Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
1998-06-17
2001-06-26
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S713000, C343S742000, C343S867000
Reexamination Certificate
active
06252550
ABSTRACT:
TECHNICAL FIELD
The present invention relates to antennas intended to be affixed to surfaces, for use with radio frequency devices such as cellular phones, GPS location systems, and other RF applications. The present invention further relates to a method for manufacturing conductive patterns on substrates.
BACKGROUND ART
Many applications currently exist where an RF antenna is provided in order to enable communication—for example, cellular telephones, GPS systems, wireless data networks and the like. In some cases the antenna is provided with the device, for example as a stub unit on a cellular phone. In other cases, however, it is necessary to provide an externally connected antenna. Further, in applications such as in-car use of cellular phones, it is desirable to provide an additional antenna to boost signal strength. Traditional antennas for this purpose have been generally externally mounted on the vehicle. This increases wind noise, is prone to vandalism, and detracts from the appearance of the vehicle.
For any antenna application of this type, various issues need to be considered. Apart from addressing the problems mentioned above, the antenna should provide maximum capture area, whilst ideally being visually unobtrusive. It should be simple to install, yet electrically and structurally reliable.
It has been proposed to provide an antenna by adhering an array to the inside of a window of a motor vehicle. U.S. Pat. No. 5,363,114 to Shoemaker describes a planar, serpentine antenna which is adhered to a carrier layer, and which is then adhered to a suitable vehicle surface. The antenna is disclosed as having a serpentine patterned arrangement.
It is an object of the present invention to provide an improved antenna for mounting on planar surfaces.
SUMMARY OF INVENTION
According to one aspect the present invention provides a planar antenna. The planar antenna has a rectangular conductive element formed from two square elements. The square elements are defined within the rectangle by a centrally located return conductor. Each square element is connected at one end to a connector element, and at the other end to the return conductor. The dimensions of the square elements are chosen so as to maximize gain for selected radio frequencies. The antenna further includes one or more additional square elements disposed within the square elements. Each additional square element is connected to the respective square element at one end being defined by the return conductor on one side.
It will be understood that the term planar is intended to mean both flat surfaces and smooth curved surfaces, such as for example the shape of a vehicle windshield.
The inventive antenna arrangement has a number of advantages over the existing designs. The intended applications, where the antenna is adhered to an existing surface such as a window, do not require that the conductive elements be structurally rigid themselves, thereby enabling the use of a sparse geometry. This also enables the antenna to have a relatively large capture area, as it is mounted on a surface and not freestanding. Further, as there are elements disposed both horizontally and vertically, the antenna can receive either vertically or horizontally polarized signals well, which is advantageous in applications where scattering due to buildings and other structures occurs.
In the preferred implementation, the antenna also has the advantage of not requiring impedance matching electronics. A simple square antenna of the proportions of one of the square elements forming the antenna, with conductors 1 mm wide and 25 microns thick, has an impedance of about 100 ohms. Because the present antenna arrangement has in effect two impedances of this size in parallel, the impedance is about 50 ohms, and so the inventive antenna can be directly connected to a standard 50 ohm cable. This reduction in impedance is inherent in the design.
The present invention also provides a method for providing conductive elements for the antenna on a substrate, including the steps of:
printing a desired conductor pattern onto a substrate, using conductive ink; and
electrodeposition further conductive material onto the conductor pattern, using the pattern formed from conductive ink as an electrode in an electroplating process.
The conductive material may be conveniently copper. The parameters of the electroplating process will depend upon the process selected, but should be such as to provide an adequate thickness of copper, but not so much that too much copper is deposited and the pattern becomes vulnerable to mechanical failure. The inventor has found that in the cellular phone application a thickness of about 25 microns is suitable.
The pattern is suitably printed using a screen printing process. In practice, a large sheet of flexible material can be printed and cut using a suitable tool to provide many antenna arrays.
After depositing, preferably a double sided adhesive film, preferably transparent, is applied both to provide a mechanism for adhesion to the desired surface, and to inhibit corrosion of the copper.
The inventors have investigated various methods for practical manufacture of the antenna. Whilst the invention arose in this context, it will be understood that the inventive method can equally be applied to manufacture of other conductor on substrate devices. The use of conductive ink alone did not provide suitable resistive properties for the antenna, and the addition of electrodepositing to the printing approach was only arrived at after significant trial and error.
REFERENCES:
patent: 2082812 (1937-06-01), Worrall
patent: 3390394 (1968-06-01), Glimvall
patent: 5198826 (1993-03-01), Ito
patent: 5363114 (1994-11-01), Shoemaker
patent: 5442368 (1995-08-01), Harada et al.
patent: 5714965 (1998-02-01), Taguchi
patent: 5757328 (1998-05-01), Saitoh
patent: 5973650 (1999-10-01), Nakanishi
Akerman & Senterfitt
Ho Tan
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