Step frequency high resolution radar
View Patent ↗The present invention is directed to an improved radar system that produces high range resolution while using existing narrow processing bandwidths and sampling rates to achieve a low cost radar product that is particularly useful for moving targets. The present invention uses a small number of closely spaced Linear Frequency Modulated Chirps. In one embodiment typically 2, 3, 4 chirps are used. Each frequency is sampled at a rate commensurate with the narrower bandwidth, corrected for motion, Time Aligned and combined to produce a single wide-band chirp but achieved using the lower sample rate commensurate with the narrower transmitted waveform.
1. A high resolution radar signal processing method using narrow processing bandwidths and sampling rates for use in detecting a location and determining a range of a moving target, said method comprising:
repeatedly broadcasting a series of frequency modulated probe signals using a step frequency radar, said step frequency radar comprising a transmitter and a receiver; each of said series of frequency modulated probe signals comprising three closely spaced linearly frequency modulated chirps, wherein said third chirp is broadcast prior to return of a first one of three corresponding target reflected echo pulses;
collecting said target reflected echo pulses resulting from said transmitted series of frequency modulated probe signals using said receiver;
measuring pulse magnitude and phase information using said receiver;
storing said measured data in a memory;
time aligning neighboring target reflected echo pulses of each series;
applying a phase ramp to said neighboring target reflected echo pulses of each series using a fast Fourier transform;
match filtering by applying individually, to each of said first, second, and third echo pulses, a conjugate of an idealized 205 MHz chirp;
blending said first, second, and third match filtered echo pulse of each series together with a 5 MHz overlap, and with concatenation of said overlap and linear weighting to produce a coherent sum;
applying an inverse fast Fourier transform for range compression; and
using a Hamming window for side lobe reduction, to produce an effective wide bandwidth return signal for improved resolution.
2. A high resolution radar signal processing method according to claim 1 wherein said closely spaced linear frequency modulated chirps have a spacing therebetween of approximately 75 microseconds or less.
3. A high resolution radar signal processing method according to claim 2 wherein said conjugate of an idealized 205 MHz chirp has a pulse bandwidth of 20 microseconds.
4. A high resolution radar signal processing method according to claim 3 wherein said hamming window is 31% wider than a cardinal sine.
5. A high resolution radar signal processing method according to claim 4 wherein said system is capable of providing 0.25 meter resolution of two targets at a distance of one thousand meters.
6. A method of detecting a moving target using a high resolution radar signal, said method comprising:
selectively broadcasting a series of frequency modulated probe signals using a transmitter; each of said series of frequency modulated probe signals comprising at least three linear frequency modulated chirps, wherein said third chirp in each series is broadcast prior to return of a first one of three target reflected echo pulses;
collecting said target reflected echo pulses resulting from said transmitted series of frequency modulated probe signals by using a receiver;
measuring pulse magnitude and phase information using said receiver;
storing said measured data in a memory;
time aligning neighboring target reflected echo pulses of each series, said time alignment comprising alignment based on linear interpolation;
applying a phase ramp to said neighboring target reflected echo pulses of each series using a fast Fourier transform;
match filtering by applying individually, to each of said first, second, and third echo pulses, a conjugate of an idealized 205 MHz chirp;
blending said first, second, and third match filtered echo pulses of each series together with a 5 MHz overlap, and with concatenation of said overlap and linear weighting to produce a coherent sum; and
applying an inverse fast Fourier transform for range compression, to produce an effective wide bandwidth return signal for improved target resolution.
7. A method of detecting a moving target according to claim 6 wherein said linear frequency modulated chirps are of short duration and close spacing.
8. A method of detecting a moving target according to claim 7 wherein said closely spaced linear frequency modulated chirps have a spacing therebetween of approximately 75 microseconds or less.
9. A method of detecting a moving target according to claim 8 wherein said conjugate of an idealized 205 MHz chirp has a pulse bandwidth of 20 microseconds.
10. A method of detecting a moving target according to claim 9 wherein a hamming window is used to reduce side lobes.
11. A method of detecting a moving target according to claim 10 wherein said hamming window is 31% wider than a cardinal sine.
12. A method of detecting a moving target according to claim 11 wherein said system is capable of providing 0.25 meter resolution of two targets at a distance of one thousand meters.
13. A method of detecting a moving target using a high resolution radar, said method comprising:
broadcasting a series of frequency modulated signals using a transmitter; each of said series of frequency modulated signals comprising at least three linear frequency modulated chirps, wherein said third chirp in each series is broadcast prior to return of a first one of at least three corresponding target reflected echo pulses;
collecting target reflected echo pulses resulting from said transmitted series of frequency modulated signals using a receiver;
measuring pulse magnitude and phase information using said receiver;
storing said measured data in a memory;
time aligning neighboring target reflected echo pulses of each series, said time alignment comprising alignment based on a pulse time center frequency determined by linear interpolation of said linear frequency modulated chirps;
applying a phase ramp to said neighboring target reflected echo pulses of each series using a fast Fourier transform;
match filtering by applying individually, to each of said first, second, and third echo pulses, a conjugate of an idealized 205 MHz chirp;
blending said first, second, and third match filtered echo pulses of each series together with a 5 MHz overlap, and with concatenation of said overlap and linear weighting to produce a coherent sum;
applying an inverse fast Fourier transform for range compression; and
using a Hamming window for side lobe reduction, to produce an effective wide bandwidth return signal for improved resolution.
14. A method of detecting a moving target according to claim 13 wherein said closely spaced linear frequency modulated chirps have a spacing therebetween of approximately 75 microseconds or less.
15. A method of detecting a moving target according to claim 14 wherein said conjugate of an idealized 205 MHz chirp has a pulse bandwidth of 20 microseconds.
16. A method of detecting a moving target according to claim 15 wherein said hamming window is 31% wider than a cardinal sine.
17. A method of detecting a moving target according to claim 16 wherein said system is capable of providing 0.25 meter resolution of two targets at a distance of one thousand meters.