Method for generating a multi-tone radio frequency signal and associated radar transceiver device

Abstract

Method for generating a multi-tone radio frequency signal and associated radar transceiver device. This method for generating a radio frequency signal comprising N distinct elementary frequency components includes at least one transmission-reception, in calibration mode, of a calibration radio frequency signal and obtaining a spectral transformation of said calibration radio frequency signal into a line spectrum, performed by a processing module of the radar transceiver device, and a calibration of attenuation signals, comprising: - a determination (38), by measurement in the line spectrum or by calculation, of at least one intermodulation frequency of an intermodulation line to be attenuated, - for each intermodulation frequency, a determination (40) of amplitude and phase parameters of a corresponding attenuation signal, as a function of the amplitude levels of the lines in the line spectrum.the attenuation signal having a frequency equal to said intermodulation frequency. The generated multi-tone radio frequency signal (50) comprises respectively said N components at elementary frequencies and said attenuation signals. Figure for the abbreviation: Figure 3,

Description

Title of the invention: Method for generating a multi-tone radio frequency signal and associated radar transceiver device

[0001] The present invention relates to a method for generating a multi-tone radio frequency signal, the radio frequency signal comprising at least two distinct elementary frequency components.

[0002] The invention also relates to an associated radar transceiver device.

[0003] The invention lies in the field of radio frequency signal processing, and finds applications in radar systems (acronym for "Radio Detection And Ranging").

[0004] In many applications, for various types of radar systems, it is useful to generate radio frequency signals, pulsed, continuous or frequency modulated continuous wave (or FMCW from the English "Frequency Modulated Continuous Wave"), comprising two or more distinct frequency components, also called multi-tone radio frequency signals.

[0005] However, it is known that when a multi-tone radio frequency signal is processed by a system with a non-linear transfer function, which is typically the case for amplifiers in certain amplification ranges, an intermodulation phenomenon occurs, and in the spectral domain, spurious lines, also called intermodulation lines, appear at so-called intermodulation frequencies. In particular, principal intermodulation lines appear at intermodulation frequencies close to the useful frequencies of the radio frequency signal, these principal intermodulation lines having a non-negligible amplitude level.Other intermodulation lines, distant from the useful frequencies of the radio frequency signal, can be removed or inhibited by a radio frequency filter known in the state of the art, but intermodulation lines of intermodulation frequencies close to the useful frequencies of the signal, located in an interval defined by the bandwidth of the applied filter, are difficult to filter, due to the limited Q factor and / or the slopes of the applied filter.

[0006] This is particularly troublesome for application in a radar system configured specifically to perform Doppler processing of RADAR targets, because spectral lines at intermodulation frequencies do not correspond to radio signals reflected by the target, and therefore may create false RADAR echoes or false alarms.

[0007] Since this intermodulation phenomenon is known, various solutions have been considered.

[0008] It has been envisaged to generate radio frequency signals of distinct frequencies independently, and to transmit these radio frequency signals either with a multiport radiating element or by using several distinct radiating elements. However, the resulting radio frequency transmitters are bulky and relatively complex.

[0009] Other known solutions involve processing radio frequency signals after reception in order to filter or attenuate disturbances due to intermodulation. These solutions are particularly complex because the frequencies of the echoes are not known a priori, and therefore it is necessary to analyze each line to determine whether it can originate from an intermodulation product of two other lines.

[0010] The invention aims to provide a method and device for generating multi-frequency radio frequency signals with attenuation of selected intermodulation lines.

[0011] To this end, the invention relates to a method for generating a multi-tone radio frequency signal, implemented by a radar transceiver device, the radio frequency signal comprising N distinct elementary frequency components, N being greater than or equal to two, the method comprising at least one transmission-reception, in calibration mode, of a calibration radio frequency signal with N frequency components and obtaining a spectral transformation of said calibration radio frequency signal into a line spectrum, the spectral transformation being performed by a processing module of the radar transceiver device, the line spectrum comprising useful lines at the elementary frequencies and intermodulation lines at intermodulation frequencies, each line having an associated amplitude level. This method includes a calibration of attenuation signals, implemented by a computing processor, said calibration comprising:

[0012] - a determination, by measurement in the line spectrum or by calculation, of at least one intermodulation frequency of an intermodulation line to be attenuated,

[0013] - for each intermodulation frequency, a determination of parameters amplitude and phase of an attenuation signal of the intermodulation line at said intermodulation frequency, as a function of the amplitude levels of the lines of said line spectrum, the attenuation signal having a frequency equal to said intermodulation frequency,

[0014] -the method further comprising a generation of a multi-tone radio frequency signal comprising respectively said N components at elementary frequencies and said attenuation signals, each attenuation signal being characterized by said determined frequency, amplitude and phase parameters.

[0015] Advantageously, the attenuation signals make it possible to strongly attenuate the spectral lines at the intermodulation frequencies being processed and to obtain a signal Multi-tone radio frequency is transmitted with a corrected spectrum, the useful spectral lines corresponding to the elementary frequencies having amplitude levels much higher than the spectral lines corresponding to the intermodulation frequencies in the corrected spectrum. Advantageously, the multi-tone radio frequency signal is improved in the transmitting part of a radar transceiver device, using radar processing modules.

[0016] According to other advantageous aspects of the invention, the method for generating a multi-tone radio frequency signal comprises one or more of the following features, taken individually or in all technically possible combinations.

[0017] The determination of parameters includes, for an attenuation signal at a given intermodulation frequency, a determination of the phase of the attenuation signal as a function of a phase reference, the phase of the attenuation signal taking a value in a selected phase domain comprising the phase reference, said value corresponding to a minimum amplitude level of a line at said given intermodulation frequency in the line spectrum.

[0018] The phase determination step includes an iteration, for a plurality of phase values ​​of the phase domain, of the steps of: generation of a first test attenuation signal, of fixed amplitude and frequency and of phase equal to said phase value, a transmission-reception, in calibration mode, of a multi-tone radio frequency signal corrected by adding said first test attenuation signal, a measurement and a storage of the amplitude level of a spectral line at the given intermodulation frequency of the line spectrum of the corrected multi-tone radio frequency signal.

[0019] The reference phase is the phase of one of the elementary components.

[0020] The method further comprises a determination of an amplitude of the attenuation signal in an amplitude attenuation range, the amplitude of the attenuation signal taking a value in said amplitude attenuation range, said value corresponding to a minimum amplitude level of a line at said given intermodulation frequency in the line spectrum.

[0021] The amplitude determination step includes an iteration, for a plurality of amplitude values ​​in the amplitude attenuation domain, of the steps of: generating a second test attenuation signal, of fixed frequency and phase and of amplitude equal to said amplitude value, a transmission-reception, in calibration mode, of a multi-tone radio frequency signal corrected by adding said second test attenuation signal, a measurement and storage of the amplitude level of a spectral line at the given intermodulation frequency of the line spectrum of the corrected multi-tone radio frequency signal.

[0022] The determination of the intermodulation frequencies is carried out by calculating a set of intermodulation frequencies as a function of distinct elementary frequencies.

[0023] The intermodulation frequency set comprises a first subset of frequencies comprising combinations of pairs of fundamental frequencies F y F j of the form:

[0024] for any pair of distinct indices i,j where 1 < i, J < N

[0025] The intermodulation frequency set further comprises a second subset comprising combinations of elementary frequencies, each combination comprising a sum of Nl distinct elementary frequencies from which is subtracted the remaining elementary frequency among the N elementary frequencies.

[0026] The determination of at least one intermodulation frequency is carried out by measuring in the line spectrum, within a predetermined filtering interval, lines whose amplitude level is greater than or equal to a predetermined amplitude level threshold.

[0027] The invention also relates to a radio frequency transceiver radar device configured to generate a multi-tone radio frequency signal comprising N distinct elementary frequency components, N being greater than or equal to two, the device being configured to perform, in a self-test mode, at least one transmission and reception of a calibration radio frequency signal with N frequency components and to obtain a spectral transformation of said calibration radio frequency signal into a line spectrum, the spectral transformation being performed by a processing module of the radar transceiver device, the line spectrum comprising useful lines at the elementary frequencies and intermodulation lines at intermodulation frequencies, each line having an associated amplitude level, the device comprising a calibration module for attenuation signals configured For :

[0028] - determine, by measurement in the line spectrum or by calculation, at least one intermodulation frequency of an intermodulation line to be attenuated,

[0029] - determine amplitude and phase parameters of an attenuation signal of the intermodulation line at said intermodulation frequency, as a function of the amplitude levels of the lines in said line spectrum, the attenuation signal having a frequency equal to said intermodulation frequency,

[0030] - the device being further configured to generate a multi-tone radio frequency signal comprising said N components respectively at elementary frequencies and said attenuation signals, each attenuation signal being characterized by said determined frequency, amplitude and phase parameters.

[0031] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0032] [Fig-1] the [Fig.1] is a theoretical diagram of a line spectrum of a 2-tone signal;

[0033] [Fig.2] [Fig.2] is a synoptic diagram of the main functional blocks of a device radar transceiver implementing a method for generating a radio frequency signal according to an embodiment;

[0034] [Fig.3] [Fig.3] is a flowchart of the main steps of a process of generation of a radio frequency signal according to an embodiment;

[0035] [Fig.4] [Fig.4] is an example of a line spectrum with 2 elementary frequencies before and after the addition of attenuation signals;

[0036] [Fig.5] [Fig.5] is a schematic example of a 3-frequency line spectrum elementary before and after the addition of attenuation signals.

[0037] The invention applies to the generation of a radio frequency signal by a radar, the radio frequency signal comprising N distinct frequency components, called distinct elementary frequencies, such a signal also being called a multi-tone signal, with N an integer greater than or equal to two.

[0038] In the following description, the case where N=2 is described in detail, for the generation of a radio frequency signal e(f), which is a two-tone signal, composed of two respective elementary frequency components Fi and F2, each elementary frequency component being a sinusoidal signal:

[0039] [Math.l] e(t)=x(t)+y(t)

[0040] x(t) = A-cos(t), «!= 2nF r

[0041] y(t) =B-COS(CO2«t), W2 = 22lF2

[0042] The signals x(t) and y(t) have a common phase.

[0043] It is theoretically known that in a system containing nonlinearities or time variations, additional frequency components appear, which are not harmonics of the radio frequency signal e(t). The additional frequency components are also called intermodulation frequencies; they are of the type H1F 11F ni and n being integers.

[0044] In particular, for the case N=2, two principal intermodulation frequencies are distinguished, respectively:

[0045] [Math.2] F3 = 2F2-F1

[0046] F4 = 2F1-F2

[0047] The non-linear system has a polynomial transfer function:

[0048] [Math.3] S(t) = K1e(t) + (t) + K3e 3 (t) + ... + K q e q (t)

[0049] Theoretical spectral lines of the signal S(t) defined in [MATH 3] are shown in Figure 1, for a particular case in which the respective components of the signal e(t) are of the same amplitude.

[0050] The intermodulation lines at frequencies F3 and F4 are close to the "useful" spectral lines at elementary frequencies Fi and F2.

[0051] In theory, the non-linear behavior is characterized by the third-order intercept point, IP3, which is the intercept point of the lines whose slopes are the first- and third-order coefficients of the polynomial approximation S(t) of the non-linear system.

[0052] It is demonstrated that the IP3 point is located 9.6 dB above the compression point at IdB in 1 tone. The amplitude levels of the intermodulation lines at F3 and F4 are theoretically calculable as a function of IP3 and the levels of the fundamental lines.

[0053] The SI spectrum illustrated in [Fig. 1] is a theoretical spectrum, represented by spectral lines in a graph illustrating the amplitude level (e.g., the power) as a function of frequency. The amplitude levels are specified as a function of the amplitudes A, B of the components x(t), y(t) at frequencies Fb F2 and the coefficients K3 of the polynomial transfer function S(t) of the system.

[0054] In the example of [Fig. 1], the lines corresponding to the elementary frequencies FB F2 are at the same level, i.e. KiA=K2B. The "BF spectrum" and "H2 spectrum" parts of the SI spectrum are likely to be eliminated by filtering.

[0055] The "H1 spectrum" part of the SI spectrum, which contains the intermodulation lines at the intermodulation frequencies F3 and F4, also contains the lines at the respective elementary frequencies Fi and F2.

[0056] The "H1 spectrum" portion corresponds to a frequency range, comprising the lowest and highest of the elementary frequencies, the width of the range depending on the bandwidth of the applied filter and the quality factor of the applied filter. This frequency range will be referred to as the "filtering range" in the remainder of this description.

[0057] In the present invention, it is proposed to modify the radio frequency signal to be emitted before its transmission, in the transmitting part of the radar transceiver device, by adding so-called attenuation signals, each attenuation signal being associated with a frequency of a line to be attenuated, called the intermodulation frequency. The intermodulation frequencies, located in the filtering interval, are part of a The intermodulation frequencies are a set of frequencies determined by measurement in the signal's line spectrum or by calculation. Each attenuation signal is designed to correct (attenuate or cancel) the intermodulation spectral line at its associated intermodulation frequency. The radio frequency signal spectrum is thus corrected, meaning that the amplitude levels of the lines at the chosen intermodulation frequencies are significantly reduced.

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066] Thus, in the case with two elementary frequencies Fi and F2, the process includes the generation of an attenuation signal of an attenuation signal Respite) [Math.4] Repfy at the intermodulation frequency F3, and at the intermodulation frequency F4 Rep^t) = C*cos[ (2^-(¾) • t + n] = C«cos[w3*t + u] Rep2(t) =D*cos[ (2w2-wJ • ü + n] = D«cos[ûj4« t + n] The respective attenuation signals at the intermodulation frequency F3, And rep2(ü) at the intermodulation frequency F4 are in opposite phase (e.g. phase-shifted by ji) with respect to the elementary components x(t) and y(t) of the signal e(t). When the elementary components are of the same magnitude, the same is true, in theory, for the respective attenuation signals D P1 (t) el ^p2(t). Advantageously, it is proposed to use a calibration mode (also called self-test mode) of a radar transceiver device in order to perform intermodulation line attenuation adapted to the radar itself, and potentially evolving during the use of the radar to take into account in particular the non-linearities actually introduced into the transmitting radar transceiver device. In an embodiment described with reference to [Fig.2], the invention is implemented in a radar transceiver device 2, also referred to as radar 2 hereafter. The invention is applicable to all types of radar devices. The radar 2 includes a multi-tone radio frequency signal generation module 4. Preferably, the multi-tone radio frequency signal generation module 4 is configured to generate a maximum number Nmax of sinusoidal signals of distinct frequencies Fi...FNmax. The maximum number Nmax is advantageously greater than the number N of elementary frequencies (or useful frequencies) of the radio frequency signal to be transmitted for a given application.

[0067] In one embodiment, the multi-tone radio frequency signal generation module 4 is a direct digital synthesis (DDS) module as described in published patent FR3126264 Bl.

[0068] The radar 2 includes an emission processing chain 6, which introduces non-linear processing of the radio frequency signal, and a transmit / receive antenna 8. The emission processing chain 6 includes in particular at least one amplifier.

[0069] The radar 2 further comprises a receiver processing chain 10, and a radar processing module 12. The receiver processing chain 10 includes in particular at least one amplifier.

[0070] The radar processing module 12 implements a spectrum calculation module 14 of a received radio frequency signal, the spectrum calculation module 14 implementing a discrete Fourier transform FFT.

[0071] Furthermore, the radar 2 is configured to operate, on command, in a calibration (or self-test) mode. In such a calibration mode, the transmit 6 and receive 10 processing chains are used in a coupled manner, using a radio frequency coupler 7 (shown in dashed lines in [Fig. 2]), with the switch 9 closed in calibration mode. In nominal operation, the switch 9 is open.

[0072] In calibration mode, radar 2 performs a transmission and reception test, which allows various operating parameters of radar 2 to be calibrated.

[0073] The use of the transmitting 6 and receiving 10 processing chains in calibration mode without causing interference is known to those skilled in the art. To avoid interfering with measurements taken using the receiver, the level of the spectrum emitted by the radar is attenuated so that the levels of the intermodulation lines produced by the receiver are negligible compared to those produced by the transmitter. The attenuation of the emitted spectrum level before it enters the receiving chain 10 is achieved using the radio frequency coupler 7.

[0074] In addition to the classic operations enabling calibration of operating parameters, the radar 2 includes, according to the present invention, a calibration module 16 of the signal parameters of attenuation of intermodulation lines at selected intermodulation frequencies.

[0075] Advantageously, for a radio frequency signal to be emitted at N elementary frequencies, Fi to FN (or signal at N tones), the intermodulation frequencies, at which the intermodulation lines appear, in the filtering interval, are determined, by measurement, using in particular the radar processing module 12 or by calculation.

[0076] The determined intermodulation frequencies form a set of intermodulation frequencies.

[0077] The set of intermodulation frequencies chosen includes intermodulation frequencies considered to be close, and which may disrupt the radar processing quality in a radar receiving the emitted radio frequency signal.

[0078] The intermodulation frequency set consists of P distinct intermodulation frequencies, or in other words, has a cardinality equal to P, P being an integer.

[0079] The calibration module 16 is configured to implement a determination of attenuation signal parameters. For each determined intermodulation frequency, the calibration module 16 is configured to implement a unit 18 for determining the amplitude of the attenuation signal as a function of the amplitude levels of the calculated line spectrum and a unit 20 for determining the phase of the attenuation signal as a function of a phase reference, for example, a phase reference associated with one of the elementary components. For example, the phase reference is the common phase of the elementary components x(t), y(t).

[0080] The calibration module 16 is for example implemented by a processor or a microcontroller 15, associated with an electronic memory 17, of the radar 2. The modules 18, 20 are for example implemented in the form of software instructions forming a computer program, which, when executed by a programmable electronic device, implements the determination of parameters of the attenuation signals.

[0081] The parameters of the attenuation signals are, in one embodiment, temporarily stored in the electronic memory 17.

[0082] Alternatively or in addition, the parameters of the attenuation signals are transmitted as they are carried out, in association with the intermodulation frequency considered, to the generation module 4, and stored in an electronic memory of the generation module 4.

[0083] Alternatively, modules 18, 20 are each implemented as programmable logic components, such as FPGAs (Field Programmable Gate Arrays), microprocessors, GPGPUs (General-purpose Processing on graphics processing) components, or dedicated integrated circuits, such as ASICs (Application-Specific Integrated Circuits).

[0084] Figure 3 shows a block diagram of the main steps in a method for generating a radio frequency signal to be transmitted, implemented by a radar transceiver device. In one embodiment, the radio frequency signal comprises N distinct elementary frequency components. The N distinct elementary frequencies are the useful frequencies of the radio frequency signal.

[0085] The number N is greater than or equal to 2.

[0086] The method is implemented using the calibration mode of the radar transmitter-receiver device.

[0087] The method includes an initial generation step 30, by the radio frequency signal generation module, of a calibration radio frequency signal with N distinct elementary frequency components Fi to FN.

[0088] The process also includes an emission processing 32 followed by a reception processing 34 of the calibration radio frequency signal, to obtain a processed radio frequency signal, then a spectral transformation step 36 applied to the processed radio frequency signal to obtain a line spectrum.

[0089] As mentioned above, spectral transformation is part of the radar processing applied by radar processing module 12.

[0090] As explained above, the line spectrum includes useful lines (corresponding to the elementary frequencies) and intermodulation lines, located at intermodulation frequencies that can be calculated theoretically and measured by radar processing.

[0091] The method further includes a step 38 of determining a set of intermodulation frequencies to be considered Eintermod={Fim_i,...Fim_p}.

[0092] In a first embodiment, the determination 38 of the intermodulation frequencies is carried out by calculation, before steps 30 to 36, and the subset of intermodulation frequencies to be considered is stored. This first embodiment is used, for example, when the number N of elementary frequencies is less than or equal to 3, because the intermodulation lines are easily identifiable.

[0093] In a second embodiment, the determination 38 of the intermodulation frequencies corresponding to the intermodulation lines is carried out by measuring the frequencies corresponding to the spectral lines in the filtering interval, which do not correspond to the elementary frequencies Fi to FN and whose amplitude level exceeds a predetermined amplitude level threshold. This second embodiment is used, for example, when the number N of elementary frequencies is greater than 3.

[0094] According to one embodiment, the two embodiments are combined, the method comprising a theoretical calculation of the intermodulation frequencies, then a measurement in the line spectrum of the line levels at the theoretical intermodulation frequencies, in order to determine the intermodulation frequencies corresponding to lines whose amplitude level exceeds the predetermined amplitude level threshold.

[0095] The set of intermodulation frequencies to be considered {Fim_i,...FimP} comprises P intermodulation frequencies considered close to the elementary frequencies Fi to FN which are the useful frequencies, and therefore difficult to filter due in particular to the limitations of the quality factors of analog filters.

[0096] When the determination is carried out by calculation, for N=2 and for two elementary frequencies Fi and F2, the intermodulation frequencies are respectively: Fim_i=2Fi-F2 and Fim_2=2F2-Fi. Thus, in this case, P=2.

[0097] For N=3, for three distinct elementary frequencies FB F2, F3, the following intermodulation frequencies are considered as potentially located in the unfiltered area:

[0098] [Math.4] Enltermod = {2F2-Fi:2! , / -.:? / , F: 2FrF3;2F2-Fy 2F3-F2: F^+F^F^F^F^Fÿ -F,FF2 + F3}

[0099] Thus, for N=3, P=9, therefore the cardinality of the set of intermodulation frequencies is equal to 9.

[0100] In the general case, for N>2 elementary frequencies, the intermodulation frequency set comprises, on the one hand, a first subset Ei comprising the frequencies obtained by combinations of pairs of elementary frequencies:

[0101] [Math.5] ^l = {(2F I -F>2FrL)} for any pair of distinct indices i,j where [Math.5] 1<É j <N

[0102] The number of pairs is equal to -2 Q_ M n 1.2 -(N-2)(Nl)jV _ ( A — Zj(N-2fZ~ 1.2.. / 7V-2) — This is the cardinality of the EL subset

[0103] The intermodulation frequency set also includes other subsets of intermodulation signals with frequencies Fi(+ / -)Fj if >0, 2Fi, 2Fj, ..., but moreover, all these lines intermodulate each other, and some of these lines may pollute the HL spectrum

[0104] For example, a subset E2 with a high probability of polluting the spectrum H1 and comprising combinations of elementary frequencies of the sum type with only one negative element:

[0105] [Math.6] , For [Math.6] 1<Ï< N

[0106] where Si j = 1 if i = j, and dij = 0 if i j-

[0107] In fact, 6i j denotes the Kronecker function.

[0108] The equation [MATH 6] above indicates the sum of all the elementary frequencies, the sign (-) being applied only for the frequency j=i.

[0109] The cardinality of the subset E2 is N.

[0110] Thus, in the general case, the subset of intermodulation frequencies considered is the union of the subsets E1 and E2, and its cardinality is: [YES] [Math.7] P = N* (N-1)+N=N 2

[0112] When the determination 38 is implemented by measurement, the method includes an iteration, in the filtering interval corresponding to the spectrum Hl, of steps of: measurement 38 of a frequency Fim_j distinct from the elementary frequencies, corresponding to a line of level higher than a threshold level of predetermined amplitude, the frequency Fim_j then being stored in the set of intermodulation frequencies.

[0113] The amplitude level threshold is dependent on the filtering applied.

[0114] The method comprises, for each intermodulation frequency determined in step 38, determining 40 the parameters of an associated attenuation signal Repj(t). For each attenuation signal, the parameters include the frequency, phase, and amplitude, the frequency of the attenuation signal being equal to the intermodulation frequency Fim j

[0115] The phase and amplitude parameters are determined by measurement from the line spectrum.

[0116] Step 40 of determining the phase and amplitude parameters of an attenuation signal Repj(t) includes a substep 42 of determining the phase of the attenuation signal as a function of a phase reference Vq, for example, a phase reference associated with one of the elementary signals. In one embodiment, the phase Vcorr is readjusted step by step until the amplitude level of the corresponding intermodulation line is minimized.

[0117] The phase of the attenuation signal Repj(t), denoted (Pcorr> j, is phase-shifted by n with respect to the reference phase Wq.

[0118] Step 40 further includes a substep 44 of determining an amplitude Aconj of the attenuation signal Repj(t), by successive adjustments, as a function of the amplitude level Aj of the intermodulation line at the frequency Fim_j of a corrected line spectrum.

[0119] Embodiments of steps 42 for determining the phase of the attenuation signal Repj(t) and 44 for determining the amplitude of the attenuation signal Repj(t) are described below.

[0120] The attenuation signal Repj(t), characterized by the following parameters: frequency Fimj, amplitude Acorr., phase ^corr.j^, is a sinusoidal signal:

[0121] [Math.8] Rep^t) = A corrJ >

[0122] A signal may be affected by a delay: C = + with T the period of the signal

[0123] If a delay is present, the delay must be corrected in addition to the phase. However, advantageously, the use of DSN (Direct Digital Synthesis) makes it possible to generate signals that are coherent in phase and have zero delay between them.

[0124] The attenuation signal parameters associated with the intermodulation frequency FimJ are stored (step 46).

[0125] Steps 40, 46 are repeated for all intermodulation frequencies of the subset of intermodulation frequencies considered.

[0126] The process then includes a step 50 of generating a radio frequency signal to be emitted, by the generator module.

[0127] The radio frequency signal to be emitted is an N+P tone signal, composed of the sum of the components at elementary frequencies Fi to FN, constituting the useful signals, and the P attenuation signals at intermodulation frequencies Fim_i to Fim P.

[0128] Thus, the multi-tone radio frequency signal to be emitted is a "corrected" signal with respect to the N-tone frequency signal:

[0129] [Math.9] Gcorr (t)= ' ( ^“9 + SL^corrJ * J J- —

[0130] The spectrum of the radio frequency signal to be emitted thus formed is a corrected, improved spectrum, because it includes lines of lower amplitude levels than the intermodulation lines at the intermodulation frequencies of the subset of intermodulation frequencies {Fim_i,...,Fim P}.

[0131] In one embodiment, the determination 42 of the ^corrj phase is carried out as explained below, by successive measurements, in a calibration loop.

[0132] A phase domain is defined around the phase reference ^0, [ a™ 1 ; where A(O is a predetermined phase difference, understood by 0 example between 2° and 3°, for example equal to 2°.

[0133] To optimize Vcorr.j^ The process includes an iteration of generating first test attenuation signals, of fixed frequency and amplitude, and of variable phases in the phase domain.

[0134] The first test attenuation signal Repj(t), has a frequency equal to the intermodulation frequency Fimj, an amplitude equal to the amplitude Aj of the intermodulation line detected in the line spectrum at the frequency FimJ, and a phase (Pq in the phase domain.

[0135] The multi-tone radio frequency signal corrected by adding the first test attenuation signal is generated, transmitted and processed in reception in the calibration loop, and the amplitude level of the corresponding line in the line spectrum is measured and stored.

[0136] For the determination 42 of the optimized phase ^corrj, the minimum amplitude level in the line spectrum of the line corresponding to the first test attenuation signal Repj(t) is sought, iteratively, by applying one of the following methods: • either by plotting the amplitude curve, representing the amplitude level of the line corresponding to the first test attenuation signal Repj(t), as a function of the phase Vq incremented step by step, by a predetermined step A«p, in the phase domain . x 1 , and by identifying the point where the derivative is zero. • either by dichotomy, by searching for the minimum of the amplitude level of the corresponding line in the line spectrum on the phase domain [¢) - A(pÿ (p^ + Atp^] • The method of searching for a minimum by dichotomy is well known to those skilled in the art.

[0137] In one embodiment, as with the phase, the determination 44 of the amplitude of the attenuation signal is carried out by successive measurements in a calibration loop.

[0138] During the amplitude determination step 44, the amplitude of the attenuation signal is adjusted step by step until the amplitude level of the corresponding intermodulation line is minimized.

[0139] The amplitude of the signal to be corrected, Aq, is measured to be applied to the correction signal Repj(t), Acorrj

[0140] An amplitude attenuation domain is defined around Acorrj, [^ - AAq; Aq + / Mq], where A Aq is an amplitude margin, for example equal to IdB. Analogously to the phase determination step 42, the multi-tone radio frequency signal corrected by the addition of a second test attenuation signal is generated, transmitted, and processed at the receiver in the calibration loop, and the amplitude level of the corresponding line in the line spectrum is measured and stored. Each second test attenuation signal has a fixed frequency and phase, and an amplitude chosen within the amplitude attenuation domain.

[0141] The frequency is equal to the intermodulation frequency FimJ and the phase is equal to the optimized phase determined in step 42.

[0142] To optimize Acorrj, the minimum amplitude level in the line spectrum of the corrected signal, for the line corresponding to the second test attenuation signal Repj(t), is sought: • either by plotting the amplitude curve representing the amplitude level of the line corresponding to the second test signal Repj(t), as a function of the amplitude Aj incremented step by step in the predefined attenuation domain [Ao - / 14g* Ao + AAq], then identifying the point where the derivative is zero; • either by dichotomy by searching for the minimum amplitude level of the corresponding line in the line spectrum over the attenuation range An - AAn; An + AAnl of the amplitude around Ao. UU* V UJ

[0143] The amplitude Acorrj which minimizes the amplitude level of the corresponding line in the line spectrum is thus obtained.

[0144] It should be noted that other intermodulation lines are created in the line spectrum of the corrected signal, but all the intermodulation lines are of lower amplitude level, and therefore easier to inhibit at the radar processing level, as can be seen from the examples illustrated in Figures 4 and 5 respectively for the case N=2 and for the case N=3.

[0145] Figure 4 illustrates the S2 spectrum of a two-tone signal (amplitude level on a logarithmic scale as a function of frequency), and the resulting S2_corr spectrum after the addition of attenuation signals according to the method described above. In the example in Figure 4, the useful frequencies Fi and F2 are 50 Hz and 70 Hz respectively, and the corresponding 60 Hz and 62 Hz lines are visible in the S2 and S2_corr spectra.

[0146] The intermodulation lines 64, 66 at intermodulation frequencies F3=30Hz and F4=90Hz, present in the spectrum S2, are of the same spectral amplitude level.

[0147] After application of the attenuation signals, a corrected spectrum S2_corr is obtained, in which attenuation lines 63 and 65 replace the intermodulation lines 64 and 66 at the respective intermodulation frequencies F3 and F4 in the corrected spectrum S2_corr. The spectral amplitude level of the attenuation lines 63 and 65 is much lower than the spectral amplitude level of the initial intermodulation lines 64 and 66. An additional intermodulation line 67 appears in the spectrum S2_corr, but its spectral amplitude level is lower than the spectral amplitude level of the initial intermodulation lines 64 and 66.

[0148] In a practical application example, the transmission chain includes an amplifier having the following characteristics:

[0149] -gain = 32 dB

[0150] - Pc at -IdB in one tone = 2.5 W, or 34 dBm

[0151] hence IP3 = Pc at -IdB + 9.6 dB = 43.6 dBm.

[0152] During the implementation of the process, the amplifier of the emission chain is used at its maximum power, i.e. at the compression point marking the end of the linear zone of the admission curve Ps= f(Pe).

[0153] The 2-tone 1 dB compression point is theoretically located 14.4 dB below IP3.

[0154] The power of the output signal of the elementary lines at Fet F 2 is -^o = 29.2 dBm, (voltage amplitude on 50 Ohms Al = 12.86 Vcr^te).

[0155] The level of the intermodulation lines at F^ and F4 is at 43.2 dB below IP3.

[0156] Indeed, theoretically, the intermodulation lines are 28.8 dB below the 2-tone compression point or 43.2 dB below IP3 or

[0157] IP3 (dBm) = Po + (A) / 2 IP3 = Po + (P0-Pi) / 2 Pj= 3P0-2.IP3. Pi = approximately 0 dBm, (V1 =223 mVpeak).

[0158] As shown in Figure 1, the intermodulation lines at F3 and F^ depend only on the 1st and 3rd order terms of the polynomial approximation of the nonlinear amplifier, namely the coefficients Ki and K3.

[0159] The transfer function to be considered is therefore: [0!60] s(t) = e(t) + j^^With e(t) =

[0161] For a gain of 32 dB k1 = 39.8 (linear) hence . _ 12.86 _ nno tt II is demonstrated that the levels of the lines at 39.8 — vcrest F3 and F^est : = ^.K^d'où k3 = |^ = 8.823'

[0162] In this example, for elementary lines at 29.2dBm, the attenuation lines 63 and 65 have amplitude levels at -29.2 dBm while the intermodulation lines 64 and 66 are at level Pl=0dBm.

[0163] Fig. 5 schematically illustrates an example with 3 elementary frequencies (or 3 tones), respectively 390 Hz, 400 Hz and 480 Hz.

[0164] Spectrum S3 is the spectrum of the 3-component radio frequency signal with Fb F2, initial F3, and S3_corr is the spectrum of the radio frequency signal corrected after the addition of attenuation signals according to the described method. Spectrum S3 includes the elementary lines and the intermodulation lines before attenuation, and the corrected spectrum S3_corr includes the elementary lines and the attenuation and intermodulation lines after application of the method. The amplitude level of the attenuation and intermodulation lines the respective levels of the S3_corr spectrum are much lower than the levels of the intermodulation lines in the S3 spectrum.

[0165] Advantageously, the proposed process makes it possible to generate a multi-tone radio frequency signal improved by the addition of attenuation signals, whose line spectrum is corrected, comprising intermodulation lines of strongly attenuated amplitude levels.

[0166] Advantageously, the parameters of the attenuation signals are determined by measurements in calibration mode of the radar transceiver device, which makes it possible to take into consideration the non-linearities actually introduced in transmission by this radar transceiver device.

[0167] .

Claims

Demands

1. A method for generating a multi-tone radio frequency signal, implemented by a radar transceiver device, the radio frequency signal having N distinct elementary frequency components, N being greater than or equal to two, the method comprising at least one transmission-reception, in calibration mode, of a calibration radio frequency signal with N frequency components and obtaining a spectral transformation of said calibration radio frequency signal into a line spectrum, the spectral transformation being performed by a processing module of the radar transceiver device, the line spectrum comprising useful lines at the elementary frequencies and intermodulation lines at intermodulation frequencies, each line having an associated amplitude level, the method being characterized in that it comprises a calibration of attenuation signals, implemented by a computing processor,said calibration comprising: - a determination (38), by measurement in the line spectrum or by calculation, of at least one intermodulation frequency of an intermodulation line to be attenuated, - for each intermodulation frequency, a determination (40) of amplitude and phase parameters of an attenuation signal of the intermodulation line at said intermodulation frequency, as a function of the amplitude levels of the lines in said line spectrum, the attenuation signal having a frequency equal to said intermodulation frequency, - the method further comprising a generation (50) of a multi-tone radio frequency signal comprising respectively said N components at elementary frequencies and said attenuation signals, each attenuation signal being characterized by said determined frequency, amplitude and phase parameters.

2. A method according to claim 1, wherein the determination (40) of parameters comprising, for an attenuation signal at a given intermodulation frequency, a determination (42) of the phase of the attenuation signal as a function of a phase reference, the phase of the attenuation signal taking a value in a selected phase range comprising the phase reference, said value corresponding to a minimum amplitude level of a line at said given intermodulation frequency in the line spectrum.

3. A method according to claim 2, wherein the phase determination step (42) comprises an iteration, for a plurality of phase values ​​of the phase domain, of the steps of: generating a first test attenuation signal, of fixed amplitude and frequency and of phase equal to said phase value, transmitting and receiving, in calibration mode, a multi-tone radio frequency signal corrected by adding said first test attenuation signal, measuring and storing the amplitude level of a spectral line at the given intermodulation frequency of the line spectrum of the corrected multi-tone radio frequency signal.

4. A method according to any one of claims 2 or 3, comprising a determination (44) of an amplitude of the attenuation signal in an amplitude attenuation range, the amplitude of the attenuation signal taking a value in said amplitude attenuation range, said value corresponding to a minimum amplitude level of a line at said given intermodulation frequency in the line spectrum.

5. A method according to claim 4, wherein the amplitude determination step (44) comprises an iteration, for a plurality of amplitude values ​​in the amplitude attenuation range, of the steps of: generating a second test attenuation signal, of fixed frequency and phase and of amplitude equal to said amplitude value, transmitting and receiving, in calibration mode, a multi-tone radio frequency signal corrected by adding said second test attenuation signal, measuring and storing the amplitude level of a spectral line at the given intermodulation frequency of the line spectrum of the corrected multi-tone radio frequency signal.

6. A method according to any one of claims 1 to 5, wherein the determination (38) of the intermodulation frequencies is carried out by calculating a set of intermodulation frequencies as a function of distinct elementary frequencies.

7. A method according to claim 6, wherein the intermodulation frequency set comprises a first subset of frequencies comprising combinations of pairs of fundamental frequencies F p Fj of the form: = 2 / ^-27)} For any pair of distinct indices i,j where 1 < i, j < N

8. A method according to claim 7, wherein the intermodulation frequency set further comprises a second subset comprising combinations of elementary frequencies, each combination comprising a sum of Nl distinct elementary frequencies from which is subtracted the remaining elementary frequency among the N elementary frequencies.

9. A method according to any one of claims 1 or 5, wherein the determination (38) of at least one intermodulation frequency is carried out by measuring in the line spectrum, within a predetermined filtering interval, lines of amplitude level greater than or equal to a predetermined amplitude level threshold.

10. A radar transceiver device (2) configured to generate a multi-tone radio frequency signal comprising N distinct elementary frequency components, N being greater than or equal to two, the device being configured to perform, in a self-test mode, at least one transmission-reception of a calibration radio frequency signal with N frequency components and to obtain a spectral transformation of said calibration radio frequency signal into a line spectrum, the spectral transformation being performed by a processing module of the radar transceiver device, the line spectrum comprising useful lines at the elementary frequencies and intermodulation lines at intermodulation frequencies, each line having an associated amplitude level, the device comprising a calibration module (16) for attenuation signals configured to: - determine, by measurement in the line spectrum or by calculation,at least one intermodulation frequency of an intermodulation line to be attenuated, - determine amplitude and phase parameters of an attenuation signal of the intermodulation line at said intermodulation frequency, as a function of the amplitude levels of the lines, of said line spectrum, the attenuation signal having a frequency equal to said intermodulation frequency, -the device (2) being further configured to generate a multi-tone radio frequency signal comprising respectively said N components at elementary frequencies and said attenuation signals, each attenuation signal being characterized by said determined frequency, amplitude and phase parameters.

Images