JP2010212980A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a directivity controllable compact antenna device. <P>SOLUTION: The antenna device is composed of a feeding element 1 and four parasitic elements 2. The parasitic elements 2 are arranged so as to be parallel with the line direction of the feeding element 1 at an interval of R. The parasitic element 2 with two metal wirings, i.e., first and second wirings 11 and 12 which are parallel each other, is a ladder type circuit in which four unit circuits 10 are tandem connected in the line direction of the first and second metal wirings 11 and 12, and operates in a left-handed system. The unit circuit 10 is composed of two capacitors 14 which are serially inserted into the first metal wiring 11, and an inductor 13 which connects the connection point of the two capacitors 14 and the second metal wiring 12. In addition, the first metal wiring 11 is arranged in the side of the feeding element 1, and the capacitance of the capacitor 14 is variable. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an antenna device that includes a feed element and a parasitic element and that can change directivity, and is particularly characterized in that it can be miniaturized.

  As an antenna device capable of changing the directivity, an antenna device called an ESPAR antenna has been conventionally known. For example, Patent Document 1 describes the antenna device. The antenna device described in Patent Document 1 has a configuration in which a plurality of parasitic elements are arranged at a position one quarter wavelength away from a feeding element, and a variable reactance element is connected to each parasitic element. The directivity of the antenna device can be changed by changing the reactance value.

JP2001-24431A

  However, in the antenna device of Patent Document 1, the distance between the feed element and the parasitic element needs to be ¼ wavelength, and the antenna device cannot be reduced in size.

  Therefore, an object of the present invention is to realize a small antenna device that can change directivity.

  According to a first aspect of the present invention, there is provided an antenna device including a feeding element and at least one parasitic element arranged in parallel with the feeding element at a certain interval. The parasitic element is arranged in parallel. A structure having a first metal wiring and a second metal wiring, an inductor connecting the first metal wiring and the second metal wiring, and a capacitor inserted in the first metal wiring is used as a unit circuit, and the same or similar pluralities An antenna device characterized in that a linear ladder-type line in which unit circuits are cascade-connected in the metal wiring direction, the element operates as a whole in a left-handed system, and the reactance of a parasitic element is variable. is there.

  When a plurality of parasitic elements are arranged around the feeding elements, the intervals from the feeding elements to the parasitic elements may all be equal or different. Further, the parasitic elements may be arranged at an equal angle with the feeding element as a center, or may not be at an equal angle. In addition, the first metal wiring and the second metal wiring may be arranged with respect to the power feeding element so that the first metal wiring is closer to the power feeding element than the second metal wiring, or arranged to be on the far side. May be. These may be designed according to the desired directivity.

  The parasitic element does not need to be arranged strictly in parallel with the feeding element, and may be arranged to such an extent that electrical coupling between the feeding element and the parasitic element can be obtained. Further, the first metal wiring and the second metal wiring 2 do not need to be arranged strictly in parallel, but may be arranged so as to obtain a left-handed operation.

  Note that the antenna device of the present invention can be used for both a transmission antenna and a reception antenna. Therefore, the term “power feeding” used in this specification is to be interpreted as meaning “power reception” when the antenna device of the present invention is used as a receiving antenna.

  A second invention is the antenna device according to the first invention, wherein the reactance of the parasitic element is made variable by making the capacitance of the capacitor variable.

  According to a third invention, in the first invention or the second invention, the antenna device has a plurality of parasitic elements, the parasitic elements are arranged concentrically around the feeding element, The antenna device is characterized in that the intervals between the parasitic elements are all equal.

  When a plurality of parasitic elements are arranged concentrically as in the third invention, each parasitic element may be arranged at an equal angle around the feeding element, or arranged at different angles. Also good.

  According to a fourth invention, in the first to third inventions, the feeding element and the parasitic element are constituted by a dielectric substrate and a conductive foil pattern formed on the dielectric substrate. Antenna device.

  The inductor can be configured, for example, by using a conductor foil as a meander pattern, and the capacitor can be configured by using an interdigital pattern. Further, the feeding element and the parasitic element can be configured by a slot pattern.

  A fifth invention is an antenna device according to any one of the first to fourth inventions, wherein the feeding element is a dipole antenna.

  In the antenna device of the present invention, the resonance frequency of the parasitic element can be changed by changing the reactance of the parasitic element. When the resonance frequency of the parasitic element is close to the resonance frequency of the feeder element, the parasitic element is electrically connected to the feeder element, and the directivity of the feeder element can be changed. In addition, since the parasitic element is structured to operate in a left-handed system, the distance between the feeding element and the parasitic element can be made shorter than λ / 4, and a small antenna device that can control directivity is realized. Can do.

1 is a diagram illustrating a configuration of an antenna device according to a first embodiment. The figure which shows the structure of the parasitic element. The figure which shows the reflection characteristic at the time of using the parasitic element 2 as a feeding element. The figure which shows the reflective characteristic of the antenna apparatus which has arrange | positioned one parasitic element. The figure which shows the structure of the antenna apparatus which has arrange | positioned one parasitic element. The figure which shows the reflection characteristic in the resonance state of the antenna apparatus which has arrange | positioned one parasitic element. The figure which shows the directivity in the resonance state of the antenna apparatus which has arrange | positioned one parasitic element. The figure which shows the phase and amplitude characteristic in 755 MHz. The figure which shows the phase and amplitude characteristic in 750 MHz. The figure which shows the phase and amplitude characteristic in 760 MHz. FIG. 3 is a diagram illustrating reflection characteristics of the antenna device according to the first embodiment. The figure which shows the directivity of the antenna apparatus of Example 1. FIG. FIG. 5 is a diagram illustrating a configuration of an antenna device according to a second embodiment.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating the configuration of the antenna device according to the first embodiment. The antenna device includes a feed element 1 and four parasitic elements 2. The feed element 1 is a dipole antenna formed of a linear conductor. The resonance frequency of the feed element 1 alone is about 740 MHz. FIG. 1A is an overhead view of the antenna device from an obliquely upward direction, with the feed point of the feed element 1 as the origin and the line direction of the feed element 1 in the direction orthogonal to the z-axis and the line direction of the feed element 1. An x-axis and a y-axis are set and shown. Moreover, FIG.1 (b) is the figure which looked at the antenna apparatus from the z-axis direction in Fig.1 (a).

  FIG. 2 is a diagram illustrating a configuration of the parasitic element 2. The parasitic element 2 includes a first metal wiring 11 and a second metal wiring 12 that are two parallel straight conductors, and an inductor 13 that communicates between the first metal wiring 11 and the second metal wiring 12. It is a ladder type circuit constituted by capacitors 14 inserted in series in the first metal wiring 11 and has a periodic structure in which four unit circuits 10 are connected in cascade. The unit circuit 10 includes two capacitors 14 inserted in series in the first metal wiring 11, and one inductor 13 communicating between the connection point of the two capacitors 14 and the second metal wiring 12. It is configured. Both the inductor 13 and the capacitor 14 are chip parts, and the capacitor 14 can change the capacitance. The capacitance may be variable by using, for example, a varactor and controlling the applied voltage, or may be variable by switching a plurality of capacitors with a switch. The length of the parasitic element 2 in the line direction is arbitrary, but it is desirable that the length of the parasitic element 2 be equal to or less than the length of the feeder element in the line direction in order to downsize the antenna device.

  The inductance of the inductor 13 of the parasitic element 2 and the capacitance of the capacitor 14 are designed to operate in a left-handed system. FIG. 3 is a diagram illustrating reflection characteristics when the capacitance of the capacitor 14 is 0.65 pF and 1.65 pF, and a feeding point is provided in the center of the first metal wiring 11 of the parasitic element 2 to be used as a feeding element. . When the capacitance is 0.65 pF, resonance occurs at about 760 MHz, and when the capacitance is 1.65 pF, resonance occurs at about 600 MHz, and the resonance frequency can be changed by changing the capacitance. I understand.

  The four parasitic elements 2 are arranged concentrically with an interval R in parallel to the feeder element 1. In addition, as shown in FIG. 2, in the xy plane, the elements are arranged radially by 90 degrees with the feeding element 1 as the center, and the parasitic element 2a is provided on the positive y axis and the parasitic element is provided on the positive x axis. The element 2b is disposed so as to be a parasitic element 2c on the negative y-axis and a parasitic element 2d on the negative x-axis. In addition, the parasitic elements 2a to 2d are arranged on the xy plane so that the direction from the second metal wiring 12 to the first metal wiring 11 is the direction toward the power feeding element 1. For this reason, the first metal wiring 11 into which the capacitor 14 is inserted is arranged on the feeder element 1 side.

  The change in the resonance frequency of the parasitic element 2 affects the characteristics of the antenna device. FIG. 4 is a diagram showing the reflection characteristics of an antenna device (see FIG. 5) in which one parasitic element 2 is arranged around the feeding element 1. For comparison, the reflection characteristics when the feeding element 1 is used alone are also shown in FIG. As shown in FIG. 4, when the capacitance of the capacitor 14 is 0.65 pF so that the resonance frequency of the parasitic element 2 is in the vicinity of the resonance frequency of the feeder element 1, the parasitic element 2 is electrically connected to the feeder element 1. It can be seen that the reflection characteristics of the feed element 1 are affected. On the other hand, when the capacitance of the capacitor 14 is 1.65 pF so that the resonance frequency of the parasitic element 2 is away from the resonance frequency of the feeder element 1, the parasitic element 2 is electrically coupled to the feeder element 1. It can be seen that the influence on the reflection characteristics of the feed element 1 is small.

  Hereinafter, the resonance state means a case where the capacitance of the capacitor 14 is selected so that the resonance frequency of the parasitic element 2 is close to the resonance frequency of the feeder element 1, and the non-resonance state means that the capacitance of the capacitor 14 is not. It means a case where the resonance frequency of the feed element 2 is selected to be a value away from the resonance frequency of the feed element 1.

  The change in directivity when in a resonance state will be described in more detail. FIG. 6 shows the reflection characteristics in the resonance state of the antenna device in which one parasitic element 2 is arranged as shown in FIG. As shown in FIG. 6, a band (hereinafter referred to as a stop band) in which the reflection characteristics are deteriorated is formed in the vicinity of 755 MHz. FIG. 7 is a diagram showing the directivity on the xy plane of the antenna device of FIG. 5 at 750 MHz which is a frequency lower than the stop band, 760 MHz which is a higher frequency than the stop band, and 755 MHz which is the stop band. . With the stop band formed in the resonance state as the center, the parasitic element 2 acts as a director at a frequency lower than the stop band, and the parasitic element 2 acts as a reflector at a frequency higher than the stop band. Recognize.

  8 to 10 are diagrams showing the phase / amplitude characteristics on the first metal wiring 11 and the second metal wiring 12 of the feed element 1 and the parasitic element 2 at 755 MHz, 750 MHz, and 760 MHz, respectively. The phase of the current flowing through the feeding element 1 and the first metal wiring 11 is substantially equal at any frequency, but the difference between the phase of the current flowing through the feeding element 1 and the phase of the current flowing through the second metal wiring 12 is 755 MHz. 180 degrees, 200 degrees at 750 MHz, and 160 degrees at 760 MHz. At any frequency, the current amplitude having the strongest current is the current flowing through the second metal wiring 12, and then the power supply element 1. Therefore, it can be seen that the phase difference between the current flowing through the power feeding element 1 and the current flowing through the second metal wiring 12 greatly affects the directivity. When the phase difference is larger than the phase difference in the stop band, the parasitic element 2 acts as a director. When the phase difference is smaller than the phase difference in the stop band, the parasitic element 2 reflects. It can be seen that it acts as a vessel.

  In the antenna device of the first embodiment, the directivity can be changed by switching between the resonant state and the non-resonant state of the parasitic elements 2a to 2d. FIG. 11 shows the reflection characteristics when R = 20 mm and the parasitic elements 2a to 2d of the antenna apparatus shown in FIG. 1 are switched between the resonance state and the non-resonance state, and FIG. 12 shows the xy plane at 760 MHz of the antenna apparatus. It is the figure which showed the directivity in.

  When all of the parasitic elements 2a to 2d are in a non-resonant state, the parasitic elements 2a to 2d have little influence on the feeder element 1 and become non-directional.

  When only the parasitic element 2a is in a resonance state and the other parasitic elements 2b to 2d are in a non-resonance state, the stop band occurs at a frequency lower than 760 MHz as shown in FIG. Therefore, the parasitic element 2a acts as a reflector, and the maximum gain directivity is obtained in the negative direction of the y-axis having a null point.

  When the parasitic elements 2a and 2b are in a resonance state and the parasitic elements 2c and d are in a non-resonance state, the stop band is generated at a frequency higher than 760 MHz. Therefore, the parasitic elements 2a and 2b function as a director, and the directivity is such that the maximum gain direction is directed to the first quadrant side.

  When the parasitic elements 2a to 2c are in a resonance state and the parasitic element d is in a non-resonance state, the stop band occurs at a frequency higher than 760 MHz. Therefore, the parasitic elements 2a to 2c act as a director, and have directivity with the maximum gain in the positive x-axis direction.

  When the parasitic elements 2a and 2c are in the resonance state and the parasitic elements 2b and d are in the non-resonance state, the stop band occurs at a frequency higher than 760 MHz. For this reason, the parasitic elements 2a and 2c function as a director. Further, 760 MHz is a frequency that is very close to the stop band, and is a frequency at which the reflection characteristics deteriorate. Therefore, the gain decreases as a whole, and an elliptical directivity having a long diameter in the y-axis direction is obtained.

  When all of the parasitic elements 2a to 2d are in a resonance state, the stop band is generated at a frequency higher than 760 MHz. Therefore, all of the parasitic elements 2a to 2d act as a director and become non-directional, but the overall gain is lower than when all of the parasitic elements 2a to 2d are in a non-resonant state. .

  As can be seen from the result of FIG. 12, by changing the capacitance of the capacitor 14 to bring only one of the parasitic elements 2a to 2d into a resonance state, the positive and negative directions of the x axis and the positive axis of the y axis are obtained. A beam can be formed in one desired direction among the four negative directions. For example, when it is desired to form a beam in the negative direction of the x-axis, only the parasitic element 2b is in a resonance state, and the parasitic elements 2a, c, and d are in a non-resonance state.

  As described above, in the antenna device of Example 1, the directivity variable function is obtained by setting the interval between the feeding element 1 and the parasitic element 2 to 20 mm of 1/20 wavelength with respect to the operating frequency of 760 MHz (wavelength of about 400 mm). Yes. In the conventional antenna device, the interval between the feeding element 1 and the parasitic element 2 needs to be ¼ wavelength, whereas in the antenna device of the first embodiment, the interval is 、, which is a small antenna. The device has been realized.

  FIG. 13 is a diagram illustrating the configuration of the antenna device according to the second embodiment. The antenna device according to the second embodiment includes dielectric substrates 20a to 20d bonded in a cross shape so that their surfaces are orthogonal to each other, and parasitic elements 22a to 22d formed of metal foils on the dielectric substrates 20a to 20d, respectively. And a feeding element 21 that is a dipole antenna and is formed of a metal foil along one side of the dielectric substrate 20a that is joined to the dielectric substrates 20b to 20d.

  The parasitic elements 22a to 22d have two parallel first metal wires 211 and second metal wires 212, and four unit circuits 210 are cascaded in the line direction of the first metal wires 211 and the second metal wires 212. It is a ladder-type circuit connected. The unit circuit 210 includes two capacitors 214 inserted in series in the first metal wiring 211, and one inductor 213 communicating between the connection point of the two capacitors 214 and the second metal wiring 212. It is configured.

  The inductor 213 is configured by a pattern in which a metal foil is a meander shape, and the capacitor 214 is configured by an interdigital pattern in which the metal foil is omitted in a comb shape. The inductance of the inductor 213 and the capacitance of the capacitor 214 are designed so that the parasitic elements 22a to 22d operate in a left-handed system. Further, the capacitor 214 is configured such that the capacitance is variable, and the resonance state and the non-resonance state of each parasitic element 22a to 22d can be switched by changing the capacitance.

  Further, the parasitic elements 22 a to 22 d are arranged in parallel to the line direction of the power feeding element 21 at a distance R from the power feeding element 21.

  Similarly to the antenna device of the first embodiment, the antenna device of the second embodiment can also control directivity by switching between the resonance state and the non-resonance state of the parasitic elements 22a to 22d. 21 and the parasitic elements 22a to 22d can be made smaller than a quarter wavelength, so that the size can be reduced as compared with the conventional antenna device. Further, the pattern of the metal foil can be easily formed by etching or the like, and can be manufactured at a low cost.

  In each embodiment, the four parasitic elements are arranged concentrically with the feeding element as the center. However, at least one parasitic element may be arranged, and it is not necessary to arrange them at an equal angle. The number of parasitic elements and the arrangement angle may be designed according to the desired beam direction.

  In each embodiment, the interval between the feeding element and each parasitic element is made equal, but it is not necessarily required to be equal. Since the distance between the feed element and each parasitic element affects the gain, the gain can be changed for each desired beam direction if the distance is different. For example, in the antenna device according to the first embodiment, if the spacing between the feeding element 1 and the parasitic elements 2a to 2c is equal and the spacing is different by the parasitic element 2d, the y-axis positive and negative directions and the x-axis having the same gain are obtained. It is possible to form a beam in the negative direction and a beam in the positive direction of the x-axis having different gains from the beams in the three directions.

  In each embodiment, the parasitic element is arranged with respect to the feeding element such that the first metal wiring is closer to the feeding element than the second metal wiring. However, the arrangement is not necessarily limited to this arrangement. It is only necessary that the element and the second metal wiring are arranged in parallel. By adjusting the distance between the feeding element and the second metal wiring and the phase of the current flowing through the feeding element and the second metal wiring, the directivity can be controlled as in the embodiment. For example, contrary to the embodiment, even when the second metal wiring is arranged to be closer to the power feeding element than the first metal wiring, the directivity can be changed by switching between the resonance state and the non-resonance state. In addition, since a stop band is formed in the resonance state, the parasitic element acts as either a reflector or a waveguide depending on whether it operates at a frequency higher or lower than the stop band. Can be made.

  In each embodiment, the feed element is a dipole antenna. However, an antenna having another structure may be used, an antenna that operates in a right-handed system, or an antenna that operates in a left-handed system. For example, a ladder circuit that operates in a left-handed system or a right-handed system that is periodic in the line direction similar to the parasitic element may be used.

  In the antenna device of the present invention, if an electric image is formed by grounding one end in the line direction by forming a feed element and a parasitic element on the ground conductor, the length in the line direction can be halved. Thus, the antenna device can be further downsized.

  In each embodiment, the resonant frequency of the parasitic element is changed by changing the capacitance of the capacitor. However, by changing the inductance of the inductor, or both the capacitance of the capacitor and the inductance of the inductor can be changed. Thus, the resonance frequency may be changed.

  Further, the structure of the parasitic element is not limited to the same unit circuit connected in each embodiment, and a similar circuit may be used as long as it operates in the left-handed system as a whole. . Circuits similar to the unit circuit include, for example, a circuit with one capacitor in the unit circuit shown in each embodiment, a circuit in which a capacitor is inserted in series or in parallel with an inductor, and an inductor in series or in parallel with a capacitor. Circuit.

  Each embodiment shows a case where the antenna device is used as a transmitting antenna, but the antenna device of the present invention can also be used as a receiving antenna.

  The antenna device of the present invention can be used for wireless communication such as mobile communication.

DESCRIPTION OF SYMBOLS 1, 2: 1: Feed element 2, 22: Parasitic element 10, 210: Unit circuit 11, 211: 1st metal wiring 12, 212: 2nd metal wiring 13, 213: Inductor 14, 214: Capacitors 20a-d: Dielectric Body substrate

Claims (5)

In an antenna device comprising: a feeding element; and at least one parasitic element disposed at a certain distance in parallel to the line direction of the feeding element,
The parasitic element is
A structure having a first metal wiring and a second metal wiring arranged in parallel, an inductor connecting the first metal wiring and the second metal wiring, and a capacitor inserted in the first metal wiring. It is a linear ladder-type line in which a plurality of the same or similar unit circuits are cascade-connected in the metal wiring direction as a unit circuit, and is an element that operates in a left-handed system as a whole,
The reactance of the parasitic element is variable.
An antenna device characterized by that.   The antenna device according to claim 1, wherein the reactance of the parasitic element is variable by changing a capacitance of the capacitor. The antenna device has a plurality of the parasitic elements,
3. The antenna according to claim 1, wherein the parasitic elements are arranged radially with the feeding element as a center, and the intervals between the feeding elements and the parasitic elements are all equal. apparatus. The feeding element and the parasitic element are configured by a dielectric substrate and a conductive foil pattern formed on the dielectric substrate.
The antenna device according to any one of claims 1 to 3, wherein the antenna device is provided.   The antenna device according to claim 1, wherein the feeding element is a dipole antenna.

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