EP1509966A1

EP1509966A1 - Integrated multi-frequency antenna for mobile telephone

Info

Publication number: EP1509966A1
Application number: EP03756023A
Authority: EP
Inventors: Christian Leray
Original assignee: Sagem SA
Current assignee: Apple Inc
Priority date: 2002-05-31
Filing date: 2003-05-28
Publication date: 2005-03-02
Also published as: FR2840457B1; WO2003103088A9; CN100563060C; CN1781212A; WO2003103088A1; FR2840457A1

Abstract

The invention relates to a PIFA-type multi-frequency antenna comprising a radiant element (10) which is placed remotely from a ground plane. The radiant element (10) comprises at least one connection to the aforementioned ground plane (32), a supply point (31) and at least one slit (20, etc.). One end of the slit is disposed on one edge (10a) of the radiant element (10) while the other end thereof is disposed inside the radiant element, said slit being shaped to define a convex area (11) on the radiant element (10). In this way, the antenna forms the centre of several resonant frequencies. The invention is characterised in that each slit (20) comprises at least one projection (40, , 50, etc.).

Description

Integrated multi-frequency antenna for mobile phone

The present invention relates to an integrated multi-frequency antenna for mobile telephone.

An antenna of this type is already described in a document entitled "Dual-Frequency Planar Inverted-F Antenna" published in IEEE Transcations on antennas and Propagation, vol 45, No 10 of October 1997 in the name of Zi Dong Liu and ail. One such antenna, shown in FIG. la, consists of a planar radiative element 100 electrically conductive placed at a distance d from a ground plane M also electrically conductive substantially parallel thereto. The radiative element 100 is divided by a slot 200 into two separate zones 101 and 102 each of which is supplied by a supply pad 101a and 102a crossing the ground plane M. Furthermore, each zone 101, 102 of the radiative element 100 is connected to the ground plane M by a conductive pad 101b, 102b hereinafter called the ground pad.

The resonance mode of such an antenna is a quarter wave mode. Therefore, we can say that the high frequency is determined by the dimensions of the area 101 while the low frequency is determined by the dimensions of the area

CP ^Î U BB € OMFimâATiQM 102. The distance d between the radiant element 100 and the ground plane M is a parameter in determining the bandwidth at each resonant frequency while the distance which separates a supply pad 101a, 102a from the ground pad corresponding is another parameter in determining the antenna impedance at each resonant frequency.

We have been able to show that the resonance frequency of a rectangular planar radiative element is approximately given by the relation:

f =

4 (a + b)

where C is the speed of light, a and b the width and length of the rectangular planar radiative element considered and ε _r is the permittivity of the medium which is between the radiative element and the ground plane.

With regard to each zone 101 and 102 of the radiative element 100 of the antenna which is shown in FIG. 1 a, this relationship is approximate because distortions are introduced therein in particular because the zones 101 and 102 are coupled together at the level of the slot 200, coupling which depends among other things on the width of the slot 200.

In the same document, there is also mentioned an antenna of the same type as above but which has only one feed pad. Such an antenna is shown in FIG. lb where it can be seen that, since the slot 200 only opens onto one edge of the radiative element 100, the zones 101 and 102 have a common part 103 where the studs are provided, on the one hand mass 101b and 102b and, on the other hand, the single supply pad 103a.

Note that such an antenna could have only one ground pad instead of two.

In the document mentioned above, it is shown that such an antenna has the same characteristics as that which is shown in FIG. the.

It has also been shown that for such an antenna, the locations of the supply pad and of the ground pad (s) are relatively indifferent on its operation. What is not, however, is the distance which separates the supply pad from the ground pad (s) and which is decisive in the value of the antenna impedance at each resonant frequency.

It will be noted that different forms can be envisaged for the radiative element 100 as well as for the slot 200 without for this to radically alter its operation. For example, the radiative element 100 could be circular, oval, even ovoid, etc. and the slot 200 could be simply straight, or curved, or the like.

Such an antenna poses the problem of tuning it to each of the resonant frequencies because it is the position of the slot 200 in the radiative element 10, the lengths of branches which constitute this slot 200 as well as its width which determine its resonant frequencies. . We therefore sought to improve this type of antenna so as to facilitate its tuning.

An antenna according to the invention is therefore a PIFA type multi-frequency antenna comprising a radiative element placed at a distance from a ground plane, said radiative element comprising at least one connection to said ground plane and a feed point and being provided with at least one slot, one end of which is on an edge of said radiative element, the other end of which is inside said radiative element and the shape of which is such that it delimits on said radiative element a convex region , said antenna then being the seat of several resonance frequencies. To solve the problem mentioned above, it is characterized in that said or each slot comprises at least one protuberance.

In a first embodiment of the invention, said or each slot comprises at its end which is inside said radiating element, a protrusion of dimension greater than the width of said slot. Advantageously, said protuberance has an edge which is substantially parallel to the edge closest to said radiative element.

An antenna according to the invention can also be as defined above but of the same type, the radiating element of which is of substantially rectangular shape, said or at least one slot comprising, on the one hand, a short branch which is substantially perpendicular to an edge of the radiating element and one end of which is on said edge and, on the other hand, a longer branch which is substantially parallel to said edge of the radiating element and which is connected to the other end of the part short.

It is then characterized in that said slot comprises at its end which is located inside said radiative element, a protuberance of which one edge is substantially parallel to the edge of the radiative element adjacent to the edge where the first end of said is located. slot.

Advantageously, said protuberance is of substantially rectangular, even square, shape. In a second embodiment of the invention, said or at least one slit comprises a protuberance in the form of a slit extending from the first slit in a zone complementary to said convex zone delimited by said slit . When said antenna is of said type of which said or at least one slot comprising, on the one hand, a short branch which is substantially perpendicular to an edge of the radiating element and one end of which is on said edge and, on the other hand , a longer branch which is substantially parallel to said edge of the radiating element and which connects to the other end of the short part, it is then characterized in that said slot comprises a protuberance in the form of a slot extending from the intersection between the short and long portions of the slot.

An antenna according to the invention is also of the type whose ground point is close to the through end of the slot on a part of said radiative element opposite with respect to the slot to said convex zone delimited by said slot, said point of power supply located at a distance from the ground point so as to adapt the impedance of said antenna.

The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which:

Figs. la and lb are perspective views of the PIFA type antenna according to the state of the art,

Figs. 2a to 2c are plan views of three embodiments of multifrequency PIFA type antennas according to the present invention, FIG. 3 is a graph showing the influence of the surface of a protuberance at the end of a slot of an antenna according to the present invention,

Fig. 4 is a graph showing the influence of a dimension of a protuberance at the end of a slot of an antenna according to the present invention,

Fig. 5 is a graph showing the influence of a dimension of a protuberance in the form of another slot extending from the slot of an antenna according to the present invention,

Fig. 6 is another embodiment of the present invention in which the radiative element is oval, even ovoid, and Fig. 7 is another embodiment of the present invention with multiple slots.

The antennas which are shown in Figs. 2a to 2c essentially consist of a radiative element 10 electrically conductive plane which is mounted parallel to a ground plane (not shown) also electrically conductive at a distance therefrom determined in particular as a function of the passband which is desired for each resonant frequency. A dielectric can be placed between the radiative element 10 and the ground plane.

The radiative element 10 is in the embodiment shown substantially rectangular. It is divided by means of a slot 20 consisting of an electrical insulator (here the absence of the conductive material constituting the radiative element 10). This slot 20 has a short part 20a which is substantially perpendicular to an edge 10a of the radiating element 10 and one end of which opens onto this edge 10a. It also has a longer part 20b which is substantially parallel to the edge 10a of the radiative element 10 and which is connected to the other end of the short part 20a by forming an elbow 20c.

The slot 20 delimits, on the radiative planar element 10, a zone 11 substantially circumscribed by the slit 20 and an edge 10a of the radiative element 10 and a zone 12 delimited by the three other edges 10b to 10d of the radiative element 10 and the slot 20. The zones 11 and 12 have a common zone 13.

In general, for proper functioning of an antenna according to the invention, the zone 11 must be a convex zone, the zone 12 being complementary to the zone 11.

The radiative element 10 is connected to the ground plane by a ground stud 32 located at a point on the radiative element 10 close to the through end of the slot 20 and opposite, relative to the slot 20, to the area convex 11 of the radiative element 10 circumscribed by the slot 20. It is also supplied by a supply pad 31 located at a point in zone 12 of the radiative element 10 relatively adjacent to the ground pad 32, also close to the corner of the radiating element 10 opposite the convex zone 11.

In this configuration of the ground pad 32 and the power pad, it has been possible to show that such an antenna is a dual-frequency antenna whose low frequency is essentially determined by the dimensions of the zones 11 and 12 while the high frequency is essentially determined by the dimensions of the single zone 11. In the first embodiment shown in FIG. 2a, the antenna shown has its slot 20 which comprises, at its end which is inside said radiating element 10, a protuberance 40 of dimension larger than the width of said slot. Thus, the zone 13 common to the two zones 11 and 12 is in a way pinched by the protuberance 40. It has been possible to obtain good results with various shapes for the protuberance 40, but the best results are obtained when the protuberance 40 has a shape with a side 40d parallel to the edge 10b closest to the radiative element 10. More particularly, a rectangular shape, even square, is advantageous because in particular relatively simple to produce. In the embodiment shown, this square is such that two of its sides 40a and 40b extend in the direction of the branch 20b, the other two 40c and 40d in a direction perpendicular to the branch 20b, but parallel to a edge 10b of the radiating element 10.

The object of this protuberance 40 is to lower the highest frequency as can be seen in FIG. 3. Without protuberance, the high frequency is approximately 1.15F _o where Fo is an arbitrary reference frequency while it is always lower in the presence of such protrusion 40.

We can also see in this Fig. 3 that the larger the area of this outgrowth, the more the decrease in frequency is. In Fig. 4, it can also be seen that the larger the dimension of the projection which is perpendicular to the slit, the greater the frequency reduction.

It has been observed that, in general, the greater the length of the zone 13 common to the two zones 11 and 12 delimited by the slot 20 and the smaller its thickness, the more important is the lowering of the single high frequency of the antenna. The dimension of this zone 13 which extends from the convex zone 11 to the complementary zone 12 is called "length of the common zone 13" and "thickness of the common zone 13" the dimension which extends between the edge 10b of the radiative element 10 and the protuberance 40. It is believed that the effect of this protuberance 40 is to modify, according to its shapes and dimensions, the value of the self that constitutes the common area 13 and thus to modify the high frequency antenna resonance.

In Fig. 2b, there is shown another embodiment of an antenna according to the invention. The slot 20 of the antenna, according to this embodiment, comprises a protuberance 50 in the form of a slit which extends from the first slit 20 inside the zone 12 delimited by the slit 20 and complementary to the convex zone 11.

In the illustrated embodiment, the slot 20 comprises, like the previous embodiment, a short part 20a, one end of which opens onto this edge 10a and a longer part 20b which is connected to the other end of the short part 20a by forming an elbow 20c.

In Fig. 2b, the protrusion 50 is therefore in the form of a slot which extends inside the complementary zone 12 from the elbow 20c formed at the intersection between the short part 20a and the long part 20b of slot 20.

In the exemplary embodiment shown in FIG. 2b, the slot 50 extends inside the zone 12 along the bisector of the angle formed by the short 20a and long 20b parts of the slot 20.

There is shown in FIG. 5 a curve showing the influence of the length of the projection slot 50 on the low resonance frequency of an antenna according to the embodiment of FIG. 2b. It is noted that the greater the length of this projection slot 20, the greater the decrease in the low frequency of the antenna.

Finally, there is shown in FIG. 2c, an embodiment of the invention which combines the protuberances 40 and 50 of the embodiments of FIGS. 2a and 2b respectively. Thus, it is possible to adjust the high and low resonance frequencies by modifying the dimensions of the protuberances 40 and 50 as just explained.

In Fig. 6, another embodiment of the present invention has been shown. In this embodiment, the radiative element 10 is ellipsoidal, the slot 20 is curved and extends from an edge 10a of the radiative element 10 towards the interior of said radiative element 10 so as to form a convex zone 11 and a complementary zone 12. The internal end of the slot 20 has a projection 40 ′ which is here circular. It can be seen that the common area 13 is in a way pinched by the projection 40 '. It will be understood that by playing on the extension length of this pinched common area 13 (for example by modifying the diameter of the circle forming the projection 40 ′ and on the thickness of this common area 13 (for example either by playing on the diameter of the circle forming the protrusion 40 ′ either by varying the position of the protrusion 40 ′ along the length of the slot 20) the high resonance frequency of the antenna can be adjusted.

The slot 20 also includes a slot 50 'which extends inside the complementary zone 12 and the length of which makes it possible to adjust the low resonance frequency of the antenna.

Note the positions of the ground point 32 and the feed point 31 of the antenna which are in the part of the complementary zone 12 opposite the convex zone 1 1. The feed point 31 is in the part the most distant from the convex zone 1 1 while the ground point 32 is located in the part of the zone 12 close to the through end of the slot 20.

As before, in this configuration of the ground pad 32 and the power pad, it has been possible to show that such an antenna is a dual-frequency antenna whose low frequency is essentially determined by the dimensions of the zones 11 and 12 while the high frequency is essentially determined by the ^'dimensions of the single area 11.

There is shown in FIG. 7 another embodiment of an antenna according to the invention. The radiative element 10 is rectangular (but it could also be, like the embodiment of Fig. 6, oval or other) and has two slots 20 'and 20 "which delimit on the radiative element 10 two convex zones 11 'and 11 "of different dimensions as well as three other zones 14, 15 and 16. Zone 14 is located between the two slots 20' and 20", zones 15 and 16 being the zones which respectively connect the zone 14 to the convex zones 11 'and 11 ". The power and ground points 31 and 32 are also shown. It can be seen that the ground point is close to the through ends of each of said slots 20 'and 20 "on a part 14 of said radiating element 10 opposite with respect to each slot 20' and 20" to the convex zones 11 ', 11 "respectively delimited by the slots 20 'and 20 ", said feed point 31 being located at a distance from the ground point 32 so as to adapt the impedance of said antenna.

Such an antenna has four resonant frequencies. The lowest frequency is mainly determined by the dimensions of zones 14, 15 and 11 ". The second resonant frequency is mainly determined by the dimensions of zones 14, 16 and 11 '. The third resonant frequency is mainly determined by the dimensions of the 11 "convex area and the fourth resonant frequency is mainly determined by the dimensions of the convex zone 11 '.

The slots 20 'and 20 "respectively have protrusions 40' and 50 ', on the one hand, and 40" and 50 ", on the other hand.

It will be understood that the protrusion 40 'makes it possible to adjust the highest resonant frequency, the protrusion 40 "makes it possible to adjust the third resonant frequency, the protrusion 50' makes it possible to adjust the second resonant frequency and that the 50 "protrusion allows the lowest resonant frequency to be adjusted.

Claims

1) PIFA type multi-frequency antenna comprising a radiative element (10) placed at a distance from a ground plane, said radiative element (10) comprising at least one connection to said ground plane (32) and a feed point (31) and being provided with at least one slot (20, 20 '), one end of which is on an edge (10a) of said radiative element (10), the other end of which is inside said radiative element (10) and whose shape is such that it delimits on said radiating element (10) a convex zone (11), said antenna then being the seat of several resonant frequencies, characterized in that said or at least one slot ( 20) comprises a protuberance (50) in the form of a slit extending from the first slit (20) in a zone complementary to said convex zone delimited by said slit (20).

2) Antenna according to claim 1, said antenna being of said type including said - or at least one slot (20) comprising, on the one hand, a short branch (20a) which is substantially perpendicular to an edge (10a) of the radiative element (10) and one end of which is on said edge (10a) and, on the other hand, a longer branch (20b) which is substantially parallel to said edge (10a) of the radiative element (10) and which connects to the other end of the short part (20a), characterized in that said slot (20) comprises a protrusion (50) in the form of a slot extending from the intersection between the short (20a) and long (20b) parts of the slot (20).

3) Antenna according to claim 1 or 2, characterized in that said or each slot (20, 20 ') comprises at its end which is inside said radiating element (10), a protuberance (40, 40') larger than the width of said slot (20).

4) Antenna according to claim 3, characterized in that said protuberance (40, 40 ') has an edge (40d, 40'd) which is substantially parallel to the nearest edge (10b) of said radiating element (10).

5) Antenna according to claim 1, said antenna being of said type whose radiating element (10) is of substantially rectangular shape, said or at least one slot (20) comprising, on the one hand, a short branch (20a) which is substantially perpendicular to an edge (10a) of the radiating element (10) and one end of which is on said edge (10a) and, on the other hand, a longer branch (20b) which is substantially parallel to said edge ( 10a) of the radiant element (10) and which is connected to the other end of the short part (20a), characterized in that said slot (20) comprises at its end which is inside said radiating element (10), a protrusion (40) including an edge (40d) is substantially parallel to the edge (10b) of the radiative element (10) adjacent to the edge (10a) where the first end of said slot (20) is located.

6) Antenna according to claim 5, characterized in that said protuberance (40) is of substantially rectangular shape, even square.

7) Antenna according to one of the preceding claims, characterized in that the ground point (32) is close to the through end of the slot (20) on a part of said radiating element (10) opposite with respect to the slot (20 ) to said convex zone (11) delimited by said slot (20), said feed point (31) being at a distance from the ground point (32) so as to adapt the impedance of said antenna.