JP2015164270A - Antenna device and radio communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna device and radio communication equipment capable of achieving size reduction and communication at a plurality of frequencies.SOLUTION: The antenna device 1 is a helical antenna whose conductor is formed into a spiral shape and includes a first helical antenna 10 and a second helical antenna 11 different in self-resonant frequency from each other, and a loop antenna 12 with a feeding section 20. Each of the first helical antenna 10 and the second helical antenna 11 is disposed at a feedable position through electromagnetic coupling with the loop antenna 12.

Description

  The present invention relates to an antenna device and a wireless communication device.

  Miniaturization of wireless communication terminals is one of important issues. A small antenna using a self-resonant action of a helical antenna in which a conductor is formed in a spiral shape is known (for example, Patent Document 1 and Non-Patent Document 1). Normal mode helical antennas are representative of small antennas, and can be self-resonant even with a small structure.

JP 2003-163531 A

Yoshihide Yamada et al. “Design Method and Performance of Small Normal Mode Helical Antenna” Special Issue on Antenna and Propagation Technology that Combines Technologies that Support Wireless Systems p.894-906.

  On the other hand, development of multi-band wireless technology is required in order to effectively use frequencies in response to an increase in traffic in future wireless communication systems. Research and development of ultra-small multiband antennas that can handle multiple frequencies with a single small antenna are underway, but there are many antennas that support multiple frequencies with a structure using a helical antenna as described above. Absent.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an antenna device and a wireless communication apparatus that are small in size and can communicate at a plurality of frequencies.

One aspect of the present invention is a helical antenna in which a conductor is formed in a spiral shape, and includes a first helical antenna and a second helical antenna having different self-resonance frequencies, and a loop antenna having a power feeding portion, Each of the first helical antenna and the second helical antenna is arranged at a position where power can be supplied through electromagnetic coupling with the loop antenna.
According to such an antenna device, impedance matching is performed at a plurality of different frequencies corresponding to the respective self-resonant frequencies of the first helical antenna and the second helical antenna, and therefore communication is possible using electromagnetic waves of different frequencies. Become.

One embodiment of the present invention is the antenna device described above, in which each of the first helical antenna and the second helical antenna is arranged on different sides of the loop surface of the loop antenna while the central axes of the spirals are parallel to each other. , Being spaced apart from the loop antenna.
According to such an antenna device, the loop surface of the loop antenna and the winding surfaces of the first helical antenna and the second helical antenna are arranged so as to face each other with a predetermined separation distance. Can be electromagnetically coupled.

One embodiment of the present invention is characterized in that, in the above antenna device, the first helical antenna and the second helical antenna have different spiral radii or lengths in the central axis direction.
According to such an antenna device, the self-resonant frequencies of the first helical antenna and the second helical antenna can be made different based on only the respective shapes.

  In one embodiment of the present invention, signals having a plurality of different frequencies corresponding to the self-resonant frequencies of the first helical antenna and the second helical antenna can be output to the above-described antenna device and the power feeding unit. And a signal output unit.

  According to the antenna device and the wireless communication device described above, it is possible to provide an antenna device and a wireless communication device that are small in size and capable of communicating at a plurality of frequencies.

It is a figure which shows the whole structure of the antenna device which concerns on 1st Embodiment. It is a 1st figure which shows the impedance characteristic of the antenna device which concerns on 1st Embodiment. It is a 2nd figure which shows the impedance characteristic of the antenna device which concerns on 1st Embodiment. It is a 1st figure which shows the return loss characteristic of the antenna device which concerns on 1st Embodiment. It is a 2nd figure which shows the return loss characteristic of the antenna apparatus which concerns on 1st Embodiment. It is a schematic diagram which shows the structure around the loop antenna which concerns on the modification of 1st Embodiment.

<First Embodiment>
The antenna device according to the first embodiment will be described below.
The antenna device according to the first embodiment is an antenna mounted on a wireless communication device that performs wireless communication at a predetermined frequency, and two normal mode helical antennas are connected to each other through electromagnetic coupling with a loop antenna. Power can be communicated at two different frequencies.

[overall structure]
FIG. 1 is a diagram illustrating an overall configuration of the antenna device according to the first embodiment.
As shown in FIG. 1, the antenna device 1 includes a first helical antenna 10, a second helical antenna 11, and a loop antenna 12.

As shown in FIG. 1, the first helical antenna 10 and the second helical antenna 11 are helical antennas (normal mode helical antennas) in which conductors (eg, copper wires) are formed in a spiral shape. The first helical antenna 10 is extended in the central axis direction while spirally winding (five windings) along a circle with a radius r ₁ centered on the central axis O. The length e ₁ of the first helical antenna 10 in the central axis direction is e ₁ = 18 mm, for example (FIG. 1). On the other hand, the second helical antenna 11 extends in the direction of the central axis while being spirally wound (five turns) along a circle having a radius r ₃ centered on the central axis O. The length e ₂ of the second helical antenna 11 in the central axis direction is e ₂ = 8 mm, for example (FIG. 1). Note that, as shown in FIG. 1, both the first helical antenna 10 and the second helical antenna 11 are open without having electrical contacts at both ends.

The first helical antenna 10 and the second helical antenna 11 are formed so that their respective self-resonant frequencies (hereinafter referred to as self-resonant frequencies f ₁ and f ₂ ) are different from each other. For example, the first helical antenna 10 has a structure of self-resonance in the 400 MHz band, and the second helical antenna 11 has a structure of self-resonance in the 900 MHz band.
Here, the self-resonant frequency f ₁ of the first helical antenna 10 is a unique value uniquely determined by the inductor component L ₁ and the capacitance component C ₁ determined from the shape of the first helical antenna 10. Specifically, it is known that the self-resonant frequency f ₁ is obtained by a calculation formula “f ₁ = 2π · 1 / √ (L ₁ · C ₁ )”. Similarly, the self-resonant frequency f ₂ of the second helical antenna 11 is a unique value uniquely determined according to the inductor component L ₂ and the capacitance component C ₂ determined from the shape of the second helical antenna 11.

As shown in FIG. 1, the loop antenna 12 includes a one-turn loop coil having a radius r ₂ with the central axis O as the center, and a power feeding unit 20 is formed. The power feeding unit 20 is formed by omitting a part of the ring of the loop antenna 12, and “+” terminal and “−” terminal of a signal output unit described later are electrically connected to both ends thereof. The loop antenna 12 includes signals having a plurality of different frequencies corresponding to the self-resonant frequencies f ₁ and f ₂ of the first helical antenna 10 and the second helical antenna 11 from the signal output unit through the power feeding unit 20. Is entered.

As shown in FIG. 1, the first helical antenna 10, the second helical antenna 11, and the loop antenna 12 are coaxially arranged with respect to the same central axis O. More specifically, the first helical antenna 10 and the second helical antenna 11 are different from each other in the loop surface S of the loop antenna 12 while making the central axes (center axes O) of the respective spirals the same (ie, parallel). On the side, it is spaced apart from the loop antenna 12. Here, of the end portions of the first helical antenna 10 extending in the central axis direction, the end portion (end portion α ₁ ) closer to the loop antenna 12 and the loop antenna 12 are separated by a separation distance d _1. It is arranged. Similarly, the end portion (end portion α ₂ ) nearer to the loop antenna 12 among the end portions of the second helical antenna 11 extending in the central axis direction is separated from the loop antenna 12 by a separation distance d _2. It is arranged.
Further, the loop antenna 12 is arranged such that the loop surface S intersects the central axis O of the spiral in the first helical antenna 10 and the second helical antenna 11 perpendicularly.

As described above, in the antenna device 1 according to the present embodiment, the two helical antennas (the first helical antenna 10 and the second helical antenna 11) are arranged on both sides of the loop antenna 12 that is an excitation loop. Thus, each of the two helical antennas is electromagnetically coupled to the single loop antenna 12 and has a structure capable of supplying power via the loop antenna 12.
Note that power feeding via electromagnetic coupling means that the loop antenna 12 and each helical antenna (the first helical antenna 10 and the second helical antenna 11) can transmit power without contact by electromagnetic induction via mutual inductance components. A phenomenon that occurs.

The two helical antennas and the loop antenna 12 described above are fixedly installed via predetermined spacers made of a nonconductive material on a flat plate (not shown). As will be described later, the flat plate may be formed of a conductive material such as copper.
In the above description, the two helical antennas have been described on the assumption that the central axes of the respective spirals are “identical (ie, parallel)”, but the central axes of the respective spirals are exactly the same (parallel). It is not necessary to be arranged in this manner, and a slight positional deviation or angular deviation is allowed.

[Method of matching impedance of antenna device]
Next, an impedance matching method of the antenna device 1 will be described with reference to FIGS.

FIG. 2 is a first diagram illustrating impedance characteristics of the antenna device according to the first embodiment.
The Smith chart shown in FIG. 2 shows impedance characteristics of the antenna device 1 when the power feeding unit 20 is used as a reference. In particular, FIG. 2 shows a change in impedance characteristics of the antenna device 1 when the distance d ₁ in the central axis direction between the end α ₁ of the first helical antenna 10 and the loop antenna 12 is changed. Here, the numerical value in the Smith chart shown in FIG. 2 is the normalized impedance, and the center value “1” of the chart circle is actually the oscillation source (signal output unit described later) connected to the power feeding unit 20. The characteristic impedance is 50Ω. FIG. 2 shows the impedance characteristics of the antenna device 1 at a frequency of 400 MHz to 500 MHz of a signal input from the power supply unit 20. Here, r ₁ = 9 mm, r ₂ = 9 mm, r ₃ = 4 mm, and d ₂ = 8.15 mm.

As shown in FIG. 2, 4 mm the distance _{d 1,} 8 mm, by changing the 12mm etc., the impedance characteristic of the antenna device 1 is changed. According to FIG. 2, when the separation distance d ₁ is relatively large, specifically, when the separation distance d ₁ = 12 mm, the normalized impedance “1” (ie, 50Ω) between the frequency of 400 MHz and 500 MHz. Impedance characteristics close to. That is, by adjusting the separation distance d ₁ = 12 mm, the antenna device 1 is impedance matched at a frequency close to the normalized impedance “1”, and the antenna device 1 can perform wireless communication at the frequency.

FIG. 3 is a second diagram illustrating impedance characteristics of the antenna device according to the first embodiment.
The Smith chart shown in FIG. 3 shows the impedance characteristics of the antenna device 1 when the power feeding unit 20 is used as a reference, as in FIG. In particular, FIG. 3 shows an antenna device when the distance r ₁ in the central axis direction between the end α ₁ of the first helical antenna 10 and the loop antenna 12 is fixed and the radius r ₂ of the loop antenna 12 is changed. 1 shows the impedance characteristic. 3 shows the impedance characteristics of the antenna device 1 at a frequency of 400 MHz to 500 MHz of a signal input from the power feeding unit 20, as in FIG. 2. Here, r ₁ = 9 mm, r ₃ = 4 mm, d ₁ = 5 mm, and d ₂ = 8.15 mm.

As shown in FIG. 3, the radius _{r 2} of the loop antenna 12 2 mm, 4 mm, 8 mm, the impedance characteristic of the antenna device 1 is also changed by changing the 12mm like. According to FIG. 3, when the radius r ₂ of the loop antenna 12 is about 4 mm, a characteristic that is close to the normalized impedance “1” (ie, 50Ω) appears between 400 MHz and 500 MHz. That is, by adjusting the radius r ₂ to 4 mm, impedance matching is performed at a frequency approaching the normalized impedance “1”, and the antenna device 1 can perform wireless communication at the frequency.

As described above, the antenna device 1 according to the present embodiment appropriately adjusts the separation distance d ₁ between the first helical antenna 10 and the loop antenna 12 and the radius r ₂ of the loop antenna 12 to thereby adjust the first helical antenna. Impedance matching is performed at a frequency corresponding to ten self-resonant frequencies f ₁ (400 MHz band), and communication is possible at the frequency.

The impedance matching adjustment described with reference to FIGS. 2 and 3 can also be applied to the second helical antenna 11. Specifically, the second helical antenna 11 is appropriately changed by appropriately changing the distance d ₂ between the end α ₂ of the second helical antenna 11 and the loop antenna 12 in the central axis direction, the radius r ₂ of the loop antenna 12, and the like. Impedance matching is performed at a frequency corresponding to 11 self-resonant frequencies f ₂ (900 MHz band).

[Return Loss Characteristics of Antenna Device 1]
Next, characteristics of the antenna device 1 optimized based on the impedance matching method described with reference to FIGS. 2 and 3 will be described.

FIG. 4 is a first diagram illustrating a return loss characteristic of the antenna device according to the first embodiment.
The horizontal axis of the graph shown in FIG. 4 indicates the frequency in a predetermined range of the 400 MHz band, and the vertical axis indicates the return loss of the antenna device 1 in the frequency band. Here, the return loss is a numerical value corresponding to the impedance mismatch in the power feeding unit 20 and indicates the ratio of the reflected power to the input power to the antenna device 1.
As shown in FIG. 4, the antenna device 1 has a characteristic that the return loss is locally reduced when the frequency of the input signal is around 447 MHz. Thereby, impedance matching is achieved at the frequency 447 MHz, and electromagnetic waves are mainly emitted from the first helical antenna 10 without causing power loss due to reflection in the power feeding unit 20. Accordingly, the antenna device 1 can transmit and receive an electromagnetic wave signal having a frequency of the first frequency 447 MHz corresponding to the resonance frequency f ₁ (400 MHz band) of the first helical antenna.

FIG. 5 is a second diagram illustrating the return loss characteristics of the antenna device according to the first embodiment.
In the graph shown in FIG. 5, similarly to FIG. 4, the horizontal axis indicates the frequency in a predetermined range of the 900 MHz band, and the vertical axis indicates the return loss in the frequency band of the antenna device 1.
As shown in FIG. 5, the antenna device 1 has a characteristic that the return loss is locally reduced when the frequency of the input signal is near 977.5 MHz. As a result, impedance matching is achieved even at the frequency of 977.5 MHz, and electromagnetic waves are mainly radiated from the second helical antenna 11 without causing power loss due to reflection in the power feeding unit 20. Therefore, the antenna device 1 can transmit and receive an electromagnetic wave signal having a frequency of the second frequency of 977.5 MHz corresponding to the resonance frequency f ₂ (900 MHz band) of the second helical antenna.

Thus, the radius _{r 1} of the first helical antenna 10, the radius _{r 2} of the loop antenna 12, the radius _{r 3} of the second helical antenna 11, by appropriately adjusting the distance _d 1, _{d 2,} etc., FIG. 4 As described with reference to FIG. 5, the antenna device 1 can communicate at two different frequencies.

[Function and effect]
As described above, the antenna device 1 according to the first embodiment has a single excitation coil (loop antenna 12) for each of the two helical antennas (the first helical antenna 10 and the second helical antenna 11). In this configuration, power can be supplied via electromagnetic coupling. By doing so, impedance matching is performed at two different frequencies corresponding to the self-resonant frequencies f ₁ and f ₂ of the respective helical antennas, and electromagnetic waves can be transmitted and received at the two types of frequencies.
Moreover, since the antenna device 1 is configured using a helical antenna having a self-resonant frequency while being small, the size of the antenna device 1 can be reduced as a whole.

Further, in the antenna device 1, each of the first helical antenna 10 and the second helical antenna 11 is separated from the loop antenna 12 on different sides of the loop surface S of the loop antenna 12 while making the central axes of the spirals parallel to each other. It is arranged. As a result, the loop surface S of the loop antenna 12 and the winding surface of each helical antenna (surface perpendicular to the central axis of the spiral) are arranged so as to face each other with the separation distances d ₁ and d ₂ . Each can be effectively electromagnetically coupled.

The antenna device 1 is formed so that the spiral radii r ₁ and r ₃ or the lengths e ₁ and e ₂ in the central axis direction of the first helical antenna 10 and the second helical antenna 11 are different from each other. As a result, the self-resonant frequencies f ₁ and f ₂ of the first helical antenna 10 and the second helical antenna 11 can be made different based on only the respective shapes. If it does so, the increase in a number of parts can be suppressed and size reduction and cost reduction of the antenna apparatus 1 can be promoted.

  As described above, according to the antenna device 1 according to the first embodiment, an antenna device and a wireless communication device that are small in size and capable of communicating at two types of frequencies (first frequency and second frequency) are provided. be able to.

In addition, the wireless communication device according to the first embodiment has a plurality of different frequencies corresponding to the self-resonant frequencies f ₁ and f ₂ of the antenna device 1 and the first helical antenna 10 and the second helical antenna 11. And a signal output unit that can output a signal. Specifically, the signal output unit is electrically connected to the power feeding unit 20 of the antenna device 1. In this case, the wireless communication device becomes a transmitter that radiates electromagnetic waves having a plurality of different frequencies to the atmosphere via the antenna device 1.

[Modification of First Embodiment]
The antenna device 1 according to the first embodiment is not limited to the above-described aspect, and can be modified as follows.

FIG. 6 is a schematic diagram illustrating a structure around a loop antenna according to a modification of the first embodiment.
As shown in FIG. 6, the loop antenna 12 may be configured such that one end of the power feeding unit 20 is connected to the signal output unit 4 and the other end is connected to the conductive plate 3 (the above-described flat plate) made of a conductive material. Good. In this case, the signal output unit 4 is provided on a side different from the loop antenna 12 with respect to the conductive plate 3, and is electrically connected to the loop antenna 12 through a hole 3 a provided in the conductive plate 3. Connected. By setting it as such an aspect, the cable etc. which connect the antenna apparatus 1 and the signal output part 4 on the back side (different side from the antenna apparatus 1) of the conductor plate 3 can be hidden, and the said cable is the antenna apparatus 1 It is possible to prevent the antenna characteristics (such as electromagnetic wave radiation characteristics) from being affected. Further, since the signal output unit 4 can also be placed on the back side of the conductor plate 3, the influence of the casing of the signal output unit 4 on the characteristics of the antenna device 1 can be prevented.

The antenna device 1 according to the first embodiment has a structure in which the central axes of the first helical antenna 10, the second helical antenna 11, and the loop antenna 12 are all common (central axis O) and are arranged in a line. However, the antenna device 1 according to another embodiment is not limited to this mode.
For example, the central axes of the first helical antenna 10 and the second helical antenna 11 may be different from each other. That is, in this case, the first helical antenna 10 and the second helical antenna 11 are arranged so as to extend along the central axes of different spirals.
The same applies to the relationship between the central axes of the first helical antenna 10 and the loop antenna 12 or the central axes of the second helical antenna 11 and the loop antenna 12.

In the antenna device 1 described above, the loop surface S of the loop antenna 12 does not necessarily have to be perpendicularly intersected with the central axis O of the first helical antenna 10 (second helical antenna 11). . Specifically, in the first helical antenna 10 (second helical antenna 11), for example, the loop surface S of the loop antenna 12 is inclined with respect to the central axis O of the first helical antenna 10 (second helical antenna 11). It may be arranged as follows.
As described above, any mode can be used as long as effective electromagnetic coupling is made so that at least each of the first helical antenna 10 and the second helical antenna 11 can be fed via the single loop antenna 12. It may be.

  In addition, the antenna device 1 according to another modification may include three or more helical antennas having different self-resonant frequencies. Thereby, the antenna device 1 can communicate at three or more different frequencies corresponding to the self-resonant frequencies of the respective helical antennas. In this case, each of the three or more helical antennas according to the modification is effectively electromagnetically coupled with the loop antenna 12 to such an extent that power can be supplied through the single loop antenna 12. It shall be arranged as follows.

The first helical antenna 10 and the second helical antenna 11 are formed so that the spiral radii r ₁ and r _{3 of} each spiral and the lengths e ₁ and e ₂ in the central axis direction are different from each other. It was explained as being. In the above-described embodiment, the first helical antenna 10 and the second helical antenna 11 thereby have different self-resonance due to the inductance components L ₁ and L ₂ and the capacitance components C ₁ and C ₂ that are determined according to the respective shapes. It is assumed that frequencies f ₁ and f ₂ are provided.
However, in the antenna device 1 according to another embodiment, as long as the self-resonant frequencies f ₁ and f _{2 of} the first helical antenna 10 and the second helical antenna 11 have different values from each other, the respective helical antennas are used. Are not necessarily formed so that the radii r ₁ and r ₃ or the lengths e ₁ and e ₂ are different from each other. That is, any mode may be employed as long as each helical antenna is configured to have different self-resonant frequencies based on the inductance components L ₁ and L ₂ and the capacitance components C ₁ and C ₂ .

For example, the pitch width of the first helical antenna 10 (or the second helical antenna 11) (extension width in the direction of the central axis per turn in the spiral shape) may be changed. By changing the pitch width, the number of turns of the first helical antenna 10 (second helical antenna 11) and the distance between the conductive wires change, so that the inductance component L ₁ (L ₂ ) and the capacitance component C ₁ (C ₂ ) are desired. Can be adjusted.
Alternatively, an external capacitor element or the like may be electrically connected to the first helical antenna 10 (or the second helical antenna 11). Then, the capacitance component C ₁ (C ₂ ) of the first helical antenna 10 (second helical antenna 11) changes according to the capacitance value of the capacitor. This makes it possible to the first helical antenna 10 even is the same shape of the second helical antenna 11, it sets each of the self-resonant frequency f _1, f ₂ different from each other.

  In addition, as in the above modification, by electrically connecting a capacitor to the first helical antenna 10 or the like, a desired self-resonant frequency can be set regardless of the shape of the helical antenna. As a result, the degree of freedom in which the self-resonant frequency of the first helical antenna 10 and the like is adjusted as desired is increased. For example, even if the area that can be installed in the mounted wireless communication device is limited, The antenna 10 or the second helical antenna 11 can be set to a desired size according to the region.

  Note that the wireless communication device according to the first embodiment includes the antenna device 1 and a signal output unit that can output signals of different frequencies, and electromagnetic waves of different frequencies via the antenna device 1. Was described as a transmitter that radiates to the atmosphere. However, the wireless communication apparatus according to another embodiment includes the antenna device 1 and receives the electromagnetic wave having a plurality of different frequencies radiated into the atmosphere selectively via the antenna device 1. It may be a machine.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof, as long as they are included in the scope and gist of the invention.

DESCRIPTION OF SYMBOLS 1 Antenna apparatus 10 1st helical antenna 11 2nd helical antenna 12 Loop antenna 20 Feed part 3 Conductive plate 4 Signal output part

Claims (4)

A helical antenna having a conductor formed in a spiral shape, a first helical antenna and a second helical antenna having different self-resonant frequencies;
A loop antenna having a power feeding unit,
Each of said 1st helical antenna and said 2nd helical antenna is distribute | arranged to the position which can be electrically fed via the electromagnetic coupling with the said loop antenna. The antenna apparatus characterized by the above-mentioned. Each of the first helical antenna and the second helical antenna is arranged on different sides of the loop surface of the loop antenna, with the central axes of the spirals being parallel to each other, spaced apart from the loop antenna. The antenna device according to claim 1. The first helical antenna and the second helical antenna are
The antenna device according to claim 1, wherein the radius of the spiral or the length in the central axis direction is different from each other. The antenna device according to any one of claims 1 to 3,
A signal output unit capable of outputting signals of a plurality of different frequencies corresponding to the self-resonant frequencies of the first helical antenna and the second helical antenna to the power feeding unit;
A wireless communication device.

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