EP3920326A1

EP3920326A1 - Antenna arrangement for electronic vehicle key

Info

Publication number: EP3920326A1
Application number: EP20465533.6A
Authority: EP
Inventors: Andreea c/o Continental Automotive GmbH Hadarig; Razvan c/o Continental Automotive GmbH Bejinaru
Original assignee: Continental Automotive Technologies GmbH
Current assignee: Aumovio Germany GmbH
Priority date: 2020-06-05
Filing date: 2020-06-05
Publication date: 2021-12-08

Abstract

An antenna arrangement comprises a first antenna section (31), a second antenna section (32), an antenna circuitry (21), and an inductive element (40). The first antenna section (31) is coupled between the antenna circuitry (21) and a first terminal of the inductive element (40), and the second antenna section (32) is coupled between a second terminal of the inductive element (40) and the antenna circuitry (21), and in series to the first antenna section (31) and the inductive element (40).

Description

The current invention relates to an antenna arrangement, in particular an antenna 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 unlock 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 vehicle key and allows the user to start the vehicle. Such systems replace the originally 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 (UHF) antenna, and an antenna for Bluetooth communication. Bluetooth or Bluetooth Low Energy (BLE) communication may be used, for example for transmitting all kind of information (e.g., tire pressure, fuel status, etc.) from the vehicle to the vehicle key or to a portable electronic device (e.g., smartphone). At least one of the antennas may be implemented as a loop antenna. Many different antennas are generally all integrated in the vehicle key, the vehicle key having comparably small dimensions. When the number of antennas increases, however, the space requirements in the vehicle key increase.
There is a need to provide an antenna arrangement for an electronic vehicle key which has comparably small space requirements.
This problem is solved by an antenna arrangement according to claim 1 and an electronic vehicle key with an antenna arrangement according to claim 10. Configurations and further developments of the invention are the subject of the dependent claims.
An antenna arrangement includes a first antenna section, a second antenna section, an antenna circuitry, and an inductive element. The first antenna section is coupled between the antenna circuitry and a first terminal of the inductive element, and the second antenna section is coupled between a second terminal of the inductive element and the antenna circuitry, and in series to the first antenna section and the inductive element.
In this way, the antenna arrangement can be implemented in a very space saving and cost-effective way. A single antenna arrangement may be used for two different frequency ranges.
When the antenna arrangement is operated at a frequency of 2.4GHz, for example, the second antenna section may be decoupled from the first antenna section by the inductive element such that only the first antenna is used to transmit and receive signals.
When the antenna arrangement is operated at a frequency of between 300MHz and 500MHz, for example, the first antenna section and the second antenna section together may form an antenna that is used to transmit and receive signals.
The inductive element may comprise an inductance of 10nH, in order to effectively decouple the second antenna section from the first antenna section at a first frequency, and to allow the first and second antenna section to form a single antenna at a frequency range that is different from the first frequency.
The first antenna section, when decoupled from the second antenna section, may form a monopole antenna.
The second antenna section together with the first antenna section may form a loop antenna.
The antenna arrangement may further include a switching element coupled between the antenna circuitry and the series connection including the first antenna section, the second antenna section and the inductive element. The antenna circuitry may include a first branch comprising a Bluetooth circuitry and a Bluetooth matching circuit. The antenna circuitry may further include a second branch comprising an ultra-high frequency circuitry and an ultra-high frequency matching circuit. The switching element may be configured to couple the series connection including the first antenna section, the second antenna section and the inductive element either to the first branch or to the second branch.
Depending on the branch the antenna is coupled to, it may be operated at a different frequency. A single antenna arrangement, therefore, may be used to perform two different wireless services or applications.
An electrical length of the first antenna section may equal a quarter of the resulting wavelength when the antenna arrangement is operated at a frequency of 2.4GHz.
The first antenna section, the second antenna section, the inductive element and the antenna circuitry may be arranged on a printed circuit board.
An electronic vehicle key may include an antenna arrangement as described above.
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 according to one example.
Figure 2 , including Figures 2A and 2B, schematically illustrates in different diagrams an input impedance for an UHF antenna without a decoupling circuit (Figure 2A) and with a decoupling circuit (Figure 2B).
Figure 3 , including Figures 3A and 3B, schematically illustrates in different diagrams an input impedance for a BLE antenna without a decoupling circuit (Figure 3A) and with a decoupling circuit (Figure 3B).
Figure 4 schematically illustrates in a smith diagram a BLE input reflection coefficient for a BLE antenna without decoupling circuit.
Figure 5 schematically illustrates in a smith diagram a BLE input reflection coefficient for a BLE antenna with decoupling circuit.
Figure 6 schematically illustrates in a diagram a comparison between the frequency response of a BLE antenna with and without decoupling circuit.
Figure 7 schematically illustrates in a block diagram an antenna arrangement according to one example.

In the following Figures, only such elements are illustrated that are useful for the understanding of the present invention. The antenna arrangement and the electronic vehicle key described below may comprise more than the exemplary elements illustrated in the Figures. However, 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 arranged in an electronic vehicle key. Signals may be sent between a vehicle and the electronic vehicle key (vehicle not 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 example, in order to prevent unauthorized users (unauthorized keys) from unlocking or starting the vehicle. Many other signals may be sent between the electronic vehicle key and the vehicle for many different applications.
An electronic vehicle key, therefore, may comprise different antennas. A first antenna may be a low frequency (LF) antenna, for example. Low frequency signals may be sent at frequencies in the range between 30 to 300kHz, for example. A second antenna may be a radio frequency (RF) or ultra-high frequency (UHF) antenna, for example. Radio frequency signals may be sent at frequencies in the range between 20kHz to 300GHz. An even further antenna may be an antenna that is configured to transmit and receive signals according to the Bluetooth standard at a frequency of 2.4GHz.
The antenna arrangement illustrated in Figure 1 comprises an antenna circuitry 21, a first antenna section 31, a second antenna section 32, and an inductive element 40. The inductive element 40 is coupled between and in series to the first antenna section 31 and the second antenna section 32. That is, the first antenna section 31 is coupled to the antenna circuitry 21 with a first end, and to a first terminal of the inductive element 40 with a second end. The second antenna section 32 is coupled to a second terminal of the inductive element 40 with a first end, and to the antenna circuitry 21 with a second end.
The inductive element 40 is configured to decouple the second antenna section 32 from the first antenna section 31 at specific frequencies. For example, when the antenna arrangement is operated at a frequency of 2.4GHz, the second antenna section 32 may be decoupled from the first antenna section 31. In other words, at a frequency of 2.4GHz, only the first antenna section 31 may be used to transmit and receive signals, while the second antenna section 32 becomes "invisible" and is not used for transmitting and receiving. The inductive element 40, for example, may comprise a capacitance of 10nH.
When the antenna arrangement is operated at a frequency of between 300 and 500MHz, for example, which fall into the ultra-high frequency range, on the other hand, the first antenna section 31 and the second antenna section 32 together form a loop antenna for transmitting and receiving signals in the ultra-high frequency band. The inductive element 40 in this case (at frequencies of between 300MHz and 500MHz) has a low impedance and, therefore, does not have an influence on the behavior of the loop antenna formed by the first antenna section 31 and the second antenna section 32. That is, the ultra-high frequency signal can flow unhindered through the loop formed by the first antenna section 31 and the second antenna section 32. According to one example, the antenna arrangement may be operated at a frequency of 315MHz or 434MHz.
The loop antenna formed by the first antenna section 31 and the second antenna section 32 may be a small loop antenna, for example. The first antenna section 31, when operated separately (second antenna section 32 is decoupled) may form a monopole antenna.
The first antenna section 31, the second antenna section 32, the inductive element 40 and the antenna circuitry 21 may all be arranged on a printed circuit board 10.
An electrical length of the first antenna section 31 may equal a quarter of the resulting wavelength when the first antenna section 31 is operated at a frequency of 2.4GHz. That is, the inductive element 40 may be arranged at a position along the loop antenna formed by the first antenna section 31 and the second antenna section 32 which is arranged at a first distance with respect to a feeding point, wherein the first distance equals a quarter of the resulting wavelength when the antenna arrangement is operated at a frequency of 2.4GHz.
The first antenna section 31 and the second antenna section 32 are both integrated into a single topology while keeping the electrical behavior of each antenna (BLE antenna, UHF antenna) essentially unaffected.
The first antenna section 31 and the second antenna section 32 may each be implemented as a copper trace on the printed circuit board 10, for example.
Now referring to Figure 2A, an ultra-high frequency antenna input impedance is schematically illustrated for an ultra-high frequency antenna that does not comprise an inductive element 40 (without decoupling circuit). Figure 2A shows both a real part of the impedance (curve having the lower peak, illustrated in a solid line), and an imaginary part of the impedance (curve having the higher peak, illustrated in a dashed line).
Figure 2B, on the other hand, schematically illustrates an ultra-high frequency antenna input impedance for an ultra-high frequency antenna comprising an inductive element 40 as exemplarily illustrated in Figure 1 (with decoupling circuit). Figure 2B also shows both a real part of the impedance (curve having the lower peak, illustrated in a solid line), and an imaginary part of the impedance (curve having the higher peak, illustrated in a dashed line). As can be seen from Figures 2A and 2B, the differences in the desired frequency range are marginal with or without the inductive element 40. The inductive element 40 does not essentially affect the antenna impedance.
Now referring to Figure 3A, an input impedance of a BLE antenna is schematically illustrated for a BLE antenna without an inductive element 40 (without decoupling circuit). Figure 2A also shows both a real part of the impedance (curve having the higher peak, illustrated in a solid line), and an imaginary part of the impedance (curve having the lower peak, illustrated in a dashed line).
Figure 3B, on the other hand, schematically illustrates in a diagram a BLE antenna input impedance for a BLE antenna comprising an inductive element 40 as exemplarily illustrated in Figure 1 (with decoupling circuit). Figure 3B also shows both a real part of the antenna impedance (curve arranged in upper half of diagram, illustrated in a solid line), and an imaginary part of the antenna impedance (curve starting in lower left part of diagram and ending in upper right part of diagram, illustrated in a dashed line).
As can be seen in Figures 3A and 3B, there are differences at the desired BLE frequency. In particular, there is no resonance in band for the arrangement without the inductive element 40. There is, however, a resonance in band for the arrangement with the inductive element 40. This is also schematically illustrated by the exemplary Smith charts illustrating a BLE input reflection coefficient in Figures 4 (without inductive element 40) and 5 (with inductive element 40). In Figure 4 the dashed circle highlights the point of interest where there is no resonance in band. In Figure 5 the dashed circle highlights the point of interest where there is a resonance in band.
In order to guarantee a maximum power transfer from the antenna circuitry 21 to the first antenna section 31, the input impedance of the first antenna section 31 may be as close as possible to 50Ohm. This results in an input reflection coefficient of below -6dB. This criteria is generally fulfilled in the arrangement of Figure 1, as can be seen in the diagram illustrated in Figure 6. Figure 6 illustrates a comparison between the frequency response of a BLE antenna with (curve with deep valley at BLE frequency, solid line) and without an inductive element 40 (upper curve, dashed line). The input reflection coefficient can be improved to below -10dB at the desired frequencies by the use of a simple matching circuit (e.g., two components, namely one series capacitance/inductance and one shunt capacitance/inductance).
Now referring to Figure 7, the antenna arrangement may further comprise a switching element 50 coupled between the antenna circuitry 21 and the series connection including the first antenna section 31, the second antenna section 32 and the inductive element 40. In Figure 7 this series connection is schematically represented by a single antenna 33. The antenna circuitry 21 may comprise a first branch comprising a Bluetooth circuitry (or Bluetooth Low Energy circuitry) 71 and a Bluetooth (or Bluetooth Low Energy) matching circuit 61. The antenna circuitry 21 may further comprise a second branch comprising an ultra-high frequency circuitry 72 and an ultra-high frequency matching circuit 62. The switching element 50 may be configured to couple the series connection including the first antenna section 31, the second antenna section 32 and the inductive element 40 (antenna 33) either to the first branch or to the second branch. That is, when connected to the first branch, the antenna 33 may be operated at a frequency of 2.4GHz to perform Bluetooth or Bluetooth Low Energy communication. The second antenna section 32 in this case may be "invisible", as has been described above. When connected to the second branch, the antenna 33 may be operated at frequencies falling into the ultra-high frequency range (e.g., 315MHz, or 434MHz). That is, when the antenna 33 is coupled to the second branch, the first antenna section 31 and the second antenna section 32 may together form a loop antenna.

Claims

An antenna arrangement comprising
a first antenna section (31);

a second antenna section (32);

an antenna circuitry (21); and

an inductive element (40); wherein

the first antenna section (31) is coupled between the antenna circuitry (21) and a first terminal of the inductive element (40), and

the second antenna section (32) is coupled between a second terminal of the inductive element (40) and the antenna circuitry (21), and in series to the first antenna section (31) and the inductive element (40).
The antenna arrangement of claim 1, wherein, when the antenna arrangement is operated at a frequency of 2.4GHz, the second antenna section (32) is decoupled from the first antenna section (31) by the inductive element (40) such that only the first antenna section (31) is used to transmit and receive signals.
The antenna arrangement of claim 1 or 2, wherein, when the antenna arrangement is operated at a frequency of between 300MHz and 500MHz, the first antenna section (31) and the second antenna section (32) together form an antenna that is used to transmit and receive signals.
The antenna arrangement of any of claims 1 to 3, wherein the inductive element (40) comprises an inductance of 10nH.
The antenna arrangement of any of the preceding claims, wherein the first antenna section (31), when decoupled from the second antenna section (32), forms a monopole antenna.
The antenna arrangement of any of the preceding claims, wherein the second antenna section (32) together with the first antenna section (31) forms a loop antenna.
The antenna arrangement of any of the preceding claims, further comprising a switching element (50) coupled between the antenna circuitry (21) and the series connection including the first antenna section (31), the second antenna section (32) and the inductive element (40), wherein
the antenna circuitry (21) comprises a first branch comprising a Bluetooth circuitry (71) and a Bluetooth matching circuit (61);

the antenna circuitry (21) further comprises a second branch comprising an ultra-high frequency circuitry (72) and an ultra-high frequency matching circuit (62); and
the switching element (50) is configured to couple the series connection including the first antenna section (31), the second antenna section (32) and the inductive element (40) either to the first branch or to the second branch.
The antenna arrangement of any of the preceding claims, wherein an electrical length of the first antenna section (31) equals a quarter of the resulting wavelength when the antenna arrangement is operated at a frequency of 2.4GHz.
The antenna arrangement of any of the preceding claims, wherein the first antenna section (31), the second antenna section (32), the inductive element (40) and the antenna circuitry (21) are arranged on a printed circuit board (10).
An electronic vehicle key comprising an antenna arrangement of any of claims 1 to 9.