FR2718292A1 - Antenna for transmitting and / or receiving electromagnetic signals, in particular microwave frequencies, and device using such an antenna. - Google Patents

Abstract

The present invention relates to an antenna for transmitting and / or receiving electromagnetic signals, in particular microwave frequencies, of the inverted F type, comprising a main conductive element (110) generally parallel to a ground plane (152), a conductive element auxiliary (120) generally perpendicular to the main element (110) and to the ground plane (152) and which connects one end of the main element (110) to the ground plane (152), and a coaxial (130) d excitation connected to the main conductive element (110), characterized in that the main conductive element (110) comprises at least two strands (111, 112) generally parallel to each other, forming one (111) an element radiating, and the other (112) a resonator, wherein the resonator strand (112) includes at least one transition (113) along its length. The invention also relates to transmission and / or reception devices using such an antenna.

Description

The present invention relates to the field of transmissions

  electromagnetic waves, in particular microwave.

  The invention applies in particular to portable transmission / reception devices comprising an integrated antenna of reduced size. Many antennas have been proposed for this

  application to portable transmitting / receiving devices.

  Most often the antennas used for this purpose are of the type

inverted type F antenna.

  The structure and operation of such an inverted F type antenna is described in the document uSmall Antennas "by K. Fujimoto, A. Henderson, K. Hirasawa and J.R. James published by Research Studies Press LTD

and John Wiley & Sons INC.

  Such an inverted F type antenna is shown.

  schematically in Figure 1 attached.

  As can be seen in this FIG. 1, an antenna 10 in inverted F essentially comprises a main rectangular conducting element 11 parallel to a ground plane 20 and an auxiliary conducting element 12 perpendicular to the main element 11 and to the ground plane 20. The auxiliary element 12 provides a short-circuit function on the main element

  11, by connecting one of its ends to the ground plane 20.

  The second end of the main element 11 is

generally open.

  The microwave signal is conveyed by an excitation coaxial 13 which is connected to the main element 11 at a location referenced 14 in FIG. 1. The choice of this location 14

  on the main element 11 determines the impedance of the antenna.

  If the wavelength of the transmitted microwave signal is called k, the inverted F antenna 10 generally has the following dimensions: length L of the main element 11: X / 4, - width 1 of the main element 11 : k / 8, and

  - height h of the auxiliary element 12: k / 25.

  For frequencies of the order of 2 GHz, which can be used on portable mobile radio terminals, the dimensions of

  the antenna 10 are a few centimeters.

  These antennas 10 in inverted F have the advantage of having a quasi-omnidirectional radiation pattern. However, these reverse F antennas have a band

  relatively low bandwidth, typically of the order of 2 to 3%.

  We have already tried to improve the performance of these antennas

known in inverted F.

  Thus, it has been described in the French patent application filed on December 23, 1992 under No. 92 15813 an improvement to antennas in inverted F consisting in producing the main conductive element in the form of at least two strands generally parallel to each other. The bandwidth of the antennas obtained with such a

  improvement is around 8 to 10%.

  The present invention now aims to further improve the antennas of the inverted F type, in particular by improving the

bandwidth of these.

  This object is achieved in the context of the present invention by means of an antenna for transmitting and / or receiving electromagnetic signals, in particular microwave, of the type in inverted F comprising a main conducting element generally parallel to a ground plane, a auxiliary conductive element generally perpendicular to the main element and to the ground plane and which connects one end of the main element to the ground plane and an excitation coaxial connected to the main conductive element, characterized in that the main conductive element comprises at least two generally parallel strands between them, forming one radiating element and the other resonator, in which the strand forming

  resonator includes at least one transition along its length.

  According to another advantageous characteristic of the present invention, the transition is formed by at least one step or change in width made on an internal or external edge of the strand forming the resonator, or else a slit which opens onto the end.

of this strand.

  More specifically, according to a preferred embodiment of the invention, the transition is formed by a recess on the internal edge of the strand forming the resonator. The present invention also relates to devices for transmitting and / or receiving electromagnetic signals, in particular microwave frequencies, comprising at least one antenna of the aforementioned type. Other features, purposes and advantages of this

  invention will appear on reading the detailed description which will

  follow, and with reference to the appended drawings given by way of nonlimiting example and in which: - Figure 1 previously described represents a schematic perspective view of a conventional inverted F antenna, Figure 2 represents a schematic perspective view of an antenna according to the present invention placed on a metal case, - the appended FIG. 3 represents the curve of the Stationary Wave Ratio measured on an antenna according to the present invention, as a function of the excitation frequency, - the Figure 4 shows the Smith chart of an antenna according to the present invention, - Figure 5 shows a top view of an antenna according to a preferred embodiment of the present invention, and - Figures 6 to 12 represent 7 alternative embodiments of an antenna

according to the present invention.

  There is shown schematically in the appended FIG. 2, an antenna 100 according to the present invention, of the type in F inxersed,

  placed on a metal case 150.

  The housing 150 can be the subject of numerous modes of

  production. It is preferably a case of parallelepiped type.

  The box 50 preferably accommodates electronic cards ensuring the processing of the microwave signals received by the antenna 10 () and / or emitted by the latter. The antenna 100 is preferably placed outside the housing 150, facing one of the faces 152 of the latter. This face 152 serves as a ground plane. The antenna 100 can be placed on

any side of the case.

  In a manner known per se, and as described above with reference to FIG. 1, the antenna 100 essentially comprises a main conductive element 110 parallel to the ground plane 152, an auxiliary conductive element 120 generally perpendicular to the element

  main 110 and ground plane 152, and an excitation coaxial 130.

  The auxiliary element 120 connects one of the ends of the element

main 110 to ground plane 152.

  The coaxial 130 provides the link between the processing means

  placed in the housing 150 and the main element 110.

  More specifically, according to the invention, the main element 110 has the general shape of a U and thus comprises at least two strands 111, 112 generally parallel to each other, forming one radiating element and the other resonator. More precisely still, according to the invention, the strand 112 forming a resonator comprises at least one transition 113 along its length. The auxiliary element 120 advantageously has a rectangular outline. Its connection edge on the ground plane 152 is referenced 121 in FIG. 2. Its connection edge on the main element 110 is

  referenced 122 in the attached FIG. 2.

  Preferably, the two main elements 110 and auxiliary 120 of the antenna 100 are formed by cutting from a common metal sheet and folding 90 'around the edge 122. The connection of the auxiliary element 120 at the level of the edge 121 on the ground plane 152 is obtained

  using any suitable conventional means.

  Preferably, the overall dimensions of the main element 110, considered parallel to the edge 122, is equal to the overall dimensions of the auxiliary element 120. That is to say that the external edges, 1110 and 1120 respectively of the radiating strand 111 and of the resonator strand 112 preferably extend the edges respectively

  123 and 124 of the auxiliary element 120 orthogonal to the edges 121 and 122.

  The strand 111 forming a radiating element and the strand 112 forming a resonator are connected to a common core 114 of outline

  rectangular adjacent to edge 122.

  The strand 111 forming a radiating element preferably has a rectangular outline. That is, its internal edge 1111 is

  straight and parallel to the aforementioned outer edge 1110.

  On the other hand, as indicated previously, there is provided according to the invention, a transition along the length of the strand 112 forming a resonator. According to the preferred embodiment shown in FIG. 2 appended, this transition 113 is advantageously formed by a step on the longitudinal internal edge 1121 of the strand 112 forming a resonator. Thus, the strand 112 forming the resonator is in the form of two juxtaposed rectangles, respectively referenced 1122 and 1124 on the

Figure 2 attached.

  The rectangle 1122 is adjacent to the core 114. The second rectangle 1124 forms the free end of the strand 112 opposite this core 114. The first rectangle 1122 has a width, considered parallel to the edge 122, constant over its length, and greater than the width of the second

  rectangle 1124, also constant over its length.

  The transition between the two rectangles 1122 and 1124 forms the

dropout 113 above.

  According to the invention, the transition or offset 113 is formed

  at a distance from the auxiliary element 120 of the order of./6, by calling.

  the wavelength used. Furthermore, according to the invention, the depth of the step 113, that is to say the difference in width between the two elements 1122 and 1124 of the resonator strand 112 is of the order of 3 / 8th of the width of the base of this radiating element 112 considered at

  its junction point with the core 114.

  The inventor carried out tests on a system comprising a metal case (simulating a telephone handset) of dimensions x 55 x 20 mm and of an antenna of the type represented in the appended FIG. 2 corresponding to the following geometry, given opposite the figure (for a central frequency of the passband f = 1.9165GHz, or X = 0.156m): - length LI of the strand 111 forming a radiating element, counted from the auxiliary element 120: 36 mm, ie 0, 23k, - length L2 of the strand 112 forming a resonator, counted from the auxiliary element 120: 38 mm, i.e. 0.24X, - length L3 of the core 114: 4.5 mm, i.e. 0.03x, - distance L4 separating the recess 113 from the auxiliary element 120 24.5 mm, i.e. 0.16 k, - width 11 of the auxiliary element 120 and the main element 110 (distance separating the longitudinal edges 1110 and 1120): 20 mm , or 0.13X, - width 12 of the strand 111 forming a radiating element: 3.25 mm, or 0.02k, - width 13 of the strand for mant resonator 112, at its base: 8 mm, i.e. 0.05k, - width 14 of the strand 112 forming the resonator, at its free end: 5 mm, or 0.03K, - width 15 of the offset 113: 3 mm, i.e. 0 , 02K, distance 16 separating the two strands 111, 112: 8, 75 mm, i.e. 0.06K, distance L5 separating the point 132 of contact of the coaxial 130 on the radiating element 111, of the auxiliary element 120: 5 mm , or 0.03K, 2O - distance 17 separating this contact point 132 from the longitudinal external free edge 1110 of the strand forming a radiating element 111: 1.6 mm, or

0.01K ,.

  Furthermore, on the system tested, the height h of the auxiliary element 120 separating the main element 110 from the ground plane 152 formed

on the case 150 was 5 mm.

  The curve of the Stationary Wave Ratio or ROS measured on the above-mentioned antenna is shown in Figure 3 attached. By adopting as bandwidth of the antenna, the frequency band for which the ROS is less than 2, which corresponds to the definition generally accepted by specialists, the curve represented in FIG. 3 leads to a bandwidth of 1.787 GHz at 2.046 GHz, or about 15%. Thus, the presence of the step 113 on the resonator strand 112 makes it possible to significantly increase the bandwidth relative to the antennas in

Inverted F previously known.

  In FIG. 3, the markers 1, 2 and 3 correspond respectively to frequencies of 1.885 GHz, 2.025 GHz and 1.787 GHz, and

  ROS rate of 1.4349, 1.3201 and 1.9998 respectively.

  The corresponding Smith chart illustrated in FIG. 4 appended, is for which the markers 1, 2 and 3 correspond to the same frequencies as those indicated previously opposite the

  Figure 3 reveals a loop corresponding to the perfect adaptation range.

  The curve illustrated on the Smith chart in Figure 4 shows that this radiating element is not perfectly optimized. Better centering relative to the center of the Smith chart would further increase

performances.

  The free ends of the strands 111 and 112, opposite the auxiliary element 120, can be opened as shown in the attached FIG. 2, or else connected by a short circuit to the ground plane 152, at least for the 'one of these strands, or it can be provided to connect at least one of the ends of these two strands 111, 112 to the ground plane 152, via a capacitor, for example via

with adjustable capacity.

  Such an adjustable capacity provided on at least one of the ends of the strands 111 and 112 can be controlled for example by circuits placed in the housing 150 in order to modify the characteristics of the antenna. The antennas according to the present invention are particularly well suited to meet the functional and ergonomic constraints of portable mobile radio terminal stations capable of communicating with a fixed station, for example, a

  pylon, satellite or equivalent.

  The large bandwidth, of the order of 15%, obtained in the context of the invention makes it possible to use a single antenna operating in transmission and in reception, respectively on two bands of

separate frequency.

  Of course the present invention is not limited to the particular embodiment which has just been described but extends to any variant

conforms to his spirit.

  In particular, the present invention is not limited to the use of a main element 110 composed only of two strands 111, 112 but may extend to main elements 110 comprising a number of upper strands, generally parallel to each other , at least one being provided with a transition along its length. Furthermore, the present invention is not limited to the use of a transition of the step type on the strand forming a resonator element, but extends to the use of any type of transition equivalent to such a step, on the '' at least one strand of

the main element.

  FIG. 6 shows for example a first alternative embodiment according to which, the recess 113, while being formed on the internal edge 1121 and directed towards the free end of the resonator strand 112, as described above, substantially covers the

  half the width of this resonator strand 112.

  According to the second variant embodiment shown in FIG. 7, the recess 113, formed on the internal edge 1121 of the resonator strand 112, is directed towards the core 114 and not towards the free end of this strand 112. The part d end 1124 of the resonator strand 112 is of this

  is wider than the part 1122 adjacent to the core 114.

  According to the third alternative embodiment shown in FIG. 8, the recess 113 is formed on the outer edge 1120 of the strand

  resonator 112 and directed towards the free end thereof.

  According to the fourth embodiment shown in Figure 9, the recess 113 is formed on the outer edge 1120 of the strand

  resonator 112 and directed towards the core 114.

  According to the fifth alternative embodiment shown in FIG. 10, two recesses 1130, 1131 are provided, directed towards the free end of the resonator strand 112, respectively on the edge

  internal 1121 and on the external edge 1120 thereof.

  According to the sixth alternative embodiment shown in Figure 11, there are two recesses 1130, 1131 directed towards the core 114, respectively on the inner edge 1121 and on the outer edge 112) thereof. According to the seventh alternative embodiment shown in FIG. 12, the transition 113 is formed of a slot which opens, for example, onto the end of the resonator strand 112. The two branches 1132, 1134 located on each side of the slot 113 can be of identical lengths as shown in FIG. 12, or of different lengths. Of course, the transition can also be formed by a

combination of the aforementioned means.

Claims (24)

  1. Antenna for transmitting and / or receiving electromagnetic signals, in particular microwave, of the inverted F type, comprising a main conductive element (110) generally parallel to a ground plane (152), an auxiliary conductive element (120 ) generally perpendicular to the main element (110) and to the ground plane (152) and which connects one end of the main element (110) to the ground plane (152), and a coaxial excitation (130) connected the main conductive element (110), characterized in that the main conductive element (110) comprises at least two strands (111, 112) generally parallel to each other, forming one (111) a radiating element, and the other (112) a resonator, in which the strand (112) forming the resonator comprises at   minus a transition (113) along its length.   2. Antenna according to claim 1, characterized in that the transition is formed by a change in width (113) of the strand resonator (112).   3. Antenna according to one of claims 1 or 2, characterized   by the fact that the transition is formed of at least one step (113).   4. Antenna according to one of claims 3 there, characterized by   the fact that the transition (113) is formed of at least one step on   the internal longitudinal edge (1121) of the resonator strand (112).   5. Antenna according to one of claims 4 there, characterized by   the fact that the transition (113) is formed of at least one step on   the outer longitudinal edge (1120) of the resonator strand (112).   6. Antenna according to one of claims 1 to 5, characterized   by the fact that the transition (113) is formed of two recesses (1130, 1131) produced respectively on the internal edge (1121) and on the edge   outer (1120) of the resonator strand (112).   7. Antenna according to one of claims 1 to 6, characterized   by the fact that the transition (113) comprises at least one step   (113) directed towards the free end of the resonator strand (112).   8. Antenna according to one of claims 1 to 6, characterized   by the fact that the transition (112) comprises at least one step   directed opposite the free end of the resonator strand (112).   9. Antenna according to one of claims 1 or 2, characterized   by the fact that the transition is formed of a slot (113). 10. Antenna according to claim 9, characterized in that   that the slot (113) opens onto the free end of the resonator strand (112).   11. Antenna according to one of claims 9 or 10, characterized   by the fact that the two branches (1132, 1134) located on each side of the slot (113) are the same length.   12. Antenna according to one of claims 9 or 10, characterized   by the fact that the two branches (1132, 1134) located on each side of the   slot (113) are of different lengths.   13. Antenna according to one of claims 1 to 12, characterized   by the fact that the resonator strand (112) has a width (13, 14),   respectively constant, on both sides of the transition (113).   14. Antenna according to one of claims 1 to 13, characterized   by the fact that the transition (113) delimits on the resonator strand (112) an end portion (1124) of width (14) narrower than the portion (1122)   of the same strand (112) connected to the auxiliary element (120).   15. Antenna according to one of claims 1 to 14, characterized   by the fact that the transition (113) delimits two rectangular portions   (1124, 1122) on the resonator strand (112).   16. Antenna according to one of claims 1 to 15, characterized   by the fact that the transition (113) is formed at a distance from the element auxiliary (120) of the order of./6.   17. Antenna according to one of claims I to 16, characterized   by the fact that the depth (15) of the step (113) forming the transition is of the order of 3 / 8th of the width (13) of the resonator strand (112) at its base.   18. Antenna according to one of claims 1 to 17, characterized   by the fact that the length (L2) of the resonator strand (112) is different from 4.   19. Antenna according to one of claims 1 to 18, characterized   by the fact that the radiating strand (111) and the resonating strand (112) have   free ends opposite the auxiliary element (12), in open circuit.   20. Antenna according to one of claims i to 18, characterized   by the fact that at least one of the radiating strand (111) or resonator (112) has its free end opposite the auxiliary element (120) connected to the plane of ground (152) by a short circuit.   21. Antenna according to one of claims 1 to 20, characterized   by the fact that at least one of the radiating strand (111) and of the resonator strand (112) has its free end opposite the auxiliary element (120) connected to the   ground plane (152) by a capacity.   22. Antenna according to claim 21, characterized in that that the capacity is adjustable.   23. Antenna according to one of claims 1 to 22, characterized   by the fact that it is produced from a common metal sheet, by cutting and folding at a connecting edge (122) between   the main element (110) and the auxiliary element (120).   24. Device for transmitting and / or receiving electromagnetic signals, in particular microwave signals, characterized in that it comprises at least one antenna conforming to one of the claims 1 to 23.