JP2011035520A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device which can be shared for reception of radio waves having different frequencies and can be miniaturized. <P>SOLUTION: The antenna device which receives signals of at least a first frequency band and a second frequency band, includes a plane antenna element having a feed point and an electrode connected to a part of the antenna element, wherein the electrode is connected to a ground via a capacitive portion forming a capacity for turning to an approximately short-circuit state for signals of the first frequency band and an approximately open state for signals of the second frequency band, and an end side on the ground side of the antenna element faces the ground non-parallel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a vehicle antenna, and more particularly to a radio reception antenna device built in a vehicle spoiler.

  A spoiler installed at the rear end of the vehicle roof (hereinafter referred to as a roof spoiler) is usually made of a resin material, and is installed integrally with the vehicle as shown in FIG.

  In recent years, the design of the vehicle has also been emphasized, and the antenna mounted on the vehicle is required to be designed so as not to impair the aesthetic appearance of the vehicle body as much as possible. In order to realize this, as shown in Patent Document 1, conventionally, a glass antenna that is installed or stuck in a rear glass or a side glass of a vehicle is used. For vehicles that cannot use glass antennas, or for vehicles that do not have sufficient antenna performance, the vehicle antenna can be realized by installing a roof spoiler with an antenna on the vehicle. Yes.

  FIG. 2 shows an example of an antenna structure in the prior art. Fig.2 (a) shows the permeation | transmission figure when the roof spoiler 2 installed in the rear-end part of the roof of the vehicle 1 shown in FIG. 1 is seen from upper direction. An FM antenna element 3 and an AM antenna element 4 are provided inside the roof spoiler 2, and each element is arranged in a vertical direction with spatial separation or an insulating member sandwiched between the elements. The elements are electrically isolated from each other. Here, an L-type antenna is shown as the FM antenna. The L-shaped antenna is obtained by bending a part of an element laterally in order to reduce the height of a quarter-wave monopole antenna. Moreover, the metal body of the vehicle 1 plays the role of a ground. The FM antenna element 3 is connected via an FM antenna feeding point 5 to an antenna amplifier (not shown) that amplifies the received signal. The FM antenna element 3 is generally formed of a metal wire or a stamped sheet metal.

  The AM antenna element 4 is provided with a metal plate having an appropriate area so that a capacitive component can be obtained between the AM antenna element 4 and the metal body of the vehicle 1 serving as a ground in order to operate as an AM antenna. Yes. The AM antenna element 4 is connected to an antenna amplifier via an AM antenna feeding point 6. The AM antenna element 4 is formed of a thin metal plate such as a sheet metal.

  However, in the above L-shaped antenna, since the antenna element is installed in parallel with the ground, a capacitance component is generated between the antenna element and the ground, so that a desired output impedance cannot be obtained. As a result, the reflection of the received signal increases (that is, the reflection coefficient increases) from the relationship between the output impedance and the input impedance of the antenna amplifier, resulting in an impedance mismatch state, resulting in mismatch loss, and the desired antenna. There arises a problem that gain cannot be obtained.

  As a solution to this problem, an antenna structure shown in FIG. The structure of the FM antenna element 3 is different from FIG. FIG. 2B shows an antenna called an inverted F type antenna. This antenna is an application of the L-shaped antenna, and is based on a 1/4 wavelength monopole antenna. This is to generate an inductive component that cancels the capacitive component generated between the ground and the antenna element by adding a short stub 7 to the element of the L-shaped antenna of FIG. The short stub 7 has one end connected to a part of the FM antenna element 3 and the other end connected to the ground. Since the electrical length (signal transmission path length) of the short stub 7 is smaller than a quarter wavelength, the short stub 7 functions as an inductor. By adjusting the electrical length, the capacitance component can be canceled by the inductive component in a desired frequency band. Good matching can be achieved between the output impedance of the antenna and the input impedance of the antenna amplifier.

  Regarding this impedance matching, FIG. 3 shows the reflection coefficient of the reflection of the reception signal generated between the output impedance of the antenna and the input impedance of the antenna amplifier. A broken line 8 indicates the reflection coefficient of the L-type antenna, and a solid line 9 indicates the reflection coefficient of the inverted F-type antenna. The larger the reflection coefficient, the larger the mismatch loss, and the smaller the reflection coefficient, the better the matching. As shown in FIG. 3, in the L-type antenna, as shown by the broken line 8, the reflection coefficient increases and the mismatch loss also increases. However, since the applicable band is wide, wideband operation can be expected. On the other hand, as shown by the solid line 9 in the inverted F type antenna, a very small reflection coefficient can be obtained, so there is no need to worry about mismatch loss. On the other hand, since the applicable band is very narrow, only narrow band operation is realized. I can't.

JP 2001-102826 A

  Therefore, the above-described conventional techniques have the following problems. When an L-type antenna is used as an FM antenna element, a capacitance component is generated between the ground and the element, and hence antenna gain is reduced due to impedance mismatch between the antenna and the antenna amplifier. In addition, when an inverted F-type antenna is used, it is easy to obtain good impedance matching because a short-circuit portion is provided, but due to a reactance component such as a capacitive component and an inductive component generated between the ground and the element. Since a resonance phenomenon occurs, only narrow-band operation can be achieved.

  In addition, when an L-type antenna is used as an FM antenna, the metal area is not sufficient to function as an AM antenna, and therefore an antenna element for AM broadcasting needs to be provided separately. For this reason, it is necessary to provide two feeding points and the antenna amplifier also supports two inputs. Therefore, the manufacturing process becomes complicated and the cost increases. On the other hand, when an inverted F-type antenna is used as an FM antenna, the FM antenna element is electrically connected to the ground via a short stub, and is completely grounded in AM broadcasting that uses a lower frequency band than FM broadcasting. In this case, it is necessary to separately provide an antenna element for AM broadcasting. Therefore, the same problem as the L-type antenna occurs.

  Furthermore, since it is necessary to spatially separate the FM and AM antenna elements from each other and to insert an insulating member between the elements, the structure becomes complicated and the cost may increase.

  Accordingly, an object of the present invention is to solve the above-described problems and provide an antenna apparatus that can operate in a wide band while realizing impedance matching in an FM antenna and can also operate as an AM antenna. It is another object of the present invention to provide an antenna device that can achieve simplification of the antenna structure and reduction in manufacturing cost.

  According to one embodiment of the present invention, in an antenna device that receives signals in at least a first frequency band and a second frequency band, a planar antenna element having a feeding point and a part of the antenna element are connected. And an electrode through a capacitance section that forms a capacitance that is substantially short-circuited with respect to a signal in the first frequency band and that is substantially open with respect to a signal in the second frequency band. The end of the antenna element on the ground side faces non-parallel to the ground. For this reason, different types of broadcast signals can be satisfactorily received by a single plate-like antenna element.

  Preferably, the electrostatic capacitance portion is a capacitor member, or includes a metal member connected to the electrode and a ground electrode facing the metal member in parallel. More preferably, the antenna element has a substantially triangular shape. The first frequency band is an FM radio broadcast band, and the second frequency band is an AM radio broadcast band. Furthermore, the antenna device is disposed in the vehicle, and the ground is a metal part of the vehicle. The antenna device may be built in the exterior member of the vehicle, and the exterior member may be a spoiler disposed on the roof of the vehicle. The antenna element is a pattern formed on a printed board.

  According to the antenna of the present invention, the structure as a shared antenna for radio waves having different frequencies can be simplified and the manufacturing cost can be reduced. Further, it is possible to provide an antenna that can easily adjust a desired output impedance while realizing a wide band operation. Furthermore, the antenna of the present invention can be produced using a general inexpensive circuit board or circuit pattern creating process without using an expensive metal mold or the like. Even after the antenna is manufactured, impedance matching can be easily achieved by adjusting the output impedance of the antenna only by changing the capacitance value of the capacitor member or the length of the metal member facing the ground electrode.

It is a figure which shows the conventional roof spoiler with a built-in antenna. (A) And (b) is a figure which shows the conventional antenna structure. It is a graph which shows the reflective characteristic of the conventional antenna. (A) And (b) is the schematic which shows the whole structure of the antenna in one Embodiment of this invention. (A) And (b) is the schematic which shows the whole structure of the antenna in one Embodiment of this invention. It is a graph which shows the reflective characteristic of the antenna in one Embodiment of this invention.

  Hereinafter, an antenna device according to an embodiment of the present invention will be described with reference to the drawings. In addition, the same number is attached | subjected, when showing the same member over several figures.

  As schematically shown in FIG. 4, an antenna element 10 is provided inside a roof spoiler 2 installed at the rear end of the roof of the vehicle 1. The antenna element 10 is formed on a circuit board 11 provided in the roof spoiler 2, and is connected to an antenna amplifier (not shown) through a FM / AM common feeding point 12. The circuit board 11 is a normal antenna circuit board, and is created by a general circuit pattern creation process. The substrate is made using a dielectric member made of a synthetic resin such as an epoxy resin. In addition to the synthetic resin, Teflon (registered trademark), ceramic, film, or the like may be used for the substrate. In the circuit pattern, a metal layer is formed on the substrate by a method such as vapor deposition, etching, or plating, but a linear member or a foil-like member made of a conductive material may be provided on the substrate surface with an adhesive or the like. .

  The antenna element shape of the antenna shown in FIG. 4A is based on an inverted F-type antenna, and is a triangular metal plate that forms a right-angled triangular slope from the vicinity of the feeding point 12 toward the tip 19 of the antenna element. However, it is the structure added to the inverted F type antenna. In addition, an antenna element used as a short stub in a conventional inverted F-type antenna is a stub 14, and the tip of the antenna element is connected to a ground pattern 18 disposed on the circuit board 11 via a capacitor member 13. The ground pattern 18 is connected to the metal body of the vehicle 1 serving as a ground by a metal wire or the like (not shown), and functions as a ground electrode. By adding such a triangular antenna element, a plurality of current paths from the feeding point 12 to the tip 19 of the antenna element are formed, which is substantially the same as when an antenna element having a plurality of adjacent electrical lengths is provided. It is possible to realize an antenna capable of wide-band operation exhibiting equivalent electrical characteristics.

  In addition, since the tip of the stub 14 is connected to the ground pattern 18 via the capacitor member 13, a short-circuit state is established for FM broadcasting in a high frequency band by appropriately selecting the capacitance value of the capacitor member 13. Thus, it operates as a short stub and operates as an open stub in an open state for an AM broadcast having a lower frequency band. Therefore, while operating as an inverted F-type antenna in the frequency band of FM broadcasting, the stub 14 operates without conduction to the ground pattern 18 in the frequency band of AM broadcasting. And since the triangular metal flat plate is provided as the antenna element 10, the element area required in order to operate | move as an antenna for AM broadcasting can also be ensured. By configuring the antenna in this way, an antenna that can be easily combined with various circuits by adding a metal member to an existing antenna can be realized. In addition, as shown in FIG.4 (b), a triangular metal flat plate can also be added to an inverted F type antenna as an antenna element which punched out the inside and provided the space | gap. Therefore, it is not necessary to configure the entire triangular antenna element portion with a metal flat plate. Even in this case, a plurality of current paths from the feeding point to the tip 19 of the antenna element are formed. The antenna element with a triangular metal flat plate may be formed by a method of obtaining a desired antenna shape by attaching a metal thin film such as a copper foil on a substrate and etching the metal film.

  5 (a) and 5 (b) show another embodiment of the antenna of the present invention. The basic structure is the same as that shown in FIGS. 4 (a) and 4 (b). Instead of providing the capacitor member 13, a stub 14 has a bowl-shaped electrode with one end connected to the antenna element 10 and the It is connected to the other end of the electrode and is formed so as to face the ground pattern 18 in parallel, and is composed of an elongated metal portion. With this structure, the same effect as that of the capacitor member 13 can be exhibited by intentionally generating a capacitance component between the metal portion of the stub 14 and the ground pattern 18. A desired capacitance component can be generated by adjusting the electrical length by changing the length of the metal portion of the stub 14. Therefore, also in this embodiment, as in FIG. 4, the metal portion of the stub 14 serves as an electrode that plays both roles of a short stub and an open stub according to the frequency band.

  4 and 5, the inductive component generated according to the electrical length of the stub 14 is parallel to the capacitance component of the capacitor member 13 in FIG. 4, and the metal portion of the stub 14 and the ground pattern 18 in FIG. Are connected in series with the capacitive component generated because of the opposite, and the reflection coefficient of the antenna can be changed by controlling the value of these capacitive components. For this reason, even when the antenna characteristics change due to the influence of the metal body of the vehicle 1 after the antenna of the present invention is manufactured, the capacitance value of the capacitor member 13 and the metal of the stub 14 are not redesigned and manufactured. The antenna characteristics can be optimized simply by changing the length of the part.

  Here, when the value of the capacitance component is changed by using the capacitor member 13 shown in FIG. 4, or the value of the capacitance component is adjusted by adjusting the length of the metal portion of the stub 14 facing the ground pattern 18 shown in FIG. The graph of FIG. 6 shows how the reflection coefficient of the antenna changes when the value is changed. Changing the output impedance of the antenna changes the reflection coefficient. Therefore, the matching state with the input impedance of the antenna amplifier also changes, and as a result, the antenna gain can be adjusted. As can be seen from the graph of FIG. 6, in the antenna of the present invention, the reflection coefficient can be changed while the operating band is maintained in a wide band. Therefore, when impedance matching with the input impedance of the antenna amplifier is performed by changing the output impedance of the antenna, the reflection coefficient becomes a solid line from the graph shown by the dashed line 15 through the graph shown by the one-dot chain line 16 as the impedance matching becomes better. As shown in FIG. 17, it becomes smaller in a desired frequency band.

  The above is the description regarding the antenna of the present invention. In the above description, the antenna of the present invention is configured to receive radio waves in the bands of FM broadcasting (for example, 76.0 MHz to 90.0 MHz) and AM broadcasting (for example, 500 MHz to 1700 MHz). By changing the electrical length of the element, it can function as an antenna for receiving radio waves in other frequency bands. In the above description, the antenna element is described as a right triangle. This is because the triangle is considered to be suitable for forming a plurality of current paths close to each other in the antenna element. However, the metal area and the plurality of antenna areas for use as an antenna for AM radio broadcasting can be used. As long as a current path, that is, a signal transmission path can be secured, the shape of the antenna element may be an arbitrary polygonal shape, or the end side facing the ground may be configured by a curve.

  Furthermore, incorporating the antenna of the present invention in a roof spoiler is only one aspect of implementing the present invention. As described above, the antenna device can be miniaturized by the present invention. Therefore, it is preferable to incorporate the antenna of the present invention into a roof spoiler. However, the present invention is not limited to a roof spoiler and can be incorporated in an appropriate exterior member of a vehicle. Furthermore, it goes without saying that the antenna of the present invention can be applied to various modes other than vehicles.

DESCRIPTION OF SYMBOLS 10 Antenna element 11 Circuit board 5, 6, 12 Feed point 13 Capacitor member 14 Stub 18 Ground pattern

Claims (9)

In an antenna device that receives signals of at least a first frequency band and a second frequency band,
A planar antenna element having a feed point;
An electrode connected to a part of the antenna element,
The electrode is grounded via a capacitance section that forms a capacitance that is substantially short-circuited with respect to the signal in the first frequency band and that is substantially open with respect to the signal in the second frequency band. Connected to
The ground-side edge of the antenna element faces the ground in a non-parallel manner,
An antenna device characterized by that.   The antenna device according to claim 1, wherein the capacitance portion is a capacitor member.   The antenna device according to claim 1, wherein the capacitance unit includes a metal member connected to the electrode and a ground electrode facing the metal member in parallel.   The antenna device according to any one of claims 1 to 3, wherein the antenna element has a substantially triangular shape.   The antenna device according to any one of claims 1 to 4, wherein the first frequency band is an FM radio broadcast band, and the second frequency band is an AM radio broadcast band.   The antenna device according to any one of claims 1 to 5, wherein the antenna device is arranged in a vehicle, and the ground is a metal part of the vehicle.   The antenna device according to any one of claims 1 to 6, wherein the antenna device is built in an exterior member of the vehicle.   The antenna apparatus according to claim 7, wherein the exterior member is a spoiler disposed on a roof of a vehicle.   The antenna device according to any one of claims 1 to 8, wherein the antenna element is a pattern formed on a printed circuit board.

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