JP6860189B2 - Spherical helical antenna - Google Patents

Description

The present invention relates to a spherical helical antenna.

For example, in various communication fields such as ship communication and satellite communication, a small and high-performance antenna is required.

A spherical helical antenna has been proposed as one of the antennas that can be miniaturized (Non-Patent Documents 1 and 2). A spherical helical antenna is an antenna in which a conductor is spirally wound along a spherical surface. Further, a method of winding a conductor so that the spherical helical antenna can be used in a wide frequency band has been studied (Non-Patent Document 3).

Steven R. Best, “The Radiation Properties of Electrically Small Folded Spherical Helix Antennas”, IEEE Transactions on Antennas and Propagation, vol. 52, No. 4, pp. 953-960, April, 2004 Steven R. Best, “Low Q Electrically Small Linear and Elliptical Polarized Spherical Dipole Antennas”, IEEE Transactions on Antennas and Propagation, vol. 53, No. 3, pp. 1047-1053, March, 2005 Oleksiy S. Kim, “Minimum Q Electrically Small Antennas”, IEEE Transactions on Antennas and Propagation, vol. 60, No. 8, pp. 3551-3558, August, 2012

A spherical helical antenna is usually provided with a feeding point at the midpoint of a spiral conductor, but the impedance seen from the feeding point is small, and impedance matching can be realized with respect to a characteristic impedance of, for example, 50 ohms. It was difficult.

An object of the present invention made in view of such a point is to provide a spherical helical antenna capable of easily realizing impedance matching.

The spherical helical antenna according to the present invention includes a first conductor having a spiral shape along the spherical surface, and the first conductor has a feeding point at a position deviated from the midpoint.

Further, in the spherical helical antenna according to the present invention, it is preferable that the first conductor is wound around a spherical or spherical shell-shaped insulator.

ただし、式（２）において、Ｊ_θは自己共振時のθ方向の電流成分を示し、Ｊφは自己共振時のφ方向の電流成分を示す。 Further, in the spherical helical antenna according to the present invention, the position of the first conductor on the spherical surface is an angle θ from the positive direction of the z-axis in the spherical coordinate system having the center of the spherical surface as the origin. , The angle from the positive direction of the x-axis is φ, and it is preferably expressed by the following equations (1) and (2).

However, in the equation (2), J _θ indicates the current component in the θ direction at the time of self-resonance, and Jφ indicates the current component in the φ direction at the time of self-resonance.

Further, in the spherical helical antenna according to the present invention, a second conductor having a spiral shape along the same spherical surface as the spherical surface along which the first conductor is aligned is further provided, and the second conductor is in an open state. Is preferable. Here, the "open state" of the conductor means a state in which the conductor is not connected to another conductor at any position and both ends of the conductor are open.

Further, in the spherical helical antenna according to the present invention, it is preferable that the second conductor is a plurality of conductors and each of the second conductors is in an open state.

Further, the spherical helical antenna according to the present invention further includes a third conductor having a spiral shape along a spherical surface having a radius different from that of the spherical surface along which the first conductor is aligned, and the third conductor is It is preferably in an open state.

Further, in the spherical helical antenna according to the present invention, it is preferable that the third conductor is a plurality of conductors, and each of the third conductors is in an open state.

According to the present invention, it is possible to provide a spherical helical antenna that can easily realize impedance matching.

It is a figure which shows the spherical helical antenna which concerns on 1st Embodiment of this invention. It is a figure which shows the spherical coordinate system. It is a figure which contrasts two kinds of winding methods of a spherical helical antenna. It is a figure which shows the spherical helical antenna which concerns on 2nd Embodiment of this invention. It is a figure which compares the radiation efficiency of various antenna configurations. It is a figure which shows the relationship between the antenna size and the position of a feeding point. It is a table which shows the data of FIG. It is a figure which shows the spherical helical antenna which concerns on 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram showing a spherical helical antenna 10 according to the first embodiment of the present invention. The spherical helical antenna 10 includes a conductor (first conductor) 11.

The conductor 11 is a linear conductor. The conductor 11 has a shape spirally wound along a spherical surface. FIG. 1 shows a state in which the conductor 11 is spirally wound along a spherical surface of a sphere centered on the origin of a Cartesian coordinate system having an x-axis, a y-axis, and a z-axis.

The length of the conductor 11 can be determined based on the wavelength of the signal targeted by the spherical helical antenna 10. The length of the conductor 11 is, for example, about half the wavelength of the signal targeted by the spherical helical antenna 10. By reducing the length of the conductor 11 to about half the wavelength of the signal targeted by the spherical helical antenna 10, the radiation efficiency of the spherical helical antenna 10 can be improved.

The radius of the spherical surface around which the conductor 11 is spirally wound can be determined according to the degree of miniaturization required for the spherical helical antenna 10 by the user. Assuming that the lengths of the conductors 11 are the same, when the radius of the sphere is large, the conductor 11 is wound sparsely along the sphere, and when the radius of the sphere is small, the conductor 11 is wound densely along the sphere.

The conductor 11 has a feeding point 12 and is connected to a transmitter or a receiver at the feeding point 12. The feeding point 12 is arranged at a position deviated from the midpoint of the conductor 11. Further, the ends on both sides of the conductor 11 are open. Here, the "midpoint" of the conductor 11 is a position on the conductor 11 corresponding to a half length of the conductor 11 along the conductor 11 from the end portion of the conductor 11.

In a normal spherical helical antenna, the feeding point is arranged at the midpoint of the conductor (in the arrangement shown in FIG. 1, the intersection of the xy plane and the conductor) from the viewpoint of symmetry and the like. In the case of this arrangement, impedance matching is difficult to achieve because the impedance is small.

On the other hand, in the conductor 11 according to the present embodiment, the feeding point 12 is arranged at a position deviated from the midpoint of the conductor 11. With this arrangement, the impedance can be increased, and the impedance can be adjusted to a desired size depending on the degree of shifting. As a result, the spherical helical antenna 10 can easily realize impedance matching even for a characteristic impedance of 50 ohms, for example, and as a result, electric power can be efficiently transmitted.

How much the feeding point 12 should be shifted from the midpoint in order to realize impedance matching can be calculated by simulation.

The simulation result of how much the feeding point 12 should be shifted from the midpoint to achieve impedance matching will be described later.

The conductor 11 may be wound around a spherical or spherical shell-shaped insulator in order to easily maintain the spiral shape. As the material of the insulator, a material having electrical characteristics close to that of air, such as Styrofoam, is preferable. Further, the conductor 11 may be a space inside without being wound around the insulator.

Subsequently, how to wind the conductor 11 will be described. When the conductor 11 has a shape wound along a spherical surface having a radius R, each point on the conductor 11 has a spherical coordinate system as shown in FIG. 2 having the center of the sphere having the spherical surface as the origin. It can be specified by θ and φ. Here, θ is the angle from the positive direction of the z-axis, and φ is the angle from the positive direction of the x-axis.

ここで、式（３）において、Ｎは導体１１の巻き数を示す。 For example, Non-Patent Documents 1 and 2 propose that the conductor 11 is spirally wound along a spherical surface according to the relationship represented by the following equation (3).

Here, in the formula (3), N represents the number of turns of the conductor 11.

The method of winding the conductor 11 according to the above formula (3) is also hereinafter referred to as a "best type".

ここで、式（５）において、Ｊ_θは自己共振時のθ方向の電流成分を示し、Ｊφは自己共振時のφ方向の電流成分を示す。 Further, for example, Non-Patent Document 3 proposes to spirally wind the conductor 11 along a spherical surface according to the relationship represented by the following equations (4) and (5).

Here, in the equation (5), J _θ indicates the current component in the θ direction at the time of self-resonance, and Jφ indicates the current component in the φ direction at the time of self-resonance.

The method of winding the conductor 11 according to the above equations (4) and (5) is also hereinafter referred to as "Kim type".

The Kim-type winding method is a winding method for making the magnetic energy and the electric energy equal to each other in order to self-resonate the conductor 11. Radiation efficiency can be improved by using a Kim-shaped winding method.

FIG. 3 shows how to wind the conductor 11 by the best type and the Kim type. The winding method indicated by reference numeral 41 is the best type winding method, and the winding method indicated by reference numeral 51 is the Kim type winding method.

As described above, according to the present embodiment, the conductor 11 has the feeding point 12 at a position deviated from the midpoint. This makes it possible to increase the impedance and adjust the impedance to a desired size, and impedance matching can be easily realized.

Further, the conductor 11 can be fixed by winding the conductor 11 around a spherical or spherical shell-shaped insulator.

Further, the radiation efficiency can be improved by winding the conductor 11 in a Kim-shaped winding method.

[Second Embodiment]
FIG. 4 is a diagram showing a spherical helical antenna 20 according to a second embodiment of the present invention. The spherical helical antenna 20 includes a conductor 11 and a conductor (second conductor) 21.

The spherical helical antenna 20 according to the second embodiment has a configuration in which a conductor 21 is added to the spherical helical antenna 10 according to the first embodiment. Since the spherical helical antenna 20 according to the second embodiment has the same configuration as the spherical helical antenna 10 according to the first embodiment except that the conductor 21 is added, the description thereof is omitted as appropriate and mainly differences. Will be described.

The conductor 21 is a linear conductor. The conductor 21 has the same length as the conductor 11. The conductor 21 has the same spiral shape as the conductor 11, and is wound along the same spherical surface as the conductor 11.

The conductor 21 is arranged at a position deviated from the conductor 11 so as not to be short-circuited with the conductor 11. For example, in the example shown in FIG. 4, the conductor 21 is arranged at a position where the conductor 11 is rotated 180 degrees around the z-axis.

Unlike the conductor 11, the conductor 21 does not have a feeding point. The conductor 21 is in an open state, is not connected to another conductor at any position, and its ends on both sides are open.

The conductor 21 can be fixed by winding it around a spherical or spherical shell-shaped insulator.

The spherical helical antenna 20 can improve the radiation efficiency by having the conductor 21 in an open state in addition to the conductor 11 having the feeding point 12.

Although FIG. 4 shows a configuration in which one conductor 21 in the open state is added, there may be a plurality of conductors 21 in the open state. When there are N conductors 11 and 21 in total, for example, by arranging the conductors 11 and 21 at an angle of 360 degrees / N around the z-axis, the conductors 11 and 21 are short-circuited. In addition, short circuits between the conductors 21 can be prevented.

FIG. 5 shows a simulation result of the dependence of radiation efficiency on the antenna size kR. Here, the antenna size kR is the product of the wave number k and the radius R of the spherical surface, and the wave number k is represented by k = 2π / λ, where λ is the wavelength of the signal targeted by the antenna.

FIG. 5 shows the theoretical value of the spherical antenna, the simulation result when the Kim type antenna has one, two, and four conductors, and the simulation result when the best type antenna has one conductor. .. Here, the number of conductors means the total number of conductors 11 and 21.

As shown in FIG. 5, when comparing the case of one conductor, the Kim type has higher radiation efficiency than the best type. Further, in the Kim type, as the number of conductors increases, the radiation efficiency increases, which approaches the theoretical value of the spherical antenna.

The theoretical value of the spherical antenna is a value of radiation efficiency when the entire spherical surface is used as a conductor. Increasing the number of conductors is considered to bring the radiation efficiency closer to the theoretical value of the spherical antenna because the area where the spherical surface is covered with the conductors increases and the entire spherical surface approaches the state of being conductors.

As described above, according to the present embodiment, the spherical helical antenna 20 further includes an open conductor 21 on the same spherical surface as the conductor 11. Thereby, the radiation efficiency can be improved.

[Simulation result of feeding point position]
FIG. 6 is a diagram showing a simulation result of the position of the feeding point 12. The horizontal axis is the antenna size kR, and the vertical axis is the angle θ from the positive direction of the z-axis at the position of the feeding point 12 (see FIG. 2 for the angle θ). When θ = 90 degrees, it means that the feeding point 12 is at the midpoint of the conductor 11, and the smaller the θ, the larger the deviation from the midpoint of the feeding point 12.

FIG. 6 is a simulation result of the position of the feeding point 12 when impedance matching is realized with respect to the characteristic impedance of 50 ohms which is usually used. FIG. 6 shows the results when there is one conductor and when there are two conductors. The number of conductors means the total number of conductors 11 and 21 as in the case of FIG.

As shown in FIG. 6, when the antenna size kR is reduced, θ becomes smaller. That is, if the antenna size kR is reduced to reduce the size of the spherical helical antenna, the deviation from the midpoint of the feeding point 12 becomes large.

Further, as shown in FIG. 6, θ is smaller in the case of one conductor than in the case of two conductors. That is, the deviation from the midpoint of the feeding point 12 is larger when there is one conductor than when there are two conductors.

FIG. 7 is a table showing the data shown in the graph of FIG.

As shown in FIGS. 6 and 7, in order to reduce the antenna size kR and reduce the size of the spherical helical antenna while achieving impedance matching, it is necessary to reduce θ, that is, from the midpoint of the feeding point 12. It is preferable to increase the deviation of the antenna.

For example, when there is only one conductor, the position of the feeding point 12 is preferably such that θ is about 31 degrees or less. As a result, the antenna size kR of the spherical helical antenna can be set to about 0.4 or less. Further, more preferably, θ is about 25 degrees or less. As a result, the antenna size kR of the spherical helical antenna can be set to about 0.3 or less. Further, more preferably, θ is about 22 degrees or less. As a result, the antenna size kR of the spherical helical antenna can be set to about 0.2 or less.

Further, for example, when there are two conductors, the position of the feeding point 12 is preferably such that θ is about 62 degrees or less. As a result, the antenna size kR of the spherical helical antenna can be set to about 0.4 or less. Further, more preferably, θ is about 48 degrees or less. As a result, the antenna size kR of the spherical helical antenna can be set to about 0.3 or less. Further, more preferably, θ is about 38 degrees or less. As a result, the antenna size kR of the spherical helical antenna can be set to about 0.2 or less.

As the characteristic impedance that is usually used, there is a value larger than 50 ohms, for example, 75 ohms. When impedance matching is performed on a characteristic impedance larger than 50 ohms, such as 75 ohms, the value of θ is smaller than when impedance matching is performed on 50 ohms.

[Third Embodiment]
FIG. 8 is a diagram showing a spherical helical antenna 30 according to a third embodiment of the present invention. The spherical helical antenna 30 includes a conductor 11 and a conductor (third conductor) 31.

The spherical helical antenna 30 according to the third embodiment has a configuration in which a conductor 31 is added to the spherical helical antenna 10 according to the first embodiment. Since the spherical helical antenna 30 according to the third embodiment has the same configuration as the spherical helical antenna 10 according to the first embodiment except that the conductor 31 is added, the description thereof is omitted as appropriate and mainly differences. Will be described.

The conductor 31 is a linear conductor. The conductor 31 has a length similar to that of the conductor 11. As shown in FIG. 8, the conductor 31 has a shape that is concentric with the spherical surface along which the conductor 11 runs and is spirally wound along a spherical surface having a radius smaller than the spherical surface along which the conductor 11 runs. .. The conductor 31 may have a shape that is concentric with the spherical surface along which the conductor 11 runs and is spirally wound along a spherical surface having a radius larger than that of the spherical surface along which the conductor 11 runs.

As described above, the conductor 31 is wound along a spherical surface that is concentric with the spherical surface along which the conductor 11 is aligned and has a different radius, so that the conductor 31 is not short-circuited with the conductor 11. The spherical surface along which the conductor 31 is aligned does not necessarily have to be concentric with the spherical surface along which the conductor 11 is aligned, and may be configured so as not to intersect the spherical surface along which the conductor 11 is aligned.

Unlike the conductor 11, the conductor 31 does not have a feeding point. The conductor 31 is in an open state, is not connected to another conductor at any position, and has open ends on both sides.

Assuming that the radius of the spherical surface along which the conductor 11 and the conductor 31 are aligned is R1 and R2 (R1> R2), respectively, the conductor 11 and the conductor 31 are wound around a spherical insulator having a radius R2, and the outside of the conductor 31 Is covered with a spherical shell-shaped insulator having a thickness of R1-R2, and the conductor 11 is wound around the spherical shell-shaped insulator to fix the conductor 11. The spherical insulator having a radius R2 may not have a spherical shape but may have a spherical shell shape with a hollowed-out central portion.

The spherical helical antenna 30 can improve the radiation efficiency by having the conductor 31 in an open state in addition to the conductor 11 having the feeding point 12.

A simulation of radiation efficiency was carried out under the following conditions.
<Simulation conditions>
Outer sphere radius (R1): 40 mm
Inner sphere radius (R2): 36 mm
Diameter of conductor 11 and conductor 31: 1 mm
Outer sphere γ: 0.17
Inner sphere γ: 0.15

This result is shown in the first embodiment (having only the conductor 11 wound along the outer sphere), the third embodiment (the conductor 31 wound along the inner sphere, and the conductor 11 wound along the outer sphere). As a result of comparison with (having), it became as follows.
<Simulation result>
Radiation efficiency of the first embodiment: 84.85% (243.64 MHz)
Radiation efficiency of the third embodiment: 91.3% (249.42 MHz)

As described above, the spherical helical antenna 30 according to the third embodiment having the conductor 31 along the inner sphere at a frequency of about 245 MHz has improved radiation efficiency as compared with the spherical helical antenna 10 according to the first embodiment. To do.

In the present embodiment, the example in which the number of conductors 31 is one has been described, but there may be a plurality of conductors 31 in the open state. In that case, the plurality of conductors 31 may be staggered and arranged in the same manner as in the second embodiment. Further, the spherical surface along which the conductor 11 is aligned (in the present embodiment, the spherical surface along the outer sphere) may have a conductor 21 in an open state in addition to the conductor 11 as in the second embodiment. Further, there may be one or a plurality of conductors 31 in an open state along each of a plurality of spherical surfaces having radii different from the spherical surface along which the conductor 11 is aligned.

As described above, according to the present embodiment, the spherical helical antenna 30 further includes an open conductor 31 on a spherical surface having a radius different from that of the spherical surface along which the conductor 11 is aligned. Thereby, the radiation efficiency can be improved.

Although the present invention has been described with reference to the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and modifications based on the present disclosure. Therefore, it should be noted that these modifications and modifications are included in the scope of the present invention.

10, 20, 30 Spherical helical antenna 11 conductor (first conductor)
12 Feeding point 21 Conductor (second conductor)
31 conductor (third conductor)
41 Conductor (best type)
51 Conductor (Kim type)

Claims (7)

It is a spherical helical antenna
It has a first conductor with a spiral shape along a spherical surface,
Said first conductor, have a feeding point at a position deviated from the midpoint,
The position deviated from the midpoint is a position for adjusting the impedance of the spherical helical antenna to a desired size, which is a spherical helical antenna. The spherical helical antenna according to claim 1, wherein the first conductor is wound around a spherical or spherical shell-shaped insulator. In the spherical helical antenna according to claim 1 or 2, the position of the first conductor on the spherical surface is an angle from the positive direction of the z-axis in the spherical coordinate system having the center of the spherical surface as the origin. A spherical helical antenna represented by the following equations (1) and (2), where θ is θ and the angle from the positive direction of the x-axis is φ.

However, in the equation (2), J _θ indicates the current component in the θ direction at the time of self-resonance, and Jφ indicates the current component in the φ direction at the time of self-resonance. In the spherical helical antenna according to any one of claims 1 to 3.
Further comprising a second conductor having a spiral shape along the same spherical surface as the spherical surface along which the first conductor is aligned.
A spherical helical antenna in which the second conductor is in an open state. The spherical helical antenna according to claim 4, wherein the second conductor is a plurality of pieces, and each of the second conductors is in an open state. The spherical helical antenna according to any one of claims 1 to 5.
Further comprising a third conductor having a spiral shape along a spherical surface having a radius different from that of the spherical surface along which the first conductor is aligned.
A spherical helical antenna in which the third conductor is in an open state. The spherical helical antenna according to claim 6, wherein the third conductor is a plurality of pieces, and each of the third conductors is in an open state.

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