Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-05-16
2002-02-26
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S909000, C343S795000
Reexamination Certificate
active
06351239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna device based on the balanced input system, including, for example, a dipole antenna and a loop antenna.
2. Description of the Related Art
In general, the basic antenna elements include, for example, a dipole antenna and a loop antenna based on the balanced input and a monopole antenna and a helical antenna based on the unbalanced input.
The antenna device based on the balanced input has a structure in which no ground plate is utilized and excitation is effected by the antenna device itself. The antenna device based on the unbalanced input has a structure in which excitation is effected by utilizing a ground plate.
When the antenna device based on the unbalanced input is mounted on a mobile communication instrument, the casing of the communication instrument functions as a ground plate. The ground plate is not an infinite plane. Therefore, an inconvenience arises in that it is necessary to adjust the antenna depending on the shape and the size of the casing.
On the other hand, the antenna device based on the balanced input is scarcely affected by the casing. The antenna device based on the balanced input is advantageous in that the adjustment is less laborious as compared with the antenna device based on the unbalanced input. As for the performance, the antenna device based on the balanced input is advantageous in gain and band width, because the antenna device itself is large as compared with the antenna device based on the unbalanced input.
A large number of suggestions have been hitherto made in order to realize a small size of an antenna device and realize a small size of a communication instrument, including, for example, those having an antenna pattern based on an electrode film formed on a surface of a dielectric substrate (for example, see Japanese Laid-Open Patent Publication Nos. 10-41722, 9-162633, and 10-32413).
The antenna device based on the unbalanced input has been hitherto used as an antenna device for the high frequency zone, because of the following reason.
That is, a 1st stage filter, which is connected to the antenna device, is based on the unbalanced output. Therefore, when the antenna device based on the balanced input is connected to the filter based on the unbalanced output, it is necessary to use a balun as a balanced-unbalanced converter.
When the balun is provided, then the number of parts is increased, and the areal size occupied by the substrate is increased. As a result, a problem arises in that it is impossible to realize a small size of the antenna device which is the basic request.
In other words, in the present circumstances, it is advantageous to use an antenna device based on the unbalanced input in view of the insertion loss and the cost.
However, it is clear that if the antenna device based on the balanced input can be connected to the filter without using the balun, then it is possible to sufficiently exhibit the advantages possessed by the antenna device based on the balanced input, and it is possible to further facilitate the realization of a small size and high performance of the antenna device.
SUMMARY OF THE INVENTION
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide an antenna device which makes it possible to appropriately select and perform a balanced input (output) and an unbalanced input (output) for the connection between a filter and an antenna, and which makes it possible to realize a small size and high performance of electronic instruments (including communication instruments) provided with the antenna.
According to the present invention, there is provided an antenna device comprising an antenna section which is based on a balanced input/output; and a filter section in which at least an input/output portion connected to the antenna section is based on the balanced input/output.
That is, the input/output system of the filter section on the side of the antenna section is the balanced input/output system. Therefore, it is possible to provide the antenna device wherein the antenna section, which is connected to the input/output terminal of the filter section, is based on the balanced input system.
As described above, in the antenna device according to the present invention, the balanced input (output) and the unbalanced input (output) can be appropriately selected and performed for the connection between the filter section and the antenna section. Thus, it is possible to realize a small size and high performance of the electronic instrument (including the communication instrument) having the antenna section.
In the antenna device constructed as described above, it is also preferable that the device further comprises a ground electrode for constructing a capacitance together with an open end of the antenna section. In this arrangement, the capacitance, which is formed between the open end of the antenna section and the ground electrode, is added to the capacitance of the parallel resonance circuit obtained by the equivalent transformation of the antenna section. Therefore, assuming that the resonance frequency is identical, it is enough that the parallel resonance circuit has a small inductance. As a result, it is possible to further decrease the length of the antenna section (antenna length). Thus, it is possible to shorten the length of the entire antenna section.
That is, the input/output of the filter section on the side of the antenna section is the balanced input/output. Therefore, it is possible to provide an antenna device wherein the antenna section, which is connected to the input/output terminal of the filter section, is based on the balanced input.
In the antenna device constructed as described above, it is also preferable that the device is composed of a dielectric substrate which includes a large number of stacked dielectric layers and which has at least an input/output terminal and a ground electrode formed on its outer circumferential surface; wherein the filter section includes a plurality of ½ wavelength resonator elements of a both ends-open type arranged in parallel to one another in the dielectric substrate respectively; and the antenna section is formed on the dielectric substrate.
In this arrangement, the antenna section may be formed on a surface of the dielectric substrate, or it may be formed at the inside of the dielectric substrate. Alternatively, the antenna section and the filter section may be formed in regions which are two-dimensionally separated from each other on the dielectric substrate.
The ½ wavelength resonator, which is used for the filter section as one of the constitutive elements of the antenna device according to the present invention, has such a form that both ends are open. Therefore, it is unnecessary to form the resonator so that it extends up to the end of the dielectric substrate. The resonance frequency is not dispersed depending on, for example, any variation in substrate size caused during the production process. Therefore, it is possible to provide a high performance antenna device.
In the antenna device constructed as described above, it is also preferable that two input/output electrodes, which are arranged at positions of linear symmetry with respect to a center in a length direction of at least the ½ wavelength resonator disposed on an output side of the plurality of ½ wavelength resonators, are provided in the dielectric substrate; and the two input/output electrodes are connected to balanced input/output terminals of the antenna section.
That is, the filter section can appropriately select and perform the balanced input (output) and the unbalanced input (output) for the connection with the antenna section. Therefore, it is possible to use an antenna based on the balanced input/output system for the antenna section.
As described above, the filter section, which is one of the constitutive elements of the antenna device according to the present invention, makes it possible to obta
Arai Hiroyuki
Hirai Takami
Mizuno Kazuyuki
Mizutani Yasuhiko
Burr & Brown
Ho Tan
NGK Insulators Ltd.
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