JP2023535509A - Radar system, antenna array for radar system, vehicle comprising at least one radar system, and method for operating at least one radar system - Google Patents

Abstract

The present invention relates to a radar system for monitoring at least one surveillance area (18) for an object, an antenna array (22), a vehicle and a method for operating the radar system (12). The radar system comprises a plurality of transmit antennas (26) controllable with respective transmit signals and operable to transmit target radar signals to at least one surveillance area. Additionally, the radar system comprises a plurality of receive antennas (28) that can be used to receive echoes of the transmitted radar signals and convert the echoes into corresponding received signals. Additionally, a radar system is connected to the transmit antenna (26) and the receive antenna (28) and can be used to generate a transmit signal to control the transmit antenna, and using said radar signal (30) It comprises at least one control and evaluation device (24) which can be used to ascertain from said received signal object information (r, φ, Θ) associated with a detected object (18). Each phase center (32) of at least four said receive antennas (28) is positioned on a virtual receiver longitudinal axis (46). Each phase center (32) of at least two adjacent receive antennas (28) are positioned at a base spacing (40) from each other. Said phase centers (32) of at least two adjacent said receiving antennas (28) are positioned relative to each other at respective receiver longitudinal spacings (48a, 48b, 48c) greater than said base spacing (40).

Description

The present invention is a radar system for monitoring at least one surveillance area for an object, comprising:
a plurality of transmit antennas controllable with respective transmit signals and operable to transmit target radar signals to at least one surveillance area;
a plurality of receive antennas operable to receive echoes of a transmitted radar signal and convert the echoes into corresponding received signals;
Connected to the transmit and receive antennas and operable to generate transmit signals to control the transmit antennas and to ascertain from the received signals object information associated with objects detected using radar signals. A radar system comprising at least one control and evaluation device that can be used.

Further, the present invention is an antenna array for a radar system monitoring at least one surveillance area for an object, comprising:
a plurality of transmit antennas controllable with each transmit signal and operable to transmit a radar signal of interest;
An antenna array comprising a plurality of receive antennas that can be used to receive echoes of transmitted radar signals and convert the echoes into corresponding received signals.

The invention also relates to a vehicle comprising at least one radar system for monitoring at least one surveillance area for objects,
At least one radar system
a plurality of transmit antennas controllable with respective transmit signals and operable to transmit target radar signals to at least one surveillance area;
a plurality of receive antennas operable to receive echoes of a transmitted radar signal and convert the echoes into corresponding received signals;
Connected to the transmit and receive antennas and operable to generate transmit signals to control the transmit antennas and to ascertain from the received signals object information associated with objects detected using radar signals. at least one control and evaluation device that can be used.

Further, the present invention is a method of operating a radar system used to monitor at least one surveillance area for an object, comprising:
controlling a plurality of transmit antennas using transmit signals and transmitting applicable radar signals to a surveillance area;
Receive echoes of radar signals transmitted using multiple receive antennas, convert the echoes to corresponding received signals, process the received signals using signal processing, and receive object information about objects within the monitored area. confirming from the signal;
about a method comprising

[Prior art documents]
From DE 102 018 118 238 A1, a method for operating a radar system and a radar system are known. The method includes using at least two transmit antennas spaced apart from each other to transmit transmit signals to the monitored area. If desired, at least one receive array element is used to receive echo signals reflected by at least one object present in the monitored area. At least one piece of object information is ascertained from the echo signal. A range steering mode in which the radar system is used to simultaneously transmit the same transmitted signal with at least two transmit antenna elements and the distance and/or velocity of at least one object relative to the radar system is ascertained from the corresponding echo signals; or A directional steering mode in which at least two transmit antenna elements are employed to transmit transmit signals that are distinguishable from each other, suitably distinguishable echo signals are assigned to the transmit antenna elements, and at least one directional component of an object is ascertained. operated by either

The present invention is for the purpose of designing a radar system, an antenna array, a vehicle and a method of the kind mentioned at the outset, in which the performance of the radar system in terms of its detection range and angular resolution for direction determination is improved. based on

According to the invention, this object is for a radar system:
a phase center of each of the at least four receive antennas positioned on a virtual receiver longitudinal axis;
said phase centers of at least two adjacent said receive antennas are spaced apart from each other by a base; and
said phase centers of at least two adjacent said receive antennas are positioned with respect to each other at respective receiver longitudinal spacings greater than said base spacing;
This is achieved by

According to the invention, the four receive antennas are arranged next to each other along a virtual receiver longitudinal axis. Here, at least two receive antennas are arranged with a base spacing. This allows the receive antenna to be used to make unambiguous direction determinations. At least two receive antennas are spaced apart by a greater distance. This may result in an overall larger receive antenna configuration. This can lead to large apertures for radar systems.

The receive antenna configuration of the present invention employs a radar system in both a directional steering mode, in which the receive antennas are controlled using different received signals, and a range operation mode, in which the receive antennas are controlled using the same received signal. can be employed for

According to one advantageous embodiment, at least one longitudinal receiver spacing may be an integer multiple of the base spacing, in particular plus or minus a tolerance. This allows the spread of the receive antenna configuration to be increased in the direction of the receiver longitudinal axis. This allows a corresponding large virtual receive antenna array formed from the transmit and receive configurations to facilitate a corresponding large aperture in the direction of the steering mode of the radar system.

According to a further advantageous embodiment, each phase center of the two receive antennas located outside the receiver longitudinal axis may be arranged at a base spacing. A corresponding virtual receive antenna array can thereby be realized that facilitates better angular resolution in the steering mode of the radar system.

According to a further advantageous embodiment, each phase center of at least two receive antennas adjacent to each other is arranged on the same side of the phase center of two receive antennas arranged at a base spacing,
The receiver longitudinal spacing between the phase centers of the nearest receive antennas of the two base-spaced receive antennas and the nearest phase centers of the two base-spaced receive antennas is the base-spaced be less than the receiver longitudinal spacing between the phase center of the receive antenna closest to the two receive antennas in the base spacing and the phase center of the receive antenna spaced apart from the two receive antennas spaced at the base;
The receiver longitudinal spacing between the phase centers of the nearest receive antennas of the two base-spaced receive antennas and the nearest phase centers of the two base-spaced receive antennas is the base-spaced may be greater than the receiver longitudinal spacing between the phase center of the receive antenna closest to the two receive antennas and the phase center of the receive antenna spaced apart from the two receive antennas spaced by the base spacing. Thereby, a virtual receive antenna array with a large aperture combined with a large angular resolution can be realized in the steering mode of the radar system.

The receive antenna configuration can be more compact if the longitudinal receiver spacing of the nearest receive antenna is smaller than the longitudinal receiver spacing of the spaced apart receive antennas.

In this case, the base interval and the two longitudinal intervals may advantageously be arranged according to the indication of the Golomb ruler.

When the longitudinal receiver spacing of the nearest receive antenna is greater than the longitudinal receiver spacing of the spaced-apart receive antennas, a corresponding spread virtual receive antenna array facilitating correspondingly large angular resolution is used in the directional steering mode of the radar system. can be realized in In this case, a larger aperture can be facilitated in range operating modes of the radar system.

According to a further advantageous embodiment, the quotient of the two larger receiver longitudinal spacings and the two smaller receiver longitudinal spacings between three adjacent receiving antennas is preferably 1.5. Or it may be an integral multiple of 1.5. This may improve the clarity of the angle measurement.

The quotient of the two larger receiver longitudinal spacings and the two smaller receiver longitudinal spacings between three adjacent receiving antennas may advantageously be twice 1.5, ie 3. .

According to a further advantageous embodiment, the base spacing may correspond to half the wavelength of the radar signal transmitted using the transmitting antenna, in particular plus or minus a tolerance. Hereby, distinctly directed radar signals at the transmitter in the directional steering mode of the radar system can be realized. In addition, explicit angle measurements can be made in the directional manipulation mode.

At least one transmit antenna may advantageously comprise a plurality of antenna elements. This may improve the transmission characteristics of the at least one transmit antenna. Alternatively or additionally, the at least one receiving antenna may advantageously comprise a plurality of antenna elements. This may improve reception characteristics of the at least one reception antenna.

The phase centers of the transmit antennas may advantageously be located in the transmit antenna plane. This allows the position of the phase center to be defined more easily. Therefore, more accurate radar measurement can be performed. The main beam direction of the transmitting antenna may advantageously run perpendicular to the plane of the transmitting antenna. This allows the main beam direction to be defined more easily.

Alternatively or additionally, the phase center of the transmit antenna may advantageously be located in the plane of the receive antenna. This allows the position of the phase center to be defined more easily. Therefore, more accurate radar measurements can be made. The main receiving direction of the receiving antenna may advantageously run perpendicular to the plane of the receiving antenna. This allows the primary receiving direction to be defined more easily.

Alternatively or additionally, the phase center of the transmitting antenna and the phase center of the receiving antenna may advantageously be arranged in a common antenna plane. This allows the position of the phase center to be located more accurately.

At least some of the transmit antennas may advantageously be implemented as antenna arrays. This allows the transmitting antennas to be manufactured and assembled together.

Alternatively or additionally, at least some of the receiving antennas may advantageously be implemented as antenna arrays. This allows the receiving antennas to be manufactured and assembled together.

Alternatively or additionally, at least some of the transmit antennas and at least some of the receive antennas may advantageously be implemented as a common antenna array. This allows the transmit and receive antennas to be manufactured and assembled together.

Advantageously, each phase center of at least two adjacent transmit antennas may be arranged on a virtual transmitter longitudinal axis, and the phase center of at least one further transmit antenna may be arranged from the transmitter longitudinal axis to the transmitter transverse axis. may be spaced apart.

A virtual transmitter horizontal axis running perpendicular to the transmitter longitudinal axis through the phase center of the at least one further transmit antenna is advantageously the one of the at least two transmit antennas on the transmitter longitudinal axis. It may be located at a base distance from said virtual transmitter horizontal axis running through the phase center and perpendicular to the transmitter longitudinal axis.

The transmitter longitudinal spacing between each virtual transmitter longitudinal axis of at least two adjacent transmit antennas on the transmitter longitudinal axis may advantageously be greater than the base spacing.

The at least two transmit antennas may advantageously be arranged along the transmitter longitudinal axis. At least one further transmit antenna may be arranged next to the transmitter longitudinal axis. At least one transmit antenna positioned next to the transmitter longitudinal axis may be positioned next to one target transmitter horizontal axis of the at least two transmit antennas at a base spacing.

This advantageous transmit antenna configuration can be operated in both a directional measurement mode, in which the transmit antennas are controllable using different transmit signals, and a range operation mode, in which the transmit antennas are controllable using the same transmit signal.

The transmitter longitudinal spacing may advantageously be an integer multiple of the base spacing, in particular plus or minus a tolerance.

Alternatively or additionally, the transverse transmitter spacing may advantageously be greater than the base spacing.

Alternatively or additionally, the transverse transmitter spacing may advantageously be smaller than the longitudinal transmitter spacing.

Hereby a particularly compact transmit antenna configuration can be achieved.

The transmitter transverse axis of at least one further transmitting antenna may advantageously be arranged between the transmitter transverse axes of at least two adjacent transmitting antennas on the transmitter longitudinal axis. This allows a more compact transmit antenna configuration to be realized.

At least some of the transmit antennas are advantageously at least temporarily controllable using the same transmit signal.

Alternatively or additionally, at least some of the transmitting antennas advantageously at least temporarily use different transmitting signals such that each transmitted radar signal is at least temporarily distinguishable at the receiving antennas. Controllable.

Alternatively or additionally, at least some of the transmit antennas are controllable in a switchable manner using the same transmit signal or different transmit signals.

At least temporarily controlling at least some of the transmit antennas with the same transmit signal allows simultaneous emission of the same radar signal from the target transmit antennas. Accordingly, the radar signals from each transmit antenna can be combined to form a common radar signal with greater signal strength. This may increase the detection range. A radar system operating mode in which at least some of the transmit antennas are controlled using the same transmit signal can be referred to as a range operating mode.

At least two adjacent receive antennas may advantageously be steered using a beamforming scheme. In a beamforming scheme, adjacent transmit antennas, particularly spaced at base intervals, can be used coherently such that multiple transmit channels each transmit the same radar signal with a defined phase offset.

The ability to distinguish between radar signals allows the assignment of corresponding echoes of radar signals received with a receive antenna to the target transmit antenna. This may reduce the investment in transmit antennas for direction determination. A mode of operation of a radar system in which at least two of the transmit antennas are controlled such that each transmitted radar signal is at least temporarily distinguishable at least at the receive antenna can be referred to as a directional mode of operation.

At least two of the transmit antennas may advantageously be operated using a MIMO scheme. In a MIMO scheme, a transmit antenna transmits each radar signal that is at least temporarily distinguishable at least at the receive antenna. This may improve angular resolution for direction determination.

Since at least some of the transmit antennas are controllable in a switchable manner using the same or different transmit signals, the radar system is switchable between directional and range operating modes. At least some of the transmit antennas are advantageously switchable automatically and/or as needed.

A higher angular resolution is possible in the directional operation mode than in the range operation mode. Conversely, in the range operation mode, a wider detection range is possible than in the direction operation mode.

A radar system, in particular at least one control and evaluation device for a radar system, advantageously has an operating mode, in particular a range active mode or a beamforming mode, in which at least some of the transmitting antennas can be controlled using the same transmitting signal, and a transmitting At least one switching means may be provided which may be used to switch the radar system between modes of operation in which at least some of the antennas are controllable using different transmitted signals, in particular a directional mode or a MIMO mode.

A particular inventive combination of receive and transmit antenna configurations is that when the radar system is operated in directional steering mode, especially MIMO mode, a virtual receive antenna array combining large aperture and large angular resolution can be realized. means

The radar system may be used to ascertain object information, particularly the range, direction, and/or velocity of the object, particularly the object target for the radar system. An object target is a region of an object from which radar signals are reflected, and the reflected radar signals can be received as echoes using a receiving antenna.

Orientation is the determination of the direction in which the target is located relative to the radar system. In this case, the direction may be specified as an angle with respect to the reference axis of the radar system, in particular the main beam direction of the transmitting antenna.

The transmitter longitudinal axis and/or the receiver longitudinal axis, as well as the main beam direction of the transmitting antenna, are advantageously spatially oriented horizontally. Thereby, a horizontally extending monitoring area can be monitored with angular resolution. Direction may be determined here as an azimuth angle.

The radar system may advantageously comprise means for controlling the transmit antenna, in particular means for generating the transmit signal. Furthermore, the radar system may comprise means for processing received signals. The means for control and/or processing may be implemented in the form of software and/or hardware using common control and evaluation equipment. The control and evaluation device may comprise suitable transmission channels for transmitted signals and/or reception channels for received signals. The transmitted and/or received signals may be electrical signals. Electronic means may thereby be used for control and/or evaluation.

The invention may be used in radar systems for vehicles, particularly motor vehicles. The invention may advantageously be used in land vehicles, in particular cars, trucks, buses, bikes, etc., or in planes and/or ships. The invention may be used in vehicles that can be operated automatically or at least semi-automatically. However, the invention is not limited to use in vehicles. The invention may also be used in stationary operating radar systems.

The radar system is advantageously connected to at least one electronic control unit of the vehicle, in particular a driver assistance system or a chassis control system and/or a driver information device and/or a parking assistance system and/or an attitude recognition system or the like. or be part of such a device or system. The vehicle can thereby be operated automatically or semi-automatically.

Radar systems can detect stationary or moving objects, especially vehicles, people, animals, plants, obstacles, especially potholes or rocky road irregularities, road boundaries, road signs, especially empty parking spaces, precipitation, etc. may be used to detect the

According to a further advantageous embodiment, the configuration of transmit and receive antennas realizes a virtual receive antenna array in which at least two adjacent virtual receive array elements are arranged on at least one virtual array longitudinal axis. used in the directional steering mode of radar systems, such as
At least two adjacent virtual receive array elements may be spaced at a base spacing from each other, and/or At least two adjacent virtual receive array elements may be spaced at a spacing greater than the base spacing, and/or At least two Two adjacent virtual receive array elements may be spaced at intervals corresponding to integer multiples of the base interval. A virtual receive antenna array spaced at a base distance from each other may be used to achieve unambiguous direction determination. In general, virtual receive antenna arrays with spacing greater than the base spacing may be used to achieve larger virtual receive antenna arrays. A larger virtual receive antenna array may be used to achieve a larger aperture. This generally allows the radar system to be used over a correspondingly large angular range to clearly and more accurately ascertain the direction of the target object.

The inventive configuration of transmit and receive antennas is achieved by a geometric convolution scheme of the position of the phase center of the transmit antenna and the phase center of the receive antenna to achieve a virtual receive antenna array comprising a large number of virtual receive antenna array elements. may be used for

According to a further advantageous embodiment, the virtual receive array elements within the virtual receive antenna may be arranged in a manner distributed over at least two virtual array longitudinal axes,
at least two virtual receive array elements arranged on different longitudinal array axes may be arranged at the same height when viewed in the direction of the longitudinal array axes; The virtual receive array elements may be arranged in a manner that is offset from each other when viewed in the direction of the array longitudinal axis, and/or at least two virtual receive array elements arranged on different array longitudinal axes They may be arranged in such a way that they are offset from each other by the base spacing when viewed in the axial direction.

The configuration of the virtual receive antenna array elements on different array longitudinal axes allows the direction of the target object to be ascertained in two dimensions. The offset configuration of the virtual receive antenna array allows achieving better angular resolution when determining the direction of the target object.

According to the invention,
a phase center of each of the at least four receive antennas positioned on a virtual receiver longitudinal axis;
each phase center of at least two adjacent receive antennas are spaced apart from each other by a base; and
said phase centers of at least two adjacent said receive antennas are positioned with respect to each other at respective receiver longitudinal spacings greater than a base spacing;
This object is thus further achieved for the antenna array.

According to the invention, this object is also achieved for a vehicle in that the vehicle is equipped with at least one radar system according to the invention.

According to the invention, the vehicle is equipped with at least one radar system capable of monitoring objects around the vehicle. Object information identified using at least one radar system can be used in conjunction with driver assistance systems to control the operation of the vehicle. The vehicle can thereby be operated automatically or semi-automatically.

According to the invention,
a range operation mode in which at least some of the transmit antennas are at least temporarily controlled using the same transmit signal; and
Switching between directional steering modes in which at least some of the transmit antennas are at least temporarily controlled using different transmit signals such that each received radar signal is at least temporarily distinguishable at the receive antenna takes place,
Thus, the object is further achieved for the method.

According to the present invention, the radar system is operated alternately between a range mode of operation to achieve long detection range and a direction mode of operation to increase the angular resolution for direction determination.

Distinction in directional steering mode allows reflected radar signals, or echoes, to be assigned to each transmit antenna in the receive antenna.

At least two transmit antennas may advantageously be used to transmit differently encoded radar signals. Thereby, the radar signals can be at least temporarily distinguished from each other at the receiving antenna.

The transmitted signals may advantageously be encoded in relation to each other, in particular by phase modulation, in order to generate distinguishable radar signals. Thereby, at least temporal signal orthogonality may be achieved between the transmitted and received signals. This allows the radar signal and the corresponding echo to be rendered separately from each other.

The received signal may advantageously be processed in the receiver, especially by suitable evaluation using a Fourier transform. The means for evaluating may advantageously be implemented in the form of software and/or hardware, in particular in at least one control and evaluation device.

Alternatively, the features and advantages indicated in connection with the inventive radar system, the inventive antenna array, the inventive vehicle, the inventive method, and their respective advantageous configurations may be referred to in a mutually corresponding manner. applied and vice versa. Of course, individual features and advantages may also be combined with each other, and advantageous effects may occur that go beyond the individual effects.

Further advantages, features and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are explained in more detail with reference to the drawings. One skilled in the art will conveniently consider the features disclosed in combination in the drawings, description, and claims individually and combine them to form meaningful further combinations. Schematically, in the figure,
FIG. 1 shows a front view of a motor vehicle with a driver assistance system and a radar system for monitoring a surveillance area in front of the motor vehicle in the direction of travel. FIG. 2 shows a plan view of the motor vehicle of FIG. Figure 3 shows a side view of the motor vehicle of Figures 1 and 2; FIG. 4 shows a front view of an antenna array of a radar system comprising transmitting and receiving antennas according to a first exemplary embodiment, which may be used in the motor vehicle of FIGS. 1-3. FIG. 5 shows a virtual receive antenna array realized with the antenna array of FIG. 4 when the radar system is operated in a steering mode. FIG. 6 shows a distance/direction graph for the antenna array of FIG. 4 showing the detection range of the radar system as a function of direction when the radar system is operated in range and direction steering modes. FIG. 7 shows a received signal/direction graph for the antenna array of FIG. 4 when the radar system is operated in a directional steering mode when a target object is detected. FIG. 8 shows a received signal/direction graph with multiple measurement curves for the antenna array of FIG. 4 when the radar system is operated in a directional steering mode when two target objects are detected. FIG. 9 shows a received signal/direction graph with multiple measurement curves for the antenna array of FIG. 4 when the radar system is operated in range operation mode when two target objects of FIG. 8 are detected. FIG. 10 shows a front view of an array comprising transmit and receive antennas of a radar system according to a second exemplary embodiment, which may be used in the motor vehicle of FIGS. 1-3. FIG. 11 shows a virtual receive antenna array realized with the antenna array of FIG. 10 when the radar system is operated in a steering mode. FIG. 12 shows a range/orientation graph for the antenna array of FIG. 10, where the detection range is shown as a function of orientation when the radar system is operated in range and directional operation modes. FIG. 13 shows a received signal/direction graph for the antenna array of FIG. 10 when the radar system is operated in a directional steering mode when a target object is detected. FIG. 14 shows a received signal/direction graph with multiple measurement curves for the antenna array of FIG. 10 when the radar system is operated in directional steering mode when two target objects are detected. FIG. 15 shows a received signal/direction graph for the radar system with the antenna array of FIG. 10 when the radar system is operated in range operation mode when two target objects from FIG. 14 are detected.

In the drawings, the same components are provided with the same reference numerals.

Detailed description of the invention

FIG. 1 shows a front view of an automotive vehicle 10 in the form of an automobile. FIG. 2 shows the motor vehicle 10 in plan view. In FIG. 3, motor vehicle 10 is shown in side view.

Motor vehicle 10 includes a radar system 12 . By way of example, radar system 12 is located on the front fender of motor vehicle 10 . The radar system 12 may be used to monitor a surveillance area 14 in front of the motor vehicle 10 for objects 18 in a direction of travel 16 . Also, the radar system 12 may be positioned and oriented differently at other locations on the motor vehicle 10 . Radar system 12 may be used to ascertain object information, eg, in the form of range r and direction, eg, azimuth φ and elevation Θ, of an object target of object 18 relative to motor vehicle 10 or radar system 12 . Optionally, the velocity of the object target relative to the motor vehicle 10 can also be ascertained. An object target of object 18 is a portion of object 18 from which a radar beam can be reflected and reflected as an echo.

Objects 18 can be stationary or moving objects, especially vehicles, people, animals, plants, obstacles, especially potholes or rocky road bumps, road boundaries, road signs, especially parking spaces, rainfall, etc. can be

Cartesian xyz coordinate axes of interest are shown in FIGS. 1-5, 10 and 11 for better orientation. In the exemplary embodiment shown, the x-axis extends in the direction of the vehicle longitudinal axis of motor vehicle 10, the y-axis extends along the vehicle lateral axis, and the z-axis extends spatially in the xy plane. perpendicular to and extending upwards. When the motor vehicle 10 is operating on a horizontal road, the x- and y-axes extend spatially horizontally and the z-axis extends spatially vertically.

Radar system 12 is configured as a Frequency-modulated continuous wave radar. Frequency modulated continuous wave radar is also called FMCW (Frequency modulated continuous wave) among experts. The radar system 12 may be used to detect an object 18 located at a large distance r with a large angular resolution in the relationship between the azimuth angle φ and the elevation angle Θ.

Radar system 12 is connected to driver assistance system 20 . Driver assistance system 20 may be used to operate motor vehicle 10 automatically or semi-automatically.

Radar system 12 comprises an antenna array 22 and control and evaluation equipment 24 . FIG. 4 shows an antenna array 22 according to a first exemplary embodiment. FIG. 10 shows an antenna array according to a second exemplary embodiment.

A radar system 12 associated with an antenna array 22 according to a first exemplary embodiment is first described below in connection with FIGS. 4-9.

By way of example, antenna array 22 comprises three transmit antennas 26 and four receive antennas 28 . By way of example, receive antenna 28 is positioned spatially below transmit antenna 26 . However, the receiving antennas 28 may be arranged above, next to, or at least in some cases at the same height as, for example, between the transmitting antennas 26 .

Each transmit antenna 26 is connected to a corresponding transmit channel. A transmit channel may be used to control each transmit antenna 26 using a suitable electrical transmit signal. Accordingly, each receive antenna 28 is also connected to a corresponding receive channel. A receive channel may be used to transmit an electrical receive signal from receive antenna 28 . The transmission and reception channels may be integrated in the control and evaluation device 24, for example.

The transmit antenna 26 may be used to transmit the target radar signal 30 using electrical transmit signals for control purposes.

The position of each transmit antenna 26 is defined by a respective phase center 32 .

Each phase center 32 of two of the transmit antennas 26 are positioned adjacently on a virtual transmitter longitudinal axis 34 . By way of example, transmitter longitudinal axis 34 extends parallel to the y-axis.

The phase center 32 of the third transmit antenna 26 is located below and adjacent to the transmitter longitudinal axis 34 in FIG. A third transmit antenna 26 is located at a transmitter lateral spacing 36 from the transmitter longitudinal axis 34 .

In each case, the corresponding virtual transmitter horizontal axis 38 runs through the phase centers of the three transmit antennas 26 . Transmitter transverse axis 38 extends perpendicular to transmitter longitudinal axis 34, illustratively parallel to the z-axis.

The transmitter transverse axis 38 of an individual transmit antenna 26 is positioned between the transmitter transverse axes 38 of two adjacent transmit antennas 26 on the transmitter longitudinal axis 34 .

The transmitter lateral axis 38 of each transmit antenna 26 is located at a base distance 40 from the transmitter lateral axis 38 of the right transmit antenna 26 in FIG. By way of example, the base spacing 40 corresponds to half the wavelength λ of the radar signal 30 transmitted using the transmit antenna 26, optionally plus or minus a tolerance.

The transmitter longitudinal spacing 42 between each transmitter transverse axis 38 of the two transmit antennas 26 on the transmitter longitudinal axis 34 is three times the base spacing 40, optionally plus or minus a tolerance. Transmitter transverse spacing 36 is less than transmitter longitudinal spacing 42 and greater than base spacing 40 .

Further, the antenna array 22 illustratively comprises four receive antennas 28 . A receive antenna 28 may be used to receive echoes 44 of the transmitted radar signal 30 and convert the echoes into corresponding electrical receive signals.

By way of example, the phase center 32 of the transmit antenna 26 and the phase center 32 of the receive antenna 28 are located in a common antenna plane. By way of example, the antenna plane extends parallel to the yz plane. The main beam direction of the transmitting antenna 26 runs, by way of example, perpendicular to the antenna plane, ie parallel to the vehicle longitudinal axis or parallel to the x-axis. The main receiving direction of the receiving antenna 28 likewise runs, by way of example, perpendicular to the antenna plane.

Each phase center 32 of receive antenna 28 is located on a virtual receiver longitudinal axis 46 . Receiver longitudinal axis 46 runs parallel to transmitter longitudinal axis 34 .

The phase centers 32 of the first and second receive antennas 28, as viewed from the left in FIG. Two base-spaced receive antennas 28 may be used to provide unambiguous directional determination of the object target.

The phase centers 32 of the third and fourth receive antennas 28 are located on the same side of the phase centers 32 of the two receive antennas 28 spaced at the base spacing 40 .

The phase center 32 of the second receiving antenna 28 from the left in FIG. 4 is located at a first receiver longitudinal spacing 48a from the phase center 32 of the third receiving antenna 28 from the left. The first receiver longitudinal spacing 48a is twice the base spacing 40, optionally plus or minus the tolerance.

The phase center 32 of the third receive antenna 28 from the left in FIG. 4 is located on the second receiver longitudinal axis 48b from the phase center 32 of the fourth receive antenna 28 from the left. The second receiver longitudinal spacing 48b is six times the base spacing 40, optionally plus or minus the tolerance. The quotient of the second longitudinal receiver spacing 48b and the first longitudinal receiver spacing 48a is three.

By way of example, the base spacing 40 and the two receiver longitudinal spacings 48a, 48b may be arranged according to the Golomb ruler designation.

The largest spacing between the two outer receive antennas, the first receive antenna 28 and the fourth receive antenna 28 from the left, is so as to achieve a corresponding large aperture of the radar system 12 in the direction of azimuth angle φ. Used.

The particular configuration of the phase centers 32 of the transmit antennas 26 and the phase centers 32 of the receive antennas 28 allows the virtual receive antenna array 50 shown in FIG. The array combines a large aperture in the direction of azimuth φ with a large angular resolution. By way of example, the receive array elements 52 are achieved by a geometric convolution scheme of the positions of the phase centers 32 of the transmit antennas 26 and the phase centers 32 of the receive antennas 28 .

Virtual receive antenna array 50 comprises a total of twelve virtual receive antenna array elements 52 . The receive array elements 52 are arranged in a distributed manner in a first virtual array longitudinal axis 54a and a second virtual array longitudinal axis 54b. The distributed configuration of the receive array elements 52 on the array longitudinal axes 54a and 54b is such that the direction of the target object is in two spatial dimensions: the y-axis or azimuth φ direction and the z-axis or elevation Θ direction; allow it to be verified in The receive array elements 52 are illustratively located in a common array plane. By way of example, the array plane extends parallel to the yz axis.

Six of the receive array elements 52 are arranged on a first virtual array longitudinal axis 54a.

Viewed from the left of FIG. 5, the first and second receive array elements 52, the third and fourth receive array elements 52, and the fifth and sixth receive array elements 52 are each on a first array longitudinal axis 54a. , are arranged at a base distance 40 from each other. Receive array elements 52 spaced at a base distance 40 from each other can be used to provide unambiguous direction determination.

2nd and 3rd receive array elements 52, 5th and 6th receive array elements 52, 6th and 7th receive array elements 52, and 7th and 8th receive array elements viewed from the left of FIG. 52 are spaced apart from each other by a first spacing 56a on a first array longitudinal axis 54a. First spacing 56 a corresponds to twice base spacing 40 .

A second spacing 56 b between the seventh and eighth receive antenna elements 52 corresponds to four times the base spacing 40 .

Four of the receive array elements 52 are arranged on the second virtual array longitudinal axis 54b. A second array longitudinal axis 54b runs parallel to the first array longitudinal axis 54a in the array plane. Two array longitudinal axes 54a and 54b extend parallel to the y-axis.

When viewed in the direction of array longitudinal axes 54a and 54b, the first receive array element 52 on second array longitudinal axis 54b, viewed from the left in FIG. It is positioned at the same height as the third receive array element 52 . When viewed along the array longitudinal axes 54a and 54b, the second receive array element 52 from the left on the second array longitudinal axis 54b is the same as the fourth receive array element 52 on the first array longitudinal axis 54a. placed at height.

When viewed in the direction of array longitudinal axes 54a and 54b, the third receive array element 52 seen from the left in FIG. Centered between the fifth and sixth receive array elements 52 on 54a at base spacing 40, ie offset from that element.

When viewed in the direction of array longitudinal axes 54a and 54b, the fourth receive array element 52 on second array longitudinal axis 54b, viewed from the left in FIG. th receive array element 52 at base spacing 40, ie offset from that element.

The first and second receive array elements 52, viewed from the left in FIG.

The second and third receive array elements 52, viewed from the left, on the second array longitudinal axis 54b are spaced from each other at a first spacing 56a corresponding to twice the base spacing 40; The third and fourth receive array elements 52 viewed from the left on the second array longitudinal axis 54b are spaced from each other at a third spacing 56c corresponding to six times the base spacing 40. FIG.

The aperture of radar system 12 in the direction of longitudinal axes 54 a and 54 b , or y-axis, is defined by the maximum width of virtual receive antenna array 50 . The maximum width of the virtual receive antenna array 50 in the direction of array longitudinal axes 54a and 54b is defined by the spacing 56d between the two outer receive array elements 52 on the first array longitudinal axis 54a. The spacing 56d between the two outer array elements 52 corresponds to twelve times the base spacing 40;

The offset configuration of the receive array elements 52 on the two longitudinal array axes 54a and 54b makes it possible to obtain better angular resolution when determining the orientation of the target object in both azimuth φ and elevation Θ.

The control and evaluation device 24 is implemented in the form of software and hardware. A control and evaluation device 24 is connected to a transmitting antenna 26 and a receiving antenna 28 . Control and evaluation device 24 may be used to generate electrical transmission signals for controlling transmit antenna 26 . Additionally, the control and evaluation device 24 may be used to ascertain object information about the object 18 detected using the radar signal 30 from the electrical received signal of the receiving antenna 28 .

The radar system 12 can be switched between range and directional modes of operation. Thus, the transmit antennas 26 may be controllable in a switching fashion using the same or different transmit signals. Accordingly, the receiving antenna 28 is switchable between range and directional modes of operation.

Switching from range operation mode to directional operation mode may occur automatically or on demand. The directional steering mode allows higher angular resolution for directional determination than the range steering mode. Conversely, the range operation mode allows a larger detection range than the directional operation mode. The control and evaluation device 24 comprises switching means 58 with which the radar system 12 can be switched between a range operating mode and a directional operating mode.

In the range operating mode of radar system 12, transmit antenna 26 can be controlled using the same transmit signal. Controlling the transmit antennas 26 with the same transmit signal allows the target transmit antennas 26 to emit the same radar signal 30 at the same time. For this purpose, the transmit antenna 26 can be steered using a so-called beamforming scheme. In this case, adjacent transmit antennas 26 can each be used coherently such that multiple transmit channels transmit the same radar signal 30 with a defined phase offset. The signal strengths of the radar signals 30 on each transmit antenna 26 are summed to a greater signal strength. Therefore, the detection range can be expanded.

The radar system 12 is used to continuously make radar measurements to monitor the surveillance area 14 for objects 18 . Each radar measurement has a range measurement sequence in which radar system 12 is operated in range operation mode and a direction measurement sequence in which radar system 12 is operated in direction operation mode. In a radar measurement, the radar system 12 switches from range operating mode to directional operating mode. Here, each radar measurement may begin with a range measurement sequence or may begin with a direction measurement sequence.

As an example, the following text describes a radar measurement starting with a range measurement sequence.

The range measurement sequence involves the control and evaluation device 24 being used to control the transmit antenna 26 over each transmit channel using the same transmit signal. Each transmit antenna 26 simultaneously emits the same radar signal 30 . The signal strength of each radar signal 30 is summed and transmitted to the surveillance area 14 with increased detection range.

When the radar signal 30 hits the object 18, the radar signal 30 is reflected by the corresponding object target. Echoes 44 of reflected radar signals 30 are received using receive antenna 28 and converted to respective received signals.

The received signals are sent to the control and evaluation device 24 and processed by the latter, for example by Fourier transformation. Object information about object 18, namely range r and direction, ie azimuth φ and elevation Θ, and optionally velocity of the detected target object relative to radar system 12, is ascertained from the received signal.

The radar system 12 is then switched from the range operating mode to the directional operating mode using, for example, the control and evaluation device 24, and a directional measurement sequence is performed.

The direction measurement sequence involves the control and evaluation device 24 being used to control the transmit antenna 26 via each transmit channel using a different transmit signal. Different transmitted signals are encoded with respect to each other. Transmit antennas 26 emit appropriately encoded radar signals 30 relative to each other. A radar signal 30 is transmitted to the surveillance area 14 .

When a distinguishable radar signal 30 hits the object 18, the radar signal 30 is reflected by the target object target. Echoes 44 of reflected distinct radar signals 30 are received using receive antenna 28 and converted into respective received signals.

The received signals are sent to the control and evaluation device 24 . Received signals are assigned to transmit antennas 26 . This is possible because the radar signal 30 and the echo 44 are differentiated. The assigned received signals are signal-processed, for example, by Fourier transformation. Object information about object 18, namely range r and direction, ie azimuth φ and elevation Θ, and optionally velocity of the detected target object relative to radar system 12, is ascertained from the received signal.

Generally, object information about object targets is ascertained at a greater detection range in range measurement sequences than in direction measurement sequences in radar measurements. Object information about the object target is ascertained in the direction measurement sequence with a shorter detection range than in the range measurement sequence, but with a higher angular resolution than in the range measurement sequence.

For comparison, FIG. 6 shows a range/direction graph 60a of radar system 12 in the range operating mode in dashed lines and a range/direction graph 60b of radar system 12 in the direction operating mode in solid lines. Here, each range is recorded in azimuth φ. From FIG. 6, it can be seen that the radar system 12 has a maximum detection range of approximately 250m in range operating mode. However, in the steering mode, the radar system 12 has a maximum detection range of only slightly less than 200m. In contrast, in the azimuth φ direction, the radar system 12 has a larger field of view in the directional operation mode than in the range operation mode.

By way of example, FIG. 7 shows a received signal/direction graph 62 a from a direction measurement sequence in which a target object was detected at an azimuth angle φ of 0 degrees in front of the motor vehicle 10 . The sidelobe level is approximately 8 dB. This is sufficient, for example, to distinguish target objects with different reflectivities in the actual driving situation of the motor vehicle 10 for that direction, ie for each azimuth angle φ.

By way of example, FIG. 8 shows that two target objects having the same range r and the same velocity relative to the radar system 12 are detected at an angular separation of about 11 degrees around an azimuth angle φ of 0 degrees in front of the motor vehicle 10. FIG. 6 shows a family of curves associated with a received signal/direction graph 62b for a plurality of direction measurement sequences plotted. The curves in the family of received signal/direction graphs 62b correspond to different phase differences of the transmitted signal. Two target objects can be distinguished at all possible phase differences. The curves of the group of received signal/direction graphs 62b can be ascertained, for example, by means of so-called beamforming methods and/or so-called super-resolution methods or similar methods.

A graph of received signal/direction for the range measurement sequence corresponding to the direction measurement sequence of FIG. 8 is shown in FIG. The angular resolution based on the azimuth angle φ is approximately 11 degrees. The sidelobe level in this case is about 3 dB, insufficient to distinguish between the two target objects in range operation mode.

FIG. 10 shows an antenna array 22 for radar system 12 according to a second exemplary embodiment. FIG. 11 shows a virtual receive antenna array 50 that is part of the antenna array 22 of FIG.

Those elements that are similar to those of the first exemplary embodiment of FIGS. 4-11 are presented with the same reference numerals. The second exemplary embodiment is characterized in that the phase center 32 of the second left receive antenna 28 is located at a receiver longitudinal spacing 48c from the phase center 32 of the third left receive antenna 28. Differs from the first exemplary embodiment. A receiver longitudinal axis 48c corresponds to three times the base spacing 40, optionally plus or minus a tolerance.

The phase center 32 of the third receiving antenna 28 from the left in FIG. 10 is located at a receiver longitudinal spacing 48a from the phase center 32 of the fourth receiving antenna 28 from the left. The receiver longitudinal spacing 48a corresponds to twice the base spacing 40, optionally plus or minus the tolerance. The quotient of the longitudinal spacing 48c and the longitudinal spacing 48a is 1.5.

The virtual receive antenna array 50 according to the second exemplary embodiment of FIG. 11 comprises only 11 receive antennas 28, of which only 7 are It differs from the virtual receive antenna array 50 according to the first exemplary embodiment of FIG. 5 in that it is arranged on the first array longitudinal axis 54a.

Unlike the first exemplary embodiment, in the second exemplary embodiment, the third receive array element 52 from the left on the first array longitudinal axis 54a is the second receive array element 52 from the left. , are spaced at a spacing 56e corresponding to three times the base spacing 40. FIG. The seventh receive array element 52 from the left is the rightmost receive array element 52 on the first array longitudinal axis 54a. The maximum width of the virtual receive antenna array 50 corresponds to the spacing 56 f between the leftmost receive array element 52 and the rightmost receive array element 52 . Spacing 56f corresponds to ten times base spacing 40. FIG.

In addition, when viewed in the direction of array longitudinal axes 54a and 54b, the first receive array element 52 from the left on second array longitudinal axis 54b is the second and third on first array longitudinal axis 54a. It is located between the third receive array element 52 and at a base spacing 40 from the third receive array element 52, ie offset from that element.

When viewed in the direction of array longitudinal axes 54a and 54b, the second receive array element 52 from the left on second array longitudinal axis 54b is the third receive array element 52 on first array longitudinal axis 54a. placed at the same height as

When viewed in the direction of array longitudinal axes 54a and 54b, in each case the fourth receive array element 52, viewed from the left, on second array longitudinal axis 54b is, for example, first array longitudinal axis 54a. Centered between the 6th and 7th receive array elements 52 above, they are arranged at a base spacing 40, ie offset from that element.

A method of monitoring a surveillance area 14 for an object 18 is provided by a radar system 12 comprising an antenna array 22 according to the second exemplary embodiment. including being operated in the same way as

For comparison, FIG. 12 shows the range/direction graph 60c of the radar system 12 in the range operation mode in dashed line and the range/direction graph 60d of the radar system 12 in the direction operation mode in solid line. Here, each range is recorded in azimuth φ. From FIG. 12 it can be seen that the radar system 12 has a maximum detection range of approximately 250m in range operating mode. However, in the steering mode, the radar system 12 has a maximum detection range of only slightly less than 200m. In contrast, at azimuth φ, the radar system 12 has a larger field of view in the directional operation mode than in the range operation mode.

By way of example, FIG. 13 shows a received signal/direction graph 62d from a direction measurement sequence in which a target object was detected at an azimuth angle φ of 0 degrees in front of the motor vehicle 10 . The sidelobe level is approximately 11.2 dB. This is sufficient, for example, to distinguish target objects with different reflectivities in the actual driving situation of the motor vehicle 10 for that direction, ie for each azimuth angle φ.

By way of example, FIG. 14 shows that two target objects having the same range r and the same velocity relative to the radar system 12 are detected at an angular separation of about 15 degrees around an azimuth angle φ of 0 degrees in front of the motor vehicle 10. Figure 6 shows a family of curves associated with the received signal/direction graph 62e for a plurality of direction measurement sequences. The family of curves correspond to direction measurement sequences in which radar signals 30 with different phase differences were transmitted. Two target objects can be distinguished at all possible phase differences. The curves of the group of received signal/direction graphs 62e can be ascertained, for example, by means of so-called beamforming methods and/or so-called super-resolution methods or similar methods.

A graph 62f of received signal/direction for the range measurement sequence corresponding to the situation of FIG. 14 is shown in FIG. The width of the main lobe is approximately 16 degrees. The sidelobe level is approximately 5.25 dB, which is insufficient to distinguish between the two target objects in range operation mode.

Claims (11)

A radar system (12) for monitoring at least one surveillance area (14) for an object (18), comprising:
a plurality of transmit antennas (26) controllable with respective transmit signals and operable to transmit target radar signals (30) to said at least one surveillance area (14);
a plurality of receive antennas (28) operable to receive echoes (44) of said transmitted radar signal (30) and convert said echoes into corresponding received signals;
connected to said transmitting antenna (26) and said receiving antenna (28) and can be used to generate a transmitted signal to control said transmitting antenna (26) and detected using said radar signal (30); A radar system (12) comprising at least one control and evaluation device (24) that can be used to ascertain object information (r, φ, Θ) associated with a detected object (18) from said received signals. and
each phase center (32) of at least four said receive antennas (28) is positioned on a virtual receiver longitudinal axis (46);
said respective phase centers (32) of at least two adjacent said receiving antennas (28) are spaced at a base spacing (40) from each other, and said respective phase centers (32) of at least two adjacent said receiving antennas (28) ) are spaced from each other at each receiver longitudinal spacing (48a, 48b, 48c) greater than said base spacing (40),
A radar system characterized by: at least one said receiver longitudinal spacing (48a, 48b, 48c) is an integer multiple of said base spacing (40), in particular plus or minus a tolerance,
2. The radar system of claim 1, wherein: the phase centers (32) of two receive antennas (28) located outside the receiver longitudinal axis (46) are spaced at the base spacing (40);
The radar system according to any one of claims 1 and 2, characterized in that: said phase centers (32) of said at least two receive antennas (28) adjacent to each other are located on the same side as said phase centers (32) of two receive antennas (28) spaced at a base spacing (40); ,
said phase center (32) of said receive antenna (28) closest to said two receive antennas (28) spaced at said base spacing (40) and said two receive spaced at said base spacing (40); the receiving antenna whose longitudinal receiver spacing (48a) between the nearest said phase center (32) of the antenna (28) is closest to said two receiving antennas (28) spaced at said base spacing (40) between said phase center (32) of (28) and said phase center (32) of said receive antenna (28) spaced from said two receive antennas (28) spaced at said base spacing (40); less than the receiver longitudinal spacing (48b) between, or
said phase center (32) of said receive antenna (28) closest to said two receive antennas (28) spaced at said base spacing (40) and said two receive spaced at said base spacing (40); the receiving antenna whose longitudinal receiver spacing (48a) between the nearest said phase center (32) of the antenna (28) is closest to said two receiving antennas (28) spaced at said base spacing (40) between said phase center (32) of (28) and said phase center (32) of said receive antenna (28) spaced from said two receive antennas (28) spaced at said base spacing (40); greater than the receiver longitudinal spacing (48a) between
The radar system according to any one of claims 1 to 3, characterized in that: between three adjacent receiving antennas (28), the larger of two longitudinal receiver spacings (48a, 48b; 48a, 48c) and the smaller of said two longitudinal receiver spacings (48a, 48b; 48a, 48c) the quotient of which is 1.5 or an integer multiple of 1.5,
The radar system according to any one of claims 1 to 4, characterized in that: said base spacing (40) corresponds to half the wavelength (λ) of said radar signal (30) transmitted using said transmitting antenna (26), in particular plus or minus a tolerance;
The radar system according to any one of claims 1 to 5, characterized in that: The configuration of the transmit antennas (26) and receive antennas (28) is such that at least two adjacent virtual receive array elements (52) are arranged on at least one virtual array longitudinal axis (54a, 54b). used in a steering mode of said radar system (12) to implement an antenna array (50);
at least two adjacent virtual receive array elements (52) are arranged at said base spacing (40) from each other and/or at least two adjacent virtual receive array elements (52) are greater than said base spacing (40) spaced (56a, 56b, 56c, 56d) and/or at least two adjacent virtual receive array elements (52) are spaced (56a, 56b, 56c) corresponding to integer multiples of said base spacing (40) , 56d),
The radar system according to any one of claims 1 to 6, characterized in that: said virtual receive array elements (52) within said virtual receive antenna (50) arranged in a manner distributed across at least two array longitudinal axes (54a, 54b);
at least two virtual receive array elements (52) arranged in different longitudinal array axes (54a, 54b) are arranged at the same height when viewed in the direction of said longitudinal array axes (54a, 54b); and/ or in such a way that at least two virtual receive array elements (52) arranged on different array longitudinal axes (54a, 54b) are offset from each other when viewed in said direction of said array longitudinal axes (54a, 54b). at least two virtual receive array elements (52) arranged and/or arranged on different longitudinal array axes (54a, 54b) relative to each other when viewed in said direction of said longitudinal array axes (54a, 54b); arranged in a manner offset by said base spacing (40);
The radar system according to any one of claims 1 to 7, characterized in that: An antenna array (22) for a radar system (12) monitoring at least one surveillance area (14) for an object (18), comprising:
a plurality of transmit antennas (26) controllable with each transmit signal and operable to transmit a target radar signal (30);
A radar system (12) comprising a plurality of receive antennas (28) operable to receive echoes (44) of a transmitted radar signal (30) and convert said echoes into corresponding received signals. hand,
each phase center (32) of at least four said receive antennas (28) is positioned on a virtual receiver longitudinal axis (46);
said respective phase centers (32) of at least two adjacent said receiving antennas (28) are spaced at a base spacing (40) from each other, and said respective phase centers (32) of at least two adjacent said receiving antennas (28) ) are spaced from each other at each receiver longitudinal spacing (48a, 48b, 48c) greater than said base spacing (40),
A radar system characterized by: A vehicle (10) comprising at least one radar system (12) for monitoring at least one surveillance area (14) for an object (18),
The at least one radar system (12) comprises:
a plurality of transmit antennas (26) controllable with respective transmit signals and operable to transmit target radar signals (30) to the at least one surveillance area (14);
a plurality of receive antennas (28) operable to receive echoes (44) of transmitted radar signals (30) and convert said echoes into corresponding received signals;
connected to said transmitting antenna (26) and said receiving antenna (28) and can be used to generate a transmission signal for controlling said transmitting antenna (26); at least one control and evaluation device (24) that can be used to ascertain object information (r, φ, Θ) associated with a detected object (18) from received signals. ) and
A vehicle (10), characterized in that the vehicle (10) comprises a radar system (12) according to any one of claims 1-9. A method of operating a radar system (12) used to monitor at least one surveillance area (14) for an object (18), comprising:
controlling a plurality of transmit antennas (26) using transmit signals and transmitting applicable radar signals (30) to a surveillance area (14);
receiving echoes (44) of the transmitted radar signals (30) using a plurality of receive antennas (28), converting the echoes into corresponding received signals, and processing the received signals using signal processing. and ascertaining from the received signal object information (r, φ, Θ) about an object within the monitored area (14);
a method comprising
a range operation mode in which at least some of said transmit antennas (26) are at least temporarily controlled using said same transmit signal between at least two radar measurements; and at least some of said transmit antennas (26) are , switching between directional steering modes controlled at least temporarily using different transmitted signals such that each received radar signal (30) is at least temporarily distinguishable at said receiving antenna (28). takes place,
A method characterized by:

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