WO2008099309A1

WO2008099309A1 - Transponder

Info

Publication number: WO2008099309A1
Application number: PCT/IB2008/050447
Authority: WO
Inventors: Gerald Schaffler
Original assignee: Nxp B.V.
Priority date: 2007-02-13
Filing date: 2008-02-07
Publication date: 2008-08-21

Abstract

A transponder (1, 31, 41) comprises a plurality of antennas (5, 6, 9, 42, 43) for capturing signals sent by a transmitter, a single radio frequency interface (7) coupled inductively to each of the antennas (5, 6, 9, 42, 43), configured to accept the signals, the radio frequency interface (7) configured to generate preprocessed signals in response to the signals, and an electronic circuitry (8) connected to the radio frequency interface (7) and configured to process the preprocessed signals. The antennas (5, 6, 9, 42, 43) are de-coupled galvanically from each other.

Description

Transponder

FIELD OF THE INVENTION

The invention relates to a transponder.

BACKGROUND OF THE INVENTION Transponders, which are also referred to as tags or labels, are well known in the art and are designed to communicate with a reader which is also known as a base station. Usually, the transponder comprises an electronic circuit, for instance, an integrated circuit and an antenna to capture signals sent by the reader. Then, the electronic circuit processes the signals captured by the antenna and may generate a response signal for the reader. US 6,078,791 discloses an RFID transceiver comprising two dipole antennas and an RFID transceiver circuit mounted on a substrate. The dipole antennas are formed by four antenna lines connected to opposite corners of an integrated circuit in a generally X-shaped configuration.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an RFID transponder whose range of received signals is increased.

The object is achieved in accordance with the invention by means of a transponder comprising a plurality of antennas for capturing signals sent by a transmitter, a single radio frequency interface coupled inductively to each of the antennas, configured to accept the signals, and configured to generate preprocessed signals in response to the signals, and an electronic circuitry connected to the radio frequency interface and configured to process the preprocessed signals, wherein the antennas are de-coupled galvanically from each other. Usually, transponders are designed to respond to signals sent by the transmitter.

The transmitter may particularly be a reader or a base station. Conventional transponders comprise only a single antenna for capturing the signals sent by the transmitter and an integrated circuit for processing the captured signals. Normally, the integrated circuit comprises a radio frequency interface for preprocessing the signals captured by the antenna and for forwarding the preprocessed signals to an electronic circuitry of the integrated circuit. Since, however, conventional transponders only comprise the single antenna, the range of frequency or the orientation of the conventional transponder to the transmitter may be limited.

The inventive transponder, however, comprises at least two antennas each coupled inductively to the single radio frequency interface while being de-coupled galvanically from each other.

As a result, it is possible, for instance, to tune at least some of the antennas to different resonance frequencies resulting in an increased frequency spectrum of signals the inventive transponder is capable to receive. Due to the fact that the inventive transponder comprises more than one antenna for capturing signals, these antennas can be placed, for instance, on a substrate of the transponder to have different directions of polarization, resulting in an increased area range in which the inventive transponder is capable to receive signals.

In addition, the inventive transponder comprises only the single radio frequency interface which preprocesses the signals captured by the antenna for the electronic circuitry of the inventive transponder. Having only a single radio frequency interface for all antennas may reduce the complexity of the inventive transponder. This may result in reduced production costs or may support manufacturing smaller electronic circuits for the inventive transponder. This may particularly be advantageous, if the radio frequency interface and the electronic circuitry are integrated into an integrated circuit, as it is the case for one embodiment of the inventive transponder.

In order to have only a single radio frequency interface for the plurality of antennas, each antenna is coupled inductively to the radio frequency interface, but is decoupled galvanically from the remaining antenna or antennas. Thus, the antennas are not connected by an ohmic connection with each other. This is necessary to have several antennas connected to the single radio frequency interface.

In one embodiment of the inventive transponder, the transponder comprises coupling means coupled inductively to each of the antennas and connected galvanically to an input of the radio frequency interface. Such coupling means are, for instance, a conductive loop whose ends are connected to the input of the radio frequency interface.

Each of the antennas may be of the same antenna type or the plurality of antennas may comprise at least two different antenna types. Suitable antenna types include, for instance, dipole, batch, or log-periodic antennas.

The dipole antennas may be orientated anti-parallel or orthogonal with respect to each other. Then, these dipole antennas may have different directions of polarization. If, for instance, two dipole antennas are used for the inventive transponder, then the dipole antennas can be placed, for instance, on a substrate of the transponder such that they are located within two parallel planes or within a common plane and are orthogonal to each other. Then, the spacial range within which the inventive transponder can receive a polarized signal transmitted by the transmitter is increased compared to a conventional transponder only having a single dipole antenna.

Additionally, a third dipole antenna of the dipole antennas may lay in a plane being anti-parallel, particularly orthogonal to the parallel planes or the common plane, further increasing the spacial range within which the inventive transponder can receive a polarized signal transmitted by the transmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail hereinafter, by way of non- limiting examples, with reference to the embodiments shown in the drawings. Fig. 1 shows an exemplary embodiment of an RFID transponder comprising two dipole antennas and an integrated circuit;

Fig. 2 shows the integrated circuit of the RFID transponder depicted in Fig. 1; Fig. 3 shows an exemplary embodiment of an RFID transponder comprising three dipole antennas; and Fig. 4 shows an exemplary embodiment of an RFID transponder comprising antennas of different types.

DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a transponder 1 which comprises a substrate 2, an integrated circuit

3 attached to the substrate 2, an electric conductive loop 4 connected to the integrated circuit 3, and first and second dipole antennas 5, 6. The integrated circuit 3 is depicted in more detail in Fig. 2 and comprises a single radio frequency interface 7 having an input 7a to which the conductive loop 4 is connected. For the exemplary embodiment, each dipole antenna 5, 6 comprises first straight lines 5a, 6a and second straight lines 5b, 6b connected by a third straight line 5c, 6c. The dipole antennas 5, 6 are made, for instance, by an ink process and are attached to the substrate 2 such that they are de-coupled galvanically. This is achieved, for instance, by placing the two dipole antennas 5, 6 into two planes being parallel to each other by, for instance, printing one of the two dipole antennas 5, 6 on one of the substrate surfaces and the other dipole antenna on the other substrate surface. Furthermore, the two dipole antennas 5, 6 are attached to the substrate 2 such that their third straight lines 5 c, 6c are approximately aligned above each other.

The third straight lines 5 c, 6c are meant for being coupled inductively to the conductive loop 4 which is attached to one of the substrate surfaces for the exemplary embodiment. Therefore, the first and second dipole antennas 5, 6 are each coupled inductively to the conductive loop 4 and, since the conductive loop 4 is connected to the single radio frequency interface 7 of the integrated circuit 3 via its input 7a, to the integrated circuit 3. For the exemplary embodiment, the dipole antennas 5, 6 are orientated on the substrate 2 such that the first dipole antenna 5 runs basically along a first direction x and the second dipole antenna 6 runs basically along a second direction y which is orthogonal to the first direction x. Thus, the dipole antennas 5, 6 have different directions of polarization.

The two dipole antennas 5, 6 are designed to capture signals sent by a transmitter, for instance, a reader or a base-station (not shown in the figures). The signals captured by the first and second dipole antennas 5, 6 are coupled into the conductive loop 4 and thus are input signals to the integrated circuit 3 and specifically to the single radio frequency interface 7.

The radio frequency interface 7 is designed to preprocess the signals captured by the first and second antennas 5, 6 and to forward the preprocessed signals to an electronic circuitry 8 of the integrated circuit 3. The electronic circuitry 8 is designed to process the preprocessed signals and, if necessary, to generate further signals in response to the preprocessed signals. The further signals may then be transmitted to the base-station or the reader, for instance, via a further antenna (not shown in the figures).

The two dipole antennas 5, 6 may be designed such that they have the same resonance frequency or may be designed such that they have different resonance frequencies.

Fig. 3 shows a further transponder 31. If not explicitly mentioned, parts of the transponder 31 of Fig. 3 which basically serve the same function as parts of the transponder 1 depicted in Fig. 1 are denoted by identical reference numbers.

The basic difference between the transponders 1, 31 is that the transponder 31 comprises, in addition to the first and second dipole antennas 5, 6, a third dipole antenna 9. The third dipole antenna 9 comprises first and second straight lines 9a, 9b which are orientated along a third direction z, which is orthogonal to each of the first and second directions x, y. Furthermore, the two straight lines 9a, 9b of the third dipole antenna 9 are connected by a third straight line 9c which is orientated in respect to the conductive loop 4 such that the third dipole antenna 9 is also inductively coupled to the single radio frequency interface 7 of the integrated circuit 3 while not being coupled gavanically to any of the first or second dipole antennas 5, 6. As a result, each of the dipole antennas 5, 6, 9 has a different direction of polarization.

The dipole antennas 5, 6, 9 may be designed such that they have the same resonance frequency or may be designed such that they have different resonance frequencies.

Fig. 4 shows a further transponder 41. If not explicitly mentioned, then parts of the transponder 41 of Fig. 4 which basically serve the same function as parts of the transponder 1 of Fig. 1 are denoted with identical reference numbers.

Instead of comprising dipole antennas 5, 6, the transponder 41 of Fig. 4 comprises a batch antenna 42 and a log periodic antenna 43. For the exemplary embodiment, the batch antenna 42 comprises a first layer 42a attached to one of the surfaces of the substrate 2 and a second layer 42b attached to the other surface of the substrate 2. Both layers 42a, 42b are made from an electric conductive material and the second layer 42b has a smaller area than the first layer 42a. Additionally, the two layers 42a, 42b are arranged on the substrate 2 such that they are aligned above each other.

The batch antenna 42 further comprises a conductive loop 42c connecting the two layers 42a, 42b electrically. In order to achieve this, the substrate 2 comprises a through hole 10 through which the conductive loop 42c of the batch antenna 42 is running through.

Additionally, the batch antenna 42 and particularly the conductive loop 42c of the batch antenna 42 is arranged such that it is coupled inductively to the inductive loop 4 which is connected to the single radio frequency 7 of the integrated circuit 3.

For the exemplary embodiment, the log periodic antenna 43 comprises several first antenna elements 43a arranged on one surface of the substrate 2 and several second antenna elements 43b arranged on the other surface of the substrate 2. In order to connect the first and second antenna elements 43 a, 43b together, the log periodic antenna 43 comprises a conductive loop 43c partly running through a through hole 11 of the substrate 2.

The conductive loop 43 c of the log periodic antenna 43 is arranged on the substrate 2 such that it is coupled inductively to the conductive loop 4 connected to the single radio frequency interface 7. As a result, both the batch antenna 42 and the periodic log antenna 43 are coupled inductively to the single radio frequency interface 7 while being decoupled galvanivcally from each other.

For the exemplary embodiment, the resonance frequencies of the batch antenna 42 and of the log periodic antenna 43 may particularly differ.

Finally, it should be noted that the aforementioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A transponder comprising: a plurality of antennas (5, 6, 9, 42, 43) for capturing signals sent by a transmitter; said antennas (5, 6, 9, 42, 43) being de-coupled galvanically from each other; a single radio frequency interface (7) coupled inductively to each of said antennas

(5, 6, 9, 42, 43), said radio frequency interface (7) configured to accept said signals and configured to generate preprocessed signals in response to said signals; and an electronic circuitry (8) connected to said radio frequency interface (7) and configured to process said preprocessed signals.

2. The transponder of claim 1, comprising coupling means (4) coupled inductively to each of said antennas (5, 6, 9, 42, 43) and connected galvanically to an input (7a) of said radio frequency interface (7).

3. The transponder of claim 1, wherein said radio frequency interface (7) and said electronic circuitry (8) are integrated into an integrated circuit (3).

4. The transponder of claim 1, wherein each of said antennas (5, 6, 9) are of the same antenna type or wherein said plurality of antennas (42, 43) comprises at least two different antenna types.

5. The transponder of claim 1, wherein each of said antennas (5, 6, 9) has a different direction of polarization.

6. The transponder of claim 1, wherein said antennas are dipole (5, 6, 9), batch (42), or log-periodic antennas (43).

7. The transponder of claim 6, wherein said dipole antennas (5, 6, 9) are orientated anti-parallel or orthogonal with respect to each other.

8. The transponder of claim 6, wherein first and second dipole antennas (5, 6) of said dipole antennas are lying in two parallel planes and a third dipole antenna (9) of said dipole antennas is lying in a plane being anti-parallel or orthogonal to said parallel planes.

9. The transponder of claim 1, wherein each of said antennas (5, 6, 9, 42, 43) is tuned to a different resonance frequency.