JP3217818B2 - Twin loop antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual loop antenna which is formed by combining two loop antennas and is particularly suitable for being installed in an automobile.

[0002]

2. Description of the Related Art An antenna device is required for transmitting and receiving various broadcast communication waves such as an automobile telephone in an automobile. A conventionally used pole antenna is provided so as to protrude from a vehicle body and has a high transmission / reception performance. It can not be said that the characteristics are sufficiently satisfactory, and in order to improve this point, a loop antenna formed by winding an antenna wire is used as an automobile antenna, and since the loop antenna has directivity, It is difficult to install at the optimal detection angle, which is the angle formed by the vehicle body that can detect radio waves efficiently and the plane on which the loop antenna is located.To solve this problem, combine multiple loop antennas. 2. Description of the Related Art There is known an antenna device for an automobile.

For example, Japanese Unexamined Patent Publication No. 61-128609 discloses an electrostatic shield case which is attached to a vehicle body and has an opening formed opposite to the vehicle body, and a plurality of antenna case-wrapped antenna wires. A loop antenna is provided in the electrostatic shield case in close proximity to the shield case opening, and each loop constituting the loop antenna is arranged in a fan shape with the side of the shield case opening side as the center. Regardless of the angle at which the electrostatic shield case is attached to the vehicle body, at least one of the plurality of loops constituting the loop antenna is positioned at the optimum detection angle of radio waves induced on the vehicle body by broadcast waves. As a result, the radio wave can be detected efficiently.

[0004]

However, in the above-described vehicle antenna device using the conventional loop antenna, the directivity, frequency characteristics, and voltage standing wave ratio (Voltage
Standing Wave Ratio; hereinafter, referred to as VSWR), a shape having desired characteristics,
It was difficult to design the size and the like. For example, with respect to the directivity of the antenna, it is preferable that the antenna be non-directional at the time of normal transmission and reception, particularly at the time of reception, and that it has a wide band characteristic, that is, the VSWR is low in a wide frequency band. There is a problem that it is difficult to obtain an automobile antenna device having such characteristics, and it is particularly difficult to reduce the size while having such characteristics.

An object of the present invention is to provide a dual loop antenna having two loops formed by winding an antenna wire,
An object of the present invention is to provide a dual loop antenna that has desired characteristics such as directivity, frequency characteristics, and voltage standing wave ratio, and that can be downsized.

[0006]

In order to achieve the above object, a twin-loop antenna according to the present invention is a dual-loop antenna which is printed and wired on a window glass and has two loops each formed by winding an antenna wire and connected to each other. Each loop is formed into an isosceles triangle , connected at a pair of parallel short sides so as to face each other at the apex, and a folded part is formed at the bottom of the isosceles triangle to be vertically / laterally symmetric. Shape twin
Loop antenna and a dual loop antenna
In the center position of a pair of short sides that is the center position of up / down / left / right symmetry
Provide a feeding point for each , and make the folded part the same distance from the feeding point.
Separated from each other, and the folded portion is located at the outer end.
And a pair of parallel leg sides, symmetrical up / down / left / right
A plurality of the folded portions may be provided at the bottom of the isosceles triangle of one of the loops, and the directivity of the antenna or the voltage standing wave ratio (VSWR) is determined. It determines the characteristics of the loop antenna, can make the directivity omnidirectional, can lower the VSWR in a wide frequency band, that is, can provide a wide band characteristic, and can promote downsizing.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the structure of a twin-loop antenna will be described. The twin-loop antenna is formed by connecting two loops 1 and 2 formed by winding an antenna wire, and printed wiring on a window glass of an automobile. It has been installed.

The loops 1 (2) are all formed of straight portions, and the oblique portions 11, 12 (21, 22) having the same length.
With the vertex angle α consisting of the bases 13 and 14 (23, 24) divided at the center, the oblique sides 11, 12 (21, 22) are formed into an isosceles triangle with the apex side ends open. A folded portion 10 (20) projecting outward of an isosceles triangle is provided at the center division position of the portions 13, 14 (23, 24), and the folded portion 10 (20) is a leg side portion 15, 16 (25, 26) and legs 15, 16 (2
5, 26) and an outer end portion 17 (27) connecting the outer ends of the leg portions 15, 16 (25, 26) with a distance w (w> 0) between the leg sides 15, 16 (25, 26). , Leg length 15, 16 (25, 26) length d
Is set within a range in which the total length of the loop 1 (2) is a predetermined value, and has an effect of making it non-directional.

The loops 1 and 2 are connected on the vertex side of an isosceles triangle, and the vertex-side ends of the oblique sides 11 and 21 and 12 and 22 are connected by short sides 18 and 19 having the same length. Side 18,
A power supply point is provided at the center of 19, and the positive (+) side power supply terminal and the negative (-) side power supply terminal are connected, and the band characteristic fluctuates depending on the distance between the two power supply points. is there.

The positional relationship between loops 1 and 2 is such that the vertices of the isosceles triangle overlap, that is, the hypotenuse 11 of loop 1 and the hypotenuse 22 of loop 2, the hypotenuse 12 of loop 1 and the hypotenuse of loop 2
21 are on the same straight line, and their intersections, that is, the vertices of both isosceles triangles of loops 1 and 2 are on the straight line connecting the feeding points A and B, and are both isosceles of loops 1 and 2. If the vertices of the triangle are separated and create a distance between them, directivity is generated in a direction parallel to the bases 13, 14 and 23, 24 (usually in the front-back direction).

Further, since the target frequency band fluctuates depending on the wire diameter d of the loops 1 and 2, it is possible to easily set a frequency bandwidth suitable for the purpose.

When the apex angle α of the loop 1 (2) is reduced, directivity is generated in a direction parallel to the bases 13 and 14 (23, 24) (usually in the front-rear direction). When the apex angle α changes, the gain at each frequency changes, and the VSWR at each frequency changes.

Furthermore, the omnidirectional gain at each frequency changes according to the length of the one-sided loop length L, which is the total distance of the center line of the loop 1 (2) from the feeding point A to the feeding point B. Can be set as a target frequency which is a frequency higher than the target frequency.

In the comparative example shown in FIG. 2, two loops a and b formed into an isosceles triangle by winding an antenna wire are connected at the vertex side of the isosceles triangle, and the oblique sides a1 and a
2, the vertex-side ends of b1 and b2 are connected at short sides c and d having the same length, and a feeding point is provided at the center of the short sides c and d, respectively. The negative (-) side power supply terminal is connected, and the expanded ends of the oblique sides a1 and a2, and b1 and b2 are connected at the bottom sides a3 and b3.

The above embodiment of the present invention in which the folded portion 10 (20) is provided at the base 13, 14 (23, 24) of the isosceles triangle, and the folded portion is provided at the base of the isosceles triangle of the loop. FIG. 3 shows that 880 MHz
Fig. 4 shows the directivity in Z, that is, the gain in each direction.
The directivity at 20 MHZ is shown, and the example
The comparative example is shown by a curve II, and the example (curve I) clearly has no directivity, that is, the gain in each direction is higher.

In FIG. 5, the horizontal axis represents the frequency, and the vertical axis represents the difference between the average gain and the minimum gain. The embodiment is represented by curve III, and the comparative example is represented by curve IV. The difference between the average gain and the minimum gain over the curve III
It is shown that (Example) is below the curve IV (Comparative Example), and the difference between the average gain and the minimum gain is closer to zero, so that a stable antenna gain can be obtained. The example shows that VSWR is low in a wide frequency band, that is, a wide band characteristic can be provided.

In the above embodiment, the folded portion provided on the bottom side is located on the opposite side to the vertex of the isosceles triangle, that is, on the outside, but the folded portion may be provided on the vertex side of the isosceles triangle, that is, on the inside. The same effect can be obtained, and the antenna device can be further reduced in size.

Further, by providing a plurality of folded portions at the bottom of the isosceles triangle of one of the loops, the size of the antenna device can be reduced. Further, the folded portion may be formed not in a U-shape but in a horizontal V-shape,
It is also good to be vertically asymmetric.

[0019]

Since the present invention is configured as described above, it has the following effects. In a dual loop antenna having two loops formed by winding antenna wires, a folded portion is formed at the base of an isosceles triangle. A plurality of the folded portions are provided at the bottom of an isosceles triangle of one loop. The directivity of the antenna and the VSWR are determined to determine the characteristics of the dual loop antenna, and the directivity can be made omnidirectional.
VSWR can be reduced in a wide frequency band, that is, a wide band characteristic can be provided, and downsizing can be promoted.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a dual loop antenna according to an embodiment of the present invention.

FIG. 2 is a schematic plan view of a twin-loop antenna according to a comparative example having no folded portion.

FIG. 3 is a characteristic diagram in each direction of an example and a comparative example (frequency 880 MHz).

FIG. 4 is a characteristic diagram in each direction of an example and a comparative example (frequency: 920 MHZ).

FIG. 5 is a characteristic diagram at each frequency of an example and a comparative example.

[Explanation of symbols]

 1,2 (one side) loop 11, 12, 21, 22 Oblique 13, 13, 23, 24 Bottom 10, 20 Folded part α Apex angle

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-138803 (JP, A) JP-A-3-2712 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01Q 1/32 H01Q 1/22 H01Q 7/00

Claims (1)

(57) [Claims] 1. A double-loop antenna comprising two loops each formed by winding an antenna wire, wherein each loop is formed into an isosceles triangle, and a pair of parallel short sides are formed so as to face each other at apex angles. connect in parts, to form a folded portion at the bottom portion of said isosceles triangle, a bi-Le vertically / laterally symmetrical shape
Loop antenna and a dual loop antenna
In the center position of a pair of short sides that is the center position of up / down / left / right symmetry
Provide a feeding point for each , and make the folded part the same distance from the feeding point.
Separated from each other, and the folded portion is located at the outer end.
And a pair of parallel leg sides, symmetrical top / bottom / left / right
A twin-loop antenna formed in a shape as described above .