RADAR SENSOR WITH TWO-DIMENSIONAL BEAM STEERING AND L-, U-, OR T-SHAPED STRUCTURE FOR INSTALLATION IN THE AREA OF THE FRONT RADIATOR IN AUTOMOBILES

Description

Technical application area

[0001] The invention relates to a device and a method for measuring the vertical and horizontal position of objects using a radar sensor that performs digital steel forming using a two-dimensional virtual array. The radar sensor has an L-, U-, or inverse T-shaped structure, which allows the sensor to be installed in the front area of ​​the automobile without significantly impairing the airflow required for the front radiator.

[0002] Millimeter-wave radar sensors for automotive applications, such as adaptive cruise control, are installed in the front of the vehicle, facing the direction of travel. Ideally, the sensor should be mounted as high as possible to minimize the influence of the road surface on the propagation of the electromagnetic wave. These influences include multipath propagation and reflections from the road, which impede object detection. Due to the overlap of signals from different directions, multipath propagation leads to amplitude fluctuations and even the temporary cancellation of the received signals. Reflections from the road surface, known as clutter, overlap with the desired object signal, thus reducing the signal-to-noise ratio.

[0003] An elevated mounting position in combination with additional vertical beam pivoting significantly reduces these influences.

[0004] Depending on the design of the body, however, this raised position cannot be realized because the air flow required for the front cooler is impaired in an unacceptable manner by the radar sensor being installed.

[0005] This conflict of requirements is advantageously resolved by the following invention. The housing and antenna array of the radar sensor are shaped so that they can be integrated into the structure of the radiator grille. The antenna aperture of the radar sensor exists only virtually, allowing the airflow required for cooling to pass unhindered in the area of ​​the antenna aperture. The virtual antenna array generates a highly focused antenna beam through the numerical linking of multiple transmitting and receiving units, similar to that generated by a planar array, but without impeding the airflow.

[0006] Another requirement is the detection of the end of a traffic jam on the road. Here, stationary vehicles must be distinguished from bridges and manhole covers. Furthermore, three-dimensional measurement of the objects is desired for object classification. This task is advantageously solved by two-dimensional beam scanning. State of the art

[0007] DE 10 2008 052 246 A1 describes a sensor system with an adjustable elevation beam direction for determining the vertical position of objects. Adjustment is achieved by the mechanical movement of a reflector.

[0008] German Patent Application DE 10 2008 061 932 A1 describes a method for digital beamforming. WO 2013 / 045232 A1 describes a radar device in which a two-dimensional imaging radar is enabled by providing multiple transmitters and multiple receivers. US 2016 / 282450 A1 describes a radar device that can achieve a maximally enlarged aperture length of a virtual receiving array. EP 2 045 612 A2 describes a detection and ranging device that uses multiple sense sensors to increase the effective aperture of a sensor array with multiple sensor elements. Description of the invention

[0009] The object of the invention is to provide a device and a method with which the installation described above can be realized in the vehicle.

[0010] In addition, it is an object of the invention to provide a device and a method with which the horizontal and vertical position of an object can be determined by two-dimensional beam shaping.

[0011] The object is achieved in accordance with the device by the features of claim 1, and in accordance with the method by the features of claim 5.

[0012] Accordingly, the device comprises an L-, U- or T-shaped structure so that the air flow of the front cooler is not or only slightly affected.

[0013] Furthermore, the device for determining the position of an object in three-dimensional space, in particular a moving object, comprises at least a number of receiving antennas arranged in a row, as well as a transmitting antenna arranged in a row, wherein the transmitting antenna row is arranged orthogonally to the receiving antenna row. The two antenna rows preferably have a T-, U-, or L-shaped structure ( Fig. 1a, 1b The antennas are preferably designed as single-patch antennas with a wide beam lobe in both the horizontal and vertical directions. Beam focusing and control are achieved exclusively through digital beamforming by combining the individual radiators. Compared to a highly focused single radiator, this has the advantage that with the digitally shaped beam, the structure of a radiator grille has only a minimal influence on the antenna's directional characteristics.

[0014] The device further comprises a frequency generator for generating a signal that is individually phase-coded for each transmitting antenna. To form a virtual two-dimensional array, a transmitting antenna and a receiving antenna are combined. The signal from the receiving antennas is first converted to an intermediate frequency level or baseband with the common uncoded transmit signal. Analog signal processing (filtering, amplification) and digitization of the signals then take place. The signal is then decoded using the code of the desired transmitting partner, and the virtual two-dimensional array is generated.

[0015] Furthermore, the transmitters must be operated simultaneously so that the digital beamforming process can also be used in highly dynamic scenarios, such as road traffic. Examples of implementation:

[0016] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Corresponding parts are provided with the same reference numerals in all figures. Example 1: FMCW radar with phase encoding from frequency ramp to frequency ramp

[0017] The invention relates to a frequency-modulated continuous wave radar (FMCW radar) according to Fig. 2 , which monitors an area using digital beamforming. The radar sensor consists of a transmitter with several, e.g., 12 outputs (Tx) and several, e.g., 16 receivers (Rx). The transmitter consists of a voltage-controlled oscillator (1) with an integrated frequency modulator (2) and 12 parallel outputs (3). The outputs are equipped with power amplifiers (4), which can change the phase of the transmitted signal by 180° by applying a control signal (11).

[0018] Fig. 3shows the sawtooth-shaped temporal progression of the transmitted frequency. During a frequency ramp, for example, the received signal is sampled with 512 points. Approximately 256 ramps are recorded during one measurement cycle.

[0019] The transmitted signal during each frequency ramp is binary-encoded in phase using a pseudo-random code generator. 0 means the phase is reversed by 180°, 1 means the phase remains the same.

[0020] The pseudo-random code is preferably generated by a shift register. Fig. 4 shows a 3-stage shift register. Depending on the initial coding, a different code is generated. The code length is calculated as N = 2 n < - 1, where n = the number of register stages. For the register shown here with 3 stages, the code repeats after 7 time stages. In practice, however, longer codes are preferred, as they provide better decoupling between the individual transmission signals.

[0021] In the receiver of the radar sensor after Fig. 2 The signal reflected from the object and received by the antenna (5) is first converted to the baseband by a mixer (6) and sampled by an AD converter (7). The sampled signal is then decoded with the codes of the respective transmitters (8). Thus, with 16 receivers and 12 transmitters, 12*16 = 192 received signals are generated. These signals can be Fig. 5 represented elements of the virtual array.

[0022] After decoding, signal processing is performed, as described, for example, in DE 10 2008 061 932 A1. This initially consists of a two-dimensional FFT, which generates a so-called distance-velocity matrix for each received signal. Fig. 6shows an example of such a matrix with an echo signal at distance cell 100 and speed cell 0. Due to the finite decoupling between the individual transmission codes, secondary lines arise in the speed direction, which, with the code length N = 255 selected here, are approximately 20 dB below the desired signal. The dynamic range in the speed direction is therefore limited. The dynamic range in the distance direction is not affected. This means that, for example, objects at the same distance but with different speeds must differ in echo amplitude by less than 20 dB to still be detected separately.

[0023] After the two-dimensional FFT (9), the antenna lobes (10) are formed. This is achieved by weighting, phase shifting depending on the desired viewing direction, and summing the individual channels, as described, for example, in DE 10 2008 061 932 A1. Alternatively, a third FFT can be calculated using the received signals, which then generates a multitude of antenna lobes in three-dimensional space, a subset of which is then used for detection in the selected field of view. Fig. 7 shows the antenna beam of a 16x12 antenna array. It has a beamwidth of 8° horizontally and 11° vertically and a sweep range of +- 60° in the vertical plane and +- 65° in the horizontal plane. Example 2: CW radar with phase encoding synchronous to the sampling frequency

[0024] Another embodiment is a binary phase coding of a monofrequency continuous wave signal (so-called CW signal). Fig. 8shows the block diagram of this radar system. An oscillator (1) is operated with a monofrequency carrier signal. This signal is first divided among all 12 transmission channels (3) and phase-modulated for each channel using a binary pseudo-random code generator (4). The object echoes detected by the receiving antennas (5) are converted to baseband using a mixer (6) and digitized using an AD converter (7). Subsequently, the digitized signal is cross-correlated (13) with the respective time-delayed code of the transmitter (14), generating 12 signal paths per receive channel. To improve the signal-to-noise ratio, several code sequences are then accumulated (12) and then fed into a signal processing step—for example, one equivalent—consisting of 2D FFT (9) and beamforming (10).

[0025] In contrast to the relatively slow phase encoding according to Example 1, the phase of a monofrequency signal is changed with each sample. The so-called chip length Tc is given by: Tc = 2*ΔR / c with ΔR: distance resolution c: speed of light

[0026] Therefore, to achieve a resolution of 10 cm, a chip length of 0.67 ns and a sampling rate of 1.5 gigasamples / s are required. With a code length of 2 13 < -1 = 8192, the code duration Lc = 5.46 µs. The code duration determines the maximum unambiguous range. Lc = 2*Rmax / c.

[0027] The maximum range in this example is 800 m, which is sufficient for automotive applications.

Claims

1. Apparatus for determining the position of an object in three-dimensional space by means of an antenna structure (5), wherein the antenna structure has an L-, U- or T-shaped structure and can be mounted in the region of the front radiator of a vehicle with radiator grille, wherein the antenna structure is a radar sensor and a housing and an antenna arrangement of the radar sensor are formed in such a way that they can be integrated into the structure of the radiator grille, wherein the antenna structure is provided behind the air-impermeable region of the radiator grille and a combined frequency and phase modulation of the transmission signals and simultaneous operation of all transmitters is enabled.

2. Apparatus according to Claim 1, wherein the antenna structure (5) comprises a plurality of radar transceiver devices, wherein each device has a plurality of receivers and a plurality of transmitters and forms a virtual antenna array for two-dimensional horizontal and vertical beam scanning, wherein the virtual antenna array comes to rest in the region of the ventilation openings of the radiator grille.

3. Apparatus according to either of Claims 1 to 2, wherein an evaluation unit is provided, which decodes (8) the incoming received signal in the receiving device with fixed transmission codes, so that a plurality of sub-signals is generated from a received signal, the plurality of which corresponds to the number of transmitters.

4. Apparatus according to any one of Claims 1 to 3, wherein a high-frequency phase modulation of the continuous-wave transmission signal and simultaneous operation of all transmitters is provided and wherein a binary 180° phase encoding is provided, which is generated by means of a pseudo-random number generator.

5. Method for determining a position of an object, in using an apparatus according to any one of Claims 1 to 4, having the following method steps: a. transmitting and receiving signals by means of an antenna structure in an L- or T-shaped arrangement, which is mounted in the region of the front radiator of a vehicle b. generating a code sequence for the transmitters in accordance with the pseudo-random principle by means of a feedback shift register c. generating sub-signals from the received signal using decoding procedures d. assigning the individual sub-signals to the individual emitters of a virtual array structure generated by the antenna structure. e. associating the sub-signals according to the method of digital beam forming with a plurality of focussed antenna beams in the horizontal and vertical direction f. displaying the horizontal and vertical position of the object6. Method according to Claim 5, wherein by means of sawtooth-shaped frequency modulation (2) of the transmitted signal a binary 0° / 180° phase encoding of the transmitted signal from frequency ramp to frequency ramp is provided.

7. Method according to Claim 5 or 6, wherein the decoding procedure is carried out by decoding (8) with the individually generated code sequence of the transmitting antennas.

8. Method according to Claim 5, wherein a high-frequency binary phase modulation of a continuous-wave transmission signal is provided.

9. Method according to either of Claims 5 or 8, wherein the de-coding procedure takes place by cross-correlation with the time-delayed, individually generated code sequence of the transmitting antennas.