FMCW radar with refined measurement using fixed frequencies
First Claim
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1. A method for operating a radar altimeter, the method comprising:
- generating a linear frequency ramp of a radar signal from a first frequency to a second frequency for one modulation period;
receiving reflection of the frequency ramp of the radar signal;
processing the reflection by determining an approximate distance to a target from which the reflections are received based on an amount of time between transmission of the radar signal having the frequency ramp and reception of the reflection of the radar signal having the frequency ramp, wherein the approximate distance is proportional to frequency difference between received reflections of the frequency ramp and generated linear frequency ramp, and wherein the approximate distance to a target is determined with a resolution based on a distance separating center points of neighboring fast fourier transform (FFT) bins in the radar altimeter; and
when the approximate distance is less than or equal to a maximum unambiguous distance;
transmitting a first radar signal having a first frequency for a first length of time;
receiving a reflection of the first radar signal at the first frequency;
transmitting a second radar signal having a second frequency for a second length of time;
receiving a reflection of the second radar signal at the second frequency; and
processing the reflections of the first radar signal and the second radar signal at the first and second frequency by;
determining a first phase of a reflection of the first radar signal transmitted at the first frequency, wherein the first phase is the difference in phase between phase of a sample of transmitted first radar signal at the first frequency and phase of the reflection of the first radar signal as received at the first frequency;
determining a second phase of a reflection of the radar signal transmitted at the second frequency, wherein the second phase is the difference in phase between phase of a sample of transmitted second radar signal at the second frequency and phase of the reflection of the second radar signal as received at the second frequency;
calculating a phase difference between the first phase and the second phase; and
refining the approximate distance to the target based on the phase difference between the first phase and the second phase, wherein refining the approximate distance includes calculating a refined distance based on the phase difference divided by 360 degrees and multiplied by the maximum unambiguous distance, where the maximum unambiguous distance equals the speed of light divided by two times the frequency difference between the first frequency and the second frequency.
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Abstract
One embodiment is directed to a method for operating a radar altimeter. The method includes transmitting a radar signal at a first frequency, ramping the frequency of the radar signal from the first frequency to a second frequency, and transmitting the radar signal at the second frequency. The reflections can be processed by determining an approximate distance to a target based reflections of the frequency ramp and the approximate distance can be refined based on a phase difference between a reflection of the radar signal transmitted at the first frequency and a reflection of the radar signal transmitted at the second frequency.
13 Citations
17 Claims
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1. A method for operating a radar altimeter, the method comprising:
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generating a linear frequency ramp of a radar signal from a first frequency to a second frequency for one modulation period; receiving reflection of the frequency ramp of the radar signal; processing the reflection by determining an approximate distance to a target from which the reflections are received based on an amount of time between transmission of the radar signal having the frequency ramp and reception of the reflection of the radar signal having the frequency ramp, wherein the approximate distance is proportional to frequency difference between received reflections of the frequency ramp and generated linear frequency ramp, and wherein the approximate distance to a target is determined with a resolution based on a distance separating center points of neighboring fast fourier transform (FFT) bins in the radar altimeter; and when the approximate distance is less than or equal to a maximum unambiguous distance; transmitting a first radar signal having a first frequency for a first length of time; receiving a reflection of the first radar signal at the first frequency; transmitting a second radar signal having a second frequency for a second length of time; receiving a reflection of the second radar signal at the second frequency; and processing the reflections of the first radar signal and the second radar signal at the first and second frequency by; determining a first phase of a reflection of the first radar signal transmitted at the first frequency, wherein the first phase is the difference in phase between phase of a sample of transmitted first radar signal at the first frequency and phase of the reflection of the first radar signal as received at the first frequency; determining a second phase of a reflection of the radar signal transmitted at the second frequency, wherein the second phase is the difference in phase between phase of a sample of transmitted second radar signal at the second frequency and phase of the reflection of the second radar signal as received at the second frequency; calculating a phase difference between the first phase and the second phase; and refining the approximate distance to the target based on the phase difference between the first phase and the second phase, wherein refining the approximate distance includes calculating a refined distance based on the phase difference divided by 360 degrees and multiplied by the maximum unambiguous distance, where the maximum unambiguous distance equals the speed of light divided by two times the frequency difference between the first frequency and the second frequency. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A frequency modulated continuous wave (FMCW) radar comprising:
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a transmitter configured to; transmit a first radar signal at a first frequency for a first length of time; generate a frequency ramp to ramp the frequency of a radar signal from the first frequency to a second frequency; transmit a second radar signal at the second frequency for a second length of time; and a receiver configured to; receive reflections of the radar signals; and process the reflections by determining an approximate distance to a target from which the reflections are received based on an amount of time between transmission of the radar signal having the frequency ramp and reception of a reflection of the radar signal having the frequency ramp, wherein the approximate distance is proportional to frequency difference between received reflections of the frequency ramp and generated linear frequency ramp, and wherein the approximate distance to a target is determined with a resolution based on a distance separating center points of neighboring of fast fourier transform (FFT) bins in the radar altimeter; and when the approximate distance is less than or equal to a maximum unambiguous distance, processing the reflections further by; determine a first phase of a reflection of the first radar signal transmitted at the first frequency, wherein the first phase is the difference in phase between phase of a sample of transmitted first radar signal at the first frequency and phase of reflection of the first radar signal as received at the first frequency; determine a second phase of a reflection of the radar signal transmitted at the second frequency, wherein the second phase is the difference in phase between phase of a sample of transmitted radar signal at the second frequency and phase of the reflection of the second radar signal as received at the second frequency; calculate a phase difference between the first phase and the second phase; and refine the approximate distance to the target based on the phase difference between the first phase and the second phase, wherein refine the approximate distance includes calculate a refined distance based on the phase difference divided by 360 degrees and multiplied by the maximum unambiguous distance, where the maximum unambiguous distance equals the speed of light divided by two times the frequency difference between the first frequency and the second frequency. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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15. A method for operating a radar altimeter, the method comprising:
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transmitting a radar signal; generating a frequency ramp of a radar signal from a first frequency to a second frequency; receiving a reflection of the radar signal having the frequency ramp; determining an approximate distance to a target from which the reflections are received based on an amount of time between transmission of the radar signal having the frequency ramp and reception of a reflection of the radar signal having the frequency ramp, wherein the approximate distance is proportional to frequency difference between received reflection of the frequency ramp and generated linear frequency ramp; and
if the approximate distance is less than or equal to a distance corresponding to a center of a first FFT bin, then;transmitting a first radar signal at the first frequency for a first length of time; transmitting a second radar signal at the second frequency for a second length of time; receiving reflections of the first and the second radar signals transmitted at the first frequency and the second frequency; and processing the reflections by; determining a first phase of a reflection of the first radar signal transmitted at the first frequency, wherein the first phase is the difference in phase between phase of a sample of transmitted first radar signal at the first frequency and the phase of the reflection of the first radar signal as received at the first frequency; determining a second phase of a reflection of the second radar signal transmitted at the second frequency, wherein the second phase is the difference in phase between phase of a sample of transmitted radar signal at the second frequency and the phase of the reflection of the second radar signal as received at the second frequency; calculating a phase difference between the first phase and the second phase; and refining the approximate distance to the target based on the phase difference between the first phase and the second phase, wherein refining the approximate distance includes calculating a refined distance based on the phase difference divided by 360 degrees and multiplied by the maximum unambiguous distance, where the maximum unambiguous distance equals the speed of light divided by two times the frequency difference between the first frequency and the second frequency. - View Dependent Claims (16, 17)
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Specification