This application claims priority from Japanese patent application serial No. 2005-192363, filed Jun. 30, 2005.
The present invention relates to an integral-type planar antenna equipped with multiple radiating elements adapting to the same frequency band. More particularly, it relates to an integral-type planar antenna with reduced mutual interference among multiple antenna elements.
As transmission techniques for increasing communications speed of wireless LANs, MIMO/SDM (Multiple Input Multiple Output/Space Division Multiplexing), MIMO/SM (Multiple Input Multiple Output/Spatial Multiplexing), and other MIMO communications systems are considered promising. In simultaneous communication, by installing multiple transmitting antennas and receiving antennas, assigning different channels in the same frequency band to different transmitting antennas, and transmitting different sequences of signals to the different channels simultaneously, it is possible to increase transmission speed without expanding the frequency band. Thus, even if the frequency band is not expanded, it is possible to increase sequences of transmission signals with increases in the number of transmitting antennas, and thereby improve the usability of frequencies and increase the wireless transmission speed. To this end, Japanese Patent Application No. 2001-119238 describes an antenna device comprising a first planar inverted F antenna and a second planar inverted F antenna installed symmetrically about a printed circuit board.
Thus, to implement a MIMO communications system, one communications device must have multiple broadband antennas, and when installing multiple antennas, as recognized herein it is necessary to provide sufficient space among the antennas to avoid interference among the antennas. The present invention understands that in MIMO communications systems, when n antennas constitute independent frequency channels, if data transfer speed per channel is A (bps), the data transfer speed T (bps) of all the antennas is nA. However, as recognized herein if there is interference among the antennas, the data transfer speed T is smaller than nA.
Recently, mobile information terminal devices have come into wide use, requiring high transmission speed even from mobile personal computers, PDAs, cell phones, or the like, but as recognized by the present invention, on small information terminal devices, it is difficult to provide enough space between antennas to reduce interference among them. Furthermore, the present invention recognizes that the size of the antennas used for small information terminals should be minimized as much as possible. Additionally, as understood by the present invention, to overcome spatial constraints and to mount a MIMO-compatible antenna on a small information terminal, it is convenient that the antenna be an integral-type multi-element antenna with multiple radiating elements formed in a single package. With these critical observations in mind, the invention herein is provided.
In one aspect, multiple radiating elements and a ground pattern are formed that are part of an antenna in a single package. Also, notches can be formed in the ground pattern between the radiating elements, thereby reducing electromagnetic interaction among the radiating elements, reducing the degree of coupling among the radiating elements (hereinafter referred to as “the degree of coupling among antenna elements”), and separating characteristics among the multiple radiating elements. In other words, the notches in the ground pattern reduce the degree of coupling among multiple independent antennas without requiring excessive space between the antennas. The present notches can be applied to any antenna that is equipped with a planar ground plane and radiating elements extending radially from the ground plane.
The degree of coupling among antenna elements can be regarded as a radio transfer factor which represents reduction in power gain of the antenna elements due to electromagnetic interaction among the antenna elements. The lower the degree of coupling among antenna elements, the easier for the individual antennas to operate independently. The degree of coupling among antenna elements is known as “S21” in electromagnetics.
The degree of coupling among antenna elements can also be expressed in terms of a correlation coefficient. The correlation coefficient is calculated by measuring radio field intensities of radiating elements on different frequency channels in a Rayleigh fading environment free of direct waves. There is no absolute standard for the correlation coefficient, but the smaller the correlation coefficient, the greater the transfer rate. The correlation coefficient represents similarity among signals received by different radiating elements in the same environment. Although the correlation coefficient and the degree of coupling among antenna elements have different physical meanings, radiating elements with a lower degree of coupling among antenna elements tend to have a lower correlation coefficient, and thus the correlation coefficient is suitable for use in MIMO communications systems.
In any case, according to a first aspect of the present invention, an integrated multi-element planar antenna includes a ground pattern with a notch formed at one end. A first radiating element is equipped with a feeder placed on one side of the notch, and a second radiating element is equipped with a feeder placed on the other side of the notch.
According to a second aspect of the present invention, an integrated multi-element planar antenna includes a ground pattern, a first radiating element disposed at an end of the ground pattern and equipped with a feeder, and a second radiating element disposed adjacent to the first radiating element at the end of the ground pattern and equipped with a feeder. A third radiating element may be disposed adjacent to the second radiating element at the end of the ground pattern, and the third element is also equipped with a feeder. A first notch is formed at the end of the ground pattern between the first radiating element and the second radiating element.
According to a third aspect of the present invention, an integrated multi-element planar antenna has a ground pattern and n radiating elements placed adjacent to each other at an end of the ground pattern. Each radiating element includes a respective feeder. A total of n−1 notches are formed between the n radiating elements at the end of the ground pattern.
Each of the above aspects allows an antenna in a single small and lightweight package to make each radiating element operate independently with reduced interference among the radiating elements. This makes it possible to reduce mounting space of the antenna as well as the number of parts. This in turn makes part management and installation easier, resulting in improved yields and reduced costs.
The present invention makes it possible to provide a small integrated multi-element planar antenna with reduced interference among radiating elements. Also, the present invention makes it possible to provide an integrated multi-element planar antenna compatible with MIMO communications systems. Furthermore, the present invention makes it possible to provide a wireless LAN card and electronic apparatus employing the antenna.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which:
Preferred embodiments of an integrated multi-element planar antenna according to the present invention will be described below with reference to the drawings.
The integrated multi-element planar antenna 1 has a feeder 5 provided for each of the radiating elements 3 and 4. Grounds 6 for the feeders 5 are installed on the ground pattern 2. Each of the feeders 5 is connected to a component (not shown) by a respective core wire 7a, e.g., an inner conductor of a coaxial cable 7, which serves as a feeder cable, while each of the grounds 6 may be connected to a respective ground connector 7b that can be a braided wire which is an outer conductor of a coaxial cable. The locations of the feeders 5 and their distances from the ground 6 can be established as desired to achieve a desired impedance adjustment.
The first radiating element 3 and second radiating element 4 of the integrated multi-element planar antenna 1 are configured, for example, for the same frequency band. If the first radiating element 3 and second radiating element 4 are adapted to the same frequency band, by assigning different channels in the same frequency band to the radiating elements and transmitting different sequences of signals to the different channels simultaneously, it is possible to increase transmission speed without expanding the frequency band. This in turn makes it possible to support MIMO communications systems. The 2.4-GHz band used for wireless LANs is suitable as this type of frequency band because it can be used by communications stations without a radio station license. The first radiating element 3 and second radiating element 4 thus may be configured to resonate with frequencies in the 2.4-GHz band at a quarter-wavelength. It is to be understood that the 5-GHz band or other frequency band used for wireless LANs may be used instead of the 2.4-GHz band.
Alternatively, the first radiating element 3 and second radiating element 4 may be configured to adapt to different frequency bands. For example, the first radiating element 3 and second radiating element 4 can be adapted to respective frequency bands that are different from each other. If these two frequency bands are the 2.4-GHz and 5-GHz bands, the antenna can be used for a wireless LAN.
The first radiating element 3 and second radiating element 4 are preferably disposed such that the separation distance will be the largest at locations where their radiation fields are the highest. This arrangement makes it possible to set radiation directivity of the first radiating element 3 and second radiating element 4 to different directions, and thus reduce a correlation coefficient of the antenna. The reduced correlation coefficient of the antenna makes channels independent from each other, and thus makes the antenna compatible with MIMO communications systems. Incidentally, a large correlation coefficient of the antenna means that the two channels are receiving the same signal, and thus makes it difficult to increase the transfer rate in the case of the MIMO communications systems. Therefore, it is preferable that the directivity of the first radiating element 3 and second radiating element 4 can be selectively set to different directions to form different propagation paths for radio waves. For example, preferably the first radiating element 3 and second radiating element 4 are placed symmetrically about the notch 2b such that separation distance will be the largest at locations where their radiation fields are the highest. If the first radiating element 3 and second radiating element 4 are of the same material and same shape, when they are placed symmetrically about the notch 2b, they give the same characteristic impedance.
Asymmetrical arrangement of the antenna elements is preferable in that it reduces the degree of coupling among the antenna elements, but it lowers directivity characteristics. To increase transfer rates in MIMO communications systems, it is necessary to form different propagation paths for radio waves by varying directivity between the two radiating elements, and thus asymmetrical arrangement which would cause the directivity characteristics of the two radiating elements to overlap is not desirable. Also, it is not desirable to place the first radiating element 3 and second radiating element 4 symmetrically in an inward direction such that the locations at which the radiation fields of the first radiating element and the second radiating element are the highest would face inward because then the locations at which the radiation fields are the highest would be brought close to each other, increasing the degree of coupling among the antenna elements.
Furthermore, if the wavelength corresponding to the resonance frequency (in Gigahertz) of the first radiating element 3 and second radiating element 4 is λ and the depth of the notch 2b is L (in millimeters), then preferably L/λ is between 0.1 and 0.3 (both inclusive). When L/λ is between 0.1 and 0.3 (both inclusive), the degree of coupling among the antenna elements can be reduced more than when there is no notch.
In the integrated multi-element planar antenna 1 configured as described above, the ground pattern 2, first radiating element 3, and second radiating element 4 are formed on a dielectric, for example. By forming the antenna on a dielectric, it is possible to make it thin and planar. Alternatively, in the integrated multi-element planar antenna 1, the ground pattern 2, first radiating element 3, and second radiating element 4 may be formed by etching a conductor layer of a flexible printed circuit board. By forming the antenna on a conductor layer of a flexible printed circuit board, it is possible to give flexibility to the antenna itself, and thus easier to incorporate the antenna into a small information terminal device such as a portable personal computer, PDA, or cell phone.
An inverted F antenna, meander line antenna, monopole antenna, or the like is suitable for the first radiating element 3 and second radiating element 4 of the integrated multi-element planar antenna 1.
The inverted F antenna 8 shown in
The meander line antenna 9 shown in
As shown in
In both the first radiating element 3 and second radiating element 4 shown in
Since the integrated multi-element planar antenna 1 with such composite antennas can make the monopole antennas 10″ resonate with the 2.4-GHz band at ¼λ and make the loop antennas 10′ resonate with the 5-GHz band at ½λ, it can fit the first radiating element 3 and second radiating element 4 in a space 10 mm long and 21 mm wide and shape the ground pattern 2 into a rectangle 20 mm long and 45 mm wide. Such size reduction is possible because the notch 2b formed in the ground pattern 2 between the first radiating element 3 and second radiating element 4 allows the first radiating element 3 and second radiating element 4 to be installed close to each other. Whereas conventional techniques can make only single-element antennas compliant with the small WFF (Wireless Form Factor) standard, the present invention can make two-element antennas compliant with the standard.
Next, an integrated multi-element planar antenna according to a second preferred embodiment of the present invention will be described below with reference to drawings.
The integrated multi-element planar antenna 1 described above has the ground pattern 2 with the notch 2b formed at the end 2a, the first radiating element 3 placed on one side of the notch 2b and equipped with the feeder 5, and the second radiating element 4 placed on the other side of the notch 2b and equipped with a feeder 5. However, the present invention is not limited to this. As shown in
The integrated multi-element planar antenna 11 has a first notch 12b formed at the end 12a of the ground pattern 12 between the first radiating element 13 and second radiating element 14. This makes it possible to separate characteristics between the first radiating element 13 and second radiating element 14 at the first notch 12b. Also, by forming a second notch 12c at the end 12a of the ground pattern 12 between the second radiating element 14 and third radiating element 15, it is possible to separate antenna characteristics between the second radiating element 14 and third radiating element 15 at the second notch 12c.
Also, by placing the first radiating element 13 and second radiating element 14 symmetrically about the first notch 12b such that separation distance will be the largest at locations where radiation fields of the first radiating element 13 and second radiating element 14 are the highest, it is possible to reduce the correlation coefficient of the antenna.
Also, by adapting the first radiating element 13 and second radiating element 14 of the integrated multi-element planar antenna 11 to the same frequency band, it is possible to support MIMO communications systems. Alternatively, the first radiating element 13 and second radiating element 14 may be adapted to different frequency bands.
Furthermore, if the wavelength corresponding to resonance frequency of the first radiating element 13 and second radiating element 14 is λ and the depth of the notch 12b is L, by setting L/λ to between 0.1 and 0.3 (both inclusive), it is possible to reduce the degree of coupling among the antenna elements more than when there is no notch.
By placing the third radiating element 15 and fourth radiating element 22 symmetrically about the third notch 12d such that separation distance will be the largest at locations where their radiation fields are the highest, it is possible to reduce the correlation coefficient of the integrated multi-element planar antenna 21.
Also, by adapting the first radiating element 13, second radiating element 14, third radiating element 15, and fourth radiating element 22 of the integrated multi-element planar antenna 21 to the same frequency band, it is possible to support MIMO communications systems. Alternatively, the first radiating element 13, second radiating element 14, third radiating element 15, and fourth radiating element 22 may be adapted to different frequency bands.
If the wavelength corresponding to a resonance frequency whose correlation is desired to be reduced among resonance frequencies of the first radiating element 13, the second radiating element 14, the third radiating element 15, and the fourth radiating element 22 is λ and depth of the first notch 12b, the second notch 12c, and the third notch 12d is L, by setting L/λ to between 0.1 and 0.3 (both inclusive), it is possible to reduce the degree of coupling among the antenna elements more than when there is no notch.
If the first radiating element 13, second radiating element 14, third radiating element 15, and fourth radiating element 22 are used for a composite antenna such as described above, the loop antennas 10′ of all the radiating elements are formed into approximately rectangular shapes and the monopole antennas 10″ are bent, as shown in
Furthermore, the first radiating element 13 has the feeder 16 installed on that side of the loop antenna 10′ which is located near the first notch 12b of the ground pattern 12, the fourth radiating element 22 has the feeder 16 installed on that side of the loop antenna 10′ which is located near the third notch 12d of the ground pattern 12, and the second radiating element 14 and third radiating element 15 each have the feeder 16 installed on that side of the loop antenna 10′ which is located near the second notch 12c of the ground pattern 12. Grounds 17 for the feeders 16 are installed on the ground pattern 12. Each of the feeders 16 is connected with a core wire 7a, e.g., an inner conductor of a coaxial cable 7 serving as a feeder cable and each of the grounds 17 is connected to a braided wire 7b serving as an outer conductor of the coaxial cable 7.
Since the integrated multi-element planar antenna 21 with such composite antennas can make the monopole antennas 10″ resonate with the 2.4-GHz band at ¼λ and make the loop antennas 10′ resonate with the 5-GHz band at ½λ, it can fit the first radiating element 13, second radiating element 14, third radiating element 15, and fourth radiating element 22 in a space 12 mm long and 21 mm wide each and shape the ground pattern 12 into a rectangle 20 mm long and 45 mm wide. This is because the notches 12b, 12c, and 12d formed in the ground pattern 12 between the radiating elements allow the radiating elements to be installed close to one another. Thus, the present invention can make four-element antennas compliant with the small WFF standard.
Since the integrated multi-element planar antennas 1, 11, and 21 configured as described above are small enough to reduce mounting space even though they are equipped with multiple radiating elements, they can be used for wireless LAN cards.
The non-limiting wireless LAN card 30 shown in
The wireless LAN card 30 configured as described above is used by being inserted, for example, in a PC card slot of a notebook personal computer. Since the integrated multi-element planar antenna 1, 11 or 21 of the wireless LAN card 30 has a low degree of coupling among the antenna elements, whose directivities are selectively set to different directions, it can form different propagation paths for radio waves, and thus transmit and receive signals at high transmission speed. Therefore, the antenna can be adapted to either the MIMO communication method or the diversity communication method.
Also, the integrated multi-element planar antennas 1, 11 and 21 can be used for wireless devices such as notebook personal computers and the like.
The non-limiting wireless device 40 shown in
If the wireless device 40 configured as described above is a notebook personal computer, since the integrated multi-element planar antennas 1, 11, and 21 are small enough to reduce mounting space even though they are equipped with multiple radiating elements, any of them can be placed without difficulty in mounting space provided in a liquid crystal panel.
To verify the effects of notch in the integrated multi-element planar antenna according to the embodiment, an experiment was conducted using an integrated multi-element planar antenna 1 equipped with a ground pattern 2, first radiating element 3, and second radiating element 4 such as shown in
The degree of coupling (S21) among the antenna elements was checked by varying the width W of the notch 2b among 1 mm, 3 mm, 5 mm, 9 mm. The degree of coupling (S21) among the antenna elements was determined by measuring how much of the electric power radiated from the first radiating element 3 were transmitted to the second radiating element 4. Specifically, numerical analysis was conducted on an electromagnetic-field simulator.
Results of the experiment are shown as a graph in
Referring to the graph, characteristic curve (1) was obtained when the frequency corresponding to the wavelength used for the normalization was 2.45 GHz and the width W of the notch 2b was 1 mm, characteristic curve (2) was obtained when the frequency corresponding to the wavelength used for the normalization was 2.45 GHz and the width W of the notch 2b was 3 mm, characteristic curve (3) was obtained when the frequency corresponding to the wavelength used for the normalization was 2.45 GHz and the width W of the notch 2b was 5 mm, and characteristic curve (4) was obtained when the frequency corresponding to the wavelength used for the normalization was 2.45 GHz and the width W of the notch 2b was 9 mm. Also, characteristic curve (5) was obtained when the frequency corresponding to the wavelength used for the normalization was 5.45 GHz and the width W of the notch 2b was 1 mm, characteristic curve (6) was obtained when the frequency corresponding to the wavelength used for the normalization was 5.45 GHz and the width W of the notch 2b was 3 mm, characteristic curve (7) was obtained when the frequency corresponding to the wavelength used for the normalization was 5.45 GHz and the width W of the notch 2b was 5 mm, and characteristic curve (8) was obtained when the frequency corresponding to the wavelength used for the normalization was 5.45 GHz and the width W of the notch 2b was 9 mm.
As can be seen from the graph in
Although integrated multi-element planar antennas with two, three, or four radiating elements have been disclosed in the above embodiments, it is to be understood that the present invention is not limited to this. In general, an integrated multi-element planar antenna according to the present invention may comprise a ground pattern, n radiating elements placed adjacent to each other at an end of the ground pattern and each equipped with a feeder, and a total of n−1 notches formed between the n radiating elements at the end of the ground pattern. That is, the number of radiating elements is not limited as long as a notch is formed between each pair of adjacent radiating elements, thereby reducing the degree of coupling (S21) among the antenna elements. Also, by placing the radiating elements in each pair symmetrically about the notch such that separation distance will be the largest at locations where their radiation fields are the highest, it is possible to reduce the correlation coefficient of the antenna.
While the particular PLANAR ANTENNA WITH MULTIPLE RADIATORS AND NOTCHED GROUND PATTERN is herein shown and described in detail, it is to be understood that the subject matter which is encompassed by the present invention is limited only by the claims.
Number | Date | Country | Kind |
---|---|---|---|
2005-192363 | Jun 2005 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
6624789 | Kangasvieri et al. | Sep 2003 | B1 |
Number | Date | Country |
---|---|---|
2001-119238 | Apr 2001 | JP |
2004-186931 | Jul 2004 | JP |
Number | Date | Country | |
---|---|---|---|
20070001911 A1 | Jan 2007 | US |