JP2012060380A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna device which can be made to be operated as a magnetic field type antenna where receiving sensitivity is satisfactory from a low region to a high region, and in which a variation in an antenna characteristic is small and the mounting is also easy.SOLUTION: There are provided: a first belt-like conductor 11 where a radiation conductor part 1 of an antenna device which is built in a portable device and can receives a broadcast signal wave is extended in a three-dimensional loop shape, and one end is made as a feeding point P1, and the other end is made as a grounding terminal Q1; and a second belt-like conductor 12 which extends branching off from the middle of this first belt-like conductor 11, and in which the tip end is made as a feeding point P2. The first belt-like conductor 11 is excited as a first loop antenna element A1 by the feeding to the feeding point P1, and a part of the first belt-like conductors 11 and the second belt-like conductor 12 are excited as a second loop antenna element A2 in cooperation with each other by the feeding to the feeding point P2. Each of feeding points P1 and P2 is connected to variable tuning means 3, and a tuning frequency of each of loop antenna elements A1 and A2 is can be made to be changed by controlling a capacitance value of a variable capacitance diode 4.

Description

  The present invention relates to an antenna device that can receive a broadcast signal such as terrestrial digital television broadcast, and more particularly to a small antenna device that can be built in a portable device.

  In recent years, mobile devices such as mobile phones capable of viewing digital terrestrial television broadcasting have become widespread. In this type of portable device, a monopole antenna (electric field antenna) such as a whip antenna having a wide band and easily improving the radiation efficiency is widely used as an antenna device for receiving digital terrestrial television broadcasting. However, if the whip antenna protrudes outward with a mobile phone etc., it looks bad and looks bad, and there is also a high risk of damaging the whip antenna. The one in which the electric field type antenna is built in the housing is becoming widespread.

  However, since the electric field antenna is easily affected by the proximity of a human body (such as a human hand or head) that is a dielectric, there is a problem in that it is difficult to stabilize reception performance when incorporated in a portable device. On the other hand, magnetic field antennas such as loop antennas have the advantage that they are not easily affected by the proximity of a human body, but on the other hand, magnetic field antennas have a narrower band and lower radiation efficiency than electric field antennas. . Therefore, special measures are required when the magnetic field antenna is used as a built-in antenna for receiving digital terrestrial television broadcasting.

  Therefore, conventionally, two large and small loop antenna elements formed by bending a metal plate are arranged in a positional relationship where electromagnetic coupling is possible, and the other antenna element can be excited by supplying power to one antenna element. An antenna device for receiving digital terrestrial television broadcasting has been proposed (see, for example, Patent Document 1). In such a conventional antenna device, variable tuning means including a variable capacitance diode (varactor diode) is connected to the feeding point of the larger low-frequency antenna element. It is possible to tune the area antenna element to the broadcast signal wave. In addition, a small high-frequency dedicated antenna element is placed close to the inside of the low-frequency antenna element, and by supplying power to the low-frequency antenna element, the high-frequency dedicated antenna element is electromagnetically coupled to produce a high-frequency broadcast signal wave. It can be tuned. By combining the two loop antenna elements in this way, a small magnetic field type antenna capable of receiving all the frequency bands of digital terrestrial television broadcasting can be realized. Even if they are close to each other, they are less affected and the reception performance is stabilized.

JP 2006-325133 A

  By the way, in the antenna device configured to combine two loop antenna elements as in the conventional example described above, the high-frequency dedicated antenna element to be arranged inside the low-frequency antenna element must be formed quite small. The frequency band that can be tuned in the band becomes narrow. Although the tuning frequency of the low-frequency antenna element can be changed to some extent by the variable tuning means, if the capacitance change ratio of the variable capacitance diode is too large, the antenna efficiency is lowered. For this reason, in such a conventional example, a frequency band with poor reception sensitivity is likely to be generated in a high frequency range, and it has been difficult to use in, for example, China where the number of high frequency reception channels is large.

  In the conventional example, since the two loop antenna elements must be arranged in a positional relationship suitable for electromagnetic coupling, the antenna characteristics vary greatly due to variations in the relative positions of the two antenna elements. Therefore, when two antenna elements formed by bending a metal plate are assembled to a mobile phone casing or the like, the installation work becomes complicated, and a slight error in the installation position is unavoidable. However, it was difficult to stabilize.

  The present invention has been made in view of such a state of the art, and an object of the present invention is to operate as a magnetic field antenna having good reception sensitivity from a low frequency range to a high frequency range, and to have variations in antenna characteristics. An object of the present invention is to provide an antenna device that is small and easy to mount.

  In order to achieve the above object, an antenna device according to the present invention includes a first belt-like conductor that extends in a loop and has one end serving as a first feeding point and the other end connected to a ground conductor, and a middle of the first belt-like conductor. And a variable tuning means connected to at least the first feeding point, and the first feeding point to feed the first feeding point to the first feeding point. The band-shaped conductor is excited as a first loop antenna element, and the tuning frequency of the first loop antenna element can be changed by the variable tuning means, and the first band-shaped conductor is fed by feeding to the second feeding point. A configuration in which a part and the second belt-like conductor cooperate to excite as a second loop antenna element, and the tuning frequency of the second loop antenna element is higher than the tuning frequency of the first loop antenna element In It was.

  In the antenna device configured as described above, the second strip conductor extends from the first strip conductor that can be excited as the first loop antenna element, and the first and second strip conductors are formed as an integrated product. In addition, since a part of the first band-shaped conductor and the second band-shaped conductor can cooperate and excite as the second loop antenna element, a desired frequency higher than the tuning frequency of the first loop antenna element can be obtained. The second loop antenna element can be tuned. In addition, it is possible not only to excite the first loop antenna element at a predetermined frequency by feeding the first feeding point, but also to operate the second feeding point like a grounding end to increase the frequency higher than that frequency. Therefore, by changing the tuning frequency with the variable tuning means, the receivable bandwidth of the antenna device can be easily widened. Therefore, this antenna device can be operated as a magnetic field type antenna with good reception sensitivity from low to high frequencies, and even if a human body (such as a human hand or head) is in close proximity, it is not easily affected. The reception performance is easy to stabilize. In addition, since the two types of loop antenna elements are integrated in this antenna device, the antenna device can be easily attached to a portable device and there is little variation in antenna characteristics.

  In the above configuration, when the variable tuning means is connected to both the first feeding point and the second feeding point, the second loop antenna element can be excited at a predetermined frequency by feeding to the second feeding point. In addition to being possible, it is possible to operate the first feeding point like a ground terminal and excite it at another frequency lower than that frequency. The receivable bandwidth of the antenna device can be expanded more easily. That is, if the tuning frequency can be changed not only when the low band is selected but also when the high band is selected, the bandwidth of the receivable high band is widened.

  In the above configuration, if the variable tuning means includes a variable capacitance diode, the tuning frequency can be changed according to the magnitude of the reverse voltage applied to the variable capacitance diode. It can be simplified and is preferable.

  In the above configuration, when the first strip conductor extends in a three-dimensional loop shape defining a plurality of non-parallel opening surfaces, the first loop antenna element (first 1 band-shaped conductor) can be formed in a compact outer shape, which is preferable. In this case, when the first strip conductor is formed as a conductor extending while being bent at a right angle at a plurality of locations, and the second strip conductor is formed as a conductor branched at a right angle from the first strip conductor, In addition, the design and manufacture of the second strip conductor are facilitated.

  Further, in the above configuration, if the first and second strip conductors are patterned on the surface of the block body made of a dielectric material, it is easier to attach to the portable device and the antenna characteristics are easily stabilized. Become.

  In the above configuration, when the receivable frequency band includes the frequency band of the signal wave of terrestrial digital television broadcasting, the digital terrestrial television broadcasting with good reception sensitivity that can be built in a portable device such as a cellular phone. A magnetic field antenna for reception is obtained.

  According to the antenna device of the present invention, the second strip conductor extends from the first strip conductor that can be excited as the first loop antenna element, and a part of the first strip conductor and the second strip conductor are connected to each other. The second loop antenna element can be excited, and not only can the first loop antenna element be excited at a predetermined frequency by feeding the first feeding point, but the second feeding point can be grounded. Thus, it is possible to excite at another frequency higher than the frequency. Therefore, the receivable bandwidth of the antenna device can be easily widened by changing the tuning frequency by the variable tuning means. In other words, this antenna device can be operated as a magnetic field type antenna having good reception sensitivity from low to high frequencies, and even if a human body is close to the antenna device, it is not easily affected, so that reception performance is easily stabilized. In addition, since the two types of loop antenna elements are integrated in this antenna device, the antenna device can be easily attached to a portable device and there is little variation in antenna characteristics.

1 is a perspective view of an antenna device according to a first embodiment of the present invention. It is the perspective view which looked at the antenna apparatus of FIG. 1 from another angle. It is a basic circuit block diagram of the antenna device. It is explanatory drawing which shows the VSWR characteristic of this antenna apparatus. It is a perspective view of the antenna apparatus which concerns on the 2nd Example of this invention. It is a perspective view of the antenna apparatus which concerns on the example of 3rd Embodiment of this invention. It is a perspective view of the antenna apparatus which concerns on the example of 4th Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. First, the antenna device according to the first embodiment of the present invention will be described. This antenna device is incorporated in a mobile phone as a built-in antenna for receiving terrestrial digital television broadcasts. As shown in FIGS. 1 and 2, the antenna device includes a radiating conductor portion 1 formed by bending a metal plate into a predetermined shape, and variable tuning means 3 provided on a circuit board 2 of a cellular phone. The radiating conductor 1 is attached to one end of the circuit board 2 in the longitudinal direction.

  The radiating conductor 1 includes a first belt-like conductor 11 that extends in a three-dimensional loop shape, and a second belt-like conductor 12 that branches off from the middle of the first belt-like conductor 11. One end of the first strip-shaped conductor 11 is a first feeding point P1 for low band, and the other end of the first strip-shaped conductor 11 is connected to a ground end Q1 connected to a ground conductor (not shown) provided on the circuit board 2. It has become. Since the 1st strip | belt-shaped conductor 11 is formed as a conductor extended in the shape of a loop, bending at right angles at several places, it defines the some opening surface orthogonal to each other. The second strip-shaped conductor 12 is formed as a conductor branched at a right angle from the first strip-shaped conductor 11, and the tip of the second strip-shaped conductor 12 is a second feeding point P2 for high band, and the base end is the first The connecting end Q2 is connected to the one-band conductor 11.

  As shown in FIG. 3, the variable tuning means 3 includes a matching circuit including a variable capacitance diode (varactor diode) 4 connected to the first feeding point P1 and the second feeding point P2, and a first feeding point P1. A high-frequency switch 5 connected to an LNA (low noise amplifier circuit) 6 is provided at the branch point of the signal path L1 and the signal path L2 for the second feeding point P2. This variable tuning means 3 is connected to a tuner circuit via an LNA 6 or the like. A reverse voltage (DC voltage of 0 to 2.8 volts) is applied to the variable capacitance diode 4 according to the control signal Sc from the tuner circuit, and the capacitance value of the variable capacitance diode 4 depends on the magnitude of the reverse voltage. It is going to change. The high frequency switch 5 operates as a changeover switch that selectively connects the signal path L1 and the signal path L2 to the tuner circuit according to the frequency of the signal. That is, when the low band is selected, the first feeding point P1 is connected to the tuner circuit, and when the high band is selected, the second feeding point P2 is connected to the tuner circuit. However, the reverse voltage of the same magnitude is applied to the variable capacitance diode 4 both when the low band is selected and when the high band is selected. It is also possible to use a diplexer instead of the high frequency switch 5. In addition, a circuit configuration in which a low-pass filter (LPF) is interposed in the signal path L1 and a high-pass filter (HPF) is interposed in the signal path L2 may be employed.

  The operation of the antenna device according to the present embodiment will be described. By feeding power to the first feeding point P1, the radiating conductor portion 1 excites the first strip-like conductor 11 as the first loop antenna element A1, and the first The tuning frequency of the antenna element A <b> 1 can be changed by the variable tuning means 3. That is, the impedance of the first loop antenna element A1 operating as a magnetic field antenna is inductive, and its inductance increases in the low range and decreases in the high range, so that the reverse voltage applied to the variable capacitance diode 4 If the capacitance value is set to be large by reducing the value, the impedance can be matched with the first antenna element A1 at a predetermined frequency in the low frequency range. If the reverse voltage is increased and the capacitance value of the variable capacitance diode 4 is set to be small, the impedance can be matched with the first antenna element A1 at a higher frequency.

  Furthermore, not only can the first loop antenna element A1 be excited at a predetermined frequency by feeding to the first feeding point P1, but the second feeding point P2 can be operated like a ground end so that the frequency exceeds the frequency. It is also possible to excite the radiation conductor portion 1 at a different frequency. That is, in this antenna device, when a low band is fed to the first feeding point P1, the VSWR (voltage standing wave ratio) changes as shown in FIG. 4 according to the frequency, and two resonance points appear. In the figure, the left solid curve indicates the VSWR characteristic when the reverse voltage applied to the variable capacitance diode 4 is 0 volts, and the right dashed curve indicates the VSWR characteristic when the reverse voltage is 2.8 volts. Is shown. As apparent from FIG. 4, by changing the tuning frequency by the variable tuning means 3, this antenna device can easily widen the receivable bandwidth on the low frequency side.

  In addition, by supplying power to the second feeding point P2, the radiating conductor portion 1 cooperates with the second strip-shaped conductor 12 and the L-shaped portion of the first strip-shaped conductor 11 extending from the connecting end Q2 to the ground end Q1. Then, it is excited as the second loop antenna element A2. Since the electrical length of the second loop antenna element A2 is much shorter than that of the first loop antenna element A1, the second loop antenna element A2 can be excited at a predetermined high frequency. . Also in this case, not only can the second loop antenna element A2 be excited at a predetermined frequency by feeding the second feeding point P2, but the first feeding point P1 can be operated like a ground end to It is also possible to excite the radiation conductor portion 1 at another frequency lower than the frequency. That is, on the high frequency side by controlling the magnitude of the reverse voltage applied to the variable capacitance diode 4 even when selecting the high band for supplying power to the second feeding point P2 based on the same operating principle as when selecting the low band described above. The receivable bandwidth can be easily increased.

  As described above, in the antenna device according to the present embodiment, the second belt-like conductor 12 is branched and extends from the first belt-like conductor 11 that can be excited as the first loop antenna element A1, and these first and second belt-like conductors extend. The conductors 11 and 12 are formed as an integral part. In addition, since a part of the first strip-shaped conductor 11 and the second strip-shaped conductor 12 can cooperate and excite as the second loop antenna element A2, a desired higher frequency than the tuning frequency of the first loop antenna element A1 is obtained. The second loop antenna element A2 can be tuned to the frequency. Moreover, the radiation conductor portion 1 of this antenna device can not only excite the first loop antenna element A1 at a predetermined frequency when the low band is selected, but also operates the second feeding point P2 like a ground end to Since it can be excited at another frequency higher than the frequency, two resonance points can be set. Similarly, when the high-band is selected, the radiating conductor 1 can not only excite the second loop antenna element A2 at a predetermined frequency, but also operate the first feeding point P1 like a ground terminal to generate the frequency. Since it can be excited at another lower frequency, two resonance points can be set. Therefore, this antenna apparatus can easily widen the receivable bandwidth by changing the tuning frequency by the variable tuning means 3. In other words, this antenna device can be operated as a magnetic field antenna with good reception sensitivity from low to high frequencies, and it is difficult to receive even if a human body (such as a human hand or head) is in close proximity. Performance is easy to stabilize. Further, since the two types of loop antenna elements A1 and A2 are integrated, this antenna device can be easily attached to the circuit board 2 of the mobile phone and has little variation in antenna characteristics.

  In the antenna device according to the present embodiment, the first strip conductor 11 is formed as a conductor extending while being bent at right angles at a plurality of locations, and the second strip conductor 12 is branched from the first strip conductor 11 at a right angle. Therefore, it is easy to reduce the size of the radiating conductor 1 by forming the first loop antenna element A1 (first strip-shaped conductor 11) having a relatively long electrical length in a compact outer shape. In addition, the first and second strip conductors 11 and 12 can be easily designed and manufactured.

  If the number of high-frequency reception channels is small, it can be handled even if the tuning frequency cannot be changed when the high band is selected. In this case, the second feeding point P2 is not connected to the variable tuning means 3. Good. However, if the tuning frequency can be changed not only when the low band is selected but also when the high band is selected as in the above-described embodiment example, the receivable high frequency bandwidth is widened. Usability is improved when the number of channels is large.

  In the above embodiment, the antenna device is incorporated in one end portion in the longitudinal direction of the mobile phone. However, even if this antenna device is incorporated in a mobile device other than the mobile phone, the same is true. The effect of can be expected.

  FIG. 5 shows a radiation conductor part of the antenna device according to the second embodiment of the present invention, and parts corresponding to those in FIG.

  The radiation conductor portion 7 shown in FIG. 5 has the same loop shape as that of the radiation conductor portion 1 shown in the first embodiment, but is greatly different in that it is formed by a conductor pattern rather than a metal plate. That is, in the radiation conductor portion 7, the first strip conductor 11 and the second strip conductor 12 are formed by patterning on the surface of a rectangular parallelepiped block body 8 made of a dielectric material.

  In the second embodiment, since the first and second strip conductors 11 and 12 are formed on the surface of the block body 8 by the conductor pattern, the positional accuracy of the strip conductors 11 and 12 is increased and the antenna characteristics are improved. It becomes easy to stabilize. Further, since the block body 8 is made of a dielectric material, the radiation conductor portion 7 can be reduced in size due to the wavelength shortening effect of the dielectric. Moreover, since it can handle as one block body 8 when attaching the radiation conductor part 7 to a portable apparatus, attachment workability | operativity improves significantly.

  FIG. 6 shows an antenna apparatus according to a third embodiment of the present invention, and portions corresponding to those in FIG.

  In the antenna device shown in FIG. 6, the shape of the second strip-shaped conductor 12 in the radiation conductor portion 9 is particularly different from that of the radiation conductor portion 1 shown in the first embodiment. That is, the second strip conductor 12 of the radiating conductor portion 9 extends in an L shape from the connection end Q2 with the first strip conductor 11 toward the second feeding point P2. However, when this radiating conductor portion 9 is compared with the radiating conductor portion 1 of the first embodiment, the loop shape of the first loop antenna element A1 (first strip-shaped conductor 11) or the second loop antenna element A2 The loop shape is basically the same.

  FIG. 7 shows an antenna apparatus according to a fourth embodiment of the present invention, and portions corresponding to those in FIG.

  In the antenna apparatus shown in FIG. 7, the shape of the first strip-shaped conductor 11 in the radiating conductor portion 10 is particularly different from that of the radiating conductor portion 1 shown in the first embodiment. That is, the first belt-like conductor 11 of the radiating conductor portion 10 extends so as to draw a loop of about one and a half turns along a surface substantially parallel to the circuit board 2. For this reason, the radiation conductor 10 is easy to increase the reception sensitivity when the low band is selected.

  The radiating conductor 9 of the third embodiment shown in FIG. 6 and the radiating conductor 10 of the fourth embodiment shown in FIG. 7 are both formed by bending a metal plate. Similarly to the second embodiment, the radiation conductor portion 9 and the radiation conductor portion 10 may be patterned on the surface of a block body made of a dielectric material. Further, the shape of the radiating conductor (first and second strip conductors 11 and 12) is not limited to the above-described embodiments, and the shape of the radiating conductor is appropriately selected according to the use and material. Is possible.

1, 7, 9, 10 Radiation conductor 2 Circuit board 3 Variable tuning means 4 Variable capacitance diode (varactor diode)
DESCRIPTION OF SYMBOLS 5 High frequency switch 8 Block body 11 1st strip | belt-shaped conductor 12 2nd strip | belt-shaped conductor P1 1st feeding point P2 2nd feeding point Q1 Grounding end Q2 Connection end A1 1st loop antenna element A2 2nd loop antenna element

Claims (7)

A first strip conductor extending in a loop and having one end serving as a first feeding point and the other end connected to a ground conductor, and branching from the middle of the first strip conductor and extending to a second feeding point. A two-band conductor and variable tuning means connected to at least the first feeding point;
The first band-shaped conductor is excited as a first loop antenna element by feeding to the first feeding point, and the tuning frequency of the first loop antenna element can be changed by the variable tuning means, and the second A part of the first strip conductor and the second strip conductor cooperate with each other by feeding to a feeding point to excite the second loop antenna element, and the tuning frequency of the second loop antenna element is the first loop antenna element. An antenna device characterized by being higher than the tuning frequency of the loop antenna element.   2. The antenna device according to claim 1, wherein the variable tuning means is connected to each of the first feeding point and the second feeding point.   3. The antenna device according to claim 1, wherein the variable tuning means includes a variable capacitance diode.   4. The antenna device according to claim 1, wherein the first strip conductor extends in a three-dimensional loop shape that defines a plurality of non-parallel opening surfaces. 5.   5. The method according to claim 4, wherein the first strip conductor is formed as a conductor extending while being bent at right angles at a plurality of locations, and the second strip conductor is formed as a conductor branching at right angles from the first strip conductor. An antenna device characterized by comprising:   6. The antenna device according to claim 1, wherein the first and second strip conductors are patterned on the surface of a block body made of a dielectric material.   7. The antenna device according to claim 1, wherein the receivable frequency band includes a frequency band of a signal wave of terrestrial digital television broadcasting.

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