JPH066585Y2 - Small antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a small antenna incorporated in a wireless device such as a cordless phone or a mobile phone.

(Prior Art and its Problems) Conventionally, as an antenna in this type of device, a whip antenna is generally attached to the outside of a wireless device for use.

However, in a mobile phone or the like that is carried by hand, the whip antenna is inconvenient in terms of usability and has a drawback that it is easily damaged when dropped. Further, when the antenna protruding to the outside is used in a wide space such as a golf course, there is a problem in that the damage to the receiver and the risk to human life due to lightning, discharge from clothes, etc. cannot be ignored.

In addition, when the antenna is touched by the hand, there is a drawback that the impedance is significantly changed and the characteristics are deteriorated.

Furthermore, even with a 1/4 wavelength whip antenna, the transmission frequency is 380MHz.
However, the length is about 20 cm, which is an obstacle in the case of a mobile phone that requires miniaturization.

In order to solve these problems, conventionally, a loop antenna is configured with a conductor foil on a dielectric substrate, built in the inside of the wireless device housing as shown in FIG. 12, and a structure is adopted in which power is supplied from the transceiver unit. Was becoming.

In FIG. 12, 1 is a loop antenna, 12 is a receiver, and 13
Is a transmitter, and 17 is a radio housing.

However, a loop antenna with a size that can be built into a wireless device is generally a small loop antenna with an electrical length of a few tenths of a wavelength, and the dipole antenna has a sensitivity of -30 dB or less. It had the drawback of being sufficient.

(Object of the Invention) The present invention solves the above-mentioned drawbacks and provides a small antenna which can be incorporated in a mobile phone, has a small impedance variation, and has high sensitivity.

(Means for Solving Problems) In order to solve the above problems, the present invention configures two loop antennas for transmission and reception on a dielectric substrate, and the loop antenna has an electric length of several wavelengths. This is a minute loop antenna with a size of one tenth, and it is made compact by forming an impedance matching circuit on a dielectric substrate, and it is housed inside the housing of a mobile phone and the power is fed from the transceiver unit to the antenna. The method is characterized by using a high-frequency transmission line such as a coaxial cable.

(Operation) With such a configuration, the small antenna according to the present invention is extremely small, can be built in the radio housing, and is not directly touched by the hand, so that there is little impedance fluctuation, and there is no drop or discharge. There is an advantage that it is not damaged at the same time and has higher sensitivity than the conventional loop antenna.

(Embodiment) An embodiment of the present invention will be described with reference to FIGS. 1 to 11.

FIG. 1 is a diagram showing the structure of a small antenna according to the present invention.
1 is a dielectric substrate, 2 is a 380MHz loop antenna for receiving antennas, 3 is a 254MHz band loop antenna for transmitting antennas, 4 to 7 are trimmer capacitors for impedance matching, 8 is a ground terminal, and 9 is a feeding terminal. .

In this embodiment, the area of the 254 MHz band for transmission is increased in order to make the efficiency of the transmitting antenna and the efficiency of the receiving antenna substantially equal.

The size of this prototype antenna actually manufactured is 20
mm × 25 mm, transmitting antenna 30 mm × 25 mm, and 0.8 mm thick glass epoxy board made of copper foil. The impedance matching trimmer capacitor is 2 to 6 pF.

2 and 3 are diagrams for explaining the electrical action of the impedance matching circuit. Here, an example of the receiving loop antenna 2 will be described, but the same applies to the case of the transmitting loop antenna 3. In FIG. 2, the impedance A of the loop element alone is A on the Smith chart of FIG.
It is plotted at the points. The impedance at the point A is converted to the impedance at the point B in FIG. 3 by the trimmer capacitor 5, and further by the trimmer capacitor 4 in FIG.
Matched to a point impedance of 50Ω.

Fig. 4 is an actual measurement diagram showing the impedance matching state (return loss) of the transmitting antenna, and Fig. 5 is an actual measurement diagram showing the impedance matching state (return loss) of the receiving antenna. At 254 MHz
It has a return loss of 53 dB and good characteristics.

6 (a), (b) and (c) are a front view, a side view and a plan view including a cross section for explaining a feeding system of a small antenna according to the present invention. In FIG. 6, 10 and 11 are coaxial cables, 12 is a receiving unit, 13 is a transmitting unit, 14 is a radio board, and 15
Is a high frequency input terminal of the receiving unit, 16 is a high frequency output terminal of the transmitting unit, and 17 is a radio housing. The wireless device board 14 is almost the entire ground conductor except the parts mounting part, and various shield cases are mounted on it.

Specific examples of the respective parts in FIGS. 6 (a) (b) (c) will be described below.

The radio housing 17 is approximately 55 mm x 130 mm, and the receiving unit 12
And the receiving loop antenna 2 are coaxial cables with a length of about 50 mm
10 is connected, and the inner conductor of the coaxial cable 10 is the power supply terminal 7.
And the high frequency input terminal 15 are connected to each other, and the outer conductor of the coaxial cable 10 connects the ground terminal 8 and the ground conductor portion of the radio device substrate 14. At this time, the outer conductor of the coaxial cable 10 on the side connected to the antenna is prevented from coming into contact with the ground conductor of the radio device substrate 14.

Similarly, the transmission unit 13 and the transmission loop antenna 3 are connected by a coaxial cable 11 having a length of about 50 mm.
The inner conductor of connects the power supply terminal 9 and the high frequency output terminal 16,
The outer conductor of the coaxial cable 11 is the ground terminal 8 and the radio board 14
The ground conductor part of is connected. Also at this time, the outer conductor of the coaxial cable 11 on the side connected to the antenna is prevented from coming into contact with the ground conductor of the wireless board 14.

As described above, the power supply system of the embodiment according to the present invention is different from that of the conventional example. That is, in the conventional example, generally, in the loop antenna and the transmission / reception unit, the ground terminal of the loop antenna and the ground conductor portion of the radio device substrate are directly connected, and
Whereas the feeding terminal of the loop antenna and the high frequency input / output terminal were directly connected, in the embodiment according to the present invention, the transmitting / receiving unit and the loop antenna are connected by a coaxial cable with a length of several tens of millimeters. I am trying. With such a configuration, not only the loop antenna portion but also the coaxial cable portion and the ground conductor portion of the wireless device substrate act as an antenna, whereby the sensitivity is improved.

FIG. 7 is a diagram showing an example of the actual configuration of the high frequency input terminal 15,
FIG. 8 is a diagram showing an example of the actual configuration of the high frequency output terminal 16.

FIG. 9 is a diagram showing a sensitivity measuring method for a small antenna according to the present invention. Here, an example of measuring the sensitivity of the transmitting loop antenna 3 is shown. The mobile phone 18 is placed on a turntable with a transmission power of 10 mW and rotates 360 °. The transmitted radio waves
The signal is received by the standard dipole antenna 19 separated by 3 m, and the electric field strength is measured by the electric field strength measuring device 20.

FIG. 10 is a diagram showing the transmission sensitivity of the small antenna of the present invention, and FIG. 11 is a diagram showing the transmission sensitivity of the conventional small antenna.

Although the sensitivity of the transmitting loop antenna has been described with reference to FIGS. 9 to 11, similar sensitivity improvement has been confirmed in the receiving loop antenna.

As described above, according to the present invention, it is possible to realize an antenna that is small in size, has a good impedance matching characteristic, and has a sensitivity improved by about 10 dB as compared with the conventional antenna.

The isolation between the transmitting and receiving antennas is 30 dB or more.

In the present embodiment, the area of the transmitting antenna (254 MHz band) is made larger than that of the receiving antenna (380 MHz band) in order to equalize the efficiency of the transmitting antenna and the receiving antenna. However, according to the specifications required for the system, The ratio of the height can be arbitrarily selected.

In FIG. 1, it is clear that the conductor width and the corner (corner) shape of the conductor pattern forming the loop antennas 2 and 3 can be arbitrarily changed according to the dielectric constant of the dielectric material, the substrate thickness, and the like. is there.

(Effect of the Invention) As described above, according to the present invention, it is possible to provide a very small antenna that can be built in a mobile phone, is very small, and is stable when used.

In addition, the antenna of the present invention is about 10 dB more sensitive than the conventional loop antenna, has a good impedance matching characteristic, and has the advantage that the impedance characteristic is stable because it is not touched directly with the hand. There is.

Further, since the small antenna of the present invention can be constructed on a dielectric substrate in the same manner as an ordinary printed wiring board, it has an advantage of being inexpensive and excellent in mass productivity.

Further, the small antenna of the present invention is characterized by being non-polarized and omnidirectional, which makes it suitable for wireless devices such as mobile phones.

[Brief description of drawings]

FIG. 1 is a front view showing the structure of a small antenna of the present invention, FIGS. 2 and 3 are circuit diagrams and Smith charts showing impedance matching, and FIGS. 4 and 5 are characteristic diagrams showing return loss. 6 (a), (b) and (c) are a front view, a side view and a plan view including a cross section for explaining a feeding system to the small antenna, and FIG. 7 shows an example of the configuration of a high frequency input terminal. circuit diagram,
FIG. 8 is a circuit diagram showing a configuration example of a high-frequency output terminal, FIG. 9 is a system diagram for explaining the sensitivity measuring method of the small antenna of the present invention, and FIGS. 10 (a) and (b) are this small antenna. FIG. 11 is a characteristic diagram showing the transmission sensitivity, FIG. 11 is a characteristic diagram showing the transmission sensitivity of the conventional small antenna, and FIG. 12 is a schematic front view showing the feeding system of the conventional small antenna. DESCRIPTION OF SYMBOLS 1 ... Dielectric substrate, 2 ... Receiving antenna, 3 ... Transmission antenna, 4, 5, 6, 7 ... Trimmer capacitor, 8 ... Ground terminal, 9 ... Feeding terminal, 10, 11 ... Coaxial cable, 12 ... Receiving unit, 13 … Transmission unit, 14… Radio device board, 15… High frequency input terminal, 16… High frequency output terminal, 17… Radio device housing, 18
… Mobile phone, 19… Standard dipole antenna, 20… Electric field strength measuring instrument.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Fumiyasu Hayakawa 1-4-10 Irune, Chuo-ku, Tokyo Tokyo Electric Power Co., Inc. System Research Laboratory (72) Kazuhide Okamura 1-4-4 Irune, Chuo-ku, Tokyo No. 10 Tokyo Denki Co., Ltd. System Research Laboratory

Claims (1)

[Scope of utility model registration request] 1. A small antenna housed inside a radio casing such as a mobile phone, wherein the small antenna is a first antenna for reception and a second antenna for transmission, which is formed of a conductor foil on a dielectric substrate. And the first antenna and the second antenna are both rectangular micro loop antennas whose electric length is less than or equal to one tenth of the wavelength, and the ratio of the loop area of the first antenna to the second antenna is Is set to be substantially equal to the ratio of the reception wavelength and the transmission wavelength, and an impedance matching circuit is formed on the dielectric substrate, and the impedance matching circuit is formed between the first antenna and the reception unit and the second unit.
One or both of the antenna and the transmission unit are connected by a high frequency transmission line such as a coaxial cable, and one end and the other end of the ground conductor of the high frequency transmission line are grounded to the radio housing. A small antenna, which is connected to a substrate and a ground conductor of the small antenna, respectively.