PRF frequency generator for a fill level measuring device

• US 10,295,391 B2
• Filed: 11/14/2014
• Issued: 05/21/2019
• Est. Priority Date: 12/20/2013
• Status: Active Grant

• Current Assignee: Endress+Hauser SE+Co. KG (Endress+Hauser AG)
• Original Assignee: Endress+Hauser SE+Co. KG (Endress+Hauser AG)
• Inventors: Gluth, Rolf, Mayer, Winfried
• Primary Examiner(s): Bythrow, Peter M
• Application Number:
  US15/104,015
• Publication Number:
  US 20160327422A1
• Time in Patent Office: 1,649 Days
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 13/103 particularities of the measurement of the distance G01S13/12, G01S13/14, G01S13/16, G01S13/18 and G01S13/20 take precedence
• CPC Class Codes: G01S 13/22 using irregular pulse repetition frequency G01S13/12 takes precedence
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 13/30 using more than one pulse per radar period
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 7/024 using polarisation effects in waveguides H01P1/165; for aerials H01Q, e.g. H01Q15/22, H01Q15/24, H01Q19/195
• CPC Class Codes: G01S 7/282 Transmitters
• CPC Class Codes: G01S 7/285 Receivers

Abstract

The invention relates to a frequency generator for generating two pulse repetition frequency signals with slightly different frequencies for a radar measuring device. The frequency generator comprises an oscillator, which generates an oscillator signal, a first signal path for generating a first pulse repetition frequency signal from the oscillator signal, and a second signal path for generating a second pulse repetition frequency signal from the oscillator signal. The first signal path comprises a frequency divider or a first DDS module which is designed to generate a first frequency signal on the basis of the oscillator signal, a first mixer which is designed to upmix the first frequency signal or a signal derived therefrom to an intermediate frequency band and to generate a first intermediate frequency signal, and a first ceramic bandpass filter which is designed to filter out a selected frequency component of the first intermediate frequency signal and to generate a bandpass-filtered first intermediate frequency signal. The second signal path comprises a second DDS component which is designed to generate a second frequency signal on the basis of the oscillator signal, said second frequency signal differing from the first frequency signal by a specified frequency offset, a second mixer which is designed to upmix the second frequency signal or a signal derived therefrom to an intermediate frequency band and to generate a second intermediate frequency signal, and a second ceramic bandpass filter which is designed to filter out a selected frequency component of the second intermediate frequency signal and to generate a bandpass-filtered second intermediate frequency signal.

Claims

1. Frequency generator for generating two pulse repetition frequency signals with slightly different frequencies for a radar measuring device that functions according to the pulse correlation principle, wherein the frequency generator has:

an oscillator (400) that generates an oscillator signal, a first signal path for generating a first pulse repetition frequency signal from the oscillator signal, wherein the first signal path comprises;

a frequency divider (401) or a first DDS module, which is designed to generate a first frequency signal based upon the oscillator signal,

a first mixer (403) that is designed to upmix the first frequency signal or a signal derived therefrom to an intermediate frequency band and to generate a first intermediate frequency signal,

a first ceramic bandpass filter (405) that is designed to filter out a selected frequency component of the first intermediate frequency signal and to generate a first bandpass-filtered intermediate frequency signal, a second signal path for generating a second pulse repetition frequency signal from the oscillator signal, wherein the second signal path comprises;

a second DDS module (408) that is designed to generate a second frequency signal based upon the oscillator signal, which second frequency signal differs from the first frequency signal by a specified frequency offset,

a second mixer (410) that is designed to upmix the second frequency signal or a signal derived therefrom to an intermediate frequency band and to generate a second intermediate frequency signal,

a second ceramic bandpass filter (411) that is designed to filter out a selected frequency component of the second intermediate frequency signal and to generate a second bandpass-filtered intermediate frequency signal;

wherein the second frequency divider is arranged in parallel to the first frequency divider or DDS respectively, and

wherein the second ceramic band pass filter is arranged in parallel to the first ceramic band pass filter.

2. Frequency generator according to claim 1, characterized by at least one of the following:

the bandpass-filtered first intermediate frequency signal or a signal derived therefrom is suitable for controlling the pulsed operation of a radar transmission oscillator of the radar measuring device as a first pulse repetition frequency signal;

the bandpass-filtered second intermediate frequency signal or a signal derived therefrom is suitable for controlling the pulsed operation of a local oscillator of the radar measuring device as a second pulse repetition frequency signal.

3. Frequency generator according to claim 1, characterized by at least one of the following:

the frequency of the oscillator signal is lower than 100 MHz;

the frequency of the oscillator signal is within the range of 1 MHz to 100 MHz;

the frequency ratio between the first frequency signal and the oscillator signal is smaller than 1.10;

the frequency ratio between the second frequency signal generated by the second DDS module and the oscillator signal is smaller than 1;

10;

the first frequency signal and the second frequency signal each have a frequency within the range of 100 kHz to 1 MHz;

the frequency offset between the first frequency signal and the second frequency signal can be variably adjusted by means of the second DDS module;

the frequency offset between the first frequency signal and the second frequency signal can be variably adjusted by means of the second DDS module, depending upon the reception conditions and radar targets;

the frequency offset between the first frequency signal and the second frequency signal lies within the range of between 5 Hz and several hundred Hz;

the first frequency signal has a frequency that is so low that the first frequency signal cannot be used directly as first pulse repetition frequency signal;

the second frequency signal has a frequency that is so low that the second frequency signal cannot be used directly as second pulse repetition frequency signal;

the first pulse repetition frequency signal has a frequency within the range of between 1 MHz and 5 MHz;

the second pulse repetition frequency signal has a frequency within the range of between 1 MHz and 5 MHz.

4. Frequency generator according to claim 1, characterized by at least one of the following:

the first signal path comprises a low-pass that is arranged between the frequency divider or the first DDS module and the first mixer and is designed to suppress high frequency interference components of the first frequency signal and to generate a first low-pass filtered frequency signal;

the second signal path comprises a low-pass that is arranged between the DDS module and the second mixer and is designed to suppress high frequency interference components of the second frequency signal and to generate a second low-pass filtered frequency signal.

5. Frequency generator according to claim 1, characterized by at least one of the following:

the first intermediate frequency signal and the second intermediate frequency signal lie in an intermediate frequency band for which ceramic bandpass filters of high quality are available;

the first intermediate frequency signal and the second intermediate frequency signal lie in an intermediate frequency band within the range of 10 MHz to 15 MHz;

the first intermediate frequency signal and the second intermediate frequency signal lie in an intermediate frequency band that lies at higher frequencies than the frequencies of the first pulse repetition frequency signal and the second pulse repetition frequency signal;

the frequency of the first intermediate frequency signal is so high that the first intermediate frequency signal cannot be used directly as first pulse repetition frequency signal;

the frequency of the second intermediate frequency signal is so high that the second intermediate frequency signal cannot be used directly as second pulse repetition frequency signal.

6. Frequency generator according to claim 1, characterized by at least one of the following:

the first ceramic bandpass filter is designed to allow a selected frequency component of the first intermediate frequency signal to pass through, to filter away all other frequency components of the first intermediate frequency signal, and to generate a bandpass-filtered first intermediate frequency signal;

the second ceramic bandpass filter is designed to allow a selected frequency component of the second intermediate frequency signal to pass through, to filter away all other frequency components of the second intermediate frequency signal, and to generate a bandpass-filtered second intermediate frequency signal;

the first ceramic bandpass filter has a quality that makes it possible to selectively filter out a selected frequency component of the first intermediate frequency signal;

the second ceramic bandpass filter has a quality that makes it possible to selectively filter out a selected frequency component of the second intermediate frequency signal.

7. Frequency generator according to claim 1, characterized by at least one of the following:

the first signal path comprises a first final frequency divider that is arranged downstream of the first ceramic bandpass filter and is designed to divide down the frequency of the bandpass-filtered first intermediate frequency signal or a signal derived therefrom and to generate the first pulse repetition frequency signal;

the second signal path comprises a second final frequency divider that is arranged downstream of the second ceramic bandpass filter and is designed to divide down the frequency of the bandpass-filtered second intermediate frequency signal or a signal derived therefrom and to generate the second pulse repetition frequency signal.

10. Radar measuring device for pulse correlation radar, which comprises:

a radar transmission path for transmitting a radar transmission signal, which is pulse-modulated in accordance with a first pulse repetition frequency signal,

a radar reception path for reception and analysis of a radar transmission signal that has been reflected by a target (104), wherein the radar reception path comprises a reception mixer (105), which mixes the radar reception signal with a local oscillator signal, which is pulse-modulated in accordance with a second pulse repetition frequency signal and that generates a reception mixer output signal,

a frequency generator according to claim 1, which is designed to generate the first pulse repetition frequency signal for a radar transmission oscillator (101) and the second pulse repetition frequency signal for a local oscillator (107), and

an analysis unit (108), which is designed, based upon the reception mixer output signal or a signal derived therefrom, to determine a target distance.

11. Radar measuring device according to claim 10, characterized by at least one of the following:

the analysis unit is designed to variably adjust the frequency difference between the first pulse repetition frequency signal and the second pulse repetition frequency signal, depending upon the ambient conditions and radar targets;

the frequency difference between the first pulse repetition frequency signal and the second pulse repetition frequency signal defines a correlation speed for the analysis of the radar reception signal, wherein a low frequency difference leads to a correspondingly slow correlation speed;

the analysis unit is designed to variably adjust the frequency difference between the first pulse repetition frequency signal and the second pulse repetition frequency signal, depending upon the distance of a radar target, wherein a smaller frequency difference is set for radar targets that are positioned at a farther distance than for radar targets that are less far away;

the analysis unit is designed to variably adjust the frequency difference between the first pulse repetition frequency signal and the second pulse repetition frequency signal, depending upon the reflectivity of a radar target;

the analysis unit is designed to periodically tune the frequency difference, depending upon the distance of the radar target, wherein a smaller frequency difference is set for radar targets that are positioned at a farther distance than for radar targets that are less far away.

12. Radar measuring device according to claim 10, characterized by at least one of the following:

the radar measuring device is a device for distance measurement;

the radar measuring device is a fill level measuring device, which is designed to determine the fill level in a container;

the radar measuring device is a field device for process automation technology.

8. Frequency generator for generating two pulse repetition frequency signals with slightly different frequencies for a radar measuring device that functions according to the pulse correlation principle, wherein the frequency generator has:

an oscillator (600) that generates an oscillator signal, a first signal path for generating a first pulse repetition frequency signal from the oscillator signal, wherein the first signal path comprises;

a frequency divider (601) or a first DDS module that is designed, based upon the oscillator signal, to generate a first frequency signal, which, in the case of the frequency divider (601), comprises a number of harmonics or, in the case of the first DDS module, a number of image frequency components,

a first ceramic bandpass filter (602) that is designed to filter out a specified harmonic or a specified image frequency component of the first frequency signal and to generate a bandpass-filtered first intermediate frequency signal, a second signal path for generating a second pulse repetition frequency signal from the oscillator signal, wherein the second signal path comprises;

a second DDS module (605) that is designed to generate a second frequency signal based upon the oscillator signal, which second frequency signal differs from the first frequency signal by a specified frequency offset, wherein the second frequency signal comprises a number of image frequency components,

a second ceramic bandpass filter (606) that is designed to filter out a specified image frequency component of the second frequency signal and to generate a bandpass-filtered second intermediate frequency signal;

wherein the second frequency divider is arranged in parallel to the first frequency divider or DDS respectively, and

wherein the second ceramic band pass filter is arranged in parallel to the first ceramic band pass filter.

9. Frequency generator according to claim 8, characterized by at least one of the following:

the bandpass-filtered first intermediate frequency signal or a signal derived therefrom is, as first pulse repetition frequency signal, usable for controlling a pulsed operation of a radar transmission oscillator of the radar measuring device,

the bandpass-filtered second intermediate frequency signal or a signal derived therefrom is, as second pulse repetition frequency signal, usable for controlling a pulsed operation of a local oscillator of the radar measuring device.

13. A method for generating two pulse repetition frequency signals with slightly different frequencies for a radar measuring device that functions according to the pulse correlation principle, wherein the method comprises the following steps:

generating an oscillator signal;

generating a first frequency signal based upon the oscillator signal by means of a frequency divider (401) or a first DDS module;

upmixing the first frequency signal or a signal derived therefrom to an intermediate frequency band and generating a first intermediate frequency signal;

filtering out a selected frequency component of the first intermediate frequency signal by means of a first ceramic bandpass filter (405) and generating a bandpass-filtered first intermediate frequency signal, wherein the bandpass-filtered first intermediate frequency signal or a signal derived therefrom is usable as a first pulse repetition frequency signal;

generating a second frequency signal based upon the oscillator signal by means of a second DDS module, wherein the second frequency signal differs from the first frequency signal by a specified frequency offset;

upmixing the second frequency signal or a signal derived therefrom to an intermediate frequency band and generating a second intermediate frequency signal;

filtering out a selected frequency component of the second intermediate frequency signal by means of a second ceramic bandpass filter (411) and generating a bandpass-filtered second intermediate frequency signal, wherein the bandpass-filtered second intermediate frequency signal or a signal derived therefrom is usable as a second pulse repetition frequency signal.

14. A method for generating two pulse repetition frequency signals with slightly different frequencies for a radar measuring device that functions according to the pulse correlation principle, wherein the method comprises the following steps:

generating an oscillator signal;

generating a first frequency signal based upon the oscillator signal by means of a frequency divider (601) or a first DDS module, wherein the first frequency signal, in the case of the frequency divider (601), comprises a number of harmonics or, in the case of the first DDS module, a number of image frequency components;

filtering out a specified harmonic or a specified image frequency component of the first intermediate frequency signal by means of a first ceramic bandpass filter (602) and generating a bandpass-filtered first intermediate frequency signal, wherein the bandpass-filtered first intermediate frequency signal or a signal derived therefrom is usable as a first pulse repetition frequency signal;

generating a second frequency signal based upon the oscillator signal by means of a second DDS module (605), wherein the second frequency signal differs from the first frequency signal by a specified frequency offset, wherein the second frequency signal comprises a number of image frequency components;

filtering out a specified image frequency component of the second intermediate frequency signal by means of a second ceramic bandpass filter (606) and generating a bandpass-filtered second intermediate frequency signal, wherein the bandpass-filtered second intermediate frequency signal or a signal derived therefrom is usable as a second pulse repetition frequency signal.