Patent Description:
<CIT> discloses a dual-band antenna for radiating electromagnetic signals of different frequencies including a first planar inverted-F antenna and a second planar inverted-F antenna.

<CIT> discloses a multiple frequency band antenna involving first to third resonant portions including an additional radiating strip which behaves as an inverted-F antenna.

<CIT> discloses a communication device includes: a split ring resonator antenna that includes a split ring unit, an impedance control unit and a power supply unit, and has a first resonant frequency; and an antenna element connected with the split ring resonator antenna via an LC parallel circuit or a first inductor. A second resonant frequency formed by the power supply unit, the LC parallel circuit or the first inductor, and the antenna element is different from the first resonant frequency.

<CIT> (Patent Document <NUM>) discloses a small and broadband antenna <NUM>. As shown in <FIG>, the antenna <NUM> of Patent Document <NUM> has a split ring resonator <NUM> using a split ring <NUM> which is a ring-shaped conductor with a split portion <NUM>. Specifically, the antenna <NUM> of Patent Document <NUM> has a main portion <NUM>, which forms the split ring <NUM>, and a feeding portion <NUM>. Here, the feeding portion <NUM> is provided to the main portion <NUM>.

The antenna <NUM> of Patent Document <NUM> operates at a resonance frequency of the split ring resonator <NUM>. In other words, the antenna <NUM> of Patent Document <NUM> resonates at only one operating frequency but cannot cope with a broad frequency band.

It is therefore an object of the present invention to provide an antenna having a structure which can resonate at a plurality of operation frequencies.

The object is achieved by the multi-resonant antenna according to claim <NUM>.

The multi-resonant antenna is provided with the additional radiation element in addition to the main antenna. With this structure, the multi-resonant antenna of the present invention can resonate at both of an operating frequency of the first resonance portion and an operating frequency of the second resonance portion. In other words, the multi-resonant antenna of the present invention has a structure which can resonate at a plurality of operation frequencies.

An appreciation of the objectives of the present invention and a more complete understanding of its structure may be had by studying the following description of the preferred embodiment and by referring to the accompanying drawings.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

As shown in <FIG>, a multi-resonant antenna <NUM> according to an embodiment of the present invention is provided with a circuit board (a substrate) <NUM> and an antenna component <NUM>. In the present embodiment, the antenna component <NUM> forms a main antenna <NUM> in part.

As shown in <FIG>, the circuit board <NUM> of the present embodiment has a conductive pattern (a pattern) <NUM>. The conductive pattern <NUM> includes a feeding portion <NUM>, a ground pattern (a ground portion) <NUM> and an additional radiation element <NUM>. Moreover, the conductive pattern <NUM> includes a first main portion <NUM>, which forms the main antenna <NUM> in part. The first main portion <NUM> is in a mount area <NUM> on which the antenna component <NUM> is mounted. The first main portion <NUM> has a pattern shape decided according to a desired antenna characteristic. The first main portion <NUM> forms the main antenna <NUM> together with the antenna component <NUM> mounted on the circuit board <NUM>. Thus, the multi-resonant antenna <NUM> of the present embodiment is provided with the main antenna <NUM> and the additional radiation element <NUM>.

As understood from <FIG> and <FIG>, the antenna component <NUM> of the present embodiment is formed of a metal member which is mounted on the circuit board <NUM> when used. In other words, the antenna component <NUM> is a discrete component which is mounted on the circuit board <NUM> when used. However, the present invention is not limited thereto. The antenna component <NUM> of the present invention may be formed by other methods, such as plating a resin body with a metal film or sticking a metal member on a resin body.

As understood from <FIG> and <FIG>, in the present embodiment, the main antenna <NUM> is formed of the antenna component <NUM> and a part of the conductive pattern <NUM> (the first main portion <NUM>) of the circuit board <NUM>. In examples not forming part of the claimed invention but nonetheless useful for the understanding of the invention, the main antenna <NUM> may be formed of the antenna component <NUM> alone, or, alternatively, the main antenna <NUM> may be formed of one or more conductive layers included in the circuit board <NUM>. For example, the main antenna <NUM> may be formed by using a multilayer wiring substrate as the circuit board <NUM> and using a plurality of conductive layers and a plurality of vias which are included in the multilayer wiring substrate.

Referring to <FIG>, the antenna component <NUM> of the present embodiment is provided with a second main portion <NUM>, a feeding leg portion <NUM> and a facing portion <NUM>. The antenna component <NUM> is further provided with a plurality of grounding portions <NUM> and a plurality of fixing portions <NUM>. The second main portion <NUM> forms a main portion of the main antenna <NUM> together with the first main portion <NUM> of the circuit board <NUM>. In other words, in the present embodiment, the main portion of the main antenna <NUM> is formed of the first main portion <NUM> of the circuit board <NUM> and the second main portion <NUM> of the antenna component <NUM>.

As shown in <FIG>, a shape of the second main portion <NUM> of the present embodiment is an approximately rectangular ring shape long in a lateral direction. However, the present invention is not limited thereto. The shape of the second main portion <NUM> of the present invention may be any one of various ring shapes, such as not only the approximately rectangular ring shape but also a circular shape, oval shapes and polygonal ring shapes. In the present embodiment, the lateral direction is an X-direction. Specifically, the negative X-direction is also referred to as a first predetermined direction in the present embodiment.

As shown in <FIG>, the second main portion <NUM> has a first end portion <NUM> and a second end portion <NUM>. The first end portion <NUM> and the second end portion <NUM> are apart from and face each other to form a split portion <NUM>. In other words, the second main portion <NUM> forms a split ring having the split portion <NUM>.

As shown in <FIG>, the feeding leg portion <NUM> branches off from the second main portion <NUM>. In the present embodiment, the feeding leg portion <NUM> branches off from the second main portion <NUM> at a position closer to the first end portion <NUM> than to the second end portion <NUM>. The feeding leg portion <NUM> extends rearward and then extends downward. The feeding leg portion <NUM> is connected to the feeding portion <NUM> when the main antenna <NUM> is mounted on the circuit board <NUM>. In the present embodiment, a front-rear direction is a Y-direction. A positive Y-direction is directed forward while a negative Y-direction is directed rearward. Specifically, the positive Y-direction is also referred to as a second predetermined direction in the present embodiment. Moreover, in the present embodiment, an up-down direction is a Z-direction. A positive Z-direction is directed upward while a negative Z-direction is directed downward.

As shown in <FIG>, the facing portion <NUM> has a first facing portion <NUM> and a second facing portion <NUM>. The first facing portion <NUM> and the second facing portion <NUM> are apart from and face each other to form a capacitor. The first facing portion <NUM> and the second facing portion <NUM> are provided to the first end portion <NUM> of the second main portion <NUM> and the second end portion <NUM> of the second main portion <NUM>, respectively. In the present embodiment, the first end portion <NUM> and the first facing portion <NUM> are integrally formed. Similarly, the second end portion <NUM> and the second facing portion <NUM> are integrally formed.

As shown in <FIG>, the first facing portion <NUM> has a first upper facing portion <NUM>, which extends downward from the first end portion <NUM>, and a first lower facing portion <NUM>, which extends forward from the first end portion <NUM> and then extends downward, and further extends rearward. Moreover, the second facing portion <NUM> has a second upper facing portion <NUM>, which extends rearward from the second end portion <NUM>, and a second lower facing portion <NUM>, which extends forward from the second end portion <NUM> and then extends downward, and further extends rearward. However, the present invention is not limited thereto. In the present invention, provided that the first facing portion <NUM> and the second facing portion <NUM> are formed to a capacitor having a desired characteristic, their shapes and sizes are not limited particularly.

As understood from <FIG>, the second main portion <NUM> forms an inductive component of the main antenna <NUM> because of the shape thereof. The first end portion <NUM> and the second end portion <NUM> form a capacitive component of the main antenna <NUM> together with the first facing portion <NUM> and the second facing portion <NUM>. With this structure, the main antenna <NUM> is operable as an LC resonance circuit (a first resonance portion). The LC resonance circuit formed by the main antenna <NUM> is also called as a split ring resonator. Thus, the main antenna <NUM> forms the first resonance portion.

Referring again to <FIG>, the feeding portion <NUM>, the ground pattern <NUM>, the additional radiation element <NUM> and the first main portion <NUM>, which are formed on the circuit board <NUM>, are formed by using a single conductive layer (the conductive pattern <NUM>). In addition, the feeding portion <NUM>, the ground pattern <NUM>, the additional radiation element <NUM> and the first main portion <NUM> are contiguous to one another. However, the present invention is not limited thereto. The feeding portion <NUM>, the ground pattern <NUM>, the additional radiation element <NUM> and the first main portion <NUM> may be formed by using the conductive layers and the vias included in the multilayer wiring substrate.

As shown in <FIG>, in the present embodiment, the conductive pattern <NUM> covers a surface of the circuit board <NUM> except for a predetermined area. The feeding portion <NUM> is formed in a slit <NUM> formed in the conductive pattern <NUM>. The feeding portion <NUM> extends in the front-rear direction.

As understood from <FIG>, the additional radiation element <NUM> extends outward of the main antenna <NUM>. In detail, as shown in <FIG>, the additional radiation element <NUM> extends outward of the main antenna <NUM> from the first main portion <NUM>. In the present embodiment, the additional radiation element <NUM> has a base portion <NUM>, which extends from the first main portion <NUM> in the second predetermined direction (the positive Y-direction), and a first extension portion <NUM>, which extends from the base portion <NUM> in the first predetermined direction (the negative X-direction). However, the present invention is not limited thereto. The additional radiation element <NUM> may not have the base portion <NUM>, provide that the additional radiation element <NUM> extends from the first main portion <NUM> in the first predetermined direction. Moreover, the additional radiation element <NUM> may extend outward of the main antenna <NUM> from the feeding portion <NUM>. In that case, the base portion <NUM> may not have a linear shape but may have a shape with a bent portion. Moreover, a shape of the first extension portion <NUM> of the additional radiation element <NUM> may have a wide portion at a tip portion thereof.

As shown in <FIG>, the additional radiation element <NUM> extends from near the first end portion <NUM> of the antenna component <NUM> and the feeding leg portion <NUM> in a plan view. In addition, the additional radiation element <NUM> does not overlap with the ground pattern <NUM> in a plan view. The additional radiation element <NUM> forms at least a part of a second resonance portion different from the first resonance portion. In detail, the additional radiation element <NUM> forms the second resonance portion solely or together with a part of the conductive pattern <NUM>.

As shown in <FIG> and <FIG>, a clearance area <NUM> is formed between the first extension portion <NUM> of the additional radiation element <NUM> and the ground pattern <NUM>. A size of the clearance area <NUM> is decided in consideration of a characteristic of the main antenna <NUM> and a characteristic of the additional radiation element <NUM>.

As shown in <FIG>, the ground pattern <NUM> has a second extension portion <NUM> and a third extension portion <NUM> which define the clearance area <NUM> in part. The second extension portion <NUM> is located apart from the first extension portion <NUM> of the additional radiation element <NUM> in the front-rear direction and extends from near the mount area <NUM> in the first predetermined direction. The third extension portion <NUM> extends from the second extension portion <NUM> in the second predetermined direction.

As shown in <FIG> and <FIG>, in the present embodiment, a tip of the first extension portion <NUM> of the additional radiation element <NUM> is apart from and faces the third extension portion <NUM> in the first predetermined direction.

An electrical length of the additional radiation element <NUM> is decided on the basis of a quarter of a length of a desired operating frequency. The desired operating frequency is different from an operating frequency of the main antenna <NUM>.

In the multi-resonant antenna <NUM> formed as described above, the first resonance portion and the second resonance portion have the operating frequencies different from each other. In other words, the multi-resonant antenna <NUM> of the present embodiment can resonate at each of the operating frequency of the main antenna <NUM> and the operating frequency of the additional radiation element <NUM>. The first resonance portion is connected to a resonance source (not shown) via the feeding portion <NUM>. The second resonance portion is connected to the first resonance portion. Thus, the multi-resonant antenna <NUM> has a structure which can resonate at a plurality of operation frequencies.

In more detail, the multi-resonant antenna <NUM> of the present embodiment has the structure which can electrically resonate at two operation frequencies, one of which is an operating frequency of the LC resonance circuit which operates as the main antenna <NUM>, and the other of which is an operating frequency of the additional radiation element <NUM> which depends on the electric length of the additional element <NUM>.

Up to this point, the description has been made about the embodiment of the present invention, and the embodiment may be modified as follows.

As shown in <FIG>, a multi-resonant antenna 10A of a first modification is provided with a main antenna 30A and an additional radiation element 230A. The main antenna 30A is provided with a main portion 320A, a feeding portion 210A, a grounding line portion <NUM> and a facing portion 350A. The multi-resonant antenna 10A is further provided with a substrate (not shown).

As understood from <FIG>, in the multi-resonant antenna 10A of the first modification, the main antenna 30A and the additional radiation element 230A are integrally formed In an example not forming part of the claimed invention, a combination of the main antenna 30A and the additional radiation element 230A may be formed of a metal member which is mounted on the substrate (not shown), for example, when used. Alternatively, in another example not forming part of the claimed invention, the combination of the main antenna 30A and the additional radiation element 230A may be formed of a conductive pattern (a pattern) or conductive patterns (patterns) formed on or in the substrate. Instead, a part of the combination of the main antenna 30A and the additional radiation element 230A may be formed of the conductive pattern(s) formed on or in the substrate and a remaining part of the combination of the main antenna 30A and the additional radiation element 230A may be formed of a metal member distinct and separated from the substrate.

As shown in <FIG>, the main portion 320A has a first portion <NUM>, a second portion <NUM>, a third portion <NUM>, a fourth portion <NUM> and a fifth portion <NUM>. Each of the first portion <NUM> and the second portion <NUM> extends in the lateral direction. The first portion <NUM> and the second portion <NUM> are arranged in a first predetermined direction. The fourth portion <NUM> extends along the lateral direction. The fourth portion <NUM> is apart from the first portion <NUM> and the second portion <NUM> in the front-rear direction and arranged in parallel to the first portion <NUM> and the second portion <NUM>. Each of the third portion <NUM> and the fifth portion <NUM> extends in the front-rear direction. The third portion <NUM> and the fifth portion <NUM> are arranged to be apart from and parallel to each other.

As shown in <FIG>, the first portion <NUM> of the main portion 320A and the second portion <NUM> of the main portion 320A have a first end portion 322A and a second end portion 324A, respectively. The first end portion 322A and the second end portion 324A are apart from and face each other to form a split portion 326A. The third portion <NUM> of the main portion 320A joins the second portion <NUM> to the fourth portion <NUM>. The fifth portion <NUM> of the main portion 320A joins the first portion <NUM> to the fourth portion <NUM>. Thus, the main portion 320A forms a split ring having the split portion 326A. However, the present invention is not limited thereto. The main portion 320A may have another ring shape, such as a circular shape or an oval shape, provided that the main portion 320A forms a split ring.

As shown in <FIG>, the feeding portion 210A branches off from the main portion 320A at a position closer to the first end portion 322A than to the second end portion 324A. Moreover, the additional radiation element 230A extends from the main portion 320A at another position closer to the first end portion 322A than to the second end portion 324A. In detail, each of the feeding portion 210A and the additional radiation element 230A branches off from the first portion <NUM> of the main portion 320A. In the lateral direction or the first predetermined direction, the additional radiation element 230A is farer from the first end portion 322A than the feeding portion 210A is. However, the present invention is not limited thereto. According to a desired characteristic, the additional radiation element 230A may be located at the same position as the feeding portion 210A or at a position closer to the first end portion 322A than the feeding portion 210A is. Moreover, the additional radiation element 230A may extend from not the main portion 320A but the feeding portion 210A according to the desired characteristic.

As shown in <FIG>, the feeding portion 210A extends from the first portion <NUM> of the main portion 320A toward the fourth portion <NUM> along the front-rear direction. The substrate (not shown) is formed with a ground pattern (not shown), and the fourth portion <NUM> of the main portion 320A is electrically connected to the ground pattern. Alternatively, the fourth portion <NUM> of the main portion 320A may be a part of the ground pattern. An end portion of the feeding portion 210A is connected to a feeding line (not shown) or a circuit element (not shown) in order to serve as a driving point <NUM>. Additionally, at least one of the third portion <NUM> of the main portion 320A, the fourth portion <NUM> of the main portion 320A and the fifth portion <NUM> of the main portion 320A should be connected to the ground pattern.

As shown in <FIG>, the additional radiation element 230A extends outward of the main antenna 30A from the main portion 320A of the main antenna 30A. In detail, the additional radiation element 230A has a base portion 232A, which extends from the first portion <NUM> of the main portion 320A in the second predetermined direction, and a first extension portion 234A, which extends from the base portion 232A in the first predetermined direction. When the substrate (not shown) has the ground pattern (not shown), the additional radiation element 230A is formed not to overlap with the ground pattern in a plan view. However, the present invention is not limited thereto. Provided that the additional radiation element 230A has the first extension portion 234A, it may not have the base portion 232A. Moreover, a shape of the first extension portion 234A is not limited to a rectangular shape but may have a wide portion at a tip portion thereof. The additional radiation element 230A corresponds to a quarter of a wavelength of a desired operating frequency.

As shown in <FIG>, the facing portion 350A has a first facing portion 352A and a second facing portion 354A. The first facing portion 352A and the second facing portion 354A extend from the first end portion 322A and the second end portion 324A, respectively, in the front-rear direction. The first facing portion 352A and the second facing portion 354A also extend inward of the main portion 320A. The first facing portion 352A and the second facing portion 354A are apart from each other by a predetermined distance and arranged in parallel with each other. However, the present invention is not limited thereto. Provided that the first facing portion 352A and the second facing portion 354A form a capacitor having a predetermined characteristic, their shapes are not limited particularly. Moreover, when the main portion 320A is formed by a pattern on the substrate (not shown), the first facing portion 352A and the second facing portion 354A may be made of metal members which are distinct and separated from the substrate.

As understood from <FIG>, in the multi-resonant antenna 10A, the main antenna 30A is fed from the driving point <NUM>. The additional radiation element 230A is connected to the main antenna 30A. With this structure, the main antenna 30A operates as a split ring resonator (an LC resonance circuit or a first resonance portion), and the additional radiation element 230A operates as a second resonance portion different from the first resonance portion. The first resonance portion and the second resonance portion have resonance frequencies different from each other. Thus, the multi-resonant antenna 10A of the first modification has the structure which can electrically resonate at two operating frequencies, one of which is an operating frequency of the main antenna (a first resonance portion) 30A, and the other of which is an operating frequency of the additional radiation element (a second resonance portion).

As shown in <FIG>, a multi-resonant antenna 10B of a second modification is provided with a second extension portion (a ground portion) 224B in addition to the structure of the multi-resonant antenna 10A of the first modification. Since the multi-resonant antenna 10B is the same as the multi-resonant antenna 10A of the first modification except for the second extension portion 224B, the detailed description of points other than the second extension portion 224B will be omitted.

As shown in <FIG>, the second extension portion 224B extends from an end of the fourth portion <NUM> of the main portion 320A in the first predetermined direction. In other words, the second extension portion 224B is arranged to be parallel to the additional radiation element 230A. In the second predetermined direction, the second extension portion 224B is apart from the additional radiation element 230A. When the main antenna 30A is made of a metal member, the second extension portion 224B may be integrally formed with the main antenna 30A by using the metal member. Alternatively, the second extension portion 224B may be formed of a conductive pattern (not shown) of a substrate (not shown). Instead, the second extension portion 224B may be connected to a ground pattern (not shown) of the substrate or may be a part of the ground pattern. However, in a plan view, the ground pattern does not exist between the second extension portion 224B and the additional radiation element 230A.

As understood from <FIG>, the multi-resonant antenna10B of the present modification also has a structure which can resonate at the two operating frequencies, one of which is the operating frequency of the main antenna (the first resonance portion) 30A, and the other of which is the operating frequency of the additional radiation element (the second resonance portion) 230A.

As shown in <FIG>, a multi-resonant antenna 10C of a third modification is provided with a third extension portion (a ground portion) 226C in addition to the structure of the multi-resonant antenna 10B of the second modification. Since the multi-resonant antenna 10C is the same as the multi-resonant antenna 10B of the second modification except for the third extension portion 226C, the detailed description of points other than the third extension portion 226C will be omitted.

As shown in <FIG>, the third extension portion 226C extends from an end of the second extension portion 224B in the second predetermined direction. The third extension portion 226C and the additional radiation element 230A do not intersect with each other. In detail, a tip portion of the third extension portion 226C is apart from the additional radiation element 230A. In the present modification, the third extension portion 226C does not protrude forward of the additional radiation element 230A in the front-rear direction. However, the present invention is not limited thereto. The third extension portion 226C may protrude forward of the additional radiation element 230A in the front-rear direction. At any rate, in the lateral direction or the first predetermined direction, a tip of the additional radiation element 230A is apart from the third extension portion 226C and faces the third extension portion 226C. The third extension portion 226C may be formed of a metal member or may be formed of a conductive pattern (not shown) of a substrate (not shown). Alternatively, the third extension portion 226C may be connected to a ground pattern (not shown) of the substrate or may be a part of the ground pattern. However, in a plan view, the ground pattern does not exist between the third extension portion 226C and the additional radiation element 230A.

As understood from <FIG>, the multi-resonant antenna 10C of the present modification also has a structure which can electrically resonate at the two operating frequencies, one of which is the operating frequency of the main antenna (the first resonance portion) 30A, and the other of which is the operating frequency of the additional radiation element (the second resonance portion) 230A.

As shown in <FIG>, a multi-resonant antenna 10D of a fourth modification is provided with an additional radiation element 230D in place of the additional radiation element 230A of the multi-resonant antenna 10A of the first modification. Since the multi-resonant antenna 10D is the same as the multi-resonant antenna 10A of the first modification except for the additional radiation element 230D, the detailed description of points other than the additional radiation element 230D will be omitted.

As shown in <FIG>, the additional radiation element 230D branches off from the second portion <NUM> of the main portion 320A. The additional radiation element 230D has a base portion 232D, which extends from the second portion <NUM> of the main portion 320A in the second predetermined direction, and a first extension portion 234D, which extends in a direction opposite to the first predetermined direction. The additional radiation element 230D is formed in order to correspond to a quarter of a wavelength of a desired operating frequency. When a substrate (not shown) has a ground pattern (not shown), the additional radiation element 230D is formed not to overlap with the ground pattern in a plan view. However, the present invention is not limited. Provided that the additional radiation element 230D has the first extension portion 234D, it may not have the base portion 232D. Moreover, a shape of the first extension portion 234D is not limited to a rectangular shape but may have a wide portion at a tip portion thereof. Furthermore, the multi-resonant antenna 10D of <FIG> may be further added with an extension portion corresponding to the second extension portion 224B shown in <FIG>. Yet furthermore, the multi-resonant antenna 10D of <FIG> may be further added with two extension portions corresponding to the second extension portion 224B and the third extension portion 226C which are shown in <FIG>.

As understood from <FIG>, the multi-resonant antenna 10D of the present modification also has a structure which can electrically resonate at the two operating frequencies, one of which is the operating frequency of the main antenna (the first resonance portion) 30A, and the other of which is the operating frequency of the additional radiation element (the second resonance portion) 230D.

Claim 1:
A multi-resonant antenna (<NUM>) comprising a main antenna (<NUM>) and an additional radiation element (<NUM>), wherein:
the main antenna comprises a main portion (<NUM>), which forms a split ring resonator, and a feeding portion (<NUM>), which branches off from the main portion; and
the additional radiation element extends outward of the main antenna from the main antenna, wherein:
the multi-resonant antenna comprises a substrate with a conductive pattern (<NUM>);
the main portion of the main antenna is formed of a combination of at least one part of the conductive pattern on the substrate and a metal member which is distinct and separated from the substrate;
the multi-resonant antenna comprises a ground portion (<NUM>);
the additional radiation element does not overlap with the ground portion in a plan view, wherein the plan view is a view of the multi-resonant antenna from a direction perpendicular to a plane where the main antenna and the additional radiation element are arranged;
the additional radiation element has a first extension portion (<NUM>) extending in a first predetermined direction (negative X-direction); and
the ground portion has a second extension portion (<NUM>) which is apart from the first extension portion in a second predetermined direction (positive Y-direction) perpendicular to the first predetermined direction and which extends in the first predetermined direction, wherein:
the ground portion has a third extension portion (<NUM>) extending from the second extension portion in the second predetermined direction; and
the first extension portion of the additional radiation element has a tip which is apart from and faces the third extension portion in the first predetermined direction.