Radar echo processing with partitioned de-ramp
View Patent ↗The spurious-free dynamic range of a wideband radar system is increased by apportioning de-ramp processing across analog and digital processing domains. A chirp rate offset is applied between the received waveform and the reference waveform that is used for downconversion to the intermediate frequency (IF) range. The chirp rate offset results in a residual chirp in the IF signal prior to digitization. After digitization, the residual IF chirp is removed with digital signal processing.
1. A method of processing a radar echo signal, comprising:
receiving a radar echo signal having a first predetermined rate of frequency variation over time;
mixing the radar echo signal with an analog reference signal to produce a frequency-downconverted signal, wherein the analog reference signal has a second predetermined rate of frequency variation over time, and wherein said second rate is selected to differ from said first rate by a predetermined amount;
processing the frequency-downconverted signal to produce a first digital signal; and
mixing said first digital signal with a digital reference signal to produce an output digital signal.
2. The method of claim 1 , wherein said digital reference signal is indicative of said difference between said second rate and said first rate.
3. The method of claim 2 , wherein said processing includes filtering the frequency-downconverted signal to produce a filtered signal, performing an analog-to-digital conversion operation on said filtered signal to produce a second digital signal, and performing a digital demodulation operation on said second digital signal to produce said first digital signal.
4. The method of claim 1 , wherein said processing includes filtering the frequency-downconverted signal to produce a filtered signal.
5. The method of claim 4 , wherein said processing includes performing an analog-to-digital conversion operation on said filtered signal to produce a second digital signal.
6. The method of claim 5 , wherein said processing includes performing a digital demodulation operation on said second digital signal to produce said first digital signal.
7. The method of claim 1 , wherein said radar echo signal is associated with one of a Synthetic Aperture Radar (SAR) mode of radar operation and a Moving Target Indication (MTI) mode of radar operation.
8. A method of processing a radar echo signal, comprising:
receiving a radar echo signal that includes a point target component produced by radar signal reflection from a point target; and
mixing the radar echo signal with an analog reference signal to produce a frequency-downconverted signal, wherein the analog reference signal is selected to ensure that said point target component is prevented from downconverting into a single frequency tone in said frequency-downconverted signal.
9. The method of claim 8 , including processing the frequency-downconverted signal to produce a first digital signal, and mixing said first digital signal with a digital reference signal to produce a second digital signal.
10. The method of claim 9 , wherein said processing includes filtering the frequency-downconverted signal to produce a filtered signal, performing an analog-to-digital conversion operation on said filtered signal to produce a third digital signal, and performing a digital demodulation operation on said third digital signal to produce said first digital signal.
11. The method of claim 8 , wherein said radar echo signal is associated with one of a SAR mode of radar operation and an MTI mode of radar operation.
12. A method of processing a radar echo signal, comprising:
receiving a radar echo signal having an associated chirp;
removing the chirp from the radar echo signal, including implementing a predetermined partitioning of chirp removal between analog signal processing and digital signal processing, wherein said predetermined partitioning allocates removal of a predetermined part of the chirp to analog signal processing and allocates removal of a remainder of said chirp to digital signal processing.
13. The method of claim 12 , wherein said radar echo signal includes a point target component produced by radar signal reflection from a point target, and wherein said analog signal processing includes mixing the radar echo signal with an analog reference signal to produce a frequency-downconverted signal such that said point target component is prevented from downconverting into a single frequency tone in said frequency-downconverted signal.
14. An apparatus for processing a radar echo signal, comprising:
an input for receiving a radar echo signal having a first predetermined rate of frequency variation over time;
an analog mixer coupled to said input for mixing the radar echo signal with an analog reference signal to produce a frequency-downconverted signal, wherein the analog reference signal has a second predetermined rate of frequency variation over time, and wherein said second rate is selected to differ from said first rate by a predetermined amount;
a signal processing path coupled to said analog mixer and configured to process the frequency-downconverted signal to produce a first digital signal; and
a digital processor coupled to said signal processing path for mixing said first digital signal with a digital reference signal to produce an output digital signal.
15. The apparatus of claim 14 , wherein said digital reference signal is indicative of said difference between said second rate and said first rate.
16. The apparatus of claim 15 , including a signal processing path coupled to said analog mixer and configured to process the frequency-downconverted signal to produce a first digital signal, and a digital processor coupled to said signal processing path for mixing said first digital signal with a digital reference signal to produce a second digital signal.
17. The apparatus of claim 16 , wherein said signal processing path includes a filter for filtering the frequency-downconverted signal to produce a filtered signal, an analog-to-digital converter coupled to said filter for converting said filtered signal into a third digital signal, and a digital demodulator coupled to said analog-to-digital converter for demodulating said third digital signal to produce said first digital signal.
18. An apparatus for processing a radar echo signal, comprising:
an in input for receiving a radar echo signal that includes a point target component produced by radar signal reflection from a point target; and
an analog mixer coupled to said input for mixing the radar echo signal with an analog reference signal to produce a frequency-downconverted signal, wherein the analog reference signal is selected to ensure that said point target component is prevented from downconverting into a single frequency tone in said frequency-downconverted signal.
19. An apparatus for processing a radar echo signal, comprising:
an input for receiving a radar echo signal having an associated chirp;
an analog signal processing portion coupled to said input; and
a digital signal processing portion coupled to said analog signal processing portion;
wherein said analog signal processing portion and said digital signal processing portion are cooperable to remove the chirp from the radar echo signal by implementing a predetermined partitioning of chirp removal between analog signal processing and digital signal processing, and wherein said predetermined partitioning allocates removal of a predetermined part of the chirp to analog signal processing and allocates removal of a remainder of the chirp to digital signal processing.
20. The apparatus of claim 19 , wherein said radar echo signal includes a point target component produced by radar signal reflection from a point target, and wherein said analog signal processing portion includes an analog mixer for mixing the radar echo signal with an analog reference signal to produce a frequency-downconverted signal such that said point target component is prevented from downconverting into a single frequency tone in said frequency-downconverted signal.