EP1184934A1 - Planar antenna - Google Patents

Abstract

Gamma-supplied antenna for radiofrequency transmitter / receiver, the components of which are connected to a printed circuit comprising a track constituting a supply line connecting the radiofrequency transmitter / receiver to the antenna, which consists of a quarter-radiating element. wave formed by a rectilinear metal track of the printed circuit, said track being arranged on the edge of one side of the support of the printed circuit, characterized in that the track forming the quarter-wave radiating element is separated from the components by at minus a cutout made in the support of the printed circuit, along the track forming the quarter-wave radiating element, said cutout extending to the vicinity of the end of said element connected to the ground plane of the printed circuit. <IMAGE>

Description

The present invention relates to a gamma feed antenna for radio frequency transceivers with components attached to a printed circuit. According to an example of a particular use of the invention, the antenna will be intended for radiocommunications in the automotive field, and will operate for transmissions to frequencies above 800 MHz, such as those by example used in GSM, DECT, ISM 868 MHz, blue standards tooth, etc ...

In the example of the automobile, transmissions by transmitters / receivers, in particular for remote controls allowing the central locking / unlocking that now equips most vehicles available on the market. However, it is about "closed" telecommunications systems that only allow unique functions mentioned above, and do not allow any extension to larger systems.

The use of technologies and standards from telecommunications, such as communications based on the DECT or blue tooth standard, allows the contrary an opening by integration into an environment of much broader reporting, and allows in particular the transfer of multiple internal and external information to vehicles. In addition to locking / unlocking the doors, it becomes therefore possible to transfer various data, up to telemetry of results obtained by sensors, for example from the tire pressure.

Like the current remote controls for locking / unlocking doors of a vehicle, the transmitters / receivers required must be small, their antenna must however obviously have the best possible performance in terms of gain and impedance matching. The in other words, the antennas used must have a maximum efficiency in radiated energy, under a characteristic impedance equal in most case at 50 Ω.

More specifically, the antennas used in these applications operate in standing wave regime, with a radiating element comparable to a line quarter wave short-circuited at one of its ends to the circuit ground transmitter / receiver, a so-called gamma supply line connecting said circuit to a point of the quarter-wave line corresponding to an impedance of about 50 Ω. Such quarter monopole antennas with gamma feed are well known in itself, but need to be adapted to the specific technical contexts in which they are used.

In the invention, the quarter-wave radiating element is used in association with an electronic circuit notably installed on a printed circuit. The particular problems to be solved are of several kinds, and aim not only to make an adaptation between the gamma supply line and the antenna aiming to transfer the maximum energy between the electronic circuit and the element quarter wave, but also to allow the simplest and least manufacturing expensive possible, and finally to obtain a minimum bulk.

Thus, we know configurations in which the antennas are consisting of a metal wire soldered to the printed circuit. The advantage of this configuration is that you can find antenna positions that reduce space, by folding, for example, the wire parallel to the printed circuit, or by soldering it to an edge of said circuit, said wire then being placed in the plane of the PCB support. A certain distance of air is then maintained between the active part of the antenna and the circuit, which allows the density control of the field lines, which must not be too close together so as not to decrease radiation from the antenna.

• augmentation du temps de fabrication ; et par conséquent
• augmentation du coût de production ;
• existence d'une faiblesse potentielle au niveau de la soudure, qui est une liaison dont la qualité mécanique n'est jamais assurée, ni d'ailleurs la pérennité.

The existence of the weld, however, raises several difficulties:

• increased manufacturing time; and therefore
• increased cost of production;
• existence of a potential weakness in the weld, which is a connection whose mechanical quality is never guaranteed, nor indeed the durability.

We also know intermediate configurations in which the antenna is a track of a printed circuit, as for example described in document US-A-5 835 063. The radiating element then consists of a conductive track forming a portion of the conductive deposit of said printed circuit separated from its main part by a rectangular slot along the element beaming.

The radiating element is supplied by a microstrip placed on the face of the support which does not include a conductive deposit, said microstrip crossing the above-mentioned slot in order to allow a double stub feeding.

For the problem of the density of field lines to be resolved, it is however necessary to have recourse to a particular material for the support of the circuit printed, for example of the Teflon glass type. A traditional material would result in effect a concentration of said lines incompatible with correct operation of the antenna, whose radiation would be too reduced.

Materials capable of forming low loss and low loss substrates dielectric constant are however much more expensive than the supports common printed circuit boards, and imply tighter tolerances in terms of dimensioning (thickness). Their use therefore has a significant influence on the cost price of the antenna.

To overcome these drawbacks, the idea on which the invention is based is to propose a configuration without welding, which takes advantage of the mass metal available in a printed circuit, and optimizes the circuit-antenna link, all with traditional materials to keep costs down of production at a level allowing to envisage an industrialization.

The invention therefore relates precisely to a gamma feed antenna for radio frequency transmitter / receiver, the components of which are connected to a printed circuit comprising a track constituting a supply line connecting the radio transmitter / receiver at the antenna, which consists of a quarter-wave radiating element formed by a rectilinear metallic track of the circuit printed, said track being arranged on the edge of one side of the circuit support printed. This antenna is mainly characterized in that the track forming the quarter-wave radiating element is separated from the components by at least one cutting in the support of the printed circuit, along the track forming the quarter-wave radiating element, said cutout extending to the vicinity of the end of said element connected to the ground plane of the printed circuit.

The existence of the cut allows to answer the problem previously city of the concentration of the lines of electromagnetic field: if the space enters the quarter wave radiating element and the ground plane is made of a material dielectric whose dielectric constancy is greater than air, which is the case for the material constituting the support of the printed circuit, the field lines will be denser and closer together. As already indicated, this reconciliation has a harmful effect and reduces the radiation from the antenna. It is therefore desirable avoid placing a dielectric material between the radiating element and the plane of mass, and to keep for example a minimum distance of air between them, which is made by cutting the dimensions (see below) are provided for this effect. It should be noted that if said distance is too small, this also results in a concentration of field lines which causes the same negative effects as the dielectric material.

The existence of this cut avoids the use of a material dielectric more expensive, theoretically just as suitable solution, but of practical scope almost zero because economically difficult to industrialize.

According to one possibility, the printed circuit is at least double-sided, one side comprising the track forming the quarter-wave radiating element, the ground plane and the track forming the link between them, the other side comprising the circuit printed, on which the radiofrequency transmitter / receiver is installed, as well as the supply line of the quarter-wave radiating element whose connection to this the latter is carried out via a metallized orifice passing through the support of the printed circuit.

As in any gamma type adaptation, by moving the position relative of the supply line and the metallized through hole, we act on the antenna impedance matching.

This metallized hole configuration is very advantageous because the position of the radiating element with respect to the mass makes it possible to minimize the length of the adaptation link, in practice to the width of the cutout in the dielectric support of the printed circuit. This reduces the inductive impedance of the gamma matching bond, and makes it unnecessary the addition of a capacity which generally equips feeding antennas gamma.

According to a configuration which takes into account traditional characteristics printed circuits, the invention can be implemented on a support which has a dielectric constant between 3 and 10. Likewise, each conductive layer has a thickness of between 15 µm and 80 µm.

The gamma jack of the invention works as indicated with an element radiating quarter wave. The length of this last is, of course, related to the frequency of use, and therefore at the emission / reception wavelength. according to one possibility, the frequency domain used is that of the DECT band centered around 1880 MHz, hence an easy calculation of the order of magnitude of the length of the radiating element (see below).

More generally, the length of the quarter-wave radiating element is between 0.9 λ / 4 and 5λ / 8.

Another advantage inherent in the configuration of the invention lies in the fact that the ground plane of the printed circuit, to which the components of the radiofrequency transmitter / receiver, is the same as the one to which it is connected the quarter-wave radiating element. The electrical reference is the same, and the manufacturing of the assembly is in particular simplified.

The importance of maintaining a volume of air between the ground plane and the antenna has been underlined: according to one possibility, the cut made in the support of the printed circuit is rectangular, with a width of at least 2 mm and a length at least three-quarters of the quarter-wave element, from the free end of the latter marking the start of cutting. This value is, of course, relating to a particular printed circuit, operating with transmission / reception according to the DECT standard, including the central wavelength (corresponding to 1880 MHz of frequency) is approximately 16 cm, which gives an element radiating quarter wave about 4 cm long. In the configuration of the invention, this means that the rectangular-shaped printed circuit has a width approximately 4 cm for a slightly longer length.

More generally, the width of the cut is taken to be at least λ / 50.

According to a possible alternative, the cut made in the support of the circuit printed is discontinuous, and formed of a succession of orifices made in the support.

More precisely, according to a possible configuration, the orifices are shaped circular.

Furthermore, the width of the quarter-wave radiating element is between λ / 10 and λ / 40. Tests have shown that a planar antenna in the form of a track printed circuit board allows optimum performance radiation with these widths.

A precise configuration of the invention has been successfully tested: in this solution, the quarter-wave radiating element has a length of 33 mm, a width of 4.5 mm, the cut in the support of the printed circuit having a width 2.5 mm.

• la figure 1 est un schéma théorique d'une liaison d'adaptation gamma à un élément rayonnant quart d'onde ;
• la figure 2 illustre la configuration d'un support de circuit imprimé comportant une antenne selon l'invention ;
• la figure 3 montre un côté du support de circuit imprimé ; et
• la figure 4 en représente l'autre côté.

The invention will now be described in more detail, in particular by means of the appended figures, for which:

• FIG. 1 is a theoretical diagram of a gamma adaptation link to a quarter-wave radiating element;
• FIG. 2 illustrates the configuration of a printed circuit support comprising an antenna according to the invention;
• Figure 3 shows one side of the printed circuit support; and
• Figure 4 shows the other side.

The gamma-feed quarter-wave radiating element antenna of the invention, a theoretical diagram of which is represented in FIG. 1, operates in regime standing waves along said radiating element (1). This element (1) is connected to ground (2) at its lower end, point where the high voltage frequency is therefore zero, while it is maximum at its end free. The current is quadrature, that is to say zero at the free end and maximum at the point of contact with the ground plane (2) which is the repository for food of the antenna.

Since the current / voltage distribution is quadrature, the impedance varies along the radiating element: it is weak and close to 0 Ω at the connection to the mass (2), and high at the free end of the radiating element (1), of the order of thousand Ohms.

Adaptation consists in adjusting the impedance by displacement along the radiating element (1) of the socket (3) until the desired value is obtained, around 50 Ω. The conductive element (4) located between said power outlet (3) and the connection terminals (5) gives its name to the designation (in gamma) of the makes the shape it takes.

Impedance comes in the form: Z = R + jX

R being the real resistive part adjustable by positioning of the socket (3), then that X is the reactive part, of an inductive nature, originating from said bond in gamma (4).

In theory, a capacitor (6) is inserted between said link (4) and the terminals (5), which cancels the imaginary jX part to give a purely impedance real.

FIG. 2 represents the configuration of a printed circuit support according to the invention, provided with a cutout (7) separating the tab (8) supporting the track forming the quarter-wave radiating element of the surface (9) supporting the circuit transmission / reception electronics (not shown). All of these are located in the same plane, which results in a considerable reduction in the size of the transmitter / receiver.

The cutout (7) introducing air between the antenna arranged on the tab (8) and the circuit makes it possible to make the characteristics of the antenna independent of variations in the dielectric constant of the material forming the circuit support printed.

FIG. 3 shows one side of the printed circuit, the black surface corresponding to the metallized coating forming the ground plane (10) on the one hand, and the quarter-wave element (11) on the other hand. The dielectric material support (12) comprises said cutout (7) which runs along approximately three quarters of the radiating element (11) which covers the tab (8). The ground plan (10) covers almost all of the surface (9).

A metallized through hole (13) makes the electrical connection between the element radiating quarter wave (11) and the gamma bond (see Figure 4) and constitutes the socket (3) of figure 1.

Referring to Figure 4, the second opposite side of the circuit support printed is shown, showing in its right part, in dotted lines, the tracks of the opposite face, and in particular the track (11) constituting the quarter element wave. The tracks of the printed circuit receiving in particular the transmitter / receiver do not are not accurately figured. In any case, they depend on components used, and are shown diagrammatically by the crossed-out rectangle. The through hole (13) metallized constituting the power outlet is located at the end of the link (14) in gamma constituting the antenna supply line.

The width of the supply line (14) is determined according to the characteristic impedance of the transmitter / receiver input and high frequency characteristics of the printed circuit. As mentioned previously, this impedance is preferably close to 50 Ω.

As in the theoretical diagram in Figure 1, by moving the position of said supply line (14) and the metallized hole (13) along the track (11), acts on the impedance adaptation of the antenna.

One of the major advantages of this structure is that the length of the element gamma (14) is reduced to the width of the cutout (7) resulting in a reduction of the inductive impedance of this adaptation element (14) which makes it possible to do without the addition of a capacity in series in the circuit.

The antenna of this invention is grounded from the point of view of low frequencies and direct current. This feature has the effect of protect the electronic components of the radio part against discharges electrostatic on the end of the antenna.

The arrangement of this antenna on the edge of the printed circuit also has the advantage of allowing the production of a product comprising the transmitter / receiver, the antenna and in addition all interface functions for the user such as a display, a keyboard, an audible signal etc ... This same arrangement of the antenna on the printed circuit makes it possible to focus the electromagnetic energy of the antenna in a preferred direction, which can prove to be advantageous for products laptops that should fit in the palm of your hand. The directions of the components of the electric field E and magnetic field H are illustrated in Figure 2 and are such that the vector product of E through H gives the direction of propagation P electromagnetic energy in space: P = E ∧ H .

• Fréquence centrale 1888 GHz
• Taux d'onde stationnaire inférieur à 2 pour une bande passante de -40 à +80 MHz autour de 1888 GHz.
• Performances radioélectriques équivalentes à une antenne quart d'onde.

The practical implementation of this antenna on an epoxy fiber printed circuit makes it possible to obtain the following minimum performances:

• Central frequency 1888 GHz
• Standing wave rate less than 2 for a bandwidth of -40 to +80 MHz around 1888 GHz.
• Radio performance equivalent to a quarter wave antenna.

The above description relates only to an example of implementation of the invention which can not be considered as limiting thereof. The invention on the contrary encompasses the variants of form and configuration which are within reach of those skilled in the art.

Claims (12)

Gamma-supplied antenna for radiofrequency transmitter / receiver, the components of which are connected to a printed circuit comprising a track constituting a supply line connecting the radiofrequency transmitter / receiver to the antenna, which consists of a quarter-radiating element. wave formed by a rectilinear metal track of the printed circuit, said track being arranged on the edge of one side of the support of the printed circuit, characterized in that the track forming the quarter-wave radiating element is separated from the components by at less a cutout made in the support of the printed circuit, along the track forming the quarter-wave radiating element, said cutout extending to the vicinity of the end of said element connected to the ground plane of the printed circuit. Gamma antenna for radiofrequency transmitter / receiver according to the preceding claim, characterized in that the printed circuit is at least double-sided, one side comprising the track forming the quarter-wave radiating element, the ground plane and the track forming the connection between them, the other side comprising the printed circuit on which the radiofrequency transmitter / receiver is installed, as well as the supply line of the quarter-wave radiating element, connected to the latter via a metallized orifice crossing the support of the printed circuit. Gamma feed antenna for radio frequency transmitter / receiver according to one of the preceding claims, characterized in that the support of the printed circuit has a dielectric constant between 3 and 10. Gamma feed antenna for radio frequency transmitter / receiver according to the preceding claim, characterized in that each conductive layer has a thickness between 15 µm and 80 µm. Gamma feed antenna for radio frequency transmitter / receiver according to any one of the preceding claims, characterized in that the length of the quarter-wave radiating element is between 0.9 x λ / 4 and 5λ / 8. Gamma antenna for radiofrequency transmitter / receiver according to any one of Claims 2 to 5, characterized in that the ground plane of the printed circuit to which the components of the radiofrequency transmitter / receiver are fixed is the same as that to which is connected the quarter wave radiating element. Gamma antenna for radio frequency transmitter / receiver according to any one of the preceding claims, characterized in that the cutout made in the support of the printed circuit is rectangular, with a width of at least 2 mm and a length of at least three-quarters of the quarter-wave element, starting from the free end of the latter marking the start of the cut. Gamma feed antenna for radiofrequency transmitter / receiver according to any one of Claims 1 to 6, characterized in that the width of the cut-out is equal to at least λ / 50. Gamma feed antenna for radiofrequency transmitter / receiver according to any one of Claims 1 to 6, characterized in that the cutting is discontinuous, and formed by a succession of orifices made in the support. Gamma feed antenna for radio frequency transmitter / receiver according to the preceding claim, characterized in that the orifices are circular in appearance. An antenna with gamma feed for a radiofrequency transmitter / receiver according to any one of the preceding claims, characterized in that the width of the quarter-wave radiating element is between λ / 10 and λ / 40. Gamma antenna for radiofrequency transmitter / receiver according to any one of the preceding claims, characterized in that the quarter-wave radiating element has a length of 33 mm, a width of 4.5 mm, the cut-out in the support of the printed circuit having a width of 2.5 mm.

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