WO2015082287A1 - Antenna system to be mounted on or above an object while protecting said object from the rays of said antennas - Google Patents

Abstract

The present invention relates to an antenna system to be mounted on or above an object while protecting said object from the rays of said antennas. According to the present invention, said antenna system consists of at least one group (21, 22; 100) of at least two antennas. The antennas (221, 222, 223; 111, 112, 113) are positioned relative to one another such that the emitting lobes thereof, which face space E, where said object is located, overlap one another. Said antennas are supplied with power such that the electromagnetic fields, respectively emitted in said emitting lobes which face space E, interfere with one another such that the power from the electromagnetic field resulting from said interferences is reduced in said space E in comparison to what the power would be without any interference.

Description

 Antenna system for mounting on or above an object while shielding said object from radiation from said antennas

The present invention relates to an antenna system for mounting on or above an object while protecting said object from radiation from said antennas.

 The present invention finds application whenever antennas are required to transmit signals and that these antennas, due to either constraints due to the particular use envisaged, or implementation constraints of the devices on which they are mounted, are mounted on or above an object which must also be protected from electromagnetic fields emitted by said antennas.

 In the present description, the term "object" is taken in its broadest sense and therefore relates to any material object, living, etc.

Thus, the object in question may be a device, for example rolling, flying or flying, which comprises, on the one hand, telecommunication means for transmitting signals by means of one or more antennas and secondly , circuits, for example, electronic, which are also sensitive to electromagnetic fields and which must be protected from those emitted by said antennas.

 The object, in the sense given here in the present description, can also be a living being, such as a human. Thus, in certain trades where the people act more than one in a field of operation, it is often necessary for them to communicate with one another or with a centralized operator to transmit information, data, images, etc. This is for example the case for firefighters, people engaged in rescue operations following natural disasters, earthquakes, or military personnel in operation.

 To do this, it is known to provide each person concerned with a transmitter / receiver connected to an antenna system that carries said person to transmit and receive RF radio signals vector vectors information, data, images, etc.. transmitting. This antenna system consists of a plurality of antennas, for example themselves constituted by radiating elements shaped to the body of the person. These radiating elements can be integrated into the clothing of the person, for example by being printed there. They can also be simple elements in a flexible material, placed and fixed for example by gluing, sewing, etc. on the garment worn by the person. By multiplying these radiating elements, the shadow zones, that is to say the zones of non-reception or non-emission, are avoided because, at least one of the radiating elements can ensure communication. In addition, by positioning them so that their radiation lobes overlap each other, the quality of remission / reception remains correct even if one or more radiating elements are in shadows.

 Reference can be made to patent document WO2011 / 095796 which describes such an antenna system for persons provided with a transmitter / receiver.

 In the applications thus envisaged of the invention, it is necessary to control the spatial distribution of the electromagnetic field radiated by the antenna or antennas used, in particular to respect minimum radio frequency field emission levels, such as an absorption rate. specific, SAR, (Specifies Absorption Rate, SAR) or an EMC (Electromagnetic Field) level imposed by the standards in force.

Two solutions are then generally considered for this purpose. The first is to position the antenna or antennas far enough from the object to maintain a level of non-damaging absorbed energy. Nevertheless, this translates into very bulky structures and a lack of penalizing ergonomics.

 A second approach is to provide protection of the object generally in the form of a metal plane, high impedance surface or layers of absorbent materials. This solution results in a complexity of implementation and also a lack of ergonomics.

 The object of the present invention is to provide an antenna system that solves the problems mentioned above.

 To do this, the present invention relates to an antenna system intended to be mounted on or above an object while protecting said object from the radiation of said antennas. It is characterized in that it consists of at least one group of at least two antennas, the antennas being positioned relative to one another so that their emission lobes turned towards the space where find said object overlap, said antennas being energized so that the electromagnetic fields respectively emitted in said emission lobes facing said space interfere with each other and so that the electromagnetic field energy resulting from these interferences is reduced in said space compared to what it would be without interference.

 According to an advantageous characteristic of the present invention, said antennas of an antenna group are flat but non-coplanar.

 According to another advantageous characteristic, in the context of an application in which said system is intended to be worn by a man constituting said object, an antenna group consists of at least two antennas, one of which is said to be intended to be positioned near the chest of said man, a scapula said to be positioned near a scapula of said man and said end to be positioned near the upper arm of said man.

 According to another advantageous characteristic, said or each group of antennas is printed on a substrate consisting of a fabric, a knit, a nonwoven or a film constituting a garment intended to be worn by said man.

According to another advantageous characteristic, it comprises several groups of antennas supplied with RF signals via a power divider. According to another advantageous characteristic, at least one group of antennas is fed via a phase shifter controlled by a control signal so that the phase of the supply signal of said group of antennas is continuously variable in time.

 According to another advantageous characteristic, several groups of antennas are supplied with RF signals via a switch controlled by a control signal in order to select said groups of antennas consecutively one after another.

 According to another advantageous characteristic, each group of antennas comprises a power divider arranged to receive the RF signal and feed each antenna of said group of antennas.

 According to another advantageous characteristic, said or each group of antennas is printed on a flexible substrate, possibly including said power divider. Said flexible substrate is for example made of a fabric, a knit, a nonwoven or a film. This substrate may be constitutive of a garment intended to be worn by a man.

 According to another advantageous characteristic, said antennas are of the monopole type in planar configuration, or of the dipole type.

 The characteristics mentioned above, as well as others, will emerge more clearly on reading the following description of exemplary embodiments, said description being given in relation to the attached drawings, among which:

 Fig. 1 is a top view of a man carrying an antenna system according to a particular embodiment of the invention,

 Fig. 2 is a view of an antenna group of an antenna system according to the invention as shown in FIG. 1

 Fig. 3 is a view of a group of antennas according to the present invention which is above a transceiver and an electronic apparatus,

 Fig. 4 is a view of a group of three antennas illustrating the general principle of the present invention,

 Fig. 5 is a block diagram of an antenna supply circuit of an antenna group of an antenna system according to the present invention,

 Figs. 6a to 6c are block diagrams of antenna group feed circuits according to various embodiments of the present invention,

Fig. 7 is a view of a monopole type antenna according to a first embodiment of an antenna system according to the present invention, Fig. 8 is a diagram showing the reflection coefficient SU in dB as a function of the frequency between 1 and 3 GHz of an antenna system according to the invention, in the configuration of FIGS. 1 to 3 above,

 Fig. 9 is a radiation diagram of an antenna of an antenna system according to the invention, in the configuration of FIGS. 1 to 3 above,

 Fig. 10 is a view of a dipole elementary antenna according to a second embodiment of an antenna system according to the present invention, and

 Fig. 11 shows an exemplary embodiment of an antenna group according to the present invention.

 An antenna system according to the present invention consists of at least one group of antennas which, because of its use, is intended to be placed on or above an object which must also be protected from electromagnetic fields. These electromagnetic fields which are respectively radiated by these antennas interfere with each other, creating field minima in particular places. The principle of the present invention is to control these places, on the one hand, by the relative positioning of each antenna of the or each group relative to the others of said group and, on the other hand, by the power supply of each antenna relatively in phase and amplitude compared to others. This control is carried out so that the minimum or minimum electromagnetic field are located where the object to be protected is located.

 The control of the position of these electromagnetic field minima is done, for example once and for all, by optimization by means of electromagnetic simulation tools, taking into account the couplings between antennas. This optimization process makes it possible to find the relative position of the antennas considered and the phase and amplitude of supply of each antenna relative to the other antennas and this, according to the desired positions of the minima.

 We will now describe in relation to FIGS. 1 and 2 a particular embodiment of the present invention, in an application where the antenna system in question is worn by a man.

 Fig. 1 represents a man 10 seen from above with his shoulders 11 and 12 and his head 13. On the shoulder 11, is a first group of antennas 21 and, on the shoulder 12, is a second group of antennas 22.

In FIG. 2, we find the shoulder 12 and antennas 221 to 223, forming the group of antennas 22. This group of antennas 22 is composed of three antennas, one 223 said chest positioned near the chest of said man, another said scapula 221 positioned near a scapula of said man, another end said 222 positioned near the upper arm of said man. Each antenna 221, 222, 223 is placed near the shoulder 12 at a distance x from the body such that its performance is correct (too close to the body, the antennas could be detuned and thus be disturbed in their operation). The distance between the end antenna 222 at the end of the shoulder and an axis passing through the two other antennas 221 and 223 is necessarily greater than the distance x. The distance between the chest antenna 223 and the scapula antenna 221 is D.

 Note that the antennas 221, 222 and 223 are not coplanar and they provide between them a space inside which is the object to be protected, in this case the shoulder of the man 10.

 According to the invention, the antennas 221, 222, 223 of the or each group of antennas 21, 22 are geometrically positioned relative to each other and relative to the body of said man and / or are energized staggered in phase and / or in amplitude with respect to each other so that the electromagnetic fields respectively emitted by said antennas interfere with one another so that the energy of the electromagnetic field resulting from these interferences is reduced in the region where the body of the human is located. compared to what it would be without interference.

 For example, chest antennas 223 and scapula 221 are phased with respect to each other while end antenna 222 is energized out of phase by an angle φ (whose value depends on the positioning of the end antenna 222 relative to the other two antennas of the same group) relative to the other antennas 221 and 223. The power amplitudes are for example identical for the three antennas.

 We will now describe in relation with FIG. 3 a particular embodiment of the present invention, in an application where the antenna system in question is above an electronic device.

Thus, in FIG. 3, there is shown a transmitter / receiver 100 to which is connected the antenna system 110 and an electronic device 120, which is for example sensitive to electromagnetic waves causing disturbances in its operation. An example could be a 2GHz radio transceiver and a Global Positioning System (GPS) on a frequency of 1.7 GHz, one and the other placed on the same device, for example a robot.

 The antenna system 110 is here constituted of a single group comprising an antenna 111, on the left side inclined with respect to the vertical, a horizontal antenna 112 just above the electronic apparatus 120 and an antenna on the side right also inclined to the vertical.

 It will be noted that the antennas 111, 112 and 113 are not coplanar and that they provide between them a space inside which is the object to be protected, in the electronic device 120.

 According to the invention, the antennas 111, 112, 113 are positioned geometrically with respect to each other and with respect to the object to be protected, here the electronic device 120, and / or are supplied shifted in phase and / or in amplitude relative to each other so that the electromagnetic fields respectively emitted by said antennas interfere with one another so that the energy of the electromagnetic field resulting from these interferences is reduced in the region where said object is located; that is, the electronic apparatus 120 compared to what it would be without interference.

 For example, the left and right antennas 111 are fed in phase with respect to each other while the horizontal antenna 112 is powered out of phase by an angle φ (whose value depends on the positioning of the horizontal antenna 112 relative to the other two antennas 111 and 113) relative to the other antennas 11 1 and 113. The power amplitudes are for example identical for the three antennas.

In FIG. 4, there is shown a group of 3 antennas 201, 202 and 203 non-coplanar. They form between them a space E within which the amplitude of the electromagnetic fields radiated by the antennas 201 to 203 is controlled. Each of these antennas 201, 202 and 203 radiates by its front face 2010, 2020, 2030 (face opposite to that which is turned towards the space E) but also by its back side 2011, 2021, 2031 (the one which is turned towards space E). The emission lobes 2012, 2022 and 2032 are represented by their respective front faces and the emission lobes 2013, 2023 and 2033 by their respective rear faces. It can be seen that, since the antennas 201 to 203 are not coplanar, the electromagnetic waves respectively emitted by the antennas 201 to 203 by their rear faces 2011, 2021 and 2031 interfere with each other in the zone E, so that the field energy electromagnetic resulting from these interferences is reduced in the space E, according to the relative position of the antennas and according to their respective power supplies shifted in phase and / or in amplitude relative to each other.

 In FIG. 5, there is shown the antenna supply circuit of an antenna group (here, for example, three antennas 201, 202 and 203. These antennas could respectively correspond to a chest antenna 223, a scapula antenna 221 and an end antenna 222, as in Fig. 2 or an inclined left antenna 111, a horizontal antenna 112 and an inclined right antenna 113). This circuit comprises a power divider 50 which receives the radio frequency signal RF on its input and which delivers it on its outputs (three in number here) to respective supply lines 51, 52 and 53. These lines 51 to 53 are provided respectively to feed the antennas 201 to 203 with respective phases which depend essentially on the respective lengths of these lines 51 to 53.

 If the number of antennas of the group considered was n, the number of outputs of the power divider 50 and the number of supply lines 51 to 5n would also be n.

 With respect to the power supply of each group of antennas (for example each group of antennas 21, 22 of Fig. 1), it can be performed in parallel. This is illustrated in FIG. 6a where it is seen that the RF radio frequency signal is supplied to the input of a power divider 5 which delivers it to lines 3 and 4 of respective power supply antenna groups 1 and 2 (which could respectively correspond to the antenna groups 21 and 22 of Fig. 1). For example, feed lines 3 and 4 consist of RF cables (such as coaxial cables).

 Depending on the characteristics of the power divider 5 and lines 3 and 4, the amplitudes and phases of the signals supplied to the antenna groups may be different or identical.

 In FIG. 6b, the power supply of each group of antennas is also performed in parallel as in FIG. 6a, but in the circuit of the supply line 4 is mounted a phase shifter 6 provided to introduce the RF signal passing through a phase shift of a variable angle according to a control signal 7 applied to another of its entries. For example, the control signal 7 varies continuously and rapidly over time.

In FIG. 6c, the power supply of each group of antennas is performed in a switched manner. To do this, the power divider 5 of the embodiments of the Figs. 6a and 6b is replaced by a switch 8 which has a control input for a control signal 9 for selecting the antenna group that will receive the RF signal. The antenna groups 1 and 2 are thus selected consecutively one after another.

 If the number of antenna groups considered is p, the number of outputs of the power divider 5 and the number of supply lines 1 to p would also be p.

 The present invention operates with any type of antenna, including monopole antennas, dipole antennas, patch antennas, etc.

 It is shown in FIG. 7 a first embodiment of an elementary antenna 30 used for each antenna of each group. It is of the monopole type in planar configuration. It comprises two planes of mass 31 and 32, of rectangular shape, and a radiating strand 33, part of which is framed by each of the two ground planes 31 and 32 and another part protrudes beyond the ground planes 31 and 32 on a length L. Such an antenna is for example made on a flexible substrate, or on a fabric, a knit, a nonwoven or a film, for example constituting a garment intended to be worn by said man.

 In one embodiment of the invention which is entirely satisfactory, a flexible polyimide substrate has been used. Its dielectric permittivity is 3.6 and the loss coefficient δ is given by tan (δ) = 0.009. For a radiation frequency of the order of 2.06 GHz, the dimensions of the various elements of the antenna are as follows:

 - small side of the rectangle of each ground plane 31, 32 = c = 25 mm,

 - large side of the rectangle of each ground plane 31, 32 = C = 28.29 mm, - length of the portion of the strand 33 projecting above the ground planes 31, 32 = L = 31, 79 mm,

 - width of the strand 33 = w = 3.2 mm,

 the width of the space between the strand 33 and each ground plane 31, 32 = g = 115 μΏΐ,

 thickness of the conductive layers between 1 and 10 μιη.

With such an antenna, an antenna system such as that which is the subject of FIGS. 1 and 2, that is to say an antenna system consisting of two groups of three antennas. More precisely, the distance between each antenna 221, 222 and 223 and the body is 2 cm, the spacing between the two breast antennas 223 and scapula 221 is D = 14.5 cm, the distance between the end antenna 222 and a line passes between the other two antennas 221 and 223 is d = 3.6 cm.

 The chest antennas 223 and scapula 221 are phase-powered while the end antenna 222 is supplied out of phase by an angle φ = 210 ° relative to the other antennas 221 and 223.

 For such an antenna system, simulations were performed to determine the SAR rate and the following results were obtained.

 For a group of antennas powered at a time, the DAS flow rate located on 10g of tissue for a peak electromagnetic power injected of 1 Watt = 1.24 W / kg. This is much lower than the maximum allowed value, 2W / kg.

 The average SAR rate for the same 1 Watt injected electromagnetic power is 0.022 W / kg, which is well below the allowed value of 0.08 W / kg.

 For two groups of antennas fed simultaneously, the DAS flow rate located on 10g of tissue for electromagnetic power injected 1 Watt is 0.62 W / kg. This is much lower than the maximum allowed value, 2W / kg. The average SAR rate for the same injected electromagnetic power of 1 Watt is also 0.022 W / kg much lower than the allowed value which is 0.08 W / kg.

 The diagram of FIG. 8 shows the reflection coefficient SU in dB as a function of the frequency between 1 and 3 GHz. As to FIG. 9, it shows the radiation pattern both in the azimuthal plane (black line) and in the site plan (double black line).

 It is shown in FIG. 10, a dipole antenna 40 which can be used as an elementary antenna of a group of antennas according to the invention. This antenna 40 is for example made in micro-planar or co-planar technology. It is the object of a double-sided printed circuit: in thin lines in FIG. 10, the printed circuit on the rear face and in strong lines, the printed circuit on the front face.

On the rear face, the antenna 40 consists of two radiating strands 41 and 42 respectively connected via coupling lines 43 and 44 to a ground plane 45. On the front face, it consists of a power supply line U-shaped main 46, with a strand 47 just above the feed line 43 and a strand 48 just above the feed line 44. The feeding of the radiating strands 41 and 42 is by coupling between the main supply line 46 and the coupling lines 43 and 44. The antenna 40 is supplied at the end of the main power supply line 46 at point 49.

 By way of example, it is shown in FIG. 11, a group of antennas made on the same circuit board 400 double-sided. This group of antennas consists of three antennas 401, 402 and 403 which are of the dipole type identical to that of FIG. 6. The feed point 491, 492 and 493 of each antenna is connected to a common supply point 495 via a line 101, 102, 103. Similarly, each ground plane 451, 452, 453 is connected to a common ground plane 455 via a ground line 201, 202, 203. The common supply point 495 and the common ground plane 455 constitute the power divider of the considered antenna group. It is powered by lines 410 and 420.

Claims

An antenna system for mounting on or above an object while shielding said object from radiation from said antennas, said antenna system consisting of at least one group (21, 22; at least two antennas, characterized in that the antennas (221, 222, 223; 111, 112, 113) of each group are positioned relative to one another so that their transmitting lobes facing the space E where said object overlaps and in that each group of said antenna system comprises a power supply circuit (5, 50, 8) provided for supplying phase shifted and / or amplitude shifted said antennas of said group relative to the others so that, on the one hand, the electromagnetic fields respectively emitted in said emission lobes facing said space E interfere with each other and, on the other hand, that the energy of the electromagnetic field resulting of these interferences is diminished in said space E compared to what it would be without interference. 2) Antenna system according to claim 1, characterized in that said antennas of an antenna group are flat but non-coplanar. 3) Antenna system according to claim 1 or 2, said system being intended to be worn by a man constituting said object, characterized in that a group of antennas (21, 22) consists of at least three antennas (221, 222, 223): one (223) said breast intended to be positioned near the chest of said man, another (221) said scapula intended to be positioned near a scapula of said man , another (222) said end intended to be positioned near the upper arm of said man. 4) Antenna system according to claim 3, characterized in that said or each group of antennas is printed on a substrate consisting of a fabric, a knit, a nonwoven or a constituent film a garment intended to be worn by said man. 5) Antenna system according to one of the preceding claims, characterized in that it comprises several groups of antennas (21, 22) supplied with RF signals via a power divider (5). 6) Antenna system according to claim 5, characterized in that at least one group of antennas is supplied via a phase shifter (6) controlled by a control signal (7) so that the phase of the supply signal of said group of antennas is continuously variable in time. Antenna system according to one of claims 1 to 5, characterized in that a plurality of antenna groups (21, 22) are supplied with RF signals via a switch (8) controlled by a control signal (9) in order to selecting said antenna groups (21, 22) consecutively one after another. 8) Antenna system according to one of the preceding claims, characterized in that each group of antennas (21, 22, 1 10) comprises a power divider (50) provided for receiving the RF signal and supplying each antenna (201, 202, 203) of said antenna group (21, 22, 1 10). 9) Antenna system according to one of the preceding claims, characterized in that said or each group of antennas is printed on a flexible substrate, possibly including said power divider. Antenna system according to claim 9, characterized in that said flexible substrate is made of a fabric, a knit, a nonwoven or a film. 11) Antenna system according to claim 10, characterized in that said substrate is a garment intended to be worn by a man. 12) Antenna system according to one of the preceding claims, characterized in that said antennas are of the monopole type in planar configuration. 13) Antenna system according to one of claims 1 to 11, characterized in that said antennas are of the dipole type.