JP2011055258A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compose an antenna device that does not cause an increase in a passing loss due to increase in the number of series stages of a circuit, and has a plurality of ports while utilizing a given full space for one antenna element. <P>SOLUTION: A variable matching circuit 30L for a low band and a variable matching circuit 30H for high-band are composed on a substrate 31. Then, the antenna device 101 is composed by packaging the antenna element 20 in which an antenna element electrode 21 is formed to a non-ground region NGA on the substrate 31. Branching paths to two output ports are extended from an antenna connection section 32 with a branching point as a boundary, and the respective paths are connected to power feed sections 40L, 40H by interposing the variable matching circuits 30L, 30H each. By controling the variable matching circuits 30L, 30H, the variable matching circuit 30L, 30H are used for both matching to an antenna and switching (diplex/multiplex) of an RF circuit. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  As a performance of an antenna device for a mobile radio terminal such as a mobile phone terminal, it is always required to be compatible with multiband and downsized.

Non-Patent Document 1 is disclosed as an antenna device corresponding to multiband. FIG. 1 is a diagram illustrating a configuration of an antenna device of Non-Patent Document 1.
In the antenna device of Non-Patent Document 1, an antenna element 6 for low band (800 MHz to 900 MHz) and an antenna element 7 for high band (1.7 GHz to 2 GHz) are installed in a given space. The matching circuit 2 is provided between the antenna switch 1 and the antenna switch 1, and the matching circuit 3 is provided between the antenna switch 1 and the feeding point 5 of the antenna element 7.

NTT DoCoMo Technical Journal Vol. No. 14 2

  However, in the antenna device disclosed in Non-Patent Document 1, a given space is divided into two antennas for low band and high band (dividing the area), so that each antenna element becomes small. As a result, the radiation Q deteriorates and the radiation capability is impaired. In addition, since the two antenna elements are close to each other, interference occurs when the frequency is close, and when the frequency is far, one appears to be a close metal body with respect to the other. In either case, there is a concern about characteristic deterioration.

  If a configuration is used in which a single antenna element is used and demultiplexed from the (output) port of the antenna element via a diplexer or the like, a passage loss occurs due to a two-stage circuit including a matching circuit and a diplexer (or switch).

  SUMMARY OF THE INVENTION An object of the present invention is to provide an antenna device having a plurality of ports without using a full space provided for one antenna element and without increasing the passage loss due to the number of series stages of the circuit. It is in.

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 plurality of variable matching circuits for each frequency band,
The antenna (output) port of each variable matching circuit is connected in common,
Each variable matching circuit matches the used communication port and the antenna (output) port, and is controlled so that the non-used communication port side has a high impedance when viewed from the antenna port (common connection point) (controllable) ) It is structured.

  With the above structure, the variable matching circuit is used for both matching with the antenna and switching of the RF circuit (diplex / multiplex), so that one antenna element can be formed without increasing the number of stages connected to the series. Can also be used. That is, an RF circuit connected to a plurality of antenna ports can also serve as one antenna element. Therefore, the antenna element can be provided in a given space, and the adverse effects associated with the area division can be avoided and good antenna characteristics (bandwidth and efficiency) can be obtained.

(2) The variable matching circuit includes a variable capacitance element, and switches between the matching state and the high impedance state by controlling the variable capacitance element.

  With this configuration, high impedance appears at the unused communication port when viewed from the branch point, which ensures isolation between the communication ports and adversely affects the current-carrying state (matching) between the antenna element and the used communication port. There is no effect.

(3) The variable capacitance element includes a MEMS switch.
Thus, matching can be achieved while suppressing generation of harmonic distortion.

(4) The variable matching circuit is configured by an impedance circuit in which return loss characteristics when the variable matching circuit is viewed in the direction from the power feeding unit to the antenna-side port have double resonance characteristics in the band of the use frequency.

This configuration has the following effects.
Since the variable matching circuit is connected to each communication port, the frequency band assigned to each communication port is well matched.
With the variable matching circuit, the antenna can be downsized or widened.
Simplification of design, standardization, or reduction in the number of antenna elements can be expected.

(5) 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 variable matching circuit side is viewed from the power supply unit is set to a value that draws a small circle locus in almost the first quadrant of the Smith chart,
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.

(6) A part or all of the 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.
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.

(7) The antenna element includes a dielectric or magnetic base and an antenna element electrode disposed on the surface of the base or inside the base, and the base includes the antenna matching circuit. .

  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.

(8) The antenna element is an antenna element having a good radiation Q as a single antenna element 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.

(9) The selection condition of 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 the ground facing the antenna elements, a size of the antenna elements, 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, an RF circuit connected to a plurality of antenna ports can also serve as one antenna element. Therefore, the antenna element can be provided in a given space, and the adverse effects associated with the area division can be avoided and good antenna characteristics (bandwidth and efficiency) can be obtained.

It is a figure which shows the structure of the antenna apparatus of a nonpatent literature 1. 1 is a perspective view illustrating a configuration of an antenna device 101 according to a first embodiment. 1 is a circuit diagram of an antenna device 101. FIG. FIG. 4A is a circuit diagram in a state where communication is performed in the low band, and FIG. 4B is a diagram illustrating frequency characteristics regarding a return loss of the antenna in a state where communication is performed in the low band. FIG. 5A is a circuit diagram in a state where communication is performed in a high band, and FIG. 5B is a diagram showing frequency characteristics regarding a return loss of an antenna in a state where communication is performed in a high band. FIG. 5 is a block diagram equivalently representing the above-described functions of the variable matching circuits 30L and 30H in the antenna device shown in FIG. It is a block diagram of the antenna element (pseudo dipole antenna including a housing current) of the antenna apparatus to be examined. These are a low-band variable matching circuit 30L and a high-band variable matching circuit 30H. It is a frequency characteristic figure of the return loss which looked at the antenna element 20 from the port in FIG. FIG. 9 is a diagram illustrating a state of deterioration of characteristics when the low-band variable matching circuit 30L and the high-band variable matching circuit 30H illustrated in FIG. 8 are directly joined at a branch point. It is a figure which shows the characteristic in the state which sets the circuit constant of the low-band variable matching circuit 30L and the high-band variable matching circuit 30H optimally, and uses the low-band variable matching circuit 30L. It is a figure which shows the characteristic in the state which sets the circuit constant of the low-band variable matching circuit 30L and the high-band variable matching circuit 30H optimally, and uses the high-band variable matching circuit 30H. This is an example in which each of the low-band variable matching circuit and the high-band variable matching circuit is configured with individual components. FIG. 5 is an exploded perspective view of an antenna device using an antenna element 20A in which an antenna element electrode 21A extending in a funnel shape is formed on the surface of a rectangular parallelepiped dielectric base. It is an exploded perspective view of an antenna device using an antenna element 20B provided with an antenna element electrode 21B having a center branched by a slit on the surface of a substantially rectangular parallelepiped dielectric base. FIG. 5 is a configuration diagram of an antenna device in which a low band and a high band variable matching circuit are provided in a lower casing of a mobile phone terminal, and the upper casing functions as an antenna element. It is a circuit diagram of some antenna apparatuses which concern on 3rd Embodiment. It is a structural example of a variable matching circuit on the low band side or the high band side. FIG. 19A is a diagram illustrating characteristics of a variable matching circuit in which the variable reactance unit RC and the matching unit M illustrated in FIG. 18 are switched to a low band, and FIG. 19A is an input when the variable matching circuit side is viewed from a used port on the low band side. FIG. 19B is a frequency characteristic diagram of return loss. FIG. 19B is a diagram showing impedance on a Smith chart. FIG. 20 is a diagram illustrating characteristics of a variable matching circuit in which the variable reactance unit RC and the matching unit M illustrated in FIG. 18 are switched to the high band side, and FIG. FIG. 20B is a frequency characteristic diagram of return loss, showing the input impedance on the Smith chart. It is a figure shown about the effect | action of the capacitor C2 of the matching part M shown in FIG. FIG. 21A is a diagram showing impedance on the Smith chart when the variable matching circuit side is viewed from the port used on the low band side, and FIG. 21B is a frequency characteristic diagram of return loss. It is a figure shown about the effect | action of the capacitor C2 of the matching part M shown in FIG. FIG. 22A is a diagram showing impedance on the Smith chart when the variable matching circuit side is viewed from the port used on the low band side, and FIG. 22B is a frequency characteristic diagram of return loss. It is a figure shown about the effect | action of the inductor L2 (parallel inductor) of the matching part M. FIG. 1 is a configuration diagram of an antenna device in which a variable matching circuit 30 in which a low band and a high band variable matching circuit are integrated is mounted on a substrate 31. FIG. FIG. 5 is an exploded perspective view of an antenna device in which an antenna element electrode 21C is formed on an antenna element 20C and a variable matching circuit 30C is configured inside a dielectric substrate. It is a perspective view of two types of antennas from which radiation Q differs.

<< First Embodiment >>
The antenna device according to the first embodiment will be described with reference to the drawings.
The basic configuration of the antenna device according to the present invention has one antenna element, which is connected in the order of antenna element → antenna matching circuit → communication port. There are a plurality of communication ports, and each communication port has an output with a different frequency band. I can take it out.

That is, as an antenna device including an antenna element to a matching circuit, a plurality of bands can be demultiplexed into a plurality of ports. In other words, the antenna device includes a variable matching circuit that also serves as a diplex function.
FIG. 2 is a perspective view showing the configuration of the antenna device according to the first embodiment. A circuit board (hereinafter simply referred to as “substrate”) 31 is provided with a ground region GA and a non-ground region NGA, and a low-band variable matching circuit 30L and a high-band variable matching circuit 30H are formed on the substrate 31. Has been. Then, the antenna device 101 is configured by mounting the antenna element 20 on which the antenna element electrode 21 is formed in the non-ground region NGA of the substrate 31.

  Branch paths to the two communication ports extend from the antenna connection section 32 at the branch point, and each path is connected to the power feeding sections 40L and 40H via the variable matching circuits 30L and 30H, respectively.

  FIG. 3 is a circuit diagram of the antenna device 101. As shown in FIG. 3, the low-band variable matching circuit 30L is configured between the antenna element 20 and the low-band power feeding unit 40L. The high-band variable matching circuit 30H is configured between the antenna element 20 and the high-band power feeding unit 40H.

  The low-band variable matching circuit 30L includes a variable reactance unit RC and a matching unit M. The variable reactance portion RC is configured by a parallel circuit of an inductor L11 and a capacitor C11, and the LC parallel circuit is connected in series to the root portion of the antenna element 20. The matching unit M is configured by a parallel circuit of an inductor L12 (parallel inductor according to the present invention) and a capacitor C12 (parallel capacitor according to the present invention), and the LC parallel circuit is between the power feeding unit 40L and the variable reactance unit RC. Connected to the shunt.

  Similarly, the high-band variable matching circuit 30H includes a variable reactance unit RC and a matching unit M. The variable reactance part RC is composed of a parallel circuit of an inductor L21 and a capacitor C21, and the LC parallel circuit is connected in series to the root part of the antenna element 20. The matching unit M includes a parallel circuit of an inductor L22 (parallel inductor) and a capacitor C22 (parallel capacitor), and the LC parallel circuit is connected to the shunt between the power supply unit 40H and the variable reactance unit RC.

FIG. 4A is a circuit diagram in a state where communication is performed in the low band, and FIG. 4B is a diagram illustrating frequency characteristics regarding a return loss of the antenna in a state where communication is performed in the low band.
FIG. 5A is a circuit diagram in a state where communication is performed in a high band, and FIG. 5B is a diagram showing frequency characteristics regarding a return loss of an antenna in a state where communication is performed in a high band.

  In the low-band communication state, as shown in FIG. 4A, the low-band variable matching circuit 30L has a matching state between the communication port on the low-band side and the antenna-side port, and is not used as seen from the branch point. Control is performed so that the communication port side (high band side communication port) has high impedance.

  Therefore, as shown in FIG. 4B, the return loss of the antenna is low on the low band side, and the antenna can be used for communication in the low band. At this time, since the variable matching circuit 30H on the high band side is equivalently disconnected, the variable matching circuit 30H does not affect the antenna characteristics on the energization line between the variable matching circuit 30L and the antenna.

  Similarly, in the state where communication is performed in the high band, as shown in FIG. 5A, in the low band variable matching circuit 30L, the communication port used on the high band side is matched with the antenna side port, and the branching is performed. From the point of view, control is performed so that the unused communication port side (low band side communication port) has high impedance.

  Therefore, as shown in FIG. 5B, the return loss of the antenna is low on the high band side, and the antenna can be used for communication in the high band. At this time, since the variable matching circuit 30L on the low band side is equivalently disconnected, the variable matching circuit 30L does not affect the antenna characteristics on the energization line between the variable matching circuit 30H and the antenna.

  FIG. 6 is a block diagram equivalently representing the above-described functions of the variable matching circuits 30L and 30H in the antenna device shown in FIG. The functions of the variable matching circuits 30L and 30H according to the present invention include a demultiplexing circuit for demultiplexing to a low-band communication port and a high-band communication port, and matching for matching between the demultiplexing circuit and the antenna element 20. Can be realized with a circuit.

  However, if the circuit shown in FIG. 6 is actually configured, the branching circuit and the matching circuit are connected in series in two stages, so that the passage loss increases. On the other hand, in the present invention, the above-described demultiplexing and matching can be realized simultaneously with a single-stage circuit configuration.

Here, a specific design example of the variable matching circuits 30L and 30H will be shown.
First, on the circuit simulation, the feasibility of having a diplex function with a variable matching circuit was verified. FIG. 7 is a configuration diagram of an antenna element (a pseudo dipole antenna including a housing current) of the antenna device to be studied. Constants of the matching circuit were determined for each of the low band and the high band for one antenna element 20 shown in FIG.

  In FIG. 7, the width dimension W of the non-ground region NGA of the substrate 31 is 40 mm, and the depth dimension L is 4 mm. The height dimension T of the antenna element 20 is 3 mm, and its length is equal to the width dimension W of the non-ground region NGA of the substrate 31.

  FIG. 8 shows a low-band variable matching circuit 30L and a high-band variable matching circuit 30H.

  FIG. 9 is a frequency characteristic diagram of return loss when the antenna element 20 is viewed from the port. In FIG. 9, a curve RL1 is a return loss when the antenna element 20 is viewed from the port through the low-band variable matching circuit 30L, and a curve RL2 is a return loss when the antenna element 20 is viewed from the port through the high-band variable matching circuit 30H. .

  If the low-band variable matching circuit 30L and the high-band variable matching circuit 30H shown in FIG. 8 are joined together at the branch point, the low-band variable matching circuit 30L and the high-band variable matching circuit 30H are joined. The matching state (the matching state between the low-band-side communication port or the high-band-side communication port and the antenna element) that is optimal for the matching circuit 30H alone is destroyed. In addition, the isolation in the low band (isolation between the low-band use communication port and the high-band use communication port) also deteriorates.

  FIG. 10 is a diagram showing this. In FIG. 10, a curve RL1 is a return loss when the antenna element 20 is viewed from the port through the low-band variable matching circuit 30L, and a curve RL2 is a return loss when the antenna element 20 is viewed from the port through the high-band variable matching circuit 30H. . S21 is a transmission amount (S parameter S21) from the low-band communication port to the high-band communication port, and indicates isolation.

  As shown in FIG. 10, it can be seen that the return loss deteriorates in the low-band frequency band centered at 900 MHz, and the isolation between the low-band communication port and the high-band communication port cannot be obtained. .

  This can be understood as a load that disturbs the matching being loaded in the middle of the path from the matching circuit to the antenna element 20 (but not 50Ω here). Therefore, this “disturbing” load may be made to appear sufficiently high impedance at the target frequency when viewed from the branch point.

Next, characteristic examples in a state where the circuit constants of the low-band variable matching circuit 30L and the high-band variable matching circuit 30H are optimally set will be described.
However, the antenna port is a non-50Ω point. Strictly speaking, the low-band communication port (port 1) or the high-band communication port (port 2) is “highly isolated” from the branch point (antenna port). I can't see if it is. Therefore, as described below, whether or not isolation between a low-band communication port and a high-band communication port is ensured will be described.

  FIG. 11 is a diagram illustrating characteristics in a state where the circuit constants of the low-band variable matching circuit 30L and the high-band variable matching circuit 30H are optimally set and the low-band variable matching circuit 30L is used. FIG. 11A is a circuit diagram of the variable matching circuits 30L and 30H, FIG. 11B is a diagram showing the impedance locus of each part of the variable matching circuits 30L and 30H on a Smith chart, and FIG. It is a frequency characteristic figure of each part of variable matching circuits 30L and 30H. In FIG. 11B, the thick line portion is the low-band frequency range.

  11B and 11C, a curve RL1 is a frequency characteristic diagram of a return loss when the antenna element 20 (port 2) side is viewed from the port 1, and a curve RL2 is a port 2 to the antenna element 20 (port 1). The frequency characteristic diagram of the return loss as seen from the side, curve S21 is the transmission amount from port 1 to port 2.

  As is clear from comparison with the characteristics shown in FIG. 10, in the low band frequency band, port 1 to port 2 appear to be open, and port 2 to port 1 appear to be short-circuited (close to total reflection). For this reason, the port 1 and the antenna port are matched in the low band, and the port 2 looks high impedance when viewed from the antenna port.

  Therefore, low-band communication can be performed using the port 1 without being affected by the high-band variable matching circuit 30H.

  FIG. 12 is a diagram illustrating characteristics in a state where the circuit constants of the low-band variable matching circuit 30L and the high-band variable matching circuit 30H are optimally set and the high-band variable matching circuit 30H is used. 12A is a circuit diagram of the variable matching circuits 30L and 30H, FIG. 12B is a diagram showing an impedance locus of each part of the variable matching circuits 30L and 30H on a Smith chart, and FIG. It is a frequency characteristic figure of each part of variable matching circuits 30L and 30H. In FIG. 12B, the bold line portion is the high-band frequency range.

  In FIGS. 12B and 12C, a curve RL1 is a frequency characteristic diagram of return loss when the antenna element 20 (port 2) side is viewed from port 1, and a curve RL2 is a port 2 to antenna element 20 (port 1). The frequency characteristic diagram of the return loss as seen from the side, curve S21 is the transmission amount from port 1 to port 2.

  As is clear from comparison with the characteristics shown in FIG. 10, in the high-band frequency band, port 2 to port 1 appear to be open, and port 1 to port 2 appear to be short-circuited (close to total reflection). For this reason, the port 2 and the antenna port are matched in the high band, and the port 2 looks high impedance when viewed from the antenna port.

  Therefore, high-band communication can be performed using the port 2 without being affected by the low-band variable matching circuit 30L.

<< Second Embodiment >>
Several antenna devices according to the second embodiment will be described with reference to FIGS.
FIG. 13 shows an example in which each of the low-band variable matching circuit and the high-band variable matching circuit is configured with individual components. The substrate 31 is provided with a ground region GA and a non-ground region NGA, and chip-like variable capacitance elements C11, C12, C21, C22 and chip inductors L11, L12, L21, L22 are mounted on the substrate 31, respectively. Yes. The symbols of these chip parts correspond to the symbols of the circuit elements shown in FIG.

  In this way, by mounting the plurality of chip components on the substrate 31, a low-band variable matching circuit and a high-band variable matching circuit are configured. An antenna device is configured by mounting the antenna element 20 on which the antenna element electrode 21 is formed in the non-ground region NGA of the substrate 31.

  Branch paths from the antenna connection section 32 to the two output ports extend from the branch point, and each path is connected to the power feeding sections 40L and 40H via two variable matching circuits.

  FIG. 14 shows an example using an antenna element 20A in which an antenna element electrode 21A extending in a funnel shape is formed on the surface of a rectangular parallelepiped (prism) -shaped dielectric substrate. In this way, by forming the antenna element electrode 21A having a pattern in which the antenna element electrode 21A gradually spreads from the feeding portion of the antenna element 20A, the antenna element 20A resonates at a quarter wavelength over a wide frequency band, and the bandwidth is increased. Is promoted.

  In the example shown in FIG. 14, since only the electrode for the antenna connection portion is formed on the bottom surface of the antenna element 20A, and the antenna element 20A has a certain volume, it is mounted directly on the ground region of the substrate 31A. Is possible.

  FIG. 15 shows an example in which an antenna element 20B having an antenna element electrode 21B whose center is branched by a slit on the surface of a substantially rectangular parallelepiped dielectric base. Since the antenna element electrode 21B is branched by the slit in this manner, it acts as a low-band antenna element with the fundamental wave of the antenna element electrode, and acts as a high-band antenna element with the second harmonic of the antenna element electrode. To do. Alternatively, one of the branch elements acts as a low-band antenna element, and the other acts as a high-band antenna element.

  FIG. 16 shows an example in which variable matching circuits for low band and high band are provided in the lower casing of the mobile phone terminal, and the upper casing functions as an antenna element. Thus, even if the antenna element is a type that is not mounted on the substrate, it can be applied.

<< Third Embodiment >>
FIG. 17 is a configuration diagram of several antenna devices according to the third embodiment. In the third embodiment, another example of the position of the branch point between the antenna element and the plurality of variable matching circuits is shown. FIG. 17A shows an example in which a branch point is provided outside the ground region GA of the substrate, which is the same as that shown in the first and second embodiments. FIG. 17B shows an example in which a branch point is provided in the antenna element 20. FIG. 17C shows an example in which the branch point is provided in the ground region of the substrate. Further, FIG. 17D is an example in which a branch point is provided in a variable matching circuit including two variable matching circuits 30L and 30H.

<< Fourth Embodiment >>
In the fourth embodiment, not only the reconfigure action of adjusting the resonance frequency of the antenna to the target frequency band, but also the matching between the antenna and the feeding circuit (= the antenna input impedance), which is shifted by the influence of the human hand or heel, is performed. An example of a variable matching circuit that corrects and has an Adjustable effect of making a better VSWR under an environment affected by a human hand or a heel is shown.

  FIG. 18 shows a configuration example of a variable matching circuit on the low band side or the high band side. This variable matching circuit 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 20. 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 unit 40 and the variable reactance unit RC. Connected to the shunt.

  It has been confirmed that the action of making the unused port high impedance is almost determined by the variable reactance part RC and the inductor L2 (parallel inductor), and in particular, the action of the LC resonator of the variable reactance part is large.

  FIG. 19 is a diagram illustrating characteristics of a variable matching circuit in which the variable reactance unit RC and the matching unit M are switched (corresponding) for low band, and FIG. 19A illustrates the communication port on the low band side to the variable matching circuit side. FIG. 19B is a frequency characteristic diagram of return loss.

  The impedance locus on the Smith chart at a frequency of 700 MHz to 2700 MHz at this time is represented by a locus SCTf. Further, the return loss at this time has a characteristic represented by a curve RLf in FIG. Thus, a return loss is ensured in a low-band frequency band with 900 MHz as the center frequency.

  For example, the antenna device is incorporated in a mobile phone terminal, the human head is close to the antenna device, and the hand holding the mobile phone terminal is further worn (hereinafter referred to as “human body proximity state”). In order to achieve an optimum matching state, the capacitor C1 of the variable reactance unit RC and the capacitor C2 of the matching unit M are made variable. As a result, as indicated by a locus SCTh in FIG. 19A, the impedance locus moves to the center of the Smith chart as the small circle (small loop) becomes smaller. As a result, sufficient return loss characteristics can be obtained in the 900 MHz band as indicated by return loss RLh in FIG.

  FIG. 20 is a diagram illustrating characteristics of a variable matching circuit in which the variable reactance unit RC and the matching unit M are switched to (corresponding to) the high band side. FIG. 20A illustrates the variable matching from the use port on the high band side. FIG. 20B is a frequency characteristic diagram of the return loss, and FIG. 20B is a diagram showing the input impedance as viewed on the circuit side on the Smith chart.

  The impedance locus on the Smith chart at a frequency of 700 MHz to 2700 MHz at this time is represented by a locus SCTf. Further, the return loss at this time has a characteristic represented by a curve RLf in FIG. Thus, a return loss is ensured in a high-band frequency band centered on 1900 MHz.

  In order to achieve an optimum matching state when the antenna device 101 is in the proximity of the human body, the capacitor C2 of the matching unit M is made variable. As a result, as indicated by a locus SCTh in FIG. 20A, the impedance locus moves to the center of the Smith chart as the loop (small circle) becomes smaller. As a result, sufficient return loss characteristics can be obtained in a high-band band centered on 1900 MHz as indicated by return loss RLh in FIG.

  The variable reactance unit RC sets the resonance frequency of the antenna to a predetermined value by adding reactance to the initial reactance value of the antenna element 20. By adjusting the value of the capacitor C1 of the variable reactance unit RC, the resonance frequency that changes due to the influence of the human body is also finely adjusted.

  FIG. 21 is a diagram illustrating the operation of the capacitor C2 of the matching unit M. FIG. 21A 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. 21B is a frequency characteristic diagram of return loss.

  The variable matching circuit having an adjustable function according to the present invention is basically based on moving the small circle locus from the first quadrant of the Smith chart to the center (50Ω) by the capacitor C2 of the matching unit M. A major feature is that a common (shared) architecture covers state transition from “no” to “present” 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. 21A shows how the small circle locus is moved from the first quadrant to the center on the Smith chart for the low band. In FIG. 21A, 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. 21B, 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. 22 is a diagram illustrating the operation of the capacitor C2 of the matching unit M illustrated in FIG. FIG. 22A is a diagram showing impedance on the Smith chart when the variable matching circuit side is viewed from the high-band side use port, and FIG. 22B is a frequency characteristic diagram of return loss.

  FIG. 22 (A) shows how the small circle locus is moved from the first quadrant to the center on the Smith chart for the high band. In FIG. 22A, a small circle locus SCTF 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. 22B, 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 is different between the low-band resonance system and the high-band resonance system. It is fixed to.

  FIG. 23 is a diagram illustrating the operation of the inductor L2 (parallel inductor) of the matching unit M. (A) is a perspective view in a state where the resonance frequency of the antenna element 20 is set to a high band, and only the inductor L2 of the matching unit is provided in the variable matching circuit, and (B) is the impedance when the variable matching circuit side is viewed from the power feeding unit. (C) is a frequency characteristic diagram of 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. 23B, when the inductor L2 of the matching unit is not provided, the range of the frequency 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. 23C, 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.

  In addition, although the high band monopole antenna is illustrated in FIG. 23, it is confirmed that the same tendency is observed with the low band monopole antenna. It has also been confirmed that the same tendency is observed not only for non-GND type antennas mounted in non-ground areas but also for On-GND type antennas mounted in ground areas.

  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.

<< Fifth Embodiment >>
In the fifth embodiment, an example is shown in which low-band and high-band variable matching circuits are integrated.
FIG. 24 shows an example in which a variable matching circuit 30 in which variable matching circuits for low band and high band are integrated (modulated) is mounted on a substrate 31. Other configurations are the same as those shown in FIG. In this way, the overall size can be reduced by modularizing the variable matching circuit for a plurality of bands.

  FIG. 25 shows an example in which the antenna element electrode 21C is formed on the antenna element 20C and the variable matching circuit 30C is configured inside the dielectric substrate. Therefore, the power supply units 40L and 40H for the respective bands may be simply provided on the substrate 31C on which the antenna element 20C is mounted.

<< Sixth Embodiment >>
In the sixth embodiment, selection of an antenna with good radiation Q will be described.
In conclusion, the efficiency when applying the variable matching circuit of the present invention is as follows: the antenna (the antenna element that does not include a matching circuit other than the loaded reactance 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 as pseudo dipole] itself. For this antenna, one having a radiation Q as good as possible (one with a small value) should be selected.

In the sixth embodiment, this effect is verified experimentally.
First, two types of antennas having different radiation Qs were prepared, a variable matching circuit was applied to each, and the characteristics were measured.

  FIG. 26 is a perspective view of the two types of antennas. In both the examples of FIGS. 26A and 26B, the resonance frequency is set to a desired frequency band between the antenna connection unit 32 and the power feeding unit 40 so as to bring the resonance frequency to a desired value. The coming loading reactance L1a is inserted, and the power feeding position is changed with respect to the antenna element 20.

  In the example of FIG. 26A, the antenna connection portion 32 is disposed at the center portion of the substrate 31 and is configured to connect the centrally fed antenna element 20. In the example of FIG. 26B, the antenna connection portion 32 is disposed at the end portion of the substrate 31B, and the end-feed antenna element 20B is connected.

  The values of the radiation Q of the two types of antennas and the average efficiency after adding the matching circuit were as follows.

<Center feeding antenna>
Low band radiation Q: 8.4
Efficiency: -2.6 dB
High band radiation Q: 25.4
Efficiency: -2.3 dB
<End feed antenna>
Low band radiation Q: 9.8
Efficiency: -2.4 dB
High band radiation Q: 35.8
Efficiency: -3.9 dB

  Thus, by using the central feeding, a good (small value) antenna radiation Q was obtained. Moreover, good efficiency was obtained in the high band by using the central power supply. If the variable matching circuit shown in each embodiment is already mounted instead of the loaded reactance L1a, the ability of the antenna radiation Q is reflected, and the higher the radiation Q is, the smaller the value is. Efficiency characteristics were 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 each of the embodiments described above, an example in which two output ports, a low band and a high band, are provided. However, the present invention can be similarly applied to a device having three or more ports. Further, the present invention may be applied to ports used for purposes other than cellular communication, for example, ports such as WLAN, Bluetooth, Wimax, and GPS.

It does not matter whether the antenna element is mounted on the ground electrode or non-ground electrode of the substrate.
Further, the configuration of the antenna element electrode and the interface between the antenna element electrode and the pattern on the substrate are not limited to those shown above. It can also be applied generally to known patterns and interfaces.

  Further, the antenna element may have a shape to which a fundamental wave and a harmonic are allocated, or may have a resonance point in a plurality of bands by inserting a reactance element in the antenna element. Further, the shape is not limited to a rectangular parallelepiped shape or a substantially rectangular parallelepiped shape, and may be a bent shape or a loop shape.

  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.

  4 shows a typical configuration of the variable matching circuit, the variable matching circuit according to the present invention is not limited to this configuration, and other configurations can be used as long as the matching circuit has a variable matching unit. Of course.

  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.

  Further, the variable capacitor may be constituted by a MEMS (Micro Electro Mechanical Systems) switch. When the MEMS switch is used, unlike the varactor diode, the capacitance generated in the capacitance forming portion hardly changes depending on the signal voltage, and hence the generation of harmonic distortion can be suppressed.

GA ... ground region M ... matching portion NGA ... non-ground region RC ... variable reactance portions SCTf, SCTh ... small circle locus SCTf0, SCTh0 ... small circle locus 20 ... antenna elements 20A-20C ... antenna element 21 ... antenna element electrodes 21A-21C ... Antenna element electrode 30 ... Variable matching circuit 30C ... Variable matching circuit 30H ... High-band variable matching circuit 30L ... Low-band variable matching circuit 31 ... Substrate 31A to 31C ... Substrate 32 ... Antenna connection part 39 ... Feeding part 40 ... Feeding part 40L, 40H ... feed unit 101 ... antenna device

Claims (9)

An antenna matching circuit connected between an antenna element and a power feeding unit, and an antenna device including the antenna element,
The antenna matching circuit is composed of a plurality of variable matching circuits for each frequency band,
The antenna side ports of the variable matching circuit are connected in common,
The said variable matching circuit is an antenna apparatus comprised so that a use communication port and an antenna side port were matched, and it can control so that a non-use communication port may become high impedance seeing from the said antenna side port.   The antenna device according to claim 1, wherein the variable matching circuit includes a variable capacitance element, and switches between the matching state and the high impedance state under control of the variable capacitance element.   The antenna device according to claim 2, wherein the variable capacitance element is configured by a MEMS switch.   2. The variable matching circuit is configured by an impedance circuit in which return loss characteristics when the variable matching circuit is viewed from the power supply unit toward the antenna-side port have double resonance characteristics in a band of a use frequency. The antenna apparatus in any one of -3. 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 variable matching circuit side is viewed from the power supply unit is set to a value that draws a small circle locus in almost the first quadrant of the Smith chart,
The antenna device according to any one of claims 1 to 4, 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 any one of claims 1 to 5, 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 includes a dielectric or magnetic base and an antenna element electrode disposed on a surface of the base or inside the base, and the antenna matching circuit is included in the base. The antenna apparatus in any one of -6.   The antenna element according to any one of claims 1 to 7, 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. 9. The antenna device according to 8.

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