Communications: directive radio wave systems and devices (e.g. – Determining velocity – Combined with determining distance
Reexamination Certificate
2000-07-31
2002-06-11
Lobo, Ian J. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
Combined with determining distance
C342S128000
Reexamination Certificate
active
06404381
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a radar sensor device for detecting the distance and/or the speed of an object relative to the sensor device.
Radar technology is particularly suitable for use in motor vehicles and in industrial applications for a contactless detection of object data such as range, speed, state or presence. The functionality, measuring accuracy and production costs of radar sensors depend in this case substantially on the modulation methods applied and on the associated radar signal processing. The respective constraints of an application determine the configuration of the components of a radar sensor device and thus, for example, the complexity or simplicity of the electronics used in this case.
A contactless measurement of distance and speed with the aid of radar has been practiced for many years, mainly in military technology. In this connection, two different standard modulation methods are known for distance measurement, specifically pulse modulation and frequency modulation.
In the pulse travel time method, a short radar pulse is emitted in the direction of a measurement object and is received again as a pulse reflected from an object after a specific travel time. The travel time of the radar pulse is directly proportional to the distance from the measurement object.
In the case of the frequency method, a frequency-modulated radar signal is emitted and is received with a phase shift or frequency shift. The measured phase or frequency difference, which is typically in the kHz region, is proportional to the object distance. A requirement for this is a temporally linear frequency modulation.
Theoretically, the measured values obtained by the pulse travel time method on the one hand and the frequency method on the other hand are equivalent. In practice, however, the methods have specific advantages and disadvantages with reference to the parameters for the sensor measuring accuracy and the achievable structural resolution which are of relevance in practice. These parameters are first and foremost the modulation bandwidth and the radar transmitted/received power. For these parameters, which determine the structural resolution and range, there are radio approval regulations and technically and economically relevant constraints or boundary conditions, in particular with regard to the functioning and the outlay on circuitry. In this context there may be mentioned, for example, the frequency bands, which can be used for short-range monitoring with the aid of radar sensors, from 24.0 to 24.25, from 61.0 to 61.5 and from 76.0 to 77.0 GHz, to which the radar parameters mentioned below also relate.
For the application of the measurements of distance and speed of objects in the surroundings of a motor vehicle, a physical structural resolution of <15 cm is required for a measuring range of 0 to 5 meters (short range). A modulation bandwidth of >1 GHz is required for this purpose. A pulse duration of <1 ns is required in the case of an appropriate pulse method. The generation of the abovementioned radar signals with a duration of a few 100 ps, a bandwidth >1 GHz and a radar central frequency at, for example, 24 or 77 GHz entails a not inconsiderable technical outlay.
For reasons of costs, known radar sensor devices for industrial applications—for example a filling level radar—and traffic applications—for example a motor vehicle distance radar—mainly use frequency-modulated methods, since in this case a flexible and very precise digital signal processing is possible. Furthermore, a high range of up to approximately 100 m is achieved even for objects of low reflectivity.
U.S. Pat. No. 5,325,097 discloses a radar system for road vehicles which distinguishes between dangerous and non-dangerous target objects inside a predetermined zone. This system uses a pair of frequency-modulated continuous wave radar cycles and a single continuous wave cycle in generating radar signals for measuring the target region and the apparent target speed. Measured values from the FM/CW (frequency modulation/continuous wave) and CW (continuous wave) cycles are used with predetermined values for distinguishing between dangerous and non-dangerous target objects. With reference to its configuration, the system known from U.S. Pat. No. 5,325,097 has a frequency-detunable oscillator, which can be driven electronically through the use of a modulation function, for generating a transmitted signal, a transmitting antenna for emitting the transmitted signal, a receiving antenna for receiving the radar received signal reflected by the target, a demodulation unit for forming a demodulated received measuring signal, and a control unit in the form of a digital processor, which serves to control the sensor device and, above all, to control the modulator, and to evaluate the received signal.
German Patent No. DE 38 30 992 C2 discloses a radar altimeter which is configured using the FM-CW principle. The power of the transmission path of the radar equipment used in this case can be controlled by a variable attenuator connected upstream of a power amplifier, specifically as a function of the altitude and, in particular flight altitude of the aircraft equipped with the radar altimeter. It is clear that the radar equipment is always to be operated with as little radar energy as possible, in order to keep the detectability by extraneous sensors as low as possible, which is important, in particular, in the case of military applications.
Despite their practical applicability, for various reasons the known radar sensor devices explained above and based on a pulse or frequency method are unsuitable for the detection tasks at short range, which are of interest in conjunction with the present invention. Specifically, in the case of the present invention, strongly differing measuring requirements, such as near and remote targets, low and high object speeds and different object reflectivities occur. These measuring requirements must be fulfilled simultaneously.
Published, Non-Prosecuted German Patent Application No. DE 195 38 309 A discloses a radar sensor device for measuring distances and relative speeds between a vehicle and one or more obstacles, which has an oscillator for generating a transmitted signal whose frequency can be varied through the use of a control modulation voltage. Radar signals are emitted via a transceiver antenna, and radar received signals reflected by an object to be detected are received. The received signal is demodulated by a single-channel mixer and evaluated in a signal processing device.
From U.S. Pat. No. 5, 287, 111 it is further known in principle to vary the detection range of radar sensors by varying the transmitter power.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a radar sensor device which overcomes the above-mentioned disadvantages of the heretofore-known devices of this general type and which has a high flexibility and, in particular, effective applicability at short range in conjunction with an acceptable outlay on circuitry.
With the foregoing and other objects in view there is provided, in accordance with the invention, a radar sensor device for detecting a distance and/or a speed of an object relative to the radar sensor device, including:
a frequency-detunable oscillator operating with a given frequency and a given phase for generating a transmitted signal;
a transmitting antenna, connected to the frequency-detunable oscillator, for emitting a radar signal based on the transmitted signal;
a receiving antenna for receiving a radar received signal reflected by an object to be detected;
a demodulation unit, connected to the frequency-detunable oscillator and to the receiving antenna, for forming a demodulated received measuring signal from the transmitted signal and the radar received signal;
a control unit, connected to the frequency-detunable oscillator, for electronically driving the frequency-detunable oscillator with a modulation function and for evaluating the demodulated received
Heide Patric
Kunert Martin
Greenberg Laurence A.
Lobo Ian J.
Mayback Gregory L.
Siemens Aktiengesellschaft
Stemer Werner H.
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