JP3925364B2 - Antenna and diversity receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle-mounted antenna, and more particularly to an FM radio or television band antenna that can be installed in a resin body portion.
[0002]
[Prior art]
FIG. 10 is a plan view of a conventional loop antenna installed on a resin roof found 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. 10 is known. . This is a loop-shaped antenna 3 disposed on a resin-made automobile roof 2, and power is supplied to the antenna using a coaxial line 4.
[0003]
In the frequency of FM radio and VHF band television, one wavelength is about 4 m. Therefore, in order to receive with high sensitivity, one side of the loop antenna needs a length of about 1 m. As shown in the figure, the entire roof has only a space for installing one antenna.
[0004]
FIG. 11 is a plan view illustrating a modification (downsizing) 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 moon roof 5, it is impossible to arrange an antenna in the front half space of the automobile roof because of vehicle specifications. Therefore, the loop antenna shown in FIG. 10 cannot be used. By using the automobile 1 as the ground, it can be easily considered to use the grounded loop antenna 3 whose perimeter is half.
[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. Even if the perimeter of this antenna is half, it can receive with almost the same sensitivity as in FIG. 10 because the vehicle body is used as the ground. These antennas are particularly good for receiving FM radio and TV broadcast charged waves.
[0006]
In addition, when receiving FM radio or television in a car, the car moves in a mobile communication environment where standing waves are generated. Therefore, reception using one antenna increases reception sensitivity depending on the location. It will decline. Therefore, in the current FM radio and television systems for automobiles, in order to obtain higher sensitivity, a diversity method is generally used in which a plurality of antennas are switched according to the mobile communication environment and reception is performed using the antenna with the highest sensitivity. It is used for.
[0007]
[Patent Document 1]
Japanese Utility Model Publication 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-described diversity system that receives the VHF band of FM radio or television with high sensitivity, it is necessary to arrange a plurality of antennas. With the antenna shape, it is often not easy to achieve both the miniaturization of the antenna and high sensitivity reception.
This is because there are not a few types of vehicles in which it is difficult to secure a sufficient space for mounting a plurality of antennas for diversity in a vehicle roof, a hood, or the like with the conventional antenna shape.
[0009]
FIG. 12 is a plan view illustrating a modified example in which the conventional loop antenna installed on the resin roof is miniaturized and pluralized. As a countermeasure against the above-mentioned problem related to diversity reception, for example, a form in which a plurality of antennas are arranged by bending a loop antenna into an inverted triangle and reducing the size as illustrated in FIG. 12 may be conceived.
However, when the loop antenna is simply reduced in size as described above, the following two problems arise.
[0010]
[1] Problem of frequency characteristics In a partial frequency band (around 200 MHz) of the VHF band of the television band, matching between the antenna and the feed line is greatly deteriorated, and reception sensitivity is lowered.
[0011]
FIG. 13 is an explanatory diagram for explaining the problems of the prior art. For example, the perimeter length L of the inverted triangular antenna shown in FIG. 13A requires about 0.5 wavelength at the lowest operating frequency. In order to receive near 100 MHz, the length is 1.5 m. In this case, the peripheral length L is one wavelength at a frequency near 200 MHz. In order to reduce the size of the antenna, an inverted triangular antenna structure is used. At a frequency of 200 MHz, the lateral width W of the antenna is smaller than the wavelength, and the antenna operates as a short-circuit stub having a length of 0.5 wavelength. As a result, the impedance is lowered, the antenna and the coaxial line cannot be matched, and the reception sensitivity is lowered.
[0012]
[2] Directivity problem In the VHF band of the TV band, there is a direction in which the reception sensitivity decreases, and the reception sensitivity decreases depending on the direction in which the vehicle travels. Therefore, stable high-quality sounds and images cannot be obtained during travel.
[0013]
For example, in the inverted triangular antenna shown in FIG. 13B, the phase of the current distribution of the antenna is inverted at the point b in the figure. However, this point b is a midpoint of the loop length of the antenna, that is, a point where L _ab = L _bc = 0.5L. Due to this phase inversion, a current of opposite phase flows at the point b in the antenna element 22 in the horizontal direction. As a result, the currents cancel each other, and the directivity causes a drop in the vertical direction of the drawing. Therefore, when this antenna is mounted on an automobile as shown in FIG. 12, the reception sensitivity decreases in the front-rear direction of the automobile.
[0014]
The present invention has been made to solve the above-described problems, and its purpose is to have high sensitivity suitable for diversity reception, mainly for FM radio and television bands, and for vehicle resin bodies, etc. It is to realize an antenna that can be easily mounted on.
[0015]
[Means for Solving the Problem, Action, and Effect of the Invention]
In order to solve the above problems, the following means are effective.
That is, according to the first means of the present invention, an in-vehicle antenna that can be disposed on a resin body of a vehicle is provided with a substantially inverted triangular loop structure with the vicinity of the feeding point downward, and the loop length of this loop structure is determined by itself. By inserting a short-circuit stub that is adjusted according to the line length of the loop structure in series with respect to the loop structure in the vicinity of one vertex of the substantially inverted triangle, the position of the loop midpoint of the loop structure and the position of the vertex Is substantially matched.
[0016]
According to such a configuration, the above-described directivity problem can be solved. FIG. 1 is an explanatory diagram for explaining the operation and effect of the present invention. For example, as a configuration according to the first means of the present invention described above, a configuration in which the short-circuit stub 21 illustrated in FIG. 1 is loaded in series with the antenna can be considered. With such a configuration, the point b where the current is reversed can be arranged at the corner portion, and the current flowing through the antenna element 22 in the lateral direction can be radiated effectively. As a result, when this antenna is mounted on an automobile as shown in FIG. 2, it is possible to eliminate a drop in reception sensitivity in the longitudinal direction of the automobile.
Moreover, the short-circuit stub 21 loaded in this way also has an effect of reducing the overall dimensions of the antenna.
[0017]
The second means of the present invention is to arrange an open stub starting from the vicinity of the feeding point in parallel with the loop structure in the first means.
[0018]
According to such a configuration, the above-described problem of frequency characteristics can be solved. For example, as a configuration according to the above-mentioned second means of the present invention, as illustrated in FIG. 1, an open stub 20 having a wavelength of 0.25 at 200 MHz is loaded in parallel with the antenna near the feeding point. It is done. As a result, the impedance value near 200 MHz increases, and a sufficient match with the coaxial line can be obtained.
[0019]
Further, the third means of the present invention is the above first or second means, above the middle point between the vertex and the feeding point, and below the wavelength of the received radio wave by 1% or more from the vertex. Forming the short-circuit stub.
[0020]
According to such a configuration, the proximity action of the short-circuit stub with respect to the lateral antenna element (eg, the antenna element 22 in FIG. 13) is alleviated, and the radiation caused by the current flowing through the short-circuit stub is caused by the current flowing through the lateral antenna element. Since it becomes difficult to cancel the radiation, it is possible to effectively radiate radio waves based on the current flowing through the antenna element in the lateral direction (for example, the antenna element 22 in FIG. 13). Of course, it is needless to say that a good operation / effect can be obtained by the same principle for the reception operation.
[0021]
According to a fourth means of the present invention, in any one of the first to third means, 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. The coil shape.
That is, the shape of the short-circuit stub according to the present invention may be arbitrary as long as the loop length of the antenna can be adjusted. In particular, when formed in a coil shape, for example, by using both the front and back sides of a printed circuit board having a short-circuit hole, or by using a three-dimensional winding, a long distance (loop length) can be achieved in a relatively narrow region. You can earn.
[0022]
The fifth means of the present invention is a vehicle-mounted diversity receiving device, in which two antennas according to any one of the first to fourth means are provided on the roof and two on the hood of the trunk room, for a total of four. Is to place.
For example, with such a configuration, a good diversity receiver can be realized based on the good characteristics of the antenna according to the present invention.
By the above means of the present invention, the above-mentioned problem can be effectively or rationally solved.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on specific examples. However, the present invention is not limited to the following examples.
[First embodiment]
2 and 3 relate to the shape of the antenna 10 according to the first embodiment of the present invention.
FIG. 2 is a plan view of the in-vehicle configuration of the antenna 10 of the first embodiment viewed from the inside of the vehicle, and shows the two antennas 10 provided on the resin roof 11 of the automobile. Reference numeral 12 denotes a moon roof. The antenna 10 of the first embodiment is installed inside the 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 composed of a linear conductor, but may be formed of a flat conductor, for example. 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 feeding part is shown enlarged on the right side of FIG. The outer conductor 16 of the coaxial line 14 is electrically fixed to the body frame by a method such as soldering 17. Further, the inner conductor 15 is electrically connected to the antenna element 10 by a technique such as soldering 17.
[0025]
FIG. 3 is a detailed view of the antenna 10 of the first embodiment, and shows the structure of the antenna 10. An open stub 20 is loaded in parallel with the antenna element in the vicinity of the feeding point on the inverted triangular loop antenna. 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]
A suitable antenna size in which the phase of the current due to the received wave is just inverted at the above-mentioned corner located at the right end of the horizontal antenna element 22 in FIG. 3 is, for example, L1 = 0.15 wavelength at 100 MHz, 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 reflection loss characteristic of the antenna of the first embodiment, and shows the reflection loss at the antenna feeding point. The reflection loss with and without the stub 20 is indicated by a solid line and a dotted line, respectively.
[0028]
In the absence of the stub 20, 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 feed line, so that the reception 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 200 MHz band of the VHF band, and reception can be satisfactorily performed in the entire VHF band and UHF band.
It should be noted that a reflection loss of −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 the horizontal plane at 100 MHz. When the stub 21 is not present, as shown in FIG. 5A, a decrease in reception sensitivity is observed particularly at the rear of the vehicle. By attaching the stub 21, there is no drop in sensitivity as shown in FIG. 5B, and reception can be satisfactorily performed 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 provided with the moon roof 12 is exemplified. However, the specification of the resin roof suitable for mounting the antenna of the present invention is shown. Is not limited to those provided with a moon roof (sunroof) or the like.
Since the antenna according to the present invention can be easily miniaturized, for example, in a resin roof that does not include a moon roof (sunroof) or the like, a plurality of three, four, or more can be mounted. 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 vehicle-mounted form of the antenna 10 according to the second embodiment as seen from inside the vehicle. In the first embodiment, the elements of the antenna 10 are arranged in the same direction and arranged symmetrically. However, for example, as illustrated in FIG. According to such an arrangement, the directivities of the two antennas can be made greatly different, and the diversity effect can be further enhanced.
[0032]
Such a left-right asymmetric arrangement is also effective when a plurality of three, four, or more antennas as illustrated in the first embodiment are mounted. For example, in the case of a resin roof that does not include a moon roof (sun roof) or the like, the orientation of each antenna may be shifted by 90 ° to take a substantially bowl-shaped arrangement. Even with such a configuration, the directivity of a large number of antennas can be varied greatly, so that the diversity effect 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 a trunk lid 30 made of resin, and with such a configuration, FM radio and television can be received as well as a resin roof.
[0034]
In addition, a diversity receiving apparatus having four, five, six, or more antennas is configured by using two such antennas together with two or more antennas of the above-described embodiments. 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]
In addition, the direction of each antenna with respect to the vehicle body may be arbitrary. With regard to these directions, a suitable or optimal combination can be selected in consideration of the presence / absence or size of the installation space, the diversity effect as exemplified in the second embodiment, or the like.
[0036]
[Fourth embodiment]
FIG. 8 is a front view showing the antenna 10 (first modification of the stub 20) of the fourth embodiment. In the first embodiment described above, 20 stubs are arranged as shown in FIG. 3, but they may be extended to the inside of 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 (second modification of the stub 20) of the fifth embodiment. For example, as shown in FIG. 9, instead of being directly connected to the antenna 10, it may be directly connected to the body frame and disposed 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.
Also in this case, the length of the open stub 20 needs to be about 0.25 wavelength at 200 MHz, as in the first embodiment.
[0038]
In each of the above embodiments, an antenna having an open stub is illustrated, but the open stub is not necessarily provided. For example, in a receiving apparatus that does not require reception of radio waves in the vicinity of 200 MHz belonging to the VHF band, the operation and effect of the present invention based on the above-described means of the present invention can be obtained even with such a configuration. .
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining the operation and effect of the present invention.
FIG. 2 is a plan view of the in-vehicle configuration of the antenna 10 of the first embodiment when viewed from the inside of the vehicle.
FIG. 3 is a detailed view of the antenna 10 of the first embodiment.
FIG. 4 is a graph illustrating the reflection loss characteristics of the antenna of the first embodiment.
FIG. 5 is a graph illustrating the directivity characteristics of the antenna of the first embodiment.
FIG. 6 is a plan view of a vehicle-mounted form of the antenna 10 of the second embodiment as seen from inside the vehicle.
FIG. 7 is a perspective view showing a vehicle-mounted form of the antenna 10 of the third embodiment.
FIG. 8 is a front view showing an antenna 10 (first modification of a stub 20) according to a fourth embodiment.
FIG. 9 is a front view showing an antenna 10 (second modification of a stub 20) of a fifth embodiment.
FIG. 10 is a plan view of a loop antenna installed on a conventional resin roof.
FIG. 11 is a plan view illustrating a modified example (downsizing) of a loop antenna installed on a conventional resin roof.
FIG. 12 is a plan view illustrating a modified example (miniaturization and multiple use) of a loop antenna installed on a conventional resin roof.
FIG. 13 is an explanatory diagram for explaining the problems of the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Antenna 11 ... Resin roof 12 ... Moon roof 13 ... Body frame 14 ... Coaxial line 15 ... Coaxial line inner conductor 16 ... Coaxial line outer conductor 17 ... Solder 20 ... Open stub (impedance improvement stub)
21 ... Short-circuit stub (directivity improving stub)
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 below,
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 in the vicinity of one vertex of the substantially inverted triangle,
The antenna characterized in that the position of the midpoint of the loop of the loop structure and the position of the apex substantially coincide. The antenna according to claim 1, wherein an open stub starting from the vicinity of the feeding point is arranged in parallel to the loop structure. The short-circuit stub is
3. The antenna according to claim 1, wherein the antenna is formed above a midpoint between the apex and the feeding point and at least 1% below a wavelength of a received radio wave from the apex. . 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 uneven shape, a wave shape, a planar coil shape, or a three-dimensional coil shape. A vehicle-mounted diversity receiver,
5. A diversity receiving apparatus comprising a total of four antennas according to claim 1, two on a roof and two on a hood of a trunk room.

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