This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-124472, filed on May 22, 2009, the entire contents of which are incorporated herein by reference.
The embodiments discussed herein are related to an antenna device and a wireless communication device having the antenna device.
Currently, in the field of the wireless communication device such as mobile terminals, the trend toward the multiband arrangement, such as the dual-band or tri-band arrangement is growing. In the wireless communication devices having the multiband arrangement, communication is performed through a plurality of frequency bands (e.g., two frequency bands in the dual-band wireless communication devices, and three frequency bands in the tri-band wireless communication devices). Therefore, various antenna structures corresponding to the multiband arrangement have been developed for antenna devices which are built in wireless communication devices. Among others, a small-sized antenna structure corresponding to a multiband arrangement has been proposed for an antenna device used in a mobile terminal.
Although the monopole antenna usually has a straight form extended away from the ground conductor, each of the linear antenna elements 102 and 104 has an L-shaped form for being built in a limited space in a chassis of a mobile terminal or the like. The common end point of the linear antenna elements 102 and 104 is a feed point 110, and electric power is supplied through a feeder 112, which is connected to a power-supply unit (not shown). The portions 102a and 102b of the linear antenna elements 102 and 104 are arranged to stand on the surface of the ground conductor 108 so that the tips of the portions 102a and 102b are located away from the surface of the ground conductor 108. Two resonances occur in the linear antenna elements 102 and 104 for multiband communication in the antenna device 100 illustrated in
However, since the two linear antenna elements 102 and 104 are arranged close to each other in the antenna device 100 illustrated in
Furthermore, in a known antenna device for a multiresonant inverted-F-shaped antenna, the antenna characteristics can be adjusted after fabrication (Japanese Laid-open Patent Publication No. 2005-252480). However, this antenna device has antenna elements which operate in resonance modes of monopole antennas. In addition, the antenna elements are closely arranged. Therefore, two resonances interfere with each other in the case where the frequency bands in which the antenna elements resonate are close to each other, so that it is difficult for the antenna device to achieve satisfactory characteristics.
According to a first aspect of the invention, an antenna device includes: a linear antenna element; a feeding portion having a first feed terminal and a second feed terminal which are arranged apart face-to-face, where the first feed terminal is connected to an end of the linear antenna element, and the second feed terminal is connected to a power supply unit; a linear branch element which branches off from the linear antenna element at an intermediate position of the linear antenna element; and a ground conductor which is connected to an end of the linear branch element.
According to a second aspect of the invention, an antenna device includes: a linear antenna element; a feeding portion having a capacitor which connects an end of the linear antenna element and a connection line connected to a power supply unit; a linear branch element which branches off from the linear antenna element at an intermediate position of the linear antenna element; and a ground conductor which is connected to an end of the linear branch element.
According to a third aspect of the invention, an wireless communication device includes: the antenna devices according to the first or second aspect of the invention; and a communication unit which performs at least one of generation of waves to be transmitted in a plurality of frequency bands and detection of a plurality of frequency bands.
The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
Referring now to the attached drawings which form a part of this original disclosure:
Hereinbelow, the embodiments of the antenna devices and the wireless communication devices are explained in detail.
The linear antenna element 2 is an antenna element which linearly extends from the feeding portion 4. The linear antenna element 2 has the function of a monopole antenna which resonates at a frequency of a radio wave where a quarter of the wavelength of the radio wave is approximately equal to the length of the linear antenna element 2. The linear branch element 3 is an antenna element which branches off from the linear antenna element 2 at an intermediate position of the linear antenna element 2. The feeding portion 4 has a first feed terminal 6 and a second feed terminal 7 which are arranged apart face-to-face, where the first feed terminal 6 is connected to an end of the linear antenna element 2, and the second feed terminal 7 is connected to a power supply unit. The ground conductor 5 is connected to an end of the linear branch element 3. The linear branch element 3 and the base portion of the linear antenna element 2 which extends from the end of the linear antenna element 2 to the position of the branch produce an inductance component. In addition, the first feed terminal 6 and the second feed terminal 7 which are arranged apart face-to-face produce a capacitance component. Therefore, an LC resonance occurs in the antenna device 1, where the resonance frequency is determined by the inductance component and the capacitance component.
As described above, a resonance occurring in the antenna device 1 is different from the resonance occurring in the linear antenna element 2, so that the two resonances do not interfere with each other. Therefore, the VSWR characteristics can be improved. As explained later, the linear antenna element 2, the linear branch element 3, and the feeding portion 4 in the antenna device 1 may be used in various embodiments.
A circuit board 16, together with antenna elements of the antenna device 10, is built in a chassis 14 of the mobile phone 12. The antenna device 10 is produced by using a flexible circuit board. One or more connectors 18 are arranged in the circuit board 16 for connection with the antenna elements in the antenna device 10, so that the circuit board 16 is connected to the antenna elements in the antenna device 10. In addition, the circuit board 16 contains a communication circuit 19 which performs generation of waves to be transmitted in the two frequency bands and detection of received waves in the two frequency bands.
A ground conductor 24a, the first feed terminal 26, the ground terminal 30, a feed line 26a, a ground line 30a, a via conductor 29, and a feed line 28a are arranged in the surface layer 22a of the dielectric substrate 22. The feed line 26a connects the first feed terminal 26 and an antenna connection terminal (connector mount land) 27 which will be explained later, the ground line 30a connects the ground terminal 30 and the ground conductor 24a, and the feed line 28a connects the power supply unit and the via conductor 29. A ground conductor 24b, the second feed terminal 28, and a feed line 28b are arranged in the inner layer 22b, which is formed in contact with the surface layer 22a in the dielectric substrate 22. In addition, a ground conductor 24c is arranged in the inner layer 22c, which is formed under and in contact with the inner layer 22b in the dielectric substrate 22.
The ground conductors 24a, 24b, and 24c constituting the ground conductor 24 do not extend to near-corner portions of the layers 22a, 22b, and 22c constituting the dielectric substrate 22, so that the near-corner portion of the surface layer 22a of the dielectric substrate 22 are exposed. The first feed terminal 26, the second feed terminal 28, the ground terminal 30, various lines, and other terminals are arranged in the exposed near-corner portion. The ground terminal 30 is arranged in the vicinity of the first feed terminal 26.
As illustrated in
The first feed terminal 26 is arranged on the surface layer 22a of the dielectric substrate 22, and the second feed terminal 28 is arranged on the inner layer 22b of the dielectric substrate 22. Therefore, the feed line 28a extending from the power supply unit is connected to the second feed terminal 28 through the via conductor 29.
As illustrated in
The end 34a of the linear antenna element 34 is connected to the antenna connection terminal (connector mount land) 27 through the aforementioned connector (not shown), and the end 36a of the linear branch element 36 is connected to the ground terminal (connector mount land) 30 through a connector (not shown).
The linear antenna element 34 extends on the surface of the dielectric substrate 22 in the direction toward the outside of the dielectric substrate 22, and bends 90 degrees at a first intermediate position of the linear antenna element 34 to extend in a first direction perpendicular to the surface of the dielectric substrate 22 so that the portion of the linear antenna element 34 beyond the first intermediate position stands on the surface of the dielectric substrate 22. Further, the linear antenna element 34 bends 90 degrees at a second intermediate position of the linear antenna element 34 to extend in a second direction parallel to the surface of the dielectric substrate 22, and further bends 90 degrees at a third intermediate position of the linear antenna element 34 to extend in a third direction perpendicular to the second direction and parallel to a side edge of the dielectric substrate 22, so that the portion of the linear antenna element 34 beyond the third intermediate position extends at an elevation identical to the elevation of the portion of the linear antenna element 34 between the second and third intermediate positions and on the different level from the surface of the dielectric substrate 22. The length from the first feed terminal 26 through the end 34a of the linear antenna element 34 to the opposite end 34b of the linear antenna element 34 is approximately λ1/4, so that a resonance at the frequency 1 occurs, where λ1 denotes the propagation wavelength of the radio wave in the air corresponding to the frequency 1.
The linear branch element 36 branches off from the aforementioned intermediate position of the linear antenna element 34, and the end 36a of the linear branch element 36 is connected to the ground terminal 30, which is arranged in the vicinity of the first feed terminal 26. As explained before, the first and the second feed terminals 26 and 28 and the surface layer 22a serve as a capacitor, since, the first and the second feed terminals 26 and 28 are arranged apart face-to-face, and the surface layer 22a of the dielectric substrate 22 as a dielectric is sandwiched by the first and the second feed terminals 26 and 28. In addition, a path formed of the linear branch element 36 and the base portion 35 of the linear antenna element 34 serve as an inductor. That is, the linear branch element 36 is arranged parallel to the base portion 35 of the linear antenna element 34, which extends from the end 34a to the position from which the linear branch element 36 branches off. Therefore, a looped current path or a U-shaped current path, as indicated by the curve arrow in
As explained above, the resonance at the frequency 1 occurs in the linear antenna element 34, and the resonance at the frequency 2 occurs since the linear branch element 36 is arranged in addition to the linear antenna element 34. At this time, the resonance at the frequency 1 occurs in a mode in which the linear antenna element 34 operates as a monopole antenna, and the resonance at the frequency 2 occurs in an LC resonance mode due to a capacitor component and an inductance component. As mentioned before, the capacitor component is set up when the first and the second feed terminals 26 and 28 serve as a capacitor, and the inductance component is set up when the base portion 35 of the linear antenna element 34 and the linear branch element 36 serve as an inductor. Since the resonance at the frequency 1 and the resonance at the frequency 2 occur in the respectively different modes, the resonances do not interfere. Thus, it is possible to achieve satisfactory VSWR characteristics.
Hereinbelow, antenna devices according to other embodiments and the VSWR characteristics of the embodiments are explained.
Similar to the antenna body 32 illustrated in
The first feed terminal 46, which is connected to the end of the linear antenna element 50, is arranged apart from a second feed terminal 48 and face-to face with the second feed terminal 48 through a dielectric substrate (not shown). The second feed terminal 48 is located at an end of a feed line 56. Electric power is supplied from a power supply unit (not shown) through the feed line 56 to the antenna body 44.
In the antenna device 40, similar to the antenna device 10, a first resonance at the frequency 1 occurs in the linear antenna element 50, which operates as a monopole antenna. In addition, a second resonance at the frequency 2 occurs in the arrangement including the structure of the first and the second feed terminals 46 and 48 facing each other via the dielectric substrate and the structure constituted by the base portion of the linear antenna element 50 and the linear branch element 52. The second resonance is an LC resonance due to a capacitor component and an inductance component. The capacitor component is set up when the first and the second feed terminals 46 and 48 serve as a capacitor, and the inductance component is set up when the base portion of the linear antenna element 50 and the linear branch element 52 serve as an inductor. Similar to the antenna device 10, the first resonance at the frequency 1 and the second resonance at the frequency 2 also occur in the respectively different modes in the antenna device 40, so that the first and second resonances do not interfere. Thus, it is possible to achieve satisfactory VSWR characteristics.
The antenna device 60 is different from the antenna device 40 illustrated in
In the antenna device 60, similar to the antenna device 10, a first resonance at the frequency 1 occurs in the linear antenna element 50 which operates as a monopole antenna, and a second resonance at the frequency 2 is caused by the capacitor 62 and the structure constituted by a base portion of the linear antenna element 50 and the linear branch element 52. At this time, the first resonance at the frequency 1 occurs in a mode in which the linear antenna element 50 operates as a monopole antenna, and the second resonance at the frequency 2 occurs in an LC resonance mode due to a capacitor component and an inductance component. The capacitor component is set up by the capacitor 62, and the inductance component is set up when the base portion of the linear antenna element 50 and the linear branch element 52 serve as an inductor. Similar to the antenna device 10, the first and second resonances in the antenna device 60 also occur in the respectively different modes, so that the first and second resonances do not interfere. Thus, it is possible to achieve satisfactory VSWR characteristics.
The antenna device 70 is different from the antenna device 40 illustrated in
In the antenna device 70, similar to the antenna device 10, a first resonance at the frequency 1 occurs in the linear antenna element 50 which operates as a monopole antenna. In addition, a second resonance at the frequency 2 is caused by the capacitor 74, the inductor 72, and the structure constituted by a base portion of the linear antenna element 50 and the linear branch element 52. At this time, the first resonance at the frequency 1 occurs in a mode in which the linear antenna element 50 operates as a monopole antenna, and the second resonance at the frequency 2 occurs in an LC resonance mode due to a capacitor component and inductance components. The capacitor component is set up by the capacitor 74, the first inductance component is set up by the inductor 72 and the structure of the base portion of the linear antenna element 50 and the linear branch element 52. Similar to the antenna device 10, the first and second resonances in the antenna device 70 also occur in the respectively different modes, so that the first and second resonances do not interfere. Thus, it is possible to achieve satisfactory VSWR characteristics. Further, the second inductance component of the inductor 72 can be adjusted according to the target frequency 2.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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2009-124472 | May 2009 | JP | national |