DE102004060087A1 - Device for especially bistatic radar applications - Google Patents

Abstract

For bistatic radar applications, control or regulation of the image frequency takes place by changing the carrier frequency of at least one of the carrier frequency oscillators (21, 22) associated transmit and receive sensors (11, 12). DOLLAR A Both internal echoes and cross echoes are evaluated. It is a hollow angular resolution and a classification of object contours possible.

Description

A device for bistatic radar applications according to the preamble of claim 1 is known from DE 102 139 87 A1 known. There, by utilizing a mirror effect in the frequency domain, cross-echo detection and distance measurement in a bistatic pulse radar system is possible without carrier frequency oscillators of each transmitter-receiver pair having to be phase-synchronized by complex measures, as is the case with other known arrangements.

Advantages of invention

With the measures according to claim 1, i. with means for controlling the at least one Mirror frequency by changing the carrier frequency at least one of the carrier frequency oscillators mutually associated transmit and receive sensors, is a very Low-cost realization of a bistatic radar system is given. To a desired Image frequency between its minimum 0 Hz (modulo PRF) and their maximum - half of Pulse repetition rate (modulo Pulswiederholrate) - set, it is sufficient, for. at a constant pulse repetition rate PRF one of the two oscillator frequencies maximum to vary the amount of the PRF (to draw), which is very little effort is feasible.

in the Unlike traditional Eigenecho evaluations for monostatic operation with a large opening angle becomes higher in the invention angular resolution achieved.

The Cross-echo evaluation increased the spatial Sampling of the automotive environment, allows the classification of object contours and enlarges the Redundancy of the sensor information.

• – Codierung des Sendesignals, wodurch einerseits eine Senkung der Störempfindlichkeit gegenüber externen Signalen im Empfangsfrequenzbereich, und andererseits eine eindeutige Senderidentifikation in Sensor-Arrays erreicht werden kann,
• – Erhöhung der Entfernungsauflösung, bzw. Sendesignalbandbreite ohne eine ansonsten notwendige Verkürzung der Pulsdauer,
• – Erfüllung von Forderungen an die spektrale Leistungsverteilung, z.B. für eine Frequenzzulassung,
• – Unterdrückung möglicher Fehlzuordnungen von Empfangspulsen zu Sendepulsen beim Auftreten von Überreichweiten,
• – Ermöglichung der Aufmodulation von Daten auf das Sendesignal zu Kommunikationszwecken.

If, according to the measures of claim 2, a synchronous frequency modulation is provided at the transmit and receive sensors and / or the measures of the further claims are used, the following advantages (goals) arise:

• Coding of the transmission signal, whereby on the one hand a reduction of the interference sensitivity to external signals in the reception frequency range, and on the other hand a unique transmitter identification in sensor arrays can be achieved,
• Increase the range resolution, or transmit signal bandwidth without an otherwise necessary shortening of the pulse duration,
• Fulfillment of requirements for the spectral power distribution, eg for frequency approval,
• Suppression of possible misallocations of received pulses to transmit pulses when overreaches occur,
• - Enabling the modulation of data on the transmission signal for communication purposes.

A time-synchronous pulse modulation of transmitter and receiver can be used advantageously. An image signal resulting from an aliasing effect in the mixed signal of the receiver is likewise used for detection and distance measurement. The frequency f _{a of} a resulting mirror signal (the image frequency) depends both on the pulse repetition frequency PRF and on the carrier difference frequency df of the transmitter and the receiver. It applies with an integer factor n: df = n * PRF ± f a

The image frequency will not be like the DE 102 139 87 A1 by varying the pulse repetition rate PRF, but by varying one or both carrier frequencies of the transmitter-receiver sensor pair, and thus set the carrier difference frequency df. The oscillators of the transmitter and receiver still do not have to be phase-synchronized and can still have distinctly different frequencies (ie, a difference greater than the bandwidth of the I / Q (inphase / quadrature phase) signal processing).

• – Synchrone Pulsansteuerung von Sendern und Empfängern in einem Array, d.h. mindestens paarweise,
• – Je Sender-Empfänger-Paar Nutzung eines Spiegelsignals in I- oder Q- oder davon abgeleiteten Signalen,
• – Steuerung/Regelung der Mittenfrequenz des Spiegelsignals f_a durch Änderung einer Trägerfrequenz oder beider Trägerfrequenzen des Sender-Empfänger-Sensorpaares,
• – Gegebenenfalls für Sender und Empfänger synchrone Trägerfrequenzmodulation.

Particularly advantageous is the combination of the following measures:

• - Synchronous pulse control of transmitters and receivers in an array, ie at least in pairs,
• - per transmitter-receiver pair use of a mirror signal in I or Q or derived signals,
• Controlling the center frequency of the mirror signal f _a by changing a carrier frequency or both carrier frequencies of the transmitter-receiver sensor pair,
• - If necessary, for transmitter and receiver synchronous carrier frequency modulation.

• – Ein kontinuierliches NF-Signal zur Kreuzecho-Detektion und -Abstandsmessung durch Leistungsmessung, o.ä. z.B. Amplitude, Quasi-Peak, etc., eines Spiegelsignals,
• – zur digitalen Weiterverarbeitung ist eine kostengünstige Abtastung des NF-Leistungssignals mit kleinen Abtastraten, im wesentlichen bestimmt durch die Scanrate und die gewünschte Auflösung, möglich,
• – Kreuzechos können parallel zu Direktechos ausgewertet werden, da das Spiegelsignal im I- und/oder Q-Signal in einem separaten Frequenzbereich platziert wird (Frequenz-Multiplex-Betrieb),
• – eine aufwendige Phasensynchronisation der Träger ist nicht nötig, aber eine minimale Kurzzeit-Frequenzstabilität (während der Pulsintegrationszeit) wird vorausgesetzt,
• – keine hohen Forderungen an die Bandbreiten von Mischer und NF-Verstärkern (mindestens oberhalb der wählbaren Spiegelfrequenz),
• – aktive Unterdrückung ansonsten sporatisch auftretenden Direktechoübersprechens, welches in Sensorarrays bei nicht synchronisiertem Betrieb mit fester PRF auftritt, wenn die Spiegelfrequenz, z.B. aufgrund von Temperaturdrift der Trägerfrequenzen, zufällig in den Frequenz-Bereich der Direktechos (0... Dopplerfrequenz) fällt,
• – Überwachung der Trägerfrequenzen (Diagnosefunktion: Erkennung ungewöhnlicher Driften oder Ausfall) durch Beobachtung des Verhaltens der Spiegelfrequenzregelung, insbesondere bei ständig gegebenem direkten Übersprechen von Sender zu Empfänger,
• – übliche Pulskompressionsverfahren können zusätzlich eingesetzt werden,
• – sehr kostengünstige Hardware-Realisierungen sind möglich, z.B. Ausführungsvariante mit konstanter PRF und geringer Verstimmung eines Oszillators um maximal PRF,
• – durch synchrone Trägerfrequenzmodulation Erreichung einer Teilmenge der oder aller zuvor genannten Ziele.

This combination has the following advantages:

• - A continuous LF signal for cross echo detection and distance measurement by power measurement, or similar. eg amplitude, quasi-peak, etc., of a mirror signal,
• - For digital processing is a cost-effective sampling of the low-frequency power signal with low sampling rates, essentially determined by the scan rate and the desired Auflö possible,
• Cross-echoes can be evaluated in parallel with direct echoes since the mirror signal in the I and / or Q signal is placed in a separate frequency range (frequency-multiplexed operation).
• - a complex phase synchronization of the carrier is not necessary, but a minimum short-term frequency stability (during the pulse integration time) is assumed
• No high demands on the bandwidths of mixers and LF amplifiers (at least above the selectable image frequency),
• Active suppression of otherwise sporadically occurring direct echo crosstalk, which occurs in sensor arrays in non-synchronized operation with fixed PRF when the image frequency, for example due to temperature drift of the carrier frequencies, coincidentally falls within the frequency range of direct echoes (0 ... Doppler frequency),
• Monitoring of the carrier frequencies (diagnostic function: detection of unusual drifts or failure) by observation of the behavior of the image frequency control, in particular with constant direct crosstalk from transmitter to receiver,
• Conventional pulse compression methods can additionally be used
• - Very cost-effective hardware implementations are possible, eg design variant with constant PRF and low detuning of an oscillator by a maximum of PRF,
• - By synchronous carrier frequency modulation achievement of a subset of or all of the aforementioned objectives.

drawings

Based The drawings are exemplary embodiments closer to the invention explained. Show it:

1 a block diagram of the radar system according to the invention with synchronously driven Pulsradransender and receiver pair,

2 a power density spectrum of the mixed, unpulsed carriers of neighboring sensors,

3 a power density spectrum of the mixed, pulsed carriers of neighboring sensors with negligible pulse duration,

4 the power density spectrum of the mixed, pulsed carriers of neighboring sensors with non-negligible pulse duration,

5 the power density spectrum of a real I (Q) signal in cross-echo reception,

6 the image frequency control by means of carrier frequency detuning of at least one of the carrier frequency oscillators,

7 the dependence of the detection signal y on the carrier frequency df at a suitable for crosstalk delay τ and illustrating a maximum value control.

description of exemplary embodiments

1 shows excerpts of two simple, ordinary pulse radar sensors 11 . 12 of which the upper sensor 11 as transmitter (Tx), the lower sensor 12 works as a receiver (Rx). The sensors generate with their respective carrier frequency oscillators 21 . 22 Carrier signals x ₁ and x ₂ with individual carrier frequencies f _LO1 and f _LO2 . These carrier signals are preferably from the same pulse source 3 with the 0-1 pulse train p modulated, that is by means of the modulators 51 . 52 are impressed on the output signals of the carrier frequency oscillators Pulse. It can of course be any of the sensors 11 . 12 be associated with a separate pulse signal source 3. Then, however, a synchronization of these pulse signal sources with each other is required. This can be done either by a connection line or otherwise by recovery of the transmit PRF from the received signal and compensation of the phase offset. The determination of the phase offset is possible by exploiting redundancy, since due to the reversibility of the signal propagation paths normally always two cross echo and possibly additionally available Eigenechomomungen an object are available (eg let: Δ = phase lead from pulse signal source 1 to Pulssignalquelle 2; tofK; Kreuzecholaufzeit from S11 to object K to S12 or return direction tofK12: cross-gauging from S11 to S12 relative to pulse signal source 2, tofK21: cross-gauging from S12 to S11 pulse signal source 1, then: tofK = tofK - Δ and tofK = tofK21 + Δ → Δ = (tofK12 - tofK21) / 2 → tofK = (tofK12 + tofK21) / 2.

The emitted signal of the transmitter is recorded by the receiver after reflection at an object after the time of flight (time-of-flight tof). The receiver delays with a delay circuit / delay line 6 the pulse sequence p by the delay time τ. If the set delay τ corresponds to the transit time tof, this results at the output of the mixer 7 to which a transmission signal on the one hand and on the other hand a reception signal can be supplied, due to the time-synchronous pulse modulation, the signal m = p * x ₁ * x ₂ if τ = tof.

• 1. Die Mischung (Multiplikation) der ungepulsten Träger, siehe x₁ und x₂ in 1, zweier Nachbarsensoren mit der mittleren Differenzfrequenz df = f_LO1 – f_LO2 würde zu einem Spektrum mit bandbegrenzten Anteilen um df = f_LO1 – f_LO2 und f_LO1 + f_LO2 führen (2). Der Summenanteil kann wegen des Tiefpassverhaltens von Mischer 7 und Verstärker 8 im Folgenden vernachlässigt werden. Die Breite des verbleibenden Spektralanteils um df ist durch die Kurzzeit-Frequenzstabilität der Trägerfrequenz-Oszillatoren während der Pulsintegrationszeit bestimmt. Wesentlich ist, dass ein solches bandbegrenztes Spektrum auch bei nicht frequenz- oder phasensynchronisierten Oszillatoren entsteht.
• 2. Die Pulsmodulation des Produktes x₁·x₂, die schließlich zum idealen Mischsignal m führt, entspricht einer Abtastung, wobei die Abtastfrequenz durch die eingestellte Pulswiederholrate PRF des Pulsgenerators gegeben ist. Im Spektrum führt eine Idealabtastung (δ-Abtastung) aber zur periodischen Fortsetzung des Spektrums des abgetasteten Signals. Es würde also das um df verteilte Spektrum je zwei mal in die Frequenzintervalle [z·PRF, (z + 1)·PRF], wobei z eine ganze Zahl ist, gespiegelt (3). Man beachte, dass immer, also auch bei der Differenzfrequenz df die wesentlich größer als die Pulswiederholrate PRF ist (also bei Unterabtastung), ein bandbegrenztes Signal im Frequenzbereich [0,PFR/2] entsteht. Die Mittenfrequenz fa des „Spiegel-Signals" in [0,PFR/2] und die Differenzfrequenz df hängen dabei gemäß df = n·PRF + –fazusammen, wobei n ∈ N₀ (ganzzahliger Teiler zwischen df und PRF). Eine ideale Abtastung liegt näherungsweise vor, wenn die Pulsdauer sehr klein gegenüber der kleinsten Periodendauer des abgetasteten Signals ist, das heißt T_p ≪ 1/df, ist. Ist dies nicht der Fall, fallen die Amplituden der wiederholten Spektralanteile mit einer Einhüllenden ab, die durch die Pulsform und die nicht vernachlässigbare Pulsdauer definiert ist (4). Bei einem Rechteckimpuls der Länge Tp ist die Einhüllende beispielsweise ein sinx/x Verlauf mit der ersten Nullstelle bei 1/Tp.
• 3. Das Spektrum des realen IQ-Signals, fällt oberhalb der Grenzfrequenz von Mischer und Verstärker/Impedanzwandler, die in aller Regel wesentlich kleiner als die Differenzfrequenz df sind, deutlich ab und ähnelt im allgemeinen einem in 5 gezeigten Verlauf. Dieser, durch ein Kreuzecho im I(Q)-Signal entstehende begrenzte Signalanteil mit seinen wesentlichen Frequenzanteilen unterhalb PRF/2 wird im Folgenden Kreuzecho-Doppler genannt. Ein Direktecho eines sich extrem schnell bewegenden Objektes mit zugehörigen Dopplerfrequenzen um f_D = df würde zu einem ähnlichen Signal führen.
• 4. Man beachte, dass die Spiegelfrequenz fa des Kreuzecho-Dopplers mit der vorgebbaren Pulswiederholfrequenz PRF (bei langsam veränderlicher Zeitfrequenz df) gemäß (1) stets auf einen gewünschten Wert eingestellt werden kann. Insbesondere ist es möglich, durch gezielte Einstellung der PRF einerseits sicher zu stellen, dass die Spiegelfrequenz fa stets unterhalb der Grenzfrequenz von Mischer und Verstärker liegt. Andererseits kann bei parallelem Empfang von Direktechos des Sensors dafür gesorgt werden, dass die Spiegelfrequenz fa stets oberhalb der maximalen Dopplerfrequenz f_Dmax liegt. Dies kann als „Frequenz-Multiplex"-Nutzung des I(Q)-Signals aufgefasst werden, bei dem Direktechos und Kreuzechos in voneinander getrennten Frequenzbereichen liegen. Wesentliche Voraussetzung für eine eindeutige Trennung ist natürlich, dass die Lokaloszillatoren so kurzzeit-frequenzstabil sind, dass die Bandbreite von x₁·x₂ stets kleiner als PRF/2-f_Dmax ist.
• 5. Der Teiler n und die Spiegelfrequenz fa charakterisieren die momentane Differenzfrequenz eines Sensorpaares bei dem Kreuzecho-Empfang besteht. Damit ist bei Sensorarrays mit mehr als 2 Sensoren, bei denen die Differenzfrequenzen aller relevanten Sensorpaare signifikant voneinander abweichen, eine Senderidentifikation auch bei parallelem Empfang mehrerer Kreuzechos möglich.

This (ideal) mixed signal is example example in an evaluation device 4 from the subsequent real amplifier 8th and from the real mixer 7 even low-pass filtered. At the output of the amplifier or impedance converter is then the I signal and in the case of a second mixer, which operates with the 90 ° out of phase carrier, also a Q signal for further LF signal processing available. The following describes the spectrum that results for the I (Q) signal.

• 1. The mixture (multiplication) of the unpulsed carriers, see x ₁ and x ₂ in 1 , two neighboring _sensors with the mean difference _frequency df = f _LO1 - f _LO2 would lead to a spectrum with band-limited portions around df = f _LO1 - f _LO2 and f _LO1 + f _LO2 ( 2 ). The sums may be due to the low-pass behavior of mixers 7 and amplifiers 8th will be neglected in the following. The width of the remaining spectral component around df is determined by the short-term frequency stability of the carrier frequency oscillators during the pulse integration time. It is essential that such a band-limited spectrum is produced even with non-frequency or phase-locked oscillators.
• 2. The pulse modulation of the product x ₁ · x ₂ , which finally leads to the ideal mixing signal m, corresponds to a sampling, wherein the sampling frequency is given by the set pulse repetition rate PRF of the pulse generator. In the spectrum, however, ideal sampling (δ sampling) results in periodic continuation of the spectrum of the sampled signal. Thus, the spectrum distributed by df would each be mirrored twice into the frequency intervals [z * PRF, (z + 1) * PRF], where z is an integer 3 ). Note that always, even at the difference frequency df, which is considerably larger than the pulse repetition rate PRF (ie under subsampling), a band-limited signal is produced in the frequency range [0, PFR / 2]. The center frequency fa of the "mirror signal" in [0, PFR / 2] and the difference frequency df depend on it df = n · PRF + -fa together, where n ∈ N ₀ (integer divider between df and PRF). An ideal sample is approximately when the pulse duration is very small compared to the smallest period of the sampled signal, that is, T _p << 1 / df. If this is not the case, the amplitudes of the repeated spectral components fall off with an envelope, which is defined by the pulse shape and the non-negligible pulse duration ( 4 ). For example, for a rectangular pulse of length Tp, the envelope is a sinx / x gradient with the first zero at 1 / Tp.
• 3. The spectrum of the real IQ signal drops significantly above the cut-off frequency of mixer and amplifier / impedance converter, which are usually much smaller than the difference frequency df, and is generally similar to one in 5 shown course. This limited signal component, which is formed by a cross echo in the I (Q) signal and has its essential frequency components below PRF / 2, will be referred to below as cross-echo Doppler. A direct echo of an extremely fast moving object with associated Doppler frequencies around f _D = df would result in a similar signal.
• 4. It should be noted that the image frequency fa of the cross-echo Doppler with the predefinable pulse repetition frequency PRF (with a slowly varying time frequency df) according to (1) can always be set to a desired value. In particular, it is possible to ensure by targeted adjustment of the PRF, on the one hand, that the image frequency fa is always below the cutoff frequency of mixer and amplifier. On the other hand, with parallel reception of direct echoes of the sensor, it can be ensured that the _image frequency fa is always above the maximum Doppler frequency f _Dmax . This can be thought of as a "frequency-multiplexed" use of the I (Q) signal, where direct echoes and cross echoes are in separate frequency ranges, and of course a clear separation is that the local oscillators are so short-term frequency stable that the bandwidth of x ₁ · x _{2 is} always less than PRF / 2-f _Dmax .
• 5. The divider n and the image frequency fa characterize the instantaneous difference frequency of a sensor pair in which cross-echo reception exists. Thus, with sensor arrays with more than 2 sensors, in which the difference frequencies of all relevant sensor pairs differ significantly from each other, a transmitter identification even with parallel reception of multiple cross echoes possible.

• – Synchrone Pulsansteuerung (Verbindungsleitung oder durch Rückgewinnung der Sender-PRF aus dem Empfangssignal und Kompensation des Phasenversatzes)
• – Nutzung des Kreuzecho-Dopplers in I, Q- oder davon abgeleiteten Signalen unterhalb von PRF/2
• – Steuerung/Regelung der Spiegelfrequenz (Mittenfrequenz f_a des Kreuzecho-Dopplers) durch Ändern (Verstimmen) der Trägerfrequenz mindestens eines der Trägerfrequenzoszillatoren 21 und 22, wobei die Differenz der Trägerfrequenzen von Sender und Empfänger maximal um die Pulswiederholrate PRF variiert werden und so fein eingestellt werden können, dass die Spiegelfrequenz innerhalb der Bandbreite eines Signaldetektors gehalten werden kann.

The device according to the invention is characterized in particular by the following features:

• - Synchronous pulse control (connection line or by recovering the transmitter PRF from the received signal and compensation of the phase offset)
• - Use of the cross echo Doppler in I, Q or derived signals below PRF / 2
• - Control / regulation of the image frequency (center frequency f _{a of} the cross-echo Doppler) by changing (detuning) the carrier frequency of at least one of the carrier frequency oscillators 21 and 22 , wherein the difference of the carrier frequencies of the transmitter and receiver are varied by a maximum of the pulse repetition rate PRF and can be adjusted so fine that the image frequency can be kept within the bandwidth of a signal detector.

As 1 ₁ , a carrier frequency oscillator or both carrier frequency oscillators has a control input for frequency _detuning (inputs _labeled f _LO1 , and f _FLO2, respectively). The main disturbance of the image frequency control loop is usually the frequency drift of the carrier frequency oscillators with the temperature.

in the Trap of direct crosstalk from transmitter to receiver, e.g. by reflection / conduction of the transmission signal at the bumper or other generating measures, is constantly and independent of the existence and location of objects in monitored detection field Mirror signal before at least one set delay τ before. Than are particularly simple, robust and constantly engaged Image frequency controls possible. moreover can be an uninterrupted monitoring of carrier frequencies be made. Such a regulation will be something below described in more detail.

It is assumed that a constant pulse repetition rate PRF is used and the power, amplitude, or the like. the mirror signal y is detected in a specific, fixed frequency band analog or digital. According to 6 to obtain the mirror signal y is a frequency-selective evaluation of the I and / or Q signal in the unit 9 , About the control unit 10 the inputs f _LO1 and / or f _{LO2 of} the carrier frequency _{oscillator are} controlled. In order to be able to measure eigen and cross echoes in parallel, it is assumed that the detection frequency band does not include 0 Hz and is below PRF / 2. The detection signal y then shows in the suitably adjusted at the time of crosstalk delay τ in the 7 indicated dependence on the carrier difference frequency df. This course is periodic with the PRF, with only one period being shown here. Within such a period, there are always two local maxima under the conditions mentioned. The object of the image frequency control is to detune one or both carrier frequency oscillators in such a way that the detection signal y assumes a maximum.

A general method of maximum value control is to constantly vary the carrier difference frequency so that the first derivative of the function y (df) is estimated, for example by time difference. From the sign of the first derivative, the average change of the carrier difference frequency can then be determined according to the following rules (see also block arrows in FIG 7 ). dy / d (df)> 0: df ↑ dy / d (df) <0: df ↓

Variants with synchronous Frequency modulation at transmitter and receiver

Synchronous changes (common mode changes) of the instantaneous, absolute carrier frequencies f _LO1 , f _LO2 are irrelevant for the _image frequency f _a , since this depends only on the difference df of the carrier frequencies. Each synchronous frequency modulation of transmitter and receiver therefore has no influence on the described image frequency control and is in this sense orthogonal to the cross-echo evaluation. Frequency modulation allows a flexible design of the transmission spectrum. In the following, frequency modulations (FM) with different time constants with their priority objectives are explained in more detail.

1. Pulse internal frequency modulation

A in-pulse, i. above the duration of a pulse made FM is known in radar technology and propagates (linear FM), or chirp, with one or more Ramps, non-linear FM, etc.) and is usually the primary goal a certain decoupling of distance resolution and pulse radar in the design, but in part also the signal coding or the targeted shaping a transmission spectrum. The pulse internal FM belongs to the pulse compression method, here with the cross-correlation with the image frequency control combined. In the literature is usually a matched filter for Frequency demodulation in the receiver described. The impulse response of the matched filter, then pulse compression filter called (PKF), but is known to be a copy of the time-mirrored and disturbed, frequency modulated transmit signal, which means that the output signal of the PKF corresponds to the autocorrelation function of the transmission signal. The above Implementation of the frequency demodulation by mixing the received signal with a copy of the transmission signal generated by one to the transmitter frequency synchronously operated carrier frequency oscillator in the receiver, and subsequent low-pass filtering but also corresponds to the Formation of an autocorrelation function. This form of frequency demodulation can therefore be considered as a practical implementation of a matched filter or PKFs are viewed.

2. Pulse-to-pulse FM

at Transmitter and receiver oscillator synchronous, continuous frequency changes with time constants in the range of pulse intervals or sudden frequency changes (Frequency hopping) between the pulses allow a unique Assignment of receive to transmit pulses across multiple pulses. It This can also be used to achieve signal coding or the transmission spectrum be specifically influenced.

3. Slow FM

this includes are, at transmitter and receiver oscillator synchronized, continuous frequency changes with time constants in the range of the pulse integration time or sudden frequency changes (Frequency hopping) with periods to understand constant frequencies comprising multiple pulses. The aim of the slow FM is primarily to reduce the susceptibility to interference or signal coding, e.g. by frequency evasion detection a foreign signal in the current receiving frequency band of a receiver. In limited Dimensions can but again the transmission spectrum can be specifically influenced. One Another potential application of slow FM is modulating from data to the transmit signal (FSK).

Claims (14)

Device for in particular bistatic radar applications, comprising at least two spatially-spaced radar sensors ( 11 . 12 ) for transmitting and / or receiving operation, each radar sensor ( 11 . 12 ) an independent, in particular free-running carrier frequency oscillator ( 21 . 22 ) and a modulator ( 51 . 52 ) for impressing pulses of a pulse signal source ( 3 ) to the respective carrier frequency oscillator ( 21 . 22 ), wherein a time synchronization control of the pulses for at least two mutually associated radar transmitter ( 11 . 12 ) is provided and wherein an evaluation device ( 4 ) for at least one image frequency, ie in particular a cross-echo Doppler signal using a mixing device ( 7 ) is provided for transmitting and receiving signals, characterized in that means for controlling or regulating the at least one image frequency by changing the carrier frequency of at least one of the carrier frequency oscillators ( 21 . 22 ) associated transmit and receive sensors ( 11 . 12 ) are provided. Device according to Claim 1, characterized in that a synchronous, in particular pulse-internal frequency modulation, a synchronous pulse-to-pulse frequency modulation or a synchronous, slow frequency modulation in the transmit and receive sensors ( 11 . 12 ) is provided. Device according to one of claims 1 to 2, characterized in that the transmit and receive sensors ( 11 . 12 ) are configured such that there is always a direct crosstalk from the transmitter to the receiver of a sensor regardless of the existence and location of objects in the detection field to be evaluated. Device according to claim 3, characterized that one through the direct crosstalk constantly present mirror signal or cross-echo Doppler signal for control or regulating the image frequency is used. Device according to claim 3 or 4, characterized that one through the direct crosstalk constantly present mirror signal for monitoring the carrier frequency control at transmitter and receiver is used as a diagnostic function. Device according to one of claims 1 to 5, characterized that for the transmitted radar pulses provide a constant pulse repetition rate is. Device according to one of claims 1 to 6, characterized in that at the pulse repetition rate of the transmitted radar pulses for each mutually associated transmit and receive sensors ( 11 . 12 ) a predetermined phase offset is adjustable. Device according to one of claims 1 to 7, characterized that the image frequency control as maximum value control of the output signal a mirror signal detector is executed. Device according to one of claims 1 to 8, characterized that an image frequency control based on a power and / or frequency estimate of Cross-echo Doppler executable is. Device according to one of claims 1 to 9, characterized in addition to the continuous image frequency control, a search engine or capture mode for first or refinding the image frequency is provided. Device according to one of claims 1 to 10, characterized that the image frequency control is designed so that a simultaneous Evaluation of eigen and cross echoes is possible. Device according to one of claims 1 to 11, characterized that means are provided, the image frequency control such perform, that crosstalk of cross echoes in the (Doppler) frequency range of the own echoes repressed becomes. Device according to one of claims 1 to 12, characterized in that the cross-echo Doppler for monitoring the carrier frequencies of the carrier frequency oscillators ( 21 . 22 ) is provided as a diagnostic function. Device according to one of claims 1 to 13, characterized a cross-echo transmitter identification based on estimated carrier frequency differences which is based in particular on estimates of the current image frequency, estimates the integer part of the quotient of carrier frequency difference and pulse repetition rate and knowledge of the current pulse repetition rate.