Patent Grant
8106830
This is a National Phase of International Application No. PCT/KR2006/002350, filed on Jun. 20, 2006, which claims priority from Korean Patent Application No. 10-2005-0052931, filed on Jun. 20, 2005.
The present invention relates, in general, to an antenna for wireless communication, and more particularly, to an antenna for wireless communication, in which an antenna radiator is formed of electrically conductive ink and the thickness of the radiator is determined according to a use frequency of an antenna.
In general, an antenna for wireless communication includes a feeding unit and a ground unit. The antenna further includes an antenna radiator connected to a RF circuit within a terminal device through the feeding unit and the ground unit, and a base supporting the antenna radiator.
The antenna radiator is formed of an electrically conductive material and has a pre-determined electrical length. Accordingly, the antenna radiator resonates at a target frequency to radiate and/or receive electromagnetic wave, and thus serves as a radiator. The antenna radiator may have a variety of shapes, such as a meander type, a helical type, a rectangular type, and a circular type, depending on its location and available space. The base is formed to support the antenna radiator and is also made of a dielectric material so that an effective wavelength of electromagnetic wave is reduced to reduce the electrical length of the antenna radiator.
Meanwhile, in recent years, as communication terminal devices are miniaturized and have light-weight, a built-in type antenna has been adopted increasingly.
In the conventional built-in type antenna constructed above, a conductor is generally deposited on the substrate 110 in order to form the antenna radiator 120. However, it is inconvenient and expensive to form the radiator 120 using the deposition process.
To solve the problem, a method of forming the antenna radiator 120 by printing electrically conductive ink on the substrate 10 has been proposed. The electrically conductive ink has conductivity since it contains micro-conductive particles such as silver (Ag). The electrically conductive ink can be printed on the substrate 110 and may serve as a radiator accordingly. The antenna radiator 120 can be formed by printing the electrically conductive ink on the substrate 110 in a predetermined shape through a method such as silkscreen printing. If the antenna radiator 120 is formed of the electrically conductive ink, the printing process is very simple, the productivity is very high, and various shapes of radiators can be formed.
If the antenna radiator is formed of the electrically conductive ink, however, there is a problem in that the gain of the antenna is low. Furthermore, since the electrically conductive ink is very expensive, the production cost of the antenna rises.
Therefore, there is a need for an antenna using electrically conductive ink and manufacturing method thereof, in which a manufacturing process of an antenna can be simplified, degree of freedom of design can be increased, a good gain can be obtained, and the production cost is low.
Technical Problem
An object of the present invention is to provide an antenna using electrically conductive ink and manufacturing method thereof, in which a good gain can be obtained.
Another object of the present invention is to provide an antenna using electrically conductive ink and manufacturing method thereof, in which the production cost can be saved.
Technical Solution
In general, if electromagnetic wave propagates in a conductor, the electromagnetic wave is attenuated by an attenuation constant α given in following equation.
α=√{square root over (πfμσ)} MathFigure 1
where
f:the frequency
μ: the permeability of the conductor
σ: the conductivity of the conductor
Therefore, the electromagnetic wave in the conductor is attenuated to 1/e and substantially disappears below a skin depth δ given in the following equation, and a current accordingly is limited within the skin depth δ. This is called a skin effect.
From Equation 2, it can be seen that the higher the frequency of the electromagnetic wave, the smaller the skin depth, and the lower the frequency of the electromagnetic wave, the greater the skin depth. For example, copper has a skin depth of 0.0038 mm in 3 MHz, but has a skin depth of 0.66 μm in 10 GHz.
As a result of an experiment performed by taking notice of the fact, the inventors of the present invention have found that the conventional antenna using the electrically conductive ink has a low gain due to the current loss resulting from the skin effect. In more detail, if the skin depth is greater than the thickness of the antenna radiator, loss is generated since a portion of electromagnetic wave is shielded by the substrate. Referring to
In contrast, if the thickness of the radiator 120 is greater than the skin depth, there is no loss of the current and no reduction of the antenna gain. However, the radiator (120) portion higher than the skin depth rarely affects the characteristic of the antenna. Therefore, the inventors of the present invention found that an amount of electrically conductive ink used can be reduced while maintaining the performance of an antenna and the production cost of the antenna can be saved accordingly, by setting the thickness of the radiator 120 to a skin depth corresponding to the used frequency of the antenna. The present invention is based on these discoveries. In accordance with an embodiment of the present invention, there is provided an antenna for wireless communication, including a substrate and an antenna radiator formed by printing electrically conductive ink on the substrate, wherein the radiator has a thickness which is substantially the same as a skin depth of the radiator with respect to a resonant frequency of the antenna.
It is preferred that the antenna has two or more resonant frequencies, and said skin depth is a skin depth of the radiator with respect to the lowest resonant frequency of the resonant frequencies.
Furthermore, the resonant frequency may be in the range of 824 to 894 MHz.
Meanwhile, it is preferred that the electrically conductive ink contains 65 to 70% by weight of silver (Ag) particles.
According to another embodiment of the present invention, there is provided an antenna for wireless communication, including a substrate and an antenna radiator formed by printing electrically conductive ink on the substrate, wherein a thickness of the radiator at a hot spot in the radiator with respect to a resonant frequency of the antenna is substantially the same as a skin depth of the radiator with respect to the resonant frequency.
It is preferred that the antenna has two or more resonant frequencies, and said skin depth is a skin depth of the radiator with respect to the lowest resonant frequency of the resonant frequencies.
It is also preferred that the thickness of the radiator other than the hot spot is substantially the same as a skin depth of the radiator with respect to the highest resonant frequency of the resonant frequencies.
Furthermore, the resonant frequency may be in the range of 824 to 894 MHz.
Meanwhile, it is preferred that the electrically conductive ink contains 65 to 70% by weight of silver (Ag) particles.
In accordance with still another embodiment of the present invention, there is provided an antenna for wireless communication, including a substrate and an antenna radiator formed by printing electrically conductive ink on the substrate, and having two or more resonant frequencies, wherein a thickness of the radiator at a hot spot in the radiator with respect to each of the resonant frequencies is substantially the same as a skin depth of the radiator with respect to each of the resonant frequencies, respectively.
It is preferred that the electrically conductive ink contains 65 to 70% by weight of silver (Ag) particles.
In accordance with still another embodiment of the present invention, there is provided a method of manufacturing an antenna for wireless communication, wherein the antenna includes a substrate and an antenna radiator formed by printing electrically conductive ink on the substrate. The method comprises printing the electrically conductive ink on the substrate to a first thickness in the shape of the antenna radiator; and printing the electrically conductive ink to a second thickness at a first hot spot in the radiator with respect to a first frequency, wherein the second thickness is a thickness such that the thickness of the radiator at the first hot spot is substantially a skin depth of the radiator with respect to the first frequency.
It is preferred that the first frequency is the lowest resonant frequency of resonant frequencies of the antenna.
Furthermore, it is preferred that the first thickness is substantially a skin depth of the radiator with respect to the highest resonant frequency of resonant frequencies of the antenna.
Meanwhile, preferably, the method further comprises printing the electrically conductive ink to a third thickness at a second hot spot in the radiator with respect to a second frequency, wherein the third thickness is a thickness such that the thickness of the radiator at the second hot spot is substantially a skin depth of the radiator with respect to the second frequency.
Advantageous Effects
According to the present invention, since the loss of current in an antenna can be prevented, an antenna with a good gain can be fabricated using electrically conductive ink through a simple process.
Furthermore, according to the present invention, since an amount of expensive electrically conductive ink used can be minimized without affecting the performance of the antenna, the antenna can be fabricated at low cost.
Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:
The present invention will now be described in detail in connection with specific embodiments with reference to the accompanying drawings.
Meanwhile, in order to facilitate printing, the viscosity of the electrically conductive ink may be set in the range of 20,000 to 24,000 cps. It is also possible to improve the interconnectivity between silver (Ag) particles by making the particles minute in various sizes and forming them in a plate shape.
Referring to
Referring to
In this case, loss is not generated with respect to not only electromagnetic wave of the lower frequency, but also electromagnetic wave of the higher frequency. A reduction in the gain of the antenna can also be prevented.
Furthermore, the skin depth δL is a minimal thickness for securing a good antenna characteristic with respect to both the electromagnetic waves of the high frequency and the low frequency. Thus, if the thickness of the radiator 18 is set to the skin depth δL, an amount of electrically conductive ink used to form the radiator 18 can be minimized, while maintaining the characteristic of the antenna, and the production cost of the antenna can be saved. By forming the antenna radiator 18 with thickness equal to the skin depth with respect to a resonant frequency of a low frequency through the printing of the electrically conductive ink as described above, an antenna having a good gain can be fabricated at a minimal cost through one printing process.
The principle of the second embodiment may be applied to not only a dual band antenna, but also a triple or more band antennas. By setting the thickness of the antenna radiator to a skin depth with respect to the lowest resonant frequency of several resonant frequencies, a triple or more band antenna with a good gain can be fabricated through one printing process to reduce production cost. In this case, a multi-band characteristic of triple or more bands can be obtained by forming the radiator 18 in various shapes, such as a meander line and a patch with a slot. Such modification falls within a scope that can be easily understood by those skilled in the art.
In general, the dual band antenna has two resonant frequencies, and the antenna radiator 18 radiates and/or receives electromagnetic waves of two kinds of frequencies. An amount of electromagnetic wave (and thus a current) has its maximum at different locations on the radiator 18 depending upon the respective frequencies. The locations may be determined according to the shape of an antenna and corresponding frequency. A point at which the current is maximum as described above is called “a hot spot” in the present description. The gain of the whole antenna is dependent on a reduction of the gain at the hot spot. Therefore, by preventing a reduction of the gain at the hot spot, the gain of the whole antenna can be improved.
Referring to
In more detail, as shown in
Meanwhile, a thickness h2 of the radiator at the end 24 can be set to the skin depth δL with respect to the resonant frequency fL of a lower frequency in accordance with Equation 3 above.
If the thickness of the radiator 18 is set to the skin depths δH
and δL as described above, an antenna radiator with a good gain can be formed using a minimum amount of electrically conductive ink. Particularly, by setting only the thickness h2 of the radiator at a hot spot with respect to a lower frequency to the skin depth δL of a lower frequency unlike the previous embodiment, an amount of electrically conductive ink used can be further reduced compared with the previous embodiment while substantially preventing a reduction in the gain of the antenna and the production cost of the antenna can be further saved.
A method of manufacturing the antenna of the present embodiment will be described below with reference to
In step S100, a screen in which the shape of the antenna radiator 18 is formed is first disposed on the substrate 10. Electrically conductive ink is then printed on the screen to a thickness substantially equal to the skin depth δH, thus forming an overall antenna radiator (step S110).
In step S120, a screen in which the shape of the end 24 is formed is disposed on the substrate 10 on which the radiator 18 is printed. The location and shape of the end 24 may be the same as those of the hot spot of the antenna. The location and shape of the hot spot can be predicted at the time of designing the antenna. Furthermore, after the first printing in step S 110, current distributions in the antenna can be measured in order to know the location and shape of the hot spot. In this case, the location and shape of the hot spot can be measured once, and the same location and shape may be used afterward for the antenna radiator 18 of the same shape.
Finally, in step S130, electrically conductive ink is secondarily printed so that the thickness of the end 24 becomes substantially the skin depth δL, thereby completing the formation of the antenna radiator 18. For the radiator having the thickness δH has already been formed in step S110, only the electrically conductive ink of a thickness δL−δH can be further printed in this step.
According to the method of manufacturing the antenna of the present embodiment, it is possible to manufacture an antenna without the gain reduced, while saving the production cost of the antenna by using small amount of conductive material.
The third embodiment has been described regarding the dual band antenna. However, the principle of the present embodiment may be applied to an antenna of triple or more bands. In this case, an overall antenna radiator may be formed to a skin depth with respect to the highest resonant frequency, and the radiator may be formed to the skin depths for the second resonant frequency and the third resonant frequency at the hot spots for the second resonant frequency and the third resonant frequency, respectively. Therefore, a good gain can be obtained for a number of frequency bands while using a minimum amount of electrically conductive ink. Meanwhile, a multi-band characteristic of triple or more bands can be obtained by forming the radiator 18 in various forms, such as a meander line and a patch with a slot. Such modification falls within a scope that can be easily understood by those skilled in the art.
Furthermore, in the method of manufacturing the antenna having triple or more bands, additional printing can be performed to a thickness of a skin depth for each frequency. For example, when a skin depth for the lowest resonant frequency fLOWEST(<fL) of a triple band antenna is δLOWEST, if the hot spot for the lowest resonant frequency fLOWEST is overlapped with a hot spot for the frequency fL, a step of printing the electrically conductive ink to a thickness δLOWEST−δL in the overlapping region may be further added after the step S130.
Meanwhile, the antennas of the first to third embodiments may be used with them being coupled to the ground unit and the feeding unit of the RF circuit within the terminal device. Furthermore, in order for the antenna to be easily connected with the RF circuit and to be fixed stably, the substrate 10 in which the antenna radiator is printed may be disposed on the base 26 of the dielectric material as shown in
Skin depths of electrically conductive ink used in respective frequencies are as follows, which are obtained based on the measurement of the resistivity.
The plots of
Plots of . Although, it was found that the improvement of the antenna gain is relatively more practical at a low frequency band.
Although the present invention have been disclosed referring to the specific embodiments which are given for the purpose of illustration not for limitation, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention. For example, the principle of the present invention may be applied to a variety of devices that transmit and/or receive RF signals, such as an antenna printed on a housing of a wireless communication terminal device and RFID tag including a printed conductive antenna radiator. Therefore, the scope of the present invention must be limited by only the following claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2005-0052931 | Jun 2005 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2006/002350 | 6/20/2006 | WO | 00 | 9/29/2009 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2006/137666 | 12/28/2006 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5763058 | Isen et al. | Jun 1998 | A |
| 5767808 | Robbins et al. | Jun 1998 | A |
| 6400329 | Barnes | Jun 2002 | B1 |
| 6590545 | McCorkle | Jul 2003 | B2 |
| 6621462 | Barnes | Sep 2003 | B2 |
| 20020080076 | Kamei et al. | Jun 2002 | A1 |
| 20030017371 | Burrows et al. | Jan 2003 | A1 |
| 20040201522 | Forster | Oct 2004 | A1 |
| 20050001770 | Ikuta et al. | Jan 2005 | A1 |
| 20050062662 | Miyoshi et al. | Mar 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 7-94933 | Apr 1995 | JP |
| 2002-111351 | Apr 2002 | JP |
| 2003-152428 | May 2003 | JP |
| 2004-007527 | Jan 2004 | JP |
| 2001-0096957 | Nov 2001 | KR |
| 10-0322385 | Jan 2002 | KR |
| 10-0323394 | Jan 2002 | KR |
| 10-0325031 | May 2002 | KR |
| 10-2002-0053737 | Jul 2002 | KR |
| 10-2002-0081096 | Oct 2002 | KR |
| 10-2002-0084639 | Nov 2002 | KR |
| 10-0365733 | Dec 2002 | KR |
| 2003-0089825 | Nov 2003 | KR |
| 10-2004-0049525 | Jun 2004 | KR |
| 10-2004-0066441 | Jul 2004 | KR |
| 10-2004-0089902 | Oct 2004 | KR |
| 10-2004-0108212 | Dec 2004 | KR |
| 10-2004-0111580 | Dec 2004 | KR |
| 10-2005-0010549 | Jan 2005 | KR |
| 10-2005-0052931 | Jun 2005 | KR |
| 10-0780554 | Nov 2007 | KR |
| Number | Date | Country | |
|---|---|---|---|
| 20100045532 A1 | Feb 2010 | US |
