Antenna system

The present invention relates to an antenna device applied to a radio terminal such as a mobile phone terminal or a mobile television terminal.

As a technique for using the earphone cord as an antenna, for example, there is one published in Japanese Patent Application Laid-Open No. 9-51222. FIG. 6 is a schematic configuration diagram thereof. 13 is a radio, 14 is a signal line, 15 is a feeder, 16 is a shield case, and 18 is an earphone or microphone. The earphone or microphone 18 is connected to the electric circuit (voice processing circuit) of the radio 13 via the signal line 14, and a part of the signal line 14 on the ground side becomes the feeding point F, and the feeding line 15 The signal line 14 operates as an antenna element when connected to.

Further, there is an antenna diversity receiver in which an antenna element is mounted on an earphone unit, which is described in Japanese Patent Application Laid-Open No. 2001-251232. FIG. 7 is a schematic configuration diagram thereof. AN0 is the main antenna, AN1 is the sub antenna, 30 is the plug, 60 is the earphone jack, 100 is the mobile phone body, 200 is the earphone part, and 300 is the cord. A chip antenna made of a high dielectric constant material is mounted in the earphone 200. Diversity reception is performed by the chip antenna and the main antenna AN0 while the cord 300 is connected to the mobile phone 100.

<patcit num="1"><text>Japanese Unexamined Patent Publication No. 9-51222</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 2001-251232</text></patcit>

<p> In recent years, radio terminals such as mobile phone terminals and mobile TV terminals, which are becoming smaller and smaller, are equipped with antenna elements such as whip antennas. In these radio terminals, the size of the entire radio terminal including the antenna element cannot be secured sufficiently large for a predetermined propagation wavelength. For this reason, a current that contributes to the transmission and reception of radio waves flows not only to the antenna element but also to the ground of the circuit board inside the radio terminal. Therefore, the size of the circuit board and the size of the radio terminal are also the characteristics of the antenna. Has a great influence on.</p><p> In addition, wireless terminals are often held and used by hand. Many of the miniaturized radio terminals are covered by hands, and the antenna efficiency deteriorates due to the influence of the human body.</p><p> In order to suppress the deterioration of the antenna efficiency due to the holding of the hand, it is sufficient to reduce the current flowing on the ground of the circuit board and contributing to the transmission and reception of radio waves. Therefore, it is also effective to lengthen the antenna element. However, when the antenna element is lengthened, the input impedance of the antenna becomes high and the frequency band that can be used for matching becomes narrow. Further, when the length of the antenna element is about 1/2, 3/4, or 1 of the predetermined propagation wavelength, nodes occur in the current distribution on the antenna element, and many nulls occur in the radiation pattern. This interferes with sensitive communication. Further, lengthening the antenna element has a great demerit in reducing the size of the entire radio terminal and improving the design.</p><p> For this reason, in the conventional antenna device shown in FIG. 6, the size of the radio terminal has a large effect on the antenna characteristics, and if the radio terminal is made smaller, the antenna efficiency is deteriorated and the usable frequency is narrowed. Bandwidth is caused, which hinders the miniaturization and freedom of shape of radio terminals. Furthermore, the antenna characteristics are susceptible to adverse effects from the human body when the radio terminal is held by hand. Further, in the conventional antenna device shown in FIG. 7, a chip antenna is used. The chip antenna uses a high dielectric constant material, and the antenna efficiency is generally low due to dielectric loss or the like, and the usable frequency band is also limited. Furthermore, since the chip antenna is built in the earphone part, the antenna characteristics are strongly influenced by the human body.</p><p> In the present invention, a part of the earphone cord is also used as a dipole antenna as it is. When the antenna is formed in this way, it is not affected by the radio terminal, so even if the radio terminal is held by hand, the antenna efficiency does not deteriorate and stable radio wave transmission / reception becomes possible. Furthermore, it also leads to an increase in the degree of freedom in the size and shape of the radio body. Further, by appropriately setting the length of the earphone cord, it is easy to form a half-wave dipole antenna, and a usable frequency band can be secured. Even when performing diversity reception with the antenna mounted on the radio terminal, the distance between the antennas used can be sufficiently separated and the isolation characteristics are very good, so that a high-performance diversity effect can be realized.</p>

<p> The antenna device of the present invention has a first metal wire that splits an audio signal from a circuit board installed inside the main body of a portable radio into two and transmits the audio signal to the first and second earphones, respectively. With two metal wires, the length from the first earphone to the second earphone of the first metal wire and the length from the first earphone to the second earphone of the second metal wire are almost the same. The first metal wire and the second metal wire are arranged close to each other in a non-contact manner, and further, near the junction point of the first metal wire and the confluence of the second metal wire, and on the earphone side, respectively. The first and second inductors are provided, and the dipole antenna is formed by the first and second metal wires on the earphone side from the branch point and the confluence point.</p>

<p> Since the antenna device of the present invention forms a dipole antenna by using the ground line and the signal line for transmitting the voice signal to the earphone as they are, the characteristic of the dipole antenna is that the circuit board 2 is built in. The degree of freedom in the size and shape of the radio main body 1 can be increased without being affected by the size and shape of the machine main body 1. Further, even if the radio body 1 is held by hand, the antenna efficiency does not deteriorate. In the present invention, the weight and cost of the earphone cord are reduced as compared with the case where the element dedicated to the antenna is separately built in the earphone cord. Further, by appropriately setting the length of the earphone cord, it is easy to form a substantially 1/2 wavelength dipole antenna, and a wide usable frequency band can be secured. In addition, when performing diversity reception with the antenna mounted on the radio terminal, the distance between the antennas used can be sufficiently separated and the isolation characteristics are very good, so a high-performance diversity effect is realized. it can.</p>

Embodiment 1. Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

FIG. 1 is a configuration diagram showing a first embodiment of the present invention. This antenna device is related to the antenna device of a wireless terminal equipped with a UHF band TV broadcast viewing function, and a part of the earphone cord is also used as a dipole antenna. The earphone cord used here is a monaural type. The configuration of the first embodiment will be described below with reference to the figure. In the figure, 1 is the main body of the radio, 2 is the circuit board installed inside the main body of the radio 1, 3 is the earphone plug, 4 is the earphone jack, 5a is the first earphone, 5b is the second earphone, and 6 is. Ground line, 6a is the left ground line that connects to the first earphone 5a after the branch of the ground line 6, 6b is the right ground line that connects to the second earphone 5b after the branch of the ground line 6, 7 is the signal line, 7a is the left signal line that connects to the first earphone 5a after the signal line 7 branches, 7b is the right signal line that connects to the second earphone 5b after the signal line 7 branches, and 8a is one of the left ground lines 6a. The first coil whose part is spirally wound near the branch point, 8b is the second coil where a part of the right signal line 7b is spirally wound near the branch point, 9a is the left ground line 6a and the left. A third coil in which a part of the signal line 7a is wound in a spiral, 9b is a fourth coil in which a part of the right ground line 6b and a part of the right signal line 7b is wound in a spiral, and S is a power supply as an antenna. The points are the branch point of the signal line 7 and the branch point of the ground line 6, respectively.

Ground line 6, left ground line 6a, right ground line 6b, signal line 7, left signal line 7a, right signal line 7b, first coil 8a, second coil 8b, third The coil 9a and the fourth coil 9b are all covered with an insulating film 12 (not shown). The earphone cord described in the following text indicates a portion covered with the insulating film 12. The radio main body 1 is provided with a speaker, a display, a battery, a microphone, a keyboard, etc., which are not shown. The circuit board 2 is provided with an RF circuit, a digital circuit, an image processing circuit, an audio processing circuit, a balun, and the like.

Next, the configuration of the first embodiment will be described in more detail. The ground line 6 and the signal line 7 are electrically connected to the circuit board 2 by connecting the earphone plug 3 installed in the radio main body 1 and connected to the circuit board 2 and the earphone jack 4. The ground line 6 and the signal line 7 form an audio signal transmission line from the circuit board 2 to the earphones 5a and 5b. The ground line 6 and the signal line 7 form a balanced two-line transmission line at a high frequency (here, a frequency in the UHF band) between the circuit board 2 and the feeding point S. The ground line 6 is bifurcated into the left ground line 6a and the right ground line 6b at the feeding point S, and the signal line 7 is also bifurcated into the left signal line 7a and the right signal line 7b at the feeding point S. The left ground line 6a and the left signal line 7a are both connected to the first earphone 5a, and the right ground line 6b and the right signal line 7b are both connected to the second earphone 5b. The left ground line 6a forms the first coil 8a in the immediate vicinity of the feeding point S, and the right signal line 7b forms the second coil 8b in the immediate vicinity of the feeding point S.

The left ground line 6a and the left signal line 7a are about 1/4 of the predetermined propagation wavelength along the side of the first earphone 5a from the feeding point S (here, about 1/4 of the wavelength at the frequency of 500 MHz in the UHF band). A third coil 9a is formed at the position of 150 mm), and the right ground line 6b and the right signal line 7b are also about 1/4 of the propagation wavelength along the side of the second earphone 5b from the feeding point S. A fourth coil 9b is formed at the position. Since the left ground line 6a and the left signal line 7a are arranged close to each other, the capacitors are distributed and connected between the left ground line 6a and the left signal line 7a. The ground line 6a and the left signal line 7a may be treated as one metal wire. The same applies to the right ground line 6b and the right signal line 7b. Here, the first coil 8a, the second coil 8b, the third coil 9a, and the fourth coil 9b are all formed to block the current in the frequency of the UHF band, and the number of coil turns. And the pitch are adjusted to make the reactance in the UHF band frequency sufficiently large (ideally infinite).

The antenna of the first embodiment according to the present invention is configured as described above. Due to the third coil 9a, the current of the frequency in the UHF band does not flow into the left ground line 6a and the left signal line 7a between the third coil 9a and the first earphone 5a. Further, due to the fourth coil 9b, the current of the UHF band frequency does not flow into the right ground line 6b and the right signal line 7b between the fourth coil 9b and the second earphone 5b. Therefore, in the left ground line 6a and the left signal line 7a, the portion from the feeding point S to the third coil 9a and the portion of the right ground line 6b and the right signal line 7b from the feeding point S to the fourth coil , Form a approximately 1/2 wavelength dipole antenna at a frequency of 500 MHz in the UHF band.

The frequency band used for audio signals is 20Hz to 20kHz, which is sufficiently smaller than the UHF band frequency, so the first coil 8a, the second coil 8b, the third coil 9a, and the fourth coil 9b are all. , Does not interfere with the transmission of audio signals. The application of the high frequency voltage to the dipole antenna is performed by the ground line 6 and the signal line 7 forming the balanced two-line transmission line at the frequency of the UHF band. However, since the circuit board 2 is an unbalanced circuit, a balun (unbalanced-balanced converter) is used to connect the ground line 6 and the signal line 7 forming the balanced two-line transmission line to the circuit board 2. A balun is configured on the circuit board 2. The dipole antenna is a balanced circuit, and a balun is not required to connect the ground line 6 and the signal line 7 forming the transmission line to the dipole antenna.

The dipole antenna according to the first embodiment of the present invention is formed in this way. Therefore, the characteristics of the dipole antenna are not affected by the size and shape of the radio main body 1 incorporating the circuit board 2, and the degree of freedom in the size and shape of the radio main body 1 can be increased. Further, even if the radio body 1 is held by hand, the antenna efficiency does not deteriorate. In the present invention, since the dipole antenna is formed by using the ground line 6 and the signal line 7 for transmitting the audio signal to the earphone 5 as they are, it is compared with the case where the element dedicated to the antenna is separately built in the earphone cord. , Contributes to weight reduction and cost reduction of earphone cord. Further, by appropriately setting the length of the earphone cord, it is easy to form a substantially 1/2 wavelength dipole antenna, and a wide usable frequency band can be secured.

In the first embodiment, in order to form a dipole antenna, a part of each of the left ground line 6a, the left signal line 7a, the right ground line 6b, and the right signal line 7b is spirally wound. The coil 8a, the second coil 8b, the third coil 9a, and the fourth coil 9b were formed, but instead of the first coil 8a, the second coil 8b, the third coil 9a, and the fourth coil 9b. A chip inductor may be connected to. The third coil 9a is formed on both the left ground line 6a and the left signal line 7a, but may be formed only on the left signal line 7a. The fourth coil 9b is formed on both the right ground line 6b and the right signal line 7b, but may be formed only on the right ground line 6b.

Instead of forming the third coil 9a and the fourth coil 9b, at the left ground line 6a and the left signal line 7a, 1/4 of the predetermined propagation frequency along the side of the first earphone 5a from the feeding point S. The left ground line 6a and the left signal line 7a are connected via a capacitor at a position of about, and at the right ground line 6b and the right signal line 7b, a predetermined propagation frequency along the side from the feeding point S to the second earphone 5b. By connecting the right ground line 6b and the right signal line 7b via a capacitor at a position of about 1/4 of the above, a substantially 1/2 wavelength dipole at a predetermined frequency can be formed.

It is also possible to change the resonance frequency of the dipole antenna by connecting a variable inductor instead of the third coil 9a and the fourth coil 9b. This is due to the change in the reactance value of the variable inductor from the variable inductor of the left ground line 6a and the left signal line 7a to the earphone 5a, or from the variable inductor of the right ground line 6b and the right signal line 7b to the earphone 5b. This is because the flow of current in the UHF band frequency of the part changes. In this case, the reverse bias voltage source applied to the variable inductor may be installed inside the radio main body 1. Since the left ground line 6a and the left signal line 7a are arranged close to each other, the capacitors are distributed and connected between the left ground line 6a and the left signal line 7a, but the left ground line 6a A chip capacitor may actually be connected between the left signal line 7a and the left signal line 7a at a sufficiently small interval with respect to a predetermined wavelength. The same applies to the right ground line 6b and the right signal line 7b.

The part from the third coil 9a to the first earphone 5a on the left ground line 6a and the left signal line 7a, and the fourth coil 9b to the second earphone 5b on the right ground line 6b and the right signal line 7b. When a high-frequency current is induced in this part, it affects various characteristics of the dipole antenna. As a means for suppressing this induced high-frequency current, the portion of the left ground line 6a and the left signal line 7a from the third coil 9a to the first earphone 5a, and the right ground line 6b and the right signal line 7b. The part from the fourth coil 9b to the second earphone 5b in the above may be coated with a magnetic paint or wound with ferrite.

Impedance matching for the dipole antenna may be performed on the circuit board 2, but by performing it near the feeding point S, the usable frequency band can be kept wide. This is because the length of the earphone cord extending from the circuit board 2 to the feeding point S has a frequency characteristic, which narrows the frequency band that can be used for impedance matching. Inserting a resonator into the matching circuit as part of impedance matching can further increase the usable frequency band.

The earphone cord shown in the first embodiment has a symmetrical structure, but it may have an asymmetrical structure, and the dipole antenna may also have an asymmetrical structure. In this case, the length from the feeding point S on the left ground line 6a and the left signal line 7a to the third coil 9a, and the length from the feeding point S on the right ground line 6b and the right signal line 7b to the fourth coil 9b. The positions where the third coil and the fourth coil are arranged may be determined so that the sum of the above is about 1/2 of the predetermined propagation wavelength.

Embodiment 2. FIG. 2 shows Embodiment 2 of the present invention, and relates to an antenna device of a wireless terminal provided with a UHF band television broadcast viewing function. In the first embodiment, a monaural type earphone cord is used, but in the second embodiment, a stereotype earphone cord is used. The difference from the first embodiment is that the signal line 7 is divided into two lines, the signal line 7L and the signal line 7R, and the signal line 7R is arranged close to the ground line 6.

The operating principle is the same as in the first embodiment. The balanced two-line transmission line in the UHF band frequency formed from the circuit board 2 to the feeding point S is composed of the ground line 6 and the signal line 7L. Since the signal line 7R and the ground line 6 are arranged close to each other, the capacitors are distributed and connected between the signal line 7R and the ground line 6, and the signal line 7R and the ground line 6 are connected at the frequency of the UHF band. It may be treated as one metal wire. In the left ground line 6a and the left signal line 7a, and the right ground line 6b and the right signal line 7b, the configurations from the feeding point S to the earphones 5a and 5b are all the same as those in the first embodiment.

In the balanced two-wire transmission line in the UHF band frequency, the signal line 7R and the signal line 7L are arranged close to each other between the circuit board 2 and the feeding point S, and between the signal line 7R and the signal line 7L. In addition, by making the capacitors distributed and connected, the signal line 7R and the signal line 7L may be treated as one metal wire in the frequency of the UHF band. Similarly, between the circuit board 2 and the feeding point S, the signal line 7L and the ground line 6 are arranged close to each other, and the capacitors are distributed and connected between the signal line 7L and the ground line 6. Therefore, the signal line 7L and the ground line 6 may be treated as one metal line in the UHF band frequency. Furthermore, in the UHF band frequency, these balanced two-wire transmission lines are constructed so that instead of arranging the metal wires in close proximity to each other, the metal wires are spaced sufficiently narrowly apart from each other for a predetermined propagation wavelength. May be configured by connecting with a chip capacitor. With the above configuration, it is possible to support stereotyped audio signals.

Embodiment 3. FIG. 3 shows Embodiment 3 of the present invention, which relates to an antenna device of a wireless terminal provided with a UHF band television broadcast viewing function, and uses a monaural type earphone cord. .. The difference from the first embodiment is that the whip antenna 10 that can be housed in the radio main body 1 is connected to the circuit board 2, and the circuit board 2 is equipped with a diversity reception processing unit (not shown). And, the whip antenna 10 enables diversity reception. The diversity processing unit is provided with a switch that can switch the electrical connection between the dipole antenna and the whip antenna 10, and determines which demodulated data of both antennas is to be adopted.

In general, it is said that a good effect can be obtained in diversity reception by separating the distances between the antennas used by about 1/2 of a predetermined propagation wavelength. When a plurality of antenna elements are connected to the circuit board and diversity reception is performed using these antenna elements, the distance between the antennas cannot be secured and the isolation characteristics are poor, so that a good diversity effect cannot be obtained.

In the present invention, assuming that the length of the earphone cord from the radio main body 1 to the feeding point S is approximately 300 mm or more, the distance between the dipole antenna and the whip antenna 10 is approximately 1/2 or more of the wavelength at the UHF band frequency of 500 MHz. Can be secured. This length is sufficiently practical in terms of convenience in actual use. Further, as described in the first embodiment, the dipole antenna has a feature that the antenna characteristics are not affected by the radio main body 1, and the isolation characteristics between the dipole antenna and the whip antenna 10 are good. These features of the present invention are very advantageous for performing diversity reception. Moreover, since the planes of polarization of the whip antenna 10 and the dipole antenna are not fixed to be the same, it is suggested that the whip antenna 10 and the dipole antenna also have high quality as polarization diversity.

The diversity reception processing unit may be configured to perform combined diversity by synthesizing the received power from each of the dipole antenna and the whip antenna 10 in the maximum ratio. The antenna element other than the dipole antenna connected to the circuit board 2 is not limited to the whip antenna 10. Further, a plurality of antenna elements may be connected to the circuit board 2 in addition to the dipole antenna and the whip antenna 10.

Embodiment 4. FIG. 4 shows Embodiment 4 of the present invention, and relates to an antenna device of a wireless terminal provided with a UHF band television broadcast viewing function. In the fourth embodiment, 7c is the inner conductor of the coaxial cable, 7d is the left signal line connecting to the first earphone 5a after the inner conductor 7c of the coaxial cable is branched, and 7e is the second after the inner conductor 7c of the coaxial cable is branched. Right signal line connecting to the second earphone 5b, 6 is the outer conductor of the coaxial cable, 6d is the left ground line connecting the end of the outer conductor 6 of the coaxial cable on the feeding point S side and the first earphone 5a, 6e Is the right ground wire connecting the end of the outer conductor 6 of the coaxial cable on the feeding point S side and the second earphone 5b, 8c is the fifth coil in which a part of the left signal line 7d is spirally wound, 8d. Is the sixth coil in which a part of the right ground wire 6e is wound in a spiral, 9c is the seventh coil in which a part of the left signal line 7d and the left ground wire 6d is wound in a spiral, and 9d is the right signal. The eighth coil in which a part of the wire 7e and the right ground wire 6e is wound in a spiral shape, and 11 is a conductor having a choke structure, and a part thereof conducts with the outer conductor 6c.

The difference from the third embodiment is that a balanced two-wire transmission line in the UHF band frequency composed of the ground line 6 and the signal line 7 is formed by a coaxial cable between the circuit board 2 and the feeding point S. The point is that the choke structure 11 is provided on the outside of the outer conductor 6c so that a current having a frequency in the UHF band does not easily flow. The method of forming a dipole antenna by the left signal line 7d and the right signal line 7e connecting the first earphone 5a and the second earphone 5b from the feeding point S, and the left ground line 6d and the right ground line 6e is an embodiment. Same as 3.

Since both the circuit board 2 and the coaxial cable are unbalanced circuits, it is not necessary to use a balun to connect the circuit board 2 and the coaxial cable. However, since the dipole antenna is a balanced circuit, it has a high frequency at the feeding point S (here, the frequency in the UHF band). A reflected current is generated in. The reflected current in the UHF band frequency flows outside the outer conductor 6c. In order to reduce the radiation caused by this current, the outer conductor 6c has a choke structure 11. As shown in FIG. 4, the choke structure 11 is a cylindrical conductor substantially parallel to the coaxial cable, and the feeding point S side is opened and the circuit board 2 side is short-circuited with the outer conductor 6c. By making the length L of the choke structure 11 shown in FIG. 4 approximately 1/4 of the predetermined propagation wavelength, at a predetermined frequency, the input outside the outer conductor 6c in anticipation of the circuit board 2 side from the feeding point S. The impedance becomes infinite, and the reflected current from the feeding point S does not flow. Here, if the distance d between the outer conductor 6c and the choke structure 11 is widened to some extent, it is possible to widen the frequency band in which the reflected current is difficult to flow. Instead of forming the choke structure 11, ferrite may be wound around the outer conductor 6c, or a magnetic paint may be applied. In the fourth embodiment, since the transmission line in the UHF band frequency is formed by the coaxial cable, the inner conductor 7c, which is a signal line, is shielded by the outer conductor 6c and is less susceptible to disturbance.

Embodiment 5. FIG. 5 shows Embodiment 5 of the present invention, which relates to an antenna device of a wireless terminal provided with a UHF band television broadcast viewing function, and the basic operation of the antenna is the same as that of Embodiment 3. Is. 12 is an earphone cord and 13 is a clip, which is connected to the earphone cord 12 so that the earphone cord 12 can be fixed to the clothes of the wireless terminal user. The earphone cord 12 is composed of any one of the ones described in the first to fourth embodiments.

When the earphone cord 12 is fixed to the clothes of the wireless terminal user with the clip 13, the position of the dipole antenna with respect to the human body is less likely to fluctuate, and stable antenna characteristics can be obtained. Further, the antenna efficiency can be improved by fixing the position of the dipole antenna to the clothes so as to be away from the human body of the wireless terminal user. Further, fixing the earphone cord 12 to the clothes of the wireless terminal user also reduces the burden of the force applied to the ear. The member connecting the earphone cord 12 and the clip 13 is not specified, but it is preferably not metal. The same applies to the members constituting the clip 13. The installation location of the clip 13 is not specified as shown in FIG.

The present invention is suitable for application to radio terminals such as mobile phone terminals and mobile television terminals.

<figref num="1">It is a block diagram which shows Embodiment 1 of this invention.</figref><figref num="2">It is a block diagram which shows Embodiment 2 of this invention.</figref><figref num="3">It is a block diagram which shows Embodiment 3 of this invention.</figref><figref num="4">It is a block diagram which shows Embodiment 4 of this invention.</figref><figref num="5">It is a block diagram which shows Embodiment 5 of this invention.</figref><figref num="6">It is a schematic block diagram of the conventional apparatus.</figref><figref num="7">It is a schematic block diagram of another conventional apparatus.</figref>

Code description

1: Radio body, 2 :: Circuit board, 3: Earphone plug, 4: Earphone jack, 5a: First earphone, 5b: Second earphone, 6: Ground wire or coaxial cable outer conductor, 6a, 6d: Left ground line, 6b, 6e: Right ground line, 7, 7L, 7R: Signal line, 7a, 7d: Left signal line, 7b, 7e: Right signal line, 7c: Coaxial cable inner conductor, 8a: No. 1 coil, 8b: 2nd coil, 9a: 3rd coil, 9b: 4th coil, 10: whip antenna, 11: choke structure conductor, 12: earphone cord, 13: clip, S: feeding point.