FR2837339A1 - Portable telecommunications terminal has planar fractal antennas on outside with separation to allow spatial diversity processing - Google Patents

Abstract

A portable telecommunication terminal has planar fractal antennas (12) placed on an outside face (13) or in a recess in the casing (11) and with spacing (d) to allow spatial diversity processing. Includes Independent claims for the use of Von Koch monopoles and loops, Sierpinski dipoles and Cantor patches.

Description

realizes on numerical signals.

1 2837339

  The invention relates to the field of telecommunications and more particularly to portable terminals equipped with an antenna for remote communication. Currently, portable telecommunication terminals comprise a receiving device consisting of an antenna and an electronic device called "RF front end". Generally the reception device operates further in transmission; the term transmission is then used. Each portable terminal operates on a frequency band that is operating band or on several frequency bands each related to a telecommunication standard. Thus, a portable terminal intended to be compatible with the UMTS standard operates in the frequency band 1.92 GHz at 2.17 GHz. The increase in the number of users of portable terminals deteriorates the performance of telecommunication networks. Since the frequency band is a limited resource, each telecommunication operator aims to constantly improve the transmission gain to satisfy ever more users. For this purpose, the manufacturer of the portable terminal seeks in particular to increase the gain of the terminal antenna. This research must take into account the operating constraints of an antenna and the constraints of available space and volume

  available specific to the portable terminal.

  Any antenna is sized according to the operating band of the portable terminal. Thus, a wired antenna generally has a length determined simply by the wavelength of the center frequency of the frequency band. Although it may be telescopic or embedded in the outer shell of the portable terminal, the wire antenna often exceeds the outer dimensions of this box, which makes it fragile, and is the cause of asperities which hinder manipulations of the terminal. There are portable terminals which do not have a wire antenna but which have a planar antenna protected inside the box. Such an antenna is printed on a traditional motherboard of the Durod type

  or epoxy with low dielectric permittivity.

  In these conditions, the wind antenna size is limited by the available surface area on the motherboard, which also includes the electronic circuits of the

portable terminal.

2 2837339

  Also, the subject of the invention is a portable terminal which makes it possible to improve the gain of the antenna without increasing the size of the outer case while overcoming the disadvantages of the prior art. A terminal according to the invention is such that the antenna is

  planar and plate on an outer face of the case.

  According to a preferred embodiment, the antenna is protected by a film of

  passivation according to known techniques.

  Thus, the direct contact with the air makes it possible to avoid the effect of screen caused by the external box and to optimize consequently the gain of the antenna

for an identical occupied surface.

  To improve the protection of the antenna, a particular embodiment of a terminal according to the invention comprises a hollow cavity in the case and in

  which is the planar antenna.

  Tonjours according to a particular embodiment of a terminal according to the invention, the antenna is a fractal antenna. The term fractal designates a fracture object, of very irregular shape. The theory of fractals was introduced by mathematicians Gaston Julia and Pierre Fatou and developed by Benoit B. Mandelbrot in a work entitled "The fractal geometry of Nature", Freeman, 1983. Some fractal antennas, like a Sierpinsky dipole, allow multiband operation, due to a phenomenon of multiresonnances. Some fractal antennas such as a Von Koch monopoly, a Von Koch dip81e or a Von Koch loop have the peculiarity of being constituted by a series of folds of the metal which allow a reduction of the physical dimensions of the antenna for use equivalent in terms of electrical dimensions. These antennas have indeed electrical dimensions that differ from the physical dimensions. Because of the reduction in size of these antennas, it is possible, according to a particular embodiment of a terminal according to the invention, to have at least two fractal antennas on the housing to allow spatial diversity processing of the signals. Electromagnetic. Other features and advantages of the invention will appear in the

  following description of particular examples of embodiment of the invention. The description

  is made with reference to the attached figures given by way of non-limiting examples. Figure 1 is a schematic view of a planar antenna printed on a map

  mother arranged in a case of a portable terminal according to the prior art.

3 2837339

  Figure 2 is a partial schematic view of a portable terminal according to the invention. Figure 3 is a diagram of a particular embodiment of a terminal according to the invention. Figure 4 is a diagram of a rectangular patch antenna.

  Figure 5 is a diagram of a fractal antenna quotes Cantor patch.

  Figure 6 is a diagram of a fractal antenna quoted from Sierpinski dip81e.

  Figure 7 is a diagram of a fractal antenna quoted monopone Von Koch.

  Figure 8 is a diagram of a fractal antenna quoted monop81e of Von Koch

  obtained by successive iterations from a single monopole.

  FIG. 9 is a representation obtained by simulation of the wave rate

  stationary of an example of Von Koch's monop81e fits on the UMTS band.

  FIG. 10 is a representation obtained by simulation of the gain of an example of

  Von Koch's monop81e depending on the frequency on the UMTS band.

  FIG. 11 is a representation obtained by simulation of the radiation pattern of an example of a Von Koch monop81e at the center frequency of 2.045

GHz of the UMTS band.

  FIG. 12 is a representation obtained by simulation of the gains obtained for two Von Koch monopoles of totally identical characteristics, one printed on a motherboard inside a case of a first mobile terminal and the other printed on a plate substrate on an external face of the boltier of a second terminal

  mobile identical to the first terminal.

  Figure 13 is a diagram of a fractal antenna cited Von Koch loop.

  FIG. 14 is a diagram of a portable terminal of the PDA type according to the invention.

  Figure 1 is a schematic view of a planar antenna available within the

  boltier of a portable terminal according to the prior art.

  Antenna 1 is a folded version of a monop81th quarter wave. Wile is printed on the motherboard 2 of the terminal and is powered through a power point 3. This provision has the disadvantage of imposing strong constraints on the development of the motherboard to take into account the dimensions of the antenna, the required clearance area and the dielectric constant stress imposed on the substrate supporting the antenna. Although this arrangement has the advantage of securing the antenna by protecting it by the boltier, in return the boltier is screened a

  the antenna and disturbs the radiation pattern.

4 2837339

  Figure 2 is a partial schematic view of a portable terminal according to the invention. In the context of the invention, a portable terminal also designates a mobile phone, a personal assistant or PDA, abbreviation of the Anglo-Saxon terms Personal Digital Assistant, a portable micro-computer. A portable terminal covers any portable device equipped with telecommunication means that allow a

  user to establish a remote communication.

  The portable terminal 10 comprises an external box 11 and a planar antenna 12 plate on a 13 of the outer faces of the box 11. This arrangement advantageously allows to remove all the constraints imposed on the printed circuit inside the box. The planar antenna 12 is printed on a specific printed circuit 14; the latter can therefore be manufactured much more easily than the motherboard according to the prior art illustrated in Figure 1. The planar antenna is mounted on an outer face 13 according to well known techniques and implemented during the manufacture of smart cards. According to a particular embodiment of the terminal illustrated in FIG. 3, the housing 11 comprises a recess 15 in which the transfer of the printed circuit 14 on which the antenna is printed is carried out.

  12 and this in a similar way to the postponement of a chip on a smart card.

  Still according to known techniques for the manufacture of smart cards, the planar antenna can undergo a so-called passivation treatment that allows to protect it

  vis-à-vis some external aggression.

  The planar antenna can be made in different forms, examples of which

given below.

  Figure 4 is a diagram of a rectangular patch antenna 12. The antenna 12 is printed on a printed circuit 14 comprising a substrate 16 and a metallized lower face 17 serving as a ground plane. The supply of the antenna 12 is performed by means of a feed point 18. The dimensions of the antenna 12 wind of the order of kg / 2 with vg the length in the substrate 16. In the UMTS frequency band, the dimensions of the patch antenna wind of the order of a few centimeters depending on the type of substrate used. Thus, for a substrate having a dielectric constant Er between two and four, the rectangular patch antenna occupies a

  surface varying between 28 and 14 cm2 at the frequency of resonance correspond to kg.

2837339

  Figure 5 is a diagram of a fractal antenna quotes Cantor patch.

  The size of Cantor 's 1 1 patch antenna is identical or almost identical to

  the size of the equivalent patch antenna shown in FIG. 4.

  Figure 6 is a diagram of a fractal antenna 12 quoted from Sierpinski dip81e. The size of this antenna 12 is identical or almost identical to the size of the equivalent patch antenna shown in FIG. 4. This antenna, like Cantor's patch antenna, has the advantage of making it possible to obtain a multiband antenna.

  multiresonance thanks to the property of auto similarity which is found in its form.

  This property appears through the change of scale of the basic pattern which constitutes the whole of the printed antenna; the basic pattern is a triangle in the case of dip81e

from Sierpinski.

  Figure 7 is a diagram of a fractal antenna 12 cited monopole of von Koch. Such an antenna 12 can be deduced from a simple single monopole antenna 19 by applying to it a number of iterations as illustrated in FIG. 8. This antenna 12 derived from a simple monopole 19 at the end of two iterations has a bulk. lower than the single monop81e. This reduction is induced by the following folds of the metal which allow a reduction of the physical dimensions for an equivalent use in terms of electrical dimensions. For example, in the UMTS frequency band, the Von Koch monop81 having a fractal dimension of 1.128 occupies a surface area of 1.75 cm 2. Taking into account a reflector plane having dimensions equivalent to those of a mobile terminal of the PDA type, this monop81e has for radiation characteristics: standing wave ratio <2 in the UMTS band - reflection coefficient at the central frequency - lSdB - maximum gain 2, 6dB (relative to an equivalent isotropic antenna) These characteristics are illustrated by figures 9, 10, and 11 which respectively represent the stationary wave rate of the monop81e adapted on the UMTS band, the gain of the monop81e as a function of the frequency on the UMTS band and the monop81e radiation pattern (field E amplitude) at the center frequency of 2.045

GHz of the UMTS band.

6 2837339

  FIG. 12 is a comparison of the gains obtained for two Von Koch monopoles of totally identical characteristics, fun printed on a motherboard inside a case of a first mobile terminal and the other printed on a substrate plate on an outer face of the case of a second mobile terminal identical to the first terminal. On the UMTS band, the gain of the monop81e plate on an outside of the case is better than the gain of the monop81e prints on a motherboard has

inside the case.

  FIGS. 9, 10, 11 and 12 wind from a simulation carried out with the simulation program having as reference IE3D from the designer Zeland Software

1 0 Inc.

  Figure 13 is a diagram of a fractal antenna 12 cited Von Koch loop.

  Like Von Koch's monop81e, the loop allows a reduction in physical dimensions. Von Koch's monop81e makes it possible, just like Von Koch's dip81e, to have several identical antennas on the same portable terminal to obtain a multi-sensor transmission device. This multi-sensor device makes it possible to perform

  then a spatial diversity treatment of the electromagnetic signals.

  FIG. 14 is a diagram of a PDA-type portable terminal according to the invention which comprises two identical fractal antennas 12, 122 on an outer face of the box 11; for example, these antennas 12, 122 are Von Koch's monopoles. In order to allow spatial diversity processing of the electromagnetic signals received by each of the antennas, the distance d between these antennas is such that d> / 2, with the wavelength of the central frequency of the frequency band of operation, and each antenna is connected to its own device

  electronic reception via a point 18, 182 supply.

7 2837339

Claims (11)

  1. A portable telecommunication terminal (10) comprising at least one external housing (11) and a first antenna (12, 12), characterized in that: - the first antenna (12, 12) is planar and plate on one face ( 13) outside   box (11) to be in direct contact with air.   2. Terminal (10) portable telecommunications according to claim 1, wherein the housing (11) comprises a recess (15) whose bottom corresponds to the face (13) outside.   3. Portable telecommunication terminal (10) according to one of claims 1 and 2,   comprising at least a second antenna (122) identical to the first antenna (12), each of the antennas (12, 122) being slotted on an outer face (13) of the housing and positioned at a distance (d) of each antenna (12). , 122) to allow spatial diversity processing of the electromagnetic signals received by each of the antennas (12, 122), said determined distance being at least greater than λ / 2, with wavelength of the center frequency of a band   frequency of operation of the mobile terminal.   4. Portable telecommunication terminal (10) according to one of claims 1 to 3,   wherein each antenna (12, 12, 122) is a fractal antenna.   Portable telecommunication terminal (10) according to claim 4, wherein   each antenna (12, 12, 122) fractal is a monop81e of von Koch.   Portable telecommunication terminal (10) according to claim 4, wherein   each fractal antenna (12, 12, 122) is a von Koch loop.   The portable telecommunication terminal (10) according to claim 4, wherein   each fractal antenna (12, 12, 122) is a Sierpinski dipole.   Portable telecommunication terminal (10) according to claim 4, wherein   each fractal antenna (12, 12, 122) is a Cantor patch antenna. 8 2837339   9. Portable telecommunication terminal (10) according to one of claims 1 to 8, consist of a mobile phone.   10. Portable telecommunication terminal (10) according to one of claims 1 to 8,   consist of a personal assistant.   Portable telecommunication terminal (10) according to one of claims 1 to 8,