GB2293050A

GB2293050A - An antenna used for the transmission or the reception of a radio frequency signal, a transmitter and a remote control receiver.

Info

Publication number: GB2293050A
Application number: GB9518098A
Authority: GB
Inventors: Jose Robineau
Original assignee: Valeo Electronique SA
Current assignee: Valeo Electronique SA
Priority date: 1994-09-05
Filing date: 1995-09-05
Publication date: 1996-03-13
Also published as: FR2724263A1; GB9518098D0; DE19528703A1; FR2724263B1

Description

1 2293050 The present invention relates to an antenna used for the

transmission or the reception of a radio frequency signal, a transmitter and a receiver, and a remote control system for a vehicle incorporating it.

Radio frequency remote controls for access to a motor vehicle have numerous advantages when compared with infrared remote controls. In fact they are not directive, i.e. it is not necessary for the user to direct the transmitter towards the receiver in order to activate the opening of the vehicle's doors.

Moreover the radio frequency link is not- necessarily by the presence of a wall or any other obstacle between the transmitter and the receiver.

In other respects the range of a radio frequency remote control is roughly double the range of an infrared remote control for substantially equivalent transmitting and operating powers.

Finally from the point of view of installation in the vehicle, it is not necessary for the receiver to be located in a position which is visible from outside the vehicle, which may be an advantage, in particular with respect to problems associated with vehicle theft.

By using a technology in the frequency spectrum in the 100MHz 1GIz band, i.e. around SOOMHz, the average wavelength (in air) of the signal transmitted is 60 cm. Therefore one quarter of this wavelength is 15 cm.

The production of a quarter-wave antenna, in particular such a receiver antenna intended for use in the receiver of the 2 remote control, therefore requires the achievement of a characteristic size in the region of 15 cm for the antenna.

In the state of the art a whip antenna situated outside the vehicle is conventionally used. This type of antenna requires connectors and wiring owing to the distance of the antenna in relation to the receiver which have a great adverse effect both on the complexity and the cost of the receiver installation.

For this reason solutions were proposed in which the antenna is integrated in a window of a vehicle. This type of construction is certainly more aesthetic but the problem of the connectors and of the length of the wires which are necessary remain the same.

The use of an add-on unit, sometimes called an aerial, has also been proposed, which is formed by a coil which is welded onto a coplanar circuit such as a printed circuit of the transmitter (or of the receiver) incorporating it, and the best radiation performances of which are used.

However this recourse to an add-on unit gives rise to increased difficulties with mechanical installation, which are unfavourable for large scale production, and also a greater spatial requirement in the housing of the transmitter (or of the receiver) creating in particular a larger thickness of the said housing.

Bearing in mind the characteristic length of the receiver antenna, which is, as has been discussed, in the order of 15 cm, it appears possible to produce the antenna in microstrip or planar technology in the located application type, i.e. for frequencies in the region of 500 MHz.

The problem associated with - the connectors and with the cable lengths disappears since the antenna can be 3 advantageously placed in the actual housing of the receiver. Moreover, this type of antenna is easy to produce industrially insofar as it involves producing strip conductors, for example of copper, in accordance with a process well mastered by the person skilled in the art. Moreover the calculation of the impedances is simple and allows an effective matching between the antenna thus formed by the copper conductors on the one hand and the input of the receiver on the other hand.

However such antennae used in the above-mentioned frequency range have poor characteristics both with respect to gain and the width of the radiation pattern.

An object of the present invention is to resolve the abovementioned problems of the prior art.

According to the present invention there is provided an antenna such as an antenna used in the transmitter or the receiver of a radio frequency remote control, this transmitter, respectively this receiver, being produced on a printed circuit placed in a housing, which is made of a mouldable material such as a plastic material, wherein the antenna comprising two parts in cascade:

a first part, called the primary, formed by at least one strip conductor produced for example in microstrip technology, which is physically connected to the transmitter, respectively to the receiver, by means of two terminals; and a secondary part, which is not physically connected to the transmitter, and which is disposed in relation to the said f irst part so as to produce an impedance conversion in order to produce a matching between the transmitter and the propagation medium, and/or to produce a better electromagnetic radiation pattern and also a better gain for the antenna.

4 The antenna according to the invention has the advantage of being of a fairly reduced size so that it can be completely housed in the housing of the receiver, whilst having good reception performances. Moreover this antenna is of a simple design and adapts well to the constraints of largescale production. Finally it is cheap.

According to other characteristics of the invention, taken individually or in combination:

- the primary of the antenna is produced by microstrip or coplanar technology on a first face of the said printed circuit; - the secondary of the antenna is produced by microstrip or coplanar technology on a second face of the said printed circuit so as to:be focused on the primary; - the secondary is produced in the form of at least one strip conductor etched on the housing so as to be focused on the primary; - the secondary of the antenna is produced in the form of at least one strip conductor which is embedded in the housing so as to be focused on the primary; - the secondary is produced in the form of at least one strip conductor disposed on an adhesive label intended to be stuck onto the housing so as to be focused on the primary; - (the secondary) is produced on a second printed circuit disposed inside the housing parallel to the first printed circuit on which the primary and also the electronics of the transmitter, respectively of the receiver, is disposed, the said second printed circuit being disposed in relation to the printed circuit bearing the primary so that the secondary is focused on the primary.

It will be noted that, all the possible embodiments, the first and the second parts of the antenna are situated in relation to one another so as to produce impedance matching, i.e. the desired tuning, hence its name of tuning device.

The invention also relates to a transmitter as well as a remote control receiver incorporating an antenna such as that defined above. Finally it relates to a remote control system incorporating such a transmitter or such a receiver.

Other characteristics and advantages of the present invention will become apparent from reading the following description with reference to the attached drawings which are:

In Figure 1: several possible embodiments of the primary of an antenna according to the invention; In Figure 2: two possible embodiments of an antenna according to the invention regarded in a diagrammatic view; In Figure 3: a method of attaching the secondary of the antenna according to the invention, by means of an adhesive label stuck to a remote control housing.

In Figure 4: a possible embodiment of the secondary of the antenna according to the invention.

The following description is intended to illustrate the principle of the invention and must in no way be interpreted as restricting its scope. In particular, the antenna which is the subject matter of the invention is consequently presented as a receiving antenna used in a radio frequency remote control receiver, but, by virtue of the reciprocity theorem of the antenna theory, the principle of the invention clearly remains applicable to a transmitting antenna.

6 On the four views of Figures i(a) to i(d) four possible embodiments are shown, in microstrip technology or equivalent, of a conventional antenna, i.e. only having one part and not two.

On these four figures the reference 10 designates the circuit of a remote control receiver which in particular includes reception and processing electronics and which will not be described in further detail in the following 10 description.

The circuit of the receiver comprises two terminals 12 and 14 for connection to an antenna outside the circuit.

is The circuit of the receiver is implanted on an electronic substrate (not represented) which also bears a conventional antenna produced in microstrip technology or equivalent.

On Figure 1 (a) the antenna is a dipole antenna which has two arms 11 and 13 respectively connected to the terminals 12 and 14 of the receiver circuit. The'latter are situated close to one another, and on either side of an angle of the circuit 10 of the receiver. Each arm 11 and 13 is bent at right angles as soon as it emerges from the terminals 12 and 14, each being disposed in a direction parallel to a determined side of the circuit of the receiver and running along beside it.

On Figure 1(b), on which the same components as in Figure 1(a) bear the same references, the antenna is a dipole antenna, the two arms 11 and 13 of which run along a same side of the circuit of the receiver 10, but in opposite directions.

On Figure 1 (c), a loop antenna 15 is connected at the two terminals 12 and 14 of the circuit 10 of the receiver. The loop is directed free from the circuit of the receiver, in 7 contrast to the antenna represented in Figure 1(d) on which the same components as in Figure 1 (c) bear the same references, and on which the loop 15 is situated around the circuit 10 of the receiver.

All the radiators or antennae made up of a single part and represented in Figures 1 (a) to 1 (d) dif f er f rom one another by their characteristics such as the radiation pattern and gain in particular.

However as none of these antennae, taken separately, has been shown to have good enough characteristics for our application, the use of a second radiator has been devised, which would form the secondary of a two-part antenna, the is primary of which would be formed by a first radiator such as one of those represented on Figures 1(a) to 1(d).

Thus, both the primary and the secondary of the two-part antenna, which is the subject matter of the invention, can be produced in accordance with-any one of the embodiments given above, or in accordance with any other embodiment known by the person skilled in the art.

The physical principle of the invention is similar to the principle used in an antenna intended for very long-range telecommunications, such as a parabolic antenna which is formed by a primary source as a horn antenna, placed in the focal point of a parabolic reflector forming the secondary of the antenna, so that the radiation emitted by the primary source is transmitted with characteristics defined by the secondary, i.e. by the reflector. These characteristics are associated with the radiation pattern and the gain of the said reflector.

The specific nature of our application, the aim of which is to produce an antenna for "receiving a control signal transmitted by the vehicle remote control transmitter, which 8 can be completely integrated in the housing of the receiver, is described below with reference to Figures 2, 3 and 4.

Figure 2(a) shows, in a diagrammatical manner by a 5 rectangular parallelepiped, a receiver 20 mounted on a substrate or printed circuit 23, on which is disposed a first radiator of the type of a dipole antenna 21 as described in more detail above with reference to Figure i(b).

The presence of a second radiator 22 or 24 disposed respectively above or below the printed circuit 23, so as to be matched with the said first radiator 21, defines an antenna in accordance with the principle of the invention, is i.e. made up of two parts 21, 22 respectively 21, 24 matched to one another in order to have, from the point of view of the single antenna thus formed, performances with respect to the radiation pattern and gain which are far superior than those which a conventional antenna made up of the first radiator 21 would have if it were used by itself.

The first radiator 21 is also called the primary and the second radiator 22 (respectively 24) is also called the secondary of the two-part antenna 21, 22 (respectively 21, 24).

On Figure 2(b), on which the same components as in Figure 2 (a) bear the same references, the primary is formed by a loop antenna, the structure of which was described in more detail with reference to Figure 1 (c), and which is connected to two terminals of the receiver 20 provided for this purpose.

In fact all the possible combinations can be considered for the structure of the primary and respectively of the secondary, the choice being determined by the desired performances of the two-part antenna which one wishes to 9 produce, and which is dimensioned as a function of the characteristics imposed by the application specified.

one may consider producing the secondary 22 directly on the printed circuit, next to the primary 21. If the printed circuit is a double-sided circuit, one may also consider producing the secondary 24 on the face of the printed circuit opposite that where the primary is located.

According to a preferred embodiment of the invention, the secondary is produced on a different support to the printed circuit on which the primary 21 is located.

This support may be formed by a second printed circuit bearing the secondary 22 (respectively 24) and which is held above (respectively below) the said printed circuit 23, or first printed circuit, on which the primary 21 is located. The second printed circuit may be held in a determined position in relation to the first printed circuit, at a determined distance therefrom, for example by joining them by means of screwed pillars, as is known by the person skilled in the art.

The two printed circuits may also be held in this manner in relation to one another by placing them in determined seats provided for this purpose in a housing not represented in Figures 2(a) and 2(b).

In another embodiment of the invention, the secondary is 30 produced directly on the housing. If the secondary has the structure of a loop, this loop is provided on the base of on the cover of the housing, for example in a trough provided for this purpose.

According to another possible embodiment of the invention, the secondary is embedded in the body of the housing. In fact, this is made from plastic material which is moulded around a loop of copper or of any other conductive metal forming the secondary of the antenna.

It is clearly evident that in all these possible embodiments of the antenna according to the invention, and also in the embodiment which is to be described below with reference to Figure 3, the relative positions of the primary and of the secondary are determined by the constraints of electromagnetic tuning or matching, to achieve a transfer of electromagnetic energy between the one and the other, which is determined so as to produce the overall characteristics sought of the two-part antenna.

By analogy with a reflector antenna in which the primary source is disposed in the focal point formed by the reflector, it will be mentioned now and again below that the secondary of the two-part antenna is focused on the primary or vice versa.

In all cases, it is noted that the secondary, which is not physically connected to the circuit of the receiver, in other words which is not connected to the circuit of the receiver by an electrical connection, forms a transition element between the propagation medium and the primary, which is physically connected to the circuit of the receiver, i.e. connected by an electrical connection to the two terminals of the receiver provided for this purpose.

In fact the electromagnetic energy present in the 30 propagation medium is intercepted, in other words it is collected, and concentrated by the secondary, the primary intercepting the electromagnetic energy present in the secondary.

It is evident that the phenomenon described above is reciprocal, as the operation of the antenna in a transmission configuration, i.e. in a transmitter, is 11 symmetrical. In other words, the circuit of the transmitter emits the electromagnetic energy in the primary, this electromagnetic energy being intercepted then radiated by the secondary in the propagation medium.

A preferred embodiment of the two-part antenna according to the invention has been represented on Figure 3. In this embodiment, the circuit of the receptor (not represented) is disposed in a tight housing 30. Only the primary 31 of the antenna is represented by broken lines, in that it is located inside the housing for example disposed on the printed circuit 23 of Figure 2 (b) which also bears the receiver circuit 20.

An adhesive label 33, which is stuck to the outer surface of the housing 30, bears the secondary 32 of the two-part antenna 31, 32. The secondary 32 is made in the form of a strip conductor, which may be looped or not, which is disposed, according to any screen printing process known to the man skilled in the art, on the adhesive label 33. The adhesive label is then stuck on to the housing in a determined position with respect to a determined position of the primary 31 which is located inside the housing.

According to a preferred embodiment, the adhesive label is in fact stuck to an inner face of the housing, so that it is protected from attacks from the exterior environment, which, in an application for the motor vehicle, is regarded as particularly hostile.

In Figure 4 a possible embodiment of the invention of the secondary 40 of the antenna has been shown. In fact on the previous figures, this was shown as a closed conductive loop, forming a radiator for the transmission or the reception of electromagnetic energy, received or transmitted to the primary of the antenna by magnetic coupling.

12 A certain advantage of the two-part structure of the antenna according to the invention lies in the fact that the secondary contributes towards performing the matching between the propagation medium, which here is the ambient air, and the receiver circuit.

This matching induces a structure of the receiver which requires a compromise with the constraints imposed by the desired performances of the antenna, with respect to the radiation pattern and the gain.

The impedance matching principle of the antenna according to the invention is inspired by the theoretical matching principle using two inductors, a primary inductor and a secondary inductor in order to produce the electromagnetic matching and thus the maximum transfer of energy.

It is for this reason that the secondary is also called the "tuning device", as it produces the tuning between the propagation medium and the receiver.

The calculations required by the dimensioning of the complete system call upon the general theory of transmission lines. In particular, tuning is produced at a determined frequency or frequency range around a resonance frequency of the two-part antenna.

The value of this resonance frequency is determined mainly as a function of the capacitive and inductive components of the radiators.

In Figure 4, the secondary 40 is thus formed by an open loop having an inductive part 41 corresponding to the loop in itself, and by a capacitive part 42 corresponding to a zone in which the two ends of the open loop extend parallel to one another.

13 It is known to the person skilled in the art to calculate, at the nominal frequency in question, the theoretical value of the capacitance of the loop 40 as a function of the length of the zone 42 in which the two ends of the loop make up the equivalent of two electrodes of a capacitor and as a function of the width of the dielectric space separating them, and also to calculate, still at the nominal frequency in question, the value of the equivalent inductance of the loop 40 as a function of the length of the part 41 of the said loop 40.

14

Claims

1.

An antenna, such as an antenna used in the transmitter or receiver of a radio frequency remote control, this transmitter, respectively this receiver, being produced on a printed circuit placed in a housing, the latter being made of a mouldable material such as a plastic material, wherein the antenna comprises two parts in cascade:

a first part, called the primary, formed by at least one strip conductor made for example in microstrip technology, which is physically connected to the transmitter, respectively to the receiver, by means of two terminals; and a second part, called the secondary, which is not physically connected to the transmitter, respectively to the receiver, and which is disposed in relation to the said first part whereby to produce an impedance conversion in order to produce a matching between the transmitter and the propagation medium, respectively between the propagation medium and the receiver, and/or to produce a better electromagnetic radiation pattern and also a better gain for the antenna.

2. An antenna according to Claim 1, wherein the primary is produced in microstrip or coplanar technology on a first face of the said printed circuit.

3. An antenna according to Claim 1, wherein the secondary is produced in microstrip or coplanar technology on a second face of the said printed circuit so as to be focused on the primary.

is An antenna according to Claim 1, wherein the secondary is produced in the form of at least one strip conductor etched on the housing so as to be focused on the primary.

is 5. An antenna according to Claim 1, wherein the secondary of the antenna is produced in the form of at least one strip conductor which is embedded in the housing so as to be focused on the primary.

An antenna according to Claim 1, wherein the secondary is produced in the form of at least one strip conductor disposed on an adhesive label which is stuck to the housing so as to be focused on the primary.

7.

An antenna according to Claim 1, wherein the secondary is produced on a second printed circuit disposed inside the housing parallel to the first printed circuit on which the primary and also the electronics of the transmitter, respectively of the receiver is disposed, the said second printed circuit being disposed in relation to the printed circuit bearing the primary so that the secondary is focused on the primary.

8. A radio frequency remote control transmitter for locking and unlocking openings of a motor vehicle, comprising an antenna as claimed in Claim 1.

9. A radio frequency remote control receiver for locking and unlocking openings of a motor vehicle, comprising an antenna as claimed in Claim 1.

10. A radio frequency remote system for locking and unlocking the openings of a motor vehicle, comprising a transmitter and a receiver, wherein the transmitter is a transmitter as claimed in Claim 8.

16 11. A radio frequency remote system for locking and unlocking the openings of a motor vehicle, comprising a transmitter and a receiver, wherein the receiver is a receiver as claimed by Claim 9.

An antenna constructed and arranged as hereinbef ore described with reference to and as shown in the accompanying drawings.