Antenna arrangement for an electronic vehicle key

The current invention relates to an antenna arrangement, in particular an an tenna arrangement for an electronic vehicle key.

Most vehicles today may be unlocked and remotely started using an electronic vehicle key. Some “start and stop” access systems are well known in which the user needs to press an unlocking button from the electronic remote key to un lock or lock the vehicle, start the engine of the vehicle, or open a trunk of the vehicle, for example. Such an electronic vehicle key usually has to be inserted into an immobilizer station located inside the vehicle which recognizes the vehi cle key and allows the user to start the vehicle. Such systems replace the origi nally known ignition switch systems. Other “start and stop” access systems do not require the user to press a button or to insert the key in an immobilizer in order to unlock or lock the vehicle or to start the engine. Such a “start and stop” access system is called a passive start and entry system, or remote keyless entry system (RKE). With passive start and entry systems, the vehicle may be unlocked automatically when the key is detected within a certain range from the vehicle. In order to start the vehicle, a start button within the vehicle usually has to be pressed.

Such an electronic vehicle key communicates with the vehicle using wireless technology. For this reason, an electronic vehicle key usually comprises two or even more different antennas. For example, an electronic vehicle key may comprise at least one low frequency (LF) antenna, one ultra-high frequency (UFIF) antenna, an ultra-wide band (UWB) antenna, and an antenna for Blue tooth communication. Bluetooth or Bluetooth Low Energy (BLE) communication may be used, for example for transmitting all kind of information (e.g., tire pres sure, fuel status, etc.) from the vehicle to the vehicle key or to a portable elec- tronic device (e.g., smartphone). For each antenna, a filter stage needs to be provided. The filter stage usually is rather costly and requires a certain amount of space.

There is a need to provide an antenna arrangement for an electronic vehicle key which has comparably small space requirements and can be implemented at comparably low costs.

This problem is solved by an antenna arrangement according to claim 1 and an electronic vehicle key according to claim 12. Configurations and further devel opments of the invention are the subject of the dependent claims.

An antenna arrangement for an electronic key includes an antenna, and an an tenna circuit configured to control the antenna, wherein the antenna and the antenna circuit are arranged on a printed circuit board, the antenna arrange ment is configured to transmit and receive ultra-wide band signals or signals according to a Bluetooth standard, and the antenna circuit comprises a filter arrangement configured to filter signals received by and to be sent by the an tenna, wherein the filter arrangement comprises a capacitance formed by at least two conducting paths formed on the printed circuit board.

Such an antenna arrangement can be formed in a cost-effective way, because the filter arrangement can be formed very cost efficiently. Only the material to form the at least two conducting paths on the printed circuit board is needed to form the filter arrangement.

The capacitance can comprise a bi-spiral shape comprising a first spiral con ducting path and a second spiral conducting path spiraling into each other.

In this way, a filter arrangement can be formed that has a satisfactory perfor mance for many applications. The first spiral conducting path and the second spiral conducting path can each have a width in a horizontal direction of between 0.1 and 0.2mm, wherein the horizontal direction is a direction parallel to a surface of the printed circuit board on which the first spiral conducting path and the second spiral conducting path are formed.

In this way, a filter arrangement can be formed that has a satisfactory perfor mance for many applications.

The first spiral conducting path and the second spiral conducting path can each have a width in the horizontal direction of 0.14mm.

The first spiral conducting path can be coupled to a first conducting path, and the second spiral conducting path can be coupled to a second conducting path.

The first conducting path and the second conducting path can each have a width in the horizontal direction of between 0.5 and 1 5mm.

The first conducting path and the second conducting path can each have a width in the horizontal direction of 0.9mm.

The first conducting path and the second conducting path can be 50W mi crostrip lines.

In this way, a filter arrangement can be formed that has a satisfactory perfor mance for many applications, in particular for ultra-wide band and Bluetooth antennas.

The at least two conducting paths can comprise copper. This allows to form the filter arrangement, and therefore the antenna arrange ment, in a very cost effective way.

The at least two conducting paths can have a thickness in a vertical direction of between 0.4 and 0.6mm, wherein the vertical direction is a direction perpendicu lar to the surface of the printed circuit board on which the conducting paths are formed.

In this way, a filter arrangement can be formed that has a satisfactory perfor mance for many applications.

The antenna can comprise a conducting path on the printed circuit board.

The antenna can be a monopole antenna or an inverted-F antenna.

A monopole antenna, for example, can be used for UWB transmission, and an inverted-F antenna can be used for Bluetooth or Bluetooth Low Energy trans mission.

An electronic vehicle key comprises an antenna arrangement.

Examples are now explained with reference to the drawings. In the drawings the same reference characters denote like features.

Figure 1 schematically illustrates an antenna arrangement accord ing to one example.

Figure 2 schematically illustrates an antenna arrangement ar ranged on a printed circuit board according to one example. Figure 3 schematically illustrates a filter arrangement according to one example.

Figure 4 schematically illustrates in a diagram different graphs with respect to the filter arrangement of Figure 3.

Figure 5 schematically illustrates a filter arrangement according to another example.

Figure 6 schematically illustrates in a diagram different graphs with respect to the filter arrangement of Figure 5.

In the following Figures, only such elements are illustrated that are useful for the understanding of the present invention. The filter arrangement, the antenna ar rangement and the electronic vehicle key described below may comprise more than the exemplary elements illustrated in the Figures. Flowever, any additional elements that are not needed for the implementation of the present invention have been omitted for the sake of clarity.

Figure 1 illustrates an antenna arrangement that may be implemented in an electronic vehicle key. Signals may be sent between a vehicle and the electron ic vehicle key (vehicle and electronic key not specifically illustrated in Figure 1). For example, the electronic vehicle key may send inquiry signals to the vehicle to indicate the desire of a user to unlock/lock the vehicle. Further, authentication signals may be sent between the electronic vehicle key and the vehicle, for ex ample, in order to prevent unauthorized users (unauthorized keys) from unlock ing or starting the vehicle. Many other signals may be sent between the elec tronic vehicle key and the vehicle for many different applications.

An electronic vehicle key, therefore, may comprise different antennas. One an tenna 10 and corresponding antenna circuit 20 are schematically illustrated in Figure 1. The antenna 10 can be an ultra-wide band (UWB) antenna, for exam ple. Ultra-wide band is a radio technology that can use a very low energy level for short-range, high bandwidth communications over a large portion of the ra dio spectrum. The antenna 10, however, can also be an antenna that is config ured to transmit and receive signals according to a Bluetooth standard at a fre quency of 2.4GHz, for example.

The antenna arrangement illustrated in Figure 1 comprises an antenna circuit 20, the antenna circuit 20 comprising a matching circuit 22, a filter stage or filter arrangement 24, and a controller 26. The matching circuit 22 can be configured to match the input impedance of the antenna 10 to the output impedance of the antenna circuit 20. The matching circuit 22 can comprise capacitors and induct ances, for example. The filter arrangement 24 is configured to filter the signals received and signals to be sent by the antenna 10. The filter arrangement 24 can comprise a front-end band pass filter, for example, to reduce or even avoid spurious emissions during transmission of signals, and to reduce or even avoid in-band noise that might negatively affect the demodulation during reception of signals. The controller 26 is configured to control the function of the antenna circuit 20 and to process the received signals and/or the signals to be sent via the antenna 10.

Filter arrangements for antenna circuits often include ceramic filters or so-called SAW filters. Such filters generally have a very satisfying performance, but are rather expensive.

Now referring to Figure 2, a printed circuit board 30 is schematically illustrated. The antenna 10 is arranged on the printed circuit board 30. For example, the antenna 10 can be formed by a conducting path arranged on the printed circuit board 30. The antenna 10 can be a monopole antenna or an inverted-F anten na, for example. In Figure 2, a monopole antenna is schematically illustrated. The antenna circuit 20 can also be arranged on the printed circuit board 30. The filter arrangement 24 can comprise a capacitance that is formed by at least two conducting paths on the printed circuit board 30. This is schematically illustrated in Figure 3. The filter arrangement 24 illustrated in Figure 3 can be used for a Bluetooth antenna 10, for example. The filter arrangement 24 comprises a bi spiral shape. The bi-spiral shape comprises a first spiral conducting path 2412, and a second spiral conducting path 2422. The first spiral conducting path 2412 can be coupled to a first conducting path 2410 and the second spiral conducting path 2422 can be coupled to a second conducting path 2420. The second spiral conducting path 2422 is illustrated with a dashed line in Figure 3 for illustration purposes only, and in particular to be able to clearly distinguish the second spi ral conducting path 2422 from the first spiral conducting path 2412. The second spiral conducting path 2422, however, is formed by a continuous conducting path on the printed circuit board 30. The first spiral conducting path 2412 and the second spiral conducting path 2422 each form a spiral and spiral into each other, thereby forming a capacitor. Each of the first spiral conducting path 2412 and the second spiral conducting path 2422 can form at least three full turns, for example. According to one example, each of the first spiral conducting path 2412 and the second spiral conducting path 2422 forms between three and ten full turns.

The first spiral conducting path 2412 and the second spiral conducting path 2422 have a small width d2 in a horizontal direction as compared to the width d1 of the first conducting path 2410 and the second conducting path 2420 in a horizontal direction. The horizontal direction is a direction parallel to a surface of the printed circuit board 30 on which the first spiral conducting path 2412 and the second spiral conducting path 2422 are formed. The width d1 of the first conducting path 2410 and the second conducting path 2420 can be between 0.5 and 1 5mm (millimeter), for example. According to one example, the width d1 of the first conducting path 2410 and the second conducting path 2420 is 0.9mm. The width d2 of the first spiral conducting path 2412 and the second spiral conducting path 2422 can be between 0.1 and 0.2mm, for example. Ac- cording to one example, width d2 of the first spiral conducting path 2412 and the second spiral conducting path 2422 is 0.14mm. A thickness of the first con ducting path 2410, the second conducting path 2420, the first spiral conducting path 2412, and the second spiral conducting path 2422 in a vertical direction z can be between 0.4 and 0.6mm, for example. According to one example, the thickness is 0.5mm. The vertical direction z is a direction perpendicular to a sur face of the printed circuit board 30 on which the first spiral conducting path 2412 and the second spiral conducting path 2422 are formed.

The first conducting path 2410 and the second conducting path 2420 can be configured to function as an input line and an output line, respectively, and can be implemented as 50W microstrip lines, for example.

The first conducting path 2410, the second conducting path 2420, the first spiral conducting path 2412, and the second spiral conducting path 2422 can com prise copper, for example.

The filter arrangement 24, therefore, can be implemented in a very cost- effective way. The material that is needed to form the filter arrangement 24 on the printed circuit board 30 is generally very cheap. The filter arrangement 24 only requires a certain amount of space on the printed circuit board 30. The per formance of the described filter arrangement 24 is somewhat inferior as com pared to SAW filters or ceramic filters, but may be acceptable for many applica tions in favor of the reduced costs.

A similar filter arrangement 24 is schematically illustrated in Figure 5 for an ul tra-wide band antenna.

The filter arrangements 24 described above provide a satisfactory transmission and low insertion losses for those frequencies that are common for ultra-wide band and Bluetooth transmission. Outside of the concerned frequency bands, insertion losses are increased such that any unwanted signals outside of the desired frequency bands will be blocked. This is schematically illustrated in Fig ures 4 (for Bluetooth) and Figure 6 (for ultra-wide band). As can be seen in Figure 4, for reception in-band (between about 2.4 and 2.5GFIz) insertion losses are about 1.79dB (curve marked with triangle). Inser tion losses increase to 10dB or more for frequencies above 2.7GFIz. The fre quency response is also illustrated in Figure 4 for input (curve marked with cross) and output (curve marked with dot).

As can be seen in Figure 6, for reception in-band (between about 6.5 and 7.2GFIz) insertion losses are about 2dB (curve marked with triangle). The bandwidth is approximately 500MFIz, which is sufficient for an ultra-wide band channel. Insertion losses increase to 8dB or more for frequencies above 7.3GFIz or below 6.2GFIz. The frequency response is also illustrated in Figure 6 for input (curve marked with cross) and output (curve marked with dot).

The filter arrangement 24 has been described with respect to Bluetooth and ultra-wide band transmission above. Flowever, the filter arrangement can be adapted for other frequency bands. The quality of the filter arrangement 24 can depend on the quality of the printed circuit board 30.

List of reference signs

10 antenna

20 antenna circuit

22 matching circuit

24 filter arrangement

2410 first conducting path

2412 first spiral conducting path

2420 second conducting path

2422 second spiral conducting path

26 controller

30 circuit board