Multi-transmission radar measuring device using time-frequency space distribution

Abstract

The invention relates to a radar measuring device (10) with frequency modulation and continuous transmission comprising: a generator (11) configured to generate N first periodic radar signals (20), the frequency of each of said first periodic radar signals varying linearly as a function of time, in a frequency band B, over sections Tx of a part Tframe of a period T, the frequencies of said first periodic radar signals (20) being different from each other at each instant of the part Tframe; N transmitting antennas (12), M receiving antennas (13), each receiving antenna being configured to receive a signal comprising echoes (21) of the first periodic radar signals; a receiving circuit (14) configured to: calculate, from the M signals (22), a distance and / or a radial speed and / or an angle, associated with a reflector detected by the radar measuring device (10). Figure for the abstract: [Fig. 4]

Description

Title of the invention: Multi-transmission path radar measuring device using time-frequency space distribution Technical field of the invention

[0001] The invention relates to radar applications with several transmission and reception channels. The invention relates in particular to a radar measuring device forming a radar transceiver system offering distance measurement, angular position measurement, low power consumption and a high signal-to-noise ratio. Prior art

[0002] The FMCW (Frequency Modulated Continuous Waveform) radar approach is based on the transmission and reception of continuous frequency modulated signals. This approach has the following advantages over UWB (Ultra Wide Band) radar approaches which are based on the transmission of pulses:

[0003] - low computational complexity, due to the fact that this approach relies on converters at low sampling rate;

[0004] - simplicity of generation of waveforms respecting an emission mask spectral as imposed by radio standards;

[0005] - low instantaneous transmission power for an equivalent signal-to-noise ratio.

[0006] The FMCW radar approach makes it possible to determine the distance between a radar device and one or more reflectors. A reflector is understood to mean an object reflecting the radar wave. This approach also makes it possible to determine the radial component of a relative velocity between the radar device and the reflector, in particular by using the Doppler effect.

[0007] [Fig. 1] is a representation of an example of a periodic FMCW radar signal and an echo in a frequency versus time graph. The frequency of the periodic FMCW radar signal increases linearly over a frequency band B for a duration T^e. The frequency of the periodic FMCW radar signal evolves periodically over a period T. After a flight time r, an echo of the periodic FMCW radar signal is received. The frequency of the echo of the periodic FMCW radar signal follows the same evolution as the frequency of the periodic FMCW radar signal. The difference between the instantaneous frequencies of the periodic FMCW radar signal and its echo, denoted IF, can be determined in particular using an FFT (Fast Fourier Transform) and makes it possible to calculate the flight time r and to deduce therefrom the distance between the FMCW radar device and the reflector at the origin of the echo considered. The distance D as a function of the flight time is calculated as follows:

[0008] [Math.l] D— CX T — 2

[0009] c being the speed of light.

[0010] The FMCW approach can be used in conjunction with a so-called SIMO (“Single input multiple output”) radar approach or a MIMO (“Multiple Input Multiple Output”) approach in order to determine, without performing a radar scan, an angle between a direction of a radar device and a direction of a reflector.

[0011] The SIMO and MIMO approaches use the phase difference, of the same wave reflected by a reflector, between several receiving antennas in order to determine this angle also called AOA (“Angle Of Arrival”). In the SIMO approach, the angular resolution, that is to say the smallest difference that can be distinguished between the AOA of two reflectors, is directly linked to the number of receiving antennas, for example a SIMO radar comprising four receiving antennas allows an angular resolution of approximately thirty degrees while a SIMO radar comprising eight receiving antennas allows an angular resolution of approximately fifteen degrees. However, each receiving antenna requires a dedicated processing chain, including in particular an LNA (“Low Noise Amplifier”), a mixer, a filter and an ADC (“Analogue to Digital Converter”).Increasing the angular resolution of a SIMO radar therefore comes at the expense of complexity, bulk due to the size of the antenna array and the consumption of the radar device. To overcome this limitation, the MIMO approach proposes to increase the angular resolution by increasing the number of transmitting antennas, for example, a MIMO radar device comprising two transmitting antennas and four receiving antennas allows an angular resolution of approximately 15 degrees. However, this approach requires distinguishing in the signal received by a receiving antenna the reflected waves, also called echoes, coming from each transmitting antenna.

[0012] [Fig.2] is a schematic representation of an example of a transmitting and receiving antenna arrangement according to the SIMO and MIMO approaches. An angle 0 is the angle formed between a y direction of a SIMO or MIMO radar measuring device and the direction of a reflector, 0 is the AOA. The upper part of the figure shows an example of a SIMO architecture composed of a transmitting antenna and 4 receiving antennas, each receiving antenna is separated by a distance d. The radar signal received by one antenna has traveled an additional distance dsin(0) compared to the adjacent receiving antenna. This additional distance causes a phase shift between the signals received by each of the transmitting antennas. This phase shift can be determined using an FFT called "angle FFT" and then used to determine 0. The lower part of the figure shows an example of a MIMO architecture composed of two transmitting antennas and 4 receiving antennas. The two transmitting antennas are separated by a distance 4d. An echo of the signal emitted by the second transmitting antenna will therefore have traveled an additional distance of 4dsin(0) compared to an echo of the signal emitted by the first transmitting antenna.

[0013] One way of distinguishing the echoes from the different transmitting antennas is called TDM ("Time Division Multiplexing"). A TDM-MIMO radar device transmits a frame made up of several time slots, each time slot is transmitted by a separate transmitting antenna, in this way the different transmitting antennas do not transmit simultaneously and an echo received by a receiving antenna at a given time comes from the transmitting antenna transmitting at that time. The time of flight, that is to say the round trip duration of the wave reflected by the reflector, is generally short compared to the duration of a time slot. This method, called TDM, has the disadvantage of underutilizing the transmission capacity of a radar device. Indeed, only one of the transmitting antennas can operate at a given time.Additionally, the frame transmitted by a TDM-MIMO radar device must be long enough to contain a time slot for each transmitting antenna, which limits the duration during which the device can be put into sleep mode between two transmission-reception cycles. This limitation of the sleep duration consequently increases the consumption of the TDM-MIMO radar device.

[0014] Another way to distinguish the echoes from the different transmitting antennas consists of modulating the phase of the signal transmitted by each transmitting antenna, an example of this way applicable to a MIMO radar device comprising two transmitting antennas is called BPM (Binary Phase Modulation). In this example, the phase of the signal transmitted by the second transmitting antenna is shifted by 180° relative to the phase of the signal transmitted by the first transmitting antenna. This way allows a MIMO radar device to transmit simultaneously on each of its antennas, with different phase shifts being applied to the signals transmitted by each antenna. However, this way has the disadvantage of suffering a lot of interference between the signals transmitted by each antenna and phase demodulation errors, the phase modulation of a signal often being incorrectly interpreted when processing the received signals.The transmitting antennas of a MIMO radar device using phase modulation are therefore often confused with each other when processing the signals received by the receiving antennas, which causes a degradation of the angular resolution and the distance resolution of such a device. Presentation of the invention.

[0015] The present invention overcomes the aforementioned drawbacks by proposing a radar measuring device with frequency modulation and continuous emission.

[0016] Said frequency modulation and continuous emission radar measuring device comprises: - a generator configured to generate N first periodic radar signals, N>1, the frequency of each of said first periodic radar signals varies linearly as a function of time, in a frequency band B, over sections Tx of a part T^e of a period T, the frequencies of said N first periodic radar signals being different from each other at each instant of the part Tframe; - N transmitting antennas, each transmitting antenna being configured to transmit one of the first N periodic radar signals; - M receiving antennas, M>1, each receiving antenna being configured to receive a signal comprising echoes of the first periodic radar signals; - a reception circuit configured for: • receive M signals, received respectively by the M receiving antennas, • calculate, from the M signals, at least one parameter associated with a reflector detected by said radar measuring device, said parameter being either a distance, a radial speed, or an angle.

[0017] A reflector is understood to mean, for example, an object on which the radar signals are reflected and for which the distance and / or radial velocity and / or an angle with the radar measuring device are to be calculated.

[0018] Radial velocity is understood to mean the component of the relative velocity of the reflector with respect to the radar device in the direction formed by a straight line passing through the reflector and the radar device.

[0019] The angle of the reflector with the radar device is understood to mean an angle, also called AOA, formed between said direction and a characteristic axis of the radar device.

[0020] The term “echoes of the first periodic radar signals” means the periodic radar signals, at the level of the reception antennas of the radar measuring device, resulting from the reflection of the first periodic radar signals on the reflector.

[0021] A periodic radar signal whose frequency varies is understood to mean a signal intended to be emitted by at least one transmitting antenna of a radar device and whose frequency varies. The variation of this frequency is periodic according to the period T.

[0022] The part T^e of the period T, said period T according to which the frequencies of the first periodic radar signals vary, is divided into several sections. Within each section, the frequency value of each first periodic radar signal varies linearly.

[0023] Such arrangements allow the radar measuring device to use the FMCW approach to estimate the distance and / or radial velocity of one or more reflectors while benefiting from the advantages inherent in this approach.

[0024] Such arrangements allow the radar measuring device to make use of the MIMO approach allowing an estimation of the AOA while using the different transmitting antennas simultaneously. The first periodic radar signals emitted by each transmitting antenna will not cause or will cause very little interference with each other because the frequency of each first periodic radar signal is different at each instant from the frequency of the other first periodic radar signals. The echoes from each transmitting antenna will also be very distinct from each other which allows an accurate estimation of the AOA.

[0025] In particular embodiments, the invention may further comprise one or more of the following characteristics, taken in isolation or in all technically possible combinations.

[0026] According to one embodiment, for each first periodic radar signal when the frequency of the first periodic radar signal considered, at the end of one of the Tx sections, is not a limit of the frequency band B, the phase of the first periodic radar signal considered, at the end of the Tx section considered, is equal to the phase of the first periodic radar signal considered at the start of one of the other Tx sections.

[0027] By "limit of the frequency band B", for example, when the frequency band B extends from a frequency fmin to a frequency fmax, B=[fmin; fmax], the frequency fmin or the frequency fmax.

[0028] The term "phase of a periodic signal" means the instantaneous phase of the periodic signal under consideration. In the context of a sinusoidal expression of the periodic signal, this is the argument of the sine function. In contrast, the value of the argument of the sine function at the start of the signal (at t = 0) is called, in this text, the initial phase.

[0029] Such an arrangement allows, after a rearrangement of the sections of the echoes of the first periodic radar signals, a phase continuity of the echoes of the first periodic radar signals on all the parts T^e. This phase continuity on the part Tframe makes it possible to estimate the distance of the reflector using an FFT (Fast Fourier Transform) applied to the entire part T^e. The distance resolution thus obtained is c / 2B, c being the speed of light and B the FMCW frequency band.

[0030] Distance resolution means the smallest distance difference between two reflectors that can be distinguished by the radar measuring device.

[0031] In contrast, in the absence of phase continuity between the sections of the first periodic radar signals, the distance estimation of the reflector will be carried out using FFTs applied to each section Tx. The distance resolution thus obtained is cX / 2B, X being the number of sections. The distance resolution would therefore be greater (which corresponds to degraded performance).

[0032] According to one embodiment, the generator comprises N synchronized digital-to-analog converters, called DACs.

[0033] Each DAC will be able, depending on a digital signal, to generate a periodic analog signal at a frequency distinct from the periodic analog signals generated by the other DACs. The DACs being synchronized, they will also be able to generate periodic analog signals in phase agreement. Said first periodic radar signals will be able to be generated using the DACs.

[0034] According to one embodiment, the generator comprises N polar modulators, each polar modulator being configured to generate a signal from which one of said first periodic radar signals is generated.

[0035] Each polar modulator may provide a frequency shift of the signal that it generates, which makes it possible to ensure that the frequency of each first periodic radar signal is different from the frequency of the other first periodic radar signals at each instant of the Tframe part. The signal generated by each polar modulator may be used as input, for example, of a multiplexer which will generate one of said first periodic radar signals as output.

[0036] According to one embodiment, the reception circuit comprises NXM mixers, each mixer being configured to perform heterodyne mixing of one of the M signals with one of N second periodic radar signals, each second periodic radar signal being generated from one of said N first periodic radar signals.

[0037] The term “heterodyne mixing” means the mixing carried out by, for example, a mixer, which produces from two signals of respective frequencies fi and f2 and respective initial phases q>i and q>2, a signal formed of several components including in particular a component of frequency f3= frf2 and of initial phase q>3= q>iq>2. Considering that each second periodic radar signal is one of the first periodic signals and that each first periodic radar signal corresponds to a second periodic radar signal. The signal at the output of each mixer may be, for example, filtered using a low-pass filter to retain only the component of frequency f3= frf2 and of initial phase<p3= q> iq>2. This makes it easy to obtain the frequency difference, also called beat frequency, noted IF, between a first periodic radar signal and its echo. This IF is directly proportional to the time of flight, noted t, and therefore the distance between the radar measuring device and the reflector. The initial phase of the signal from each mixer will also make it possible to determine the AOA of the reflector.

[0038] According to one embodiment, the second periodic signal has a time delay called focus delay, noted Rfocus, relative to the first periodic radar signal from which the second periodic radar signal is generated.

[0039] The focus delay Rfocus, by being configured to be close to the time of flight r, makes it possible to overcome the windowing effects that FMCW radar measuring devices may suffer from when the distance from the reflector increases or when the duration T^e is reduced.

[0040] According to one embodiment, the first N periodic radar signals are generated from a reference periodic radar signal whose frequency varies linearly in the frequency band B according to a period Tref.

[0041] The term periodic reference radar signal means an FMCW radar signal according to the prior art. The period Tref may be equal to the period T or the value of the period Tref may be equal to the value of the part T^e.

[0042] Sections of the reference periodic radar signal may be used to generate the Tx sections of the first periodic radar signals, using different orders of arrangement of the sections of the reference periodic radar signal for each first periodic radar signal.

[0043] According to one embodiment, the first N periodic radar signals are generated by applying time shifts to the reference periodic radar signal.

[0044] By applying time shifts to the reference periodic radar signal, first periodic radar signals are generated with frequencies varying in the B band and whose frequencies at each instant may be different by using different time shifts for the generation of each first periodic radar signal.

[0045] According to one embodiment, the period Tref of variation of the frequency of the reference periodic radar signal is equal to the part Tframe and the first periodic radar signal of index k, k being an integer between 1 and N, is generated by applying a time shift to the reference periodic radar signal.

[0046] [Math.2] D k = [kl]x^

[0047] The duration of each section Tx is defined by the difference of each time offset Dk with the previous index time offset Dk h

[0048] This time shift of index k ensures that the duration of each Tx section is equivalent to that of the other Tx sections and that the difference between the frequencies of the first periodic radar signals at each instant is maximum for a frequency band B used. Brief description of the figures

[0049] The invention will be better understood on reading the following description, given by way of non-limiting example, and made with reference to the figures:

[0050] [Fig. 1] a representation of an example of a periodic FMCW radar signal and an echo in a frequency versus time graph,

[0051] [Fig.2] a schematic representation of an example of a transmitting and receiving antenna arrangement according to the SIMO and MIMO approaches,

[0052] [Fig.3] a representation of an example of first periodic radar signals and echoes according to the invention in a frequency versus time graph,

[0053] [Fig.4] a schematic representation of an example of a radar measuring device according to the invention,

[0054] [Fig.5] a schematic representation of an example of steps for generating first periodic radar signals according to the invention.

[0055] In these figures, identical references from one figure to another designate identical or similar elements. For reasons of clarity, the elements represented are not necessarily on the same scale, unless otherwise stated. Detailed description of the invention

[0056] [Fig. 3] is a representation of an example of first periodic radar signals 20 and echoes 21 according to the invention in a graph representing the frequency as a function of time. In this exemplary embodiment, 3 first periodic radar signals 20 are represented. The frequency of each first periodic radar signal 20 evolves linearly as a function of time, in a frequency band B, over sections Tx (in this example N=3 and there are 3 sections) of a part Tframe of a period T. The first periodic radar signals 20 are transmitted during the part T^.

[0057] Each first periodic radar signal 20 is emitted by a transmitting antenna of a radar measuring device 10 according to the invention. A reflector reflects the first periodic radar signals 20 which induces echoes 21 of the first periodic radar signals. The reflector may in particular be characterized by a radar equivalent surface. Each first periodic radar signal 20 induces an echo 21 which is received by receiving antennas 13 of the radar measuring device 10 according to the invention, after a flight time r. Each receiving antenna 13 of the device radar 10 according to the invention receives a signal 22, this signal comprises the echoes 21 of each first periodic radar signal 20 caused by at least one reflector.

[0058] The frequency of each first periodic radar signal 20 is different from the frequencies of the other first periodic radar signals 20 at each instant of the part T^e. In this way, the first periodic radar signals 20 transmitted by each transmitting antenna 12 do not cause interference with each other.

[0059] The frequency shift between a first periodic radar signal 20 and its echo 21, also called frequency difference IF, makes it possible to calculate a distance between the radar measuring device and the reflector having caused the echo 21 considered.

[0060] A reception circuit 14 of the radar device 10 according to the invention will be able, from at least one signal 22 received by a reception antenna 13, to determine the IF associated with a reflector and then, from this IF, to calculate the distance between the radar measuring device and the reflector in question. Several reflectors at different distances will each cause an echo 21 with a distinct IF, which will make it possible to calculate the distance of each reflector.

[0061] Additionally, after receiving the echoes 21 of the first periodic radar signals 20, the echo 21 of each first periodic radar signal 20 is distinct in frequency from the echoes of the other first periodic radar signals 20. The flight time r being considered to be low compared to the transmission duration Ttrame, the echo 21 close in frequency to one of the first periodic radar signals 20 is the echo 21 of the first periodic radar signal 20 considered. This makes it possible to distinguish, from one another, the echoes of the first periodic radar signals 20 emitted by each transmission antenna 12 of the radar measuring device 10 according to the invention. The reception circuit 14 of the radar measuring device 10 according to the invention can then determine a phase shift between the echoes 21 of the first periodic radar signals 20 emitted by each transmission antenna 12. By phase shift is meant an initial phase difference.

[0062] The receiving circuit may also determine a phase shift between the signals received by each receiving antenna.

[0063] In this way, the device 10 according to the invention can implement a MIMO architecture making it possible to calculate the AOA of a reflector while exploiting the entire transmission capacity of the radar device according to the invention (each transmitting antenna transmits simultaneously).

[0064] Additionally, when the frequency of each first periodic radar signal 20 at the end of a section Tx (Ti or T2 or Tlr.ime in [Fig.3]) is not the maximum frequency of the frequency band B, the phase of the first periodic radar signal considered at the end of the section Tx considered is equal to the phase of the first periodic radar signal 20 at the beginning of one of the other Tx sections. This allows, for each echo of the first periodic radar signal, after a rearrangement of the sections, carried out for example digitally, to maintain phase continuity of the echo considered on the part Tframe. Phase is understood to mean the instantaneous phase of a periodic signal. In the context of a sinusoidal expression of the periodic signal, it is the argument of the sine function. In contrast, the value of the argument of the sine function at the start of the signal (at t = 0), is called, in the present text, the initial phase. The phase continuity between the sections of the first periodic radar signals 20 allows phase continuity on the part T^e of the signals 22 received by the receiving antennas. These signals 22 may be directly or indirectly (after one or more transformations) processed using a fast Fourier Transform (FFT) over the entire Tframe part in order to determine frequency deviations IFs. In the absence of this continuity phase on the Tframe part, FFTs will allow the T^me section part to be processed by section (each section presenting phase continuity) which degrades the precision of determining the IFs and therefore degrades the distance resolution of the radar measuring device.

[0065]

[0066]

[0067]

[0068]

[0069] In the case N=3, the first periodic radar signals could, for example, be generated according to the following equations: [Math.3] sin(2n((f c -B / 2)t+at 2)), Vtë[o, 81^2^-5 / 2^-7))+ah-Tj^.V të[7 lf 7 days .sin^^-B^t+Tj+att+T)) 2 ))^ të[72, 7 trame ] If being the first periodic radar signal 20 of index 1 (represented in solid line on [Fig.3]), fc being the central frequency of frequency band B and has the slope of variation of frequency. [Math.4] S2 = ' sïn(2n((f c -B / 2\t-TÙ+c^^ Vte[0,Tj sin(2n((.f c -B / 2)(t+T^+a(t+^ T2] > sin(2n((f c -B / 2^t + at 2 )), Y te[r2, T trame ] S2 being the first periodic radar signal 20 of index 2 (represented in large dotted lines in [Fig.3]).

[0070] [Math.5] ' 3111(24( / ,-5 / 2)( / -72)+4 / -7 / )), v / e[o,TJ sin(24(f c -B / 2) / +a / 2 )), V rj ,5^(24(^-3 / 2)( / +7^+0( / +77)), V / e[72.7 tram I

[0071] S3 being the first periodic radar signal 20 of index 3 (represented in small dotted lines in [Fig.3]).

[0072] [Fig.4] is a schematic representation of an example of a measuring device radar 10 according to the invention. According to one embodiment, a generator 11 comprises, in the example shown, N = 2 polar modulators 111. Each polar modulator 111 generates a signal from which a first periodic radar signal 20 is created, for example, using a multiplier “MUL.” then a power amplifier “PA”.

[0073] The frequency of each signal generated by one of the polar modulators 111 is different at each instant from the frequency of the signals generated by the other polar modulators 111. In this way, the frequency of each first periodic radar signal 20 is different at each instant from the frequency of the other first periodic radar signals 20. Each first periodic radar signal 20 is emitted by at least one transmitting antenna (one transmitting antenna per first signal in the example shown).

[0074] According to an embodiment not shown, the generator 111 comprises N digital-to-analog converters “DAC” (“Digital Analogue Converter”). Each first signal 20 is generated using a digital-to-analog converter from a digital signal.

[0075] The radar measuring device 10 also comprises M = 2 (in the example shown) receiving antennas. Each receiving antenna is configured to receive a signal 22 comprising, if a reflector is present in a radar visibility zone, the echoes of the first signals 20. Each signal 22 may, for example, be amplified by a low noise amplifier “LNA” (“Low Noise Amplifier”) and then be mixed according to a heterodyne mixture by a mixer 141 with a second periodic radar signal generated from one of the first signals 20. In the example shown in [Fig. 4] each second periodic radar signal is one of the first periodic radar signals 20, coming from a splitter 15, and each first signal 20 corresponds to a second periodic radar signal. The heterodyne mixing makes it possible to produce a mixed signal comprising several components, one of which has a frequency f3 = f 1 — f2 and an initial phase<p3 = q> i - q>2.The frequencies / and f2 and the initial phases q>i and q>2 being respectively the frequencies . and the initial phases of the signal 22 and of the second periodic radar signal at the input of one of the mixers 141. A low-pass filter 142 will isolate the frequency component f3 and initial phase q>3 which can then be digitized using an analog-to-digital converter ADC (“Analogue Digital Converter”). The reception circuit 14 of the radar measuring device 10 comprises, for example, a digital signal processor DSP (“Digital Signal Processing”) configured to perform FFTs making it possible to calculate the distance between the reflectors and the radar measuring device and the AOAs of the reflectors.

[0076] According to an embodiment not shown, the reception circuit 14 may not include a mixer 141. The received signals 22 may be directly digitized as well as the first signals 20 and the frequency differences IFs determined without heterodyne mixing but by digital processing only. Such an embodiment however has the disadvantage of requiring ADCs having a much higher sampling frequency in order to be able to digitize the signals 22 directly without losing useful information.

[0077] According to an embodiment not shown, each second periodic radar signal has a time delay Rfocus relative to the first signal 20 from which it is generated. A radar measurement device as described in application FR3125887 allows this time delay and uses it, by configuring it to be close to the time of flight r, to reduce the IFs (which makes it possible to use ADCs with even lower sampling frequencies) and to avoid windowing effects (producing reflector ghost images) when the distance between the reflector and the device is such that the time of flight r is greater than the period T.

[0078] [Fig. 5] is a schematic representation of an example of steps for generating first periodic radar signals according to the invention. In this example, the radar measuring device 10 comprises at least N=3 transmitting antennas. A reference periodic radar signal 23 is represented, it is an FMCW signal as present in the prior art. The frequency of the reference periodic radar signal varies linearly in the frequency band B. The variation of the frequency of the reference periodic radar signal 23 is periodic according to a period Tref. Each section Tx of the first periodic radar signals 20 may be generated from a section of the reference periodic radar signal 23, for example, digitally, when the first periodic radar signals 20 are generated using DACs.

[0079] According to one embodiment, time shifts Dk may be applied to the reference periodic radar signal 23 to generate the first periodic radar signals 20. In an example not shown, the period Tref is equal to the period T and each section Tx comes from the offset reference periodic radar signal 23 of a time shift Dk to which is applied a time window, also called gate, of width Tx and starting at the start time of the Unconsidered section. Each first periodic radar signal can then be constituted, using for example a switch, of the different sections Tx generated from the reference periodic radar signal 23. This makes it possible to generate the first periodic radar signals 20 in such a way that their frequency is different from each other at each time and in such a way that the signals 22 formed by the echoes 21 and received by the reception antennas 13 of the radar measuring device 10 have phase continuity over the part Tframe of the period T.

[0080] According to an embodiment shown in [Fig.5], Tref = Frame. That is to say that the duration of the period Tref of variation of the frequency of the reference periodic radar signal 23 is equal to the duration of the part Tframe of the period T of the first periodic radar signals 20. The first periodic radar signal of index k, k being an integer between 1 and N, is generated from the reference periodic radar signal 23 to which a time shift is applied.

[0081] [Math.2] D t = (kl)x^

[0082] Once the time shift has been applied, a time window of width Tframe and starting at the beginning of the part T^e makes it possible to generate an intermediate signal of duration Tframe. The intermediate signal is then repeated according to the period T to form the first periodic radar signal 20 of index k. This way of generating the first periodic radar signals 20 allows in particular an equal duration for each section Tx. This way also allows, for a given frequency band B, a maximum difference between the frequency at each instant of a first periodic radar signal 20 and the frequency of the other first periodic radar signals 20. Having a maximum difference between the frequencies at each instant of the first periodic radar signals makes it possible to limit as much as possible the interference between the first periodic signals 20 during their simultaneous transmissions.

Claims

1. Claims Radar measuring device (10) with frequency modulation and continuous emission comprising: - a generator (11) configured to generate N first periodic radar signals (20), N>1, the frequency of each of said first periodic radar signals varies linearly as a function of time, in a frequency band B, over sections Tx of a part T^e of a period T, the frequencies of said N first periodic radar signals (20) being different from each other at each instant of the part T^e; - N transmitting antennas (12), each transmitting antenna being configured to transmit one of the first N periodic radar signals (20); - M receiving antennas (13), M>1, each receiving antenna being configured to receive a signal comprising echoes (21) of the first periodic radar signals; - a receiving circuit (14) configured to: • receive M signals (22), received respectively by the M receiving antennas (13), • calculate, from the M signals (22), at least one parameter associated with a reflector detected by said radar measuring device, said parameter being either a distance, or a radial speed, or an angle, in which, for each first periodic radar signal, when the frequency of the first periodic radar signal (20) considered, at the end of one of the Tx sections, is not a limit of the frequency band B, the phase of the first periodic radar signal (20) considered at the end of the Tx section considered is equal to the phase of the first periodic radar signal (20) considered at the start of one of the other Tx sections; the radar measuring device being characterized in that each first periodic radar signal (20) is obtained, on each section (Tx), by applying to a reference periodic radar signal (23), a time shift and by applying a time window of width of the section (Tx) considered and starting at a start time of the section (Tx) considered, a frequency of the periodic reference radar signal (23) varying linearly in the frequency band B.

2. Radar measuring device (10) according to one of the preceding claims in which the generator (11) comprises N synchronized digital-analog converters, called DACs.

3. Radar measuring device (10), according to any one of claims 1 to 2, wherein the generator (11) comprises N polar modulators (111), each polar modulator (111) being configured to generate a signal from which one of said first periodic radar signals (20) is generated.

4. Radar measuring device (10) according to one of the preceding claims, wherein the reception circuit (14) comprises N kM mixers (141), each mixer (141) being configured to perform heterodyne mixing of one of the M signals with one of N second periodic radar signals, each second periodic radar signal being generated from one of said N first periodic radar signals (20).

5. Radar measuring device (10) according to claim 4, in which the second periodic signal has a time delay called focus delay, noted Rfocus, relative to the first periodic radar signal (20) from which the second periodic radar signal is generated.

6. Device according to any one of the preceding claims, in which the period Tref of variation of the frequency of the reference periodic radar signal (23) is equal to the part T^e and in which the first periodic radar signal (20) of index k, k being an integer between 1 and N, is generated by applying to the reference periodic radar signal (23) a time shift Dk=(kl)x V'

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