Communications: directive radio wave systems and devices (e.g. – Determining distance – With frequency modulation
Patent
1992-12-11
1995-02-07
Hellner, Mark
Communications: directive radio wave systems and devices (e.g.,
Determining distance
With frequency modulation
G01S 1332
Patent
active
053879180
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for measuring distances using the reflected beam principle, in which on the basis of a periodically frequency modulated electrical transmission signal a transmission wave is transmitted with the frequency (named the transmission frequency) of the transmission signal, the echo wave reflected at a target is converted into an electrical reception signal with the frequency (named the reception frequency) of the echo wave, the transmission and the reception frequencies are converted, using a constant reference frequency and in a common mixer, into a transmission/reception intermediate frequencies mixture which contains a transmission intermediate frequency, formed by conversion of the transmission frequency using the reference frequency, and a reception intermediate frequency formed by conversion of the reception frequency using the reference frequency, and the transit time dependent frequency difference (named the distance frequency) between the transmission and the reception frequencies is determined, as a measure of the distance between the target and the transmission/reception location, from the frequency difference between the transmission intermediate frequency and the reception intermediate frequency, and to an arrangement for implementing the method.
A method of this type has been disclosed, see the German patent publication 3,203,677A1, which has certain advantages over methods, in which the distance frequency is determined directly by forming the difference between the transmission frequency and the reception frequency; since the transmission frequency and the reception frequency are very high and are very close to each other, the difference frequency found by direct establishment of the difference between these two frequencies is very much subject to noise, and this is not conducive to exact measurement of the distance. On the other hand the transmission and reception intermediate frequencies obtained by conversion using the reference frequency are in a lower frequency range, which is an advantage for further processing. The frequency difference between these two intermediate frequencies is again the desired distance frequency; it can be determined with simpler means and with a better accuracy by formation of the difference between these two lower frequencies and is substantially free of noise.
A further substantial condition for the correct measurement of distance using the already mentioned method is the exact maintenance of the waveform of the frequency modulation of the transmission frequency. Every departure from the predetermined waveform leads to errors of measurement. Thus for instance in the case of linear frequency modulation, the most frequently employed method, any departure from linearity in the modulation curve must be avoided. The PCT application WO 90/13049 discloses, in connection with an arrangement for distance measurement using the reflected beam method, the control of the frequency modulator by the signal processing circuit which also functions to determine the distance from the distance frequency. A correction of the frequency modulation is however impossible with this arrangement, since the signal processing circuit is only supplied with the distance frequency, which is directly produced by difference formation between the transmission frequency and the reception frequency and in which the information on the departures of the frequency modulation from the prescribed waveform is not included.
One object of the invention is to provide a method of the type initially mentioned, in the case of which exact adherence to the waveform of the frequency modulation of the transmission frequency is ensured.
This object is attained by the invention in that the transmission intermediate frequency comprised in the transmission/reception intermediate frequencies mixture is utilized for correction of the frequency modulation of the transmission frequency.
In the case of the invention advantage is taken of the fact that the transmission intermediate frequency inc
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Frank J. Cerra, "Introduction to Radar Systems", McGraw-Hill, Inc., 1962, four pages.
Hermann Franks, "Lueger Lexikon der Technik", Deutsche Verlags-Anstalt GMBH, Stuttgart, 1969, p. 276.
Heidrich Eberhardt
Kehrbeck Jurgen
Wiesbeck Werner
Endress & Hauser GmbH & Co.
Hellner Mark
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