JP2009207088A - Antenna apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna apparatus which can miniaturize an antenna apparatus wherein an antenna is conventionally built in a protection case for corrosion prevention. <P>SOLUTION: The antenna apparatus 1A includes an antenna 2 and a high frequency module 4A. The high frequency module 4A includes a coupling electrode 6A, an intermediate capacitor 7 and a high frequency circuit 8. The high frequency module 4A is excellent in corrosion prevention since it is covered with an insulating protection case 5. Since the antenna 2 is covered with an insulating film 3, the antenna 2 can be disposed outside the insulating protection case 5, thus contributing to miniaturization of the antenna apparatus 1A. Since the insulating film 3 is dielectrics, the antenna 2 and the coupling electrode 6A are capable of electrostatic coupling without deteriorating corrosion resistance of the antenna 2 by cutting the insulating film 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antenna device, and more particularly, to an antenna that is anodized (generic name for anodized aluminum film) on a wireless communication module such as a TPMS (tire pressure monitoring system) covered with a protective resin case. The present invention relates to an antenna device that can be suitably used in a combined wireless communication system.

  As an example, the conventional antenna device mainly includes a plate-shaped antenna, a high-frequency circuit formed on the front surface side of the wiring board, and a ground electrode formed on the back surface side thereof. It was enclosed in a protective case. As for the installation effect of the protective case, if it is made of metal, noise removal and improvement of environmental resistance can be expected, and if it is made of resin, improvement of environmental resistance can be expected. In either case, by incorporating the antenna etc. in the protective case, they are isolated from the external environment of the protective case, so the environmental resistance of the antenna etc. is improved and they are prevented from corroding (patented) Reference 1).

JP 2006-325110 A

  However, if the antenna is built in the protective case, the size of the protective case is increased by the installed volume of the antenna, which makes it difficult to reduce the size of the antenna device.

  Accordingly, the present invention has been made in view of these points, and an object of the present invention is to provide an antenna device capable of reducing the size of the antenna device.

  In order to achieve the above-described object, as a first aspect of the antenna device according to the present invention, the antenna is covered with an insulating film, and is in contact with or close to the insulating film of the antenna. And a high-frequency circuit electrically connected to the coupling electrode.

  According to the antenna device of the first aspect of the present invention, the insulating film of the antenna serves as a dielectric between the capacitor electrodes, so that the coupling capacitor is formed between the antenna and the coupling electrode. The antenna can be connected to the high-frequency circuit without removing the insulating coating formed on the antenna.

  The antenna device according to the second aspect of the present invention is the antenna device according to the first aspect, wherein an intermediate capacitor having a smaller capacity than the coupling capacitor formed by the antenna and the coupling electrode is interposed between the coupling electrode and the high-frequency circuit. It is characterized by being connected.

  According to the antenna device of the second aspect of the present invention, the capacitance change of the composite capacitor formed by connecting the coupling capacitor and the intermediate capacitor in series is smaller than the capacitance change of the large capacitance coupling capacitor. Therefore, even if the capacitance error of the coupling capacitor is large, the capacitance error of the composite capacitor can be reduced.

  An antenna device according to a third aspect of the present invention is the antenna device according to the first or second aspect, wherein the insulating film is a passive film.

  According to the antenna device of the third aspect of the present invention, the corrosion resistance of the antenna can be improved.

  An antenna device according to a fourth aspect of the present invention is the antenna device according to the third aspect, wherein the antenna is formed using aluminum, and the passive film is anodized.

  According to the antenna device of the fourth aspect of the present invention, aluminum is excellent in conductivity among valve metals (passive metals), so that the communication efficiency of the antenna device can be improved. In addition, anodized is easy to form a thin film among passive films and has a high dielectric constant, so that the capacitance of the coupling capacitor can be increased as compared with the case where other passive films are used.

  The antenna device according to a fifth aspect of the present invention is the antenna device according to any one of the first to fourth aspects, wherein the coupling electrode is in contact with the insulating film.

  According to the antenna device of the fifth aspect of the present invention, the distance between the antenna and the coupling electrode is reduced by eliminating the insulator other than the insulating coating such as air or resin from between the antenna and the coupling electrode. The capacity of the coupling capacitor can be increased.

  The antenna device according to a sixth aspect of the present invention is the antenna device according to any one of the first to fourth aspects, wherein the coupling electrode is covered with an insulating protective case, and the antenna is interposed via the insulating protective case. It is characterized by being close to the insulating film.

  According to the antenna device of the sixth aspect of the present invention, it is possible to improve the environmental resistance, particularly the corrosion resistance of the coupling electrode.

  The antenna device according to a seventh aspect of the present invention is the antenna device according to any one of the first to sixth aspects, wherein the high-frequency circuit is covered with an insulating protective case and is connected to the high-frequency circuit. The electrode is characterized in that it is electrostatically coupled to the ground portion by facing the ground portion of the antenna through an insulating protective case or an insulating film.

  According to the antenna device of the seventh aspect of the present invention, it is possible to improve the environmental resistance, particularly the corrosion resistance of the high-frequency circuit and its ground electrode.

  According to the antenna device of the present invention, since the antenna can be connected to the high frequency circuit without removing the insulating coating of the antenna, even if the antenna is installed outside the insulating protective case, corrosion of the antenna can be prevented. As a result, the antenna device can be reduced in size.

  Hereinafter, the antenna device of the present invention will be described with reference to two embodiments thereof.

  First, the antenna device 1A of the first embodiment will be described.

  FIG. 1 shows an overall perspective view of the antenna device 1A of the first embodiment, and FIG. 2 shows a cross-sectional view taken along arrow 2-2 of FIG. The antenna device 1A according to the first embodiment is used as a weak wireless module including TPMS, and includes an antenna 2 and a high frequency module 4A as shown in FIG.

  As the antenna 2 of the first embodiment, a plate-like inverted F antenna that is easy to miniaturize in a metal antenna having excellent sensitivity is selected. The antenna 2 includes a plate-like ground portion 2g, an antenna portion 2a arranged in parallel with the ground portion 2g above the ground portion 2g, two plate-like short pins 2s connecting the ground portion 2g and the antenna portion 2a, and Between the two short pins 2s, a feed line 2f suspended from near the center of the antenna portion 2a is provided. The upper end of the feeder line 2f is a feeding point P, and the lower end thereof is a coupling area 2e with the high frequency module 4A. The feeding point P is set so that a desired impedance can be obtained in the antenna unit 2a.

  As a material for the antenna 2, a metal that can easily form an insulating film 3 such as an oxide film on the surface is selected. The insulating film 3 is preferably a passive film. Therefore, the antenna 2 is preferably made of a valve metal such as aluminum, chromium, or titanium. For example, in the case of aluminum, a passive film called alumite (aluminum anodic oxide film) is formed on the surface. In the case of chromium, a passive film called a chromium oxide film is formed on the surface of stainless steel in which a predetermined ratio of chromium is contained in iron. Aluminum is selected as the material of the antenna 2 of the first embodiment, and the passive film that is the insulating film 3 is anodized as described above.

  As shown in FIG. 2, the high frequency module 4A to which the antenna 2 is connected includes a coupling electrode 6A, an intermediate capacitor 7, a high frequency circuit 8, and a ground electrode 10A. The intermediate capacitor 7 and the high-frequency circuit 8 are disposed on the surface of a flat wiring board 9, and the surface of the wiring board 9 is covered with a rectangular container-shaped insulating protective case 5 formed of a resin.

  As shown in FIG. 2, the coupling electrode 6A has a flat plate portion 6Aa and a protruding portion 6Ab. The flat plate portion 6Aa of the coupling electrode 6A is in contact with the insulating coating 3 of the antenna 2 and is electrostatically coupled to the antenna 2 through the insulating coating 3 that is a dielectric. The protruding portion 6Ab protrudes from the flat plate portion 6Aa in the normal direction and penetrates the side surface 5s of the insulating protective case 5. The material of the coupling electrode 6A is a metal having excellent conductivity such as Cu or Au.

  As the intermediate capacitor 7 of the first embodiment, a commercialized capacitor such as a chip-type capacitor or an insert-type capacitor is selected. A commercialized capacitor refers to a capacitor whose capacitance and its error are determined by product specifications. As the manufactured capacitor, a high-accuracy capacitor with a small capacitance error is preferable.

  The intermediate capacitor 7 is electrically connected between the coupling electrode 6 </ b> A and the high frequency circuit 8. That is, the intermediate capacitor 7 is connected in series with the coupling electrode 6A. The capacitance of the intermediate capacitor 7 is preferably extremely small as compared with the capacitance of the coupling capacitor 20 formed by the antenna 2 and the coupling electrode 6A.

  As the high frequency circuit 8, a communication circuit that is a transceiver of the antenna device 1A is selected. The high-frequency circuit 8 is connected to the intermediate capacitor 7 and is electrically connected to the coupling electrode 6 </ b> A via the intermediate capacitor 7.

  The ground electrode 10A is formed on the back surface of the wiring board 9 in the form of a flat thin film. The ground electrode 10A is electrically connected to the high-frequency circuit 8 through a via or a through hole (not shown). As the material of the ground electrode 10A, a metal having excellent conductivity such as Cu or Au is used.

  The ground electrode 10 </ b> A faces the ground portion 2 g of the antenna 2 with the insulating film 3 interposed therebetween. Since the ground electrode 10A and the ground portion 2g of the antenna 2 are formed in a flat plate shape, they are electrostatically coupled by facing each other.

  Next, the operation of the antenna device 1A according to the first embodiment will be described with reference to FIGS. Here, FIG. 3 shows an equivalent circuit diagram of the antenna device 1A.

  In the antenna device 1 </ b> A of the first embodiment, the antenna 2 is covered with an insulating film 3. Therefore, as shown in FIG. 1, the antenna 2 can be prevented from corroding even if the antenna 2 is disposed outside the insulating protective case 5, so that the insulating protective case 5 can be made small. . This contributes to downsizing of the antenna device 1A.

  Moreover, as shown in FIG. 2, the passive film is employ | adopted about the insulating film 3 of 1st Embodiment. Since this coating does not dissolve even when exposed to a solution or acid, the corrosion resistance of the antenna 2 can be dramatically improved.

  Further, aluminum is selected for the material of the antenna 2. Since this aluminum is excellent in electrical conductivity among valve metals, the communication efficiency of the antenna device 1A can be improved.

  In addition, the coupling electrode 6A of the first embodiment is in contact with the insulating coating 3 of the antenna 2 as shown in FIG. Then, the coupling electrode 6A is electrostatically coupled to the antenna 2 via the insulating coating 3, and the insulating coating 3 of the antenna 2 becomes a dielectric between the capacitor electrodes, so that the coupling capacitor 20 is interposed between the antenna 2 and the coupling electrode 6A. It is formed. Therefore, the antenna 2 can be connected to the high-frequency circuit 8 without removing the insulating coating 3 of the antenna 2 formed to improve the corrosion resistance.

  In particular, since the coupling electrode 6A is in contact with the insulating coating 3 of the antenna 2, electrostatic coupling occurs more effectively than when the insulating coating 3 of the antenna 2 and the coupling electrode 6A are brought close to each other. That is, since the insulator other than the insulating coating 3 such as air or resin can be excluded from between the antenna 2 and the coupling electrode 6A, the distance between the antenna 2 and the coupling electrode 6A is reduced by that amount, and the coupling capacitor is reduced. The capacity of 20 can be increased.

  Here, the material of the antenna 2 is aluminum. Therefore, the insulating film 3 of the antenna 2, that is, the passive film becomes anodized. Anodized is easy to form a thin film among passive films and has a high dielectric constant, so that the capacitance of the coupling capacitor 20 can be further increased as compared with the case where other passive films are used.

  In the antenna device 1A of the first embodiment, an intermediate capacitor 7 is connected. If only the antenna 2 covered with the insulating film 3 is connected to the high-frequency circuit 8, the intermediate capacitor 7 does not need to be arranged. However, the coupling capacitor 20 formed by the antenna 2 and the coupling electrode 6A includes an error in the thickness of the insulating film 3, an error in the dielectric constant of the insulating film 3, an error in the facing area of the coupling electrode 6A, and a dimensional error in the antenna 2. The capacity changes greatly due to various factors such as.

  Therefore, in the antenna device 1A of the first embodiment, the intermediate capacitor 7 is connected in series between the coupling electrode 6A and the high frequency circuit 8. Then, the coupling capacitor 20 and the intermediate capacitor 7 described above form a composite capacitor. Here, the capacity of the composite capacitor is a value obtained by reversing a value obtained by adding the reciprocal of the capacity of the intermediate capacitor 7 to the reciprocal of the capacity of the coupling capacitor 20. Therefore, the capacitance change of the composite capacitor is more dependent on the capacitance change of the small-capacity intermediate capacitor 7 than the capacitance change of the large-capacity coupling capacitor 20. Furthermore, if the intermediate capacitor 7 has a very small capacity compared to the coupling capacitor 20 and the capacity thereof is highly accurate, the capacity of the coupling capacitor 20 becomes extremely stable. That is, even if the small-capacity and high-precision intermediate capacitor 7 is connected in series to the coupling electrode 6A as in the first embodiment, the capacitance error of the coupling capacitor 20 may increase due to various factors. The capacitance error of the composite capacitor can be reduced.

  The high-frequency circuit 8 connected to the antenna 2, the coupling electrode 6A, and the intermediate capacitor 7 is covered with an insulating protective case 5 as shown in FIGS. Therefore, as in the past, the high-frequency circuit 8 can be improved in environmental resistance, in particular, corrosion resistance.

  The ground electrode 10 </ b> A is electrostatically coupled to the ground portion 2 g of the antenna 2 through the insulating coating 3 of the antenna 2. For this reason, similarly to the operation of the antenna 2 and the coupling electrode 6A, the ground electrode 10A is provided on the ground portion 2g of the antenna 2 without removing the insulating coating 3 of the antenna 2 formed to improve the environmental resistance, particularly the corrosion resistance. Can be connected.

  That is, according to the antenna device 1A of the first embodiment, since the antenna 2 can be connected to the high-frequency circuit 8 without removing the insulating coating 3 of the antenna 2, the antenna 2 is provided outside the insulating protective case 5. Even if the antenna 2 is installed, corrosion of the antenna 2 can be prevented. Therefore, the antenna device 1A can be downsized.

  Next, the antenna device 1B according to the second embodiment will be described with reference to FIGS. 4 and 5. Here, FIG. 4 is a longitudinal sectional view showing the antenna device 1B of the second embodiment, and FIG. 5 shows an equivalent circuit diagram of the antenna device 1B of the second embodiment.

  Similar to the first embodiment, the antenna device 1B of the second embodiment is used as a weak wireless module, and includes an antenna 2 and a high-frequency module 4B as shown in FIG. The high frequency module 4B has a coupling electrode 6B, an intermediate capacitor 7, a high frequency circuit 8, and a ground electrode 10B. The difference from the first embodiment is that not only the intermediate capacitor 7 and the high-frequency circuit 8 but also the coupling electrode 6B and the ground electrode 10B are covered with the insulating protective case 5. Only differences from the first embodiment will be described below.

  As shown in FIG. 2, the coupling electrode 6B is formed in a flat plate shape, and is fixed to the inner surface of the side surface 5s of the insulating protective case 5 facing the coupling area 2e of the feeder 2f integrally formed with the antenna 2. ing. Therefore, the coupling electrode 6 </ b> B is not in contact with the insulating film 3 of the antenna 2, and is close to the insulating film 3 of the antenna 2 through the insulating protective case 5. Since the insulating protective case 5 and the insulating coating 3 are dielectrics, the feeder 2f and the coupling electrode 6B integrally formed with the antenna 2 are electrostatically coupled via the insulating protective case 5 and the insulating coating 3.

  The ground electrode 10 </ b> B is fixed to the inner surface of the bottom surface 5 b of the insulating protective case 5 facing the flat ground portion 2 g of the antenna 2, and is covered with the insulating coating 3 through the insulating protective case 5. It is close to the ground part 2g. Since the insulating protective case 5 and the insulating coating 3 are dielectrics, the ground portion 2g and the ground electrode 10B in the antenna 2 are electrostatically coupled via the insulating protective case 5 and the insulating coating 3.

  Next, the operation of the antenna device 1B of the second embodiment will be described.

  The coupling electrode 6B is electrostatically coupled to the feeder 2f formed integrally with the antenna 2 through the insulating protective case 5 and the insulating coating 3. Similarly, the ground electrode 10B is electrostatically coupled to the ground portion 2g through the insulating protective case 5 and the insulating coating 3. Therefore, the coupling electrode 6B or the ground electrode 10B can be connected to the antenna 2 or its ground portion 2g without removing the insulating coating 3 and the insulating protective case 5 of the antenna 2. From this, even if the coupling electrode 6B and the ground electrode 10B are built in the insulating protective case 5, the antenna device 1B can be operated normally. Therefore, the environment resistance of the coupling electrode 6B and the ground electrode 10B, in particular, the corrosion resistance. Can be improved.

  That is, according to the antenna device 1B of the second embodiment, the antenna 2 can be prevented from corroding even if the antenna 2 is installed outside the insulating protective case 5 as in the first embodiment. Furthermore, since the coupling electrode 6B and the ground electrode 10B are also built in the insulating protective case 5, their corrosion can be prevented. Therefore, there is an effect that the antenna device 1B can be reduced in size while enhancing the improvement in environmental resistance.

  In addition, this invention is not limited to embodiment mentioned above etc., A various change is possible as needed.

1 is an overall perspective view showing an antenna device according to a first embodiment. 2-2 sectional view of FIG. Equivalent circuit diagram showing the antenna device of the first embodiment A longitudinal sectional view showing an antenna device according to a second embodiment The equivalent circuit diagram which shows the antenna apparatus of 2nd Embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A, 1B Antenna apparatus 2 Antenna 2a Antenna part 2e Coupling area 2f Feed line 2g Ground part 3 Insulation coating 4A, 4B High frequency module 5 Insulation protective case 5s (side of insulation protection case) 6A, 6B Coupling electrode 7 Intermediate capacitor 8 High frequency circuit 9 Wiring board 10A, 10B Ground electrode 20 Coupling capacitor P Feed point

Claims (7)

An antenna covered with an insulating coating;
A coupling electrode that is in contact with or in proximity to the insulating coating of the antenna and is electrostatically coupled to the antenna through the insulating coating;
An antenna device comprising: a high-frequency circuit electrically connected to the coupling electrode. The antenna device according to claim 1, wherein an intermediate capacitor having a smaller capacity than a coupling capacitor formed by the antenna and the coupling electrode is connected between the coupling electrode and the high-frequency circuit. . The antenna device according to claim 1, wherein the insulating film is a passive film. The antenna is formed using aluminum,
The antenna device according to claim 3, wherein the passive film is alumite. The antenna device according to claim 1, wherein the coupling electrode is in contact with the insulating film. The said coupling electrode is covered with the insulating protective case, and it adjoins to the insulating film of the said antenna through the said insulating protective case, The any one of Claims 1-4 characterized by the above-mentioned. The antenna device according to 1. The high-frequency circuit is covered with an insulating protective case,
A ground electrode connected to the high-frequency circuit is electrostatically coupled to the ground portion by facing the ground portion of the antenna through the insulating protective case or the insulating film. The antenna device according to any one of claims 1 to 6.

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