Multi-pixel high-resolution three-dimensional imaging radar
A three-dimensional imaging radar operating at high frequency e.g., 670 GHz radar using low phase-noise synthesizers and a fast chirper to generate a frequency-modulated continuous-wave (FMCW) waveform, is disclosed that operates with a multiplexed beam to obtain range information simultaneously on multiple pixels of a target. A source transmit beam may be divided by a hybrid coupler into multiple transmit beams multiplexed together and directed to be reflected off a target and return as a single receive beam which is demultiplexed and processed to reveal range information of separate pixels of the target associated with each transmit beam simultaneously. The multiple transmit beams may be developed with appropriate optics to be temporally and spatially differentiated before being directed to the target. Temporal differentiation corresponds to a different intermediate frequencies separating the range information of the multiple pixels. Collinear transmit beams having differentiated polarizations may also be implemented.
1. A radar imaging system, comprising:
a quasioptical device for dividing a source transmit beam into a first transmit beam and a second transmit beam and multiplexing them, where both the first transmit beam and the second transmit beam are directed to be reflected off a target such that the second transmit beam is time-delayed from the first transmit beam to correspond to a distinct IF frequency for demultiplexing and processing and received as a single multiplexed receive signal with the quasioptical device; and
a system for signal mixing and a digital signal processor for performing fast Fourier transform (FFT) processing for demultiplexing and processing the single multiplexed receive signal to determine range information of the target for both a first pixel from the first transmit beam and a second pixel from the second transmit beam.
2. The radar imaging system of claim 1 , wherein the system for mixing comprises a first wave synthesizer for generating the source transmit beam, the source transmit beam comprising a frequency modulated continuous wave (FMCW) chirp signal from a source signal;
a second wave synthesizer for generating a FMCW local oscillator chirp signal from a source local oscillator signal;
a first mixer for combining the reflected FMCW chirp signal and the FMCW local oscillator chirp signal to generate a first intermediate frequency (IF) signal for each of the first transmit beam and the second transmit beam;
a second mixer for combining the source signal and the source local oscillator signal to generate a second IF signal; and
a third mixer for combining the first IF signal and the second IF signal to generate a final IF signal for each of the first transmit beam and the second transmit beam;
wherein the digital signal processor performs fast Fourier transform (FFT) processing the final IF signal for each of the first transmit beam and the second transmit beam to determine range information for the target of both a first pixel from the first transmit beam and a second pixel from the second transmit beam.
3. The radar imaging system of claim 2 , further comprising a waveform generator generating a common chirp signal in 1 millisecond or less;
wherein the first wave synthesizer generates the frequency modulated continuous wave (FMCW) chirp signal from the source signal mixed with the common chirp signal and the second wave synthesizer generates the FMCW local oscillator chirp signal from the source local oscillator signal mixed with the common chirp signal.
4. The radar imaging system of claim 1 , wherein the quasioptical device spatially offsets the second transmit beam along a substantially parallel path from the first transmit beam to a distinct point on the target.
5. The radar imaging system of claim 1 , wherein the quasioptical device directs the first transmit beam and the second transmit beam along substantially collinear paths and polarizes the second transmit beam to that of the first transmit beam to correspond to a distinct polarization for demultiplexing and processing.
6. The radar imaging system of claim 1 , wherein the quasioptical device comprises a coupler for dividing the source transmit beam into the first transmit beam and the second transmit beam;
a polarization twist waveguide for rotating polarization of the second transmit beam relative to that of the first transmit beam; and
quasioptical components for imparting a path length differential to induce a time delay between the second transmit beam and the first transmit beam and for directing the first transmit beam and the second transmit beam to the target along a substantially parallel path with a spatial offset.
7. The radar imaging system of claim 1 , wherein a three dimensional map of the target is derived from the range information determined for each of multiple pixels scanned over the target, where the range information for the multiple pixels are determined in simultaneously processed pairs associated with the first transmit beam and the second transmit beam.
8. The radar imaging system of claim 7 , wherein a peak-finding algorithm is applied to the determined range information to differentiate material layers of the target.
9. The radar imaging system of claim 7 , wherein the quasioptical device comprises a reflector coupled to a two-axis rotation stage and the range information is determined by positioning the two-axis rotation stage for each of the pairs of the multiple pixels scanned over the target with the reflector directing the FMCW chirp signal from the reflector to be reflected off the target and received from the target.
10. A method of radar imaging, comprising:
dividing a source transmit beam into a first transmit beam and a second transmit beam and multiplexing them with a quasioptical device;
directing both the first transmit beam and the second transmit beam to be reflected off a target such that the second transmit beam is time-delayed from the first transmit beam to correspond to a distinct IF frequency for demultiplexing and processing and received as a single multiplexed receive signal with the quasioptical device; and
signal mixing and performing fast Fourier transform (FFT) processing for demultiplexing and processing the single multiplexed receive signal to determine range information of the target for both a first pixel from the first transmit beam and a second pixel from the second transmit beam with a signal system and a digital signal processor.
11. The method of claim 10 , wherein signal mixing and performing FFT processing comprises:
generating the source transmit beam with a first wave synthesizer, the source transmit beam comprising a frequency modulated continuous wave (FMCW) chirp signal from a source signal;
generating a FMCW local oscillator chirp signal from a source local oscillator signal using a second wave synthesizer;
combining the reflected FMCW chirp signal and the FMCW local oscillator chirp signal to generate a first intermediate frequency (IF) signal for each of the first transmit beam and the second transmit beam using a first mixer;
combining the source signal and the source local oscillator signal to generate a second IF signal using a second mixer; and
combining the first IF signal and the second IF signal to generate a final IF signal for each of the first transmit beam and the second transmit beam using a third mixer;
wherein the digital signal processor performs fast Fourier transform (FFT) processing the final IF signal for each of the first transmit beam and the second transmit beam to determine range information for the target of both a first pixel from the first transmit beam and a second pixel from the second transmit beam.
12. The method of claim 11 , further comprising generating a common chirp signal in 1 millisecond or less with a waveform generator;
wherein the first wave synthesizer generates the frequency modulated continuous wave (FMCW) chirp signal from the source signal mixed with the common chirp signal and the second wave synthesizer generates the FMCW local oscillator chirp signal from the source local oscillator signal mixed with the common chirp signal.
13. The method of claim 10 , wherein the quasioptical device spatially offsets the second transmit beam along a substantially parallel path from the first transmit beam to a distinct point on the target.
14. The method of claim 10 , wherein the quasioptical device directs the first transmit beam and the second transmit beam along substantially collinear paths and polarizes the second transmit beam to that of the first transmit beam to correspond to a distinct polarization for demultiplexing and processing.
15. The method of claim 10 , wherein the quasioptical device comprises a coupler for dividing the source transmit beam into the first transmit beam and the second transmit beam;
a polarization twist waveguide for rotating polarization of the second transmit beam relative to that of the first transmit beam; and
quasioptical components for imparting a path length differential to induce a time delay between the second transmit beam and the first transmit beam and for directing the first transmit beam and the second transmit beam to the target along a substantially parallel path with a spatial offset.
16. The method of claim 10 , wherein a three dimensional map of the target is derived from the range information determined for each of multiple pixels scanned over the target, where the range information for the multiple pixels are determined in simultaneously processed pairs associated with the first transmit beam and the second transmit beam.
17. The method of claim 16 , wherein a peak-finding algorithm is applied to the determined range information to differentiate material layers of the target.
18. The method of claim 16 , wherein the quasioptical device comprises a reflector coupled to a two-axis rotation stage and the range information is determined by positioning the two-axis rotation stage for each of the pairs of the multiple pixels scanned over the target with the reflector directing the FMCW chirp signal from the reflector to be reflected off the target and received from the target.
19. An apparatus for multiplexing in a radar imaging system, comprising:
a coupler for dividing the source transmit beam into a first transmit beam and a second transmit beam and multiplexing them;
a polarization twist waveguide for rotating polarization of the second transmit beam relative to that of the first transmit beam;
quasioptical components for imparting a path length differential to induce a time delay between the second transmit beam and the first transmit beam and for directing the first transmit beam and the second transmit beam to the target along a substantially parallel path with a spatial offset;
wherein both the first transmit beam and the second transmit beam are directed to be reflected off a target and received as a single multiplexed receive signal by the quasioptical device and the single multiplexed receive signal is demultiplexed and processed to determine range information of the target for both a first pixel from the first transmit beam and a second pixel from the second transmit beam.
20. The apparatus of claim 19 , wherein the source transmit beam comprises a frequency modulated continuous wave (FMCW) chirp signal.