Method of generating a high-power wave using a reverberant cavity system.

Abstract

The invention relates to a method for generating and transmitting a high-power signal composed of a plurality of Dirac distribution type signals, by means of a system for generating and transmitting a high-power signal provided with a reverberant cavity, and comprising a phase of calibrating the cavity over a calibration duration and a phase of time reversal of a signal before its injection into the cavity. Figures for the abstract: [Fig.3A] and [Fig.3B]

Description

Title of the invention: Method for generating a high-power wave using a reverberant cavity system.

[0001] The invention relates to a method of generating a high power wave using a reverberant cavity system.

[0002] The invention relates to the present invention seeks to satisfy the need for generating very impulsive signals of high peak power. The principle is based on the time reversal technique illustrated in [Fig.l].

[0003] The time reversal principle comprises a cavity calibration phase and a signal time reversal phase.

[0004] The calibration phase comprises a step of generating an analog impulse signal Sent,cav(t), or in other words of the Dirac distribution type, then a step of injecting this signal into the cavity. Finally, the time reversal phase comprises a step of measuring and learning the analog response of the cavity Hcav(t) (estimated channel impulse response or CIR for "Channel Impulse Response" in English).

[0005] By Dirac distribution type signal we mean d(t) at t0 (often we take t0=0 by convention): => d(t) = 1 if t=tO d(t) = 0 if t tO => in the spectral domain this gives a spectrum D(f) proportional to exp(-2ipf.t0 ) and a "constant" PSD on the band considered.

[0006] The time reversal phase of a signal comprises a step of generating an analog signal Sret,Cav(t) which approximates the returned response HretjCav(t)= H*cav (Tt), then a step of injecting this signal into the cavity. Finally, the time reversal phase of a signal comprises a step of recovering an output signal from the cavity Sret,s,cav(t) of the cavity compressed by the cavity, approximating an analog input signal Sent,cav(t).

[0007] State-of-the-art methods mainly deal only with real signals on carrier, particularly in the generation of pulsed signals, which is crucial for the precedent. We then have the simplification Hret>cav>anaiog(t)=H*cav(Tt)=Hcav(Tt)).

[0008] In this context, an example of implementation of the time reversal phase, as illustrated in [Fig.2] called "1 bit reversal". It uses a "Non-return to Zero" type modeling of the acronym NRZ of the signal returned by an analog signal Sret,cav,ana(t) of slot type taking opposite values ​​+A or -A depending on the positive or negative value of the returned signal Hcav(Tt) (NB: the signals are real, H*cav (Tt)=Hcav(Tt)).

[0009] When the bandwidth of the generator is significantly greater than the band of interest specific to the bandwidth of the cavity and subject to suitable low-pass filtering, the NRZ signal Sretjcav,ana(t) thus constituted by the slots of duration Ts, and of opposite extreme values ​​+A or -A, sufficiently correctly approximates the returned response Hcav(Tt)) to allow the obtaining of reversal gains k typically reaching 20.log 10(k) =15 dB.

[0010] More precisely, the current state of the art consists of a direct synthesis of the returned signal Hret>cav(t) or of an approximation SretjCav(t) of Hret>cav(t) whose implementation proves to be sub-optimal due to hardware constraints, and this whatever the frequency band of the cavity, and whatever the frequency band of the signal targeted at the cavity output.

[0011] When we want to implement a purely analog generation as in [Fig.l], we are limited by the reduced dynamics of the filtering and clipping generation systems which in practice reduce the achievable reversal gains k to 15 dB.

[0012] When we want to implement potentially more efficient digital filtering generation and processing and digital-to-analog conversion before amplification as in [Fig.3B], this implies strong constraints on the sampling frequency: - This limits the maximum frequency of Sret,Cav(t) of Hretjcav(t) by the sampling frequency of the DAC. For example: a direct synthesis limited to 5 GSPS only allows a maximum frequency of 2.5 GHz (Shannon condition on real signals: 2 x maximum frequency < sampling frequency) while the ASTRE cavity for example has a bandwidth of 1 GHz -10 GHz - This limits the waveforms that can be used for the SretjE,cav(t) approximation of HretjE>cav(t).

[0013] As a result, the state of the art poorly covers various needs necessary for improving the time reversal method, such as: - measurement of the complete response of the complete transmission chain (amplifier + cavity); - the approximation, generation and more efficient amplification of the returned signal Hr and,cav(l) • - to better take advantage of the cavity bandwidth (subsampling, transposition, etc.); - to relieve / improve the use of an amplifier in the transmission chain (adaptation to the cavity); - to produce carrier-modulated signals at the cavity output; - control of the signal at the cavity output Sretjcav(t): stiffness of the wave fronts, duration and repetition of the output pulses, modulation of the output pulses, etc.

[0014] An aim of the invention is to improve the generation of a high-power wave by means of a system for generating a high-power wave with a reverberant cavity, by improving the time reversal carried out by the cavity.

[0015] According to one aspect of the invention, there is proposed a method for generating and transmitting a high-power signal composed of a plurality of Dirac distribution type signals, by means of a system for generating and transmitting a high-power signal provided with a reverberant cavity, and comprising a phase of calibrating the cavity over a calibration duration and a phase of time reversal of a signal before injection into the cavity, in which: the cavity calibration phase over the calibration duration comprises the steps of: - generation of a first digital signal in the time domain of the Dirac distribution type; - conversion of the first signal into a second analog signal, then transposition on carrier of the second signal into a third analog signal, and amplification of the third signal on the frequency band of the cavity into a fourth analog signal; - injection of the fourth signal into the cavity; and - measurement, recording over the calibration period and learning of a fifth analog signal corresponding to the impulse response of the cavity over the calibration period; and digitization of the impulse response in the form of samples at a sampling frequency respecting the Shannon condition for the bandwidth of the cavity; the time reversal phase of the signal injected into the cavity over a reversal duration less than or equal to the calibration duration comprises the steps of: - generation in the time domain of a sixth digital returned signal corresponding to the reversal of the fifth signal taken in its digitized form; - filtering, truncation and digital modulation of the sixth signal to deliver an improved seventh digital returned signal; - analog conversion, filtering, clipping, transposition to carrier and amplification to carrier, of the seventh improved digitized returned signal, to deliver an eighth improved analog returned attack signal at the cavity input; - injection of the eighth signal into the cavity; and - emission by the cavity of a ninth analog signal, corresponding to the re resultant of the eighth signal after compression in said cavity.

[0016] According to one embodiment, the cavity calibration phase further comprises a step of measuring and learning the cavity in the frequency domain: by injecting into the input a plurality of pure frequency signals emitted on a plurality of carriers separated by a frequency step less than the inverse of the calibration duration on which the cavity is calibrated, and in sufficient number to cover a bandwidth greater by an oversampling factor than the bandwidth of the cavity; by recording the frequency responses at the cavity output for each of the pure frequency signals on the carriers injected at the cavity input.

[0017] By pure frequency signal f0 we mean a complex baseband signal: sc (t) = exp (2iirf 0t); corresponding to a real signal: sR (t) = cos (2iirf 0t) In the spectral domain this corresponds to a line of amplitude 1 in f0 for Sc(t); to two lines of amplitude 1 / 2 in f0 and -f0 for SR(t).

[0018] According to one embodiment, the calibration and time reversal phases of the cavity also relate to additional analog elements of the transmission chain constituting with the cavity an analog sub-assembly, in which: the calibration phase takes into account, in addition to the cavity, the additional analog elements upstream and / or downstream of the cavity for the determination of the impulse responses corresponding to the fifth signal and its digitized form of the analog subassembly; the reversal phase takes into account, in addition to the cavity, the additional analog elements upstream and / or downstream of the cavity for the determination of the eighth signal injected at the input of the additional analog elements upstream of the analog subassembly.

[0019] In one embodiment, the fifth signal is transposed and sampled in baseband to obtain a sampled digital complex signal centered around the zero frequency, by using a Hilbert transform, low-pass filtering, then baseband sampling at the sampling frequency respecting the Shannon condition for the cavity bandwidth refocused on the zero frequency.

[0020] According to one embodiment, the frequency response signals at the output of the analog subassembly of the transmission chain are frequency shifted by the half-sum of the terminals of the frequency band of the cavity, then undergo an inverse Fourier transform to obtain the time impulse response in digitized baseband over the number of samples.

[0021] In one embodiment, the phase of time reversal of a transmitted signal comprises the step of digitally generating the sixth complex reversed signal in baseband or corresponding to the reversal of the fifth sampled complex signal centered around the zero frequency.

[0022] According to one embodiment, the time reversal phase of a transmitted signal comprises a step of filtering, truncation and digital modulation of the sixth complex returned baseband signal, to deliver a seventh simplified returned baseband signal.

[0023] In one embodiment, the step of filtering, truncating and digitally modulating the sixth complex returned baseband signal to deliver a seventh simplified returned baseband signal uses a quasi-constant amplitude transformation, or a discrete phase state digital modulation of the BPSK or QPSK type.

[0024] According to one embodiment, the step of filtering, truncation and digital modulation of the sixth complex returned baseband signal to deliver a seventh simplified returned baseband signal uses a strictly constant amplitude transformation, or a digital modulation with continuous phase state MSK or CPM with 2 or 4 states.

[0025] The invention will be better understood by studying some embodiments described as non-limiting examples and illustrated by the appended drawings in which:

[0026] [Fig-1] schematically illustrates the principle is based on the time reversal technique, according to the state of the art;

[0027] [Fig.2] schematically illustrates an example of implementation of the time reversal phase, according to the state of the art; and

[0028] [Fig.3A] and [Fig.3B] schematically illustrate a method according to one aspect of the invention.

[0029] Throughout the figures, elements having identical references are similar.

[0030] [Fig.3A] and [Fig.3B] schematically illustrate the method according to one aspect of the invention.

[0031] The method for generating and transmitting a high-power signal composed of a plurality of Dirac distribution type signals, by means of a system for generating and transmitting a high-power signal provided with a reverberant cavity, and comprising a calibration phase I of the cavity over a calibration duration T and a time reversal phase II of a signal before injection into the cavity, is such that the calibration phase I of the cavity over the calibration duration T includes the steps of: - generation I-1 of a first digital excitation signal Sexc,cav(n) in the time domain of Dirac distribution type emitted at time n0 (Sexc,cav(n) “ô(n-no)) ; - conversion of the first signal into a second analog signal close to a Dirac pulse at time t0, then 1-2 transposition on carrier of the second signal into a third analog signal, and amplification of the third signal on the cavity frequency band into a fourth analog signal (Sent_cav(t)) whose envelope is close to a Dirac pulse at time t0 (ô(t-t0)); - injection 1-3 of the fourth signal Sent_Cav(t) into the cavity; and - measurement, recording over the calibration duration T and learning of a fifth analog signal corresponding to the impulse response Hcav(t) of the cavity over the calibration duration T; and digitization 1-4 of the impulse response Hcav(t) in the form of samples Hcav(n) indexed from 0 to N-1 at a sampling frequency Fe respecting the Shannon condition for the bandwidth [Fmin; Fmax] of the cavity; the time reversal phase II of the signal injected into the cavity over a reversal duration T' less than or equal to the calibration duration T comprises the steps of: - generation II-1 in the time domain of a sixth returned signal digital HretjCav(n) corresponding to the reversal of the fifth signal Hcav (t) taken in its digital form Hcav(n) = H*cav(Nln)), n varying from 0 to N-1; - filtering, truncation and digital modulation II-2 of the sixth signal to deliver an improved seventh digital returned signal H'ret>cav(n'), n' varying from 0 to N'-l, N' <N ; - analog conversion, filtering, clipping, transposition on carrier and amplification on carrier II-3, of the seventh improved digitized returned signal H' ret,cav(n), to deliver an eighth improved analog returned attack signal SretjE,cav(t) at the cavity input; - injection II-4 of the eighth signal SretjE,cav(t) into the cavity; (Sretjs,cav(t) ~ Sent,cav (t), which produces an amplification factor of the peak signal at the cavity output k, inducing a power compression gain 20.1ogi0(k)); and - emission II-5 by the cavity of a ninth analog signal Sretjs,cav(t), corresponding to the resultant of the eighth signal SretjE,cav(t) after compression in said cavity.

[0032] In the time domain, a particularly effective mode of implementing the invention in phase I is the transposition and baseband sampling of the response / signature Hcav(t) of the cavity to obtain a complex signal Hcav>BB(n) (part I and Q) sampled centered around the zero frequency. This digitization transposition implements: - a Hilbert transform of Hcav(t) and low-pass filtering (the real signal response / signature Hcav(t) then becomes complex (part I and Q): Hcav(t) —> Hcav,BB(t)); - a baseband sampling Hcav>BB(t) —» Hcav>BB(n.Te) = Hcav>BB(n) respecting the Shannon condition (sampling period Te verifying 1 / T e > Fmax CjBB: maximum frequency of the complex signal in baseband, duration T= N.Te.

[0033] The present invention allows in particular: - either, at fixed bandwidth, to limit the sampling frequency Fe = 1 / Te, - or, at a fixed sampling frequency Fe=l / Te, to increase the bandwidth and the carrier of the signals injected into the cavity to aim for measurements of cavity responses and generation of increasingly brief pulses and in an increasingly high frequency range.

[0034] The calibration phase of the cavity I may further comprise a step of measuring and learning the cavity in the frequency domain (L4a): - by injecting at the input a plurality of pure frequency $ent,cav(f,t) signals emitted on a plurality of carriers separated by a frequency step less than the inverse of the calibration duration T on which the cavity is calibrated, and in a number M sufficient to cover a bandwidth greater by an oversampling factor than the bandwidth of the cavity; spectrally, this is written in the complex domain $ent,cav(v) ô(vf)) and this corresponds to the emission of a real signal $ent,cav(f)(t) Re{exp(2iir.ft)}. - by recording the frequency responses Hcav(fm) at the cavity output for each of the pure frequency signals on the fm carriers injected at the cavity input.

[0035] In the frequency domain, a particularly effective mode of implementing the invention in phase I consists of the following steps: - the injection at the input of a plurality of signals gent,cav(fm)(t) ~ Re{exp(2iir.fm .t)} emitted at pure frequency fm on a plurality of M carriers fm separated by the frequency step ôf less than the inverse of the duration T assumed or previously estimated of the cavity impulse response Hcav(t); the set of channels of width fm.±ôf / 2 on the carrier frequencies fm covering a bandwidth greater by an oversampling factor K than that of the cavity [Fmin; Fmax] (fm = Fmin + m.ôf with m= 0,...,Ml; M > K.IFmax-Fminl / ôf; k > 1); - digital recording of the frequency responses Hcav(fm) of the output cavity for each of the pure frequency signals on the input fm carriers of cavity; - the frequency shift of -AF=-(Fmin+Fmax) / 2 to center the spectrum around the zero frequency; and - the inverse Fourier transform of the series of Hcav(fm) m=0,...,M-1 associated with suitable filtering known to those skilled in the art to obtain the time impulse response in digitized baseband Hcav>BB(m) at the output of the cavity on the number of samples M and the band K.IFmax-Fminl.

[0036] The advantage of this mode of implementation lies in particular in the fact of being able to use network analyzers with a very wide frequency range, to ultimately obtain a pulse estimate of the baseband cavity with significant oversampling factors k.

[0037] Hcav(n) and Hcav(fn) can then be directly reused in phase II.

[0038] The previously mentioned state of the art mainly describes implementations of the cavity calibration phases I and time reversal II by analog methods, which in practice prove to be quite inefficient and limit the compression gain to no more than 20 dB.

[0039] The invention makes it possible to very significantly improve these performances by adapting (for the very particular problem of generating impulsive waveforms by time reversal) digital techniques specifically adapted to improve all the steps of phase I and phase II of the method.

[0040] The calibration phases I and time reversal II of the cavity can also relate to additional analog elements of the transmission chain constituting with the cavity an analog sub-assembly, in which: - calibration phase I takes into account, in addition to the cavity, the additional analog elements upstream and / or downstream of the cavity for the determination of the impulse responses corresponding to the fifth signal Hcav (t) and to its digitized form Hcav (n) of the analog subassembly; - the reversal phase II takes into account, in addition to the cavity, the additional analog elements upstream and / or downstream of the cavity for the determination of the eighth signal SRetjE,cav(t) injected at the input of the additional analog elements upstream of the analog subassembly.

[0041] The fifth signal (Hcav(t) can be transposed and sampled in baseband to obtain a digital complex signal Hcav>BB(n) sampled centered around the zero frequency, by using a Hilbert transform, low-pass filtering, then baseband sampling at the sampling frequency Fe respecting the Shannon condition for the cavity bandwidth refocused on the zero frequency.

[0042] The frequency response signals Hcav(fm) to the fm carriers at the output of the sub- The analog set of the transmission chain can be frequency-shifted by the half-sum of the cavity frequency band terminals, then undergo an inverse Fourier transform to obtain the digitized baseband time impulse response Hcav>BB(ni) over the number of samples M.

[0043] The time reversal phase II of a transmitted signal may comprise step 11-1 of digital generation of the sixth complex returned signal in baseband Hr and,cav,BB(n) or HretjCaVjBB(m) corresponding to the reversal of the fifth complex signal HcaVjBB(n), HcaVjBB(ni) sampled centered around the zero frequency.

[0044] The time reversal phase II of a transmitted signal may comprise a step II-2 of filtering, truncation and digital modulation of the sixth complex returned baseband signal HretjCaVjBB(n), HretjCaVjBB(ni) to deliver a seventh simplified returned baseband signal H'retjCav>BB(n'), H'ret>caVjBB(m').

[0045] Step 11-2 of filtering, truncation and digital modulation of the sixth complex returned baseband signal Hretjcav,BB(n) to deliver a seventh simplified returned baseband signal H'retjcav,BB(n) can use a quasi-constant amplitude transformation, or a discrete phase state digital modulation of the BPSK or QPSK type.

[0046] Alternatively, step 11-2 of filtering, truncation and digital modulation of the sixth complex returned baseband signal Hretjcav,BB(n) to deliver a seventh simplified returned baseband signal H'retjcav,BB(n) may use a strictly constant amplitude transformation, or a 2- or 4-state MSK or CPM continuous phase state digital modulation.

[0047] In other words, the steps of phase II of reversal are as follows.

[0048] The generation phase 11-1 performs a direct reuse of the digitized versions of the amplifier and cavity chain responses from the calibration phase I, on carrier or after baseband filtering, to construct the returned digital signal Hret>cav(n) by the operation Hret>cav(n) = H*cav(Nln).

[0049] A particularly effective mode of implementation of the invention in phase II at the end of phase I including a transposition / digitization in baseband of the response / signature Hcav(t) of the cavity producing the complex signal Hcav>BB(n) sampled centered around the zero frequency, consists of the generation in baseband of the signal returned by the operation HretjCaVjBB(n) = H*cav>BB(Nln).

[0050] Step 11-2 of filtering, truncation and digital modulation of the samples of the sixth returned signal Hretjcav(n) to produce a simplified seventh approximate signal H ret,cav(H )•

[0051] This corresponds to an approximation of the returned signal Hretjcav(n), n=0.. .N-1 by a simplified signal H'retjCav(n'), n=0...N'-l N' <N - which promotes the control of the energy of the generated signal and its PAPR or "Peak to Average Power Ratio" in English, - which also aims for less complexity in generation and amplification (for example, an approximation by constant amplitude modulation makes it possible to work in the saturation regimes of the amplifiers inserted in the transmission chain).

[0052] These filtering, truncation, and digital modulations specific to the present invention are made particularly effective on the complex baseband signal Hret>cav >BB(n), to produce a simplified approximate signal H'ret>cav>BB(n) also in baseband before the following step of analog conversion, transposition to carrier and amplification.

[0053] Possible examples of digital modulation of the samples of the signal returned to baseband are as follows: Transformation Hret>caVjBB(n) —> H'ret>caVjBB(n') with quasi-constant amplitude (not strictly constant due to filtering). - BPSK modulation of amplitude A: for all n'=n, H'ret>cav>BB(n') = A.Signe{Re[Hret>caVjBB(n)]}. This corresponds to a digital implementation of the 1-bit or NRZ modeling of the returned signal, as illustrated in [Fig.2]: we code in the BPSK modulation at each sample n the half-plane corresponding to the sign of the real part of the impulse response (in baseband) returned from the cavity. - QPSK modulation of amplitude A: for all n'=n, H'ret>cav>BB(n') = A.Signe{Re[Hret>cav>BB(n)]} + Ai Signe {Im[Hret>cav>BB (n)]} In the QPSK modulation, at each sample n, the quadrant corresponding to the signs of the real part and the imaginary part of the complex impulse response (in baseband) returned from the cavity is coded. Transformation Hret,cav,BB(n) —> H'ret,cav,BB(n') with strictly constant amplitude (even with filtering): - Forcing constant amplitude A: for all n'=N, H'ret>cav>BB(n') = A.Hret>caVjBB(n) / IHretjCaVjBB(n)l MSK modulation, CPM 2 or 4 states.

[0054] Step 11-3 of analog conversion of the seventh simplified returned signal H'ret>cav (n), filtering and clipping, transposition and amplification on carrier, to produce an improved cavity drive signal Sret^,Cav(t) (11-3) in terms of: - energy, - peak power (PAPR limitation), and - adaptation to the cavity band.

[0055] The carrier signal wo=2jr.fo exciting the cavity is then written (excluding filtering and possible clippings) in the following form: For n'= O,...,N'-1 and t verifying (n'-l).Te< t < n'.Te ; SretÆ,cav(t)=Re[H'ret,cav,BB(n'Te)]*cos(wot)-Im[H'ret,cav,BB(n'Te)]*sin(wot)

[0056] Step 11-4 performs the injection of the eighth analog signal returned on carrier Sret ,E,cav(t) into the cavity.

[0057] Finally, step 11-5 performs the compression of the eighth signal by the cavity and controls the ninth compressed signal at the output Sretjs,cav(t).

[0058] The present invention has the following advantages: - Improved management of the digital-to-analog converter DAC by sampling in baseband BB; - Go beyond the limit of Shannon theory (generation with Faster Than Nyquist processes used in communication); - Reduction of synthesis costs and digitization / analysis of signals by using SDR cards; - Significantly reduced weight / volume ratio; - Reduction of constraints on the amplifier, peak power / average power ratio greatly reduced, relaxed dynamics; - Better overall control of output waveforms; - "Arbitrary" waveforms at output by time-shifted serial generation and modulation of the excitation signals H'retjcav(n) in the digital domain or SretjE,cav(t) in the analog domain.

Claims

Claims

1. Method for generating and transmitting a high-power signal composed of a plurality of Dirac distribution type signals, by means of a system for generating and transmitting a high-power signal provided with a reverberant cavity, and comprising a phase of calibrating the cavity over a calibration duration (T) and a phase of time reversal of a signal before injection into the cavity, in which: the cavity calibration phase (I) over the calibration duration (T) includes the steps of: - generation of a first digital signal in the time domain of the Dirac distribution type (1-1); - conversion of the first signal into a second analog signal, then transposition on carrier of the second signal into a third analog signal, and amplification of the third signal on the frequency band of the cavity into a fourth analog signal (1-2); - injection of the fourth signal into the cavity (1-3); and - measurement, recording over the calibration duration (T) and learning of a fifth analog signal corresponding to the impulse response (Hcav(t)) of the cavity over the calibration duration (T); and digitization of the impulse response (Hcav(t)) in the form of samples (Hcav(n)) at a sampling frequency (Fe) respecting the Shannon condition for the bandwidth ([Fmin; Fmax]) of the cavity (1-4); the time reversal phase (II) of the signal injected into the cavity over a reversal duration (T1) less than or equal to the calibration duration (T) comprises the steps of: - generation in the time domain of a sixth digital returned signal (Hretjcav(n)) corresponding to the reversal of the fifth signal (Hcav(t)) taken in its digitalized form (H cav(n)) (II-1); - filtering, truncation and digital modulation of the sixth signal to deliver an improved seventh digital returned signal (H'ret>cav(n')) (II-2); - analog conversion, filtering, clipping, transposition to carrier and amplification, of the seventh improved digitized returned signal (H'retjcav(n)), to deliver an eighth improved analog returned attack signal (SretjE,cav(t)) at the input of the cavity (II-3); - injection of the eighth signal (SretjE,cav(t)) into the cavity (II-4); and - emission by the cavity of a ninth analog signal (Sret,s,cav (t)), corresponding to the resultant of the eighth signal (SretjE,cav (t)) after compression in said cavity (II-5).

2. Method according to claim 1, in which the phase of calibrating the cavity (I) further comprises a step of measuring and learning the cavity in the frequency domain (I-4a): - by injecting at the input a plurality of pure frequency signals emitted on a plurality of carriers separated by a frequency step less than the inverse of the calibration duration (T) on which the cavity is calibrated, and in sufficient number (M) to cover a bandwidth greater by an oversampling factor than the bandwidth of the cavity; - by recording the frequency responses (Hcav(fm)) at the cavity output for each of the pure frequency signals on the carriers (fm) injected at the cavity input.

3. Method according to one of claims 1 or 2 in which the calibration (I) and time reversal (II) phases of the cavity also relate to additional analog elements of the transmission chain constituting with the cavity an analog sub-assembly, in which: - the calibration phase (I) takes into account, in addition to the cavity, the additional analog elements upstream and / or downstream of the cavity for the determination of the impulse responses corresponding to the fifth signal (Hcav(t)) and its digitized form (Hcav(n)) of the analog subassembly; - the reversal phase (II) takes into account, in addition to the cavity, the additional analog elements upstream and / or downstream of the cavity for the determination of the eighth signal (Sret,E,cav(t)) injected into the input of the additional analog elements upstream of the analog subassembly.

4. Method according to one of claims 1 to 3, in which the fifth signal ((Hcav(t)) is transposed and sampled in baseband to obtain a digital complex signal (Hcav>BB(n)) sampled centered around the zero frequency, by using a Hilbert transformation, low-pass filtering, then baseband sampling at the sampling frequency (Fe) respecting the Shannon condition for the bandwidth of the cavity refocused on the zero frequency.

5. Method according to claim 3 or 4, in which the frequency response signals (Hcav(fm)) at the output of the analog subset of the transmission chain are frequency shifted by the half-sum of the terminals of the frequency band of the cavity, then undergo an inverse Fourier transform to obtain the digitized baseband time impulse response (Hcav>BB(m)) over the number of samples (M).

6. Method according to claim 4 or 5, in which the time reversal phase (II) of a transmitted signal comprises the step (II-1) of digital generation of the sixth complex returned signal in baseband (Hretjcav,BB(n) or HretjCav,BB(ni)) corresponding to the reversal of the fifth complex signal (Hcav>BB(n), HcaVjBB(ni)) sampled centered around the zero frequency.

7. Method according to claim 6, in which the time reversal phase (II) of a transmitted signal comprises a step (II-2) of filtering, truncation and digital modulation of the sixth complex returned baseband signal (HretjCav,BB(n), HretjCav,BB(ni)) to deliver a seventh simplified returned baseband signal (H'ret>caVjBB(n'), H' ret,cav,BB(m ))•

8. The method of claim 7, wherein the step (II-2) of filtering, truncating and digitally modulating the sixth complex returned baseband signal (Hret>caVjBB(n)) to deliver a seventh simplified returned baseband signal (H'ret>caVjBB(n)) uses a quasi-constant amplitude transformation, or a discrete phase state digital modulation of the BPSK or QPSK type.

9. Method according to claim 7, in which the step (II-2) of filtering, truncation and digital modulation of the sixth complex returned baseband signal (HretjCaVjBB(n)) to deliver a seventh simplified returned baseband signal (H'retjCaVjBB(n)) uses a strictly constant amplitude transform, or a 2- or 4-state MSK or CPM continuous phase state digital modulation.

Images