Antenna device and communication apparatus including the same

[0002] 1. Field of the Invention

[0003] The present invention relates to an antenna device and a communication apparatus including the same, and more specifically, the present invention relates to an antenna device and a communication apparatus including the same for use in mobile communications or the like.

[0004] 2. Description of the Related Art

[0005] With a recent advance in miniaturization and high performance of mobile communication devices, particularly in those of mobile phones, an antenna device, which is to be mounted therein, has also been required to be further miniaturized and to have higher gain.

[0006] FIG. 5 and FIG. 6 show a conventional surface-mount type antenna and an antenna device incorporating the same, respectively. The basic structure of the surface-mount type antenna 1 shown in FIG. 5 is described in Japanese Unexamined Patent Publication No. 9-98015.

[0007] In FIG. 5, the surface-mount type antenna 1 is arranged by disposing some electrodes on a surface of a base member 2 of a rectangular parallelepiped configuration, which comprises a dielectric material such as ceramic or resin as one of the insulation materials. First, a ground electrode 3 is disposed on substantially the entirety of one major surface 2aof the base member 2. In addition, a strip-shaped radiation electrode 4 is disposed along the length direction of the base member 2 on the other major surface 2bof the base member 2. One end 4aof the radiation electrode 4 extends onto one end surface of the base member 2 to form an open-circuited end and the other end 4bextends onto a major surface 2aand over another end surface of the base member 2 to be connected to the ground electrode 3. Furthermore, a power feeding terminal 5 is disposed in the vicinity of the end 4aof the radiation electrode 4 on the end surface on which the end 4aof the radiation electrode 4 of the base member 2 is disposed. In this arrangement, the power feeding terminal 5 extends over the end surface of the base member 2 to the major surface 2ato be insulated from the ground electrode 3.

[0008] In an antenna device 6 incorporating the surface-mount type antenna 1 shown in FIG. 6, a mounting substrate 7 includes a substrate 8 comprising a dielectric material, i.e., an insulating material, having a major surface 8a,another major surface 8b,a substrate-ground electrode 9 disposed on the other major surface 8band a power feeding line (not shown) which is insulated from the substrate-ground electrode 9. The surface-mount type antenna 1 is mounted on the substrate-ground electrode 9 in the vicinity of a corner of the mounting substrate 7. In this arrangement, the ground electrode 3 and the power feeding terminal 5 of the surface-mount type antenna 1 are connected to the substrate-ground electrode 9 and the power feeding line, respectively, on the mounting substrate 7 by soldering or the like.

[0009] In order to achieve miniaturization of a communication apparatus in which an antenna device has been mounted, miniaturization of the antenna device, i.e., reduction in the cubic volume taken by the surface-mount type antenna on a mounting substrate, is required. Thus, the effort required for making the surface-mount type antenna itself smaller is considerable. When the surface-mount type antenna 1 shown in FIG. 5 is miniaturized, the entire size of the base member 2 of the surface-mount type antenna 1 must be made smaller. However, with a surface-mount type antenna, there is a tendency in which the smaller the size of the base member, the smaller the antenna gain. Accordingly, miniaturization in the size of the base member 2 of the surface-mount type antenna 1 permits the antenna gain of the surface-mount type antenna 1, i.e., the antenna gain of the antenna device 6, to be reduced.

[0010] To overcome the above described problems, preferred embodiments of the present invention provide an antenna device (and a communication apparatus including the same) in which miniaturization does not cause the antenna gain to be deteriorated, i.e., antenna gains can be enhanced without increasing in size.

[0011] One embodiment of the present invention provides an antenna device comprising a surface-mount type antenna and a mounting substrate on which said surface-mount type antenna is mounted; said surface-mount type antenna comprising: a base member comprising an insulating member and having a first major surface, a second major surface opposite to said first major surface, and a plurality of end surfaces extending between said first and second major surfaces; a ground electrode disposed substantially on said first major surface of said base member; a strip-shaped radiation electrode disposed substantially on said second major surface of said base member and including an open-circuited end and a grounded end; a ground terminal connected to said ground end of the radiation electrode and insulated from said ground electrode; and a power feeding terminal disposed in the vicinity of said open-circuited end of the radiation electrode; said mounting substrate comprising: an insulation substrate comprising a first major surface and a second major surface; a first substrate-ground electrode disposed on said first major surface of said insulation substrate; a second substrate-ground electrode and a connection electrode respectively disposed on said second major surface of said insulation substrate and insulated from each other; and a through-hole connecting said connection electrode and said second substrate-ground electrode to said first substrate-ground electrode; and said ground electrode of said surface-mount type antenna being connected to said second substrate-ground electrode of said mounting substrate; and said ground terminal of said surface-mount type antenna being connected to said connection electrode of said mounting substrate.

[0012] Another embodiment of the present invention provides a communication apparatus including the above described antenna device.

[0013] Such an arrangement permits the antenna gain in the antenna device of the present invention to be increased without increasing in size. That is, since a ground terminal, to which the other end of a radiation electrode of a surface-mount type antenna is connected, is grounded by connecting to a first substrate-ground electrode disposed on a first major surface of a mounting substrate through a connection electrode and through-holes formed on a second major surface of the mounting substrate, the thickness of the base member of the surface-mount type antenna can be substantially increased, leading to improvement of antenna gains.

[0014] Furthermore, in the communication apparatus of the present invention, use of the antenna device above permits communication quality to be enhanced and permits cost reduction to be achieved.

[0015] Other features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention which refers to the accompanying drawings, wherein like reference numerals indicate like elements to avoid duplicative description.

[0016] FIG. 1 is a perspective view showing one embodiment of a surface-mount type antenna used in an antenna device of the present invention.

[0017] FIG. 2 is a partial perspective view showing one embodiment of the antenna device of the present invention.

[0018] FIG. 3 is a sectional view of the antenna device shown in FIG. 2.

[0019] FIG. 4 is a perspective view showing another embodiment of a communication apparatus of the present invention.

[0020] FIG. 5 is a perspective view showing a prior art surface-mount type antenna.

[0021] FIG. 6 is a perspective view showing a prior art antenna device.

[0022] Referring to the surface-mount type antenna 10 shown in FIG. 1, the other end 4bof a radiation electrode 4 is connected to a ground terminal 11 formed on a first major surface 2aof a base member 2. In this case, the ground terminal 11 is insulated from a ground electrode 3 similarly formed on the major surface 2aof the base member 2. As a result, the other end 4bof the radiation electrode 4 is insulated from the ground electrode 3.

[0023] In the antenna device 12 shown in FIG. 2, a mounting substrate 13 is arranged by disposing a first substrate-ground electrode 14 on a first major surface 8aof a substrate 8 and forming a second substrate-ground electrode 15 and a connection electrode 16 (which are mutually insulated) on a second major surface 8bof the substrate 8. In this case, the connection electrode 16 is connected to the first substrate-ground electrode 14 through three through-holes 17. In addition, the second substrate-ground electrode 15 is also connected to the first substrate-ground electrode 14 through a plurality of through-holes 19. The surface-mount type antenna 10 is mounted in the vicinity of a corner of the mounting substrate 13 by connecting the ground electrode 3 to the second substrate-ground electrode 15 of the mounting substrate 13 and connecting the ground terminal 11 to the connection electrode 16 of the mounting substrate 13.

[0024] The power feeding terminal 5 (not shown) of the surface-mount type antenna 10 is connected to a power feeding line disposed on the mounting substrate 13 (not shown). The power feeding line is hidden from view behind the surface-mount type antenna 10 and is not a principal part of the present invention.

[0025] FIG. 3 shows a sectional view in which the antenna device 12 is cut along a surface which is parallel to the XZ-sided face and passes through the radiation electrode 4 of the surface-mount type antenna 10 and the through-hole 17 of the mounting substrate 13.

[0026] As is clear from FIG. 3, in the antenna device 12, the other end 4bof the radiation electrode 4 of the surface-mount type antenna 10 is grounded by connecting to the first substrate-ground electrode 14 through the ground terminal 11, the connection electrode 16 of the mounting substrate 13, and the through-holes 17.

[0027] The power feeding terminal 5 of the surface-mount type antenna 10 is connected to a power feeding line 18 disposed on the mounting substrate 13, although this is not shown in FIG. 2.

[0028] In such an arrangement of the antenna device 12 of the present invention, the grounded position on the end 4bof the radiation electrode 4 of the surface-mount type antenna 10 is substantially different from that of the prior art. Indeed, the position of the substrate-ground electrode 9 (FIG. 6) disposed on the second major surface 8bof the substrate 8 in the prior art antenna device 6 is quite different from the position of the first substrate-ground electrode 14 formed on a first major surface 8aof the substrate 8 of the invention. Thus, the thickness of the surface-mount type antenna 10 of the invention is greater than the thickness of the base member 2 alone as is the case in the prior art. Indeed, the thickness of the antenna 10 of the invention is obtained by adding the thickness of the mounting substrate 8 with the thickness of the base member 2. Advantageously, although the actual size of the surface-mount type antenna 10 is not increased, the effective thickness of the surface-mount type antenna 10 is increased, and antenna gains of the antenna device 12 can be enhanced.

[0029] An experiment was conducted by the inventor of this application on the conventional antenna device 6 in which the bandwidth was 34.0 Mhz, the VSWR (Voltage Standing Wave Ratio), obtained when the antenna is viewed from the power feeding terminal side, was the bandwidth of 3.5 or less, the average of the YZ-sided face gain was −9.14 dBd (obtained in a direction horizontal to the YZ-sided face while putting the antenna device at the center), and the average of the ZX-sided face gain was −9.96 dBd (obtained in a direction horizontal to the ZX-sided face while putting the antenna device at the center). In the antenna device 12 of the present invention, experiments revealed that the bandwidth was 33.2 MHz, the average of the YZ-sided face gain was −8.33 dBd, and the average of the XZ-sided face gain was −9.09 dBd. The antenna gain of the invention improved although the bandwidth did not substantially change.

[0030] Generally, the larger the antenna gain, the narrower the bandwidth of a surface-mount type antenna, and the wider the bandwidth, the smaller the antenna gain. In the antenna device of the present invention, there is an advantage in which the antenna gain is improved without sacrificing the bandwidth. In this arrangement, the antenna device is formed by using a surface-mount type antenna which is designed with a slightly smaller gain and a wider bandwidth such that the antenna gain of the antenna device is substantially the same value as that of the conventional antenna device.

[0031] In the above described embodiment, the configuration of the radiation electrode of the surface-mount type antenna is made substantially into a straight-line form. However, other configurations such as an L-shaped form, a U-shaped form, or a meandering (e.g., S-shaped) form can be used. Furthermore, the number of the through-holes disposed on the mounting substrate is not restricted to three. Indeed, in order to reduce the inductance of the through-hole part, one or any number of through-holes can be employed. In addition, although the base member of the surface-mount type antenna comprises a dielectric member such as ceramics or resin, a magnetic material can also be used.

[0032] FIG. 4 shows a preferred embodiment of a communication apparatus including the antenna device of the present invention. In FIG. 4, the communication apparatus 20 includes an antenna device 12 disposed in a case 21. The antenna device 12 comprises a surface-mount type antenna 10 and a mounting substrate 13. Additionally, a first substrate-ground electrode (not shown) is disposed on a major surface of a substrate 8 comprising the mounting substrate 13. A second substrate-ground electrode 15, a connection electrode 16, and a power feeding line 18 are also formed on the substrate 13. In this arrangement, the connection electrode 16 is connected to the first substrate-ground electrode through through-holes 17. The surface-mount type antenna 10 is mounted at a corner of the mounting substrate 13. The ground electrode (not shown) of the surface-mount type antenna 10 is connected to the second substrate-ground electrode 15 of the mounting substrate 13, the ground terminal (not shown) is connected to the connection electrode 16, and the power feeding terminal (not shown) is connected to the power feeding line 18. Furthermore, the power feeding line 18 is connected to a transmission circuit 23 and a reception circuit 24 formed on the mounting substrate 13 through a switching circuit 22 similarly formed on the mounting substrate 13.

[0033] As describe above, use of the antenna device 12 of the present invention permits the antenna gain of the antenna device 12 to be improved and thereby permits the antenna gain of the communication apparatus 20 itself to be improved, resulting in improvement of the communication quality of the communication apparatus 20. Moreover, improvement of the antenna gain allows for a relaxation of the specifications of peripheral circuits and components such as a filter, an amplifier, a mixer, and a resonator included in the transmission circuit 23 and the reception circuit 24 of the communication apparatus 20. This leads to cost reductions of the peripheral circuits and components, and results in cost reductions of the communication apparatus itself.

[0034] While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the forgoing and other changes in form and details may be made therein without departing from the spirit of the invention.