JP2011019081A - Glass antenna for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high antenna performance, even when an antenna element is arranged in close proximity to a body edge.SOLUTION: The glass antenna 20 for vehicle is mounted on a window glass 13 provided on a vehicle body 11 so as to close an opening in the vehicle body 11 includes a linear first antenna element 21 extended in the opening along a body edge 24 from a power supplying part 20c, a second antenna element 22 folded back from a front end of the first antenna element by about 180 degrees to be extended to face the first antenna element, and a third antenna element 20b folded back from a front end of the second antenna element by about 180 degrees to be extended to face the second antenna element.

Description

  The present invention relates to an antenna provided on a window glass of a vehicle, and more particularly to a vehicle glass antenna suitable for reception of a digital television band.

  For a DTV (Digital Television) antenna for a vehicle, a form in which a film is mounted on a window glass of a vehicle is mainly adopted for reasons of mounting space and aesthetics. 2. Description of the Related Art A high-frequency glass antenna for automobiles that is mounted on a window glass of a vehicle is known (for example, see Patent Document 1 (see FIG. 1)).

The technique of Patent Document 1 will be described with reference to FIG.
As shown in FIG. 15, the antenna conductor 100 is formed on the windshield 110. The antenna conductor 100 includes a first antenna element 101, a second antenna element 102, a first connection conductor 103, and a loop forming element 104. A U-shaped conductor pattern is formed by the first antenna element 101, the second antenna element 102, and the first connection conductor 103.

  In addition, the first antenna element 101 and the power feeding unit 105 are connected via the second connection conductor 106, and the first antenna element 101, the first connection conductor 103, the loop forming element 104, Thus, a loop portion is formed.

  Thus, since the antenna conductor 100 has a loop portion, the antenna conductor 100 can have a plurality of resonance frequencies, and is flat and has a high antenna gain and a high FB ratio (Front / Back power ratio) can be obtained.

By the way, when the distance between the second antenna element 102 and the body edge made of metal is ¼ wavelength or less, the radiation impedance becomes small and the radiation efficiency as the antenna is lowered, and the bandwidth and directivity characteristics are reduced. There will be restrictions.
Therefore, according to the technique of Patent Document 1, the second antenna element 102 serving as the main antenna needs to be separated from the body edge of the vehicle roof by about 100 mm.

If it is about 100 mm away from the body edge, the second antenna element 102 may enter the driver's field of view, and improvement is required.
Therefore, a technique that can bring the second antenna element 102 closer to the body edge is desired.

JP 2008-22538 A

  It is an object of the present invention to provide a glass antenna for a vehicle that can obtain high antenna performance even when an antenna element is disposed close to a body edge.

  According to the first aspect of the present invention, the vehicle glass antenna is attached to a window glass provided in the vehicle body so as to close the opening of the vehicle body, and includes an antenna element having a folding pattern of at least two times. It is characterized by that.

  According to a second aspect of the present invention, in the glass antenna for a vehicle according to the first aspect, the antenna element is a linear first antenna that extends from the feeding portion into the opening and along the edge of the opening. An element, a second antenna element that is folded back approximately 180 degrees from the front end of the first antenna element, and extends to face the first antenna element, and is folded back approximately 180 degrees from the front end of the second antenna element. And a third antenna element extending opposite to the second antenna element.

  The invention according to claim 3 is the glass antenna for a vehicle according to claim 2, wherein the third antenna element is the glass antenna for a vehicle according to claim 1. It is arranged within a distance corresponding to 1/16 of one wavelength of a predetermined frequency from the edge of the opening.

  According to a fourth aspect of the present invention, in the vehicle glass antenna according to the first or second aspect, the length of the third antenna element is multiplied by half of one wavelength of a predetermined frequency by a shortening rate. It is characterized by being set to the value obtained in the above.

  According to the first aspect of the present invention, the vehicle glass antenna has a folding pattern that extends at least twice along the edge of the opening of the vehicle body, thereby reducing impedance due to the proximity of the vehicle body edge. The reception sensitivity can be improved while suppressing the above.

  In the invention according to claim 2, the antenna pattern is composed of first, second, and third antenna elements, and the first antenna element extends from the feeding portion into the opening and along the edge of the opening. The second antenna element is folded back approximately 180 degrees from the tip of the first antenna element so as to be opposed to the first antenna element, and the third antenna element is the second antenna element. The first antenna element is folded 180 degrees from the tip of the first antenna element so as to face the second antenna element. In this way, the first, second, and third antenna elements can form a folding pattern twice, thus improving the reception sensitivity while suppressing a decrease in impedance due to the proximity of the vehicle body edge. be able to.

  In the invention according to claim 3, the third antenna element located at the lowermost part of the glass antenna is arranged away from the edge of the opening by a short distance corresponding to within 1/16 of one wavelength of the predetermined frequency. , Do not disturb the field of view when driving.

  In the invention according to claim 4, since the length of the third antenna element is set to a value obtained by multiplying 1/2 of one wavelength of the predetermined frequency by the shortening rate, the design of the antenna pattern is easy. Become.

It is a top view of a vehicle provided with the glass antenna for vehicles concerning the example of the present invention. It is a figure which shows the basic structure of the glass antenna for vehicles which concerns on the Example of this invention, and the dimension of each part. It is a figure which shows the typical pattern of the glass antenna for vehicles used for the measurement. It is a graph which shows the correlation of the folding | turning dimension of a glass antenna for vehicles, and a sensitivity. It is a graph which shows the change of VSWR for every folding | turning dimension (0, 25, 50 mm). It is a graph which shows the change of VSWR for every folding | turning dimension (75, 80, 90 mm). It is a graph which shows the change of VSWR for every folding | turning dimension (95, 100, 105 mm). It is a graph which shows the change of VSWR for every folding | turning dimension (110,115,120mm). It is a graph which shows the change of VSWR for every folding | turning dimension (125, 130, 140 mm). It is a graph which shows the change of VSWR for every folding | turning dimension (150 mm). It is a figure of the pattern which shows the distance of the main antenna element with which it uses for a measurement, and a body edge. It is a graph which shows the correlation with the distance of a main antenna element and a body edge, and a sensitivity change. It is a figure of the pattern which shows the element length of the main antenna element with which it uses for a measurement. It is a graph which shows the correlation of the element length of a main antenna element, and a sensitivity. It is a figure which shows the structure of the conventional glass antenna for vehicles.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  The glass antenna for vehicles according to the present invention can be attached to a window glass of a vehicle. That is, as shown in FIG. 1, the vehicle 10 includes a windshield 13 fitted between the left and right front pillars 12 </ b> L and 12 </ b> R of the vehicle body 11 (L is a subscript indicating left and R is right; the same applies hereinafter); Rear glass 15 fitted between the rear pillars 14L and 14R, front door glasses 17L and 17R attached to the front doors 16L and 16R so as to be movable up and down, and rear parts attached to the rear doors 18L and 18R so as to be raised and lowered. The window glass which consists of door glass 19L and 19R is provided.

  The vehicle glass antenna 20 can be attached to any of the above-mentioned window glasses, but in the present embodiment, it is provided substantially at the upper center of the windshield 13. The glass antenna 20 for a vehicle is a DTV antenna designed to receive radio waves of digital terrestrial broadcasting using a terrestrial UHF (Ultra High Frequency) band mainly for in-vehicle TV.

Details of the vehicle glass antenna 20 will be described with reference to FIG.
As shown in FIG. 2A, the vehicle glass antenna 20 is attached to a window glass 13 provided on the vehicle body 11 so as to close the opening of the vehicle body 11. The glass antenna 20 for vehicles includes an impedance adjustment element 20a, a main antenna element 20b, and a feeding point 20c, which are antenna bodies, which are close to the edge of the opening of the vehicle body 11 (hereinafter referred to as the body edge 24). Attached. Reference numeral 25 denotes a glass edge of the window glass 13 mounted inside the vehicle body 11.

The impedance adjustment element 20a will be described in more detail.
As shown in FIG. 2B, the impedance adjustment element 20 a is made of a linear conductor and includes a first antenna element 21 and a second antenna element 22.

The first antenna element 21 is a linear conductor that extends from the power feeding portion 20 c along the body edge 24. The second antenna element 22 is a linear conductor that is formed by extending 180 degrees from the distal end position of the first antenna element 21 and extending opposite the first antenna element 21. Here, it is assumed that they are extended so as to be substantially parallel to each other.
Note that the main antenna element 20b shown as the third antenna element is formed by extending 180 degrees from the tip of the second antenna element 22 constituting the impedance adjusting element 20a and facing the second antenna element 22. It is a linear conductor. Here, it is assumed that they are extended so as to be substantially parallel to each other.

Next, the optimal example of the dimension of each linear conductor mentioned above is demonstrated.
The folding dimension a of the first and second antenna patterns 21 and 22 constituting the impedance adjustment element 20a is 100 mm, the element length d of the main antenna element 20b is 150 mm, the first and second antenna patterns, and the impedance The optimal conductor spacing c between the adjusting element 20a (second antenna pattern 22) and the main antenna element 20b is 5 mm. Here, the reason why the conductor interval c is set to 5 mm is that there is a trade-off relationship between the high performance of the antenna and the size (reduction of mounting space) in terms of design. This is because the size is given priority from 20 mm.

  Further, the distance b between the main antenna element 20b and the body edge 24 of the vehicle body 11 is optimally within 30 mm. The reason will be described later. The distance e between the feeding point 20c and the turning point of the impedance adjusting element 20a is optimally 5 mm. In addition, the dimension of the feeding point (terminal 20b) applied here shall be 20 mm x 12 mm, and antenna line width shall use 0.2 mm-1.0 mm.

The impedance adjustment element 20a is electrically equivalent to the addition of inductance due to the folding pattern of two times. In addition, the distance b from the body edge 24 of the vehicle body 11, which was conventionally about 100 mm, has been shortened to 30 mm.
As a result, it is possible to suppress a decrease in impedance due to the in-vehicle glass antenna 20 being disposed close to the body edge 24 so as not to obstruct the driving field of view, and as a result, the reception sensitivity can be improved.

  Next, the grounds for the optimum dimensions of the folded dimension a of the impedance adjusting element 20a, the distance b between the main antenna element 20b and the body edge 24, and the element length d of the main antenna element 20b will be described.

(Folding dimension a of the impedance adjusting element 20a)
The inventors measured the antenna sensitivity while changing the folded dimension a of the impedance adjusting element 20a shown in FIG. 2B from 0 to 150 mm and changing the frequency from 400 MHz to 800 MHz.

  In order to facilitate understanding, a representative example of the impedance adjustment element 20a is shown in FIGS. That is, when the antenna length d is made constant and the folding dimension a is changed, for example, the shape of the impedance adjusting element 20a is changed as shown in (a) to (d).

FIG. 4 is a graph showing the sensitivity corresponding to each of the impedance adjustment elements 20a when the folding dimension a is changed from 0 to 150 mm. The horizontal axis represents the frequency [MHz] centered on the DTV band (473 MHz to 713 MHz), and the vertical axis represents the relative sensitivity [dBd].
Here, the sensitivity curves when the folding dimension a is changed to 0 (no folding), 25 mm, 50 mm, 75 mm, 80 mm, 90 mm, 95 mm, 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 150 mm, It is indicated by a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14.

The curve indicated by the thick line a8 is more stable than the thin lines a1 to a7 and a9 to a14, particularly in the DTV band.
Curve a8 is the sensitivity when the folded dimension a = 100 mm, and is superior in sensitivity compared to other folded dimensions, for example, a = 25 mm, 75 mm, and a = 150 mm shown in FIG. Was confirmed.

  By the way, the ratio between the maximum voltage value and the minimum voltage value of the standing wave generated at the feeding point 20c is indicated by VSWR (Voltage Standing Wave Ratio), and the degree of matching between the characteristic impedance of the feeder line and the load impedance It is known to represent In case of perfect matching, VSWR = 1.

  VSWR also changes when the folding size is changed. Therefore, the inventors examined the correlation between the folding dimension and VSWR. The results are shown in FIGS.

  5 to 10, the frequency {MHz} on the horizontal axis, the VSWR on the vertical axis, the measurement start point at 400 MHz, and the measurement stop point at 800 MHz, and points at 473 MHz, 575 MHz, 586 MHz, and 713 MHz. VSWR is shown.

As a result, it was found that the VSWR in the DTV band was low overall when the turn-around dimensions were 90 mm and 95 mm shown in FIGS. 6C and 7A. However, at 90 mm in FIG. 6C, 473 MHz is in the middle of a steep change curve, and for this reason, 95 mm is more stable.
As described above, from the VSWR, it was confirmed that the folding dimension is a desirable value of 95 mm.

Next, an attempt is made to theoretically explain that 95 mm obtained by measurement is a desirable value.
The frequency used for the theoretical explanation is 473 MHz shown in FIG.
This 473 MHz has the worst impedance in the DTV band (473 to 713 MHz). This is because if the explanation is given at 473 MHz, which is an unfavorable condition, explanation on other frequencies with better conditions is not necessary.

  The folded dimension can be obtained by [one wavelength of a predetermined frequency (design frequency)] × (1/4) × shortening rate. [One wavelength of a predetermined frequency (design frequency)] is obtained by 300/473. Then, the folding dimension a is 95 mm by calculation of (300/470) × (1/4) × 0.6. However, when the turn-back is 95 mm, as shown by a6 in FIG. 4, there is a sudden decrease in sensitivity in the vicinity of 473 MHz of the digital TV band. Therefore, in this embodiment, 100 mm is a preferable value as the optimum turn-back dimension.

  As described above, in the glass antenna 20 for a vehicle according to the embodiment of the present invention, the impedance adjustment element 20a is formed into a folding pattern extending at least twice along the edge of the opening of the vehicle body 11, so that the vehicle The reception sensitivity can be improved while suppressing a decrease in impedance due to the proximity of the body edge 24 to the body edge 24. It should be noted that the folding dimension at this time is optimally obtained by multiplying 1/4 of one wavelength of a predetermined frequency by the shortening rate.

(Distance b between main antenna element 20b and body edge 24)
FIG. 11 shows a sensitivity measurement pattern according to the distance between the main antenna element 20b and the body edge 24, and FIG. 12 shows a graph showing the sensitivity change.

  Specifically, the sensitivity changes when the distance b ′ shown in FIG. 11 is changed to 20 mm, 30 mm, 40 mm, 60 mm, 80 mm, 100 mm, and 30 mm (folded back at 100 mm) are shown in FIG. , B3, b4, b5, b6, b7, respectively.

  As is apparent from FIG. 12, as the main antenna element 20b is arranged closer to the body edge 24 (100 mm → 20 mm), it can be understood that the sensitivity decreases at any frequency and the performance deteriorates. However, in the DTV band, a curve indicated by a thick line b7 in which the folded dimension a of the impedance adjusting element 20a is 100 m and the distance b ′ between the main antenna element 20b and the body edge 24 is 30 mm (folded at 100 mm). It can be seen that high sensitivity is maintained over the entire DTV band as compared with the other graphs b1 to b6.

  The impedance adjustment element 20a is provided with a fold having a size that matches a frequency whose sensitivity is insufficient due to an impedance mismatch. However, since this fold is for the purpose of matching, it is necessary to be close to the body edge 24 so as not to be an antenna receiver. is there. In this embodiment, it is desirable that the frequency is within 1 wavelength × 1/16. For example, when the design frequency is 470 MHz, b ′ = 300/470/16 = 40 mm.

  In the vehicle glass antenna 20 according to the embodiment of the present invention described above, the impedance adjustment is performed on the main antenna element 20b as the third antenna element located at the lowermost part of the folded pattern by the impedance adjustment element 20a. It can arrange | position in the vicinity of the body edge 24, and does not interfere with a visual field at the time of a driving | operation.

(Element length d of the main antenna element 20b)
FIG. 13 shows a sensitivity measurement pattern and its dimensions by changing the element length of the main antenna element 20b, and FIG. 14 shows a graph showing the relationship between the element length and sensitivity.

  Specifically, the sensitivity changes when the length (element length) d ′ of the main antenna element 20b shown in FIG. 13 is changed at intervals of 5 mm from 130 mm to 170 mm are shown in FIG. 14 as d1, d2, d3. , D4, d5, d6, d7, d8, d9, respectively.

  As can be seen from FIG. 14, when the element length of the main antenna element 20b is 150 mm, it can be understood that an average high sensitivity is obtained over the entire band of the DTV.

  In the vehicle glass antenna 20 according to the embodiment of the present invention described above, the element length of the main antenna element 20b is set to a value obtained by multiplying 1/2 of one wavelength of a predetermined frequency by the shortening rate. Antenna pattern design becomes easy.

  The present invention can be applied not only to domestic DTV bands but also to overseas digital TV bands. In order to obtain a good field of view during driving, a vehicle glass antenna is mounted close to the body edge. In this case, the resonance impedance is optimized, which is suitable as a means for improving reception sensitivity.

  DESCRIPTION OF SYMBOLS 10 ... Vehicle, 13 ... Windshield, 20 ... Glass antenna for vehicles, 20a ... Impedance adjustment element, 20b ... Main antenna element (third antenna element), 20c ... Feed point, 21 ... First antenna element, 22 ... Second antenna element, 24 ... body edge, 25 ... glass edge.

Claims (4)

A vehicle glass antenna attached to a window glass provided in the vehicle body so as to close an opening of the vehicle body,
A glass antenna for a vehicle comprising an antenna element having a folding pattern of at least two times. The antenna element is
A linear first antenna element extending from the feed section into the opening and along the edge of the opening;
A second antenna element that is folded back approximately 180 degrees from the tip of the first antenna element and extends to face the first antenna element;
A third antenna element that is folded back approximately 180 degrees from the tip of the second antenna element and extends to face the second antenna element;
The glass antenna for a vehicle according to claim 1, comprising: The third antenna element is
The glass antenna for a vehicle according to claim 2, wherein the glass antenna is disposed within a distance corresponding to 1/16 of one wavelength of a predetermined frequency from an edge of the opening. The length of the third antenna element is:
The glass antenna for a vehicle according to claim 2 or 3, wherein the glass antenna is set to a value obtained by multiplying 1/2 of one wavelength of a predetermined frequency by a shortening rate.

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