JP2014120954A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna device that supports a plurality of frequencies, suppresses a performance degradation due to the approach of a human body, and is hard to be affected by the noise generated by components on a substrate.SOLUTION: The antenna device includes: a feed part; a first element connected to the feed part; a second element connected to the feed part; a first fold part connected to an end point of the first element; a second fold part connected to a second fold part connection point that is a predetermined position of the second element; a foldback element connected so as to couple end points of the first fold part and the second fold part; and a second resonance circuit disposed at a second resonance circuit connection point that is a predetermined position of the second element between an open end and the second fold part connection point.

Description

  The present invention relates to an antenna device for a portable wireless device, and more particularly to an antenna device that supports multiple frequencies.

  A dipole antenna, a folded dipole antenna, or the like is used for an antenna device for a portable wireless device. The configuration of the folded dipole antenna is shown in FIG. 11, and the configuration of the dipole antenna is shown in FIG.

  In the folded dipole antenna, the first element 101 is disposed on the right side (left side) of the power feeding unit 100, the second element 102 is disposed on the left side (right side), and the folded element 105 is disposed in parallel with the first element 101 and the second element 102. Has been. A first folding unit 103 and a second folding unit 104 are provided at both ends of the folding element 105, and the first element 101 and the second element 102 are connected to the folding element 105.

  The operating frequency of the folded dipole antenna is determined by the lengths of the first folding unit 103 and the second folding unit 104. Specifically, the length between the first folding unit 103 and the second folding unit 104 operates at a frequency at which the half wavelength is obtained.

  On the other hand, as shown in FIG. 12, the dipole antenna has the most basic structure in which the folded element 105, the first folded portion 103, and the second folded portion 104 are omitted from the folded dipole antenna shown in FIG.

  13A and 13B are diagrams showing characteristics of the folded dipole antenna. FIG. 13A shows impedance characteristics, and FIG. 13B shows return loss.

  14 shows the characteristics of the dipole antenna of FIG. 12, FIG. 14 (a) shows the impedance characteristics, and FIG. 14 (b) shows the return loss.

  These are diagrams showing the impedance locus with respect to frequency using the Smith chart. The intersection of the horizontal line passing through the center of the Smith chart and the impedance locus is the operating frequency of the antenna, and the impedance is higher as this intersection is located to the right. Is shown. The impedance is represented by a numerical value on the horizontal line passing through the center of the Smith chart × 50 (Ω). That is, when the numerical value of the intersection of the horizontal line passing through the center of the Smith chart and the impedance locus is 5.6, the impedance is 5.6 × 50 = 280Ω.

  The return loss is obtained by the same measurement as the impedance, and the display method (diagram) is simply different. The chart made so that the closer the impedance is to 50Ω, the smaller the value is, and it shows that the impedance is close to 50Ω and the antenna characteristics and circuit are improved at the frequency of the valley portion of the chart. This valley portion is called an antenna resonance point. That is, the valley portion indicates the frequency at which the antenna is operating.

  Now, comparing the impedance of the operating frequency between the folded dipole antenna of FIG. 13A and the dipole antenna of FIG. 14A, it can be seen that the folded dipole antenna is about 280Ω and the impedance of the dipole antenna is about 75Ω. Also, it can be seen that the impedance of the folded dipole antenna is nearly four times that of the dipole antenna.

  At this time, it can also be seen from FIGS. 13B and 14B that there is no difference in operating frequency between the folded dipole antenna and the dipole antenna.

  By the way, miniaturization in today's portable wireless devices is remarkable, and metal parts and the like of peripheral circuits are arranged close to antennas. Therefore, in the built-in antenna (not shown) such as the dipole antenna, the monopole antenna (not shown), or the inverted F antenna shown in FIG. 12, the impedance is lowered due to the approach to the metal part or the like, and the antenna performance is deteriorated. There is a case.

  However, since the folded dipole antenna has high impedance characteristics as compared with the dipole antenna as described above, it is generally known that high performance can be maintained even if the folded dipole antenna is disposed near a metal part or the like.

  By the way, in today's portable wireless devices, it is common to communicate using a plurality of frequency bands. Furthermore, due to the significant miniaturization of portable wireless devices, high performance is maintained even if metal parts are placed close to each other. However, there is a demand for an antenna that operates at multiple frequencies.

  Therefore, as disclosed in Japanese Patent Application Laid-Open No. 2005-203878 and Japanese Patent No. 3805572, a technique has been proposed in which a folded antenna that operates at a plurality of frequencies is branched from one power feeding unit.

  Japanese Patent Laid-Open No. 2008-205680 proposes a technique for increasing the frequency by adding a resonance circuit to a folded monopole antenna.

Japanese Patent Laid-Open No. 2005-203878 Japanese Patent No. 3805572 JP 2008-205680 A

  However, the technique disclosed in Japanese Patent Application Laid-Open No. 2005-203878 and Japanese Patent No. 3805572 has a problem that the frequency adjusting means is complicated because a plurality of antenna elements are connected to one feeding point.

  In the technique disclosed in Japanese Patent Application Laid-Open No. 2008-205680, the monopole antenna also uses a ground plate such as a substrate on which a component or the like is surface-mounted as a radiating element. There is a problem that it is easily affected by noise generated by the parts.

  Accordingly, a main object of the present invention is to provide an antenna device that can cope with a plurality of frequencies, suppress performance deterioration due to the approach of a human body, and is less susceptible to noise generated by components on a board.

  In order to solve the above-mentioned problem, an invention relating to a folded dipole antenna is connected to a feeding part, a first element connected to the feeding part, a second element connected to the feeding part, and an end point of the first element. End points of the first folding part, the second folding part connected to the second folding part connection point, and the first folding part and the second folding part with the predetermined position of the second element as the second folding part connection point And a predetermined position between the open end of the second element and the connection point of the second folded portion as a second resonance circuit connection point, provided at the second resonance circuit connection point. And a second resonance circuit.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to respond | correspond to a some frequency, it becomes possible to suppress the performance degradation by the approach of a human body, and to provide the antenna apparatus which is hard to receive to the influence of the noise which components etc. on a board | substrate emit.

It is a block diagram of the antenna apparatus concerning this embodiment. It is the figure which showed the circuit and characteristic of a 1st resonant circuit and a 2nd resonant circuit, (a) is a circuit, (b) is a Smith chart which shows an impedance characteristic. FIG. 5A is an equivalent circuit of the antenna device, where FIG. 5A is an equivalent circuit of the antenna device for the first frequency, and FIG. 5B is an equivalent circuit of the antenna device for the second frequency and the third frequency. It is the schematic diagram which showed the operation | movement of the antenna apparatus with respect to a 2nd frequency and a 3rd frequency, (a) is a figure which shows the operation | movement with respect to a 2nd frequency, (b) is a 3rd frequency. It is the figure which showed the characteristic of the antenna apparatus, (a) is a Smith chart which shows an impedance characteristic, (b) has shown the return loss characteristic. It is explanatory drawing in the case of changing the position of a 2nd folding | turning part and a 2nd resonance circuit. The characteristic of an antenna device is shown, (a) is a Smith chart which shows an impedance characteristic, (b) is a figure which shows a return loss characteristic. It is a block diagram of the antenna apparatus at the time of providing the 1st resonance circuit in the middle of the folding element. The antenna characteristic of the antenna apparatus which provided the 1st resonance circuit in the middle of the folding element is shown, (a) shows an impedance characteristic, (b) is a figure which shows a return loss characteristic. It is a block diagram of the antenna apparatus concerning 2nd Embodiment. It is a block diagram of the folding | turning dipole antenna applied to description of a related technique. It is a block diagram of the dipole antenna applied to description of related technology. It is a figure which shows the characteristic of the folding dipole antenna applied to description of a related art, (a) is an impedance characteristic, (b) is a figure which shows a return loss. It is a figure which shows the characteristic of the dipole antenna applied to description of a related art, (a) is an impedance characteristic, (b) is a figure which shows a return loss.

  An embodiment of the present invention will be described. FIG. 1 is a configuration diagram of an antenna device 2A according to the present embodiment. This antenna device 2A is a folded dipole antenna, in which a first element 11 is arranged on the right side of the power feeding unit 10 and a second element 12 is arranged on the left side. A first resonance circuit 16 a is provided at an intermediate position of the first element 11, and a second resonance circuit 16 b is provided at an intermediate position of the second element 12.

  Hereinafter, the first element between the power supply unit 10 and the first resonance circuit 16a is referred to as a first element 11a, and the first element on the right side of the first resonance circuit 16a is referred to as a first element 11b. Similarly, the second element between the power supply unit 10 and the second resonance circuit 16b is referred to as a second element 12a, and the second element on the left side of the second resonance circuit 16b is referred to as a second element 12b. In addition, the position of the second element 12b to which the second folding part 14 is connected is described as a second folding part connection point, and the position of the second element 12b to which the second resonance circuit 16b is connected is described as a second resonance circuit connection point. .

  And the 1st return part 13 is connected to the 1st element 11b, the 2nd return part 14 is connected to the position near the electric power feeding part 10, and the 1st return part 13 and the 2nd return part 14 are the return elements 15 Connected by.

  FIG. 2 is a diagram showing the circuits and characteristics of the first resonance circuit 16a and the second resonance circuit 16b. FIG. 2 (a) is a circuit, and FIG. 2 (b) is a Smith chart showing impedance characteristics. . Hereinafter, the first resonance circuit and the second resonance circuit may be appropriately described as the resonance circuit 16.

  As shown in FIG. 2A, the resonance circuit 16 has an inductor L1 and a capacitor C1 connected in parallel, and the capacitor C2 is connected in series at this connection point. The inductor L1 and the capacitor C1 constitute a parallel resonance circuit, and the parallel resonance circuit (more precisely, the combined inductor of the parallel resonance circuit) and the capacitor C2 constitute a series resonance circuit.

  The resonance frequency of the series resonance circuit is described as a first frequency, and the resonance frequency of the parallel resonance circuit is described as a second frequency and a third frequency. At this time, the first to third frequencies are different frequencies.

  The resonance frequency f of the resonance circuit (LC resonance circuit) is given by f = 1 / (2π (L × C) 1/2). In the parallel resonance circuit, the impedance becomes ∞Ω (infinite) at this resonance frequency. On the other hand, in the series resonance circuit, the impedance becomes 0Ω (infinitesimal) at this resonance frequency. Accordingly, the first resonance circuit 16a and the second resonance circuit 16b exhibit open characteristics (impedance is ∞Ω) with respect to the second frequency and the third frequency, and are short-circuited (impedance is 0Ω) with respect to the first frequency. ) It comes to show characteristics. It can be confirmed from the Smith chart of FIG. 2B that the resonance circuit has an open characteristic with respect to the second frequency and the third frequency, and shows a short-circuit characteristic with respect to the first frequency.

  FIG. 3 is a diagram showing the above in an equivalent circuit. 3A is an equivalent circuit of the antenna device 2A for the first frequency, and FIG. 3B is an equivalent circuit of the antenna device 2A for the second frequency and the third frequency.

  As can be seen from FIG. 3A, the antenna device 2A behaves in the same manner as the folded dipole antenna with respect to the first frequency, and its impedance is about 280Ω. On the other hand, the antenna device 2A behaves as follows with respect to the second frequency and the third frequency. FIG. 4 is a schematic diagram showing the operation of the antenna device 2A for the second frequency and the third frequency. FIG. 4 (a) shows the operation for the second frequency, and FIG. 4 (b) shows the operation for the third frequency.

  For the second frequency, the antenna device 2A behaves as an antenna in which only the folding element 15 operates as shown in FIG. In FIG. 4A, a region indicated by a dotted arrow P1 is a region operating with respect to the second frequency.

  For the third frequency, the antenna device 2A includes a power feeding unit 10, a second folding unit 14, a folding element 15, a first folding unit 13, and a first element 11b, as shown in FIG. 4B. Behaves as an antenna that operates with the antenna element configured and the antenna element configured with the first element 11a. A region indicated by a dotted arrow P2 in FIG. 4B is a region operating at the third frequency.

  5A and 5B are diagrams showing the characteristics of the antenna device 2A. FIG. 5A shows a Smith chart showing the impedance characteristics, and FIG. 5B shows the return loss characteristics. FIG. 5A shows that the impedance with respect to the first frequency is about 280Ω. Further, it can be seen from FIG. 5B that there are three return loss valleys. This indicates that the antenna device 2A operates for all of the first frequency, the second frequency, and the third frequency.

  Now, the connection positions (second folding part connection point and second resonance circuit connection point) of the second folding part 14 and the second resonance circuit 16b in the antenna device 2A shown in FIG. 1 will be described. FIG. 6 shows the antenna device when the positions of the second folding unit 14 and the second resonance circuit 16 b are moved away from the power feeding unit 10. In FIG. 6, an arrow K indicates the moving direction of the second folding unit 14 and the second resonance circuit 16b. FIG. 7 shows the characteristics of such an antenna device. FIG. 7A is a Smith chart showing impedance characteristics, and FIG. 7B shows return loss characteristics.

  It can be seen from FIG. 7A that the impedance for the first frequency is about 280Ω. Further, comparing FIG. 7B and FIG. 5B, it can be seen that the return loss hardly changes with respect to the first frequency but decreases with respect to the second frequency and the third frequency. .

  From this, as shown in FIG. 6, it can be seen that the second frequency and the third frequency can be adjusted by the positions of the second folded portion connection point and the second resonance circuit connection point. Accordingly, the positions of the second folded portion connection point and the second resonance circuit connection point are set according to the second frequency and the third frequency. That is, the second turn-up point connection point and the second resonance circuit connection point are set with the positions corresponding to the desired second frequency and third frequency as predetermined positions.

  In the above description, the first resonance circuit 16 a is provided in the middle of the first element 11. On the other hand, FIG. 8 shows a case where the folding element 15 is provided in the middle. FIG. 9 shows antenna characteristics in this case, FIG. 9A shows impedance characteristics, and FIG. 9B shows return loss characteristics.

  FIG. 9A shows that the impedance is maintained at about 280Ω with respect to the first frequency. Further, comparing FIG. 9B and FIG. 5B, it can be seen that there is no change in the first frequency and the second frequency, and only the third frequency is lowered. From this, it can be seen that the third frequency can be adjusted by the insertion position of the first resonance circuit 16a as shown in FIG.

  As described above, in the folded dipole antenna that operates at the first frequency, the high impedance that is characteristic of the folded dipole antenna is maintained at the first frequency by inserting the first resonant circuit 16a and the second resonant circuit 16b. Thus, it is possible to realize a multi-frequency antenna that operates as an antenna at the second frequency and the third frequency higher than the first frequency.

  Further, the second frequency and the third frequency can be adjusted according to the positions of the second folding unit 14, the first resonance circuit 16a, and the second resonance circuit 16b.

  Therefore, with respect to the first frequency, it is possible to suppress the deterioration of the antenna characteristics even in a device (for example, a portable terminal) in which metal parts or the like of the peripheral circuit are close to each other.

  Furthermore, since a ground plate such as a substrate is not required at the first frequency, the second frequency, and the third frequency, the configuration is not easily affected by the human body.

  Therefore, it is possible to improve such problems as deterioration of characteristics due to proximity arrangement of metal parts in peripheral circuits, complexity of frequency adjustment circuit, deterioration of characteristics due to the influence of the human body, and deterioration of characteristics due to the noise generated by parts on the board. .

Second Embodiment
Next, a second embodiment of the present invention will be described. In addition, about the same structure as 1st Embodiment, description is abbreviate | omitted suitably using the same code | symbol. The first embodiment relates to an antenna device that does not require a ground plate such as a substrate. In contrast, the present embodiment relates to an antenna device including a ground plate. FIG. 10 is a configuration diagram of the antenna device 2B according to the present embodiment.

  In the antenna device 2B, the power feeding unit 10 is mounted on a ground plate 23, and a second element 12b is grounded to a terminal (not shown) of the ground plate 23 via a ground wire 22. The first element 11 b is connected to a terminal (not shown) of the ground plate 23 via the feeder line 21.

  At this time, the feeder line 21 and the ground line 22 are provided so as to overlap each other at a predetermined distance, or are arranged in parallel to the left and right. The feed line 21 and the ground line 22 form a feed line such as a microstrip line or a coplanar line to feed power to the first element 11b or the second element 12b, so that the antenna device 2A shown in FIG. Resonant operation is performed with respect to the first frequency, the second frequency, and the third frequency. Therefore, the power supply line 21 and the ground line 22 can be used as wiring on the printed circuit board, and even if the metal parts and the like of the peripheral circuit are arranged at close positions, the characteristic deterioration and the frequency adjustment circuit can be reduced. It is possible to improve complication, characteristic deterioration due to the influence of the human body, characteristic deterioration due to the influence of noise generated by components on the board, and the like.

2A, 2B Antenna device 10 Feeding section 11 (11a, 11b) First element 12 (12a, 12b) Second element 13 First folding section 14 Second folding section 15 Folding element 16a First resonance circuit 16b Second resonance circuit 16 Resonant circuit 21 Feed line 22 Ground line 23 Ground plate

Claims (7)

A folded dipole antenna,
A power feeding unit;
A first element connected to the power supply unit;
A second element connected to the power supply unit;
A first folded portion connected to an end point of the first element;
A second folded part connected to the second folded part connection point, with the predetermined position of the second element as a second folded part connection point;
A folding element connected to connect end points of the first folding part and the second folding part;
A second resonance circuit provided at the second resonance circuit connection point, with a predetermined position between the open end of the second element and the second folded portion connection point as a second resonance circuit connection point;
A folded dipole antenna characterized by comprising: The folded dipole antenna according to claim 1,
A folded dipole antenna comprising a first resonance circuit provided in the middle of the first element. The folded dipole antenna according to claim 1,
A folded dipole antenna comprising a first resonant circuit provided in the middle of the folded element. The folded dipole antenna according to any one of claims 1 to 3,
The folded dipole antenna, wherein the second folded portion connection point and the second resonant circuit connection point are set according to a resonance frequency of the antenna. The folded dipole antenna according to any one of claims 2 to 4,
At least one of the first resonant circuit and the second resonant circuit is
A parallel resonant circuit formed by connecting an inductor and a capacitor in parallel;
A series resonant circuit formed by connecting the parallel resonant circuit and the capacitor in series;
A folded dipole antenna characterized by including: The folded dipole antenna according to any one of claims 1 to 5,
A ground plate on which the power feeding unit is mounted;
A power supply line connecting the power supply unit and the first element;
A ground line connecting the power feeding unit and the second element;
A folded dipole antenna characterized by comprising: The folded dipole antenna according to claim 6,
The folded dipole antenna, wherein the feeding line and the grounding line are provided so as to overlap each other at a predetermined distance or are arranged in parallel to the left and right.

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