JP2006311273A - Loop antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and effectively compensate the frequency deviation of a broad band antenna. <P>SOLUTION: A portion (ss) of a line (s) confronts in parallel to a portion (tt) of a line (t). A variable capacitance element C1 is provided on a metal wiring shared by an outermost circumferential loop Z and a folded dipole. By changing the capacitance of the variable capacitance element C1, a series of frequency bands covering resonance frequencies f<SB>1</SB>and f<SB>2</SB>can be adjusted at the same time. Then, it is possible to compensate a frequency deviation that occurs when a human body or an object exists near an antenna over a wide band. the circumference of the outermost circumferential loop Z is almost equal to wavelength λ<SB>1</SB>corresponding to the resonance frequency f1 in the vicinity of the resonance frequency f<SB>1</SB>. In addition, since current is strong at almost the middle of the metal wiring shared by the outermost circumferential loop Z and the folded dipole, the variable capacitance element C1 is provided almost at the middle, thereby maximizing a variable capacitance range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a broadband transmission / reception antenna having two or more resonance modes, and more particularly to a loop antenna having an effect of simultaneously adjusting the resonance frequency.
This method is very useful for widening an antenna and dynamic tuning (optimization of transmission and reception levels) for an arbitrary frequency within the band.

  An antenna mounted on a mobile phone or a wireless LAN device is often used in an environment where a human body or an object is nearby. There is also a metal body in the vicinity of the antenna mounted on the window glass of the automobile. Thus, when there is a human body or an object in the vicinity of the antenna, the input impedance of the antenna changes under the influence. The influence mainly appears as a deviation of the matching frequency from the use frequency band.

As an antenna apparatus in which such a frequency shift is compensated, for example, an antenna disclosed in Non-Patent Document 1 below is known. A circuit diagram of this conventional automatic matching antenna apparatus is shown in FIG. A matching circuit M10 is provided between the conventional antenna A10 and the receiver R10. The matching circuit M10 is a π-type circuit including an inductor LM2 and variable capacitance elements CM1 and CM3. In this conventional automatic matching antenna apparatus, even when the impedance on the antenna side viewed from the antenna terminal m changes due to the environment near the antenna A10, the amount of change is canceled out by the matching circuit M10, and the matching between the antenna and the receiver is achieved. The capacitances of the variable capacitance elements CM1 and CM3 are variably controlled so as to be maintained.
Ida, Takada, and two others, "Automatic antenna matching device for mobile communication devices by adaptive control", 2004 IEICE General Conference, B-1-262.

  In general, a matching circuit composed of an inductor and a capacitor exhibits narrow band characteristics. Therefore, the conventional technology as described above is effective as an automatic matching device for an antenna having a narrow bandwidth, but cannot be used as an automatic matching device for a broadband antenna having two or more resonance modes. That is, the conventional antenna cannot adjust two or more resonance frequencies simultaneously.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to easily and effectively compensate for a frequency shift of a wideband antenna having two or more resonance modes.

In order to solve the above problems, the following means are effective.
That is, the first means of the present invention comprises a feeding antenna O composed of two sets of feeding points and a feeding unit O in a loop antenna composed of a metal wiring developed substantially in a plane. The outermost loop Z, a folded dipole having a substantially parallel-shaped metal wiring sharing a part with the outermost circumferential loop Z, and a metal wiring constituting a shared portion of the outermost circumferential loop Z and the folded dipole Two other metal wirings that are not shared by the outermost loop Z of the folded dipole and that have no crossing points or contacts arranged inside the outermost loop Z. The loop antenna is formed in a series of frequency bands including the resonance frequency f ₁ of the outermost loop Z and the resonance frequency f _{2 of the} folded dipole. It is to combine.

  The second means of the present invention is the above-mentioned first means, wherein the metal wiring p forming one open curve having two end points close to each other and the metal wiring forming one simple closed curve. The loop antenna is composed of q, a metal wire r forming a simple closed curve, and a variable reactance element inserted on the metal wire p, and the metal wire p and the metal wire q are mutually connected to the line s. The metal wiring p and the metal wiring r share the line t, the metal wiring q and the metal wiring r are arranged apart from each other, and the power supply unit O is configured by the two end points. The portion pp of the metal wiring p located between q and the metal wiring r is provided with the above-mentioned power feeding portion O, and the metal wiring q and the metal wiring r are connected via the power feeding portion O by this portion pp. By the above metal wiring p, the above O over to form a Le dead dipole, and is to form a outermost loop Z above the remaining portion except for the line s and line t the metal wiring p, q, from r.

According to a third means of the present invention, in the first or second means, the variable reactance element is a variable capacitance element.
The fourth means of the present invention is that in any one of the first to third means described above, the variable reactance element is disposed on the outermost loop Z on the opposite side of the power feeding portion O. .

  The fifth means of the present invention is the above-mentioned first to fourth means, wherein a part ss of the line s located near the power feeding part O and a part of the line t located near the power feeding part O are used. In other words, tt is arranged to be opposed to each other by a distance D1.

According to a sixth means of the present invention, in the fifth means, the distance D1 satisfies 0.005 λ2 ≦ D1 ≦ 0.05λ2 with respect to the wavelength λ2 corresponding to the resonance frequency f _2. Is to set.

Further, a seventh means of the present invention is the above-described first to sixth means, in which any metal wiring constituting the loop antenna is connected to one center line passing through the feeding portion O. It is to form in a substantially line symmetrical form.
An eighth means of the present invention is to make the resonance frequency f ₂ higher than the resonance frequency f ₁ in any one of the first to seventh means.

Further, the ninth means of the present invention is the wavelength corresponding to the resonance frequency f ₂ in the interval D2 between the substantially parallel metal wires forming the folded dipole in any one of the first to eighth means. For λ2, it is set to satisfy 0.01λ2 ≦ D2 ≦ 0.2λ2.

Further, a tenth means of the present invention is the pi-type high-pass filter that advances the output phase by 90 ° in any one of the first to ninth means, and is connected in parallel to the high-pass filter. A balanced line-unbalanced line comprising a low-pass filter that delays the output phase by 90 °, and a capacitive element inserted in series between a feeding point of a bias voltage that variably controls the reactance of the variable reactance element and the high-pass filter It is connecting a connector to said electric power feeding part O. FIG.
By the above means of the present invention, the above-mentioned problem can be effectively or rationally solved.

The effects obtained by the above-described means of the present invention are as follows.
That is, according to the first means of the present invention, the effective length of the antenna is dynamically controlled by variably controlling the reactance of the variable reactance element provided in the metal wiring shared by the outermost peripheral loop Z and the folded dipole. Thus, the frequency characteristic of the input impedance at the feeding point of the antenna can be changed. Therefore, according to the variable control of the above, it is possible to change the resonance frequencies f _1, f ₂ above. Assuming that a series of frequency bands including these resonance frequencies f ₁ and f _{2 and} having a VSWR value at a feeding point equal to or less than a predetermined value is a band A, the upper limit frequency of the band A is The lower limit frequency can be appropriately slid (that is, increased or decreased).

In addition, since the value of VSWR at the feeding point is not constant in the above band A, the sensitivity (transmission / reception level) of the antenna is set for an arbitrary frequency included in the use frequency band as a result of this sliding operation. Can be optimized dynamically.
Therefore, according to the first means of the present invention, it is possible to compensate for a frequency shift that occurs when a human body or an object is in the vicinity of the antenna over a wide band.

The open curve or simple closed curve referred to in the second means of the present invention may be interpreted as the axis (center line) of the metal wiring itself. Actually, the metal wiring is formed of a well-known metal conductor such as a metal wire. Needless to say, it has a thickness and a volume.
And also by this 2nd means, the same effect | action and effect as said 1st means can be acquired.

  Further, according to the third means of the present invention, the variable reactance element can be simply provided by a variable capacitance element such as a varactor diode, thereby simplifying the configuration of the target antenna. Can do.

  Further, according to the fourth means of the present invention, since the variable reactance element can be provided in the portion where the current on the metal wiring is the strongest, the frequency compensation range can be more effectively widened.

According to the fifth or sixth means of the present invention, the input impedance of the folded dipole can be adjusted by adjusting the distance D1. Therefore, the voltage standing wave ratio (VSWR at the feeding point) at the resonance frequency f ₂ of the folded dipole can be easily reduced.

  According to the seventh means of the present invention, the gain of the antenna can be increased more effectively. However, it is more desirable to finally determine the wiring pattern of the loop antenna by comprehensively considering the shape and area of the installation area, and also the visual effect.

Moreover, according to the eighth means of the present invention, a wide reception band (or transmission band) can be effectively secured. For example, if the difference between the resonance frequencies (f ₂ −f ₁ > 0) is set as large as possible within a range where the reception band (or transmission band) is not separated into two, this setting allows the target reception band (or transmission band). ) Can be more effectively secured.

According to the ninth means of the present invention, the voltage standing wave ratio (VSWR at the feeding point) at the resonance frequency f ₂ can be further reduced.

  According to the tenth means of the present invention, the bias voltage is favorably applied to the variable reactance element provided in the loop antenna from the unbalanced terminal of the balanced line-unbalanced line connector connected to the loop antenna. Can be applied.

  When an inductor element is used as a component of the variable reactance element, the composite element is operated as a variable inductor element by connecting the inductor element and another variable capacitance element in parallel or in series. good. In this case, the composite can be operated as a variable inductor element by variably controlling the capacitance value of the variable capacitor.

Hereinafter, the present invention will be described based on specific examples.
However, the embodiments of the present invention are not limited to the following examples.

  A plan view of a loop antenna A1 according to an embodiment of the present invention is shown in FIG. The wire pp is a metal wiring part (pp right part) that is located on the right side of the power feeding part O and connects the end point α and the point e, and a metal wiring part that is located on the left side of the power feeding part O and that connects the end point β and the point g. (Pp left part) is a general term. Starting from the end point α, the outermost peripheral loop Z is formed of a metal wire on a route that sequentially passes counterclockwise through points a, b, c, and d and finally returns to the end point β. The line s is a line that connects only two points g and h on the outermost loop Z through only the rectangular inner region surrounded by the outermost loop Z, and is not located on the outermost loop Z. . Similarly, the line t is a line that passes through only the rectangular inner region surrounded by the outermost loop Z and connects two points e and f on the outermost loop Z. The line t and the line s have neither intersection nor contact point.

Let U be a two-dimensional region surrounded by the line segment connecting the left and right end points α and β of the wire pp and the outermost peripheral loop Z. The two-dimensional area U coincides with the rectangular internal area having points a, b, c, and d as vertices.
This two-dimensional region U is composed of the sum region of the three two-dimensional regions P, Q, and R shown in FIG. 1 and the two lines s and t. However, none of P, Q, R, s, and t intersect each other. The metal wiring (wire p) forming an open curve surrounding the two-dimensional region P and the metal wiring q forming the circumference (simple closed curve) of the two-dimensional region Q share a part of the metal wiring s. Similarly, the metal wiring (wire p) forming the open curve surrounding the two-dimensional region P and the metal wiring r forming the circumference (simple closed curve) of the two-dimensional region R share a part of the metal wiring t. Yes.

The wire p is a portion of the metal wiring that surrounds the substantially T-shaped two-dimensional region P in FIG. The wire p forms a substantially T-shaped folded dipole including a power feeding unit O.
The length D2 is a distance between two lines of the substantially parallel shape of the folded dipole. The left end portion of the T-shape is bent at a right angle in the negative direction in the y-axis direction at a portion ahead of the point c. Similarly, the right end portion of the T-shape is bent at a right angle in a negative direction in the y-axis direction at a portion ahead of the point b. The power feeding portion O is provided at the approximate center at the bottom of the T-shape.

  In other words, the wire p surrounding the substantially T-shaped two-dimensional region P forms an open curve, and the two end points of the open curve are the left and right ends of the wire pp placed on the power feeding unit O. It corresponds to points α and β. That is, the two end points α and β of the wire p forming the open curve surrounding the two-dimensional region P are close to each other at the power feeding unit O. The portion pp of the wire p provided with the power supply unit O includes a point g on the wire q that forms the circumference (simple closed curve) of the two-dimensional region Q and a wire r that forms the circumference (simple closed curve) of the two-dimensional region R. The upper point e is connected via a power feeding unit O.

A part ss of the line s faces the part tt of the line t in parallel. The opposing portions ss and tt may be hereinafter referred to as stubs (ss and tt).
The variable capacitance element C1 is provided on the metal wiring shared by the outermost peripheral loop Z and the folded dipole. By changing the capacitance C of the variable capacitance element C1, the effective length of the antenna can be changed. Therefore, according to this variable control, a series of frequency bands including the resonance frequencies f ₁ and f ₂ can be adjusted at the same time. Therefore, a frequency shift that occurs when a human body or an object is in the vicinity of the antenna, It is possible to compensate over a wide band.
In the vicinity of the resonance frequency f ₁ , the circumference of the outermost loop Z is substantially equal to the wavelength λ ₁ corresponding to the resonance frequency f ₁ . In the vicinity of the resonance frequency f ₂ , the length of the folded dipole is approximately half of the wavelength λ ₂ corresponding to the resonance frequency f ₂ .

In addition, the substantial center of the metal wiring sharing the folded dipole with the outermost loop Z is a portion where the current is strong. By providing the variable capacitance element C1 at the substantial center, the variable capacitance range can be maximized. it can.
The appropriate range of the stub width D1 (interval between the wire ss and the wire tt) is 0.005 λ2 ≦ D1 ≦ 0.05λ2, and at this time, the voltage standing wave at the feeding point O at the resonance frequency f ₂ . The ratio (VSWR) can be reduced.
The appropriate range of the distance D2 between the two lines of the folded dipole is 0.01λ2 ≦ D2 ≦ 0.2λ2, and the voltage standing wave ratio (VSWR) at the feeding point O at the resonance frequency f ₂ is further reduced. can do.

FIG. 2 shows a loop antenna A1 and its power supply circuit configuration. The loop antenna A1 is connected to a coaxial line or the like via a balanced line-unbalanced line connector BL and a bias circuit BT. Since the loop antenna A1 is a balanced antenna, a balanced line-unbalanced line connector is required when connecting to a coaxial line that is an unbalanced line. Here, the balanced terminal of the balanced line-unbalanced line connector BL is connected to the balanced terminals α and β of the loop antenna. Moreover, for supplying a bias voltage to the variable capacitance element C1 provided on the metal wire of the loop antenna A1, the inductor element L _BT and consisting of the capacitive element C _BT bias circuit BT a balanced line - unbalanced line connector BL coaxially It is provided between the tracks. Inductor element L _BT, as the RF signal does not leak to the bias supply source side, the capacitor C _BT acts to bias voltage from leaking coaxial line side.

A specific configuration of the balanced line-unbalanced line connector is shown in FIGS. The description will be made assuming that the unbalanced terminal γ is the input side and the balanced terminals α and β are the output side. The balanced line-unbalanced line connector has a configuration in which a high-pass filter that advances the output phase by 90 ° and a low-pass filter that delays the output phase by 90 ° are connected in parallel. In FIG. 3A, a fifth-order π-type high-pass filter (consisting of L _H1 , C _H2 , L _H3 , C _H4 , and L _H5 ) is connected to the terminal β, and a fifth-order π-type low-pass filter (C _L1 , L _L2 , C _L3 , L _L4 , and C _L5 ) are connected to the terminal α. Capacitance so that the bias voltage supplied from the terminal γ is not supplied to the fifth-order π-type high-pass filter side, that is, the direct current that can be generated based on the bias voltage is not grounded through the inductor element L _H1. The element C _C is provided between the fifth-order π-type high-pass filter and the branch point i.

The bias voltage supplied from the terminal γ passes through the fifth-order π-type low-pass filter and is supplied from the terminal α to the variable capacitance element C1 provided in the loop antenna. The ground terminal of the variable capacitance element C1 is grounded from the terminal β by an inductor element L _H5 near the terminal β of the fifth-order π-type high-pass filter. Thus, by making the high-pass filter a π-type, the ground terminal of the variable capacitance element C1 can be grounded.
On the other hand, as shown in FIG. 3B, the low-pass filter may be a T-type low-pass filter (configured with L _L1 , C _L2 , L _L3 , C _L4 , and L _L5 ). 3A and 3B, the filter order is 5, but other values may be used. Increasing the filter order increases the bandwidth.

FIG. 4 shows the voltage standing wave ratio (VSWR) of the loop antenna A1 viewed from the feeding point O when the capacitance C of the variable capacitance element C1 provided in the loop antenna is changed. The vertical axis is the VSWR, and the horizontal axis is the normalized frequency normalized by the frequency f ₀ . The center frequency of the frequency band where VSWR <3 when the capacitance C of the variable capacitance element C1 is 8 pF is f ₀ . When the capacitance C is 8 pF, the bandwidth where VSWR <3 is 0.77f ₀ to 1.23f ₀ .
Further, when the capacitance C is reduced, a series of frequency bands including the resonance frequency f ₁ of the outermost loop and the resonance frequency f _{2 of the} folded dipole can be increased. For example, when the capacitance C is 1 pF, the bandwidth where VSWR <3 is 0.8 f ₀ to 1.3 f ₀ , and when the capacitance C is 0.5 pF, the bandwidth where VSWR <3 is 0.83 f ₀ to 1.36. the f _0.

The frequency characteristics of the radiation pattern on the xy plane when the capacitance C is changed are shown in FIGS. 5 to 7 show radiation patterns on the xy plane when the capacitance C of the variable capacitance element C1 is changed to 8 pF, 1 pF, and 0.5 pF, respectively. 5 to 7 correspond to the lower limit, the center, and the upper limit of each frequency band where VSWR <3, respectively.
All of these nine radiation patterns have a directivity of approximately 8 shapes. The loop antenna A1 according to the embodiment of the present invention operates as a loop antenna near the resonance frequency f ₁ and as a folded dipole near the resonance frequency f ₂ . Since both the approximately one-wavelength loop antenna and the approximately half-wavelength folded dipole have a figure eight directivity, the loop antenna A1 of the embodiment of the present invention also has a figure eight figure over the frequency band where VSWR <3. It becomes directivity.

  In addition, you may introduce | transduce other arbitrary things to the structure of the balanced line-unbalanced line connector (BL) in said Example. With respect to the basic configuration of these balanced line-unbalanced line connectors, various modifications can be made with reference to, for example, “Japanese Patent Application No. 2004-004112: Balanced Line-Unbalanced Line Connector”.

When the loop antenna of the present invention is arranged on a transparent insulator such as a window glass, for example, the advantage of the loop antenna is particularly remarkable. For example, it can be used in any form of use for transmission / reception of radio waves of any frequency that can be used for communication.
Therefore, the loop antenna of the present invention is very useful for mobile communication in a vehicle, for example.

Configuration diagram of loop antenna A1 of Embodiment 1 Circuit diagram showing the configuration of the loop antenna A1 and its feeding circuit Circuit diagram illustrating the configuration of the balanced line-unbalanced line connector BL Circuit diagram illustrating the configuration of the balanced line-unbalanced line connector BL Graph illustrating frequency dependence of voltage standing wave ratio (VSWR) Radiation pattern of loop antenna A1 at C = 8 pF (f = 0.77f ₀ ) Radiation pattern of loop antenna A1 at C = 8 pF (f = f ₀ ) Radiation pattern of loop antenna A1 at C = 8 pF (f = 1.23f ₀ ) Radiation pattern of loop antenna A1 at C = 1 pF (f = 0.80 f ₀ ) Radiation pattern of loop antenna A1 at C = 1 pF (f = 1.05f ₀ ) Radiation pattern of loop antenna A1 at C = 1 pF (f = 1.30f ₀ ) Radiation pattern of loop antenna A1 at C = 0.5pF (f = 0.83f ₀ ) Radiation pattern of loop antenna A1 at C = 0.5pF (f = 1.10f ₀ ) Radiation pattern of loop antenna A1 at C = 0.5pF (f = 1.36f ₀ ) Configuration of conventional automatic matching antenna device

Explanation of symbols

A1: Loop antenna O: Feeding part p: Wire (forms an open curve)
q: Wire (forms a closed curve)
r: Wire (forms a closed curve)
s: shared part of p and q t: shared part of p and r pp: part of p (near the power feeding part O)
ss: a part of s (opposite to tt)
tt: a part of t (opposite part with ss)

D1: Distance between ss and tt D2: Distance between two lines of a folded dipole having a substantially balanced shape C1: Variable capacitance element BT: Bias circuit BL: Balanced line-unbalanced line connector C _H2 , C _H4 , C _L1 , C _L2 , C _L3 , C _L4 , C _L5 , C _C , C _BT : Capacitance elements L _H1 , L _H3 , L _H5 , L _L1 , L _L2 , L _L3 , L _L4 , L _L5 , L _BT : Inductor elements

Claims (10)

A loop antenna composed of metal wiring developed in a substantially planar shape,
One power supply unit O composed of two points and one set of power supply points;
An outermost loop Z provided with the power feeding portion O;
A folded dipole having a substantially parallel-shaped metal wiring sharing a part with the outermost peripheral loop Z;
A variable reactance element inserted on a metal wiring constituting a shared portion of the outermost peripheral loop Z and the folded dipole,
Other metal wiring that is not shared by the outermost peripheral loop Z of the folded dipole is:
Consists of two lines s, t that are arranged inside the outermost loop Z and have no intersections or contacts with each other,
A loop antenna characterized by matching in a series of frequency bands including the resonance frequency f ₁ of the outermost loop Z and the resonance frequency f _{2 of the} folded dipole. A metal wiring p forming one open curve having two end points close to each other;
Metal wiring q forming one simple closed curve;
A metal wire r forming a single simple closed curve;
The variable reactance element inserted on the metal wiring p,
The metal wiring p and the metal wiring q share the line s with each other,
The metal wiring p and the metal wiring r share the line t with each other,
The metal wiring q and the metal wiring r are arranged apart from each other,
The two end points constitute the power feeding unit O,
A portion pp of the metal wiring p located between the metal wiring q and the metal wiring r is:
The power supply unit O is provided, and the metal wiring q and the metal wiring r are connected via the power supply unit O.
The metal wiring p forms the folded dipole,
The remaining part excluding the line s and the line t from the metal wiring p, q, r is
The loop antenna according to claim 1, wherein the outermost peripheral loop Z is formed. The variable reactance element is:
The loop antenna according to claim 1, wherein the loop antenna is a variable capacitance element. The variable reactance element is:
The loop antenna according to any one of claims 1 to 3, wherein the loop antenna is disposed on the outermost peripheral loop Z on the opposite side of the power feeding unit O. A part ss of the line s located near the power feeding part O and a part tt of the line t located near the power feeding part O are:
The loop antenna according to any one of claims 1 to 4, wherein the loop antenna is disposed to be opposed to each other by a distance D1. The distance D1 is
For a wavelength λ2 corresponding to the resonance frequency f ₂ ,
0.005 λ2 ≦ D1 ≦ 0.05λ2
6. The loop antenna according to claim 5, wherein the loop antenna is set so as to satisfy. Any of the metal wires constituting the loop antenna
7. The loop antenna according to claim 1, wherein the loop antenna is formed so as to be substantially line symmetrical with respect to one center line passing through the power feeding portion O. The resonance frequency f ₂ is
Loop antenna according to any one of claims 1 to 7 and greater than the resonant frequency f _1. The interval D2 between the substantially parallel metal wirings forming the folded dipole is:
For a wavelength λ2 corresponding to the resonance frequency f ₂ ,
0.01λ2 ≦ D2 ≦ 0.2λ2
9. The loop antenna according to claim 1, wherein the loop antenna is set so as to satisfy the following. A π-type high-pass filter that advances the output phase by 90 °;
A low-pass filter connected in parallel to the high-pass filter and delaying the output phase by 90 °;
A balanced line-unbalanced line connector having a bias voltage feeding point for variably controlling the reactance of the variable reactance element and a capacitive element inserted in series between the high pass filter is provided in the feeding unit O. The loop antenna according to any one of claims 1 to 9, wherein the loop antenna is connected.

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