the square element are chosen so as to have maximum gain for the selected radio frequency, characterized in that the antenna further comprises one or more additional each additional partial square element terminates on one end adjacent to the corresponding square element and is defined on one side by a lead of the return conductor. 2. An antenna according to claim 1, wherein the conductive element is formed on a substrate. 3. An antenna according to claim 2, wherein the substrate is a flexible film. 4. An antenna according to claim 2 or 3, wherein the substrate is transparent. 5. An antenna according to claim 1, wherein all the square elements are electrically connected to the same connector element, and the return wire is connected to an electrically separate connector element. 6. An antenna according to claim 2, wherein the conductive element is provided by a method comprising the steps of: printing a conductive pattern on the substrate using conductive ink; and In an electroplating process using patterns formed from conductive ink as electrodes, additional conductive material is electrodeposited on top of printed conductive patterns. 7. An antenna according to claim 6, wherein the conductive pattern is screen printed on said substrate. 8. An antenna according to claim 7, wherein a plurality of conductive patterns are printed on said substrate, and after electrodeposition, a protective film is applied to the conductive patterns. 9. An antenna according to claim 8, wherein the film is adhesive on both sides.

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