Patent ID: 12235388

DETAILED DESCRIPTION OF THE INVENTION

FIG.1shows a radar device1of the type according to the invention, in one of many possible application situations. The radar device is stationary and is provided with its own mount111, by way of which it is set up in the terrain in a stationary manner and can be anchored. The radar device is set up such that a monitoring region in a terrain101can be monitored. A danger region102from which, for example, rock fall or avalanches and/or mudslides are to be feared, and which could endanger a road104that leads through therebelow is drawn schematically inFIG.1. As is known, per se, for example from DE 10 2017 106 851 or from DE 10 2018 104 281, the radar device1is configured to control signal facilities105, by way of which the road below the danger region102can be blocked if a dangerous event has been ascertained. Since the monitoring region can be relatively large—a typical distance between the radar device and the monitoring region is between a fraction of a kilometre and several kilometres, for example 0.5-5 km—the measures to be taken can also be dependent on where the potentially harmful event has been ascertained, which is likewise described in DE 10 2018 104 281. Additionally or alternatively, the radar device can be provided with a communication unit, via which it can send measurement results, for example, via a network112to at least one external device113and via which it can also receive, for example, programming commands.

Apart from the monitoring of a natural terrain, which is represented inFIG.1, a possible application of a radar device of the type according to the invention is also the monitoring of huge constructions such as dams, dikes the like. The connection to a signal facility or the like is advantageous or is also not necessary depending the selected use. For example, one can also envisage an alarm simply being activated on determining an imminent event or one that has already began, and the necessary measures then be activated by an operating person.

In contrast to Doppler radar devices according to the state of the art, the radar device1, in addition to detecting events in real time, also permits the highly-resolved imaging of a terrain in the monitoring region as well as the detection of very slow movements or of movements of a medium speed which, will be dealt with in more detail hereinafter.

As is schematically represented inFIG.2, the radar device includes a housing2that is assembled in a stationary manner, for example with a mount111of the aforementioned type, as well as a plurality of transmitting antennae4, which is arranged in a stationary manner relative to the housing. The transmitting antennae are arranged distanced to one another at predefined distances with respect to a horizontal direction (y-direction; azimuth direction). Apart from this, the radar device likewise includes a module5, which is likewise arranged in a stationary manner during the operation, and which is with an arrangement of several receiving antennae6, which are likewise arranged in predefined, essentially regular distances and distanced to one another in the same horizontal direction (y). The distances of the adjacent receiving antennae do not have to be precisely the same, but can also slightly differ in a defined and known manner. This can even be advantageous since slightly varying distances can be used in order to reduce artefacts on evaluation.

The distance of the receiving antennae to one another can correspond to a value between roughly half a wavelength and a wavelength, i.e., at 17 GHz between just short of 0.9 cm and just short of 1.8 cm. The distance between the transmitting antennae4can correspond roughly to the number of receiving antennae in a module5multiplied by their number, thus in the present example given16receiving antennae approx. 15 cm to 30 cm.

Further virtual receiving antennae6′ result by way of the combination of the different transmitting antennae4with the receiving antennae6of the receiving antennae module. For example, the combination of the transmitting antennae4, which is shown at the bottom inFIG.2with the receiving antennae6of the receiving antenna mode5, corresponds to an arrangement of virtual receiving antennae6′, which are drawn inFIG.2below the receiving antenna module5in a dotted manner in combination with the transmitting antenna4, which is drawn inFIG.2in the middle. In this manner, the MIMO principle enlarges the virtual aperture of the antenna arrangement.

In order to be able to enlarge the virtual aperture even further, furthermore further stationarily arranged receiving antennae modules15can be present.

The distance between the receiving antenna modules5,15in the represented example. for example. corresponds roughly to the number of transmitting antennae4multiplied by their distance. As a whole and on account of the MIMO principle, an arrangement of in total n*m′*M virtual receiving antennae, which are distanced to one another at regular distances in the horizontal y-direction (corresponding to the distance of adjacent receiving antennae with a module) results, where n is the number of transmitting antennae, m′ the number of receiving antennae per module and M the number of receiving antennae modules.

The same arrangement of virtual receiving antennae would also be achievable with a correspondingly larger number of transmitting antennae (for example, grouped in transmitting antenna modules), a larger number of receiving antennae per module or an arrangement of several receiving antenna modules directly next to one another combined with transmitting antennae, which are accordingly arranged at greater distances. The type of combination of transmitting and receiving antennae can be varied in this manner without compromising the functionally, which is yet to be illustrated hereinafter by way ofFIG.9-11.

The radar device also includes a control and evaluation unit7, which is likewise configured for communication with the external device/external devices113.

The control and evaluation unit includes various electronic components, which hereinafter to some extent are described in more detail. These can be designed in an integrated manner to a greater or lesser extent. In particular, the control and evaluation unit can also include components that are arranged at different locations and can be combined, for example, also with other entities, for example by way of them being implemented in an external computer or being integrated directly in an antenna. The control and evaluation unit is therefore to be understood as a unit in the functional sense and is not necessary also integrated physically.

The transmitting antennae4—for example sequentially, as is yet explained hereinafter—generate primary radio waves11, which are reflected back from the terrain101, to which possibly moving objects107also belong, so that the thus arising secondary radio waves12can be detected by the receiving antennae6.

FIG.3shows a schematic diagram of elements of the control and evaluation unit each together with a transmitting antenna4and a receiving antenna6. A clock generator OSC cycles a numerically controlled oscillator (DDS) which with the help of a control signal29generates a frequency ramp, which in turn serves as a reference for a downstream phase control loop with a high-frequency oscillator (PLL) and produces a frequency-modulated, phase-stable first signal, for example in a frequency band in the low Gigahertz region. A frequency multiplier22, for example, from the first signal produces a higher-frequency emitting signal whose frequency is an integer multiple of the first signal (multiplication of the frequency by a factor F). The path via the frequency multiplier is optional, i.e., the oscillator can also be configured for generating the emitting signal in the desired frequency in a direct manner. The diversion via the less high-frequency first signal makes sense in particular in combination with the optical signal transmission, which is yet described in more detail hereinafter.

The frequency-modulated emitting signal has a frequency that is suitable for radio waves for the envisaged application and if applicable released by law. For example, it varies in a frequency band about 17 GHz. The emitting signal is amplified in a suitable manner, for example by way of a power amplifier PA and is fed to the transmitting antenna, which emits the corresponding primary radio waves11.

On using several transmitting antennae, it is also possible to optically feed the signal to the various transmitting antennae. It is then converted electrically and is amplified with a power amplifier before the transmitting antennae.

Secondary radio waves12, which are reflected back by the terrain, produce a receiving signal in the receiving antenna6, the receiving signal after a suitable amplification (LNA) being mixed with the emitting signal (mixer24). Herein, an individual mixer24, which is located spatially in the direct vicinity of the receiving antenna, is generally assigned to each receiving antenna6. In the embodiment ofFIG.3, it is not the emitting signal, but the first signal, which is transmitted to the location of the mixer, which is why a second frequency multiplier23must be present there, in order to generate the emitting signal with the frequency that is higher by a factor F.

As is known per se, a mixed signal results at the output side of the mixer24, and this mixed signal includes signal components with the sum of the frequencies of the emitting signal and receiving signal as well as signal components with the differential frequency Δf. By way of a low-pass filter, the high-frequency components are filtered out, so that only signal components with the differential frequency Δf are processed further. This filtered mixed signal is also denoted as an “intermediate frequency signal” in the present text. It provides information on the basis of the relationship that is represented schematically by way ofFIG.4and that has already been known for some time for FMCW (frequency modulated continuous wave) radar devices of the type that are described here.

The radar device can include, for example, precisely one oscillator, wherein the emitting signal is fed to the respectively current transmitting antenna in a manner controlled by a switch, in the sequence that is yet explained hereinafter by way of examples. The radar device can furthermore each include a mixer and an A/D converter per receiving antenna, so that the receiving signals can be produced and detected in parallel. The emitting signal is therefore fed in parallel to the current transmitting antenna as well as to all receiving antennae.

On signal detection, a larger number of parallel receiving signals results with a high sampling frequency, which is necessary for a sufficiently good resolution and unambiguity regions, the receiving signals having to be processed very quickly in particular for the evaluation of the events at high speeds in real time. For this purpose, the control and evaluation unit can include suitable means for the very rapid execution of computation-intensive processing steps, for example Fourier transformations. For example, the signals from the A/D converters can be received and processed by way of at least one FPGA (field programmable gate array) or a GPU of the control and evaluation unit.

FIG.4schematically shows the frequency as a function of time for a succession of chirps, wherein the emitting signal is represented in unbroken lines and the receiving signal in a dotted manner. The delay of the receiving signal (echo) Δt effects a frequency difference Δf between the emitting signal and receiving signal, the frequency difference being dependent on Δt and the course of the chirp. Given a linear frequency modulation, as illustrated, the delay Δt is proportional to the frequency difference Δf, at least if one were to ignore possible Doppler shifts of the receiving signal. Since Δt is proportional to the covered path and, thus, to the distance between the radar device and the reflection location, the “range” resolution results in an essentially direct manner from the spectrum of the intermediate frequency signal.

Additionally to the mentioned low-pass filter, whose significance has been explained by way ofFIG.4, also a high-pass filter can be applied to the mixing signal, in order to filter out very low-frequency signal components, which in particular originate from reflections close to transmitting antenna. Such low-frequency signal components are of then comparatively high in energy and provide little information.

The functionalities of the low-pass filter and of the optional high-pass filter, in the embodiment ofFIG.3are implemented in a bandpass filter25, but it is also possible for the low-pass filter and the high-pass filter to be present as separate elements that are connected one after the other.

The resulting, possibly high-pass filtered intermediate frequency signal is fed to a subsequent evaluation after the analog-digital conversion.

FIGS.5-7schematically show different possibilities for the transmitting antenna control.

During first sequences, successive chirps with a frequency bandwidth B1are fed as emitting signal in each case per sequence to the same transmitting antenna TX1. As is illustrated inFIG.5(and as is also applied in the subsequent examples) one can use the same transmitting antenna in particular for all first sequences. Herein, the chirps are selected such that their repetition frequency is as large as possible, i.e., the chirp-to-chirp time duration is selected as small as possible. A first Fourier transformation can be carried out per chirp and provides a range resolution per chirp. On evaluation, the temporal development over the chirps can be evaluated in order to detect rapid movements in the terrain. In particular, this can be effected in a manner that is known per se from Doppler radar systems by way of a second Fourier transformation over the whole first sequence or at all events also over only a part of the first sequence, which result in the Doppler frequency shift as well as a (coarsely resolved) phase. The result of this evaluation is therefore a so-called ‘range Doppler map’.

In particular, one can envisage the signal detection and mixing being carried out during the first sequences for a plurality of the receiving antennae, for example for all receiving antennae6of a module5. By way of a comparison of signals, which are received by the different receiving antennae6of the one module, additionally to the resolution in range and the speed (Doppler frequency) resolution, one can also effect a coarse azimuth resolution, i.e., a resolution in the lateral angle by way of a so-called beamforming algorithm. Such a comparison can be effected for example analogously to an evaluation of interferometry radar signals, wherein the achievable accuracy is limited by the aperture, i.e., the horizontal extension of the respective receiving antennae module5is limited.

The frequency bandwidth B1which determines the range resolution can be adapted in accordance with requirements. Specifically, the frequency bandwidth B1can be selected comparatively small. This, on the one hand, is because the frequency difference Δf is also proportional to the steepness of the frequency rise per flank (seeFIG.4) and given higher intermediate frequency values the signal detection and processing effort is larger than with smaller intermediate frequency values on account of the higher sampling rate which becomes necessary—which is why the flanks cannot be selected in an arbitrarily steep manner. On the other hand, the maximal unambiguously detectable speed with the described method is directly dependent on the repetition frequency of the chirps, which is why the chirps must be short. For example, it can be advantageous if the chirp-to-chirp time is not larger than between 40 and 100

The time duration T1of a first sequence is computed by the number N of chirps per first sequence—expediently for a sufficiently good signal-to-noise ratio for example at least a few hundred, for example 512—multiplied by the chirp-to-chirp time. The number of first chirps required in practise depends on the minimum radar cross section (RCS) of an object to be observed, as well as on the distance; the smaller are the objects that are to be detected and the more distanced they are, the larger does the so-called Doppler gain have to be. The gain rises with the number of first chirps per first period. With a large N, the fact that concerning the moved objects the distance to the radar device also changes during the first sequence is of relevance under certain circumstances and this effect must be taken into account with the Fourier transformation.

The second sequences serve for obtaining an imaging of the monitored terrain, which is angularly resolved to an improved extent and in particular also in order to measure slow movements and changes. For this purpose, firstly the second chirps of the second sequences are emitted by different transmitting antennae, in the represented embodiment examples sequentially, i.e., in each case not simultaneously. Secondly, the second chirps have a comparatively large bandwidth. In particular, the bandwidth of the second chirps is larger than that of the first chirps, for example by at least a factor of 3 or by a factor 5, 8 or more.

However, as is also illustrated, for example inFIGS.5-7, one can envisage the steepness of the chirps of the first and second chirps being the same. “Steepness” here is denoted as the change ∂f/∂t of the frequency of the primary radiation per unit of time, i.e., given a frequency increase or frequency decrease, which is linear as a function of time, the gradient of the respective flanks. An equal steepness of the first and second chirps has the advantage that the intermediate frequency signal is in the same frequency region during the first and second sequences.

InFIG.5, the second sequences each include a chirp from each of the transmitting antennae, i.e., the transmitting antennae successively emit a chirp, in order to form a second sequence. The scattered back secondary radio waves, which are generated as a reaction to the respective primary radio waves, are detected by each of the receiving antennae. In total n*m signals result, wherein m is the number of receiving antennae and n the number of transmitting antennae.

The evaluation of the second receiving signals, i.e., of the receiving signals that originate from the second chirps, is effected, for example, by way of approaches as are known per se from radar interferometry, with the particularities that are explained in more detail hereinafter. Whilst using trigonometric relations, an imaging, which is resolved in the azimuth angle, results from the phase differences between the different second receiving signals (whilst using a so-called “phase unwrapping” for eliminating ambiguities). A phase comparison in dependence on time furthermore points to slow movements in the terrain. The maximal thus observable and unambiguously ascertainable speed is given by the period Tp, i.e., by the time duration of a complete cycle corresponding to the time duration between two second chirps TXithat depart from a certain transmitting antenna. In the embodiment example ofFIG.5, this time duration Tpcorresponds to the sum of the time duration T1of a first sequence and the time duration T2of a second sequence. If a movement is quicker than vmax,I=λ/4*(1/Tp), then due to the aliasing effect it can no longer be unambiguously differentiated from a slow movement solely by way of a phase comparison.

Without further ado, it is realistic that vmax,Iis significantly larger than the speeds of maximally a few metres per year, which until now were determined in the state of the art by way of evaluating interferometric measurements. If for example—as an example with randomly but realistically selected number values—one were to assume 512 chirps with a chirp-to-chirp duration of 70 μs during a first sequence and 5 chirps with a chirp-to-chirp time duration of 600 μm, then a period of 38.84 ms results for Tpwhich via vmax,I=λ/4*(1/Tp) at 17 GHz corresponds to a speed of more than 100 mm/s.

If vmax,Iis of the same magnitude as the minimal speed vmin,dwhich can be resolved by the evaluation of the first sequences, then the procedure according to the invention for the first time permits essentially the whole speed spectrum to be covered, without gaps at medium speeds.

If, as in the embodiments represented here, the first sequences and the second sequences are not simultaneous or overlapping, but one after the other, the monitoring of very rapid events is interrupted during the second sequences. If such a rapid event (avalanche, rock fall, etc.) begins during a second sequence, then from this and in the most unfavourable case a certain lengthening of the best possible reaction time by maximally the length of a second sequence results. For many applications, such delays of the magnitude of a few milliseconds (3 ms in the number example specified above) are absolutely tolerable and do not significantly include the functionality of the complete radar device. The detectability of medium sized speeds of typically a few millimetres per second is to be weighted more greatly with such applications, since from this results the possibility of reacting already before the beginning of events, by way of the event being announced by way of increased movements at such medium speeds in the terrain, generally shortly before the release of an avalanche or a rock fall or shortly before a dam break.

In the case that such an interruption of the first sequences for milliseconds cannot be tolerated in very specific application cases, the subdivision between first and second sequences can also be selected in another manner, so that the second sequences—and herewith the “interruptions”—become shorter, wherein in turn the unambiguity region of the detectable medium speeds becomes smaller.

FIG.6illustrates a corresponding example, in which the second sequences only each include a single chirp and the second chirps are each emitted by different transmitting antennae from second sequence to second sequence. The time duration T2of a second sequence, by which the monitoring of rapid events is interrupted, is then correspondingly smaller. In exchange, the time duration Tpbetween two second chirps that are emitted by the same transmitting antennae increases, since it includes several—corresponding to the number of transmitting antennae—first sequences, so that the unambiguity region of the speeds of movements detected via second sequences is correspondingly smaller.

FIG.7finally shows the general case, of which the embodiments ofFIGS.5and6represent special cases. Per cycle, several second sequences can be present and these in principle can have different lengths, wherein the number of the second chirps adds over all second sequences per cycle into the total number, which, in the examples that are represented here, corresponds to the number of transmitting antennae. In particular, one can envisage the second sequences each being equally long, which apart from in the special cases ofFIGS.5and6presupposes the number of transmitting antennae not being a prime number. For example, given six transmitting antennae, two second sequences each with three chirps or three second sequences each with two chirps can occur per cycle.

A respective equal number of second chirps per second sequence simplifies the evaluation of the measurement results which are generated by the second sequences. This being due to the fact that the correction of the measured phases requires more effort if the length of the second sequences is not equal: the monitored terrain indeed possibly also moves between the chirps. These phases must be corrected before the virtual receiving antennae of a complete measurement can be computed over the chirps of all n transmitting antennae. This is potentially simpler if the phase difference from chirp to chirp can be assumed as being constant.

Generally, the radar device is configured to cyclically repeat the succession of the first sequences and of the second sequences, wherein as mentioned the cycle length Tpis particularly short if, as inFIG.5, the second sequences each include chirps of all transmitting antennae.

The radar device can be configured to always run in the same operating mode, i.e., the length of the second sequences can be configured in a fixed manner. However, it is also an option for the radar device to permit a setting of the operating mode and thus for the length of the second sequences—and herewith the length Tpof the complete cycles as is explained by way ofFIG.5-7—to be able to be selected and thus adapted to the current demands.

Such an adaption can also be carried out automatically by the control and evaluation unit7or by an external device. If, for example, accelerated regions are recognised in a mode as is represented inFIG.6, then one can change to a mode as is represented inFIG.5, in order to be able to track this acceleration even longer interferometrically with the second sequences and with higher maximal speeds.

The relationship that is already outlined above, that the frequency bandwidth determines the resolution in range, the length of the sequences the speed resolution, the temporal interval of two chirps that are used for the speed measurement (i.e., in the ideal case of directly consecutive chirps the time duration of the chirps) the maximal determinable speed and the time duration of a measurement the signal-to-noise ratio, is very generally the case. Against this background, the parameters can be adaptively selected, for example given the determining of an event, the measurement value that characterises this event in a particularly informative manner being measured particularly quickly and/or particularly accurately. There is also the possibility, if of an event one knows in which azimuth region this takes place, of being able to measure in only this direction.

The evaluation of the signals which correspond to the second sequences, in embodiments can be effected as follows:In a first step, as with the aforedescribed evaluation of the first sequences, a so-called range Doppler map is computed per transmitting antenna—receiving antenna combination each by way of a Fourier transformation, i.e., the frequency and phase are detected as a function of the distance (range).In a second step, the correction of the phases of moved objects is effected. This is necessary since the transmitting antennae do not emit simultaneously and the objects could have moved between recordings. The range Doppler maps, which correspond to the receiving signals that are produced by the various transmitting antennae, represent the monitored region at different points in time. The adaptation is effected whilst taking into account the temporal interval between the second chirps such that the adapted range Doppler maps correspond to a momentary recording at a same point in time.In a third step, the so-called beamforming is effected, i.e., the computing of a range Doppler map for each azimuth angle or indeed a phase picture as a function of range and azimuth. Corresponding imaging evaluation methods, with which from a comparison of range Doppler pictures of receiving signals from different receiving antenna positions, corresponding different aspect angles are acquired, are known per se. They have been developed in particular for the so-called SAR interferometry (synthetic aperture radar interferometry), concerning which a synthetic antenna apparatus is achieved by way of the transmitting and receiving antenna being moved along a so-called baseline (corresponding to the line in the y-direction inFIG.2, along which the antennae are rowed). Corresponding evaluation software is commercially available.

The following generally applies to aspects and embodiments of the present invention:Particular challenges can result firstly on evaluating the temporal development of the phase pictures, since the atmospheric constraints change as a function of time. Secondly, challenges can result due to the fact that a distortion of the resolution in the azimuth (azimuth warping) can occur on account of slight inaccuracies on signal transmission over distances between the antennae as well as on account of the temporal staggering of the second chirps together with fluctuations of the atmospheric constraints.

For the elimination of the influence of atmospheric fluctuations as a function of time upon the temporal development of the phase pictures, the following method, for example, is suggested:For determining medium speeds of for example a few mm/h to a few mm/s, interferograms (phase differences of pairs of interferometric measurements that are resolved in range and azimuth) are generated with recordings, which have arisen shortly after one another, for example within a second or a few seconds up to minutes. Here, a simple correction, for example, based on the assumptions that the constraints change in a simple manner, for example linearly as a function of time (sliding atmosphere model), is sufficient.For determining very slow speeds of, for example, a few mm per year to mm/day, interferograms of measurements can be made, these having arisen at larger temporal intervals, for example at intervals of months. The atmospheric constraints as well as also the nature of surfaces etc. (e.g., due to ground humidity, snow covering, etc.) can fluctuate so greatly within such a large time interval that a simple correction of the aforementioned type is not sufficient. Instead of this, it is suggested to proceed as follows: on setting up the stationary radar device, at least one stationary region41(seeFIG.8) is identified and defined in the terrain. Such stationary regions41are regions of which it is known on account of geological conditions that no slow terrain movement is to be expected. For the evaluation during the operation, interferograms are computed from pairs of recordings that have arisen after one another at a larger temporal interval of, for example, a few months. In a first evaluation step, pairs of recordings that have successively arisen at roughly the same temporal interval and concerning which the pictures of the stationary regions41correspond as well as possible to one another are sought. Picture processing algorithms, which can identify the similar as possible recordings, can be used for this. Of such recording pairs with good as possible corresponding pictures of the stationary regions41, the phase pictures of other regions are compared, in order to determine movements in the terrain.

A stationary region41of the described type can at all events be used in order to compensate travel time changes at the cables and in the electronics as a result of temperature fluctuations and/or ageing.

A new type of method is also suggested for eliminating distortions in the azimuth. The fact that not only the phase picture, but also the amplitude picture, i.e. the receiving signal amplitude as a function of the resolved coordinates “range” and azimuth” are characteristic of the terrain is utilised. In particular, characteristics points42in the terrain can also be identified in the amplitude picture. Such characteristic points42can be distinguished by their particular position or particular nature (reflection characteristics). The use of characteristic patterns instead of characteristic points is also possible. It is suggested to correct the dependency of the picture on the azimuth angle in the context of equalisation such that the characteristic points42are imaged onto the—prior known—azimuth coordinate. An equation system can be set up for this purpose, with the equalisation corrections (the noisy phase differences between RX antennae or different TX antennae) as unknowns, by way of which system the current amplitude picture is imaged onto a reference amplitude picture—with the characteristic points at the correct location.

According to a particular embodiment, for obtaining such a reference amplitude picture on setting up the stationary radar device, a calibration measurement is carried out as follows: The characteristic points42in the terrain are identified and a drone is controlled and programmed such that its flight path corresponds to a section of a straight beam between the respective characteristic point42and the radar device. The drone is captured by the radar device during this flight. The real azimuth angle of the drone location during the flight results from the flight path of the drone. This procedure is repeated in a timely manner for different characteristic points42. The amplitude picture, which is recorded during this drone flight, is used for generating the reference amplitude picture, wherein an equalisation correction is carried out on the basis of known drone azimuth angles during the differently carried out flights.

The evaluation of the measurements that are effected during the second sequences (of the second receiving signals), despite the possibility of equalisation corrections of the aforedescribed type, creates a particularly high stability of the phases. This also means that the measuring accuracy is very sensitive to phase shifts between the emitting signal and the associated receiving signal, caused by the apparatus. Such can result in practise, for example, if the corresponding analog signal must be transmitted over longer distances, for example due to temperature fluctuations and length and other dimensional fluctuations that are caused by this.

For this purpose, according to the second aspect of the invention, one suggests the transmission of the emitting signal—for example in the form of the first signal, from which the high-frequency emitting signal is obtained by way of frequency multiplication—being effected optically over larger distances. In the example illustrated inFIG.2, on using several receiving antenna modules, in particular larger distances from the oscillator (formed from the clock and phase control loop) to the receiving antenna modules result. For this reason, inFIG.3one suggests transmitting the first signal to the mixer24via an electrical-optical converter (E/0) in the proximity of the oscillator, an optical signal lead and an optical-electric converter (O/E) in the vicinity of the corresponding receiving antenna module. Particularly with arrangements with transmitting antenna, which are arranged further remotely from one another (for example, of the transmitting antenna are arranged on a different circuit board than the oscillator, in combination with a larger receiving antenna module and/or on using particularly many transmitting antennae), the transmission of the emitting signal or of the first signal to the transmitting antennae can supplementarily or alternatively be effected optically.

The generation of the first signal of a somewhat lower frequency and the obtaining of the emitting signal from this signal by way of frequency multiplication (frequency multipliers22,23inFIG.3)—inasmuch as one is not dependent on the phase coherence of emitting signal, upon which the signal that is used for the mixing at the mixer is reliant—makes particular sense in the context of the optical transmission of the signal for the following reason: The optical transmission of signal with frequencies of for example 17 GHz would be relatively complicated and for this reason the components that are required for this are not obtainable on the market without further ado or are expansive. The procedure with the generation of the first signal of a somewhat lower frequency in combination with the frequency multiplication in front of the power amplifier PA or the mixer24solves this problem in an elegant manner and thus permanently improves the economics.

FIG.9shows an arrangement of a receiving antenna module5, which is similar toFIG.2, with a plurality of receiving antennae6that are arranged at a regular distances, as well as with three transmitting antennae4(transmitting antennae I-III). Given an object that throws back the secondary radio waves12and which is arranged at a greater distance, the difference between the path distance of radiation that departs from two different ones of the transmitting antennae4is the same as if the radiation were to come from a single transmitting antenna and were to be incident upon receiving antennae which are arranged at a corresponding distance to one another. The drawn arrangement therefore with respect to this is equivalent to an arrangement with a single transmitting antenna4—corresponding to the first antenna—in combination with a correspondingly enlarged array of—virtual—receiving antennae6′. The virtual receiving antennae6′ could be assigned according to the physical transmitting antennae (group II, I and III). If the transmitting antennae emit the second chirps successively, then the signals of the virtual receiving antennae6′ of the respective group are detected one after the other.

FIG.10shows an alternative arrangement—likewise with only a single receiving antenna module5. In this embodiment, the distance of adjacent receiving antennae is larger (here corresponding to a whole wavelength λ instead of merely half a wavelength as in the previously described embodiment examples). For this, the arrangement of the transmitting antennae4is such that the virtual receiving antennae6′ from a staggered arrangement. In the represented example, this staggered arrangement results from the transmitting antennae4forming groups of each two transmitting antennae that are arranged at a distance of one and a half wavelengths to one another. Groups at a distance of half a wavelength or five wavelengths, etc., would also result in this effect. For illustration, those virtual receiving antennae, which correspond to the real receiving antennae6at the far left, are characterised by a dot inFIG.10.

The embodiment ofFIG.10as other embodiments with real receiving antennae, which are arranged at a somewhat larger distance to one another, has the advantage that the receiving antennae can be used with a larger gain.

FIG.11finally shows a particularly simple arrangement with only one receiving antennae module5but with several transmitting antenna modules50each with a plurality of transmitting antennae4. The distances of adjacent transmitting antennae4correspond to the “width” of the receiving antennae module, i.e., to the number of receiving antennae multiplied by the distance of adjacent receiving antennae.

Embodiments with transmitting antennae modules or with several receiving antenna modules permit a simple adaptability of the hardware to user-specific requirements: Depending on the demands on the azimuth resolution, a larger or smaller number of modules can be used.

Numerous further combinations of transmitting and receiving antennae that result in a regular arrangement of virtual receiving antennae6′ are conceivable.