JP2004096618A - Antenna and diversity receiving apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an antenna which is suited to diversity reception or the like, can be easily mounted on a resin-made body of a vehicle or the like and is excellent in directivity. <P>SOLUTION: In the constitution of loading a short-circuit stab 21 serially to the antenna, a point b at which current is inverted is located in the corner, and current flowing to traverse antenna elements 22 is effectively radiated. As a result, when the antenna is mounted on an automobile, drop of a receiving sensitivity in the longitudinal direction of the automobile is eliminated. Further, the short-circuit stab 21 loaded like this also presents the effect of reducing a dimension of the whole antenna. Further, an open stab 20 which becomes 0.25 wavelength in 200 MHz is loaded near a feeding point parallel to the antenna, so that a value of impedance near 200 MHz is increased to be sufficiently matched with a coaxial line, thereby realizing excellent reception. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a vehicle-mounted antenna, and more particularly, to an antenna for an FM radio or television band that can be installed in a resin body.
[0002]
[Prior art]
FIG. 10 is a plan view of a conventional loop antenna installed on a resin roof shown in, for example, Patent Document 1 below. That is, as a conventional vehicle-mounted antenna that can be installed on a resin body such as a resin roof or a resin trunk, for example, an antenna installed on a resin roof 2 of an automobile 1 as illustrated in FIG. . This is a loop-shaped antenna 3 arranged on a resin-made automobile roof 2, and power is supplied to the antenna using a coaxial line 4.
[0003]
Since one wavelength is about 4 m near the frequency of FM radio or VHF band television, one side of the loop antenna needs to be about 1 m long in order to receive with high sensitivity. As shown in the figure, there is only space for installing one antenna on the entire roof.
[0004]
FIG. 11 is a plan view illustrating a modified example (miniaturization) of a loop antenna installed on a conventional resin roof. For example, as shown in FIG. 11, in a vehicle equipped with a sunroof or a moonroof 5, it is impossible to arrange an antenna in the space in the front half of the vehicle roof due to the specifications of the vehicle. Therefore, the loop antenna shown in FIG. 10 cannot be used. By using the automobile 1 as a ground, it is easily conceivable to use a grounded loop antenna 3 having a half circumference.
[0005]
In this case, power is supplied to the gap between the antenna element 3 and the vehicle body 1 at the location 6 using the coaxial line 4. This antenna can receive with almost the same sensitivity as that of FIG. These antennas are particularly designed to improve reception of FM radio and television broadcast charged waves.
[0006]
Also, when an automobile receives FM radio or television, the automobile moves in a mobile communication environment in which a standing wave is generated. Therefore, if only one antenna is used for reception, the reception sensitivity may be large depending on the location. Will drop. Therefore, in the current FM radio and television systems for automobiles, in order to obtain higher sensitivity, a diversity system in which a plurality of antennas are switched according to a mobile communication environment and reception is performed using the antenna with the highest sensitivity is common. Used in
[0007]
[Patent Document 1]
Japanese Utility Model Application Laid-Open No. 2-30611 (pages 3 to 5, FIGS. 1 to 4)
[0008]
[Problems to be solved by the invention]
In general, in order to implement the above-mentioned diversity system for receiving the VHF band of FM radio or television with high sensitivity, it is necessary to arrange a plurality of antennas. With an antenna shape, it is often not easy to achieve both miniaturization of the antenna and high-sensitivity reception.
This is because it is difficult to secure a sufficient space for mounting a plurality of antennas for diversity on a roof, a hood, or the like of a vehicle with a conventional antenna shape.
[0009]
FIG. 12 is a plan view illustrating a modified example in which a conventional loop antenna installed on a resin roof is reduced in size and pluralized. As a countermeasure against the above-mentioned problem related to the diversity reception, for example, a mode in which the loop antenna is bent into an inverted triangle to reduce the size and a plurality of antennas are arranged may be conceived as illustrated in FIG.
However, simply reducing the size of the loop antenna in this way causes the following two problems.
[0010]
[1] Problem of frequency characteristics In a part of the frequency band (around 200 MHz) of the VHF band of the television band, the matching between the antenna and the feed line is greatly deteriorated, and the receiving sensitivity is reduced.
[0011]
FIG. 13 is an explanatory diagram for explaining a problem of the related art. For example, the circumference L of the inverted triangular antenna shown in FIG. 13A requires about 0.5 wavelength at the lowest operating frequency. For receiving near 100 MHz, the length is 1.5 m. In this case, at a frequency around 200 MHz, the perimeter L is one wavelength. In order to reduce the size of the antenna, the antenna has an inverted triangular antenna structure. At a frequency of 200 MHz, the width W in the horizontal direction of the antenna becomes narrower than the wavelength, and the antenna operates as a short-circuit stub having a length of 0.5 wavelength. As a result, the impedance decreases, the antenna and the coaxial line cannot be matched, and the receiving sensitivity decreases.
[0012]
[2] The problem of directivity In the VHF band of the television band, there is a direction in which the receiving sensitivity decreases, and the receiving sensitivity drops depending on the direction in which the vehicle travels, so that stable high-quality sound and images cannot be obtained during traveling.
[0013]
For example, in the inverted triangular antenna shown in FIG. 13B, the phase of the current distribution of the antenna is inverted at a point b in the figure. However, this point b is the midpoint of the loop length of the antenna, _i.e., a point which becomes L _ab = L bc = 0.5L. Due to this phase inversion, currents of opposite phases flow through the antenna element 22 in the lateral direction at the point b. As a result, the currents cancel each other, and a drop occurs in the directivity in the vertical direction of the drawing. Therefore, when this antenna is mounted on an automobile as shown in FIG. 12, the reception sensitivity drops in the front-rear direction of the automobile.
[0014]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a high sensitivity suitable for diversity reception and the like, mainly in an FM radio and television band, and a resin body for a vehicle. An object of the present invention is to realize an antenna that can be easily mounted on a vehicle.
[0015]
Means for Solving the Problems, Functions and Effects of the Invention
In order to solve the above-mentioned problems, the following means are effective.
That is, a first means of the present invention is to provide an in-vehicle antenna that can be disposed on a resin body of a vehicle, by providing a substantially inverted triangular loop structure having the vicinity of a feeding point downward, and setting the loop length of the loop structure to itself. By inserting a short-circuit stub, which is adjusted according to the line length, in series with the loop structure near one vertex of the above-mentioned substantially inverted triangle, the position of the loop midpoint of the loop structure and the position of the vertex Is to be substantially matched.
[0016]
According to such a configuration, the problem of directivity described above can be solved. FIG. 1 is an explanatory diagram illustrating the operation and effect of the present invention. For example, as a configuration according to the above-described first means of the present invention, a form in which a short-circuit stub 21 as illustrated in FIG. 1 is loaded in series to an antenna can be considered. With such a configuration, the point b at which the current is inverted can be arranged at the corner, and the current flowing in the lateral antenna element 22 can be effectively radiated. As a result, when this antenna is mounted on an automobile as shown in FIG. 2, it is possible to eliminate a drop in the reception sensitivity in the front-rear direction of the automobile.
Further, the short-circuit stub 21 loaded in this manner also has an effect of reducing the size of the entire antenna.
[0017]
According to a second aspect of the present invention, in the first aspect, an open stub starting from the vicinity of the feeding point is arranged in parallel with the loop structure.
[0018]
According to such a configuration, the problem of the frequency characteristics described above can be solved. For example, as a configuration according to the above-mentioned second means of the present invention, as shown in FIG. 1, a form in which an open stub 20 having a 0.25 wavelength at 200 MHz is loaded in parallel with an antenna near a feeding point is considered. Can be As a result, the value of the impedance near 200 MHz increases, and a sufficient matching with the coaxial line can be obtained, so that good reception can be achieved.
[0019]
Further, the third means of the present invention, in the above first or second means, is located above the middle point between the apex and the feeding point and below the apex by 1% or more of the wavelength of the received radio wave. The short circuit stub is formed.
[0020]
According to such a configuration, the proximity effect of the short-circuit stub to the lateral antenna element (eg, the antenna element 22 of FIG. 13) is reduced, and the radiation caused by the current flowing through the short-circuit stub is reduced by the current flowing through the lateral antenna element. Since it becomes difficult to cancel the radiation, it is possible to effectively radiate a radio wave based on the current flowing through the antenna element in the lateral direction (eg, the antenna element 22 in FIG. 13). Of course, it goes without saying that a good operation and effect can be obtained in the receiving operation based on exactly the same principle.
[0021]
Further, the fourth means of the present invention is the method according to any one of the first to third means, wherein the shape of the short-circuit stub is changed to a one-step concave shape, a multi-step uneven shape, a wave shape, a planar coil shape, or a three-dimensional shape. It is to make a coil shape.
That is, the shape of the short-circuit stub of the present invention may be any shape as long as the shape can adjust the loop length of the antenna. In particular, when formed in a coil shape, for example, a long distance (loop length) can be obtained in a relatively narrow area by using both front and back surfaces of a printed circuit board having a short-circuit hole or using a three-dimensional winding. You can earn.
[0022]
In a fifth aspect of the present invention, there are provided a diversity receiver for a vehicle, two antennas according to any one of the first to fourth means on a roof and two antennas on a hood in a trunk room, for a total of four antennas. It is to arrange.
For example, with such a configuration, it is possible to realize a good diversity receiving apparatus based on the good characteristics of the antenna according to the present invention.
By the means of the present invention described above, the above problems can be effectively or rationally solved.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on specific examples. However, the present invention is not limited to the embodiments described below.
[First embodiment]
2 and 3 relate to the shape and the like of the antenna 10 according to the first embodiment of the present invention.
FIG. 2 is a plan view of the on-vehicle configuration of the antenna 10 according to the first embodiment as viewed from inside the vehicle, and shows two antennas 10 provided on a resin roof 11 of the vehicle. Reference numeral 12 indicates a moon roof. The antenna 10 of the first embodiment is installed inside a resin roof.
[0024]
The antenna 10 is fixed to a resin roof 11 attached to a vehicle body frame 13 of an automobile, and is formed of a linear conductor. Alternatively, the antenna 10 may be formed of a flat conductor or the like. The antenna 10 is fed by a coaxial line 14 and is connected to an amplifier, a selector, a tuner, and the like.
The structure of the power supply unit is enlarged and shown on the right side of FIG. The outer conductor 16 of the coaxial line 14 is electrically fixed to the vehicle body frame by a method such as soldering 17. The inner conductor 15 is electrically connected to the antenna element 10 by a method such as soldering 17.
[0025]
FIG. 3 is a detailed view of the antenna 10 according to the first embodiment, and shows the structure of the antenna 10. An open stub 20 is mounted near the feeding point on the inverted triangular loop antenna in parallel with the antenna element. Further, a stub 21 for adjusting the current distribution is loaded in series with the antenna element at the upper right corner of the antenna element.
[0026]
At the above-mentioned corner located at the right end of the horizontal antenna element 22 in FIG. 3, a suitable antenna size at which the phase of the current due to the received wave is just inverted is, for example, at 100 MHz, L1 = 0.15 wavelength, L2 = 0.13 wavelength, L3 = 0.01 wavelength, L4 = 0.03 wavelength, L5 = 0.01 wavelength, L6 = 0.15 wavelength, L7 = 0.04 wavelength, L8 = 0.03 wavelength, L9 = 0.125 wavelength.
[0027]
FIG. 4 is a graph illustrating the return loss characteristics of the antenna according to the first embodiment, and illustrates the return loss at the antenna feed point. The reflection loss with and without the stub 20 is shown by a solid line and a dotted line, respectively.
[0028]
When the stub 20 is not provided, the reflection loss deteriorates to about -3 dB around 200 MHz in the VHF band, and more than half of the power is not transmitted to the power supply line, so that the receiving sensitivity is greatly deteriorated.
However, when the stub 20 is loaded, for example, as can be seen from FIG. 4, the reflection loss is suppressed to -5 dB or less in the VHF band of 200 MHz, and the signal can be satisfactorily received in the entire VHF band and the UHF band.
The fact that the reflection loss is -5 dB or less is one measure for good reception.
[0029]
FIG. 5 is a graph illustrating the directivity characteristics of the antenna of the first embodiment, and shows the directivity in a horizontal plane at 100 MHz. When the stub 21 is not provided, as shown in FIG. By attaching the stub 21, the drop in sensitivity does not occur as shown in FIG. 5B, and it becomes possible to receive signals satisfactorily in all directions of the automobile.
[0030]
In the first embodiment (FIG. 2), the form of the antenna 10 mounted on the resin roof 11 having the moon roof 12 is exemplified. However, the specification of the resin roof suitable for mounting the antenna of the present invention is described. Is not limited to those having a moon roof (sun roof) or the like.
Since the antenna according to the present invention can be easily miniaturized, three, four or more plural antennas can be mounted on a resin roof having no moon roof (sun roof) or the like. According to such a configuration, an antenna group effective for diversity reception can be easily mounted on the resin roof of the vehicle.
[0031]
[Second embodiment]
FIG. 6 is a plan view of the on-vehicle configuration of the antenna 10 according to the second embodiment viewed from the inside of the vehicle. In the first embodiment, the elements of the antenna 10 are arranged in the same direction and arranged symmetrically. However, as illustrated in FIG. 6, for example, the antenna 10 may be rotated 90 ° and arranged asymmetrically. According to such an arrangement, the directivities of the two antennas can be made significantly different, and the effect of diversity can be further enhanced.
[0032]
Such an asymmetric arrangement is also effective when three, four, or more antennas are mounted, as exemplified in the first embodiment. For example, in the case of a resin roof not provided with a moon roof (sun roof) or the like, the orientation of each antenna may be shifted by 90 ° to take a substantially swastika arrangement. Even with such a configuration, the directivity of a large number of antennas can be greatly different from each other, so that the effect of diversity can be enhanced.
[0033]
[Third embodiment]
FIG. 7 is a perspective view showing a vehicle-mounted form of the antenna 10 of the third embodiment. As shown in FIG. 7, an antenna may be arranged on the trunk lid 30 made of resin, and even with such a configuration, it is possible to receive FM radio and television as well as the resin roof.
[0034]
Further, such two antennas are used in combination with the two or more antennas of the above-described embodiments to configure a diversity receiving apparatus having four, five, six, or more antennas. As a result, the diversity receiver that can be mounted on the resin body of the vehicle can be configured with much higher performance than before.
[0035]
The orientation of each of these antennas with respect to the vehicle body may be arbitrary. Regarding these directions, a suitable or optimum combination can be selected in consideration of the presence or absence of the installation space, the size thereof, the effect of diversity as exemplified in the second embodiment, and the like.
[0036]
[Fourth embodiment]
FIG. 8 is a front view showing an antenna 10 (a first modification of the stub 20) of the fourth embodiment. In the above-described first embodiment, the twenty stubs are arranged as shown in FIG. 3, but may be configured to extend inside the loop as shown in FIG. 8, for example. Even with such a configuration, the operation and effect of the present invention based on the above-described means of the present invention can be obtained.
[0037]
[Fifth embodiment]
FIG. 9 is a front view showing the antenna 10 (a second modification of the stub 20) of the fifth embodiment. For example, instead of being directly connected to the antenna 10 as shown in FIG. 9, it may be directly connected to the vehicle body frame and arranged along the antenna. Even if the stub is not directly connected to the antenna element, the effect of loading the stub in parallel with the antenna element can be obtained with this configuration.
In this case, the length of the open stub 20 needs to be about 0.25 wavelength at 200 MHz, similarly to the first embodiment.
[0038]
In each of the above embodiments, the antenna having the open stub is illustrated, but the open stub may not necessarily be provided. For example, in a receiving device or the like that does not need to receive a radio wave in the vicinity of 200 MHz belonging to the VHF band, the operation and effect of the present invention based on the means of the present invention can be obtained even with such a configuration. .
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating the operation and effect of the present invention.
FIG. 2 is a plan view of the on-vehicle configuration of the antenna 10 according to the first embodiment as viewed from inside the vehicle.
FIG. 3 is a detailed view of an antenna 10 according to the first embodiment.
FIG. 4 is a graph illustrating the reflection loss characteristics of the antenna according to the first embodiment.
FIG. 5 is a graph illustrating the directivity characteristics of the antenna according to the first embodiment.
FIG. 6 is a plan view of the on-vehicle configuration of the antenna 10 according to the second embodiment as viewed from inside the vehicle.
FIG. 7 is a perspective view showing an in-vehicle configuration of an antenna 10 according to a third embodiment.
FIG. 8 is a front view showing an antenna 10 (a first modification of the stub 20) of the fourth embodiment.
FIG. 9 is a front view showing an antenna 10 (a second modification of the stub 20) according to a fifth embodiment.
FIG. 10 is a plan view of a conventional loop antenna installed on a resin roof.
FIG. 11 is a plan view illustrating a modification (miniaturization) of a loop antenna installed on a conventional resin roof.
FIG. 12 is a plan view illustrating a modified example (small size and multiple sizes) of a loop antenna installed on a conventional resin roof.
FIG. 13 is an explanatory diagram for explaining a problem of the related art.
[Explanation of symbols]
10 Antenna 11 Resin roof 12 Moon roof 13 Body frame 14 Coaxial cable 15 Inner conductor 16 of coaxial cable Outer conductor 17 of coaxial cable Solder 20 Open stub (impedance improving stub)
21… short-circuit stub (stub for improving directivity)
22 ... horizontal antenna element 30 ... resin trunk (trunk lid)

Claims (5)

An in-vehicle antenna that can be disposed on a resin body of a vehicle,
It has a substantially inverted triangular loop structure with the vicinity of the feeding point as a downward,
A short-circuit stub that adjusts the loop length of the loop structure by its own line length is inserted in series with the loop structure near one vertex of the substantially inverted triangle,
An antenna, wherein the position of a loop midpoint of the loop structure substantially coincides with the position of the vertex. The antenna according to claim 1, wherein an open stub starting from the vicinity of the feed point is arranged in parallel with the loop structure. The short-circuit stub is
3. The antenna according to claim 1, wherein the antenna is formed above a middle point between the apex and the feeding point and below the apex by 1% or more of a wavelength of a received radio wave. 4. . The shape of the short-circuit stub is
The antenna according to any one of claims 1 to 3, wherein the antenna has a one-step concave shape, a multi-step concave-convex shape, a wave shape, a planar coil shape, or a three-dimensional coil shape. An in-vehicle diversity receiver,
A diversity receiver comprising two antennas according to any one of claims 1 to 4, two on a roof and two on a hood in a trunk room.

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