JP2008042584A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device which can be made compact and dispenses with an impedance matching circuit using elements of L and C to be a cause of increasing loss. <P>SOLUTION: The antenna device has spiral conductors 11, 12 of which the respective ends 11a, 12a are capacitively coupled with a feeding point 20 and the other ends 11b, 12b are opened. The spiral conductors 11, 12 are formed on planes different from each other and of which the winding direction from one end 11a to the other end 11b of the spiral conductor 11 viewed from an arrow A and the winding direction from one end 12a to the other end 12b of the spiral conductor 12 viewed from the arrow A are in the directions reverse to each other. Thus, the spiral conductors 11, 12 are made compact. Moreover, input impedance is adjusted by capacitance values between the spiral conductors 11, 12 and the feeding point 20, then, the antenna device does not need to use the impedance matching circuit using the elements of L and C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an antenna device, and more particularly to an antenna device having a spiral radiating conductor.

  Some electronic devices are equipped with a wireless communication function using weak radio waves. Since weak radio waves do not require authorization when used, they have been widely used in portable devices such as keyless entry systems for automobiles and security countermeasure devices in recent years. In such a portable device, since it is very important to be small in size, it is desirable that the antenna device incorporated therein is as small as possible.

  However, since the size of the radiation conductor used in the antenna device depends on the frequency to be used, it may be difficult to reduce the size depending on the frequency band. For example, in a car keyless entry system, a weak radio wave having a frequency of about 315 MHz is often used. In this case, one wavelength (= λ) in the air reaches about 952 mm. Therefore, when a normal half-wave dipole antenna is used, the total length of the radiation conductor is required to be about 476 mm, and it cannot be built in a car key.

For this reason, conventionally, an impedance matching circuit composed of elements such as L and C is inserted between the radiation conductor and the RF circuit, thereby enabling the use of a small radiation conductor. However, when an element such as L or C is used in the impedance matching circuit, the insertion loss is greatly increased. Therefore, it is necessary to increase the output of the RF circuit, and the driving time of the battery is shortened.
Japanese Patent Publication No. 6-20163 JP 2002-319809 A

  In order to solve the above-mentioned problem, it is necessary to devise a device such as spirally winding the radiation conductor inside a housing such as an automobile key or bending it into a meander shape. In this case, depending on the shape of the radiation conductor Antenna characteristics vary greatly.

  Therefore, an object of the present invention is to provide an antenna device that can be reduced in size and does not require an impedance matching circuit using elements of L and C that cause an increase in loss.

  An antenna device according to the present invention is an antenna device including first and second spiral conductors, one end of which is capacitively coupled to a feeding point and the other end is opened, and the first and second spiral conductors are mutually connected. Formed in different planes, the winding direction from the one end to the other end of the first spiral conductor viewed from one direction, and the one end to the other end of the second spiral conductor viewed from the one direction The winding direction is opposite to each other.

  According to the present invention, the pair of spiral conductors are wound in opposite directions, and both the spiral conductors are capacitively coupled to the feeding point, so that the spiral conductors can be miniaturized. It becomes possible. In addition, since the input impedance can be adjusted by the capacitance value between the spiral conductor and the feed point, it is necessary to use an impedance matching circuit using elements of L and C that cause an increase in loss. Disappear.

  The antenna device according to the present invention preferably further includes a dielectric block. In this case, the first spiral conductor is formed on one main surface of the dielectric block, and the second main surface of the dielectric block is second. It is preferable to form a spiral conductor. According to this, it is possible to manufacture a small and high-performance antenna device by printing spiral conductors on both surfaces of the dielectric block.

  In this case, the feeding conductor constituting the feeding point, the one end of the first spiral conductor formed at a predetermined interval from the feeding conductor, and the second spiral conductor formed at a predetermined interval from the feeding conductor. The one end is preferably formed on the side surface of the dielectric block. According to this, since it is not necessary to separately use a component for capacitively coupling the spiral conductor and the feeding point, the number of components can be reduced.

  In the present invention, it is preferable that the length of one circumference of the outermost peripheral portions of the first and second spiral conductors is set to about λ / 8 when the wavelength of the center frequency is λ. The total length of the first and second spiral conductors is preferably set to about λ / 3 when the wavelength of the center frequency is λ. Further, the distance between the first spiral conductor and the second spiral conductor is preferably set to about λ / 100, where λ is the wavelength of the center frequency. If these conditions are satisfied, it is possible to sufficiently reduce the overall size while ensuring good antenna characteristics.

  As described above, according to the present invention, it is possible to provide an antenna device that is miniaturized and does not require an impedance matching circuit using L and C elements that cause an increase in loss. Therefore, it can be suitably used as an antenna device for portable electronic devices that are required to be small and power-saving, such as keyless entry systems for automobiles.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic perspective view schematically showing a basic structure of an antenna device 10 according to a preferred embodiment of the present invention, and FIG. 2 is a schematic side view.

  As shown in FIGS. 1 and 2, the antenna device 10 according to the present embodiment includes a first spiral conductor 11 and a second spiral conductor 12. The first and second spiral conductors 11 and 12 are formed on mutually different XY planes. In this embodiment, the positions of the first and second spiral conductors 11 and 12 in the X direction and the Y direction are substantially the same. Is consistent. That is, the first and second spiral conductors 11 and 12 differ only in the position in the Z direction, and the centers of both are substantially coincident.

  The antenna device 10 according to the present embodiment includes capacitors C1 and C2. The capacitor C <b> 1 has one electrode connected to the feeding point 20 and the other electrode connected to one end 11 a of the first spiral conductor 11. The capacitor C <b> 2 has one electrode connected to the feeding point 20 and the other electrode connected to one end 12 a of the second spiral conductor 12. The other ends 11b and 12b of the first and second spiral conductors 11 and 12 are both open.

  Furthermore, when the antenna device 10 according to the present embodiment is viewed from the Z direction, the winding direction from the one end 11a to the other end 11b of the first spiral conductor 11 and the other end from the one end 12a of the second spiral conductor 12 are different. The winding directions around the end 12b are opposite to each other. Specifically, when viewed from the arrow A shown in FIG. 1, the first spiral conductor 11 is wound counterclockwise (counterclockwise) from the one end 11a to the other end 11b. The second spiral conductor 12 is wound clockwise (clockwise) from one end 12a to the other end 12b.

  In the present embodiment, both the first and second spiral conductors 11 and 12 have a quadrangular outer diameter. When the length in the X direction at the outermost peripheral portion is Lx and the length in the Y direction at the outermost peripheral portion is Ly, it is preferable that both be set to about λ / 32 when the wavelength of the center frequency is λ. In other words, it is preferable that the length of one circumference of the outermost peripheral portions of the first and second spiral conductors 11 and 12 is set to about λ / 8. If the length of the outermost peripheral portion is made longer than this, the outer diameters of the spiral conductors 11 and 12 become larger, so that it is difficult to reduce the size of the antenna device 10, while the length of the outermost peripheral portion is made longer than this. If the length is too short, the antenna characteristics deteriorate due to an increase in line capacitance. On the other hand, if the outermost circumferences of the first and second spiral conductors 11 and 12 are set to about λ / 8, the size of the antenna device 10 can be reduced while obtaining good antenna characteristics. It becomes.

  The total length of the first and second spiral conductors 11 and 12 is preferably set to about λ / 3 when the wavelength of the center frequency is λ. If the overall length of the spiral conductors 11 and 12 is made longer than this, the outer diameter of the spiral conductors 11 and 12 will increase or the line-to-line capacitance will increase. On the other hand, if the overall length is made shorter than this, It becomes difficult to obtain a desired impedance. On the other hand, if the total length of the first and second spiral conductors 11 and 12 is set to about λ / 3, the size of the antenna device 10 can be reduced while obtaining good antenna characteristics. Become.

  Furthermore, the distance H in the Z direction between the first spiral conductor 11 and the second spiral conductor 12 is preferably set to about λ / 100, where λ is the wavelength of the center frequency. If the distance H in the Z direction is made longer than this, the antenna device 10 becomes larger. On the other hand, if the distance H is made shorter than this, the magnetic influence between the two spiral conductors 11 and 12 can be ignored. As a result, the antenna characteristics deteriorate. In contrast, if the distance in the Z direction is set to about Hλ / 100, it is possible to reduce the size of the antenna device 10 while obtaining good antenna characteristics.

Regarding the capacitors C1 and C2 for capacitively coupling the feeding point 20 and the first and second spiral conductors 11 and 12, as shown in FIG. 1, a part of the wire connected to the feeding point 20 and the first And it can comprise by arrange | positioning a part of wire which comprises the 2nd spiral conductors 11 and 12 in parallel. Therefore, the capacitance value of the capacitor C1, C2 can be adjusted by the length L _H of the parallel portion of the wire. When the capacitance values of the capacitors C1 and C2 are changed, the frequency at which a desired impedance (for example, 50Ω) is obtained varies. Therefore, the length L _H of the parallel portion of the wire may be adjusted according to the target frequency. .

  The antenna device 10 according to the present embodiment having the above configuration functions in principle as a ½ wavelength dipole antenna. However, its outer diameter is very small compared to a general half-wave dipole antenna, and therefore it can be accommodated in a casing such as a car key. In addition, the frequency at which the desired impedance (eg, 50Ω) can be fine-tuned, so it can be connected to an RF circuit without going through an impedance matching circuit that uses L or C elements that cause an increase in loss. It becomes. As a result, since the insertion loss is extremely reduced, the output of the RF circuit can be suppressed, so that the life of the battery can be extended.

  FIG. 3 is a schematic perspective view showing a specific configuration example of the antenna device 10 according to the present embodiment.

  As shown in FIG. 3, when the antenna device 10 is actually manufactured, a plate-like dielectric block 19 is prepared, the first spiral conductor 11 is formed on one main surface 19a, and the other main block 19 is formed. A second spiral conductor 12 (not shown in FIG. 3) is formed on the surface 19b. Further, on the side surface 19c of the dielectric block 19, the portion including the one end 11a of the first spiral conductor 11, the portion including the one end 12a of the second spiral conductor 12, and the feeding point 20 (FIGS. 2) is formed. The thickness of the dielectric block 19 corresponds to the distance H shown in FIGS.

The material of the dielectric block 19 is not particularly limited, but a Ba—Nd—Ti-based material (relative permittivity of 80 to 120), Nd—Al—Ca—Ti based material (relative permittivity of 43 to 46). ), Li—Al—Sr—Ti (relative permittivity 38 to 41), Ba—Ti based material (relative permittivity 34 to 36), Ba—Mg—W based material (relative permittivity 20 to 22), Mg— Use Ca-Ti-based materials (relative permittivity 19-21), sapphire (relative permittivity 9-10), alumina ceramics (relative permittivity 9-10), cordierite ceramics (relative permittivity 4-6), etc. It can be manufactured by firing using a mold. It is possible to reduce the size of the antenna device by the dielectric constant of the dielectric. Specifically, when the relative dielectric constant of the dielectric used is ε,
1 / √ε
The size can be reduced.

  Silver, silver-palladium, silver-platinum, copper, or the like can be used as the material of the first and second spiral conductors 11 and 12 and the power supply conductor 21, and these materials can be used by a method such as screen printing or transfer. After applying the paste containing, it can be formed by baking under a predetermined temperature condition.

  The power supply conductor 21 formed on the side surface 19c of the dielectric block 19 is formed at the electrode portion 21a facing the vicinity of the ends 11a, 12a of the first and second spiral conductors 11, 12 at a predetermined interval, and at the end. And a wide portion 21b.

The capacitance formed by the electrode portion 21a of the power supply conductor 21 and the vicinity of the one end 11a of the first spiral conductor 11 corresponds to the capacitance C1 shown in FIGS. Similarly, the capacitance formed by the electrode portion 21a of the power supply conductor 21 and the vicinity of the one end 12a of the second spiral conductor 12 corresponds to the capacitance C2 shown in FIGS. That is, the length of the portion of the first and second spiral conductors 11 and 12 facing the electrode portion 21a in the vicinity of the ends 11a and 12a is equal to the length of the parallel portion shown in FIGS. corresponding to the length _{L H.} Therefore, in order to adjust the capacitance values of the capacitors C1 and C2, the lengths near the ends 11a and 12a of the first and second spiral conductors 11 and 12 may be adjusted.

  On the other hand, the wide portion 21b of the power supply conductor 21 is used as a terminal for connecting to a wiring on a printed board (not shown). In order to ensure sufficient electrical and mechanical connection between the printed circuit board and the antenna device 10, it is preferable to set the area of the wide portion 21b sufficiently wide.

  As described above, the antenna device 10 according to the present embodiment can be manufactured simply by forming a conductor on the surface of one dielectric block.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in the above embodiment, the planar shape of the spiral conductors 11 and 12 is a quadrangle, but it is not essential that the outer diameter is a quadrangle, and a circular or octagonal shape may be used. It does not matter.

  Hereinafter, although the Example of this invention is described, this invention is not limited to this Example at all.

First, assuming an antenna having the same structure as the antenna device 10 shown in FIGS. 1 and 2, the test frequency was set to 314.36 MHz (≈315 MHz = λ ₃₁₅ ) by the FDTD method (Finite Difference Time Domain Method). The case characteristics were analyzed.

The condition is that the lengths in the X direction and Y direction at the outermost peripheral portions of the first and second spiral conductors 11 and 12 are Lx and Ly, respectively (see FIG. 1), and the first and second spiral conductors. 11 and 12 in the Z direction is H (see FIGS. 1 and 2), the total length of the first and second spiral conductors 11 and 12 is L _wire, and the first and second spiral conductors 11 , 12 is Lp (see FIG. 1), the radii of the first and second spiral conductors 11 and 12 are ρ, and the distance from the feeding point 20 to the capacitors C1 and C2 is Lv1 (FIG. 2). (See FIG. 2), the distance from the capacitors C1 and C2 to the winding portions of the first and second spiral conductors 11 and 12 is Lv2 (see FIG. 2), and the distance between the electrodes of the capacitors C1 and C2 is δ (see FIG. 2), set these as shown in Table 1. It was.

The length _{L H} of the parallel portions of the wire forming the capacitor C1, C2, was changed 2 mm, 4 mm, in three steps of 6 mm.

The analysis result of the resistance component (R _in ) of the input impedance is shown in FIG. Moreover, the analysis result of the reactance component (X _in ) of the input impedance is shown in FIG.

As shown in FIGS. 4 and 5, when L _H = 6 mm, the resistance component (R _in ) of the input impedance is about 50Ω and the reactance component (X _in ) of the input impedance is 314.36 MHz as the test frequency. Almost zero. The frequency of such characteristics can be obtained, it was confirmed that the move as in the high-frequency direction to shorten the L _H.

The analysis result of the radiation pattern when L _H = 6 mm is shown in FIG. 6A shows a radiation pattern on a plane parallel to the z axis, and FIG. 6B shows a radiation pattern on a plane parallel to the x axis. Further, in FIG. 6 (a), the solid lines represent the E _theta, a broken line indicates the E _phi. When the gain in the x direction is calculated from the analysis result shown in FIG. 6, it is confirmed that the gain is 1.67 dBi, and an extremely high gain can be obtained.

1 is a schematic perspective view schematically showing a basic structure of an antenna device 10 according to a preferred embodiment of the present invention. FIG. 2 is a schematic side view of the antenna device 10 shown in FIG. 1. 1 is a schematic perspective view showing a specific configuration example of an antenna device 10. FIG. It is a graph which shows the analysis result of the resistance component ( _Rin ) of input impedance. Is a graph showing the analysis results of the reactance component of the input impedance (X _in). It is a graph which shows the analysis result of a radiation pattern.

Explanation of symbols

10 Antenna Device 11 First Spiral Conductor 11a First Spiral Conductor One End 11b First Spiral Conductor Other End 12 Second Spiral Conductor 12a Second Spiral Conductor One End 12b Second Spiral Dielectric block 19a Dielectric block 19a One main surface 19b of the dielectric block The other main surface 19c of the dielectric block Side surface 20 of the dielectric block 20 Feed point 21 Feed conductor 21a Electrode portion 21b Wide portions C1, C2 Capacitance

Claims (6)

An antenna device including first and second spiral conductors having one end capacitively coupled to a feeding point and the other end open,
The first and second spiral conductors are formed on different planes;
A winding direction from the one end to the other end of the first spiral conductor as viewed from one direction, and a winding direction from the one end to the other end of the second spiral conductor as viewed from the one direction. Antenna devices characterized in that they are in opposite directions.   A dielectric block is further provided, the first spiral conductor is formed on one main surface of the dielectric block, and the second spiral conductor is formed on the other main surface of the dielectric block. The antenna device according to claim 1.   The power supply conductor constituting the power supply point, the one end of the first spiral conductor formed at a predetermined interval from the power supply conductor, and the second spiral shape formed at a predetermined interval from the power supply conductor. The antenna device according to claim 2, wherein the one end of the conductor is formed on a side surface of the dielectric block.   The length of one circumference of the outermost peripheral portions of the first and second spiral conductors is set to about λ / 8 when the wavelength of the center frequency is λ. The antenna device according to any one of 1 to 3.   5. The total length of the first and second spiral conductors is set to about λ / 3 when the wavelength of the center frequency is λ. 5. The antenna device according to 1. 6. The distance between the first spiral conductor and the second spiral conductor is set to about λ / 100, where λ is a wavelength of a center frequency. The antenna apparatus as described in any one.

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