Sparse array apertures with integrated uniform linear antenna array for reducing hypothesis space of angle estimation

Abstract

The invention relates to an antenna structure (320) for a multiple-input-multiple-output radarsystem, MIMO radarsystem, a radar system of this type and an evaluation method for angle evaluation, said MIMO radar system comprising a plurality of receiving antennas (650,650-n) and a plurality of transmitting antennas (750,750-n) which are arranged at a distance from one another and form a sparsely occupied antenna aperture, and a plurality of receiving antennas (650,650-n) form a uniform linear antenna array. According to the invention, for an angle determination, on the basis of the echo information of these receiving antennas (650, 650-n) of the uniform linear antenna array, the approximate angles to the detected objects are determined and these approximately determined angles are each used in order to limit the number of angle hypotheses to be taken into account when determining the precise angles of the objects, in that only those angle hypotheses are taken into account which, within the scope of uncertainty of the respective approximately estimated angle, correspond to said angle.

Description

[0001] Description

[0002] Sparse array apertures with integrated uniform linear antenna array for reducing the hypothesis space of angle estimation

[0003] The invention relates to vehicle radar systems with distributed antenna structures and the evaluation of radar signals from such a vehicle radar system for environmental detection, in particular an improvement in the efficiency of angle evaluation, i.e., an improvement in computational efficiency.

[0004] Distributed radar antenna structures, also known as distributed, multi-static or bi-static or multiple-input-multiple-output (MIMO) antenna structures, are used in vehicle radar systems for environmental detection.

[0005] Radar systems with distributed antenna structures observe potential targets from different angles to minimize fluctuation losses. However, calculating the target coordinates before coherently summing the individual signals is significantly more complex and computationally intensive compared to monostatic radar systems due to the varying signal propagation times for the different antennas.

[0006] When using MIMO functionality and spatial multiplexing, virtual antenna positions are defined as a virtual array. The virtual positions of the resulting receive channels can be separated by multiples or only fractions of wavelengths. This characteristic significantly increases the complexity of angle calculations and necessitates the use of extensive signal processing algorithms.

[0007] For the environmental sensing of vehicles, especially motor vehicles, a further difficulty arises in that sufficiently powerful computing systems would exceed the cost framework for an application in the automotive environment. This is due to a multitude of hypotheses. A hypothesis depends on the physical positions of transmitting and receiving antennas, a target distance (distance to an object in the environment), and a spatial orientation angle (a direction to the object). In particular, the improved resolution achieved with large apertures massively increases the number of angular steps that need to be considered for parameterizing the hypothesis space.

[0008] Furthermore, the design of a complex implementation variant on a corresponding target hardware involves lengthy development times, specialized knowledge about the target hardware, and high development costs.

[0009] The invention is therefore based on the objective of improving a distributed antenna structure, a radar system, in particular for vehicles, with a distributed antenna structure and its evaluation method, in particular reducing the computing power required for angle determination.

[0010] The invention is solved by an antenna structure with the features of claim 1, a radar system with the features of claim 6 and a method with the features of claim 7; advantageous embodiments are set forth in the dependent claims.

[0011] The basic idea of ​​the invention is to integrate receiving antennas into a distributed antenna structure, which has the characteristics of a sparsely designed large aperture, forming a uniform linear antenna array. This means that a plurality of antennas are arranged at intervals along a straight line, and the distances between adjacent receiving antennas are equal. This distance is preferably equal to half a wavelength, which corresponds to the center frequency of the transmitted radar signal. Due to the structure of a uniform linear antenna array, it is possible to determine an angle to objects in the vicinity using known methods. However, this does not allow for sufficient object separation. The determined angles have only limited angular resolution and thus a relatively large uncertainty.Nevertheless, the number of angle hypotheses that must be considered for an accurate determination of an object's angle can be significantly reduced. This considerably decreases the required computing power. We therefore propose designing an antenna structure with a large, sparsely designed aperture such that a portion of the receiving antennas forms at least a uniform linear antenna array. If so-called chirps—linearly monotonically modulated signal segments with respect to frequency—are emitted with a time delay from the transmitting antennas of the antenna structure, the chirps received during such a chirp can be used simultaneously at the receiving antennas of the uniform linear antenna array to determine a rough angle for detected objects at which they are seen by the radar system.This significantly reduces the number of angle hypotheses that need to be considered for an accurate angle determination based on the measurement results from all receiving antennas. In this type of evaluation, the measurement results, which are simultaneously acquired by the receiving antennas for a large number of chirps within a measurement sequence, are evaluated together. Chirps within a measurement sequence are emitted by different transmitting antennas at different times. Such a measurement sequence is also referred to as a frame.

[0012] In particular, an antenna structure for a multiple-input multiple-output radar system, MIMO radar system, is thus comprising a plurality of receiving antennas and a plurality of transmitting antennas spaced apart from each other and forming a sparsely populated aperture, wherein a plurality of receiving antennas form a uniform linear antenna array.

[0013] Furthermore, a multiple-input multiple-output radar system (MIMO radar system) is described, comprising a plurality of receiving antennas and a plurality of transmitting antennas spaced apart from one another and forming a sparsely populated aperture, wherein each of the transmitting antennas is associated with a transmitting module for processing the radar signal to be transmitted and each of the receiving antennas with a receiving module for processing the detected radar echo signal and deriving radar echo information, and a central station which is connected to the transmitting and receiving modules by means of information technology, wherein the central station is configured to generate radar signal information, transmit it to the transmitting modules and control its transmission via the plurality of transmitting antennas, and receive the echo information from the receiving modules and evaluate it together in order to detect objects in the environment and locate them relative to the radar system.In this system, a plurality of receiving antennas form a uniform linear antenna array, and the central station is configured to roughly determine angles to objects based on the echo information from the plurality of receiving antennas forming the uniform linear antenna array. When determining the precise angles of the detected objects based on the echo information from all receiving antennas of the plurality of receiving antennas, only a limited number of possible angle hypotheses for the respective detected objects are considered, which agree with the roughly determined angle within a certain uncertainty. Additionally, a method for environmental detection using a multiple-input multiple-output radar system (MIMO radar system) is created, which comprises a plurality of receiving antennas and a plurality of transmitting antennas arranged at intervals and forming a sparsely populated aperture.wherein each of the transmitting antennas is linked to a transmitting module for processing the radar signal to be transmitted and each of the receiving antennas to a receiving module for processing the detected radar echo signal and deriving radar echo information, and comprising a central station which is connected to the transmitting and receiving modules via information technology, wherein the central station is configured

[0014] to generate radar signal information, transmit it to the transmitting modules and control its emission via the multitude of transmitting antennas, and to receive and jointly evaluate the echo information from the receiving modules in order to detect objects in the environment and locate them relative to the radar system, the method comprising the following steps:

[0015] Generating radar signal information comprising a sequence of chirps, linearly monotonically modulated signal segments with respect to frequency; time-shifted transmission of the chirps via the multiple transmitting antennas, such that in each time interval only one of the transmitting antennas transmits a chirp as a radar signal; simultaneous reception of radar echo signals generated at the objects and derivation of the echo information; joint evaluation of the echo information to determine a distance and an angle of the detected objects relative to the MIMO radar system, wherein, to determine the angle of each object, a multiple of angle hypotheses are evaluated which depend on the determined distance of the object.In this system, multiple receiving antennas form a uniform linear antenna array. Based on the echo information from these antennas, approximate angles to the detected objects are determined. These approximate angles are then used to limit the number of angle hypotheses to be considered when determining the precise angles of the objects. Only angle hypotheses that agree with the approximate angle within a certain uncertainty are considered. The advantage is that the determination of the angles of the detected objects in the environment is accelerated, and the number of calculations is significantly reduced. This allows for the use of less powerful hardware. Due to the accelerated evaluation, real-time determination of the object angles with higher resolution is possible.

[0016] To enable the assignment of the roughly determined angles to the objects, which is carried out on the basis of an evaluation of all echo information from all receiving antennas, one embodiment provides that, in addition, distances to the objects are determined on the basis of echo information from all receiving antennas of the multitude of receiving antennas, and furthermore, on the basis of the echo information from the majority of receiving antennas, which form a uniform linear antenna array, further distances corresponding to the detected objects, whose angles have been roughly determined, are determined, and an assignment of the roughly determined angles to the objects detected on the basis of the echo information from all receiving antennas is carried out by assigning the roughly determined angle to the object detected on the basis of all echo information with whose distance the further distance corresponds within a tolerance range.

[0017] A tolerance range size can be predetermined. A more accurate and up-to-date estimate of the tolerance range for determining distance based on all echo information can be obtained by determining distances to objects using the echo information from the receiving antennas of the uniform linear antenna array, each captured during the transmission of a chirp. This determination should be repeated multiple times during a measurement sequence in which the chirps are transmitted with time delays via the different transmitting antennas, in order to estimate any differences in distance determination between different transmitting-receiving antenna pairs.

[0018] In order to enable an unambiguous determination of distances and angles, one embodiment provides that the distances of adjacent receiving antennas of the majority of receiving antennas forming the uniform linear antenna array are less than or equal to half the wavelength of the radar signals to be emitted.

[0019] To optimally exploit this advantage even in planar antenna arrangements, one embodiment provides that a further plurality of receiving antennas form another uniform linear antenna array, wherein one linear orientation direction of the plurality of receiving antennas of the first uniform linear antenna array differs from another linear orientation direction of the further plurality of receiving antennas of the first uniform linear antenna array. For each antenna arrangement axis, assuming that these are arranged along two arrangement curves more or less approximated by straight lines, each of these arrangement axes has a uniform linear antenna array.In this way, both an azimuth angle and an elevation angle can initially be roughly determined independently of each other, which further restricts the solid angle for the corresponding angle hypotheses to be considered when precisely determining the solid angle of the recorded object.

[0020] It is therefore particularly preferred that one alignment direction and the other alignment direction enclose an angle greater than 70°, preferably 90°. The closer the enclosed angle approaches 90°, the better the angle determination can be correlated with the azimuth and elevation angle.

[0021] The rough angle determination is preferably based on the echo information captured during a chirp. This ensures a fast angle determination.

[0022] The invention is explained in more detail below with reference to a drawing. The drawing shows:

[0023] Fig. 1 shows a schematic representation of a photonic radar system;

[0024] Fig. 2 shows a flowchart for an angle evaluation;

[0025] Fig. 3 shows a schematic view of semiconductor structures for forming transmitting antennas and transmitting modules according to one embodiment;

[0026] Fig. 4 shows a schematic view of semiconductor structures for forming receiving antennas and receiving modules according to one embodiment;

[0027] Fig. 5 shows a schematic view of a semiconductor structure for forming multiple transmitting antennas and a transmitting module according to a further embodiment; and Fig. 6 shows a schematic view of a semiconductor structure for forming multiple receiving antennas and a receiving module according to a further embodiment;

[0028] Figure 1 schematically depicts a photonic radar system 100. This system comprises a central station 200 and a plurality of radar head units 300, 300-n, configured as transmit and / or receive modules. The central station 200 and radar head units 300, 300-n are each individually coupled via two optical fibers 401, 401-n, 501, 501-n. The optical fibers 401, 401-n serve as transmission media 400 for transmitting optical signals from the central station to the radar head unit 300, 300-n. The optical fibers 501, 501-n serve as return transmission media 500. Additionally, the radar head units 300, 300-n are preferably connected to the central station 200 via an electronic control line 460 and an electronic return line 550. The electronic control line 460 and the electronic return line 560 can be configured as a bus system.Alternatively or additionally, the individual radar head units 300, 300-n can each be equipped with an individual control line and individual electronic return line.

[0029] Lowercase letters -n ... stand for natural numbers to indicate countability and distinguishability of the corresponding objects.

[0030] In the illustrated embodiment, the central station 200 is configured to generate radar signal information for transmission, whereby, in the illustrated example, this occurs at a frequency eight times lower than the transmission of a radar signal via an antenna 350, 350-n of one of the radar head units 300, 300-n configured as transmitter modules. For this purpose, the central station 200 comprises a control unit 210, which controls a coherent light source 220, preferably configured as a laser. In an environment detection operating state, radar signal information is modulated onto the optical carrier signal generated by the laser 220 via a modulation unit 230. For example, in a MIMO radar according to the prior art, the radar signal information is a frequency-modulated continuous wave (FMCW) signal intended for transmission, divided by a factor of eight.The modulation device is, for example, designed as a Mach-Zehnder modulator (MZM). The optical signal is forwarded via an optical control device 240 to a distribution device 250. The distribution device 250 preferably includes a switch that controls an optical signal fed into an input and switches it to one or more outputs. The distribution device 250 is also controlled by a control device 210 and selectively switches the optical signal to one or more fiber outputs. The optical signal is thus switched to one or more of the transmission media 400, 400-n and transmitted to one or more of the radar head devices 300, 300-n.

[0031] The fiber output is coupled to one of the optical waveguides 401, 401-n, i.e., one of the fibers 402, 402-n. The optical fibers 402, 402-n are connected at their other end to one of the radar head devices 300, 300-n.

[0032] The radar head units 300, 300-n each have a fiber input 305, 305-n, to which the fiber 402-n coming from the central station 200 is connected. The optical carrier signal with the modulated and transmitted radar signal information is coupled via a photoreceiver coupler 310 into an electronic photonic integrated circuit (EPIC) 315. The photonic components are preferably formed in a region where silicon is located on an insulator, whereas the electronic components are formed on so-called bulk silicon. Embodiments are also possible that are based on other materials or use separate photonic integrated circuits and electronic integrated circuits.In the radar head assembly 300, 300-n, the fiber input 305, 305-n is optically coupled to a fiber output 395, 395-n, such that at least part of the optical signal transmitted to the radar head assembly 300, 300-n via the fiber 402, 402-n serving as the transmission medium 400, 400-n is transmitted back to the central station 200 via the fiber 502, 502-n serving as the return transmission medium 500, 500-n. The fiber 502, 502-n serving as the return transmission medium 500 is connected to the corresponding fiber output 395, 395-n.

[0033] The transmitted optical signal can be converted into an electronic signal in the radar head unit 300, 300-n, whereby the radar signal information is separated from the carrier signal. The radar signal information is typically amplified in the radar head unit, which is designed as a transmitter module, and its frequency is often also multiplied and / or converted. It is then emitted as electromagnetic radiation from the corresponding antenna 350 of the radar head unit 300, 300-n as a radar signal.

[0034] The electromagnetic radiation reflected from an object in the vicinity is also received as a radar echo signal by an antenna 350, 350-n of one or more radar head units 300, 300-n. In a mixing process, radar echo signal information is typically derived from the radar echo signal and generated and processed as an intermediate frequency signal. This intermediate frequency signal is then optically modulated onto the carrier signal transmitted by the radar head unit and transmitted back to the central station 200 via the corresponding return transmission medium 500, 500-n. No carrier signal is actively generated in the radar head unit 300, 300-n, but it can be modified by modulation.

[0035] In the central station 200, a detection unit 260 separates the radar echo information from the optical carrier signal and converts it into an electrical signal during conversion into an electronic signal. The radar echo information received via the various transmission media is evaluated together in a processing unit 270 of the central station to determine the distance, relative velocity, and relative angular position of individual objects in the surrounding area. Upon transmission to the processing unit 270, electrical signals can be digitized in a digitizing unit 280 and pre-processed in a processing unit 290, for example, by undergoing a Fourier transform, which can be implemented in special modules.

[0036] For the sake of simplicity, a return transmission medium 500, 500-n is shown here for each radar head assembly, which may include a transmitting module with at least one transmitting antenna and / or a receiving module with at least one receiving antenna. It is understood by those skilled in the art that radar head assemblies 300, 300-n designed as transmitting modules do not necessarily have to include a return transmission medium, but are generally not connected to such a return transmission medium 500, 500-n.

[0037] Angle estimation using sparsely populated large apertures is not readily achievable with conventional methods such as Fourier transforms. Instead, various derivatives of a matched filter are used in combination with compressive sensing techniques. This approach is based on the specific configuration of the physical antenna positions using MIMO functionality and spatial multiplexing to construct a virtual antenna array. This virtual antenna array represents a kind of template or signature that defines a spatial aperture signal depending on the object distance (also referred to as target distance) and the solid angle of the object / target. This aperture signal can be formally described according to Formula 1. where Ts is the sampling interval, n a counting index, A the mean wavelength of the radar radiation, and Co the radar wavelength. For bistatic radars where transmitting and receiving antennas are spatially distributed, the radial distance between the transmitting antenna position is "p". Tx “and an object, target, “p” and radial distance between the receiving antenna position, “p” Rx “and the object, target, “p” differs. Therefore, for a total distance “d(p)” traveled by a radar signal and radar echo signal, the following applies:

[0038] The second phase term in equation 1 “exp ( I2n— dp)nT s)“ specifies a spectral value at a certain distance as part of a preceding Fourier transformation. During angle estimation, all hypotheses that must be considered due to the radar's field of view and its resolving power are taken into account based on Equation 1. Therefore, for the position of a target according to Equation (2):

[0039] According to equation (3), the angle “0” describes the elevation angle and “< > ” the azimuth angle. For example, assuming a resolution of “A9 = A< > = 0.1°” and a field of view (FoV) of 120° in azimuth and 30° in elevation, then, with a known

[0040] 120°*30°

[0041] Target distance “r”: N = — — — = 360,000 hypotheses are constructed to deal with the spatial

[0042] Aperture signal can be correlated according to formula (1). Such a hypothesis is constructed according to formula 4:

[0043] The suffix “v” indicates a transmitting / receiving antenna pair against which the phase value in equation 4 is calculated as part of the hypotheses.

[0044] To reduce the computational effort required for angle estimation, an approach is chosen that significantly reduces the hypothesis space for angle correlation by utilizing at least one uniform linear array (ULA) within a sparsely populated array aperture. This ULA is used to obtain an initial rough angle estimate for a detected object (target) at a determined radial distance using conventional methods such as a fast Fourier transform. Preferably, such a ULA is implemented for both vertically and horizontally oriented antennas. A rough determination of the angle of a detected object is subject to uncertainty. This uncertainty defines an angular interval around the roughly determined angle of the object at which the radar system perceives it.As a basis for this angular interval, the angular resolution of the ULA structure could be used, for example. Assuming an angular resolution of the ULA structure, i.e., an angular resolution in elevation A0 and azimuth A< >, of 5° each, A0 = A< > = 5°, the number of angular hypotheses to be correlated, i.e., to be considered, would be, for example, N = 2*A0*2*A >. 1000 This reduces the computational effort, which corresponds to that of a conventional fast Fourier transform. Based on this approach, a flowchart 1000 for an angle evaluation is shown in Fig. 2.

[0045] The echo information, representing the measurement data transmitted from the receiving antennas or their associated receiver modules to a central station, is evaluated. The echo information originating from all receiving antennas of the sparsely populated antenna array is referred to here as "one set of echo information." For the sake of simplicity, the echo information originating from the receiving antennas of the uniform linear antenna array(s) is referred to here as "further echo information." The adjective "further," in its various forms, can thus be interpreted as "received by the receiver modules of the receiving antennas of the uniform linear antenna array." The same distinction is made for derived quantities, such as determined distances to objects.Distances determined using all echo information are referred to as "distances" or "one distance," while distances determined using additional echo information are referred to as "further distances." This applies analogously to other quantities.

[0046] Distance spectra are generated both from the echo information 1100, which also includes the further echo information 1200, and separately from the further echo information 1200 (1110, 1210). Distances to detected objects are derived from the distance spectra 1110 and 1120 (1120, 1220).

[0047] For the additional objects detected, or for the further distances at which objects in the vicinity are detected based on the additional echo information, rough angle estimates are made (1230), meaning the angles to the detected objects are roughly determined. Such a roughly determined angle indicates an angular position at which the radar system sees the corresponding object. These roughly determined angles have an uncertainty, and therefore an angular range is associated with them, expressing this uncertainty. For example, the angular resolution of the rough angle determination can be assumed to be an uncertainty.

[0048] Based on the determined distances and the distances obtained, the roughly estimated angles are assigned to the objects detected using the total echo information. Due to the varying distances between the transmitting and receiving antennas of the entire antenna structure, which forms a sparsely populated apparatus, the distances determined using individual transmitting-receiving antenna pairs vary for one and the same object. Thus, the determined object distances are associated with a tolerance range that takes this into account. If a further distance determined using the echo information of the uniform linear antenna array agrees within its tolerance range with a distance determined using all echo information, then the roughly determined angle can be assigned to the associated object in the vicinity.The assignment is therefore made by correlating the further distances with the distances.

[0049] For objects identified using echo information, to which a rough angle can be assigned in this way, the number of angle hypotheses required for precise angle determination can be significantly reduced compared to the number of possible angle hypotheses when a desired angular resolution is applied. Only angle hypotheses are calculated or generated that correlate with angles falling within the range representing the uncertainty of the rough angle determination around the roughly determined angle. When angles are mentioned in this context, they refer to a solid angle in each of two non-collinear spatial directions, specifically in the case of a two-dimensional antenna array that exhibits a uniform linear array in two such directions.If one assumes an angular resolution for the rough determination for the angle estimation and determines the azimuth angle using a uniform linear antenna array, <p mit einer Winkelauflösung von A< > = 5° and with the further echo information from the other uniform linear antenna array, the elevation angle 0 with an angular resolution of also A0 = 5°.

[0050] 2 * 2 * so the number of angle hypotheses to be considered is N = — — — - = 1000. This is a significant reduction compared to the possible number of angle hypotheses to be considered of 360,000 with an assumed field of view (FoV) of 120° in azimuth and 30° in elevation with an angular resolution of 0.1 in each of the two angles.

[0051] To determine the precise angle, the angle hypotheses calculated or generated for one of the detected objects are correlated with all the acquired measurement data, i.e., all the echo information, to find the angle hypothesis that shows the best correlation. The angle associated with the angle hypothesis then indicates the precisely determined angle. This process is carried out for all detected objects. The precisely determined angles are then output and can be used, for example, by the assistance systems of the vehicle in which the radar system is integrated.

[0052] Fig. 3 schematically shows the transmitting antennas 350-n and their associated transmitting modules 700-n for an embodiment that corresponds to the embodiment of a MIMO radar system according to Fig. 1.

[0053] Each of the transmitting antennas 750-n of the antennas 350 is formed on a semiconductor structure 705-n, together with the associated transmitting module 700-n. The optical carrier signal, onto which the radar signal information is modulated and transmitted via a fiber 402-2, is coupled into the semiconductor structure 705-n at a coupling element 730-n. The semiconductor structure 705-n can be configured as an integrated photonic electronic semiconductor circuit (EPIC) 315. At a converter device 740-n, which is configured, for example, as a photodiode 741-n, the radar signal information is separated from the optical carrier signal and converted into an electronic signal. This electronic signal is amplified in a transmitting amplifier 760-n before being emitted as a radar signal via the corresponding transmitting antenna 750-n. In this embodiment, a separate semiconductor structure 705-n exists for each of the transmitting antennas 750-n.

[0054] Figure 4 shows the corresponding receiving antennas 650-n to the embodiment shown in Figure 1, which are formed together with a receiving module 600 on a semiconductor structure 605-n, for example an EPIC. The carrier signal modulated with the radar signal information is also transmitted to the receiving module 600-n via an optical fiber 402-n. A coupling element 640-n ensures that the optical carrier signal with the radar signal information modulated thereon is coupled into the semiconductor structure 605-n of the receiving module 600-n. At a converter device 640-n, which is also preferably designed as a photodiode 641-n, the radar signal information is again separated and converted into an electronic signal, which is fed to a mixer 670-n. A radar echo signal received at the receiving antenna 650 is also forwarded to the mixer 670 via a receiving amplifier 660.This device derives an intermediate frequency signal from the radar echo signal using a mixing process. This intermediate frequency signal contains echo information. This echo information is modulated, for example, onto the optical carrier signal looped through the semiconductor structure 605-n by an optical modulation device 680-n. The signal is then transmitted via a further coupling device 690-n to another optical fiber 502-n, which is connected to a further fiber connector, for evaluation at the central station. Due to the use of one or more optical carrier signals, all provided by the central station, a coherent evaluation of the received signals from all receiving antennas is possible at the central station. Each of the receiving antennas 650 of the antennas 350 is configured with its associated receiving module on a separate semiconductor structure 605-n.In one embodiment, this applies to all receiving antennas, including those forming the uniform linear antenna array or one of the uniform linear antenna arrays.

[0055] Figure 5 shows a semiconductor structure 705 with a transmitter module 700 and several transmitting antennas 750-n. All or only some of the transmitting antennas of the entire antenna structure can be configured on the semiconductor structure 705. This embodiment differs from that shown in Figure 3 in that the multiple transmitting antennas 750-n are configured together on the single semiconductor structure 705 and each has its own transmitting amplifier 760-n. An electronic switching device 720 can be arranged between the converter unit 740-n and the various transmitting amplifiers 760-n. This switching device ensures that the chirps, which are provided sequentially as radar signal information, are alternately emitted as a radar signal via the different transmitting antennas 750-n with a time delay. In a corresponding central station, the distribution device 250 can thus be configured, for example, as a beam splitter.The control of the switching device 720 can, for example, be carried out electronically via signals that are sent from the central station via the electronic control line (compare 460 in figure one, not shown here for the sake of simplicity).

[0056] The embodiments of semiconductor structures for transmitting antennas 750 according to Figures 3 and 5 can be combined arbitrarily in an antenna structure. Figure 6 schematically shows a semiconductor structure 605 with several receiving antennas 650-n and a receiving module 600. In contrast to the embodiment according to Figure 4, the semiconductor structure includes several receiving antennas 650-n, which can be the receiving antennas 650 forming a uniform linear antenna array, or receiving antennas contributing to the formation of the sparsely populated antenna apparatus, or comprise both receiving antennas 750 of a uniform linear antenna array and other receiving antennas 750 of the antenna array.

[0057] The semiconductor structure 605 of this embodiment further differs in that a receiving amplifier 660-n is connected to each of the receiving antennas in 650-n, i.e., several receiving amplifiers 660-n are formed on the semiconductor structure. Another difference is that a mixer 670-n is formed on the semiconductor structure 605 for each of the receiving antennas 650-n and thus also for each of the receiving amplifiers 660-n.

[0058] These mixers 670-n are each connected on one side to the receiver amplifier 660-n for receiving the useful signal in the form of an amplified radar echo signal, and on the other side to the radar signal information converted into an electronic signal, i.e., a signal that sequentially comprises the emitted chirps. The mixers thus derive the radar echo information acquired at the corresponding receiving antenna 650-n from the radar echo signal and output it in the form of an intermediate frequency signal. All these signals are routed to the modulation unit 680, which modulates the various echo information onto the optical carrier signal for transmission back to the central station.The mixers 670-line N are designed to generate the intermediate signals at different center frequencies, allowing them to be modulated together onto the optical carrier signal during frequency multiplexing without interfering with each other or resulting in information loss. The modulated carrier signal is then coupled into the next fiber 502-n via a further optical coupler 690-n.

[0059] The various configurations of the semiconductor structures 605 described in Figures four and six can be used in any combination in an antenna structure. Reference list for photonic radar systems

[0060] Central station

[0061] Control unit

[0062] Laser

[0063] Modulation device optical control device

[0064] Distribution system

[0065] Detection device

[0066] Unit of calculation

[0067] Digitization facility

[0068] Processing unit, 300-n radar head unit, 305-n fiber input

[0069] Photoreceive coupler electronic-photonic integrated circuit (EPIC)

[0070] Antenna structure: uniform linear array

[0071] Antenna, 395-n fiber output, 400-n transmission medium, 401-n optical fiber, 402-n fiber, 450-n further transmission medium electronic control line, 500-n return transmission medium, 501-n optical fiber, 502-n fiber, 550-n further return transmission medium electronic return line, 600-n receiver module, 630-n coupling element 640, 640-n converter unit

[0072] 641, 641-n photodiode

[0073] 650, 650-n receiving antenna

[0074] 660, 660-n receiver amplifier

[0075] 670, 670-n mixer

[0076] 680, 680-n optical modulation device

[0077] 690, 690-n further coupling device

[0078] 700, 700-n transmitter module

[0079] 705, 705-n semiconductor structure

[0080] 720, 720-n switching device

[0081] 730, 730-n coupling element

[0082] 740, 740-n converter unit

[0083] 741, 741-n photodiode

[0084] 760, 760-n transmitting amplifier

[0085] 1000 Flowchart

[0086] 1100 echo information

[0087] 1110 Forming distance spectra

[0088] 1120 Deriving / Determining distances

[0089] 1150 Assigning the angles

[0090] 1160 Calculating angle hypotheses

[0091] 1170 Correlating the angle hypotheses / precise angle determination

[0092] Spend 1180

[0093] 1200 more echo information

[0094] 1210 Forming further distance spectra

[0095] 1220 Deriving / Determining distances

[0096] 1230 Rough determination of the angles

Claims

Patent claims 1. Antenna structure (320) for a multiple-input multiple-output radar system, MIMO radar system, comprising a plurality of receiving antennas (650, 650-n) and a plurality of transmitting antennas (750, 750-n) which are spaced apart from each other and form a sparsely populated antenna aperture, characterized in that a plurality of the plurality of receiving antennas (650, 650-n) form a uniform linear antenna array.

2. Antenna structure (320) according to claim 1, characterized in that the distances between adjacent receiving antennas (650, 650-n) of the plurality of receiving antennas (650, 650-n) forming the uniform linear antenna array are less than or equal to half the wavelength of the radar signals to be radiated.

3. Antenna structure (320) according to claim 1 or 2, characterized in that a further plurality of receiving antennas (650, 650-n) form a further uniform linear antenna array, wherein a linear orientation direction of the plurality of receiving antennas (650, 650-n) of the one uniform linear antenna array is different from a further linear orientation direction of the further plurality of receiving antennas (650, 650-n) of the one further uniform linear antenna array.

4. Antenna structure (320) according to claim 3, characterized in that one alignment direction and the further alignment direction enclose an angle of greater than 70°, preferably 90°.

5. Antenna structure (320) according to one of the preceding claims, characterized in that the plurality of receiving antennas (650, 650-n) and the A multitude of transmitting antennas (750, 750-n) form a two-dimensional antenna aperture.

6. Multiple-input multiple-output radar system, MIMO radar system, comprising a plurality of receiving antennas (650, 650-n) and a plurality of transmitting antennas (750, 750-n) spaced apart from one another and forming a sparsely populated aperture, wherein each of the transmitting antennas (750, 750-n) is associated with a transmitting module (700, 700-n) for processing the radar signal to be transmitted and each of the receiving antennas (650, 650-n) is associated with a receiving module (600, 600-n) for processing the detected radar echo signal and deriving radar echo information, and a central station which is informationally connected to the transmitting and receiving modules (600, 600-n), wherein the central station is configured to generate radar signal information to the transmitting modules (700, 700-n) to transmit and control their radiation via the multitude of transmitting antennas (750, 750-n) and to receive and jointly evaluate the echo information from the receiving modules (600, 600-n),to detect objects in the environment and locate them relative to the radar system, characterized in that a plurality of receiving antennas (650, 650-n) form a uniform linear antenna array, and the central station is configured in such a way that, when evaluating the echo information from the plurality of receiving antennas (650, 650-n) forming the uniform linear antenna array, angles to objects are roughly determined, and when accurately determining the angles of the detected objects based on the echo information from all receiving antennas (650, 650-n) of the plurality of receiving antennas (650, 650-n), only a limited number of possible angle hypotheses for the respective detected objects are considered, which agree with the roughly determined angle within the scope of an uncertainty.

7. Method for environmental detection using a multiple-input multiple-output radar system, MIMO radar system, comprising a plurality of receiving antennas (650, 650-n) and a plurality of transmitting antennas (750, 750-n) spaced apart from one another and forming a sparsely populated aperture, wherein each of the transmitting antennas (750, 750-n) is associated with a transmitting module (700, 700-n) for processing the radar signal to be transmitted and each of the receiving antennas (650, 650-n) is associated with a receiving module (600, 600-n) for processing the detected radar echo signal and deriving radar echo information, and a central station which is connected to the transmitting and receiving modules (600, 600-n) via information technology, wherein the central station is configured to generate radar signal information, transmit it to the transmitting modules (700, 700-n) and control its emission via the plurality of transmitting antennas (750, 750-n), and receive and jointly evaluate the echo information from the receiving modules (600, 600-n) in order to detect objects in the environment and locate them relative to the radar system, the method comprising the steps of: generating radar signal information comprising a sequence of chirps, linearly monotonically modulated signal segments with respect to frequency; emitting the chirps with time offsets via the plurality of transmitting antennas (750, 750-n) such that in each time interval only one of the transmitting antennas (750, 750-n) emits a chirp as a radar signal; simultaneously receiving radar echo signals generated at the objects and deriving the echo information; and jointly evaluating the echo information to determine a distance and angle of the detected objects relative to the MIMO radar system to determine,wherein, to determine the angle of each object, a plurality of angle hypotheses are evaluated which depend on the determined distance of the object, characterized in that a plurality of receiving antennas (650, 650-n) form a uniform linear antenna array and, based on the echo information of these receiving antennas (650, 650-n) of the uniform linear antenna array, angles to the detected objects are roughly determined and these roughly determined angles are each used to determine the number of objects to be considered. - 21 - To restrict angle hypotheses when determining the exact angles of objects, only angle hypotheses that agree with the roughly determined angle within the scope of uncertainty are considered.

8. Method according to claim 7, characterized in that, in addition, distances to the objects are determined on the basis of echo information from all receiving antennas (650, 650-n) of the plurality of receiving antennas (650, 650-n), and furthermore, on the basis of the echo information from the plurality of receiving antennas (650, 650-n) which form a uniform linear antenna array, further distances are determined for the detected objects, whose angles have been roughly determined, and an assignment of the roughly determined angles to the objects detected on the basis of the echo information from all receiving antennas (650, 650-n) is carried out by assigning the roughly determined angle to the object detected on the basis of all echo information, with whose distance the further distance corresponds within a tolerance range.

9. Method according to claim 7 or 8, characterized in that the rough determination of the angle is carried out on the basis of the echo information acquired for one of the chirps.

10. Method according to one of claims 7 to 9, characterized in that the distances to objects are determined on the basis of the echo information of the receiving antennas (650, 650-n) of the uniform linear antenna array, which are each acquired during the emission of a chirp, and this determination is carried out several times during a measurement sequence in which the chirps are emitted via the different transmitting antennas (750, 750-n) with a time delay for chirps emitted via the different transmitting antennas (750, 750-n) in order to estimate a difference in the distance determination based on different transmitting antenna-receiving antenna pairs.

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