HK1074535B - Bifrequency shared antenna apparatus - Google Patents

Description

Dual-frequency shared antenna device

Technical Field

The present invention relates to a dual-band shared antenna device for short-range communication corresponding to two frequencies.

Background

Conventionally, a wireless tag reading system has been put to practical use in which a wireless ID tag (transponder) is attached to a commodity, an article, or the like, and unique identification data set in advance in the wireless ID tag is read by an ID reader in a wireless manner. Further, in addition to the above-described ID tag, a system of reading data stored in an IC card or the like wirelessly by a reader, such as an automatic ticket checking system or the like, has also been put into practical use.

Fig. 3 shows a general configuration example of the wireless tag system. The ID reader 10 has a transmitting section 11 and a receiving/demodulating section 12. The transmission section 11 amplitude-modulates a transmission carrier wave with an inquiry signal and a clock and outputs it. The transmission signal output from the above-described transmission section 11 is output to the antenna 15 through the directional coupler 13 and the circulator 14, and is transmitted from the antenna 15 to the wireless ID tag 20. As the antenna 15 of the ID reader 10 described above, for example, a loop antenna is used (see, for example, japanese patent laid-open publication No. 9-98014). Also, a part of the output signal of the above-described transmitting section 11 is input to the receiving/demodulating section 12 through the directional coupler 13.

The wireless ID tag 20 is generally configured using an IC chip, and receives a radio wave transmitted from the antenna 15 of the ID reader 10 by the tag antenna 21, generates drive power based on the received radio wave, operates an internal logic circuit, reads unique identification data stored in advance in a memory, amplitude-modulates a transmission carrier wave from the ID reader 10, and retransmits the transmission carrier wave as a return wave to the ID reader 10.

The ID reader 10 receives a return wave from the wireless ID tag 20 by the antenna 15, and inputs it to the reception/demodulation section 12 through the circulator 14. The reception/demodulation section 12 extracts a clock signal from the output signal inputted to the transmission section 11 through the directional coupler 13, demodulates the identification data from the wireless tag 20, converts the data into digital data, and transmits the digital data to a host device such as a personal computer (not shown).

The ID reader 10 as described above can read the identification data of the wireless ID tag 20 and confirm the data content.

In fig. 3, the identification data of the wireless ID tag 20 is confirmed by the ID reader 10, and the following system is recently considered: one ID reader 10 can confirm not only the wireless ID tag 20 but also identification data of other media such as an IC card. In this case, for example, a frequency of 2.4GHz is used for data identification of the wireless ID tag 20, and a frequency of 13.56MHz is used for data identification of the IC card. Therefore, as the antenna 15 of the ID reader 10, it is necessary to consider the antenna for 2.4GHz and the antenna for 13.56 MHz.

In the ID reader 10 as described above, when media data of different frequencies of use is identified in addition to the wireless ID tag 20, 2 antennas corresponding to the respective frequencies of use are necessary, which is an obstacle to downsizing of the device. In recent years, attempts have been made to maintain the function of the ID reader 10 in the portable information terminal, and miniaturization of the antenna has been desired.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a dual-band antenna device in which 2 antenna elements are mounted on 1 antenna substrate, and which can be made compact and obtain desired characteristics in accordance with different frequencies.

In order to achieve the above object, according to the present invention, an antenna device includes:

a dielectric substrate;

a first frequency receiving patch antenna having a first size and provided on a first surface of the dielectric substrate;

a second frequency receiving coil antenna having a second size larger than the first size, provided on the first surface of the dielectric substrate, and surrounding the patch antenna; and

a ground member having a third size larger than the first size and smaller than the second size, provided to a second face of the dielectric substrate,

wherein a minimum interval between an outer edge of the patch antenna and an outer edge of the ground member and a minimum interval between an inner edge of the coil antenna and an outer edge of the ground member is 2 times or more of a thickness of the dielectric substrate.

By combining a patch antenna and a coil antenna on a dielectric substrate, it is possible to cope with 2 frequencies and effectively use the area of the dielectric substrate, thereby achieving miniaturization. Further, by appropriately selecting the minimum distance between the patch antenna and the coil antenna corresponding to the ground plane for the patch antenna, it is possible to achieve coexistence of antenna characteristics.

Drawings

Fig. 1 is a front view of a dual-band shared antenna apparatus according to an embodiment of the present invention;

fig. 2 is a rear view of the antenna arrangement of fig. 1;

FIG. 3 shows a general example of a wireless tag reader system.

Detailed Description

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

Fig. 1 is a front view of a dual-band shared antenna apparatus according to an embodiment of the present invention, and fig. 2 is a rear view of the same apparatus. In fig. 1 and 2, 31 is a square antenna substrate, that is, a dielectric substrate, formed to have a thickness of about 1.6mm, a short side of about 65mm, and a long side of about 75mm, for example. On the upper surface of the dielectric substrate 31, a rectangular coil antenna 32 is formed along the peripheral portion by etching or the like, and a circular polarized wave radiating means such as a circular patch antenna 34 is formed at the central portion.

The coil antenna 32 is a first frequency antenna using, for example, 13.56MHz, is formed into about 4 turns by a microwave transmission line, and has both end portions connected to the power feeding terminals 33a, 33 b. The power feeding terminals 33a and 33b are provided in the lower center portion of the coil antenna 32, for example.

The patch antenna 34 is a 2.4GHz second frequency antenna, for example, and has a feed point 35 provided adjacent to the center portion and a pair of circularly polarized wave cutouts 36 provided in the outer peripheral edge. The diameter of the patch antenna 34 is set to about λ g/2. The λ g represents a wavelength corresponding to a reception frequency, and the value thereof takes into consideration the wavelength shortening rate of the dielectric substrate 31.

The dielectric substrate 31 is formed in a vertically rectangular shape, and has a lower portion as a mounting portion to another device, and mounting holes 37 are provided at right and left corner portions of the mounting portion.

A square ground plane 41 for the patch antenna is formed on the back surface of the dielectric substrate 31 by etching or the like corresponding to the patch antenna 34. The patch antenna is formed smaller than the coil antenna 32 and larger than the patch antenna 34 by the size of the ground plane 41. For example, the minimum distance d1 from the coil antenna 32 to the outer periphery of the ground plane 41 for the patch antenna and the minimum distance d2 from the patch antenna 34 to the outer periphery of the ground plane 41 for the patch antenna are set to be at least 2 times the thickness of the dielectric substrate 31 at the same time.

Further, in the ground plane 41 for patch antenna, a window 42 larger than the feeding point 35 is formed at a position corresponding to the feeding point 35 of the patch antenna 34, and a feeding portion 43 is formed at the center of the window. Between the above-described feeding point 35 and the feeding portion 43, electrical connection is made, for example, by a through hole. A power feeding connector is provided in the power feeding portion 43 as needed.

Since the coil antenna 32 has the ground plane 41 for patch antenna, a reverse magnetic field is generated by eddy current, and the minimum distance d1 between the inner edge of the coil antenna 32 and the outer edge of the ground plane 41 for patch antenna is preferably at least 2 times the thickness of the dielectric substrate 31. In the present embodiment, the coil antenna 32 can be kept well in characteristics by separating the coil antenna 32 from the patch antenna ground plane 41 by a distance of about 4 mm.

On the other hand, the patch antenna 34 is excellent in that the patch antenna ground plane 41 is large, and therefore, it is desirable that the minimum distance d2 between the outer edge of the patch antenna 34 and the outer edge of the patch antenna ground plane 41 is at least 2 times the thickness of the dielectric substrate 31. In the present embodiment, the characteristics of the patch antenna 34 can be maintained by forming the width of the patch antenna ground plane 41 to be larger than the diameter of the patch antenna 34 by 4mm or more.

By forming the coil antenna 32 and the patch antenna 34 on 1 dielectric substrate 31 as described above, it is possible to correspond to 2 frequencies of 13.56MHz and 2.45 GHz. Further, by combining the coil antenna 32 and the patch antenna 34, the area of the dielectric substrate 31 can be effectively used, and the size reduction thereof can be achieved. Further, by appropriately selecting the minimum distances d1 and d2 between the coil antenna 32 and the patch antenna 34 corresponding to the patch antenna ground plane 41, the antenna characteristics can be compatible with each other.

By using the antenna device as an antenna of an ID reader, it is possible to correspond to a plurality of kinds of devices having different frequencies of use, such as a wireless ID tag, an IC card, and an ID card, and to achieve miniaturization of the ID reader. The antenna device is not limited to an ID reader, and can be used for a small information device such as a portable information terminal, and can be used for multiple purposes.

Also, in the above-described embodiment, only the case of the frequencies of 13.56MHz and 2.45MHz is shown, and it is needless to say that it is also possible to have other frequencies.

In the above embodiment, the case of using the circular patch antenna 34 is described, but the same effect can be obtained also in the case of using another antenna such as a rectangular patch antenna or a loop patch antenna.

In the above embodiment, the coil antenna 32 and the patch antenna ground plane 41 are formed in a square shape, but may be formed in a circular shape. The dielectric substrate 31 is not limited to a square shape, and may be formed in a circular shape.

The present invention is not limited to the above embodiments as it is, and can be embodied by modifying the components within the scope not departing from the spirit thereof at the stage of implementation.

Claims (1)

1. An antenna device has:

a dielectric substrate;

a first frequency receiving patch antenna having a first size and provided on the first surface of the dielectric substrate;

a second frequency receiving coil antenna having a second size larger than the first size, the second frequency receiving coil antenna being provided on the first surface of the dielectric substrate so as to surround the patch antenna; and

a ground member having a third size larger than the first size and smaller than the second size and provided on a second surface of the dielectric substrate,

wherein a minimum interval between an outer edge of the patch antenna and an outer edge of the ground member and a minimum interval between an inner edge of the coil antenna and an outer edge of the ground member is 2 times or more of a thickness of the dielectric substrate.