JP2011055428A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compose an antenna device capable of coping with a multiband as required by effectively changing directional patterns in some space allocated to an antenna within a portable phone terminal without requiring a complicated control system and a data processing system. <P>SOLUTION: An antenna element 21 is disposed at an intermediate position between a ground region GA and a non-ground region NGA on a substrate 50. First and second power feed terminals 22, 23 are led out from the antenna element 21. A directivity control circuit 30 is provided between the first and second power feed terminals 22, 23 and a power feed circuit 40. When the directivity control circuit 30 selects the side of the first power feed terminal 22, a terminal at a side far from the ground region GA becomes an open terminal to show monopole-like directivity. When the directivity control circuit 30 selects the side of the second power feed terminal 23, an upper portion of the ground region GA becomes an open terminal to show inverted-L-like directivity. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an antenna device provided in, for example, a mobile phone terminal.

  Patent Documents 1 and 2 are disclosed in which antenna directivity characteristics are controlled in an antenna device for a mobile phone terminal according to the state of proximity of a human body or the like.

  In Patent Document 1, the directivity of the antenna is switched according to two usage situations, that is, voice communication (call) used in a state where the human head is close and data communication used in a state where the head is separated. An antenna device is disclosed. In the voice communication, the viewpoint of reducing the human head SAR (Specific Absorption Rate) is emphasized, and directivity in the direction opposite to the head is desired. However, since the restriction is removed in the data communication, it is possible in any direction as much as possible. It is desired to be non-directional so that radio waves can be transmitted and received reliably. In response to this proposition, a parasitic element loaded / unloaded by switching is installed, and directivity is switched by switching between loading / unloading of the parasitic element.

  FIG. 1 is a diagram illustrating a configuration of an antenna device disclosed in Patent Document 1. In FIG. The antenna device 2 includes a rectangular plate-shaped finite ground plane 11, a telephone speaker 12 connected to the finite ground plane 11, a folded monopole antenna 14 having a feeding point 13 on the back side of the finite ground plane 11, and a front side of the finite ground plane 11. It has a parasitic L-element 16 that is grounded via a switch 15 and a communication identification unit 17 that includes a function of controlling the switch 15.

  With such a configuration, the antenna device 2 attempts to switch the directivity of the antenna by switching loading / non-loading of the parasitic L-element 16 under the control of the switch 15.

  Patent Document 2 discloses an antenna device in which a metal plate connected to a substrate ground by reactance is disposed on the bottom surface side of an antenna element (= the head side, a position interposed between the antenna and the head). Yes. There is also an idea of making this metal plate a “reflecting plate” having directivity in the direction opposite to the head, but considering that a distance of λ / 4 (83 mm at 900 MHz) is necessary to operate as a reflector, It is more appropriate to interpret it as a “shield”. That is, the metal plate can be regarded as a “shield plate” that reduces the influence of the head on the antenna and the influence of the antenna on the head. That is, the deterioration due to the influence of the human body is reduced by adopting an On-GND configuration in which the antenna element is substantially disposed on the ground electrode.

  From the viewpoint of “switching directivity”, array antennas have been studied for a long time. However, the array antenna is a subject field of this application because the control system and data processing system are complicated and expensive, the space for configuring the array cannot be secured, and it is necessary to support multiband. It is not suitable for mobile terminals.

JP 2007-174121 A WO 2007-054616 pamphlet

  However, it is said that the directivity control by the reflector / director in Patent Document 1 generally requires a space of λ / 4 or more. For this reason, even if it is applied in a straight line, the effect is low in a thin mobile phone terminal, or a considerably large structure is provided in the mobile phone terminal, which places a heavy burden on the set design. In other words, there is a problem that the space is occupied by the appendage, but it is also a concern that the adaptive design of the substrate or the housing and the antenna device must be repeated at the design stage.

  In general, it is difficult for a reflector / waveguide to exert a directivity effect in any band, and the degree of difficulty in dealing with multibands is high.

  In Patent Document 2, a method is conceivable in which the open end position is left as it is, and a method of switching between disposing / not disposing the shielding plate is conceived, but the effect of unidirectionality is small in the On-GND state, and the shielding plate in the Non-GND state There is a possibility that the characteristics deteriorate due to the presence of.

  In other words, the space cannot be utilized to the maximum extent from the viewpoint of “displaying different directivities within the space allocated to the antenna”. It also means that there is room for improvement.

  Accordingly, an object of the present invention is to switch the directivity characteristics effectively in a space that is allocated to an antenna in a mobile phone terminal without involving a complicated control system or data processing system. An object of the present invention is to provide an antenna device that can handle a band.

In order to solve the above problems, the present invention is configured as follows.
(1) An antenna device comprising: an antenna element; and an antenna matching circuit connected between the antenna element and a power feeding unit,
The antenna matching circuit is composed of a variable matching circuit that matches in accordance with a use frequency band,
The antenna element is a feeding port, and a plurality of feedings whose directivity is switched by switching a feeding position (by changing a positional relationship of an open end of the antenna element with respect to a ground electrode adjacent to the antenna element). With a port,
A switch that selectively connects the antenna matching circuit to the plurality of feeding ports;
A high-impedance circuit connected to a non-connection port of the switch.

  With this configuration, directivity is controlled by switching the power supply port, so there is no need for complicated control systems and data processing systems, high cost merit, and ease of handling when designing sets such as mobile phone terminals. Become.

  In addition, when the power feeding position is switched, nothing is connected to the non-connection port (in terms of high frequency) (ie, a capacitor is connected between the non-connection port and the substrate ground). Therefore, there is no significant disturbance in the open end position on the voltage distribution on the antenna element. Therefore, it is possible to effectively switch the directivity and to obtain an antenna device with little deterioration in antenna efficiency.

(2) The variable matching circuit switches between a matching state and a high impedance state.
This configuration eliminates the need for a high impedance load and a switch for selectively terminating at the high impedance load.

(3) The variable matching circuit includes a variable reactance unit connected to a base portion of the antenna element, and a matching unit connected between the power feeding unit and the variable reactance unit,
The matching unit includes a parallel inductor and a parallel capacitor connected to the shunt between the power feeding unit and the ground,
The variable reactance unit is set to a reactance value that finely adjusts the resonance frequency that changes due to the influence of the human body, while switching the resonance frequency to correspond to a plurality of frequency bands,
In the parallel inductor, the impedance locus when the antenna matching circuit side is viewed from the power feeding unit is determined to be a value that draws a small circle locus in almost the first quadrant of the Smith chart,
It is assumed that the parallel capacitor is set to a value that moves the small circle locus to the center on the Smith chart.

  With this configuration, it is possible to provide a good matching state according to the ambient influence. That is, the matching between the antenna and the feeding circuit (= input impedance of the antenna), which is shifted due to the influence of the human hand or heel, is corrected, and the VSWR characteristics are improved in an environment affected by the human hand or heel.

(4) The variable capacitance element is composed of, for example, a MEMS switch.
Thus, matching can be achieved while suppressing generation of harmonic distortion.

(5) Part or all of the circuit elements constituting the antenna matching circuit are packaged in, for example, a multilayer board.
Thereby, it can be handled as a component that can be mounted on the circuit board of the mounting destination, and the occupied area on the circuit board can be reduced.

(6) The antenna element includes, for example, a dielectric or magnetic base, and an antenna element electrode disposed on the surface of the base or inside the base.
With this configuration, it is unnecessary or less necessary to mount the antenna matching circuit component on the circuit board as a mounting destination, as well as downsizing the element, and the overall size can be reduced accordingly.

(7) The antenna element is an antenna element having good radiation Q of the antenna element alone among a plurality of types of antenna elements connectable to the antenna connection portion of the antenna matching circuit.
With this configuration, an antenna device with high efficiency can be configured by connecting an antenna with good radiation Q to the antenna matching circuit.

(8) The selection condition for the plurality of types of antenna elements is any one of a position of a feeding point with respect to the antenna element, a distance between the antenna element and the ground facing the antenna element, a size of the antenna element, or a combination thereof.
Thereby, an antenna element with good radiation Q can be selected easily and reliably, and a highly efficient antenna device can be configured.

  According to the present invention, from the viewpoint of reducing a human head SAR (Specific Absorption Rate), it is possible to provide an antenna device capable of directivity control suitable for voice communication and data communication.

  At least two states with greatly different directivities can be expressed in a space allocated to the antenna in the electronic device to be embedded.

  Fusing the switching function (Reconfigurable function) and directivity switching function for small and multi-band compatibility, or fusing the matching function (Adjustable function) and directivity switching function to cope with matching deviation caused by the human body. Can do.

It is a figure which shows the structure of the antenna apparatus currently disclosed by patent document 1. FIG. 2A is an exploded perspective view showing the configuration of the antenna device according to the first embodiment, and FIGS. 2B and 2C are perspective views showing the configuration of the antenna device according to the first embodiment. It is. FIG. 3A is a view of the electric field loop viewed from the side surface of the substrate 50 when the directivity control circuit 30 selects the first feeding end 22 side. FIG. 3B is a view of the electric field loop viewed from the side surface of the substrate 50 when the directivity control circuit 30 selects the second feeding end 23 side. FIG. 4A is a diagram showing the distribution of electric field strength in the antenna device in a monopole-like state. FIG. 4B is a diagram illustrating the distribution of the electric field strength of the antenna device in a reverse L-like state. 3 is a perspective view showing a specific configuration example of a directivity control circuit 30. FIG. 2 is a diagram illustrating a specific configuration example of a directivity control circuit 30 on a plan view. FIG. It is a figure shown about the effect | action of the capacitor C2 of the matching part M in a low band. It is a figure shown about the effect | action of the capacitor C2 of the matching part M in a high band. It is a figure shown about the effect | action of the inductor L2 (parallel inductor) of the matching part M. FIG. It is the figure which represented both the low band and the high band about the frequency characteristic of the return loss of an antenna apparatus. It is a block diagram of the two antenna devices which concern on 2nd Embodiment. It is a block diagram of the two antenna devices which concern on 3rd Embodiment. It is a block diagram of the antenna apparatus which concerns on 4th Embodiment. It is a figure which shows two structural examples of the antenna device which concerns on 5th Embodiment. It is a block diagram of the antenna apparatus which concerns on 6th Embodiment.

<< First Embodiment >>
2A is an exploded perspective view showing the configuration of the antenna device according to the first embodiment, and FIGS. 2B and 2C are perspective views showing the configuration of the antenna device according to the first embodiment. It is. A circuit board (hereinafter simply referred to as “substrate”) 50 is provided with a ground region GA and a non-ground region NGA, and a directivity control circuit 30 is formed on the substrate 50. The antenna element 21 is arranged at an intermediate position between the ground region GA and the non-ground region NGA of the substrate 50 (so as to straddle the ground region GA and the non-ground region NGA).

  A first feeding end 22 and a second feeding end 23 are drawn out from the antenna element 21. A directivity control circuit 30 is provided between the first feeding end 22 and the second feeding end 23 and the feeding circuit 40.

2B shows a state in which the directivity control circuit 30 selects the first power supply end 22 side, and FIG. 2C shows the directivity control circuit 30 in the second power supply end 23 side. Each of the selected states is shown. In FIG. 2B and FIG. 2C, a plurality of curves in the drawings are electric lines of force schematically drawn in order to show the electric field distribution.
When the directivity control circuit 30 selects the first feeding end 22 side, as shown in FIG. 2B, the first feeding end 22 out of the two ends of the antenna element 21. The far side, that is, the side far from the ground area GA is the open end (the end portion with the maximum electric field).
When the directivity control circuit 30 selects the second feeding end 23 side, the second feeding end 23 out of the two ends of the antenna element 21 as shown in FIG. The far side, that is, the upper part of the ground region GA is the open end (the end portion with the maximum electric field).

  FIG. 3A is a view of the electric field loop viewed from the side surface of the substrate 50 when the directivity control circuit 30 selects the first feeding end 22 side. FIG. 3B is a view of the electric field loop viewed from the side surface of the substrate 50 when the directivity control circuit 30 selects the second feeding end 23 side.

  When the open end of the antenna element 21 is away from the ground region of the substrate, it acts like a monopole antenna. Hereinafter, this state is referred to as “monopole-like”.

  When the open end of the antenna element 21 is close to the ground area of the substrate, it acts like an inverted L antenna. Hereinafter, this state is referred to as “reverse L-like”.

  FIG. 4A is a diagram showing the distribution of electric field strength in the antenna device in a monopole-like state. FIG. 4B is a diagram illustrating the distribution of the electric field strength of the antenna device in a reverse L-like state.

  In the monopole-like state, as shown in FIG. 3A and FIG. In the reverse L-like state, as shown in FIG. 3B and FIG. 4B, the antenna element 21 of the substrate 50 is mounted so that the electric field strength facing the back side (the human head side) of the substrate 50 is mounted. It is weaker than the electric field strength facing the surface side (surface side away from the human head).

  The directivity control circuit 30 selects the first power supply end 22 during data communication and uses it as a monopole-like antenna, and selects the second power supply end 23 during voice communication and uses it as an inverted L-like antenna. .

  Thus, different directivities can be expressed in the limited antenna space 20 where the antenna element 21 is disposed.

  By the way, since the human body is a low-conductivity / high-dielectric material, when the human body is in proximity, electric lines of force are sucked into the human body, and electromagnetic field energy is scattered as loss in the human body. In the vicinity of the human body, the reverse L-like has less loss (= 1 / Qloss) in the human body than the monopole-like. Therefore, SAR is greatly reduced in reverse L-like. However, a 1 / Qr (Qr: radiation Q) deteriorates in an inverted L-like antenna, so that the bandwidth is inevitably narrowed. However, broadband characteristics can be maintained by matching with the variable matching circuit described above.

  As described above, the directivity state obtained by the selection of the feeding end switches between the case where the open end is in a position opposite to the substrate ground in the direction opposite to the head and the case where the open end is located farther from the substrate ground. is there. From this intention, the position of each feeding end is provided so as to be a position returned from the open end of the antenna element 21 by approximately λ / 4 (× integer multiple).

FIG. 5 is a perspective view showing a specific configuration example of the directivity control circuit 30, and FIG. 6 is a plan view thereof.
The directivity control circuit 30 includes a four-port switch 31, a high impedance load 32, and a variable matching circuit 33.

  The switch 31 conducts the ports P1 and P3, and conducts the ports P2 and P4 (first state), conducts the ports P1 and P4, and conducts the ports P2 and P3. (Second state). In the first state, the second feeding end 23 is connected to the high impedance load 32, and the first feeding end 22 is connected to the variable matching circuit 33. In the second state, the first power supply end 22 is connected to the high impedance load 32, and the second power supply end 23 is connected to the variable matching circuit 33.

  The high impedance load 32 is provided in order to perform a termination process by connecting a sufficiently high impedance load to a non-connection port of the switch 31.

  In other words, the two feed ends are provided so that the open end positions are as far apart (different) as possible within a limited antenna space, so when one feed end is selected, the other feed end is open. End side. The power supply end (non-selective power supply end) to which the variable matching circuit 33 is not connected has an off-capacitance of the switch as it is, and is connected to the substrate ground via the off-capacitance. In other words, the intended open end position is disturbed. In order to prevent this, the non-selection power supply end is terminated with a high impedance load 32, so that a “clear” state appears in terms of high frequency.

  The variable matching circuit 33 includes a variable reactance unit RC and a matching unit M. The variable reactance part RC is configured by a parallel circuit of an inductor L1 and a capacitor C1, and the LC parallel circuit is connected in series to the root part of the antenna element 21. The matching unit M is configured by a parallel circuit of an inductor L2 (parallel inductor according to the present invention) and a capacitor C2 (parallel capacitor according to the present invention), and the LC parallel circuit is between the power feeding circuit 40 and the variable reactance unit RC. Connected to the shunt.

  The capacitors C1 and C2 are variable capacitance elements each formed by a MEMS switch. The resonance frequency of the antenna is switched between the low band and the high band by the reactance of the variable reactance unit RC. Further, by switching the capacitance of the capacitor C2 of the matching unit M, double resonance is performed in both the low band and the high band.

  In addition, by configuring the variable capacitance element with a MEMS switch, loss reduction, power consumption reduction, and power durability / distortion resistance are improved.

  FIG. 7 is a diagram illustrating the operation of the capacitor C2 of the matching unit M. FIG. 7A is a diagram showing impedance on the Smith chart when the variable matching circuit side is viewed from the communication port on the low band side, and FIG. 7B is a frequency characteristic diagram of return loss.

  The variable matching circuit that has an Adjustable effect is based on moving the small circle locus from the first quadrant of the Smith chart to the center (50Ω) near the center (50Ω) by the capacitor C2 of the matching unit M. (1) “No” of human body influence The major feature is that the common (shared) architecture covers the state transition from “Yes” to “Yes” and (2) widening of the frequency band when switching. The reason why both (1) and (2) can be covered by a common architecture (= circuit configuration) will be described below.

  FIG. 7A shows a state where the small circle locus is moved from the first quadrant to the center on the Smith chart for the low band. In FIG. 7A, a small circle locus SCTF0 is an impedance locus in a free state, and a small circle locus SCTh0 is an impedance locus in a human body proximity state. Further, the small circle locus SCTf is a small circle locus after the small circle locus SCTf0 is moved by the capacitor C2 of the matching unit M. The small circle locus SCTh is a small circle locus after the small circle locus SCTh0 is moved by the capacitor C2 of the matching unit M.

  As will be described later, the influence of the human body acts so that the size of the small circle locus in the first quadrant of the Smith chart becomes smaller at that position.

  In FIG. 7B, a curve RLf0 is a return loss corresponding to the small circle locus SCTF0, and a curve RLh0 is a return loss corresponding to the small circle locus SCTh0. A curve RLf is a return loss corresponding to the small circle locus SCCTf, and a curve RLh is a return loss corresponding to the small circle locus SCTh.

  FIG. 8 is a diagram showing the operation of the capacitor C2 of the matching unit M shown in FIG. FIG. 8A is a diagram showing the impedance when the variable matching circuit side is viewed from the low band side use port on the Smith chart, and FIG. 8B is a frequency characteristic diagram of return loss.

  FIG. 8A shows how the small circle locus is moved from the first quadrant on the Smith chart to the center for the high band. In FIG. 8A, a small circle locus SCTF0 is an impedance locus in a free state, and a small circle locus SCTh0 is an impedance locus in a human body proximity state. Further, the small circle locus SCTf is a small circle locus after the small circle locus SCTf0 is moved by the capacitor C2 of the matching unit M. The small circle locus SCTh is a small circle locus after the small circle locus SCTh0 is moved by the capacitor C2 of the matching unit M.

  In FIG. 8B, a curve RLf0 is a return loss corresponding to the small circle locus SCTF0, and a curve RLh0 is a return loss corresponding to the small circle locus SCTh0. A curve RLf is a return loss corresponding to the small circle locus SCCTf, and a curve RLh is a return loss corresponding to the small circle locus SCTh.

  Although the small circle locus SCTh0 is not only in the first quadrant but also in the second quadrant, the small circle locus SCTh0 approaches the center of the Smith chart by the action of the capacitor C2 (parallel C) of the matching unit M. In the inductor L2 (parallel inductor) of the matching unit M, the impedance locus when the variable matching circuit side is viewed from the power feeding unit draws a small circle locus in the first quadrant of the Smith chart, but the small circle locus is the parallel C. Any position close to the center of the Smith chart may be used. That is, the meaning of “almost” in the “almost first quadrant” is this meaning.

  In this way, a small circle of the impedance locus is drawn by the inductor L2 of the matching unit M (a small circle that is later rotated around the center on the Smith chart), and the small C is detected from the first quadrant of the Smith chart by the capacitor C2 of the matching unit M. The rotation of the locus including the circle is moved near the center (50Ω) on the Smith chart. That is, the impedance locus on the Smith chart due to the frequency change draws a small circle at the center of the Smith chart. This means that the matching unit M constitutes an impedance circuit in which the return loss characteristic viewed from the power feeding unit to the antenna connection unit performs double resonance in a predetermined frequency band.

  As will be described later, the inductor L2 of the matching unit M has an effect of making the impedance locus small and positioning it in the first quadrant of the Smith chart. The optimum value of the inductor L2 differs between the low-band resonance system and the high-band resonance system, but an intermediate (compromise) value between the two so that the low-band / high-band switching is not necessary. It is fixed to.

  FIG. 9 is a diagram illustrating the operation of the inductor L2 (parallel inductor) of the matching unit M. (A) is the figure which represented on the Smith chart the impedance which looked at the variable matching circuit side from the electric power feeding part, (B) is a frequency characteristic figure of a return loss.

  Another feature of the variable matching circuit architecture of the present invention is that the impedance locus on the Smith chart is made into a small circle and positioned in the first quadrant on the Smith chart. This is because both the low band and the high band act in the direction in which the small circle becomes smaller in the first quadrant (initial position) when affected by the human body. It works well when aiming.

  In FIG. 9A, when the inductor L2 of the matching unit is not provided, the range of frequencies 1710 to 2170 MHz in the locus SCT0 exists in the first quadrant and the third quadrant on the Smith chart, and is originally in a region lower than 50Ω. is there. By providing the matching portion inductor L2, the locus SCT0 becomes a small circle like the locus SCT1 and moves in the first quadrant direction on the Smith chart.

  In terms of return loss, as shown in FIG. 9B, the return loss RL0 when there is no matching section inductor L2 changes to the return loss RL1 when there is a matching section inductor L2.

  As described above, when the small circle locus formed in the first quadrant of the Smith chart is moved to the vicinity of the center (50Ω) by the capacitor C2 of the matching unit M, (1) from “none” of the human body influence to “ “Yes” state transition and (2) widening at the time of switching the frequency band can be handled by a common (shared) architecture. That is, it has both Reconfigure function and Adjust function.

  FIG. 10 is a diagram showing both the low band and the high band for the frequency characteristics of the return loss of the antenna device. As described above, the variable matching circuit 33 causes double resonance (two resonances) in both the low band and the high band. The antenna directivity is switched by the switch 31. The characteristics shown in FIG. 10 can be obtained in both cases of monopole-like and reverse L-like.

<< Second Embodiment >>
FIGS. 11A and 11B are configuration diagrams of two antenna devices according to the second embodiment.
Both of FIG. 11A and FIG. 11B include a variable matching circuit 33M that operates when used in a monopole-like manner and a variable matching circuit 33I that operates when used in an inverted L-like manner.

  In FIG. 11A, when used as a monopole-like antenna, the switches 31M, 31I, 34 are selected so that the switch 31M and the switch 34 select the variable matching circuit 33M side and the switch 31I selects the high impedance load 32I side. To control. When used as an inverted L-like antenna, the switches 31I and 31I are controlled so that the switch 31I and the switch 34 select the variable matching circuit 33I side and the switch 31M selects the high impedance load 32M side.

  FIG. 11B shows a configuration in which the switch 31 is configured so that the high impedance loads 32M and 32I shown in FIG. Other structures are similar to those in FIG.

  With such a configuration, it is possible to design and use a variable matching circuit suitable for switching the feeding end of the antenna element. Further, in the example of FIG. 11A, the termination with a high impedance load suitable for switching the feeding end of the antenna element can be performed.

<< Third Embodiment >>
FIG. 12A and FIG. 12B are configuration diagrams of two antenna devices according to the third embodiment.
In both FIG. 12A and FIG. 12B, a switch is arranged between the variable reactance part and the matching part of the variable matching circuit.

  In FIG. 12A, the variable reactance unit RCM and the matching unit MM function as a monopole-like variable matching circuit. Further, the variable reactance unit RCI and the matching unit MI act as a variable matching circuit for reverse L-like.

  When used as a monopole-like antenna, the switches 31M, 31I and 34 are controlled so that the switch 31M and the switch 34 select the matching unit MM side and the switch 31I selects the high impedance load 32I side. When used as an inverted L-like antenna, the switches 31I, 31I, and 34 are controlled so that the switch 31I and the switch 34 select the matching unit MI side, and the switch 31M selects the high impedance load 32M side.

  In FIG. 12B, the matching units MM and MI shown in FIG. 12A are combined with one matching unit M, and the high impedance loads 32M and 32I shown in FIG. 32 is also used. Other structures are similar to those in FIG.

<< Fourth Embodiment >>
FIG. 13 is a configuration diagram of an antenna device according to the fourth embodiment. In this antenna device, variable matching circuits 33M and 33I are connected to two feeding ends of the antenna element 21 without a switch, and a switch 34 is provided between the feeding circuit 40 and the variable matching circuits 33M and 33I. .

  In FIG. 13, both the monopole-like variable matching circuit 33M and the inverse L-like variable matching circuit 33I can be switched between a matching state and a high impedance state in the operating frequency band.

  In a state where the switch 34 selects the monopole-like variable matching circuit 33M, the variable matching circuit 33I is controlled so that the reverse L-like variable matching circuit 33I acts as a high impedance load.

Further, the variable matching circuit 33M is controlled so that the monopole-like variable matching circuit 33M acts as a high impedance load while the switch 34 selects the reverse L-like variable matching circuit 33I.
With such a configuration, the variable matching circuit can also be used as a high impedance load.

<< Fifth Embodiment >>
FIG. 14 is a diagram illustrating two configuration examples of the antenna device according to the fifth embodiment.
The circuit configuration in FIG. 14A is the same as that shown in FIG. When the directivity control circuit 30 is modularized, the monopole-like variable matching circuit 33M and the inverse L-like variable matching circuit 33I may be modularized. These two may be modularized as one variable matching circuit 33. Further, one module 35 may be configured including the high impedance loads 32M and 32I. Furthermore, the entire directivity control circuit 30 including the switch 34 may be made into one module.

  The circuit configuration in FIG. 14B is the same as that shown in FIG. When modularizing the directivity control circuit, the matching unit MM of the monopole-like variable matching circuit and the matching unit MI of the inverse L-like variable matching circuit may be modularized. These two may be used as one matching unit module M. Further, one module 36 may be configured including the high impedance loads 32M and 32I. Furthermore, one module 37 including the switch 34 may be configured.

The module can be packaged by a multilayer process using LTCC (low temperature co-fired ceramics) or the like.
Further, the antenna element may be configured by a structure mainly including a substrate, and the variable matching circuit may be included in the structure.
With these configurations, it is possible to contribute to space saving on the mounting substrate as well as the overall size. In addition, handling at the time of mounting at the set maker becomes easy.

<< Sixth Embodiment >>
FIGS. 15A and 15B are configuration diagrams of two antenna devices according to the sixth embodiment.
In these examples, the dielectric 60 is loaded at a position that becomes an open end in the reverse L-like state in the end portion of the antenna element 21. Therefore, in the reverse L-like state, the dielectric constant between the open end of the antenna element 21 and the ground region GA increases, and the electric field that faces the arrangement surface side of the antenna element 21 of the substrate 50 (opposite side of the human head). Strength becomes stronger. This can emphasize the directivity state.

  In particular, as shown in FIG. 15B, a switch SW may be provided so that the loaded state of the dielectric 60 is turned on during reverse L-like and the loaded state of the dielectric 60 is turned off during monopole-like.

<< Seventh Embodiment >>
In the seventh embodiment, selection of an antenna with good radiation Q will be described.
In conclusion, when the antenna matching circuit of the present invention is applied, the efficiency of the antenna (the antenna element that does not include a matching circuit other than the variable reactance part that brings the resonance frequency to a desired frequency band and the housing part that contributes to radiation) It depends on the radiation Q of the antenna itself. For this antenna, one having a radiation Q as good as possible (one with a small value) should be selected.

The inventor experimentally verified this effect.
First, two types of antennas having different radiation Qs were prepared, an antenna matching circuit was applied to each, and the characteristics were measured.

  In either of the two types of antennas, a variable reactance portion is inserted at the feed end so as to bring the resonance frequency to a desired value, and the longitudinal direction of the antenna element shown in FIG. ) To change the power feeding position.

As a result, it was found that a good (small value) antenna radiation Q with respect to the high band can be obtained by using the central feeding to the antenna element.
In addition, when a variable matching circuit is loaded, the ability of the antenna's radiation Q is reflected in the high band, and the higher the radiation Q is, the higher the efficiency characteristic is obtained.

  In the above example, it is shown that the antenna having good radiation Q should be selected by comparing the center feeding antenna and the end feeding antenna. However, in addition to the feeding type, the distance between the antenna element and the ground facing the antenna element Since the radiation Q varies depending on the size of the antenna element, an antenna element having a good radiation Q (small value) may be selected using any one or a combination of these as a selection condition.

  In the example shown in FIG. 2, the antenna element 21 is arranged at an intermediate position between the ground area GA and the non-ground area NGA of the substrate. However, if the directivity can be switched, the antenna element is placed in the ground area or the non-ground area. You may arrange in any.

The variable matching circuit adjusts the matching according to the surrounding environment while having a broadband two-resonance characteristic in two frequency bands, but the present invention is not limited to this. For example,
(A) One resonance
(B) π-type / T-type circuit configuration including a variable reactance element (no reconfigure viewpoint),
(C) A plurality of matching circuits are prepared in advance, and the matching circuits are switched by route selection in accordance with the degree of proximity to the human body.
You may apply to.

  Further, the antenna element is not limited to the one in which the electrode pattern is formed on the dielectric substrate, and may be configured by forming the electrode pattern on the magnetic substrate.

  The configuration of the antenna element electrode and the interface between the antenna element electrode and the conductor pattern on the substrate are not limited to the above-described embodiments, and other known configurations may be adopted.

  The target of reconfiguration is not limited to switching between low band [GSM800 / 900] / high band [DCS / PCS / UMTS]. Another system may be added (WLAN / Bluetooth / Wimax, etc.), and Pentaband may be covered with fine frequency band division. At that time, the capacity value to be prepared is set finely.

  The antenna element may be one to which a fundamental wave / harmonic wave is assigned or one having a resonance point in a plurality of bands by inserting a reactance element in the element. Moreover, the shape is not limited to a shape in which the conductor is continuously spread on a plane, but may be bent or looped.

  Moreover, in the example shown above, although the variable reactance part was comprised with the parallel LC resonance circuit, it is not restricted to this. As long as the reactance can be varied as a whole, an LC series resonance circuit or an LC resonator such as Patent Document 3 (Japanese Patent Laid-Open No. 2008-113233) may be added with a + α discrete element.

  Further, the inductor of the LC resonator of the variable reactance unit and the inductor of the matching unit are not limited to the discrete elements, and may be replaced with, for example, a line pattern.

  In addition, it has been explained that the inductor of the matching unit is fixed to a common value (intermediate [compromise] value between low band / high band) so that the switching operation is not required as much as possible. In order to realize an optimum inductance value for each band, a variable inductor may be used. For this purpose, an LC resonance circuit may be configured.

GA ... ground region M ... matching portion MI ... matching portion MM ... matching portion MM, MI ... matching portion NGA ... non-ground region RC ... variable reactance portion RCI ... variable reactance portion RCM ... variable reactance portion 20 ... antenna space 21 ... antenna element 22 ... 1st feeding end 23 ... 2nd feeding end 30 ... Directivity control circuit 31 ... Switch 31M, 31I, 34 ... Switch 32 ... High impedance load 32M, 32I ... High impedance load 33 ... Variable matching circuit 33M, 33I ... variable matching circuit 34 ... switches 35, 36, 37 ... module 40 ... power feeding circuit 50 ... circuit board 60 ... dielectric

Claims (8)

An antenna device comprising: an antenna element; and an antenna matching circuit connected between the antenna element and a power feeding unit,
The antenna matching circuit is composed of a variable matching circuit that matches in accordance with a use frequency band,
The antenna element includes a plurality of power supply ports that are power supply ports whose directivity is switched by switching the power supply position,
A switch that selectively connects the antenna matching circuit to the plurality of feeding ports;
A high-impedance circuit connected to a non-connecting port of the switch.   The antenna device according to claim 1, wherein the variable matching circuit switches between a matching state and a high impedance state. The variable matching circuit includes a variable reactance unit connected to a root portion of the antenna element, and a matching unit connected between the power feeding unit and the variable reactance unit,
The matching unit includes a parallel inductor and a parallel capacitor connected to the shunt between the power feeding unit and the ground,
The variable reactance unit is set to a reactance value that finely adjusts the resonance frequency that changes due to the influence of the human body, while switching the resonance frequency to correspond to a plurality of frequency bands,
In the parallel inductor, the impedance locus when the antenna matching circuit side is viewed from the power feeding unit is determined to be a value that draws a small circle locus in almost the first quadrant of the Smith chart,
The antenna device according to claim 1, wherein the parallel capacitor is set to a value that causes the small circle locus to move to a center on the Smith chart.   The antenna device according to claim 1, wherein the variable matching circuit includes a variable capacitance element configured with a MEMS switch.   The antenna device according to any one of claims 1 to 4, wherein a part or all of circuit elements constituting the antenna matching circuit are packaged in a multilayer substrate that is a laminate of a dielectric layer and a conductor layer.   The antenna element is composed of a dielectric or magnetic substrate, and antenna element electrodes disposed on the surface of the substrate or inside the substrate, and the antenna matching circuit is included in the substrate. 6. The antenna device according to any one of 5.   The antenna element according to any one of claims 1 to 6, wherein the antenna element is an antenna element having a good radiation Q among a plurality of types of antenna elements connectable to an antenna connection portion of the antenna matching circuit. The antenna device described.   The selection condition for the plurality of types of antenna elements is any one of a position of a feeding point with respect to the antenna elements, a distance from a ground facing the antenna elements, a size of the antenna elements, or a combination thereof. 8. The antenna device according to 7.