Patent Application
20100141533
In modern wireless communications, there is a growing need for small-size, low-cost antennas for a wide range of portable and handheld devices. Currently, most antennas for mobile devices are fabricated by patterning copper traces on a substrate or stamped metal. These substrates are large and costly to fabricate. Another problem with regard to the size of the antenna may be for example, antennas for an Ultra High Frequency (UHF) spectrum (e.g., 470 MHz to 860 MHz) which are longer in size (e.g., a dipole antenna for 680 MHz is 20 cm in length by 1.5 cm wide) and that may be used for small size mobile devices such as, for example, laptop computers, handheld devices and the like.
Magnetic meta-materials have been explored for use as antenna substrates, but they are complex and expensive to manufacture. A study that used ferrite to increase the bandwidth of the antenna had as a side effect, a 7.5% reduction in the resonant frequency as compared to an air-core antenna. Another study obtained a mere 1.2% reduction in the resonant frequency. It is compelling to have small antennas in a space limited mobile device
The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanied drawings in which:
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
According to embodiments of the invention antenna substrates with increased permeability that may lead to antenna miniaturization, enhanced bandwidth, and improved radiation and polarization characteristics are presented. For example, the antenna structures may use a magnetic material that includes depositing magnetic material such as, for example amorphous CoZrTa. The amorphous CoZrTa may be applied for example, to a backside of a textured antenna substrate of a dipole antenna which may miniaturize the dipole antenna and/or improve the dipole antenna bandwidth.
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According to some exemplary embodiments of the invention, wireless communication system may include a base station 110 and mobile stations 120 and 130. Base station 110 may include an at least one antenna 115, mobile station 120 may include an at least one antenna 125 and mobile station 130 may include an at least one antenna 135, although it should be understood that this example wireless communication system is not limited in this respect.
According to this exemplary embodiment, mobile stations 120 and 130 may include a mobile handheld device, a laptop computer, a netbook computer, a mobile telephone device, a mobile game console and the like.
Although the scope of the present invention is not limited in this respect, at least one of antennas 115, 125 and 135 may include a dipole antenna with a magnetic film coated on a textured backside of the dipole antenna. The magnetic film may include Cobalt (Co), Zirconium (Zr), Tantalum (Ta) alloy, although it should be understood that other magnetic film alloy with other elements which provide similar properties may be used with embodiment of the invention.
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According to exemplary embodiments of the invention, magnetic film 440 is coated on the textured backside of antenna substrate 420. This texturing may create isotropic magnetic properties and may change the effective permeability of magnetic film 440. The resulting size of the exemplary dipole antenna 400 may be less than half the length of the air-core antenna, although the scope of the present invention is not limited in this respect.
In another embodiment of the invention, magnetic film alloy 440 may be used on textured antenna substrates of a folded dipole antenna. It should be understood that magnetic film alloy 440 may be used with many different antenna structures in order to reduce the size of the antennas. Furthermore, the properties of the magnetic film alloy 440 are designed to reduce an average size of antenna for use in a predetermined frequency band by at least 10% of the average size of the antenna for the predetermined frequency band.
According to an embodiment of the invention, in order to reduce the size of antennas, there is a need to design the material and the structure of magnetic film alloy 440 by optimizing properties for the magnetic material to minimize losses from eddy currents and from the skin depth effect in combination with an optimal surface texture and thickness for the antenna substrate. The CoZrTa alloy with the receptivity of 100 micro-ohm cm, the eddy currents at 600 Mhz may be controller by keeping the thickness at less then 1 micrometer and the surface texture may be more than 1 micrometer. In this embodiment, the magnetic film thickness may be less than the surface roughness (rms or root-mean-square roughness). For example, for a 0.5 um thick CoZrTa film, the surface roughness would be greater than 0.5 um thick, if desired.
Alternatively, incorporating a multilayered film consisting of dielectric and magnetic materials that may match the impedance between the substrate and the magnetic material so as to reduce reflections and improve efficiency. According to embodiments of the invention, magnetic materials may be used to reduce the size of the antenna. For example, amorphous CoZrTa alloy that balances the magnetic properties with the antenna structure may be used.
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Texturing of the antenna substrate is designed to alter the magnetic properties. For example, texturing of the antenna substrate may be 1 to 2 micrometer. High quality amorphous soft magnetic films may be deposited by physical vapor deposition with low cost and at room temperature, which leads to easy integration into an antenna fabrication process, although the scope of the present invention is not limited in this respect.
According to embodiments of the invention, the CoZrTa alloy may obtain a good combination of high permeability, high saturation magnetization, low magnetostriction and high resistivity. For example, the CoZrTa alloy may obtain a combination permeability, μr, greater then 25, saturation magnetization greater than 0.5 Tesla, less then 1 parts per million (ppm) magnetostriction and greater 25 micro-ohm cm resistivity, if desired. For example, Cobalt (Co) may be prepared by incorporating Zr to create an amorphous film and Ta to minimize magnetostriction, to 0.2 ppm, if desired. This may leads to excellent magnetic softness with coercivity less than 0.02 Oe, high 4πMs wherein Ms depicted a saturation magnetization, a high ferromagnetic resonance (FMR) frequency of 1.4 GHz, and a low magnetostriction coefficient of less than 0.2 ppm (significantly better than the coefficient of 60 ppm for pure cobalt).
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Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.
