JPH08222936A - Antenna for theft prevention device - Google Patents

Abstract

PURPOSE: To avoid a dead band from being caused in a tag sensing area. CONSTITUTION: First and second antennas 1, 2 whose loop is crossed at one point horizontally are arranged not overlapped with each other on a same plane vertically, and have common elements 3a, 3b overlapped with each other and exclusive use elements 4, 5 for the 1st and 2nd elements 4, 5, the common elements 3a, 3b are integrated into one common element, and the common element 3 and the exclusive element 4 of the 1st antenna 1 are connected via a high frequency switching diode 6. Then the common element 3 and each of the exclusive elements 5 of the 2nd antenna 2 are connected via high frequency switching diodes 6, 6,..., and the connection polarity of the high frequency switching diodes 6, 6,... is reverse between the 1st and 2nd antennas and a switching circuit 8 is used to extract an output of the 1st and 2nd antennas alternately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna for an anti-theft device, and more particularly to an antenna suitable for reception.

[0002]

2. Description of the Related Art As an anti-theft device, for example, 22KHZ
A method of operating a self-tapping tag using the long-wave band or the ultra-long-wave band, and a tag that receives a re-radiated radio wave from a tag having a resonance circuit using the short-wave band of 8.2 MHz, for example. A method of detecting the presence of the is known. As shown in FIG. 8, the anti-theft device adopting the latter method has a detection area between a pair of antennas 9 and 10 arranged to face each other, and when the tag 11 passes through the detection area, one antenna is detected. The resonance circuit incorporated in the tag 11 picks up the radio wave transmitted from 9 and resonates, and the radio wave is re-radiated from the resonance circuit (tag). Therefore, the re-radiated radio wave is transmitted to the other antenna 10. By receiving
The presence of the tag 11 is detected. This other antenna 10
Receives radio waves radiated from one of the antennas 9 and radio waves for communication / broadcasting, etc. coming from a distance, and these radio waves become an obstacle to reception of radio waves re-radiated from the tag. The radio waves radiated from the one antenna 9 and the radio waves for communication / broadcasting are transmitted to the other antenna 10.
Since it is received uniformly over the entire surface of the antenna, the loops of the antenna 10 on the receiving side are crossed in order to reduce the influence of the radio wave, and a plurality of small loops 10 (two in the figure) with different phases are provided.
a) and 10a are formed, and the electric waves radiated from the transmission antenna are canceled by the reception signals of the small loops 10a and 10a. As the antenna having the plurality of small loops, one that is crossed once or twice is generally adopted.

[0003]

If the antennas are designed so that the loop areas of the plurality of small loops having different phases are equal to each other, the antenna for communication is radiated from the antenna on the transmission side, or for communication coming from a distance. The radio waves such as
The output from the receiving antenna is not output, and the influence of the radio waves is eliminated. However, since the resonance radio waves of the tag transmitted from the height of the cross portion are equally received by both small loops, they are similarly canceled out, and that portion becomes a dead zone S substantially, and the dead zone is reduced. Even if the tag is located in S, the presence cannot be detected even though it is in the detection area. Therefore, even if it happens, if the tag slips through the dead zone, the presence of the tag is not detected, and the reliability of the detection function is 1.
One of the antennas on the transmitting side, which is one of the antennas, will also have a cross section, but in that case, a dead zone may occur at the height position of the cross section, and it passes through the dead zone. Since the tag that does not receive electric waves does not resonate, the problem of detection failure similar to the above occurs.

[0004]

SUMMARY OF THE INVENTION The invention is
Alternatively, the shared common element and the first and second antennas, which are arranged vertically on the same plane and overlap each other, at least in a portion where the left and right sides of the loop intersect at one or more locations and have the same phase It is divided into a dedicated element for exclusive use, the shared element is integrated into one, and each dedicated element and the shared element in the first antenna are connected through a high frequency switching diode, and each dedicated element in the second antenna is connected. The element and the shared element are also connected via a high frequency switching diode, and the high frequency switching diode is in a reverse connection relationship between the first and second antennas, and the first antenna and the second antenna are connected by a switching circuit.
The gist is to alternately take out the output from the antenna. When the first antenna and the second antenna are offset from each other, they can be crossed at one location in the center to form a set of two loop types in which small loops are continuously provided above and below, and when they are overlapped with each other, It is possible to make a combination of a three-loop type in which upper and lower parts are crossed at two places and the above-mentioned two-loop type.

[0005]

Since the high-frequency switching diode has a reverse connection relationship between the first and second antennas, the switching circuit causes the first antenna and the second antenna to alternately operate, whereby The position (number) of the dead zone changes. Also, for each element, only one of the antennas becomes effective each time it is switched, and the other antenna is divided into elements, so that there is no interference between the antennas. If this antenna is used as a receiving antenna, the dead zone can be substantially eliminated, and thus a detection error can be completely prevented.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an anti-theft device antenna according to the present invention will be described with reference to the drawings. FIG. 1 shows a pattern of an antenna, and this antenna pattern is shown in FIG.
By crossing the loop once at the center, as shown in Fig.8, the two small loops 1a and 1a are arranged in the upper and lower parts.
The first antenna 1 that operates for the Z short-wave band, and 8.2 MHz in which two small loops 2a and 2a are similarly arranged above and below
2 and the second antenna 2 operating for the short-wave band are arranged vertically on the same plane by a height corresponding to the width L of the dead zone S, and as shown in FIG. .. and dedicated elements 4, 4 ... Dedicated to the first antenna and dedicated elements 5, 5 ... Dedicated to the second antenna, and each shared element 3a, 3a, 3
b, 3b ... Are integrated into one shared element 3 to
1, the dedicated elements 4 and the shared elements 3 of the antenna 1 are connected via the high-frequency switching diodes 6, 6 ... And the dedicated elements 5, 5 ... of the second antenna 2 are connected. And the shared element 3 as well as the high frequency switching diodes 6, 6
., And the high frequency switching diodes 6, 6 ... Are reversely connected by the first and second antennas.

A switching circuit 8 having a switch controlled by the CPU 7 is provided in the antenna output terminal section through a coil 12 and a capacitor 13, and the antenna output terminal sections T ₁ and T ₂ are connected to the antenna connection terminals. Are switched alternately to the plus side and the minus side at a rate of several tens of times per second, and the current direction is reversed each time the switching is performed. Since the first antenna and the second antenna are arranged so as to be vertically offset from each other, the dead band S ₁ of the _first antenna 1 and the dead band S of the second antenna 2 are arranged as shown in FIG. ₂ and ₂ are formed to be vertically offset.

The antenna thus formed operates as a first antenna when the antenna output terminal portion T ₁ side is made positive and the T ₂ side is made negative, and it becomes possible to detect the range excluding the dead zone S ₁ . On the contrary, when the T ₁ side changes to the negative side and the T ₂ side changes to the positive side, it operates as the second antenna, and it becomes possible to detect the range excluding the dead zone S ₂ , and as a result, the total coverage of the detection area becomes the receivable range. Are covered.

Although the embodiment has explained the antenna which is crossed once and is composed of two loops, the upper and lower loops, as shown in FIG. In the first antenna 1 and the second antenna 2, the dedicated element 4 and the common element 3 of the first antenna 1 are connected to the high frequency switching diode 6,
.. and the dedicated element 5, 5 ... In the second antenna 2 and the common element 3 are also connected via the high frequency switching diodes 6, 6 ,. Switching diode 6,
6 ... Can be configured to reversely connect the first and second antennas, or can be applied to an antenna that is crossed three times or more.
In an antenna composed of two small loops, the size of each small loop is set to be equal to the size of the upper and lower small loops.

Further, the first antenna and the second antenna are not limited to the set of the same pattern, and for example, the first antenna that has been crossed once and the second antenna that has been crossed twice. Even if the switching operation is performed at the overlapping position, the dead zone position is switched between the central portion and the upper and lower portions, and the entire area can be covered.

Next, a modified example will be described. The names of the respective members that are the same as those in the above-described embodiment are designated by the same reference numerals. The first antenna is a 2-loop type antenna that operates for the short wave band of 8.2 MHZ, where the center is crossed once and the small loops are arranged in series at the top and bottom. It is a 3-loop type antenna that operates for the short wave band of 8.2 MHZ in which small loops are arranged in the upper and lower sides and in the center, and these two antennas are superposed and overlap each other in the part where the phase is common as shown in FIG. The shared elements are divided into dedicated elements 4, 4 ... Dedicated to the first antenna and dedicated elements 5, 5 ... Dedicated to the second antenna, and each shared element is integrated into one shared element 3. The dedicated element 4 and the shared element 3 in the first antenna 1 are connected via the high frequency switching diodes 6, 6 ... Also a shared element 3 and each dedicated elements 5,5 ... in Na 2, connected via a high-frequency switching diodes 6,6 ...,
The high-frequency switching diodes 6, 6, ... Are reversely connected to the first and second antennas, and are basically the same as in the above-mentioned embodiment.

In the antenna formed in this way, FIG.
As shown in FIG. 5, the dead zone S ₁ of the first antenna is formed between the _two dead zones S ₂ and S ₂ of the second antenna, and as described above, the dead zone is located at the central portion and the upper and lower portions by the switching operation. Since it switches to and, the dead zone can be virtually eliminated.

The circuits shown in these embodiments are merely examples, and each antenna operates reliably in the circuit described above. However, for example, in the antenna which is crossed once and composed of two upper and lower loops, As shown in FIG. 7, for each element connecting portion, coils 12, 12 ... Which pass a direct current and block a high frequency signal, and conversely, capacitors 13, 13 ... Which pass a direct current and pass a high frequency signal. , And switching circuits 8 and 8 are respectively provided to disconnect the connection with unnecessary elements to further improve the antenna performance. Further, although the embodiment has been described with respect to the receiving side antenna, the same effect can be expected in a device having a dead zone where radio waves are not felt by switching the transmitting side antenna between the first and second antennas. Furthermore, the location and the number of crosses are not limited to those in the embodiment, and for example, the frequency to be used may be changed to avoid the influence of the communication signal in the short wave band. The antenna of the present invention changes the position of the dead zone by electrically switching between the antennas of the same pattern arranged vertically shifted or the antennas of different patterns arranged in an overlapping manner to change the position of the dead zone. It does not require a drive unit and is highly reliable.

[0014]

According to the present invention, the positions and the number of dead zones are changed by switching the first antenna and the second antenna in which the positions of the dead zones do not coincide with each other, so that there is substantially no dead zone. Since it is almost the same, there is no detection error caused by passing through the dead zone.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an antenna according to the present invention.

FIG. 2 is an explanatory diagram showing the antenna principle of the present invention.

FIG. 3 is an explanatory diagram showing positions of dead zones.

FIG. 4 is an explanatory diagram of a modified example.

FIG. 5 is an explanatory diagram of a modification example.

FIG. 6 is an explanatory diagram showing a position of a dead zone in a modified example.

FIG. 7 is an explanatory diagram showing a modification example.

FIG. 8 is an explanatory diagram showing a conventional example of an apparatus.

[Explanation of symbols]

1 ... 1st antenna, 2 ... 2nd antenna, 3, 3
a, 3b ... Common element, 4 ... Dedicated element (for first antenna), 5 ... Dedicated element (for first antenna), 6 ... High frequency switching diode, 7 ... CPU, 8 ... Switching circuit, 9, 10
..Antennas, 11 ... Tags, 12 ... Coils, 13 ...
・ Capacitor, S ・ ・ dead band, S ₁・ ・ dead band (for the first antenna), S ₂・ ・ dead band (for the second antenna) L
· Dead zone width, T _1, T ₂ ·· antenna output terminal section.

Claims (4)

[Claims] 1. A first antenna and a second antenna, which are vertically shifted and arranged on the same plane and intersect at least one of the left and right sides of a loop, are shared by an overlapping shared element and are dedicated to the first and second antennas. It is divided into a dedicated element and the shared element is integrated into one, and each dedicated element and the shared element in the first antenna are connected via a high frequency switching diode,
The dedicated element and the common element in the second antenna are also connected via the high frequency switching diode, and the high frequency switching diode is the first
An antenna for a theft prevention device, characterized in that the output of the first antenna and the output of the second antenna are alternately taken out by a switching circuit in a reverse connection relationship between the antenna and the second antenna. 2. Each of the first and second antennas has a structure in which small loops are arranged in series at the top and bottom with one center crossed.
The anti-theft device antenna according to claim 1, which is a loop type. 3. Overlapping each other and arranged in the same plane,
The first and second antennas, which intersect at least one of the left and right sides of the loop at different positions from each other, have a shared element that overlaps at a portion having a common phase, and a first antenna.
And or a dedicated element dedicated to the second antenna,
In addition to integrating the shared element into one, each dedicated element and shared element in the first antenna are connected via a high frequency switching diode, and each dedicated element and shared element in the second antenna are also connected, Connected via a high frequency switching diode, the high frequency switching diode,
An anti-theft device antenna, characterized in that the first and second antennas are in a reverse connection relationship, and the outputs of the first antenna and the second antenna are alternately taken out by a switching circuit. 4. One of the first and second antennas, one of which has a center crossed at one place and two small loops are vertically arranged.
The anti-theft device antenna according to claim 3, wherein the antenna is a loop type and the other is a three-loop type in which upper and lower portions are crossed at two places and small loops are continuously provided on the upper and lower portions.