Communications: directive radio wave systems and devices (e.g. – Determining distance – With frequency modulation
Reexamination Certificate
1999-08-30
2001-07-03
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
With frequency modulation
C342S027000, C342S120000, C342S122000, C342S175000, C342S195000, C342S200000
Reexamination Certificate
active
06255984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensor system with frequency modulated continuous wave FMCW radar and with a mechanism for correcting phase errors.
In sensor systems with FMCW radar, particularly microwave radar systems, a simultaneous distance and speed measurement is possible. These types of sensor systems have multiple application possibilities, such as in automotive or automation technology. In a sensor of this type, a frequency-modulable signal source (e.g. a microwave oscillator) is present, which emits a linearly frequency-modulated transmit signal via a transceiver (e.g. one or more antennae), for example. The signal, which is received after a delay of the transit time to a measurement subject and back, is separated from the transmit signal as a receive signal by a transceive separating filter and is forwarded to a mixer. In this mixer, the receive signal is demodulated with the transmit signal. A low-pass filtering preferably occurs subsequently, in order to eliminate undesirable frequency portions. In this type of sensor, the information about the distance between the transceiver and the measurement subject is proportional to the phase-angle deviation ( or respectively, the frequency) of the measuring signal. By virtue of this fact, in practice primarily errors of the phase of the signal have a limiting effect on the performance capability (range, measurement accuracy, sensitivity) of the system. For example, as such phase errors, stochastically distributed errors can arise which originate in a phase noise of the signal source. When measurement distances are great, such errors have disadvantageous effects. For example, systematic phase errors are brought about by a non-ideally linearly progressing frequency modulation of the signal source. Errors of this type frequently interfere considerably, even given measurement in the near environment.
2. Description of the Prior Art
In order to suppress these types of phase errors in the described sensors, an appreciable technical outlay is required. DE 27 10 841 A1 teaches an arrangement for measuring distance wherein a linearly frequency-modulated oscillator is used, and mechanisms are provided which correct deviations from the linearity of the modulation with the aid of a delay line and a control loop.
SUMMARY OF THE INVENTION
It is the object of the present invention to propose a sensor system for measuring distance or speed by means of a frequency-modulated signal, where the system can be produced with a relatively low outlay of resources, and has an improved accuracy compared to sensor systems with phase errors.
This object is achieved with the sensor system having a signal source that generates a FM signal, a transceiver, and a mixer that mixes the transceiver signal with the FM signal into a measuring signal. A reference signal is created by mixing a delayed FM signal with the undelayed FM signal, and a detector defines definite phases of the reference signal. Modulation linearization of the signal source is achieved by a measuring signal detector by measuring the signal at the definite phases, and determining a correction from these measurements. Additional embodiments may be envisioned from the following text.
In the inventive sensor system, a reference signal which can be compared to the measuring signal is generated with the aid of an internal delay circuit. At all times at which this reference signal has a definite phase, e.g. a zero crossing, the measuring signal is stored, preferably in digitized form. These values of the measuring signal can then be evaluated regardless of the erroneous fluctuations of the phase caused by the signal source or by other components of the device. The evaluated measurement result thus corresponds to a measurement with a signal medium that is frequency-modulated in an ideally linear manner, for example. In addition to this improved evaluation, the reference signal can be used to carry out a continuous correction of the signal generated by the signal source. The controlling of this correcting mechanism likewise ensues in that the times at which the reference signal has a definite phase are determined, and a respective correction value is calculated by computer from the appertaining phases of the measuring signal. This value is subsequently used to trim the frequency of the signal source.
REFERENCES:
patent: 4593287 (1986-06-01), Nitardy
patent: 5172123 (1992-12-01), Johnson
patent: 5189427 (1993-02-01), Stove et al.
patent: 27 10 841 A1 (1977-09-01), None
patent: 0 466 258 A2 (1992-01-01), None
Heide Patric
Kreppold Bernhard
Vossiek Martin
Gregory Bernarr E.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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