JP2015070352A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna device with improved antenna performance.SOLUTION: An antenna device 10 is configured for including: a rectangular parallelepiped housing 11; an antenna element 13 which is disposed along a first side face in the housing 11 parallel thereto; a first passive element 15 disposed being separated a predetermined distance with the antenna element 13; a second passive element 16 disposed on a second side face of the housing 11 opposing to at least a part of the first passive element 15; and a connection conductor 17 which is disposed on a third side face of the housing 11 perpendicular to the first side face and the second side face so as to electrically connect with the first passive element 15 and the second passive element 16.

Description

  The present invention relates to an antenna device mounted on a vehicle.

  In recent years, as a method for locking and unlocking a door of a vehicle, a smart entry method, which is an evolution of the keyless entry method, is becoming popular.

  In the smart entry method, a vehicle and a key (hereinafter referred to as “smart key”) have a short-range wireless function, and the vehicle door is locked and unlocked by wireless communication between the vehicle and the smart key.

  Specifically, the user unlocks the smartphone by simply touching the touch sensor of the vehicle while the vehicle door is locked with the smart key in the bag or pocket, and touches the touch sensor while the vehicle door is unlocked. Just lock it. In the smart entry method, when a smart key is detected inside the vehicle, the engine can be started without inserting the key into the keyhole of the vehicle.

  In such a keyless entry system and a smart entry system, an antenna control unit is provided in the vehicle compartment. As this type of antenna, for example, an antenna disclosed in Patent Document 1 is known.

  Patent Document 1 discloses an antenna device in which a capacitor electrode portion is provided at the edge of an antenna and the capacitor electrode portion and a bracket are capacitively coupled. As a result, the antenna resonance frequency is lowered and the antenna can be miniaturized.

JP 2006-325110 A

  However, since the antenna device disclosed in Patent Document 1 described above is configured to cover the ground, that is, the circuit board, with the bracket, there is a problem that the antenna performance is not improved even if the resonance frequency is lowered. The performance of the antenna provided in the vehicle compartment tends to deteriorate due to the influence of nearby metal parts and the like. For good wireless communication between the vehicle and the smart key, it is desirable to improve the performance as much as possible.

  An object of the present invention is to provide an antenna device that improves antenna performance.

  The antenna device of the present invention includes a housing, an antenna element provided substantially parallel to the first side surface in the housing, and a first parasitic element provided at a predetermined interval from the antenna element. And a second parasitic element provided on a second side surface of the housing facing at least a part of the first parasitic element, and substantially perpendicular to the first side surface and the second side surface. A configuration is provided that includes a connection conductor that is provided on a third side surface of the housing and electrically connects the first parasitic element and the second parasitic element.

  According to the present invention, antenna performance can be improved.

The perspective view which shows the structure of the antenna apparatus which concerns on Embodiment 1 of this invention. The figure which shows a mode that an antenna apparatus is fixed to a vehicle. Diagram showing improvement in antenna efficiency The perspective view which shows the structure of the antenna apparatus which concerns on Embodiment 2 of this invention. Diagram showing improvement in antenna efficiency The perspective view which shows the structure of the antenna apparatus which concerns on Embodiment 3 of this invention. Diagram showing the location of connecting conductors The figure which shows the improvement amount of the antenna efficiency corresponding to each figure shown in FIG. The figure which shows a mode that the length of the short side of a 1st parasitic element and a 2nd parasitic element is defined. The figure which shows the relationship between the length of the short side of a 1st parasitic element and a 2nd parasitic element, and the improvement amount of antenna efficiency. The figure which shows a mode that the length of the long side of a 1st parasitic element and a 2nd parasitic element is defined. The figure which shows the relationship between the length of the long side of a 1st parasitic element and a 2nd parasitic element, and the improvement amount of antenna efficiency.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, in the embodiments, the same components are denoted by the same reference numerals, and redundant description is omitted.

(Embodiment 1)
FIG. 1 is a perspective view showing a configuration of an antenna device 10 according to Embodiment 1 of the present invention. Hereinafter, the configuration of the antenna device 10 will be described with reference to FIG.

  The casing 11 is made of a rectangular parallelepiped resin, and accommodates the circuit board 12, the antenna element 13, and the like inside. The total length of the long sides of all sides of the housing 11, that is, the total length of the sides of the top surface (or bottom surface) is less than one wavelength of the operating frequency.

  Various electronic components are mounted on the circuit board 12, and a feeding point 14 is provided in the vicinity of one vertex of the rectangular circuit board 12. An antenna element 13 is connected to the feeding point 14 and feeds power from the feeding point 14 to the antenna element 13.

  The antenna element 13 is arranged such that a linear conductive member is raised from the feeding point 14 and is bent so as to be parallel to the first side surface of the housing 11 (the left side surface in the drawing). .

  The first parasitic element 15 is a plate-like conductor having the same size as the first side surface of the housing 11, and is provided on the opposite side (outside) of the antenna element 13 across the first side surface of the housing 11. It is done. Since the thickness of the casing 11 is about 1/100 wavelength, the first parasitic element 15 and the antenna element 13 are separated by about 1/100 wavelength.

  The second parasitic element 16 is a plate-like conductor having the same size as the first side surface of the casing 11, and the second side surface of the casing 11 facing the first parasitic element 15 (in the drawing). , Provided on the outer side of the right side of the paper).

  The connection conductor 17 is a plate-like conductor having the same length as the third side surface that is perpendicular to the first side surface and the second side surface of the housing 11, and is provided at the lower outer portion of the third side surface of the housing. The first parasitic element 15 and the second parasitic element 16 are electrically connected. Accordingly, the first parasitic element 15, the connection conductor 17, and the second parasitic element 16 constitute one large parasitic element. This also allows the first parasitic element 15, the connection conductor 17, and the second parasitic element 16 to function as a bracket that holds the three side surfaces of the housing 11, for example, as shown in FIG. Further, it can be fixed to the vehicle via the connection conductor 17.

  Note that the connection conductor 17 does not have to cover the entire third side surface of the housing 11. Incidentally, the total length of the first to third side surfaces is preferably 1/3 wavelength or less.

  FIG. 3 is a diagram illustrating an improvement in antenna efficiency. The case where there are no first and second parasitic elements and connection conductors is used as a reference (an improvement in antenna efficiency is 0 dB). On the other hand, when there is a first parasitic element and there is no connection conductor, the improvement is about 0.7 dB. In the case where the first and second parasitic elements and the connecting conductor are present, a significant improvement of about 2.9 dB can be expected.

  As described above, in the antenna device according to the first embodiment, the antenna element is provided in parallel along the first side surface in the housing, and the first parasitic power is provided on the opposite side of the antenna element across the first side surface of the housing. A third side surface that is provided with an element and that is provided with a second parasitic element outside the second side surface of the housing that faces the first parasitic element, and that is perpendicular to the first side surface and the second side surface of the housing. A connection conductor is provided outside of the first parasitic element, and the first parasitic element and the second parasitic element are electrically connected.

  Thus, the first parasitic element, the connection conductor, and the second parasitic element function as one large parasitic element, and the antenna performance can be improved. Further, the first parasitic element, the connection conductor, and the second parasitic element can function as a bracket that holds the three side surfaces of the housing.

(Embodiment 2)
FIG. 4 is a perspective view showing the configuration of the antenna device 20 according to Embodiment 2 of the present invention. FIG. 4 differs from FIG. 1 in that the first parasitic element 15 is changed to a first parasitic element 21.

  The first parasitic element 21 is a plate-like conductor having the same width as the first side surface of the housing 11 and longer than the height of the first side surface, and sandwiches the first side surface of the housing 11. Is provided on the opposite side (outside) of the antenna element and is bent on the upper surface of the housing 11.

  Thereby, the electromagnetic coupling degree of the 1st parasitic element 21 and the antenna element 13 increases, and antenna performance can further be improved.

  The length of the first parasitic element 21 on the upper surface of the housing 11 is preferably from the position where the position of the feeding point 14 is projected onto the upper surface to the first side surface side.

  FIG. 5 is a diagram illustrating the amount of improvement in antenna efficiency. In FIG. 5, the black graph shows the case where the first parasitic element is not bent, similar to that shown in FIG. 3. On the other hand, the white graph shows a case where the first parasitic element is bent. The case where there are no first and second parasitic elements and connection conductors is used as a reference (an improvement in antenna efficiency is 0 dB). On the other hand, when there is a first parasitic element and there is no connection conductor, the improvement is about 1.5 dB. In the case where the first and second parasitic elements and the connecting conductor are present, a significant improvement amount of about 3.4 dB can be expected.

  As described above, according to the second embodiment, the first parasitic element is formed by bending the plate-shaped first parasitic element so as to cover a part of the upper surface from the first side surface of the housing. The degree of electromagnetic coupling between the antenna element and the antenna element increases, and the antenna performance can be further improved.

(Embodiment 3)
FIG. 6 is a perspective view showing the configuration of the antenna device according to Embodiment 3 of the present invention. FIG. 6 differs from FIG. 1 in that the first parasitic element, the second parasitic element, and the connection conductor are arranged in the housing.

  The first parasitic element 31 is a plate-like conductor having the same size as the first side surface of the housing 11, and is inside the first side surface of the housing 11 (the left side surface in the drawing). The antenna element 13 is provided at a predetermined interval. The predetermined interval is about 1/100 wavelength.

  The second parasitic element 32 is a plate-like conductor having the same size as the first side surface of the casing 11, and the second side surface of the casing 11 facing the first parasitic element 31 (in the drawing). , Provided on the inner side of the right side surface).

  The connection conductor 33 is a plate-like conductor having the same length as the third side surface perpendicular to the first side surface and the second side surface of the housing 11, and is formed on the inner lower portion of the third side surface of the housing 11. The first parasitic element 31 and the second parasitic element 32 are electrically connected.

  As described above, according to the third embodiment, by arranging the first parasitic element, the connection conductor, and the second parasitic element in the casing, the influence of metal parts existing in the vicinity of the casing is reduced. The deterioration of the antenna performance can be suppressed.

(Modification 1)
In each of the above embodiments, the case where the connection conductor is disposed at the lower part of the third side surface of the housing has been described, but the present invention is not limited to this. For example, as shown in FIG. 7A, the connection conductor may be disposed on the upper part of the third side surface of the housing. Moreover, as shown in FIG.7 (b), you may arrange | position to the lower part of the 4th side surface facing the 3rd side surface of a housing | casing, or as shown in FIG.7 (c), It may be arranged at the top. Although FIG. 7 shows the case where the first and second parasitic elements and the connection conductor are provided outside the housing, the same applies to the case where they are provided inside the housing.

  FIG. 8 is a diagram showing the amount of improvement in antenna efficiency corresponding to each diagram shown in FIG. Each graph of (a) to (c) in FIG. 8 corresponds to (a) to (c) of FIG. From this figure, it can be seen that the improvement in antenna efficiency is almost equal regardless of where the connection conductor is provided.

(Modification 2)
As shown in FIG. 9, the length of the short side of the first parasitic element and the second parasitic element is defined as L1, and the relationship between the length L1 and the improvement in antenna efficiency is shown in FIG. From FIG. 10, it can be seen that if L1 is approximately 1/100 wavelength or longer, improvement in antenna efficiency is expected.

  Therefore, the height of the housing may be reduced in accordance with the minimum L1 that improves the antenna efficiency. Thereby, the antenna device can be reduced in size.

(Modification 3)
As shown in FIG. 11, the length of the long side of the first parasitic element and the second parasitic element is defined as L2, and the relationship between the length L2 and the improvement in antenna efficiency is shown in FIG. From FIG. 12, it can be seen that if L2 is approximately 7/100 wavelengths or longer, improvement in antenna efficiency is expected.

  Therefore, the width of the housing may be reduced in accordance with the minimum L2 that improves the antenna efficiency. Thereby, the antenna device can be reduced in size.

  The antenna device according to the present invention is suitable for mounting on a vehicle adopting a keyless entry method or a smart entry method.

DESCRIPTION OF SYMBOLS 11 Case 12 Circuit board 13 Antenna element 14 Feed point 15, 21, 31 1st parasitic element 16, 32 2nd parasitic element 17, 33 Connection conductor

Claims (5)

A housing,
An antenna element provided substantially parallel along the first side surface in the housing;
A first parasitic element provided at a predetermined interval from the antenna element;
A second parasitic element provided on a second side surface of the casing facing at least a part of the first parasitic element;
A connection conductor provided on a third side surface of the casing that is substantially perpendicular to the first side surface and the second side surface, and electrically connects the first parasitic element and the second parasitic element. When,
An antenna device comprising: The first parasitic element, the second parasitic element, and the connection conductor are provided outside the housing;
The antenna device according to claim 1. The first parasitic element, the second parasitic element, and the connection conductor are provided inside the housing;
The antenna device according to claim 1. The first parasitic element is provided by being bent from the first side surface to a part of the upper surface of the housing.
The antenna device according to any one of claims 1 to 3. The connection conductor is provided at any one of an upper portion and a lower portion of the third side surface, an upper portion of the fourth side surface of the housing facing the third side surface, or a lower portion.
The antenna device according to any one of claims 1 to 4.

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