Method for locating transmitting sources by the use of the mutual coupling of a small -base antenna array and fast -switching singlechannel receiving system using the method 5 The present invention relates to the field of radiogoniometry and more precisely that of the location of sources by determination of the direction of arrival of the signal transmitted by these sources. The invention relates to a method and a system of single -channel location, that is to say for which the receiver that is used has only one io receiving channel associated with a small -base or small-diameter antenna array. The switching of the receiving channel between the various elements of the antenna array must be fast enough compared with the duration of a symbol of the source signal. In the rest of the description , the expression "source location" is aimed is notably at the determination of the number of sources transmitting a given signal in a given radioelectric environment and the determination of the directions of arrival of the signals transmitted by these sources . A sourcelocation method comprises , in the broad sense , any method of radiogoniometry , of separation of sources, of identification of spatial 20 signatures or of identification of source -directing vectors. The objective of the invention is to propose a method and a system of locating sources based on the signals transmitted by these sources and received by a single-channel receiver associated with a small -base antenna 25 array. The system produced must have a limited manufacturing cost and space requirement , notably for the purpose of incorporating it into a portable item of equipment fitted with a small -base antenna array . It must also make it possible to relax the constraints on the calibration of the said array. 30 The method according to the invention makes it possible notably to carry out an analysis of the received signal in a continuous or a quasi2 continuous manner and thereby is applied to a large number of different signals transmitted in continuous or discontinuous waveforms, for example waveforms associated with protocols of the TDMA type or associated with frequency-evasion mechanisms , with broad or narrow-band frequency, and in 5 any type of stationary or non-stationary , even complex , radioelectric environment in the presence of interference or of scrambling. The field of radiogoniometry has been the subject of many works. However, the performance of the systems that are low cost and/or have a to reduced number of receiving channels has limitations with respect to the performance that they can achieve. In particular, certain systems use sectorized or directive antennas which provide a reduced interception capability and which are limited in low frequency by the insufficient size of the antennas. In order to increase the is interception capability , scans that are costly in time or in mechanical components are required for those solutions. Other solutions are based on Doppler methods which require a largebase antenna array and are not adapted to the small -base antenna arrays for portable systems. 20 The known single -channel systems also have a limitation with respect to the discontinuity of the observations made. Specifically, when the radiogoniometry system has only one receiving channel , the latter switches, by means of a switch , to the various antenna elements of the array. A discontinuity associated with the switching time therefore appears over the 25 overall observation made by the antenna array . This problem has an impact because it requires a consequent increase in the switching speed and the sampling frequency and requires reducing the integration periods . Moreover, a discontinuous observation causes degraded performance for signals to be located that are transmitted in a waveform that is in bursts. This type of signal 30 is characterized by rapid non-stationarities of the waveform in contrast to a continuous waveform . The discontinuity of the observations is also 3 problematical when it involves discriminating between several sources transmitting simultaneously. Furthermore, the solutions of the prior art are not adapted to smallbase or small-diameter antenna arrays. Specifically, this type of array 5 induces not inconsiderable contributions of the couplings between antenna elements of which it is difficult to take account reliably in the calibration processes. Also known are solutions based on the use of antennas with parasitic to elements, for example that described in the publication entitled "High- Resolution Direction Finding using a switched parasitic antenna", Thomas Svantesson et al, 11th IEEE-Signal processing workshop, Singapore 2001, p. 508-511. The principle of these solutions is based on a switching of the antenna is diagram. The antenna array consists of several antenna elements of which the majority are in open circuit and are used as concentrators. At a given instant, the voltage at the terminals of a single element is measured. A control circuit, based on diodes, is used to independently activate each antenna element in order to form the desired antenna diagram and thus 20 achieve a rapid switching. These solutions have the drawback that their performance is closely linked to the constricted geometries of the antennas and to the calibration tables of the various diagrams formed by the various configurations of the parasitic elements, tables that have to be very precisely determined. 25 Moreover, if the switching is not rapid enough, the interception capability is reduced because the generated antenna diagram is directional, the "parasitic" antenna elements being used mainly as reflectors in order to increase the antenna gain in the main direction of the diagram. Finally, these solutions also suffer from problems of discontinuity and 30 of transitory regime of the observations made during the switchings, even when they are rapid. 4 The object of the invention is to remedy the aforementioned limitations of the prior art by proposing a single-channel radiogoniometry solution adapted to a fast switching of the receiving channel on the various antenna 5 elements of the antenna array. The invention makes it possible to reconstitute a quasi-continuous observation of the input signal by using couplings and the mutual influence between antenna elements. The invention therefore makes it possible to produce statistical estimators of the observed signal over long periods of io integration in order to significantly improve the performance of the processes of source separation or of determination of the direction of arrival of a signal. Accordingly, the subject of the invention is a method for locating sources each transmitting a signal S , characterized in that it comprises at 15 least the following steps executed by a single-channel receiving system: ® Receiving the signal or signals at the input of an antenna array comprising a plurality N of radiating elements by successively switching the receiving channel to the N radiating elements, the switching period At being configured to be strictly less than the 20 ratio between the half-duration TS/2 of a symbol of the said signal S and the number N of radiating elements, ® Sampling, after each successive switching , at the output of each radiating element , a sample of the received signal in order to construct a vector X' of the spatial signal received by the antenna 25 array, ® Computing at least one first statistical estimator MQQ;,, of order Q greater than or equal to 1 of the spatial signal X ' at the output of the antenna array, ® Determining at least one second statistical estimator MQ of the 30 same order Q, for the spatial signal X at the input of the antenna 5 array by resolving the systems of equations MM.o = C«I.MQ X where C(Q) is a self tensor product of order Q of the coupling matrix C of the antenna array , the components of the said coupling matrix C being equal to the mutual coupling coefficients between each 5 pair of radiating elements of the said antenna array , the said coupling matrix C being previously determined and stored in a database contained in the said system, Applying a source-location method, such as a method of radiogoniometry , of separation of sources, of identification of to spatial signature or of identification of source-directing vectors, to the said second statistical estimatorMQ'X . According to a particular aspect of the invention, the said statistical estimators are estimators of the moments or of the cumulants of order Q or more precisely estimatiors of the crossed products, of the variance or of the 15 covariance. In a variant embodiment , the method according to the invention also comprises a step of compensating for the components of the second statistical estimator of the spatial signal X with the values of the autocorrelation function rs ( r) of the modulation of the said transmitted signal 20 S, the said values being delayed by a multiple delay of the switching period AT. According to a particular aspect of the invention , the said statistical estimators are estimators of the quadricovariance. In a variant embodiment , the method according to the invention also 25 comprises a step of compensating for the components of the second statistical estimator of the spatial signal X with the values of the quadricovariance function gs ('ci, T2, i3) of the modulation of the said signal S, the said values being delayed by multiple delays cl, T2, i3 of the switching period AT. 6 In a variant embodiment of the invention, the successive sampling at the output of each radiating element is carried out according to a circular switching. According to a particular aspect of the invention, in order to generate the s coupling matrix C, each mutual coupling coefficient between a first and a second radiating element is predetermined by imposing a voltage and/or by injecting a current at the terminals of the first radiating element and by measuring the voltage and/or the current at the terminals of the second radiating element. to The location of a source may consist in determining the direction of arrival of the wave transmitted by this source. The source-location method may be chosen from the following methods: a correlative interferometry method, a vector correlation method, an adaptive channel formation method, a second-order or fourth-order subspace method, is or a JADE method. In a variant embodiment of the invention, the signal S is sought in an instantaneous frequency band of minimum value F1 and of maximum value F2, the said switch also being configured so that its switching period AT is strictly less than the quantity 1/(2.N.F2). 20 A further subject of the invention is a receiving system for the location of sources each transmitting a signal S comprising an antenna array consisting of a plurality of radiating elements, of a switch in order to successively sample the output signal of each radiating element, of a receiving channel comprising an analogue-digital converter and of means of analysis and of 25 computation comprising a computing unit and a database, characterized in that the said switch is configured so that its switching period AT is strictly less than the ratio between the half-duration Ts/2 of a symbol of the said signal S and the number N of radiating elements, the database contains tho predetermined values of the coupling matrix C of the antenna array, and the 30 means of analysis and of computation are adapted to apply the sourcelocation method according to the invention. 7 Other features and advantages of the invention will become evident from the following description made with respect to appended drawings which represent: - Figure 1, a block diagram of a receiving system adapted to use the 5 method according to the invention, - Figure 2, a diagram showing the switching and sampling of the received signal, - Figure 3, a diagram illustrating the construction of the vector of the signals at the input of the computing unit of a receiving system 10 according to the invention, - Figures 4a and 4b, two diagrams illustrating the principle of measurements of the coupling coefficients between elements of an antenna array. 15 Figure 1 represents, in a block diagram, a receiving system 100 adapted to use a method of radiogoniometry or of source separation according to the invention. The system 100 comprises at least one antenna array 101 with a small base or small diameter comprising a plurality of radiating elements 20 111,112,113.... 11 n, that are capable of receiving a signal X transmitted by a source to be located in a predetermined frequency band, for example the HF (High Frequency) or VHF (Very High Frequency) band. The system 100 also comprises a switch 102 capable of successively switching on the output of one of the radiating elements of the array 101 in order to transmit the output 25 signal X' of this element to a receiving channel 103. An important parameter of the switch 102 is its switching speed, or its period At for switching between two radiating elements. A short switching period or a fast switching speed has the advantage of limiting the discontinuities in the acquisition of the signal that are associated with the time necessary to switch from one 3o antenna element to another. 8 The receiving channel 103 comprises at least one amplification and/or filtering system 131 and an analogue/digital converter 132 capable of digitizing the received signal at a given sampling frequency Fe. The system 100 also comprises means 104 for analyzing and 5 processing the digitized signal, which means comprise a computing unit, a database and optionally an operating interface. The computing unit is adapted to use a method of processing the received signals in order to characterize them. The database contains certain items of predetermined information concerning the antenna array and, where necessary, concerning to the nature of the received signal, notably its modulation. The method according to the invention can be applied in the situation in which the switch 102 is configured so that its switching speed is fast relative to the symbol frequency of the received signal to be located. In this is way, the duration of a spatial sampling of the received signal on all of the elements of the antenna array remains much less than half the duration of a symbol of the received signal. More precisely, an essential feature of the invention is that the switching period At is strictly less than the ratio between the half-duration Ts 20 of a symbol of the observed signal and the number N of elements of the antenna array 101. In this manner, the switch 102 carries out, on each symbol at least, a complete run-through of the antenna array before the end of a symbol of the observed signal. Figure 2 illustrates, in a diagram, the principle of a fast switching 25 relative to the symbol time of the received signal. Figure 2 represents a symbol indexed by K of the received signal S of duration Ts defined by its modulation rhythm and the samplings x'l,...x'N made by the switch 102 on each output of a radiating element of the antenna array 101 at the instants t, t+At,... t+ (N-1)At, where At is the switching 30 period. A complete run-through of the antenna array 101 is carried out by the switch 102 before the end of the symbol K. Specifically, in the example of 9 Figure 2, a complete run-through is carried out before the end of half of the symbol K. The signal sampled by the switch 102 is then digitized at a given sampling frequency Fe. In the non-limiting example of Figure 2, the sampling 5 rhythm Te is equal to a quarter of the switching period At. All of the samplings x'l,...x'N made during the duration N.At form a vector X' of the output signal of the antenna array 101. The samples x'j ,...x'N of this signal X' can be taken in the same symbol K of the received signal because of the fast switching of the switch 102 in less than a half-duration of to a symbol. The construction of the vector X' is illustrated in Figure 3. Each component of the vector X' is equal to the sample taken at an instant t+k;At of the output signal of a radiating element of the antenna array. The switching period At also corresponds to the spatial sampling period of the received is signal . Specifically, the same signal is received by the various elements of the antenna array and the use of the spatial diversity in receive mode makes it possible to better characterize the signal for the purpose of identifying its direction of arrival. 20 In a variant embodiment of the invention, the run-through of the elements of the antenna array at the instants t+k;At, where i is the index of an element, i varying from 1 to N, is not necessarily circular. Specifically, the series kl,...kN is not necessarily increasing or strictly periodic . In the case of a circular switching as described in the examples of Figures 2 and 3 , k;+1=k; + 25 1, but the run -through of the antenna array may also be carried out according to a pseudo-random series . In this case , Ak is the maximum value Ik; - kjI of the difference between two temporal indices k; and kj after switching on all the elements of the array . Ak.At is the temporal medium of the digital samplings making it possible to constitute the vector X from the instant t. It is 30 this value Ak.At that must be strictly less than the half -duration TS/2 of a symbol . In the case of a circular switching, Ak = N. 10 The method and the system according to the invention advantageously apply for small -base or small-diameter antenna arrays. For such arrays, the radiating elements are close to one another and the mutual 5 radioelectric influence of one element on the others is not inconsiderable. Making use of the mutual influence between elements of the array makes it possible to ensure a quasi-continuous observation of the received signal. The electromagnetic field received by the antenna array induces a voltage signal at the terminals of the matching circuit of each antenna to element. This voltage signal consists of the total of one direct signal and several indirect signals. The direct signal is the voltage signal induced at the terminals of the matching circuit of a radiating element by the electromagnetic field in the 15 immediate vicinity of this element. The indirect signals are the voltage signals induced at the terminals of the matching circuit of a radiating element by the electromagnetic fields in the immediate vicinities of the other antenna elements of the array. When the distance between the antenna elements is small, the 20 indirect signals are not negligible. The signal x'no(t) sampled at the output of an element of index no of the antenna array therefore results both in the received signal xno(t) at the input of this element and also in the received signals xn(t) at the input of the other elements of the array. 25 The input signal xn(t + n.At) corresponding to a transmitting source, sampled on the antenna element n on the nth switching of duration At, may therefore be modelled with the aid of the following general relation: x, (t + n.AT) = p,, .e''°' .S(t + n.AT - z) + b„ (t + n.AT) S being the signal transmitted by the source , pn, cpn and in being the phase 3o attenuation and delay induced by the propagation, bn being the received noise. 11 The output signal x'„ o(t + no.At) sampled on the antenna element no on the nth switching of duration At can therefore be modelled with the aid of the following general relation: N N x'nn (t +n 0AT) _ XCn,,n.Xn(t +n0AT-Znpn ) XCnon.Xn(t+n0AT) (1) n=1 ,1=1 5 Vn0,n =1...N; x',, ,, (t t o N.4T«Ts/2 ; X' - O ; x n(t+n0AT) N.AT<>]ode ,]+ ,,© ,^]®4 °'}®1E ]+24 ^® 1®4 ° 1® ^1 and when the signals are centred: 20 1 The quadricovariance is the 4th order tensor most widely used in the methods of source separation and of goniometries at the orders higher than 21 2. It corresponds to the 4th order cumulant defined by the conjugation indices 1 and 3. For a centred complex scalar signal X with zero delays, it corresponds to the product of the flattening (or Kurtosis) coefficient by the variance, and 5 equals Quadx = E [ Ix14] - 21E[Ix12]12 - IE[x2]12. For a real scalar signal X that is centred and with zero delays, it equals Quadx = E[x4] - 3(E[x2])2. For a complex signal vector X that is centred and has zero delays, it is written in the tensor form Quadx =Cum4,x( ,*, ,*) = E[XOX*OXOX*]-2. E[XOX*]O(E[XOX*])-E[XOX]O(E[X*OX*]) to For a real signal vector X that is centred and with zero delays, it is written in the tensor form Quadx=Cum4,x(,*,*)=E[XOXOXOX] - 3E[XOX]O(E[XOX]). If X is a Gaussian signal, then Quadx =0. 15 In practice , on signals that are appropriately sampled at a sampling frequency Fe = 1/Te complying with the Shannon condition, these tensors are estimated by temporal means of the products of order q <_ Q of the signal vector. At the 1St order, in order to construct the mean of the signal vector, the 20 probabilistic means of each component of the signal is estimated by a time integration K no =1,...,N; E[x,,,, (koTe )] .1 x,,0 ((ko + k)Te ) K »_, Since communication signals are usually centred, the mean is a priori zero. 25 At the order 2, in order to construct moments and covariances, the 2nd order products of each component of the signal vector are estimated with and without conjugation by a time integration: K 110 , n,=1,...,N; E[x*°(koT)xn'(k,T)] 1 1x*°((ko +k)T ).x;' ((k,+k)Te) ~ Kk=1 22 At the order 3, the same process is carried out with the 31d order products, with and without conjugation, then time integration. Since communication signals are considered to be centred and balanced, the 3rd order moments and cumulants are usually zero. 5 At the order 4, in order to construct moments and quadricovariances, the means, 2nd order products and 4th order products of each component of the signal vector are estimated with and without conjugation by a time integration: 0 11 12 Y1. ,711117"173 =1, ...,^; E[xno (k 0I )x i (k1T )X (k,T') Xn3 (k37 )] 1 I 13 x1° (( 0 - f k)T,,).xni((/q +k) ).x ((/i,+ ^i)T,,).xn,A11^;+k)Te) K k_1 10 An equivalent process is carried out in order to construct any moment or cumulant of an order higher than 4. The relations between a statistical estimator of the signal X at the output of the antenna array and its equivalent for the signal X at the input of 1s the antenna array will now be described. These relations involve the coupling coefficients between elements of the array. The relations (1 bis) and (2) correspond to a linear transformation of the signal at the input of the antenna array X into an output signal of the 20 antenna array X'=CX. The products, moments and cumulants of the signal X then sustain the following multilinear transformations. The products of order Q of the received signals X with or without conjugation 25 (marked (*) by convention) are linked to the products of order Q of the signals X by the relation: ,(*,,) •(*J...x1(*Q) X no ) .C(*') ...C(*p') (*").x(*')...x(*Q-') ) .x ni nQ, npmp nom np. mQ. / Xmo m, mQ-I m^=1 m^=1 m^-,=1 23 Similarly, the moments of order Q of the signal X' are written: (C(*I,) C(*1) ...C(*Q-1) '. -'o. - lmi nQ_lrQ_I 1110=1 1111=1 711Q_I=1 and the cumulants of order Q: k I , I, z,..., (J_Il II.,.11,..;.,,,Q_I C2[YI?* (C(*") n m 'Cnm Cn m _ )• Q^,A'^I ..;X ,, 11i 1 U V 1 1 Q-I Q I Cun? Q,IX,, ,Xm1 ;...;X Q_I l111 =1 111 p_1=1 All the above formulations are written in condensed tensor forms in which the linear operator of the transformation by coupling of the input signal X of antenna array into an output signal X' (transformation x,= c.x, operator c) is to considered to be a 2nd order tensor. At the statistical order Q, the tensor autoproducts of order Q of this 2nd order tensor c, formally marked c«'' define tensors of order 2Q (which may be seen as matrices of dimensions (N° x N°) appropriately ordered); these tensor autoproducts of order Q operate on tensors of order Q (which can be seen as vectors of size N° x 1 15 appropriately ordered). These tensor operations are written according to the following formal relations: 20 - the tensor Q-power of X' as a function of that of X ] fC ®C®...®C (^^^^: •Q^) Y ®X®...®Xh^^^^ QI) - expression of the moments of order Q of X', as a function of those of X *o, *I,*v...,*Q-I) Q, Y' = QC ®C ®... ®C]I K.h'z...,•Q-I) * * * +g-I) - expression of the cumulants of order Q of X' as a function of those of X 24 Cu,n 0 = QC®C®...®CB Clin i In general , the equation linking a statistical estimator of order Q of the output signal X', marked MM i, , with the statistical estimator of order Q 5 corresponding to the input signal X, marked MM' is: to> (^?) coy co) Mex. =QCOCO...OC^ M^„=C .M x (3) where C(Q) is the formal notation of the tensor autoproduct of order Q of the coupling matrix C of the antenna array , Q being the order of the moment or cumulant that the statistical estimators MME and MMit represent. 1 0 For example, the covariance of the output signal X, which is a 2nd order moment, is linked to the covariance of the input signal X by the relation (4): R,,.=C C(*).Rx (4) is where C®C(*) is the tensor product of the coupling matrix by its conjugate represented by a matrix of dimension N2 by N2. where R.i., Ri are defined as being 2nd order tensors represented by vectors of dimension N2 or by matrices of dimension N by N. 20 The method according to the invention will now be described for the particular example of determining the covariance of the signal to be located. The method is applied in a similar manner for the other statistical estimators described or their equivalents. 25 By virtue of the taking account of the coupling coefficients between antenna elements, each sampling of signal x'n by the switch contains the contribution of the input signal on the antenna element of weighted index by 25 the impedance specific to this element, and the contribution of the other antenna elements , at the same instant, weighted by the associated coupling coefficient. The observation of the signal is thus made continuous to the extent. that the antenna elements to which the switch is not connected 5 contribute indirectly to the received signal via the antenna coupling. The statistical estimators of the signal X', for example its covariance, appear as linear combinations of the statistical estimators of the signal X, considered at all the instants not only at the instants of taking of reception by the switch. 10 The method according to the invention therefore consists in carrying out the following steps. The signal vector X is sampled by the switch 102 at the output of the antenna array 101 with a sufficiently rapid switching speed compared with is the speed of modulation of the received signal. The signal vector X is digitized at a given sampling frequency Fe and then integrated over a predetermined period of observation. The covariance Rx. of the signal X' is computed , then the covariance Rx of the signal X at the input of the antenna array is determined by resolving 20 the system of equations (4) based on the coupling matrix C of the antenna array that has been previously determined and stored. A method of radiogoniometry or a method of source separation is applied to the matrix of covariance Rx in order to determine the number of sources and/or their direction of arrival . In advance or alternatively , a method 25 of source separation or of identification of source -directing vectors may also be applied. In order to improve the performance of the method , a sampling, by the switch , of the signal samples in the middle of the switching intervals, as 3 0 illustrated in Figure 2, is preferred so as to prevent a sampling during the transitory regime of the control circuits of the switch. 26 In a variant embodiment of the invention , the performance of the method can be improved by assuming that the modulation of the received signal S is known and more precisely the autocorrelation function rs ('C) of the modulation of the signal S. 5 The term rs(,r) intervenes as a corrective term in the relation (4) which makes it possible to connect the covariances of the signals X and X. Starting from the general expression ( 1), the relation (4) is modified to arrive at the relation (6). 10 R,. = c ©c(*).[,s & n, I _ (6) The & operator indicates the term-to-term product of the 2nd order tensors rs and Rx. More precisely , the component of index (i-1)N + j of the tensor ^•,. is equal to the autocorrelation function rs((j-i).At) of the transmitted signal S(t) delayed by the delay (j-i).At. 15 The components of the tensor , can be precalculated for all the delays 0, At... N. At, when the information on the modulation of the transmitted signal S(t) is available, In this variant of the invention, the method therefore comprises an additional step which consists , after having computed the covariance Rx of 20 the signal X with the aid of the relation (4), in compensating for each of its components by dividing it by the delayed values of the autocorrelation function rs of the transmitted modulated signal S(t). This additional step makes it possible to improve the performance but is not essential to the application of the method because the samples of the 25 signal vector X' belong to one and the same symbol of the received signal. This requirement is fulfilled if the switching time At is less than the ratio between the half-duration of a symbol Ts/2 of the appropriately filtered source signal and the number of antenna elements N. The modulation of the signal S can be estimated by means external to 27 the invention intervening as a preamble or may be known when the very nature of the signal of which the direction of arrival is desired to be estimated is known. 5 If a 4th order estimator is used , for example the quadricovariance or a 4th order cumulant , the relation (6) becomes: Quads = [C® Ct*1 ® C ®C(*)]. [[9s & Quadx ]] where qs is the delayed quadricovariance function of the source signal S, of which the modulation is assumed to be known, represented by the io expression: r gs(t1,ti2,^3)= E[s(t) S(t+tl)*S(t+t2) S(t+t3)*]- E[s(t) S(t+tl)*7]7 E[s(t+t2)S(t+t3)*1 - E[s(t) S(t+t2)]E[s(t+tl)*S(t+t3) *J 1 - E[s(t) S(t+t3)*]E[s(t+tl)S(t+t2)*]) The quadricovariance function qs can be predetermined in the same manner as the autocorrelation function rs for all the sets of delays 0, At.... NAt when is the information on the modulation of the signal S is available or previously determined by analysis. The method according to the invention makes it possible to restore the statistical estimators of the input signal X of the antenna array that are then used to apply a method of goniometry or of source separation. 20 The possible uses of the abovementioned statistics in signal processing and antenna processing will now be described. All the information on the signal is contained in the series of its moments which appear as the coefficients of the development in series of the 25 first characteristic function of probability distribution of the random signal vector X (at the instant t omitted for the purposes of simplification in the following formulae) 28 (I/I ) X = ) I1fNJ E CN; (DN(U)E C x m q [ 02 x(U)= E exp(iRe {UH .X})] =1+> (I)x(U)=1+y Re Q=1 combinntlons *0, * * Q-1 i,Ii,!..J. Re 1,+i2 +..,+1,=q M(*1„*r,*Z,..., *Q_r ) ^),[x] (*o) x,(*r) ...x [*yt] 1u (*o) u (*r) .., u1[o*vr] All the information on the signal is also contained in the series of its cumulants which appear as the coefficients of the development in series of 5 the second characteristic function of probability distribution of the signal X random variable UEC';`u (U)EC r `I'r(u)= Log(E[exp(jRe{U' .X}b = 1+^ J I' I I `1',(U)=1+Z I J Re Q=I conrhinalons IIl12l..'N! o' Q-1 10 Re^ Cum^x;`°)xhr mrAlnntiars 021731 (*°'*r'*z,...,*Q r) U x(*vr)}u(*J (*r).. U!*,,) ly_, 1^ li 1q_1 Therefore, knowing the series of the moments or the series of the cumulants of the signal at the input of an antenna array makes it possible to completely characterize the "input signal X vector" statistical process. When the input signal vector is real , the first characteristic function is 1s determined at the order Q by a single tensor of the moments , of order Q; the second characteristic function is determined at the order Q by a single tensor of the cumulants , of order Q. When the input signal vector is complex, the first characteristic function is determined at the order Q by ^Q=1+LQ/2] tensors of moments of order Q 20 where LQ/2J is the entire portion of Q/2 (E1=1, E2=43=2, ,4=3), the other moments being deduced by conjugation; the second characteristic function is .Q 29 determined at the order Q by ^Q tensors of cumulants of order Q , the other cumulants being deduced by conjugation. Often, the study of the statistics of the 1St orders I and 2 provides the main s information on the process X. For example, the principal component analysis that is well known to those skilled in the art consists in breaking down the matrices of covariances into specific elements and directions, which makes it possible to determine and classify in order of importance the principle relations of statistical dependencies between coordinates of the vector X. In to antenna processing , these methods lead to the subspace methods such as MUSIC2 (" Multiple Signal Classification 2"). When X additionally has strongly non-Gaussian characteristics , which is frequently the case with transmission signals, the statistics of orders higher than 2 provide additions of discrimination . In antenna processing , these methods lead to the methods 15 known as "with higher orders" such as MUSIC4 which works on the 4th order cumulants , or the JADE method which uses 2nd and 4th order cumulants jointly. The possible uses of the abovementioned statistics will now be 20 described for applying a known method of source separation or of radiogoniometry. With respect to communication transmitters, most of the methods of source separation, of identification of directing vectors and of conventional 25 parallel goniometry at super and high resolution that are known to those skilled in the art use the 2nd order and 4th order moments or cumulants of the input signal vector. It is possible to cite for example: 30 - The correlative interferometry that consists in considering the N phases of one of the column vectors of the covariance matrix of the input signal, and in 30 searching in a precomputed calibration table the phase N-uplet closest to the direction of a distance criterion (for example a criterion of least squares), the direction associated with this N-uplet then providing the estimate of the direction of arrival of the signal. 5 - The vector correlation which consists in considering the N phases and the N amplitudes of one of the column vectors of the covariance matrix of the input signal, and in searching in a precomputed calibration table for the 2N-uplet of phases and amplitudes that is closest to the direction of a distance criterion (for example a criterion of least squares ), the direction associated with this io 2N-uplet then providing the estimate of the direction of arrival of the signal. - The formation of adaptive channel which consists in using the estimate of the covariance matrix of the signal to form the spatial filter in each direction defined by a directing vector as by the relation 1UrAS( s ) - [R[NJI '.as is then in applying this filter to the input signal X vector in order to construct the criterion CFAS (as) =XH RX the maximization of which gives an estimate of the directing vector or vectors as corresponding to the sources received at the input; the corresponding 20 directions of arrival are then produced by searching in a calibration table previously produced by computation and/or measurement. - The subspace methods of the MUSIC type which consist in breaking down the covariance tensors (for a 2nd order MUSIC method) and quadricovariance tensors (for a 4th order MUSIC method) in order to search for the specific 25 subspaces thereof, constructing orthogonal projectors, then producing estimates of the directing vectors as of the estimated input sources which produce a criterion of minimization of the said projections; the corresponding directions of arrival are then produced by searching in a calibration table previously produced by computation and/or measurement. 31 The reference works entitled "Advances in DOA estimation, chap 8, S. Chandran" and "J.L. Lacoume, P.O. Amblard, P. Comon, "Statistiques d'Ordre Superieur pour le traitement de signal" ["Higher order statistics for 5 signal processing"] Editions Masson, 1997" describe the aforementioned MUSIC2, MUSIC4 and JADE methods and other methods of radiogoniometry and of source separation that use the statistical estimators of a signal X with spatial diversity and which are compatible with the use of the method according to the invention. 10 The invention advantageously applies when the transmitting sources to be located are homogeneous, that is to say that they all transmit a signal generated according to the same waveform. The invention may be used in a radiogoniometry system, a 15 radioelectric sensor, a land, maritime or aeronautical radio system. It can be used to produce a control function of the spectrum or a sensing function in a cognitive radio for the purpose of optimizing the access of the radio to the array by the detection, the estimation of spatial signatures and the determination of angle of arrival of the adjacent interfering sources. 20 The method according to the invention can advantageously be applied to all of the signals acquired in an instantaneous frequency band delimited by two frequencies F1 and F2 where F2 > Fl. In this case, the constraint of fast switching is reflected by the fact that the switching period AT between two samplings must be configured to remain compatible with a signal of which the 25 symbol frequency is as high as possible in the band in question, namely equal to F2. This condition is obtained when the switching period AT is strictly less than the quantity 1/(2.N.F2). The invention uses the couplings between antenna elements of a 30 small-base array and has the advantage of enhancing the performance of the methods known to those skilled in the art by making the observation of the 32 received signal virtually continuous despite the switching of a single receiving channel on several antenna elements. The invention therefore makes it possible to detect any type of signal whether they are generated with a continuous or discontinuous waveform , to process complex environments 5 (propagation multipath interference) and non -stationary environments. Finally, the use of the coupling matrix of the antenna array has the advantage of preventing a too precise and awkward antenna calibration. 33 CLAIMS 1. Method for locating sources each transmitting a signal S, characterized in 5 that it comprises at least the following steps executed by a single-channel receiving system: ® Receiving the signal or signals at the input of an antenna array (101) comprising a plurality N of radiating elements (111,112,11n) by successively switching the receiving channel to the N radiating 10 elements, the switching period At being configured to be strictly less than the ratio between the half-duration TS/2 of a symbol of the said signal S and the number N of radiating elements, ® Sampling, after each successive switching, at the output of each radiating element ( 111,112,11n), a sample of the received signal in is order to construct a vector X of the spatial signal received by the antenna array (101), ® Computing at least one first statistical estimator M(Q(Q'X) , of order Q greater than or equal to 1 of the spatial signal X' at the output of the antenna array (101), 20 Determining at least one second statistical estimator MQ ) of the same order Q, for the spatial signal X at the input of the antenna array ( 101) by resolving the systems of equations MQ(°i, = O`'i.lYtQ where C(Q) is a self tensor product of order Q of the coupling matrix C of the antenna array ( 101), the components 25 of the said coupling matrix C being equal to the mutual coupling coefficients between each pair of radiating elements of the said antenna array ( 101), the said coupling matrix C being previously determined and stored in a database contained in the said system, ® Applying a source- location method, such as a method of 30 radiogoniometry , of separation of sources, of identification of 34 spatial signature or of identification of source-directing vectors, to the said second statistical estimator MQ; 2. Source-location method according to Claim 1, characterized in that the 5 said first and second statistical estimators A'IQI,,MQI are estimators of the moments or of the cumulants of order Q. 3. Source-location method according to Claim 2, characterized in that the said first and second statistical estimators MQ , , MQ Y are estimators of fo the crossed products, of the variance, or of the covariance. 4. Source-location method according to Claim 3, characterized in that it also comprises a step of compensating for the components of the second statistical estimator of the spatial signal X with the values of the 15 autocorrelation function rs(ti) of the modulation of the said transmitted signal S, the said values being delayed by a multiple delay ti of the switching period AT. 5. Source-location method according to Claim 2, characterized in that the 20 said statistical estimators are estimators of the quadricovariance. 6. Source-location method according to claim 5, characterized in that it also comprises a step of compensating for the components of the second statistical estimator of the spatial signal X with the values of the 25 quadricovariance function gs('r1, i2, T3) of the modulation of the said signal S, the said values, being delayed by multiple delays rl, T2, i3 of the switching period AT. 7. Source-location method according to one of the preceding claims, 30 characterized in that the successive sampling at the output of each radiating element is carried out according to a circular switching. 35 8. Source-location method according to one of the preceding claims, characterized in that, in order to generate the coupling matrix C, each mutual coupling coefficient between a first and a second radiating 5 element is predetermined by imposing a voltage and/or by injecting a current at the terminals of the first radiating element and by measuring the voltage and/or the current at the terminals of the second radiating element. to 9. Source-location method according to one of the preceding claims, characterized in that the location of a source consists in determining the direction of arrival of the wave transmitted by this source. 10. Source-location method according to one of the preceding claims, is characterized in that the source-location method is chosen from the following methods: a correlative interferometry method, a vector correlation method, an adaptive channel formation method, a secondorder or fourth-order subspace method, or a JADE method. 20 11. Source-location method according to one of the preceding claims, characterized in that the said signal S is sought in an instantaneous frequency band with a minimum value F1 and a maximum value F2, the said switch (102) also being configured so that its switching period AT is strictly less than the quantity 1/(2.N.F2). 25 12. Receiving system for the location of sources each transmitting a signal S comprising an antenna array (101) consisting of a plurality of radiating elements (111,112,113,11n), of a switch (102) in order to successively sample the output signal of each radiating element, of a receiving channel 30 (103) comprising an analogue-digital converter (132) and of means (104) of analysis and of computation comprising a computing unit and a database, characterized in that the said switch (102) is configured so that 36 its switching period AT is strictly less than the ratio between the halfduration Ts/2 of a symbol of the said signal S and the number N of radiating elements , the database contains the predetermined values of the coupling matrix C of the antenna array, ( 101), and the means (104) of 5 analysis and of computation are adapted to apply the source - location method according to one of Claims 1 to 11. 13. Receiving system according to Claim 12, characterized in that the said signal S is sought in an instantaneous frequency band with a minimum to value F1 and a maximum value F2, the said switch (102) also being configured so that its switching period AT is strictly less than the quantity 1/(2. N. F2).