JP4059998B2 - Antenna device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an antenna device that can resonate and transmit signals of three or more predetermined frequency bands.
[0002]
[Prior art]
A conventional antenna device for in-vehicle use and indoor desk use for transmitting and receiving signals in the three frequency bands of VHF (LOW), VHF (HIGH), and UHF of domestic TV broadcasting is about 1 m A monopole antenna having a length has been widely used. This is set to approximately ¼ wavelength with respect to VHF (LOW) which is the lowest frequency among the three frequency bands.
[0003]
[Problems to be solved by the invention]
The conventional antenna device has a large occupied space of about 1 m, and since it is long, there is a high risk of breakage such as breakage, and there has been a strong demand for a smaller antenna device. Therefore, it is conceivable to simply reduce the size of the conventional antenna. However, when the size is simply reduced, the antenna characteristics such as gain and VSWR tend to deteriorate, and the bandwidth that can be transmitted and received with the predetermined antenna characteristics becomes narrower. However, the practical use is difficult due to a problem that a sufficient bandwidth cannot be secured in a desired frequency band.
[0004]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an antenna device that does not deteriorate the antenna characteristics even if it is downsized, and that can obtain a predetermined bandwidth for a desired frequency band. .
[0005]
[Means for Solving the Problems]
In order to achieve such an object, an antenna device of the present invention includes a first element portion having a loading circuit composed of a parallel resonance circuit of a coil and a capacitor at an intermediate portion of a helical element, and an axial direction of the first element portion. A second element portion formed by capacitively coupling a base end of the antenna element portion arranged in parallel and close to the outside thereof to a feeding point of the first element portion, and setting a parallel resonance frequency of the loading circuit to a first The effective length of the first element unit is set to approximately ¼ for each of the first frequency band and the second frequency band by setting an intermediate value between the frequency band and a second frequency band having a higher frequency. The wavelength is set, and the physical length of the second element portion is made shorter than the physical length of the first element portion, and the effective length of the second element portion is set to a frequency higher than that of the second frequency band. 3 before with respect to the frequency band Is constructed by setting a substantially quarter wavelength include capacitance of the capacitive coupling.
[0006]
In addition, a first element part having a loading circuit composed of a parallel resonance circuit of a coil and a capacitor in the middle part of the helical element, and a base end of the antenna element part arranged coaxially or coaxially with the first element part A second element unit that is capacitively coupled to the feeding point of the first element unit, and the parallel resonance frequency of the loading circuit is between the first frequency band and a second frequency band of a higher frequency. The effective length of the first element unit is set to approximately ¼ wavelength for each of the first frequency band and the second frequency band, and the physical length of the second element unit is set to The effective length of the second element part is made shorter than the physical length of the first element part and includes the capacitance of the capacitive coupling with respect to the third frequency band having a frequency higher than the second frequency band. 4 it is configured by setting the wavelength There.
[0007]
In addition, the physical length of the first element unit may be set to 1/10 to 1/20 wavelength of the first frequency band.
[0008]
In addition, the antenna element portion can be composed of a rod-shaped element.
[0009]
Further, the coil of the loading circuit may be configured coaxially with the same winding diameter as the helical element.
[0010]
In addition, the capacitive coupling of the second element portion can be configured by arranging the base end of the antenna element portion close to the feeding point without being electrically connected to the feeding point.
[0011]
Further, both the first element portion and the second element portion can be elastically deformed, and a single rod-like shape is formed with an insulating resin having elasticity so as to integrally cover the first element portion and the second element portion. The cover may be molded on the body.
[0012]
A demultiplexer that demultiplexes a signal of a predetermined frequency band for each band may be provided at the feeding point, and an amplifier that amplifies the signal that is demultiplexed and output may be provided.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of a first embodiment of an antenna device according to the present invention. FIG. 2 is a diagram for explaining the operation of the loading circuit. FIG. 3 is an equivalent circuit diagram. FIG. 4 is a VSWR characteristic diagram. FIG. 5 is a gain characteristic diagram.
[0014]
In FIG. 1, a helical element 10 made of a conductive metal wire having elasticity has an intermediate portion with the same winding diameter and is coaxially wound on a pitch to form a coil 10a for a loading circuit 12, and this coil A capacitor 14 is electrically connected in parallel to both ends of 10a. A loading circuit 12 is formed by a parallel resonance circuit of the coil 10 a and the capacitor 14. The first element portion 16 is constituted by the helical element 10 and the loading circuit 12 provided at the intermediate portion thereof. Further, a rod-shaped element serving as an antenna element portion 18 made of a conductive metal wire having elasticity in the vicinity of the outer side of the helical element 10 and substantially parallel to the axial direction is disposed. The base end of the antenna element portion 18 is slightly separated from the feeding point 20 of the first element portion 16, is placed in close proximity without being electrically connected in direct current, and is capacitively coupled with the stray capacitance 28. The central conductor of the coaxial cable 22 is electrically connected to the feeding point 20, and the ground wire 24 is electrically connected to the outer conductor near the feeding point 20. Further, the cover 26 is molded with an insulating resin having elasticity so that the entire first element portion 16 and the second element portion 32 are integrally covered so that the outer shape becomes a single rod shape.
[0015]
As an example, the resonance frequency of the loading circuit 12 is set to an intermediate value between VHF (LOW) as the first frequency band f1 and VHF (HIGH) as the second frequency band f2, which is a higher frequency. The Therefore, as shown in FIG. 2, the loading circuit 12 acts as an inductance component for the first frequency band f1, and acts as a capacitance component for the second frequency band f2. As a result, the first element portion 16 has an effective length of ¼ wavelength due to the inductance effect for the first frequency band f1, and also has a ¼ wavelength due to the capacitance effect for the second frequency band f2. It can have an effective length and can resonate together as shown in FIG.
[0016]
Further, since the antenna element portion 18 of the second element portion 32 is disposed close to the helical element 10, there is a possibility that mutual coupling interference occurs and the bandwidth of the second element portion 32 becomes narrow. However, in the present invention, since the base end of the antenna element portion 18 is capacitively coupled to the feeding point 20 by the stray capacitance 28, interference can be greatly reduced due to the low-frequency cutoff effect due to this capacitive coupling. The width can be maintained. Then, the effective length of the second element unit 32 is set to approximately ¼ wavelength including the capacitive coupling stray capacitance 28 with respect to UHF as the third frequency band f3 having a frequency higher than the second frequency band f2. As shown in FIG. In addition, the physical length of the 1st element part 16 is about 250 mm as an example. And the physical length of the rod-shaped element as the antenna element part 18 is 100 mm as an example. Moreover, the space | interval of the helical element 10 and the antenna element part 18 is 5-10 mm, and is about 1/100 wavelength of the 3rd frequency band f3. Further, the distance between the base end of the antenna element portion 18 constituting the stray capacitance 28 and the feeding point 20 is about 1 to 2 mm.
[0017]
When the antenna characteristics of the antenna device having such a configuration were measured, as shown in FIG. 4, any one of the first frequency band f1, the second frequency band f2, and the third frequency band f3 of VHF (LOW), VHF (HIGH), and UHF was measured. Also, a good VSWR characteristic was shown. Further, as shown in FIG. 5, a good gain and a sufficient bandwidth were obtained for any of the first frequency band f1, the second frequency band f2, and the third frequency band f3.
[0018]
By the way, if the physical length of the first element portion 16 is shortened as much as possible to a length of about 1/10 wavelength of the frequency to be resonated, the antenna characteristics are deteriorated. If the length is further shortened to about 1/20 wavelength, the antenna characteristics are extremely deteriorated and cannot be practically used. Therefore, in the present invention, as shown in FIG. 1, by taking measures such as interposing a loading circuit 12, the deterioration of the antenna characteristics is suppressed, and the first reduction is made as much as possible within the practical range. The element part 16 having a length of about 250 mm is realized to achieve both a demand for downsizing and a performance that can sufficiently withstand practical use.
[0019]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a block diagram of a second embodiment of the antenna apparatus of the present invention. In FIG. 6, the same or equivalent members as those shown in FIG. 1 to FIG.
[0020]
In the second embodiment shown in FIG. 6, the antenna element portion 18 constituting the second element portion 32 is disposed at the axial center of the helical element 10 of the first element portion 16, and the base end thereof is a discrete component. It is electrically connected to the feeding point 20 through the capacitor 30. In such a configuration, the outer shape can be made thinner than in the first embodiment, and it is axially symmetric with respect to the axial center, which is favorable with no directionality to bending. Here, by arranging the antenna element portion 18 at the axial center of the helical element 10 as in the second embodiment, mutual coupling interference is likely to occur, and it is difficult to obtain a sufficient bandwidth. Therefore, although it is not suitable for a frequency band that requires a wide band such as UHF, it can be sufficiently used in a frequency band with a relatively narrow bandwidth such as a cellular phone. In the second embodiment, the capacitive coupling is performed by the capacitor 30 as a discrete component. However, it is needless to say that the capacitive coupling may be performed by a stray capacitance.
[0021]
The antenna device of the present invention is configured as described above, and VHF (LOW), VHF (HIGH), and UHF are set to a first frequency band f1, a second frequency band f2, and a third frequency band f3, respectively. What is not limited to what is applied to is described below. First, in the AM broadcast frequency band, even a conventional monopole antenna of about 1 m does not resonate, and even in an antenna device having a short physical length without resonating as in the present invention, its physical length The signal can be received with a signal strength corresponding to. Further, in the FM broadcast frequency band, VHF (LOW) and the frequency band substantially coincide with each other, and the first frequency band f1 can be shared. The frequency band of BAND3 of DAB (digital, audio, broadcasting) is almost included in the frequency band of VHF (HIGH), and the second frequency band f2 can be shared. Furthermore, the 800 MHz band such as a cellular phone is close to the UHF frequency band, and can share the third frequency band f3. Moreover, it is possible to include a telephone band of 1.5 GHz or 1.9 GHz by setting a wide bandwidth of the third frequency band f3. The third frequency band f3 can be set to 1.5 GHz band or 1.9 GHz band instead of UHF.
[0022]
Therefore, the antenna device of the present invention can not only transmit and receive signals in the three frequency bands described in the embodiments, but can also transmit and receive signals in four or more frequency bands by appropriate settings. An example thereof will be described with reference to FIG. In FIG. 7, the feeding point 20 of the antenna device of the present invention is electrically connected to a duplexer 48 in which a low-pass filter 40, an FM bandpass filter 42, a DAB BAND3 bandpass filter 44, and a highpass filter 46 are connected in parallel. Is done. The low-pass filter 40 outputs an AM broadcast frequency band signal, which is output to the AM / FM output terminal 54 via the buffer amplifier 50 and the low-pass filter 52. The FM bandpass filter 42 outputs an FM broadcast frequency band signal, which is output to the AM / FM output terminal 54 via the FM amplifier 56 and the highpass filter 58. Further, the BAND3 band pass filter 44 outputs a signal in the BAND3 frequency band of DAB and outputs it to the BAND3 output terminal 62 via the BAND3 amplifier 60. The high-pass filter 46 outputs a DAB L-band frequency band signal and outputs it to the L-band output terminal 66 via the L-band amplifier 64. In FIG. 7, it is a matter of course that a filter for demultiplexing for each frequency band by the duplexer 48 is appropriately set according to a desired frequency band.
[0023]
In the above-described embodiment, a coil element may be used instead of the antenna element portion 18 of the second element portion 32 instead of the rod-shaped element. In the second embodiment, when a coil element is used as the antenna element portion 18, it may be disposed coaxially with the helical element 10. Further, the capacitor 14 constituting the loading circuit 12 is not limited to the one constituted by the discrete component, and may be appropriately constituted using a parallel two-wire cable or the like. Furthermore, in the embodiment, the coil 10a of the loading circuit 12 has the same winding diameter as that of the helical element 10. However, the present invention is not limited to this, and it is needless to say that the winding diameter may be reduced.
[0024]
【The invention's effect】
As described above, since the antenna device of the present invention is configured, the following special effects can be obtained.
[0025]
In the antenna device according to claim 1, since signals in three frequency bands can be resonated and transmitted and received, and the physical length thereof can be shortened, it is suitable as a multi-frequency antenna for in-vehicle use or indoor desk use. . In particular, since the second element portion is capacitively coupled to the feed point, interference can be greatly reduced by the low frequency cutoff effect due to this capacitive coupling , and the bandwidth of the third frequency band of the highest frequency can be widened. This is suitable for receiving UHF that requires a wide band.
[0026]
Further, the antenna device according to claim 2 has the same effect as that of claim 1, and the second element portion is disposed in the helical element of the first element portion, and the outer shape thereof is made thinner. It is aesthetically pleasing and has no direction for elastic deformation. However, the bandwidth of the third frequency band tends to be narrowed due to mutual coupling interference, which is suitable for transmission / reception of signals in a frequency band such as a telephone having a narrow bandwidth.
[0027]
In the antenna device according to claim 3, since the physical length is shortened, the antenna device is particularly suitable as a vehicle-mounted antenna device disposed outside the body.
[0028]
Further, in the antenna device according to claim 4, since the rod-shaped element is used as the antenna element portion, when this is disposed outside the helical coil, the antenna device portion is compared with that using the coil element as the antenna element portion. Thus, the outer shape of the entire antenna device can be reduced.
[0029]
In the antenna device according to claim 5, the coil of the loading circuit can be manufactured by changing the pitch, etc., coaxially with the same winding diameter with respect to the helical element, and the manufacturing process is small, and the manufacturing can be performed accordingly. Easy. Moreover, since it comprises in a series, a number of parts can be reduced rather than comprising with another member.
[0030]
Further, in the antenna device according to claim 6, since the capacitive coupling at the base end of the antenna element portion is configured to be arranged close to each other without being electrically connected in a direct current, parts as a capacitor are omitted, The number of parts is reduced and the number of assembly steps is also reduced, which is suitable for mass production.
[0031]
Furthermore, in the antenna device according to the seventh aspect, the cover is molded so as to integrally cover the whole by molding, so that the number of assembling steps is small. Moreover, the insulating resin of the cover is also filled in the helical element, so that its strength against bending and the like is increased and the pitch of the helical element is not changed, and the antenna characteristics are stabilized.
[0032]
In the antenna device according to the eighth aspect, the antenna device of the present invention can be applied as an antenna having a desired number of frequency bands.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a first embodiment of an antenna device according to the present invention;
FIG. 2 is a diagram illustrating an operation of a loading circuit.
FIG. 3 is an equivalent circuit diagram.
FIG. 4 is a VSWR characteristic diagram.
FIG. 5 is a gain characteristic diagram.
FIG. 6 is a block diagram of a second embodiment of the antenna apparatus of the present invention.
FIG. 7 is a diagram for explaining that signals of a large number of frequency bands can be transmitted and received by an appropriate setting in the antenna device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Helical element 10a Coil 12 Loading circuit 14, 30 Capacitor 16 1st element part 18 Antenna element part 20 Feeding point 26 Cover 28 Floating capacitance 32 2nd element part 48 Demultiplexer 50 Buffer amplifier 56 FM amplifier 60 BAND3 amplifier 64 L band Amplifier f1 First frequency band f2 Second frequency band f3 Third frequency band

Claims (8)

A first element part having a loading circuit composed of a parallel resonance circuit of a coil and a capacitor in the middle part of the helical element, and a base of an antenna element part arranged substantially parallel to the axial direction of the first element part and close to the outside thereof A second element portion having an end capacitively coupled to a feeding point of the first element portion, and a parallel resonance frequency of the loading circuit between a first frequency band and a second frequency band having a higher frequency than the first resonance band. The effective length of the first element unit is set to an intermediate value, and the effective length of the first element unit is set to approximately ¼ wavelength for each of the first frequency band and the second frequency band, and the physical length of the second element unit is set. Is shorter than the physical length of the first element part, and the effective length of the second element part is substantially equal to the third frequency band having a frequency higher than the second frequency band , including the capacitance of the capacitive coupling. set up and configure to a quarter wavelength Antenna apparatus characterized by a. A first element part having a loading circuit composed of a parallel resonance circuit of a coil and a capacitor in the middle part of the helical element, and a base end of the antenna element part arranged coaxially or coaxially with the first element part A second element unit that is capacitively coupled to a feeding point of the one element unit, and the parallel resonance frequency of the loading circuit is set to an intermediate value between the first frequency band and a second frequency band of a higher frequency. The effective length of the first element unit is set to approximately ¼ wavelength for each of the first frequency band and the second frequency band, and the physical length of the second element unit is set to the first frequency band. The effective length of the second element part is made shorter than the physical length of the element part and the third frequency band having a frequency higher than the second frequency band , including the capacity of the capacitive coupling, is almost ¼ wavelength. That is configured with And the antenna device. 3. The antenna device according to claim 1, wherein a physical length of the first element unit is set to 1/10 to 1/20 wavelength of the first frequency band. . 3. The antenna device according to claim 1 or 2, wherein the antenna element portion is composed of a rod-shaped element. 3. The antenna device according to claim 1, wherein the coil of the loading circuit is coaxially configured with the same winding diameter as the helical element. 3. The antenna device according to claim 1, wherein the capacitive coupling of the second element unit is configured by arranging the proximal end of the antenna element unit close to the feeding point without being electrically connected in a direct current manner. A feature antenna device. 7. The antenna device according to claim 1, wherein the first element part and the second element part are both elastically deformable and integrally cover the first element part and the second element part. An antenna device comprising: a cover formed by molding a single rod-like body with an insulating resin having elasticity. 3. The antenna device according to claim 1, wherein a demultiplexer for demultiplexing a signal of a predetermined frequency band for each band is provided at the feeding point, and an amplifier for amplifying the signal output by demultiplexing the demultiplexer is provided. An antenna device characterized in that it is provided.

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