JP4123079B2 - Ferrite loop antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ferrite loop antenna used in a receiver for FM radio waves and the like.
[0002]
[Prior art]
As a receiving antenna of a radio receiver or the like, a ferrite antenna configured by forming a coil by winding a round ferrite bar is used.
In recent years, mounting of antennas according to this embodiment on portable wireless communication devices, proposals for installing receivers on wristwatches, etc. have been studied.
At that time, as the usage of receivers expanded, miniaturization of the entire receiver was promoted, and as a result, there was an increasing demand for miniaturization and cost reduction of components such as antennas. It is coming.
[0003]
In order to satisfy the above requirements, a conventional ferrite antenna has a configuration in which the plane and side surfaces of the ferrite core are covered with a substantially C-shaped metal case (see, for example, Patent Document 1), and the antenna is wound around the outer periphery of the wristwatch body with a metal plate. A rotated configuration (see, for example, Patent Document 2) has been proposed, and various miniaturizations have been attempted.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 8-97616 (FIG. 1)
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-277469 (FIGS. 3 and 4)
[0005]
[Problems to be solved by the invention]
However, in the above conventional ferrite antenna, since the ferrite core plane is covered with a metal case, the antenna opening surrounded by the metal case inevitably has the same area as the side surface of the ferrite core, and the reception area is small. As a result, there is a problem in that the reception sensitivity decreases as the antenna becomes smaller.
In addition, since the metal case is disposed on the plane of the ferrite core, the thickness of the entire antenna increases, and it is similarly difficult to reduce the size.
[0006]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a ferrite loop antenna that can obtain a high receiving sensitivity of the antenna even if it is downsized.
[0007]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems.
The present invention is a ferrite loop antenna that includes a rectangular parallelepiped ferrite core and a metal plate that covers the periphery of the ferrite core and has both ends as a pair of electrode portions, and receives radio waves, and the metal plate includes the metal plate, The outer periphery of the ferrite core is disposed around the outer peripheral surface having the widest cross-sectional area, and the metal plate is wider than the outer peripheral surface of the ferrite core, and both ends of the metal plate Is bent toward the vertical outer side of the outer peripheral surface of the ferrite core .
[0008]
According to this ferrite loop antenna, since the metal plate orbits the outer peripheral surface having the widest cross-sectional area of the ferrite core, the widest antenna opening area can be obtained, and the magnetic field generation efficiency by the ferrite core is also increased. Reception sensitivity increases.
In addition, since the metal plate is formed wide, the electric resistance value of the metal plate is reduced, and loss can be suppressed even when high frequency radio waves are received.
Further, since both end portions of the metal plate are bent toward the vertical outer side of the outer peripheral surface of the ferrite core, a tuning circuit for receiving radio waves can be connected to the outer peripheral surface of the metal plate, and the antenna The opening portion is not hindered, and the entire antenna can be thinned.
[0009]
The present invention is the ferrite loop antenna according to claim 1, wherein capacitors are connected to both ends of the metal plate.
[0010]
According to this ferrite loop antenna, since the capacitor is disposed on the side surface side of the ferrite core, tuning adjustment in radio wave reception can be performed, and a decrease in reception sensitivity can be prevented without blocking the antenna opening. it can.
Further, since the thickness of the entire antenna is not increased, the thickness can be reduced.
[0011]
The ferrite loop antenna according to the present invention is characterized in that the capacitor connected to one end of the metal plate is a trimmer capacitor.
[0015]
The present invention is the ferrite loop antenna according to any one of claims 1 to 3 , wherein a case side concave portion or a case side convex portion provided in a case housing the ferrite core and the metal plate therein. On the other hand, the antenna-side convex portion or the antenna-side concave portion that is engaged therewith is provided on the outer surface of at least one of the metal plate and the ferrite core.
[0016]
According to this ferrite loop antenna, the antenna-side convex portion and the case-side concave portion or the antenna-side concave portion and the case-side convex portion are engaged and positioned with each other, so that even if the ferrite core vibrates inside the case Misalignment is suppressed.
[0017]
The present invention is the ferrite loop antenna according to any one of claims 1 to 4 , wherein the radio wave is an FM wave.
[0018]
According to this ferrite loop antenna, by selecting a ferrite core made of a material suitable for FM wave reception, FM waves in a predetermined radio wave band can be satisfactorily received, and a small FM receiver can be realized.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Next, a first embodiment of the present invention will be described with reference to FIGS.
A ferrite loop antenna 10 shown in FIGS. 1 and 2 covers a rectangular parallelepiped ferrite core 12 and an outer peripheral surface 12a having the widest cross-sectional area of the periphery of the ferrite core 12 so that both ends are a pair of electrode portions 14. A copper metal plate 16 is provided, and is connected to both ends of the tuning circuit portion 18 and the electrode portion 14.
[0020]
The metal plate 16 is formed wider than the width of the outer peripheral surface 12a of the ferrite core 12, and as a loop antenna part that receives FM waves, the metal plate 16 is substantially rounded in close contact with the outer peripheral surface 12a by a conductive adhesive. It is arranged.
Further, the electrode portion 14 is formed by being bent toward the vertical outer side of the outer peripheral surface of the ferrite core 12.
[0021]
The tuning circuit portion 18 is connected in parallel via the wiring portion 24a between the electrode of the substrate 24, the wiring portion 24a formed on the substrate 24 and fixed to the electrode portion 14 by soldering. A trimmer capacitor 26, a pair of terminal portions 28 fixed to the wiring portion 24a by soldering and connected to a receiver body (not shown), and a fixed connection connected in parallel between the terminal portions 28 via the wiring portion 24a. And a capacitor 30. The substrate 24 is a rectangular printed wiring board, and is soldered to the bottom surface portion of the electrode portion 14.
[0022]
Next, an FM wave receiving method by the ferrite loop antenna 10 of the present embodiment having the above configuration will be described.
As shown in FIG. 1, since the metal plate 16 circulates around the outer peripheral surface 12 a having the widest cross-sectional area of the ferrite core 12, the plane 12 b that is the surface having the largest surface area of the ferrite core 12 is the ferrite loop 12. It becomes an antenna opening surface of the antenna 10.
[0023]
For example, an FM wave having a frequency of 100 MHz is received by the plane 12b serving as the antenna opening surface. Then, a magnetic field is generated in a loop formed by the metal plate 16, and an induced current associated therewith flows through the metal plate 16. At this time, since the ferrite core 12 is disposed inside the metal plate 16, the ferrite core 12 serves as a magnetic core to increase the magnetic field density.
[0024]
Since the metal plate 16 is formed wide, the electrical resistance value in the metal plate 16 can be kept small. Therefore, a high-frequency current with little loss flows between the electrode portions 14.
The current is tuned by the inductance of the loop antenna by the metal plate 16 and the capacitor capacitance of the tuning circuit unit 18 and flows to the receiver body (not shown).
[0025]
According to the ferrite loop antenna 10, the antenna opening can be secured larger than the conventional one even if the antenna is downsized. Therefore, even when the antenna arrangement space is severely restricted, the antenna can be installed while maintaining high reception performance. .
[0026]
When the ferrite loop antenna 10 is housed and installed in a case, as shown in FIG. 3, for example, a case-side recess 32 a is provided in the case 32, and the metal is formed wider than the ferrite core 12. The side end portion 16a (antenna side convex portion) of the plate 16 is provided so as to engage with the case side concave portion 32a, and these are engaged with each other to house the ferrite loop antenna 10.
By doing in this way, it is suppressed that a position shift arises in ferrite loop antenna 10 in case 32 by vibration etc.
[0027]
Next, a second embodiment of the present invention will be described with reference to FIG.
In the following description, the same reference numerals are given to the components described in the above embodiment, and the description thereof is omitted.
[0028]
The difference between the second embodiment and the first embodiment is that, in the first embodiment, the side end 16b of the metal plate 16 formed wide and the case side recess 32a formed in the case 32 are different. In the ferrite loop antenna 100 of the second embodiment, the metal plate 116 has an antenna-side convex portion 116a that protrudes vertically outward of the outer peripheral surface 12a. The case 132 is provided with a case-side recess 132a to be engaged therewith.
[0029]
In other words, in the present embodiment, the outer peripheral surface 12a of the ferrite core 12 is positioned by the antenna-side convex portion 116a and the case-side concave portion 132a that are engaged with each other. Therefore, misalignment due to vibration or the like is suppressed as in the first embodiment.
[0030]
The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in each of the above embodiments, the antenna side convex portion and the case side concave portion are engaged with each other for positioning, but the concave portion is provided on the antenna side and the convex portion that engages with this is provided on the case side. The positioning may be performed by engaging with each other.
[0031]
Moreover, in each said embodiment, although the rectangular parallelepiped ferrite core is used, a flat plate shape may be sufficient.
Further, in each of the above embodiments, the fixed capacitor and the trimmer capacitor on the substrate are connected to both ends of the metal plate. However, the capacitor is not limited to these, and an integrated circuit such as an LSI connected to both ends of the metal plate. It may be connected to a capacitor configured in the circuit.
The ferrite core and the metal plate are brought into close contact with the conductive adhesive, but the metal plate is circulated by other fixing means such as a high-frequency varnish or a double-sided tape or simply holding the ferrite core. It doesn't matter.
[0032]
【The invention's effect】
The ferrite loop antenna of the present invention described above has the following effects.
According to the present invention, since a wide antenna aperture area can be obtained even if the size is reduced, high reception sensitivity can be obtained due to high generation efficiency of the magnetic field.
[0033]
In addition, according to the present invention, since both ends of the metal plate are bent toward the vertical outer side of the outer peripheral surface of the ferrite core, other circuits and the like can be disposed on the outer peripheral surface side. The overall thickness can be reduced. This makes it possible to provide a ferrite loop antenna suitable for a receiver body that is required to be thin.
[0034]
Furthermore, according to the present invention, since the concave portion or the convex portion is formed on the ferrite loop antenna side of the portion engaged with the case side, the positional deviation of the ferrite loop antenna in the case is suppressed, and the product is strong against vibration and the like. Can be obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an entire ferrite loop antenna according to a first embodiment of the present invention.
FIG. 2 is a plan view showing a ferrite loop antenna according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a state in which the ferrite loop antenna according to the first embodiment of the present invention is housed in a case.
FIG. 4 is a cross-sectional view of a main part in a direction along a metal plate showing a state in which a ferrite loop antenna according to a second embodiment of the present invention is housed in a case.
[Explanation of symbols]
10, 100 Ferrite loop antenna 12 Ferrite core 12a Outer peripheral surface 14 Electrode part 16, 116 Metal plate 16a, 116a Side end antenna side convex part 32a, 132a Case side concave part 26 Trimmer capacitor (capacitor)
30 Fixed Capacitor

Claims (5)

A ferrite loop antenna that includes a rectangular parallelepiped ferrite core and a metal plate that covers the periphery of the ferrite core and has both ends as a pair of electrode portions, and receives radio waves, wherein the metal plate is around the ferrite core And the metal plate is made wider than the outer peripheral surface of the ferrite core, and both end portions of the metal plate are made of the ferrite. A ferrite loop antenna , wherein the outer peripheral surface of the core is bent outward in the vertical direction .   The ferrite loop antenna according to claim 1, wherein capacitors are connected to both ends of the metal plate. The ferrite loop antenna according to claim 2, wherein the capacitor connected to one end of the metal plate is a trimmer capacitor. The antenna-side convex portion or the antenna-side concave portion engaged with the case-side concave portion or the case-side convex portion provided in the case that accommodates the ferrite core and the metal plate therein includes the metal plate and The ferrite loop antenna according to any one of claims 1 to 3 , wherein the ferrite loop antenna is provided on at least one outer surface of the ferrite core. The ferrite loop antenna according to claim 1 , wherein the radio wave is an FM wave.

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