JP2014110626A - Antenna device and connection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna device including an antenna which eliminates the need for a bottom board, makes an annular radiation element into a meander form, and narrows a region required for the installation.SOLUTION: An antenna device 1 includes: an antenna 2 formed by an annular radiation element 21; and a coaxial cable 3 where an inner conductor 31 is connected with the annular radiation element 21. The annular radiation element 21 of the antenna 2 is capacitively coupled to an outer conductor 32 of the coaxial cable 3.

Description

  The present invention relates to an antenna device including an antenna and a coaxial cable. The present invention also relates to a connection method for connecting an antenna and a coaxial cable.

  As an antenna device installed in a vehicle such as an automobile, an antenna device including a transparent dielectric sheet and a planar antenna formed on the dielectric sheet is widely used. Such an antenna device is usually used by being attached to a windshield.

  Patent Document 1 discloses an antenna device including a transparent dielectric sheet and a loop antenna formed on the dielectric sheet. Patent Document 1 describes that the total length (loop length) of a radiating element of a loop antenna is set to 60 cm in order to use this antenna device for reception of digital television broadcasting.

JP2007-158450 (released on June 21, 2007)

  However, when the antenna device described in Patent Literature 1 is used for FM broadcast reception, there is a problem that it is difficult to use the antenna device by attaching it to a windshield.

  Actually, the total length of the radiating element of the loop antenna is about the same as the resonance wavelength λ = c / f (where c is the speed of light and f is the resonance frequency), as is well known. Therefore, in order to be able to receive FM broadcasts with a carrier frequency of about 100 MHz, the total length of the radiating element of the loop antenna needs to be about 300 cm. On the other hand, the area on the windshield that can be used for attaching the antenna device is preferably 10 cm × 10 cm or less in order to ensure the visibility of the driver. The difficulty of forming a loop antenna having a total length of 300 cm of the radiating element in a region having an area of 10 cm × 10 cm or less will be apparent without needing to be explained.

  As a method for solving such a problem, (1) a method of making a radiating element constituting a loop antenna into a meander, and (2) a method of replacing a planar antenna provided in an antenna device from a loop antenna to an inverted F antenna, etc. Is mentioned.

  However, when adopting a meandering method for the radiating elements constituting the loop antenna, the reception gain of the antenna device may be lowered. This is because, among the segments constituting the meandered radiating element, reverse currents flow in adjacent segments, and the electric and / or magnetic fields formed around these segments interfere so that they cancel each other. Because.

  In addition, when the method of replacing the planar antenna included in the antenna device from a loop antenna to an inverted F antenna is adopted, although the total length of the radiating element is reduced to λ / 4, it is necessary to provide a ground plane separately from the radiating element. There was a problem that a sufficiently small size could not be expected.

  The present invention has been made in view of the above-described problems, and the object thereof is not to require a ground plane, and the area required for installation can be reduced by making the annular radiating element meandering. An object is to realize an antenna device including an antenna.

  In order to solve the above-described problem, an antenna device according to the present invention includes an antenna configured by an annular radiating element, and a coaxial cable having an inner conductor connected to the annular radiating element. The outer conductor of the coaxial cable is capacitively coupled.

  According to said structure, the antenna comprised by a cyclic | annular radiation | emission element can be functioned as a novel antenna which follows the operation principle different from the conventional antenna (for example, a monopole antenna, a loop antenna, etc.). This antenna does not require a ground plane, and the area required for installation can be reduced by making the annular radiating element meandering. That is, according to said structure, a small antenna apparatus is realizable.

  In the antenna device according to the present invention, the annular radiating element includes a plurality of linear portions parallel to a first direction and a plurality of folded portions parallel to a second direction orthogonal to the first direction. And a second meander part starting from the terminal end of the first meander part, wherein the straight part is parallel to the second direction and the return is parallel to the first direction. A second meander part comprising a first part and a third meander part starting from a terminal end of the second meander part, wherein the plurality of straight parts parallel to the first direction and the second direction A third meander part composed of a plurality of folded parts parallel to the first meander part, and a fourth meander part starting from the end of the third meander part and ending at the start of the first meander part, A plurality of straight portions parallel to the first direction and a plurality of folds parallel to the second direction A fourth meander part formed of a section, and is made of, it is preferable.

  According to said structure, the fall of the reception gain which may arise accompanying making a cyclic | annular radiation element meander can be suppressed small.

  In the antenna device according to the present invention, the annular radiating element is formed in a rectangular region including a short side parallel to the first direction and a long side parallel to the second direction, and the rectangular region is , And is divided into two isosceles trapezoidal regions having the long side of the rectangular region as the base and two isosceles triangular regions having the short side of the rectangular region as the base, and the first meander portion is The second meander portion extends over one of the two isosceles trapezoidal regions, the second meander portion extends over one of the two isosceles triangular regions, and the third meander portion is Preferably, the fourth meander part extends over the other of the two isosceles trapezoidal regions, and the fourth meander part extends over the other of the two isosceles triangular regions.

  According to said structure, the fall of the reception gain which may arise accompanying making a cyclic | annular radiation element meander can be suppressed further smaller.

  In the antenna device according to the present invention, the overall length of the first meander part is L1, the overall length of the second meander part is L2, the overall length of the third meander part is L3, and the overall length of the fourth meander part. Is L4, L1: L2: L3: L4 = 3: 1: 3: 1 is preferable.

  According to said structure, the fall of the reception gain which may arise accompanying making a cyclic | annular radiation element meander can be suppressed further smaller.

  In the antenna device according to the present invention, the inner conductor of the coaxial cable is connected to a feeding point provided on the folded portion located at the center of the long side among the folded portions constituting the first meander portion. The coaxial cable is preferably laid on a straight line passing through the feeding point and parallel to the short side.

  When the above connection mode is adopted as the connection mode between the antenna and the coaxial cable, capacitive coupling between the annular radiating element and the outer conductor of the coaxial cable can be easily realized. Moreover, the VSWR value in the vicinity of the resonance frequency can be reduced as compared with the case where another connection mode is adopted as the connection mode between the antenna and the coaxial cable.

  In order to solve the above-described problem, a connection method according to the present invention is a connection method of connecting a coaxial cable to an antenna constituted by an annular radiating element, and connecting an inner conductor of the coaxial cable to the annular radiating element. And a laying step of laying the coaxial cable so that an outer conductor of the coaxial cable is capacitively coupled to the annular radiating element.

  The antenna device provided with the antenna and the coaxial cable connected according to the above connection method has the same effect as the antenna device described above.

  ADVANTAGE OF THE INVENTION According to this invention, the antenna apparatus containing the antenna which can narrow the area | region required for installation can be implement | achieved by making an annular radiation element meander without requiring a ground plane.

It is a circuit diagram which shows the structure of the antenna apparatus which concerns on one Embodiment of this invention. It is a top view which shows the 1st specific example of the annular radiation element which can be used for the antenna apparatus shown in FIG. FIG. 3 is a plan view showing the annular radiating element shown in FIG. 2 in a state where a coaxial cable is connected. It is a top view which shows the 2nd specific example of the annular radiation element which can be used for the antenna apparatus shown in FIG. It is a graph which shows the direction dependence of the reception gain in the antenna device provided with the annular radiation element shown in FIG.

  The configuration of the antenna device 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a circuit diagram showing a configuration of the antenna device 1.

  As illustrated in FIG. 1, the antenna device 1 includes an antenna 2 and a coaxial cable 3 connected to the antenna 2.

  The antenna 2 is configured by an annular radiating element 21. The annular radiating element 21 is a linear or belt-like conductor in which one end and the other end are connected. The specific shape and the like of the annular radiating element 21 will be described later with reference to another drawing.

  The coaxial cable 3 includes an inner conductor 31 connected to the annular radiating element 21 of the antenna 2 and an outer conductor 32 connected to the ground.

  A characteristic point of the antenna device 1 is that the annular radiating element 21 of the antenna 2 and the outer conductor 32 of the coaxial cable 3 are capacitively coupled. In FIG. 1, the capacitance generated between the annular radiating element 21 and the outer conductor 32 is expressed as a capacitor 4.

  According to the knowledge obtained by the inventors, the antenna 2 does not function as an antenna when the annular radiating element 21 is not capacitively coupled to the outer conductor 32 of the coaxial cable 3. That is, it does not have a function of mutually converting electromagnetic waves and high-frequency currents. On the other hand, the antenna 2 functions as an antenna when the annular radiating element 21 is capacitively coupled to the outer conductor 32 of the coaxial cable 3. That is, it has a function of mutually converting electromagnetic waves and high-frequency currents. In other words, capacitive coupling between the annular radiating element 21 of the antenna 2 and the outer conductor 32 of the coaxial cable 3 is a key structure for making the antenna 2 an additional antenna.

  The outer conductor (ground) connected to the outer conductor 32 of the coaxial cable 3 is a plate-like conductor that is orthogonal or substantially orthogonal to the surface on which the annular radiating element 21 is formed (hereinafter also referred to as “radiating element forming surface”). It is preferable that For example, the antenna 2 is placed on a plane parallel to or substantially parallel to the ground of the automobile (for example, a roof in a hard-top type vehicle or a lid (storage for storing a top) in an open-top type vehicle). For example, the outer conductor 32 of the coaxial cable 3 may be connected to the side surface or pillar of the body of the automobile. This is due to the same reason that a high reception gain is obtained when the radiating element forming surface and the ground plane forming surface are orthogonal to each other in the monopole antenna.

  Next, a first specific example of the annular radiating element 21 will be described with reference to FIGS. 2 and 3 are plan views showing a first specific example of the annular radiating element 21. FIG. 2 shows the annular radiating element 21 before the coaxial cable 3 is connected, and FIG. 3 shows the annular radiating element 21 after the coaxial cable 3 is connected.

  In this specific example, the annular radiating element 21 is constituted by a strip-shaped conductor having a total length of 4600 mm and a width of 2 mm (may be at least 1/2000 of the resonance wavelength λ). The reason why the total length of the annular radiating element 21 is 4600 mm is to make the antenna 2 function as a vehicle-mounted antenna that covers the frequency band (76 MHz to 108 MHz) of FM broadcasting.

  In this specific example, the annular radiating element 21 is formed on a rectangular region 5 having a long side of 183 mm parallel to the x axis and a short side of 93 mm parallel to the y axis. Hereinafter, in order to describe the shape of the annular radiating element 21, the rectangular region 5 is divided into two isosceles trapezoidal regions 51 and 53 that are congruent to each other and two isosceles triangular regions 52 and 54 that are congruent to each other.

  The first isosceles trapezoidal region 51 is an isosceles trapezoidal region having one long side of the rectangular region 5 (long side on the y-axis positive direction side in FIG. 2) as a base. The second isosceles trapezoidal region 53 is an isosceles trapezoidal region having the other long side of the rectangular region 5 (the long side on the y-axis negative direction side in FIG. 2) as the base. The upper bases of these isosceles trapezoidal regions 51 and 53 are 63 mm. The first isosceles triangular area 52 is an isosceles triangular area having one short side of the rectangular area 5 (the short side on the x-axis positive direction side in FIG. 2) as a base. The second isosceles triangular region 54 is an isosceles triangular region having the other short side (the short side on the x-axis negative direction side in FIG. 2) of the rectangular region 5 as a base. The heights of these isosceles triangular regions 52 and 54 are 60 mm.

  The annular radiating element 21 includes four meander parts 211 to 214. That is, the first meander unit 211 starting from the end of the fourth meander unit, the second meander unit 212 starting from the end of the first meander unit 211, and the end of the second meander unit 212 A third meander unit 213 having a start end and a fourth meander unit 214 having a start end of the third meander unit 213 are configured.

  As shown in FIG. 2, the first meander unit 211 includes a plurality of straight line portions 211 a parallel to the short side of the rectangular region 5 and a plurality of folded portions 211 b parallel to the long side of the rectangular region 5. The first isosceles trapezoidal region 51 extends so as to cover the first isosceles trapezoidal region 51. In addition, the space | interval between the linear parts 211a which mutually adjoin is 2 mm (it should be 1/2000 or more of resonance wavelength (lambda)).

  As shown in FIG. 2, the second meander part 212 includes a plurality of straight line parts 212 a parallel to the long side of the rectangular area 5 and a plurality of folded parts 212 b parallel to the short side of the rectangular area 5. The first isosceles triangular area 52 is spread over the entire first isosceles triangular area 52. In addition, the space | interval between the linear parts 212a adjacent to each other is 2 mm (it should be 1/2000 or more of the resonance wavelength λ).

  As shown in FIG. 2, the third meander part 213 includes a plurality of straight line parts 213 a parallel to the short side of the rectangular area 5 and a plurality of folded parts 213 b parallel to the long side of the rectangular area 5. The second isosceles trapezoidal region 53 extends so as to cover the second isosceles trapezoidal region 53. Note that the interval between the adjacent linear portions 213a is 2 mm (may be at least 1/2000 of the resonance wavelength λ).

  As shown in FIG. 2, the fourth meander part 214 includes a plurality of straight line parts 214 a parallel to the long side of the rectangular area 5 and a plurality of folded parts 214 b parallel to the short side of the rectangular area 5. The second isosceles triangle area 54 is spread over the second isosceles triangle area 54. Note that the interval between the adjacent linear portions 213a is 2 mm (may be at least 1/2000 of the resonance wavelength λ).

  The feeding point P to which the inner conductor 31 of the coaxial cable 3 is connected is on the folded portion 211 b ′ located at the center of the long side of the rectangular region 5 among the plurality of folded portions 211 b constituting the first meander portion 211. Provided. As a result, it is possible to suppress a decrease in reception gain (described later) that can be caused by making the annular radiating element 21 meandering.

  The coaxial cable 3 is drawn from the feeding point P in parallel with the short side of the rectangular region 5. That is, the coaxial cable 3 is laid on a straight line L that passes through the feeding point P and is parallel to the short side of the rectangular region 5. If the annular radiating element 21 with the coaxial cable 3 connected thereto is illustrated, it is as shown in FIG. As a result, the capacitive coupling between the annular radiating element 21 and the outer conductor 32 can be easily formed in the portion where the antenna 2 and the coaxial cable 3 overlap, and further, the VSWR value in the vicinity of the resonance frequency can be kept small. Can do.

  In the specific example shown in FIG. 2, the capacitance generated between the annular radiating element 21 and the outer conductor 32 is 5 pF.

  By making the annular radiating element 21 meander, the area required for the arrangement of the annular radiating element 21 is narrowed without shortening the entire length of the annular radiating element 21 (that is, without increasing the resonance frequency of the antenna 2). can do. However, if the annular radiating element 21 is made into a meander without any special contrivance, the reception gain of the antenna 2 may be lowered. This is because, in the segments constituting the annular radiating element 21, reverse currents flow in adjacent segments, and the electric field and / or magnetic field formed around these segments interfere with each other so as to cancel each other. is there.

  However, when the shape of the annular radiating element 21 is as shown in FIG. 2, it has been clarified by the inventors that it is possible to suppress a decrease in reception gain at the resonance frequency. This is considered to be because the current flowing through the folded portion arranged along the outer periphery of the rectangular region 5 among the folded portions 211b to 214b constituting the annular radiating element 21 has a radiation function.

  In particular, the ratio L1: L2: L3 of the overall length L1 of the first meander part 211, the overall length L2 of the second meander part 212, the overall length L3 of the third meander part 213, and the overall length L4 of the fourth meander part 214: As a result of verification by the inventors, it has been found that the reduction in the reception gain at the resonance frequency can be further suppressed by setting L4 to 3: 1: 3: 1. This is because (1) the direction of the current flowing through the folded part 211b constituting the first meander part 211 is coincident with the direction of the current flowing through the folded part 213b constituting the third meander part 213, and ( 2) It is considered that this is because the direction of the current flowing through the folded portion 212b constituting the second meander unit 212 matches the direction of the current flowing through the folded unit 214b constituting the fourth meander unit 214.

  Next, a second specific example of the annular radiating element 21 will be described with reference to FIGS. 4 and 5. FIG. 4 is a plan view showing a second specific example of the annular radiating element 21. FIG. 5 is a graph showing the direction dependency of the reception gain obtained when the annular radiating element 21 has the shape shown in FIG.

  In this specific example, the annular radiating element 21 is configured by a strip-shaped conductor having a total length of 4631 mm and a width of 2 mm. The reason why the total length of the annular radiating element 21 is 4631 mm is to make the antenna 2 function as a vehicle-mounted antenna that covers the frequency band (76 MHz to 108 MHz) of FM broadcasting.

  The annular radiating element 21 according to this specific example is (1) a first meander part 211 starting from the end of the fourth meander part 214, and a plurality of linear parts 211a parallel to the y axis and the x axis A first meander part 211 composed of a plurality of parallel folding parts 211b, and (2) a second meander part 212 starting from the end of the first meander part 211, wherein a plurality of parallel parts are parallel to the x-axis. A second meander part 212 comprising a straight line part 212a and a plurality of folded parts 212b parallel to the y-axis; and (3) a third meander part 213 starting from the end of the second meander part 212, a third meander part 213 comprising a plurality of straight line parts 213a parallel to the y-axis and a plurality of folded parts 213b parallel to the x-axis; and (4) a fourth start point starting from the end of the third meander part 213 The meander part 214, which is parallel to the x-axis It is characterized in that the straight portions 214a and y-axis is constituted by a fourth meander portion 214 comprising a plurality of folded portions 214b parallel. This feature is common to the annular radiating element 21 according to the first specific example.

  If the annular radiating element 21 has this feature, even if the shape of the annular radiating element 21 is modified from that shown in FIG. 2, the effect of suppressing the decrease in reception gain is generally maintained. Actually, even if the shape of the annular radiating element 21 is as shown in FIG. 4, the reception gain in the frequency band of FM broadcasting (specifically, 76 MHz and 84 MHz) is −35 dB or more, as shown in FIG. It is as follows.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The antenna device according to the present invention can be suitably used as, for example, a vehicle-mounted antenna device, particularly a vehicle-mounted antenna device for receiving FM broadcasting.

DESCRIPTION OF SYMBOLS 1 Antenna apparatus 2 Antenna 21 Annular radiation | emission element 211 1st meander part 211a (several) linear part 211b (several) folding | returning part 212 2nd meander part 212a (several) linear part 212b (several) folding | returning part 213 Third meander part 213a (several) straight part 213b (several) folded part 214 Fourth meander part 214a (several) straight part 214b (several) folded part 3 Coaxial cable 31 Inner conductor 32 Outer conductor 4 Capacitor (Capacitive coupling)
5 Rectangular area 51, 53 Isosceles trapezoid area 52, 54 Isosceles triangle area

Claims (6)

An antenna constituted by an annular radiating element;
A coaxial cable having an inner conductor connected to the annular radiating element, and
The annular radiating element and the outer conductor of the coaxial cable are capacitively coupled.
An antenna device characterized by that. The annular radiating element is
A first meander part comprising a plurality of straight line parts parallel to the first direction and a plurality of folded parts parallel to the second direction orthogonal to the first direction;
A second meander part starting from the end of the first meander part, comprising a plurality of straight line parts parallel to the second direction and a plurality of folded parts parallel to the first direction. 2 meander parts,
A third meander part starting from the end of the second meander part, comprising a plurality of linear parts parallel to the first direction and a plurality of folded parts parallel to the second direction. 3 meander parts,
A fourth meander portion starting from the end of the third meander portion and ending at the start end of the first meander portion, wherein a plurality of straight portions parallel to the first direction and the second meander portion A fourth meander part composed of a plurality of folded parts parallel to the direction,
The antenna device according to claim 1. The annular radiating element is formed in a rectangular region including a short side parallel to the first direction and a long side parallel to the second direction,
The rectangular region is divided into two isosceles trapezoidal regions with the long side of the rectangular region as the base, and two isosceles triangular regions with the short side of the rectangular region as the base,
The first meander portion extends over one of the two isosceles trapezoidal regions,
The second meander part extends over one of the two isosceles triangle regions,
The third meander part extends over the other of the two isosceles trapezoidal regions,
The fourth meander part extends on the other of the two isosceles triangle regions,
The antenna device according to claim 2. L1: L2: L3 where L1 is the total length of the first meander part, L2 is the total length of the second meander part, L3 is the total length of the third meander part, and L4 is the total length of the fourth meander part. : L4 = 3: 1: 3: 1
The antenna device according to claim 3. The inner conductor of the coaxial cable is connected to a feeding point provided on the folded portion located at the center of the long side among the folded portions constituting the first meander portion,
The coaxial cable is laid on a straight line passing through the feeding point and parallel to the short side,
The antenna device according to claim 3 or 4, wherein A connection method for connecting a coaxial cable to an antenna constituted by an annular radiating element,
Connecting the inner conductor of the coaxial cable to the annular radiating element;
Laying the coaxial cable so that the outer conductor of the coaxial cable is capacitively coupled to the annular radiating element.
A connection method characterized by that.

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