Patent Grant
7808440
The disclosures of Japanese Patent Application No. 2007-313967 filed on Dec. 4, 2007 and Japanese Patent Application No. 2007-203400 filed on Aug. 3, 2007 including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a small multiple-resonance antenna, more specifically a dipole antenna and an inverted-L antenna that includes a plurality of parallel metal wires as its basic structure and a plurality of identical or similar unit circuits arranged in a row in the direction of the metal wires and connected with each other.
2. Description of the Related Art
As stated in R. A. Shelby, D. R. Smith, and S. Schults, “Experimental verification of a negative index of refraction”, Science, vol. 292, pp. 77-79, April 2001, left-handed materials have been studied and applied to antennas vigorously since their appearance. The term “left-handed material” refers to a material having both a negative permittivity and a negative magnetic permeability. When an electromagnetic wave is propagated in the left-handed material, its group velocity and phase velocity of the electromagnetic wave are opposite in direction. The left-handed material also shortens the wavelength of the electromagnetic wave as its frequency decreases.
Examples of antennas that operate as a left-handed antenna include: a leaky wave antenna disclosed in L. Liu, C. Caloz, and T. Ito, “Dominant mode Leaky-wave antenna with backfire-to-endfire scanning capability”, Electron. Lett., vol. 38, no. 23, pp. 1414-1416, November 2002; a small antenna formed on a ground disclosed in M. Schuessler, J. Freese, and R. Jakoby, “Design of compact planar anarantennas using LH-transmission lines”, 2004 IEEE MTT-S Int. Microwave Symp. Dig., vol. 1, pp. 209-212, Fort Worth, Tex., June 2004, C. J. Lee, K. M. H. Leong, and T. Itoh, “Design of resonant small antenna using composite right/left-handed transmission line”, IEEE Int. Antennas Propagat. Symp. Dig., vol. 2B, pp. 218-221, Washington D.C., July 2005, and F. Qureshi, M. A. Antoniades, and G. V. Eleftheriades, “A compact and low-profile metamaterial ring antenna with vertical polarization”, IEEE Antennas and Wireless Propagat. Lett., vol. 4, pp. 333-336, 2005; and a dipole antenna disclosed in Japanese Patent Application Publication No. 2006-295873 (JP-A-2006-295873).
With the capacitors CSE10 and the inductors LSH10 arranged periodically, the dipole antenna A10 may operate as a left-handed antenna. As described above, the left-handed material reduces the wavelength shorter as the frequency decreases. Therefore, the antenna length L10 of the dipole antenna A10 may be reduced to about one tenth the operating wavelength by controlling the capacitance of the capacitor CSE10 and the inductance of the inductor LSH10.
A dual-resonance antenna that operates with a right-handed material and a left-handed material is disclosed in S. Otto, A. Rennings, C. Caloz, P. Waldow, and T. Itoh, “Composite Right/Left-Handed λ-Resonator Ring Antenna for Dual-Frequency Operation”, IEEE Int. Antennas Propagat. Symp. Dig., vol. 1A, pp. 684-687, Washington D.C., July 2005.
The frequency band of electromagnetic waves allocated to tire air pressure warning systems and smart entry systems, which are in-vehicle applications, is the 400 MHz band in Europe, and the 300 MHz band in North America and Japan. Antennas for use used in these systems are preferably small, because their installation space is occasionally limited, and can able to use both the two frequency bands, namely the 300 MHz band and the 400 MHz band, because their installation space is occasionally limited.
In normal right-handed antennas, if a first resonance occurs at 300 MHz, for example, a second resonance occurs at about 900 MHz, about three times the frequency of the first resonance. The dipole length is equivalent to half the operating wavelength for the first resonance, and 1.5 times the operating wavelength for the second resonance. Since there is a wide gap between the frequencies of the first and second resonances as described above, right-handed antennas cannot be used for the applications mentioned above.
In contrast, in left-handed antennas, decreases in frequency shorten the wavelength and reduce the gap between the frequencies. That is, a first resonance may occur at about 400 MHz (half the wavelength), and a second resonance may occur at about 300 MHz (1.5 times the wavelength). When the antenna length is short relative to the operating wavelength, however, the dipole antenna A10 in accordance with the above related art does not operate as an antenna, because currents flow in opposite directions to cancel each other at the second resonance.
With the dual-resonance antenna that operates as a left-handed antenna and a right-handed antenna disclosed in IEEE Int. Antennas Propagat. Symp. Dig., vol. 1A, pp. 684-687, Washington D.C., July 2005, the gap between the resonance frequencies cannot be reduced. In addition, it is necessary to improve the radiation efficiency by impedance matching at the feed point.
The present invention provide a small multiple-resonance antenna that resonates at narrowly gapped frequencies and that may be easily subjected to impedance matching at the feed point.
A first aspect of the present invention is directed to a dipole antenna including a plurality of parallel metal wires. In the dipole antenna, the plurality of metal wires have a plurality of identical or similar unit circuits arranged in a row in an extending direction of the metal wires and connected with each other; the unit circuits each have a tie portion that connects the metal wires with each other via at least one first inductor, and at least one first capacitor provided on at least one of the metal wires; and the plurality of metal wires each have a base portion and an extended portion, and the plurality of metal wires are each bent such that the extended portion extends at an angle of 90 degrees with respect to the base portion.
According to the above configuration, the dipole antenna may operate as a left-handed antenna due to the configuration in which the unit circuits constituted of the first capacitor and the first inductor are arranged periodically. Due to the structure in which the metal wires are bent to obtain symmetry with respect to a line, the current components in the base portion, which extends in the direction perpendicular to the extended portions, contain no components in the opposite direction. As a result, multiple-resonance characteristics may be obtained. In addition, a small antenna that operates as a left-handed antenna and with narrowly gapped resonance frequencies may be realized.
In the dipole antenna in accordance with this aspect, a pair of the extended portions may be provided, and the extended portions may be symmetric with respect to a symmetry axis perpendicular to each of the plurality of metal wires forming the base portion and passing through a middle portion, in the extending direction of the metal wires, of each of the plurality of metal wires forming the base portion. According to the above configuration, due to the structure in which the metal wires are bent to obtain symmetry with respect to a line, the current components in the extended portions may be in opposite directions to each other and hence canceled by each other.
In the dipole antenna in accordance with this aspect, a continuing body composed of the base portion and the extended portions may form a squared U-shape.
In the dipole antenna in accordance with this aspect, the symmetry axis may be perpendicular to a plane in which the plurality of metal wires composing the base portion are disposed. According to the above configuration, the planes composed of the plurality of metal wires are composed of the base portion and the extended portion bent at an angle of 90 degrees.
In the dipole antenna in accordance with this aspect, the symmetry axis may be positioned in a plane in which the plurality of metal wires composing the base portion are disposed. According to the above configuration, the plurality of metal wires are each bent at an angle of 90 degrees within the plane defined by the plurality of metal wires to form the base portion and the extended portion.
In the dipole antenna in accordance with this aspect, the base portion may be provided on a ground conductor and the extended portion may be disposed parallel to the ground conductor. According to the above configuration, an inverted-L antenna is provided on the ground conductor. In this antenna, a pair of upper and lower base portions perpendicular to the ground conductor and a pair of parallel extended portions parallel to the ground conductor are formed by the base portion and the extended portion provided on the ground conductor and their mirror images with the ground conductor as a mirror surface. Since half of the symmetric antenna is formed as a mirror image with the ground conductor as a mirror surface, the size of the antenna may be reduced to about half that of conventional dipole antennas.
The dipole antenna in accordance with this aspect may further include a connection line constituted of at least one of the plurality of unit circuits, disposed parallel to the base portion and connected to the extended portion. According to the above configuration, the connection line is composed of unit circuits similar to those of the base portion and the extended portion. The connection line is provided parallel to the base portion and on the side of the distal end of the extended portion with respect to the base portion. Since the connection line is disposed parallel to the base portion and connected to the extended portion, the impedance of the antenna side at the feed point is increased, which allows impedance matching at the feed point. As a result, the power efficiency is improved.
In the dipole antenna in accordance with this aspect, the base portion and the connection line may be provided on a ground conductor; and the extended portion may be disposed parallel to the ground conductor. According to the above configuration, an inverted-F antenna is provided on the ground conductor. In this antenna, which has a connection line, a pair of upper and lower base portions and a pair of upper and lower connection lines perpendicular to the ground conductor and a pair of parallel extended portions parallel to the ground conductor are formed by the base portion, the connection line, and the extended portion provided on the ground conductor and their mirror images with the ground conductor as a mirror surface.
In the dipole antenna in accordance with this aspect, a feed point of the dipole antenna may be provided in the base portion or at the connection line.
In the dipole antenna in accordance with this aspect, a ratio in length between the base portion and the extended portion may be 1:n, where n is a positive integer. According to the above configuration, a dipole antenna having (n+1)-resonance characteristics may be realized.
In the dipole antenna in accordance with this aspect, the unit circuits may each be an identical circuit; and the unit circuits may each be arranged periodically in the direction of the metal wires and connected with each other. According to the above configuration, the design, the configuration, and the manufacture of the antenna may be simplified.
In the dipole antenna in accordance with this aspect, both ends of each of the plurality of metal wires may be open. According to the above configuration, since the current is strong around the feed point of the antenna, that is, the peak of the resonance is produced around the feed point which is at the middle of the antenna, the generation and increase of reflected waves at the feed point may be controlled.
In the dipole antenna in accordance with this aspect, the unit circuits may have a second inductor provided in series on a metal wire other than the one on which the first capacitor is disposed. According to the above configuration, the design of a left-handed circuit is facilitated.
In the dipole antenna in accordance with this aspect, the tie portion of each of the unit circuits may have a second capacitor connected in parallel with the first inductor.
In the dipole antenna in accordance with this aspect, the first inductor may be composed of a meandering inductor pattern. According to the above configuration, a small antenna with multiple-resonance characteristics is realized, and the dipole antenna may be formed on an inexpective substrate, by forming the metal wires with conductor patterns.
In the dipole antenna in accordance with this aspect, the first capacitor may be composed of a comb-shaped interdigital capacitor pattern.
In the dipole antenna in accordance with this aspect, the first capacitor and the first inductor may be composed of a lumped element. According to the above configuration, since the antenna may be composed of metal wires and lumped elements (chip elements), a dipole antenna with desired characteristics may be manufactured within a short period.
The dipole antenna in accordance with this aspect may include a flexible substrate on which conductor patterns are stacked; the first inductor may be composed of a meandering inductor pattern constituted of the conductor patterns; and the first capacitor may be composed of a comb-shaped interdigital capacitor pattern constituted of the conductor patterns. According to the above configuration, the dipole antenna may be formed using only the conductor patterns, and the use of the flexible substrate facilitates the formation of the bent portions.
The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
Referring to the drawings, a description will be made of specific embodiments of the present invention, to which the present invention is not limited.
The unit circuits U1 are each composed of two capacitors CSE1, as an example of the first capacitor of the present invention, connected in series on a part of the metal wire p1, two inductors LSE1, as an example of the second inductor of the present invention, connected in series on a part of the metal wire q1, and a tie portion that ties the metal wires p1 and q1 via an inductor LSH1, as an example of the second inductor of the present invention. The inductors LSE1 are provided to adjust the two resonance frequencies and the impedance.
The dipole antenna A1 has a base portion 10 constituted of metal wires p1b and q1b formed to extend in the polarization direction of radiation waves, and a pair of extended portions 30, 31 constituted of a pair of metal wires p1a bent at bent portions 11, 13 at an angle of 90 degrees with respect to the base portion 10 and a pair of metal wires q1a bent at bent portions 12, 14 at an angle of 90 degrees with respect to the base portion 10. At the middle portion of the base portion 10, a feed point F constituted of points FT, FB is provided at the midpoint of the metal wire q1b on which the inductors LSE1 are provided in series.
The metal wires p1, q1 are bent at two bent portions (11, 12) and (13, 14) at an angle of 90 degrees with respect to the plane including the metal wires p1b, q1b, that is, the plane including the base portion 10 which is the middle portion of the metal wire p1, q1 (an x-z plane of
The dipole antenna A1 may operate as a left-handed antenna with the capacitors CSE1, which are provided on the metal wire p1, and the inductors LSH1, which are provided between the metal wires p1 and q1, arranged periodically. Currents I1 and I2 respectively flow through the metal wires q1, p1 in opposite phases and with different amplitudes. Thus, the current components that contribute to the radiation is represented by |I1|−|I2|.
A description will next be made of the operation of the dipole antenna A1 as a dual-resonance antenna that operates as a left-handed antenna, with reference to
As shown in
The dipole antenna A2 is composed by connecting six generally identical unit circuits. In the same way as in the dipole antenna A1, the unit circuits are each composed of two capacitors CSE1 connected in series on a part of the metal wire p2, two inductors LSE1 connected in series on a part of the metal wire q2, and a tie portion that ties the metal wires p1 and q1 via an inductor LSH1.
The dipole antenna A2 may also operate as a left-handed antenna, with the capacitors CSE1, which are provided on the metal wire p2, and the inductors LSH1, which are provided between the metal wires p2 and q2, arranged periodically. Due to the squared U-shape of the metal wires p2, q2, multiple-resonance characteristics can be obtained, with current components in the x-axis direction canceling each other and with current components in the y-axis direction containing no components in the opposite direction.
In the above first and second embodiments, the dipole antennas A1, A2 are provided with the inductors LSE1 to facilitate adjustment of the impedance. However, the dipole antennas A1, A2 may also operate as a dual-resonance antenna as a left-handed antenna even without resonance frequencies and the inductors LSE1.
The unit circuit is not limited to the configuration in accordance with the first and second embodiments, and may be configured as disclosed, for example, in JP-A-2006-295873. For example, as a unit circuit U2 shown in
In the dipole antennas A1, A2, the capacitors CSE1 and the inductors LSE1, LSH1 are composed of a lumped element. However, the metal wires p1, q1 may be composed of a conductor pattern, the capacitors CSE1 may be composed of comb-shaped interdigital capacitor patterns Cp1, Cp2 shown in
In a third embodiment of the present invention, the dipole antenna A1 is formed using a multilayer printed circuit board. That is, as shown in
In a fourth embodiment of the present invention, as shown in
An inverted-L antenna A3 shown in
In the dipole antenna A1 in accordance with the first embodiment, the ratio between 2h and L is set to 1:1 to obtain dual-resonance characteristics. Meanwhile, triple-resonance characteristics may be obtained if the ratio 2h:L is set to 1:2, and in general, (n+1)-resonance characteristics may be obtained when the ratio 2h:L is set to 1:n. This also applies to the dipole antenna A2 in accordance with the second embodiment.
An embodiment of the present invention is not limited to the squared U-shape as in the first embodiment, each metal wire may be formed with bent portions at an angle of 90 degrees so as to be symmetric with respect to a symmetric axis perpendicular thereto. With such a shape, multiple-resonance characteristics can be obtained with current components in directions other than the z-axis direction canceled as in the first embodiment. For example, in a dipole antenna A4 in accordance with a sixth embodiment of the present invention shown in
Although two metal wires are used in the first and second embodiments, three or more metal wires may be used.
The dipole antenna A5 is composed of eight unit circuits with length a and width d. Some of the unit circuits each have two series capacitors CSE1 on a part of the metal wire p1, two series inductors LSE1 on a part of the metal wire q1, an a parallel inductor LSH1 between the metal wires p1, q1. Likewise, the other unit circuits each have two series capacitors CSE1 on a part of the metal wire r1 composing the connection line 50, two series inductors LSE1 on a part of the metal wire s1 composing the connection line 50, an a parallel inductor LSH1 between the metal wires r1, s1.
The feed point F constituted of the two points FT, FB is positioned generally at the middle of the metal wire r1. The metal wires p1, q1 with the total length 6a are bent at two bent portions (11, 12) and (13, 14) at an angle of 90 degrees to have a squared U-shape. Of the metal wires p1, q1 in the squared U-shape, the metal wires composing a pair of parallel extended portions 30, 31 and extending for length 2a (corresponding to two unit circuits) from both ends are disposed to extend in the y-axis direction. Also, the metal wires composing a base portion 10 and extending for length 2a between the extended portions 30, 31 are disposed to extend in the z-axis direction, or the polarization direction of radiation waves. The metal wires r1, s1 with length 2a composing the connection line 50 are disposed to extend in the z-axis direction parallel to the base portion 10, with a gap of a/2 from the base portion 10. The dimensions of the antenna A5 in the x-, y-, and z-axis directions are respectively set to d=20 mm, L=2a=60 mm, and 2h=2a=60 mm.
As in the first embodiment, the antenna A5 operates as a left-handed antenna with the series capacitors CSE1 and the parallel inductors LSH1. The series inductors LSE1 are provided to adjust the two resonance frequencies and the impedance. Currents I1 and I2 respectively flow through the metal wires q1, p1 in opposite phases and with different amplitudes. Thus, the current components that contribute to the radiation is represented by |I1|−|I2|, the difference in amplitude between the currents.
The amplitude and the phase of the impedance are respectively shown in
Since the connection line 50 is provided parallel to the base portion 10 in the above seventh, eighth, and ninth embodiments, the impedance of the antenna side at the feed point F is increased, which allows impedance matching at the feed point F. As a result, the power efficiency may be improved.
In a tenth embodiment of the present invention, as shown in
In the dipole antennas A5, A6, and A7, the series inductors LSE1 are provided to facilitate adjustment of the resonance frequencies and the impedance. However, the dipole antennas A5, A6, and A7 may operate as a left-handed antenna as a dual-resonance antenna without the series inductors LSE1.
In the dipole antennas A5, A6, and A7, the capacitors CSE1 and the inductors LSH1, LSE1, composed of a lumped element, are provided on the metal wires. However, the metal wires may instead be composed of a conductor pattern, the capacitors CSE1 may be composed of comb-shaped interdigital capacitor patterns shown in
In the first embodiment, the feed point F is provided on the metal wire q1 on which the inductors LSE1 are provided. However, the feed point F may also be provided on the metal wire p1 on which the capacitors CSE1 are provided.
In the dipole antennas A5, A6, and A7, the ratio of 2h:L is set to 1:1 to obtain dual-resonance characteristics. However, the length L of the extended portions 30, 31 may be increased relative to the length 2h of the base portion 10 to obtain triple- or more-higher resonance characteristics. Such characteristics may be obtained in the case where if the current components in the z-axis direction contain no components in the opposite phase.
Although the dipole antennas A5, A6, and A7 have been described as a dual-resonance antenna, it should be understood that they may also be used as a single-resonance antenna.
Further, the dipole antennas A5, A6, and A7 in accordance with the seventh, eighth, and ninth embodiments may be formed by disposing the metal wires p1, r1 and the capacitors CSE1 on the front surface of the substrate 10, disposing the metal wires q1, s1 and the inductors LSE1 on the back surface of the substrate 10, and forming the inductors LSH1 in the through holes 11 as in the third embodiment shown in
In the configurations of
In the above embodiments, the base portion 10 may emit and receives radiation waves. That is, the base portion 10 may be formed in the polarization direction of waves to be transmitted when the dipole antenna functions as a transmission antenna, and may be formed in the polarization direction where waves are most efficiently received when the dipole antenna functions as a reception antenna. The extended portions 30, 31 may be bent at an angle of 90 degrees with respect to the base portion 10, and formed to be continuous with the base portion 10. However, the angle between the base portion and the extended portion is not limited to being 90 degrees. The extended portions may be formed to extend from both ends of the base portion not necessarily and strictly at an angle of 90 degrees and parallel to each other but in such a manner that they may be considered as equivalently parallel in terms of excitation.
The dipole antenna in accordance with the present invention is not restricted to one that is symmetric with respect to a line. In addition, the plurality of metal wires may be parallel to each other.
Similar unit circuits that may be used in the present invention may include circuits obtainable by a symmetric transformation with respect to a line, a point, a rotation, and so forth. Unit circuits including a feed point or disposed at an end occasionally may have input/output boundary conditions different from those of other unit circuits. The similar unit circuits may also include unit circuits subjected to slight deformation or element volume adjustment to adjust their peculiar boundary conditions. The distance between the base portion and the connection line disposed parallel to the base portion and connected to the extended portions are preferably the length of a unit circuit or a half that. A combined use of capacitors in comb-shaped interdigital capacitor patterns and inductors in a meandering inductor pattern are preferable.
The present invention may be applied to antennas for use in other in-vehicle applications, such as smart entry systems or the like.
While example embodiments of the invention have been described above, it is to be understood that the invention is not limited to the particulars of the described embodiments, but may be embodied with various changes, modifications or improvements, which may occur to those skilled in the art, without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-203400 | Aug 2007 | JP | national |
| 2007-313967 | Dec 2007 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3277487 | Berry et al. | Oct 1966 | A |
| 6965353 | Shirosaka et al. | Nov 2005 | B2 |
| 7265730 | Iizuka et al. | Sep 2007 | B2 |
| Number | Date | Country |
|---|---|---|
| 2006-135605 | May 2006 | JP |
| 2006-295873 | Oct 2006 | JP |
| 2006-333429 | Dec 2006 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20090040124 A1 | Feb 2009 | US |
