Communications: directive radio wave systems and devices (e.g. – Determining distance – With frequency modulation
Reexamination Certificate
1999-07-12
2001-01-30
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
With frequency modulation
C342S131000, C342S135000, C342S132000
Reexamination Certificate
active
06181273
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a near-range radar distance sensor upon employment of microwave signals.
A basic task of sensor technology is the non-contacting, precise measurement of distances. Due to their rugged nature and dependability, particularly under difficult conditions of use, microwave radar sensors offer critical advantages compared to other sensors that work ultrasound or optical methods. Microwave radar sensors are therefore suitable for versatile applications such as, for example, for non-contacting measurement of range and velocity in automation technology or in automotive technology. A number of distance sensors according to the radar principle are known and described in textbooks. A particularly preferred embodiment works according to the FMCW Principle (Frequency Modulated Continuous Wave). An example of such a radar distance sensor is schematically illustrated in FIG.
2
. The sensor emits a preferably linearly frequency-modulated transmission signal s (t) via the antenna A, this transmission signal s (t) being supplied by an electronically tunable microwave oscillator VCO. The reception signal e (t) received by the antenna is delayed in time relative to the transmission signal corresponding to the running time to the target and back and has a different momentary frequency dependent on running time compared thereto. A separation between the transmission signal and the reception signal in this indicated example is effected by a transmission/reception diplexer SEW. Such a transmission/reception diplexer can, for example, be formed by a circulator. An alternative is the employment of separate antennas for the transmission and reception (bistatic radar system). The measured signal mess (t) is generated by mixing the transmission signal s (t) and the reception signal e (t), for example in a mixer MI, and corresponds to the product of transmission signal and reception signal. The measured signal mess (t) arising during the mixing process has the difference frequency between the transmission signal s (t) and the reception signal e (t) as frequency. This frequency (or, respectively, the phase boost) of the measured signal mess (t) is proportional to the distance given such a sensor.
In practice, such distance sensors have technologically conditioned weaknesses in the near range, i.e. for extremely short distances to be measured. Due to unavoidable crosstalk because of the non-ideal separation of transmission signal and reception signal (e (t) contains parts of s (t)), noise/multiple reflections within the sensor, reactances of the frequency modulation onto the components of the sensor and low-frequency amplitude/phase noise of the sensor components, the sensitivity of such sensors is highly limited in the near range, i.e. the internal noise signals of the sensor superimpose a payload signal produced by a target in the near range to such an extent that the measured signal supplies no usable range information. U.S. Pat. No. 5,337,052 discloses a radar sensor that employs phase-modulated microwaves and is provided for identifying the presence of a target in a specific distance range. Existing noise is eliminated from the measurement with a special digital code of the phase modulation.
DE 195 33 125 C1 discloses an apparatus for distance measurement wherein a transit time line is employed as delay line for improving the precision of the distance measurement in the near range. A frequency-modulated signal is converted with a further microwave signal onto a high carrier frequency of the transmission signal, and the reception signal is demodulated with this frequency. The delayed signal is mixed with the frequency-modulated microwave signal to form a measured signal.
International Reference WO 83/0283 discloses a continuous wave radar apparatus with intermediate frequency formation wherein a superimposition oscillator is provided for mixing the transmission signal and the reception signal onto an intermediate frequency before the demodulation. The sensitivity of the radar apparatus is intended to be enhanced therewith.
SUMMARY OF THE INVENTION
An object of the present invention is to specify a radar distance sensor that enables a reliable measurement in the near range as well, given low technical outlay.
In general terms the present invention is an apparatus for distance measurement. A signal source generates a frequency-modulated microwave signal. An antenna arrangement emits the microwave signal and receives a signal reflected at an object. A modulation unit additionally modulates the microwave signal provided for emission and/or the reflected signal with a modulation signal. A mixer generates a mixed product of the microwave signal generated by the signal source and the reflected signal modulated by the modulation unit. A demodulation and filter unit removes a portion of this mixed product that lies below the lowest frequency of the modulation signal with a filter and processes a remaining part by mixing with the modulation signal to form a measured signal. The antenna arrangement is composed of an antenna that is provided for transmission and reception. A transmission/reception diplexer conducts the microwave signal from the signal source to the antenna and conducts the reflected signal from the antenna to the demodulation and filter unit. The modulation unit has a bidirectional modulator that is arranged between this transmission/reception diplexer and the antenna.
Advantageous developments of the present invention are as follows.
The modulation signal effects a phase modulation with a phase boost of 180°.
The modulation and filter unit has a high-pass filter and a further mixer. The high-pass filter is arranged between the mixer and this further mixer. This further mixer is arranged such that it can mix the signal coming from the high-pass filter with the modulation signal.
The demodulation and filter unit has a low-pass filter and a further mixer. This further mixer is arranged such that it can mix a signal coming from the mixer with the modulation signal. The signal supplied by the further mixer is supplied to the low-pass filter.
Given the inventive arrangement, a microwave radar is employed that works according to the initially described principle. An additional modulation of the microwave signal provided for emission or of the reception signal makes it possible to separate the payload signal from noise signal parts in a demodulation and filter unit that follows the reception mixer MI. To this end, a modulation unit is provided preceding the antenna in the arrangement illustrated in
FIG. 2
in order to suitably modulate the signal to be emitted. The undesired noise signals produced by the components of the radar sensor itself are not modulated and can therefore be separated from the payload signal by filtering. This separation ensues before the demodulation by high-pass filtering and/or following the demodulation by low-pass filtering.
REFERENCES:
patent: 4744040 (1988-05-01), Kawata et al.
patent: 5337052 (1994-08-01), Lohrmann et al.
patent: 5598130 (1997-01-01), Mesuda et al.
patent: 5659321 (1997-08-01), Burger et al.
patent: 5920281 (1999-07-01), Grace
patent: 6087833 (2000-07-01), Jackson
patent: 195 33 125 C1 (1997-01-01), None
patent: 0 527 443 A2 (1993-02-01), None
patent: WO 83/0283 (1983-08-01), None
Saito, T. et al, “An FM-CW Radar Module With Front-end Switching Heterodyne Receiver”, International Microwave Symposium Digest, Albuquerque, Jun. (1992), vol. 2, No. 1, pp. 713-716.
Heide Patric
Nalezinski Martin
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
Sotomayor John B.
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