Abstract:
The present invention relates to a radiating device intended to receive and/or transmit electromagnetic signals comprising at least two antennas connected by slot and having a common slot. Connection means enable at least one antenna to be connected to processing means of electromagnetic signals. The connection means include two connection lines connected to the processing means. The two lines are terminated by an open circuit and are coupled electromagnetically to the common slot of the two antennas so as to enable a phase difference to be introduced between the electromagnetic signals of the two antennas when the connection is switched from one line to the other by means of a switching device present on the connection lines.

Description:
[0001]     The present invention relates to a radiating device intended to receive and/or emit electromagnetic signals comprising at least two means for receiving and/or transmitting electromagnetic signals of the slot connected antenna type and, more particularly, these antennas having a common slot and a connection means for connecting at least one of the said reception and/or transmission means to means for processing electromagnetic signals.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the field of “indoor” communications, wireless links are required to connect different devices in a house. For this, means for receiving and/or transmitting electromagnetic signals, or antennas, of the end-fire tapered slot type are used. Such antennas mainly constituted by a tapered slot realised on a metallic substrate are commonly called Vivaldi antennas or LTSA (Linear Tapered Slot Antenna). They can be integrated more easily into the devices because they radiate in the plane of the substrate. When several antennas of this type are used, for example in a network, the connection of the radiating device rapidly becomes complex.  
         [0003]     The dimensioning of a Vivaldi antenna is well-known by those in the profession. It can be divided into three parts shown in  FIG. 1 , which are the dimensioning of the antenna A 1  (Vivaldi profile), the dimensioning of the connection line  2  linked to a connection port P and the dimensioning of the line  2 /slot F 1  transition that enables the energy of line  2  to be transmitted to the antenna A 1 . To ensure the correct coupling of energy between the line  2  and the slot F 1 , it is necessary to obtain a position in specific geometrical conditions concerning the relative positions of the connection lines  2  and the slots F 1  of the antennas A 1 . An example is given, for example, in the document U.S. Pat. No. 6,246,377.  
         [0004]     There are two techniques for placing Vivaldi antennas A 1  and A 2  in a network. A first technique, shown in  FIG. 2 , involves connecting them in series by the same line  2 . The length of line between the two line  2 /slot F transitions determines the phase difference between the signals transmitted or received by two successive antennas A 1  and A 2 . By taking an odd multiple of line length of the guided half-wavelength under the connection line realized for example according to the microstrip line technique, namely L=nLm/2 (n=2k+1, with k an integer), the transmitted fields E 1  and E 2  are symmetrical with respect to the axis of symmetry of the two antennas A 1  and A 2 . For such a connection in series, the coupling to the antennas A 1  and A 2  is different from the point of view of the amplitude and the frequency phase difference. This is due to different line lengths between a connection port P and each of the antennas A 1  and A 2 .  
         [0005]     A second technique, shown in  FIG. 3 , consists of connecting them in parallel. The difference in length between L 1  and L 2  enables the phase difference between the transmitted fields E 1  and E 2  to be determined. By taking equal lengths, or such that |L 1 −L 2 |=n*Lm (where n is an integer), the transmitted fields E 1  and E 2  are as shown in  FIG. 3 . This connection technique gives a balanced connection but requires a more complex connection circuit. In particular, if the number of antennas increases, the dimensions of the connection network increase and its implementation sometimes requires the use of components. The cost of the structure consequently increases.  
         [0006]     One solution, presented in document EP 0,301,216, is to replace the two line/slot transitions by a single line  2 /slot FC transition by connecting the two slots together as shown in  FIG. 4 . There is therefore only a single line  2 /slot FC transition and the slot FC terminates in an antenna, A 1  and A 2 , at each of its two extremities. The coupled energy of the line  2  to the slot FC, is directed equally to the antennas A 1  and A 2 .  
         [0007]     However, such a radiating device has a fixed radiation pattern possessing, in particular, a null in the axis of symmetry of the antennas when the line  2  cuts the slot at an equal distance of A 1  and A 2 . Such characteristics can prove to be very damaging within the framework of applications that require great isotropy in the radiating device.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     The present invention proposes a radiating device presenting a radiation pattern that can be reconfigured dynamically with a simple connection.  
         [0009]     The present invention relates to a radiating device as described in the introduction section in which the connection means include two connection lines connected to processing means, the two lines terminated by an open circuit being coupled electromagnetically with the common slot of the two means of reception and/or transmission so as to enable a phase difference to be introduced between the electromagnetic signals of the two means of reception and/or transmission when the connection is switched from one line to the other using at least a switching device present on the connection lines.  
         [0010]     Indeed, the common connection allowed by two lines coupled to a slot common to two antennas enables the radiation pattern of the radiating device to be modulated by switching from one line to the other.  
         [0011]     According to one embodiment, the means of reception and/or transmission are grouped in pairs with a common slot, the connection of each pair being realised using two lines placed so as to cut the common slot at different distances from the axis of symmetry of the pair of means of reception and/or transmission so as to introduce a phase difference between the means of reception and/or transmission of the pair.  
         [0012]     In this case, one line is, for example, centred on the axis of symmetry of the antennas and the other is offset by a quarter of the wavelength. A phase difference of 180° is then introduced between the signals transmitted by the two antennas of the pair. Hence, the radiation pattern no longer has any null points in the axis.  
         [0013]     According to one embodiment, the pairs are grouped by groups of two pairs connected by the same two connection lines, a fixed phase difference having been introduced on one of the lines for the connection of one of the two pairs.  
         [0014]     This embodiment enables, for example, four antennas to be controlled with two lines. For example, the fixed phase difference is 180°.  
         [0015]     According to one embodiment, the means of reception and/or transmission are grouped in groups of N means of reception and/or transmission by connecting the N slots in a common slot having N branches, connection lines, isolated from each other, forming N′ branches centred on the common slot and arranged in an offset manner in rotation with respect to the branches of the common slot.  
         [0016]     The embodiment enables a simplified connection of many antennas. It can, for example, be advantageously used in a multi-layer substrate where each line occupies a separate plane.  
         [0017]     It is advantageous to choose an even number N. It is also advantageous to choose N′=N. In this manner, the rotation shift is such that the lines are each inserted in each angular sector formed between the branches of the common slot.  
         [0018]     According to one embodiment, the means of reception and/or transmission are Vivaldi type antennas evenly spaced around a central point.  
         [0019]     Such antennas are commonly used and well known by those in the profession. The invention is advantageously realised with these antennas but can also be realised by any type of antennas connected by a line/slot transition, for example printed dipoles, LTSA (Linear Tapered Slot Antenna) devices.  
         [0020]     According to one embodiment, the connection lines are constituted by microstrip lines or coplanar lines.  
         [0021]     According to one embodiment, the switching device includes at least one diode.  
         [0022]     According to another embodiment, the switching device includes a discrete switch for selectively activating one connection line or the other. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     Other characteristics and advantages of the present invention will emerge on reading the description of different embodiments, the description being made with reference to the annexed drawings wherein:  
         [0024]      FIG. 1  is a block diagram view of the connection of an antenna of the slot/line coupling type according to the prior art.  
         [0025]      FIG. 2  is a block diagram view of the series connection of two antennas of the slot/line coupling type according to the prior art.  
         [0026]      FIG. 3  is a block diagram view of the parallel connection of two antennas of the slot/line coupling type according to the prior art.  
         [0027]      FIG. 4  is a block diagram view of the advantageous parallel connection of two antennas of the common/slot line coupling type according to the prior art.  
         [0028]      FIGS. 5   a  and  5   b  are block diagram views of connection means of two antennas used in the present invention.  
         [0029]      FIGS. 6   a ,  6   b  and  6   c  show the radiation patterns of the device of  FIG. 5  as a function of the angle between two antennas.  
         [0030]      FIGS. 7   a  and  7   b  show a case of a radiating device with 2N antennas and a corresponding circuit diagram.  
         [0031]      FIG. 8  is a block diagram view of an embodiment of the invention with two pairs of antennas.  
         [0032]      FIG. 9  is a block diagram view of an embodiment of the invention with a number N=4 antennas.  
         [0033]      FIG. 10  is a section of a radiating device as proposed in  FIG. 9 .  
         [0034]      FIG. 11  is a relief view of the radiation patterns obtained with a radiating device as shown in  FIG. 9 . 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0035]      FIGS. 5   a  and  5   b  show a first embodiment of the invention. In these figures, two antennas A 1  and A 2  are connected and fed by the same line (L 1  or L 2 )/slot FC transitions. According to the position of the lines L 1  and L 2 , linked to a port P, on the slot, a phase difference between the signal E 1  sent by A 1  and the signal E 2  sent by A 2  can be defined. This phase difference is due to a difference in distance between the line/slot transition and the antennas A 1  and A 2 .  
         [0036]     This enables different patterns to be obtained according to the position of the line/slot transition. Hence, when the angle between the two antennas A 1  and A 2  is 90°, two distinct radiation patterns are obtained, shown in  FIG. 6   b.    
         [0037]     In this figure it is seen that, as the line L 1  crosses the slot at equal distance from the antennas A 1  and A 2 , the pattern D 1 , corresponding to a connection by the line L 1 , has a null in the axis because the signals sent are of the same amplitude and in phase at the level of the antennas A 1  and A 2  but recombine negatively in phase opposition along this axis. However, the line L 2  is offset by a quarter of the guided wavelength in the slot Ls/4, which enables a phase difference of 90° to be introduced. Hence, a phase difference of 180° is introduced on the signal arriving at the antenna A 2  in comparison with the signal arriving at the antenna A 1 . The radiation sent by the two antennas thus recombines constructively along the axis. Hence, the pattern D 2 , corresponding to the line L 2 , no longer has any null along the axis.  
         [0038]      FIGS. 5   a  and  5   b  differ by the implementation of the switching device  3  between the two lines L 1  and L 2 . The switching device enables the connection of one line to be switched to another one and, consequently, obtain a structure with a diverse radiation pattern.  
         [0039]     In  FIG. 5   a , the switching device  3   a  includes diodes at the end of lines L 1  and L 2  to authorize the coupling on a line at the same time that it is forbidden on the other.  
         [0040]     In  FIG. 5   b , the switching device  3   b  between the two lines L 1  and L 2  includes a discrete or integrated switch, for example an SPDT (Single Port Double Through).  
         [0041]     It will be noted that in the embodiment shown in  FIG. 5 , one of the lines is centred on the axis of symmetry of the antennas, the other line being off-centre. However, it is also possible that such connection lines are both off-centre and placed at different distances from the antennas. This particularly enables the phase difference introduced between two antennas in a device according to the invention to be controlled and therefore to control the global radiation pattern.  
         [0042]     The concept of diversity of radiation patterns was validated in simulation for several values of the angle α, with the device shown in  FIG. 5 . The results in terms of radiation pattern are given in  FIG. 6 . It emerges that irrespective of the angle between the antennas, an efficient diversity is found with radiation nulls at the locations of the radiation maximas when the connection line is offset. The shape and location of the maximas and nulls depend on the distance and angle between the antennas. This geometric phase difference is added to the electrical phase difference. This effect, specific to the invention, enables the device to be dimensioned in order to obtain the required patterns.  
         [0043]     It will be noted that the transition between a line, for example, microstrip and several slots operates correctly. When two antennas are combined on the same slot and are connected by the same line, this results, from the point of view of the electrical diagram, in putting the antenna impedances in parallel. As shown in  FIG. 7   a , when the number of antennas A is increased, the common slot comprises branches B toward which the electromagnetic signals are coupled, several branches B intersecting at the same place at the level of the line L/common slot transition constituted by the branches B. From the point of view of the circuit diagram shown in  FIG. 7   b , this results in putting the impedances Z A  of the antennas A in series. It is therefore possible to multiply the number of antennas connected by a same line L. One embodiment of the invention multiplying the number of antennas of the radiating device is shown in  FIG. 8 . Four antennas A 1 , A 2 , A 3 , A 4  are grouped in pairs, respectively (A 1 , A 4 ) and (A 2 , A 3 ), with a common slot, respectively FC 1  and FC 2 . Such a structure, presenting a parallel connection has a good bandwidth and therefore enables operation at diverse frequencies. A switching device  3  is constituted by a switch, for example comprising two diodes, as shown in  FIG. 5   b , and enabling the slots FC 1  and FC 2  to be connected to one or other of the lines L 1  and L 2 . The switching device  3  is connected to a connection port that is itself connected to a signal feed and/or processing means.  
         [0044]     When the connection switches from line L 1  to line L 2 , the signal E 3  present in the antenna A 3  is phase shifted by 180° wth respect to signal E 2  present in antenna A 2 , represented by the change in orientation of the vector E 3  on  FIG. 8 . When the phase difference introduced is 180°, the orientation of the signal E 3  in the antenna A 3  then changes, as shown in  FIG. 8 .  
         [0045]     The behaviour of the electromagnetic signals is similar, all things being the same, for the antennas A 4  and A 1 . However, in order to obtain phase changes that enable the genuine observation of radiation pattern diversity, a fixed phase difference of 180° is realised on line L 1 , next to the antenna pair A 1  and A 4 .  
         [0046]     Another embodiment enabling the number of antennas to be increased is shown in  FIG. 9 . In this figure, four antennas A 1 , A 2 , A 3 , A 4  are connected by their common slot FC in the form of a four-branched star. As shown in  FIG. 10 , they are, for example, engraved in a ground plane M. A first feeder line L 1  is arranged above the ground plane M, on a first substrate S 1 , and the second feeder line L 2  is arranged above the ground plane M, on a second substrate S 2 . Hence the lines are insulated from each other. This structure is advantageous where a low-cost multi-layer substrate S is used, for example the FR 4 . This type of substrate can particularly be used to realise RF boards.  
         [0047]     Such a multi-layer substrate enables antennas and the connection means to be realised on the same substrate without using additional components between the two.  
         [0048]     The radiating device thus obtained has an operating bandwidth for matching as well as in transmission, with an equal distribution of energy between the antennas. Owing to the excellent intrinsic insulation of the connections, this embodiment does not require any additional components to provide the insulation between the lines. A good diversity of radiation is obtained, the radiation patterns obtained for each of the lines being complementary.  
         [0049]      FIG. 11  shows the radiation patterns Da and Db in a relief view of the quadruple antenna structure, shown in  FIG. 9 . It is noted that these two patterns Da and Db obtained, each for one of the lines, respectively L 1  and L 2 , are different and show excellent complementarity. Hence, by switching from one line to another, a dynamically configurable radiation is available. Such a complementarity of patterns is also seen in  FIG. 6  at two dimensions but only for two antennas.  
         [0050]     The invention is not limited to the embodiments described and those in the profession will recognise the existence of diverse embodiment variants such as, for example, the multiplication of antennas connected according to the principle of the invention.