JP2009111999A - Multiband antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiband antenna, in which a radiation line of which one end is connected with a feeding point and the other end is an open end is formed as a loop-like line having a return part in the middle, capable of easily performing a frequency adjustment for each frequency band while accomplishing, with space saving, a multiband antenna which resonates over a plurality of frequencies, and is capable of widening bands and obtaining excellent gain and radiation characteristic within each frequency band by providing a capacitive coupling section in which a part of the line is disposed face-to-face via dielectrics. <P>SOLUTION: A multiband antenna is provided in which a line of which one end is connected with a feeding point and the other end is an open end is returned in the middle to become a loop-like line, a capacitive coupling section is provided in a part of which the dielectrics are disposed, and which resonates over a plurality of frequencies. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antenna device, and more particularly to an antenna device capable of supporting a plurality of bands (transmission / reception bands) and a wireless communication device using the antenna device.

In recent years, wireless communication devices such as mobile phones are rapidly spreading, and the bandwidth used for communication is also wide-ranging. In particular, in recent mobile phones, there are an increasing number of examples in which a plurality of transmission / reception bands are provided in a communication device such as a single mobile phone as called a dual band method, a triple band method, a quad band method, or the like.
Under such circumstances, development of a multiband antenna capable of supporting a plurality of transmission / reception bands as described above is urgently required as an antenna constituting a built-in antenna circuit of a mobile phone or the like. Furthermore, due to the demand for further miniaturization of wireless communication devices such as mobile phones, it is necessary not only to achieve miniaturization, but also to have higher performance despite the increasing trend of antenna components.

A multiband antenna equipped in a wireless communication device used in a conventional mobile phone or the like is, for example, a small multiband antenna configured by connecting a plurality of chip antennas having different resonance frequencies to one feeding point. Has been proposed (Cited document 1).
However, in the above-described multiband antenna, it is necessary to provide a chip antenna individually according to the resonance frequency, and in response to the demand for further miniaturization associated with the expansion of the downsizing, weight reduction, or multifunctionality of communication devices, In some cases, miniaturization of the multi-band antenna is hindered, and this cannot be satisfied.

In response to such a demand for miniaturization, in another example, a single radiating electrode formed in a loop shape is provided on a substrate such as a dielectric or a magnetic material, and an open end thereof is set as a predetermined electrode on the power feeding unit side. The resonant frequency of the fundamental resonance mode and the higher-order resonance can be obtained without significantly changing the resonant frequency of the fundamental resonant mode of the radiation electrode by forming a coupling capacitor by opposingly arranging them with an interval of, and adjusting the coupling capacitance. The interval with the resonance frequency of the mode is variably controlled (Cited document 2).
JP 09-199939 A JP 2002-158529 A

However, in the above-described multiband antenna, the radiation electrode is miniaturized by using a dielectric material or a magnetic material. However, since the entire radiation electrode is provided on the base, Q is 100. There is a problem that the resonance is sharp, the frequency band is narrow, the capacitive effect of the radiation electrode is strong, and each resonance frequency varies greatly depending on the length and width of the radiation electrode, making it difficult to set. Furthermore, no consideration has been given to the control of the resonance frequency of the fundamental resonance mode.
Therefore, the present invention has been made in view of the various problems as described above, and its purpose is to save a space for a multiband antenna that can be widened and obtains good gain and radiation characteristics in each frequency band. An object of the present invention is to provide a multiband antenna that can be easily adjusted in frequency for each frequency band.

  In the present invention, a radiation path in which one end is connected to a feeding point and the other end is an open end is formed as a loop-like line having a folded portion in the middle, and a capacitive coupling in which a part of the line is arranged to face each other via a dielectric. A multiband antenna that resonates at a plurality of frequencies, wherein the first resonance frequency f1 is controlled by a line length from a feeding point to an open end of the loop-shaped line, and a capacitive coupling unit from the feeding point And the second resonance frequency f2 is controlled by the length of the line and the capacitance of the capacitive coupling portion, and the loop from the feeding point is used. The third resonance frequency f3 is controlled by using a part of the continuous loop-shaped line up to the part, and the second resonance frequency f2 and the third resonance frequency f3 are controlled by the line length. Higher order than frequency f1 It is a multi-band antenna, which is a frequency.

FIG. 16 shows a schematic diagram of a general inverted-F antenna. When the line is resonated at λ / 4 (λ; wavelength) of the fundamental wave (first resonance frequency f1), the current becomes maximum at the feeding point and becomes zero at the open end. The voltage is maximum at the open end. Considering impedance matching at the feeding point, the line can resonate with the third harmonic of the fundamental wave, so that a multiband antenna having a frequency ratio of 1 (fundamental wave) to 3 can be obtained simply. .
However, if the frequency band of a wireless communication device currently used is a typical mobile phone frequency band, GSM (Global System for Mobile Communications) is about 900 MHz, DCS (Digital Cellular System) 1800 or PCS (Personal
(Communications Service) 1900 is a frequency band of 1.8 to 1.9 GHz, and has a one-to-two relationship in terms of frequency ratio.
For this reason, in the multiband antenna, when the resonance frequency of the fundamental wave is the first resonance frequency f1, it is necessary to cause the second resonance within a band including about twice this frequency.

A multiband antenna up to the present invention is shown in FIG. By turning the line back in the middle to form a loop-shaped line, the weak coupling due to the parasitic capacitance generated between the lines is used to reduce the frequency of the third harmonic as shown in FIG. However, this alone was not enough to reduce the frequency.
Therefore, in the multiband antenna of the present invention, a capacitive coupling portion having a dielectric constant disposed on a part of the loop-shaped line and having a higher dielectric constant than other parts is provided, and the frequency (second frequency) is about twice that of the fundamental wave. The resonance frequency f2) is a multiband antenna having a resonance frequency ratio of about 1 (fundamental wave) to 2.

It is preferable that the capacitive coupling portion be provided between the portion where the current value of the third harmonic is zero and the voltage reaches the maximum and the open end of the loop-shaped line. The capacitance provided in the capacitive coupling portion is short-circuited in terms of high frequency. The inventors resonate the loop-shaped line at a third frequency (third resonance frequency f3) in the path passing through the capacitive coupling portion, and the second resonance frequency f2 and the third resonance frequency. The idea was to create a multi-band antenna having a wider bandwidth by making f3 close to each other and overlapping frequency bands excellent in the voltage standing wave ratio VSWR.
In the present invention, the second resonance frequency f2 and the third resonance frequency f3 are close to each other, but may be separated from each other, may be substantially the same frequency, and may be appropriately set according to the frequency to be handled. Set it.

A first line having one end connected to a feeding point; a second line connected to the other end of the first line; and a third line connected to the other end of the second line. It is preferable that the first line and the third line be opposed to form a capacitive coupling portion.
The substrate is preferably a printed substrate, and FR4 (glass epoxy substrate) or the like can be used. A ceramic substrate such as an alumina substrate can also be used. The first line and the third line are lines provided on the substrate, and are preferably formed by printing or etching with a good conductor such as low resistance Au, Ag, or Cu. The second line is easy to process, but is preferably formed of a sheet metal such as phosphor bronze that is not easily deformed by an external force.

The capacitive coupling part is preferably provided on the substrate, and the first line and the third line are arranged on the same surface of the substrate with a predetermined interval, or the first line and the third line are different surfaces of the substrate. It can be formed by being opposed to each other at a predetermined interval.
The first line and the third line are configured as belt-like lines, and a coupling capacitor can be formed by making the edges face each other or face each other with a substrate interposed therebetween. Further, a capacitive coupling conductor (electrode pattern) extending from the first line and / or the third line may be provided to form the capacitive coupling part.

In the present invention, an extended conductor portion is provided on the second line and connected to a capacitor forming electrode formed on the substrate, and the capacitor forming electrode and the third line are arranged on the same surface of the substrate with a predetermined interval. Alternatively, a capacitive coupling portion may be additionally formed by arranging the capacitance forming electrode and the third line so as to face each other on a different surface of the substrate with a predetermined interval.
In addition, a dielectric piece having a dielectric constant different from that of the substrate is disposed on the substrate, a capacitance forming electrode is formed on the dielectric piece, the second line is connected to the extension conductor portion, and the capacitor is opposed to the third line. A coupling portion may be additionally formed.

  In the present invention, the fourth resonance frequency f4 may be controlled by providing a branch line that further branches from the feeding point side of the loop-shaped line. A branch line may be arranged in parallel with a part of the loop-shaped line. In adjusting the resonance frequency, it is preferable that the branch line and the loop line have less electromagnetic interference because they can be adjusted independently. When electromagnetic coupling occurs, it is difficult to adjust the resonance frequency, but the branch line and the loop line can be shortened, which is preferable in downsizing.

  According to the present invention, it is possible to easily adjust the frequency for each frequency band while realizing a multiband antenna capable of widening the band and obtaining a good VSWR characteristic in each frequency band in a space-saving manner. A multiband antenna can be provided.

Embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not limit the invention according to the claims, and all the combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent.
First, basic features of the multiband antenna of the present invention will be described. FIG. 1 is a diagram for explaining a basic configuration of a multiband antenna according to the present invention. As shown in FIG. 1, the multiband antenna 1 of the present invention is provided with a feeding point at one end of a loop-shaped line 10 that is a radiating electric circuit, and is connected to a high-frequency circuit 20 and the other end is an open end. 35.
The loop-shaped line 10 includes a folded portion 40, and at least a part of the line between the feeding point and the folded portion 40 is juxtaposed with the line from the folded portion 40 to the open end. Furthermore, in this embodiment, a capacitive coupling portion 35 is provided in which a capacitance is formed between the open end 35 of the radiation path and the line from the feeding point side to the folded portion 40. A shunt inductor is connected as a matching circuit 200 between the feeding point and the high-frequency circuit 20.

FIG. 2 shows an equivalent circuit of the multiband antenna. Here, the parasitic capacitance generated between the lines or between the line and the ground is omitted. In the figure, inductors L1 to L3 represent inductance components formed by the loop-shaped line 10, and a capacitor Cg represents a capacitance component formed by the capacitive coupling portion 35.
The inductors L <b> 1 to L <b> 3 are equivalent inductances formed by a loop line portion, and the inductor L <b> 1 is an inductance formed between the capacitive coupling portion 35 and the folded portion 40. The inductor L2 is an inductance formed between the folded portion 40 and the open end 35. The inductor L3 is an inductance formed between the feeding point and the folded portion 40.

The multiband antenna of the present invention is configured to resonate at the first to third frequencies. FIG. 3A to FIG. 3C are diagrams for explaining the first to third resonances.
The fundamental wave is configured to resonate at the first resonance frequency f1, and is formed by a line having an electrical length that is approximately ¼λ of the wavelength λ.
It consists of a series circuit of inductors L1 to L3. The second resonance is generated by a series resonance circuit of inductors L2 and L3 and a capacitor Cg, and the third resonance is generated by a series resonance circuit of inductors L1 and L3. A parasitic capacitance (not shown) is connected in parallel with the inductor, or is connected between the ground.

As shown in the frequency characteristic diagram of the multiband antenna of FIG. 4, when the entire line length of the loop-shaped line 10 is increased, the resonance frequency f1 in the first frequency band, the resonance frequency f2 in the second frequency band, The resonance frequency f3 in the third frequency band (resonance frequency f3 in the figure is omitted) moves to the low frequency side, and when it is shortened, it moves to the low frequency side.
The second resonance frequency f2 can be controlled by the coupling capacitance formed in the capacitive coupling unit 35 when the entire line length of the loop-shaped line is constant. As shown in the frequency characteristic diagram of the multiband antenna shown in FIG. 5, the second resonance frequency f2 and the third resonance frequency f3 are brought close to each other to widen the frequency band having an excellent voltage standing wave ratio. Is possible.

FIG. 6 is a perspective view of a multiband antenna according to the present invention. In the drawing, the substrate 45 is shown in a transparent manner so that the structure on the back side of the substrate becomes clear. A non-ground region without a ground pattern is formed on the substrate, and is soldered to the end of a line 10a (first line) extending from the ground region to the non-ground region. A loop-shaped line 10b (second line) made of sheet metal is disposed. The line 10b is folded back to the end side of the line 10a, reaches the back of the substrate through a notch provided in the substrate, extends horizontally to the end side along with the conductor on the main surface side, It connects with the track | line 10c (3rd track | line) formed in the back surface of the board | substrate 45. FIG. The line 10c is arranged to face the line 10a via the substrate 45 to form a capacitor Cg. The end side of the line 10 a is configured as a capacitive coupling unit 30.
The effect can be reduced by standing the line 10b on the substrate and separating the distance from the ground region. Further, in such a multiband antenna, Q can be 100 or less, and the band can be widened. If the Q of the multi-band antenna is too small, the function as an antenna is deteriorated. More preferably, it is 15-50.

  In this embodiment, the conductor 10b is folded on the back side of the substrate, but may be connected to the line 10c through a through hole provided in the folded substrate on the main surface side. Alternatively, the line 10c may be provided on the main surface so that the edge of the line 10c faces the line 10a, and the end of the line 10b turned back on the main surface side may be connected.

(Example 1)
Embodiments according to the present invention will be described in detail with reference to the drawings. FIG. 7 is a diagram for explaining a multiband antenna according to an embodiment of the present invention. The basic configuration of the multiband antenna of this embodiment is substantially the same as that shown in FIG.
The multiband antenna shown in FIG. 7 is provided with a capacitive coupling conductor 10d at the end of a line 10a (first line) extending to the non-ground region, and a line 10b (second line) connected to the end is provided. The main surface side conductor 10b1 and the back surface side conductor 10b2 of the substrate 45 are divided and connected by through holes provided in the substrate 45. A line 10c (third line) connected to the end of the line 10b is opposed to the capacitive coupling conductor 10d via the substrate 45 to form a capacitive coupling 30. The end of the line 10 c further extends from the capacitive coupling unit 30.
FIG. 8 is a plan view of the capacitive coupling portion 30 as viewed from the upper surface side of the substrate. The capacitive coupling conductor 10d is formed with a length a, and the entire surface faces the line 10c (length b).
FIG. 9 shows an equivalent circuit of the multiband antenna according to the present embodiment. The line 10c (third line) is formed longer than the capacitive coupling conductor 10d, and the inductor L2-2 is connected to the end of the capacitor Cg accordingly. In this case, resonance due to the series resonance circuit of the inductors L2-2 and L3 and the capacitor Cg appears. However, if the extension is short, the resonance point becomes higher than the frequency at which the multiband antenna is used.

FIG. 10 is a frequency characteristic diagram of the VSWR of the multiband antenna according to the present invention. No. No. 1 is used as a reference, and the capacitive coupling conductor 10d is a sample in which the length a is increased to increase the coupling. No. 2 is a sample in which the extension of the line 10c is shortened. When the coupling of the capacitive coupling part 3 is strengthened, the VSWR characteristic on the high frequency side moves to the low frequency side, and if the extension of the line 10c is shortened, the VSWR characteristic on the high frequency side is not greatly affected. The VSWR characteristics could be controlled. Note that, in the loop-shaped line 10, when the length of the line 10b was changed, the VSWR characteristics on both the low frequency side and the high frequency side were changed.
According to this example, a broadband multi-antenna can be obtained with one loop-shaped line.

(Example 2)
FIG. 11 is a side view of a multiband antenna according to another embodiment.
In the multiband antenna shown in FIG. 11, a line 10b (second line) is connected to an end of a line 10a extending to a non-ground region, and the line 10b is folded on the main surface side of the substrate 45 and is connected to the back surface of the substrate. It is connected to the formed belt-like electrode through a through hole. The strip electrode constitutes a capacitive coupling conductor 10d and a line 10c across a connection point with the through hole.
Also in this example, a broadband multi-antenna can be obtained with one loop-shaped line.

(Example 3)
FIG. 12 is a side view of a multiband antenna according to another embodiment.
The multiband antenna shown in FIG. 12 is provided with an extended conductor portion 16 in the middle of the line 10b located on the main surface side of the substrate 45, and is connected to the capacitance forming electrode 10d formed on the substrate. The electrode 10d for use and the line 10c are arranged facing each other to form the capacitive coupling portion 30. Also in this example, a broadband multi-antenna can be obtained with one loop-shaped line.

Example 4
FIG. 13 is a perspective view of a multiband antenna according to another embodiment, and FIG. 14 is a side view thereof. FIG. 15 is a schematic diagram of a multiband antenna.
The multi-antenna according to the present embodiment includes a branch line that branches from the feeding point side of the loop line 10 and controls the fourth resonance frequency f4. The branch line is juxtaposed with the line 10b of the loop line. Also in the present embodiment, a broadband multi-antenna can be obtained with one loop line, and the fourth resonance frequency f4 can be controlled with the branch line.

  According to the present invention, it is possible to easily adjust the frequency for each frequency band while realizing a multiband antenna capable of widening the band and obtaining good gain and radiation characteristics in each frequency band in a space-saving manner. A possible multiband antenna can be provided.

It is a schematic diagram of the multiband antenna which concerns on one Example of this invention. 1 is an equivalent circuit diagram of a multiband antenna according to an embodiment of the present invention. It is an equivalent circuit diagram of three resonant circuits of the multiband antenna which concerns on one Example of this invention. It is a frequency characteristic figure of VSWR of the multiband antenna which concerns on one Example of this invention. It is a frequency characteristic figure of VSWR of the multiband antenna which concerns on one Example of this invention. It is a perspective view of the multiband antenna which concerns on the other Example of this invention. It is a perspective view of the multiband antenna which concerns on the other Example of this invention. It is a plane enlarged view of the capacitive coupling part of the multiband antenna which concerns on the other Example of this invention. It is the equivalent circuit schematic of the multiband antenna which concerns on the other Example of this invention. It is a frequency characteristic figure of VSWR of the multiband antenna which concerns on the other Example of this invention. It is a side view of the multiband antenna which concerns on the other Example of this invention. It is a side view of the multiband antenna which concerns on the other Example of this invention. It is a perspective view of the multiband antenna which concerns on the other Example of this invention. It is a side view of the multiband antenna which concerns on the other Example of this invention. It is a schematic diagram of the multiband antenna which concerns on the other Example of this invention. It is a schematic diagram of the conventional inverted F antenna. It is a schematic diagram of the conventional multiband antenna. It is a frequency characteristic figure of VSWR of the conventional multiband antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multiband antenna 10 Loop line 20 High frequency circuit 30 Capacitance coupling part 45 Board | substrate

Claims (9)

A radiation path whose one end is connected to the feeding point and the other end is an open end is formed as a loop-shaped line having a folded part in the middle, and a part of the line is provided with a capacitive coupling part arranged oppositely via a dielectric. A multiband antenna that resonates at multiple frequencies,
The first resonance frequency f1 is controlled by the line length from the feed point to the open end of the loop-like line, and the line from the feed point to the capacitive coupling part and the discontinuous loop form from the capacitive coupling part to the folded part Using a part of the line, the second resonance frequency f2 is controlled by the line length and the capacitance of the capacitive coupling unit,
Using a part of a continuous loop-shaped line from the feeding point to the folded portion, the third resonance frequency f3 is controlled by the line length,
The multiband antenna, wherein the second resonance frequency f2 and the third resonance frequency f3 are higher-order resonance frequencies than the first resonance frequency f1.   2. The multiband antenna according to claim 1, wherein the second resonance frequency f <b> 2 and the third resonance frequency f <b> 3 are close to each other to widen a frequency band having an excellent voltage standing wave ratio.   The loop line includes a first line having one end connected to a feeding point, a second line connected to the other end of the first line, and a third line connected to the other end of the second line. The multiband antenna according to claim 1, wherein the first line and the third line are opposed to each other to form a capacitive coupling unit.   A substrate supporting a multiband antenna is provided, the first line is formed on the first surface of the substrate, the third line is formed on the second surface and arranged to face each other, and the second line is disposed on the substrate. The multiband antenna according to claim 3, wherein the multiband antenna is erected on the first surface side and the second surface side.   A substrate for supporting a multiband antenna is provided, the first line and the third line are formed on the first surface of the substrate, arranged so that the edges of each other face each other, and the second line stands on the substrate. The multiband antenna according to claim 3, wherein the multiband antenna is provided.   The first line is provided with an extended conductor extending from a connection portion with the second line, and the extended conductor is opposed to the third line to form a capacitive coupling conductor. The multiband antenna according to 4 or 5. The loop line includes a first line having one end connected to a feeding point, a second line connected to the other end of the first line, and a third line connected to the other end of the second line. ,
An extended conductor portion extending in the middle of the second line to the substrate side is provided, connected to a capacitor forming electrode formed on the substrate, and the capacitor forming electrode and the third line are on the same surface of the substrate Arrangement is made so that edges are opposed to each other with a predetermined interval, or the capacitance forming electrode and the third line are arranged opposite to each other on a different surface of the substrate with a predetermined interval to form the capacitive coupling portion. The multiband antenna according to claim 1 or 2, wherein the multiband antenna is provided.   The multiband antenna according to any one of claims 1 to 7, wherein a branch line that branches from a feeding point side of the loop-shaped line is provided to control the fourth resonance frequency f4.   The multiband antenna according to claim 8, wherein the branch line is juxtaposed with the loop line.

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