초록 ▼

A method and apparatus for finding a relative direction to, a radial speed of, and a distance to a target is described. A laser source illuminates the target and the Doppler shifted return beam is incident upon a window system at an angle and is transmitted therethrough. The magnitude of the transm

A method and apparatus for finding a relative direction to, a radial speed of, and a distance to a target is described. A laser source illuminates the target and the Doppler shifted return beam is incident upon a window system at an angle and is transmitted therethrough. The magnitude of the transmitted Doppler shifted beam decreases due to Fresnel transmittance. Opposing photomixers then detect this transmitted Doppler shifted beam, thereby creating a pair of detection signals that are mixed with a local oscillator signal. The mixing process creates Doppler frequency signals that are subsequently processed to determine the radial speed of the target. Due to the Doppler frequency component of the signals, objects in the same direction, but moving at different radial speeds, can be discriminated, as the relative direction processing occurs after the Doppler processing.

대표청구항 ▼

What is claimed is: 1. An apparatus for determining a direction to a target, the apparatus comprising: a laser source for emitting a laser beam; a beamsplitter for splitting the laser beam into first and second portions, the first portion being a transmit beam, the second portion being a local osci

What is claimed is: 1. An apparatus for determining a direction to a target, the apparatus comprising: a laser source for emitting a laser beam; a beamsplitter for splitting the laser beam into first and second portions, the first portion being a transmit beam, the second portion being a local oscillator beam; a transmitting window system for transmitting the transmit beam toward the target; a receiving window system for receiving a Doppler shifted beam, the Doppler shifted beam being a portion of the transmit beam reflected by the target, a wavelength of the Doppler shifted beam being Doppler shifted due to a radial speed of the target, the receiving window system having an optical axis, the receiving window system having Fresnel transmittance properties, the receiving window system being configured such that if the Doppler shifted beam is parallel to the optical axis, the Doppler shifted beam is incident upon a surface of the receiving window system at a boresight incidence angle such that an instantaneous rate of change of the Fresnel transmittance as a function of angle of incidence at the boresight incidence angle is significantly different from zero; at least four beam combiners for combining the Doppler shifted and local oscillator beams; at least four photomixers, each photomixer being adapted to receive a portion of the thus combined Doppler shifted and local oscillator beams, each photomixer for photomixing the combined Doppler shifted and local oscillator beams, each photomixer for generating a respective photomixed signal; at least four phase shifting elements, each phase shifting element for phase shifting a corresponding one of the photomixed signals, the at least four phase shifting elements for outputting corresponding shifted photomixed signals; at least eight A/D converters, each A/D converter for converting a corresponding one of the photomixed or shifted photomixed signals, the at least eight A/D converters for outputting digital data; a Doppler bin array for receiving the digital data, the Doppler bin array for storing the digital data by Doppler frequency; and an angle processor for processing the digital data from the Doppler bin array to determine azimuth, elevation, and summation signals for the target at each Doppler frequency, the angle processor thereby discriminating the target from a background at a corresponding azimuth and elevation based upon Doppler frequency. 2. An apparatus in accordance with claim 1, further comprising a radial speed processor for determining a radial speed of the target based upon a magnitude of the Doppler frequency. 3. An apparatus in accordance with claim 2, wherein the radial speed processor determines if the radial speed is positive, a distance between the apparatus and the target is increasing, or if the radial speed is negative, the distance between the apparatus and the target is decreasing. 4. An apparatus in accordance with claim 1, further comprising a range processor for determining a distance from the apparatus to the target. 5. An apparatus in accordance with claim 1, further comprising a field of view limiter for limiting a field of view of the at least four photomixers. 6. An apparatus in accordance with claim 1, further comprising at least four bandpass filters, each bandpass filter for filtering a corresponding one of the combined Doppler shifted and local oscillator beams. 7. An apparatus in accordance with claim 1, further comprising at least four lowpass filters, each lowpass filter for filtering a corresponding one of the photomixed signals. 8. An apparatus in accordance with claim 1, further comprising at least four amplifiers, each amplifier for amplifying a corresponding one of the photomixed signals. 9. An apparatus in accordance with claim 1, wherein a spectral width of the laser source is not greater than 10 kHz. 10. An apparatus in accordance with claim 1, wherein the laser source includes an external cavity diode laser. 11. An apparatus in accordance with claim 1, wherein the laser source further includes a doped fiber amplifier. 12. An apparatus in accordance with claim 1, wherein the laser source is a pulsed laser source. 13. An apparatus in accordance with claim 1, further comprising an acousto-optic modulator, the acousto-optic modulator for modulating a frequency of the laser beam. 14. An apparatus in accordance with claim 1, further comprising an acousto-optic modulator, the acousto-optic modulator for modulating a frequency of the local oscillator beam. 15. An apparatus in accordance with claim 1, wherein the Fresnel transmittance at the boresight incidence angle is 90 percent or less. 16. An apparatus in accordance with claim 1, wherein the Fresnel transmittance at the boresight incidence angle is 80 percent or less. 17. An apparatus in accordance with claim 1, wherein the Fresnel transmittance at the boresight incidence angle is 70 percent or less. 18. An apparatus in accordance with claim 1, wherein the boresight incidence angle is at least 60 degrees. 19. An apparatus in accordance with claim 1, wherein the boresight incidence angle is at least 70 degrees. 20. An apparatus in accordance with claim 1, wherein each of the at least four beam combiners includes a beamsplitter. 21. An apparatus in accordance with claim 1, wherein each of the at least four beam combiners includes a mirror with an aperture. 22. An apparatus in accordance with claim 1, wherein each of the at least four photomixers includes a photodetector. 23. An apparatus in accordance with claim 22, wherein each photodetector is a photodiode. 24. An apparatus in accordance with claim 1, wherein the angle processor integrates corresponding pluralities of azimuth, elevation, and summation signals, thereby increasing a tracking range. 25. An apparatus for determining a direction to a target, the apparatus comprising: a laser source for emitting a laser beam; a beamsplitter for splitting the laser beam into first and second portions, the first portion being a transmit beam, the second portion being a first local oscillator beam; a transmitting window system for transmitting the transmit beam toward the target; a receiving window system for receiving a Doppler shifted beam, the Doppler shifted beam being a portion of the transmit beam reflected by the target, a wavelength of the Doppler shifted beam being Doppler shifted due to a radial speed of the target, the receiving window system having an optical axis, the receiving window system having Fresnel transmittance properties, the receiving window system being configured such that if the Doppler shifted beam is parallel to the optical axis, the Doppler shifted beam is incident upon a surface of the receiving window system at a boresight incidence angle such that an instantaneous rate of change of the Fresnel transmittance as a function of angle of incidence at the boresight incidence angle is significantly different from zero; at least four beam combiners for combining the Doppler shifted and first local oscillator beams; at least four photomixers, each photomixer being adapted to receive a portion of the thus combined Doppler shifted and first local oscillator beams, each photomixer for photomixing the combined Doppler shifted and first local oscillator beams, each photomixer for generating a respective photomixed signal; an oscillator for generating a second local oscillator signal; a phase shifting element for phase shifting the second local oscillator signal, the phase shifting element for outputting a thus shifted second local oscillator signal; at least four first mixers, each of the at least four first mixers for mixing the second local oscillator signal with a corresponding one of the photomixed signals, the at least four first mixers for outputting corresponding mixed photomixed signals; at least four second mixers, each of the at least four second mixers for mixing the shifted second local oscillator signal with a corresponding one of the photomixed signals, the at least four second mixers for outputting corresponding shifted mixed photomixed signals; at least eight A/D converters, each A/D converter for converting a corresponding one of the mixed photomixed or shifted mixed photomixed signals, the at least eight A/D converters for outputting digital data; a Doppler bin array for receiving the digital data, the Doppler bin array for storing the digital data by Doppler frequency; and an angle processor for processing the digital data from the Doppler bin array to determine azimuth, elevation, and summation signals for the target at each Doppler frequency, the angle processor thereby discriminating the target from a background at a corresponding azimuth and elevation based upon Doppler frequency. 26. An apparatus in accordance with claim 25, further comprising a radial speed processor for determining a radial speed of the target based upon a magnitude of the Doppler frequency. 27. An apparatus in accordance with claim 26, wherein the radial speed processor determines if the radial speed is positive, a distance between the apparatus and the target is increasing, or if the radial speed is negative, the distance between the apparatus and the target is decreasing. 28. An apparatus in accordance with claim 25, further comprising a range processor for determining a distance from the apparatus to the target. 29. An apparatus in accordance with claim 25, further comprising a field of view limiter for limiting a field of view of the at least four photomixers. 30. An apparatus in accordance with claim 25, further comprising at least four bandpass filters, each bandpass filter for filtering a corresponding one of the combined Doppler shifted and first local oscillator beams. 31. An apparatus in accordance with claim 25, further comprising at least four lowpass filters, each lowpass filter for filtering a corresponding one of the photomixed signals. 32. An apparatus in accordance with claim 25, further comprising at least four amplifiers, each amplifier for amplifying a corresponding one of the photomixed signals. 33. An apparatus in accordance with claim 25, further comprising at least eight lowpass filters, each lowpass filter for filtering a corresponding one of the mixed photomixed and shifted mixed photomixed signals. 34. An apparatus in accordance with claim 25, wherein a spectral width of the laser source is not greater than 10 kHz. 35. An apparatus in accordance with claim 25, wherein the laser source includes an external cavity diode laser. 36. An apparatus in accordance with claim 25, wherein the laser source further includes a doped fiber amplifier. 37. An apparatus in accordance with claim 25, wherein the laser source is a pulsed laser source. 38. An apparatus in accordance with claim 25, further comprising an acousto-optic modulator, the acousto-optic modulator for modulating a frequency of the laser beam. 39. An apparatus in accordance with claim 25, further comprising an acousto-optic modulator, the acousto-optic modulator for modulating a frequency of the first local oscillator beam. 40. An apparatus in accordance with claim 25, wherein the Fresnel transmittance at the boresight incidence angle is 90 percent or less. 41. An apparatus in accordance with claim 25, wherein the Fresnel transmittance at the boresight incidence angle is 80 percent or less. 42. An apparatus in accordance with claim 25, wherein the Fresnel transmittance at the boresight incidence angle is 70 percent or less. 43. An apparatus in accordance with claim 25, wherein the boresight incidence angle is at least 60 degrees. 44. An apparatus in accordance with claim 25, wherein the boresight incidence angle is at least 70 degrees. 45. An apparatus in accordance with claim 25, wherein each of the at least four beam combiners includes a beamsplitter. 46. An apparatus in accordance with claim 25, wherein each of the at least four beam combiners includes a mirror with an aperture. 47. An apparatus in accordance with claim 25, wherein each of the at least four photomixers includes a photodetector. 48. An apparatus in accordance with claim 47, wherein each photodetector is a photodiode. 49. An apparatus in accordance with claim 25, wherein the oscillator is a variable frequency oscillator. 50. An apparatus in accordance with claim 25, wherein the angle processor integrates corresponding pluralities of azimuth, elevation, and summation signals, thereby increasing a tracking range. 51. A guidable munition for striking a target, the guided munition comprising: a body; control means for controlling a direction of the guidable munition, the control means being responsive to guidance signals, the control means being attached to the body; a radome attached to a forward portion of the body; and a guidance apparatus, the guidance apparatus including: a laser source for emitting a laser beam; a beamsplitter for splitting the laser beam into first and second portions, the first portion being a transmit beam, the second portion being a local oscillator beam; a transmitting window system for transmitting the transmit beam toward the target; a receiving window system for receiving a Doppler shifted beam, the Doppler shifted beam being a portion of the transmit beam reflected by the target, a wavelength of the Doppler shifted beam being Doppler shifted due to a radial speed of the target, the receiving window system having an optical axis, the receiving window system having Fresnel transmittance properties, the receiving window system being configured such that if the Doppler shifted beam is parallel to the optical axis, the Doppler shifted beam is incident upon a surface of the receiving window system at a boresight incidence angle such that an instantaneous rate of change of the Fresnel transmittance as a function of angle of incidence at the boresight incidence angle is significantly different from zero; at least four beam combiners for combining the Doppler shifted and local oscillator beams; at least four photomixers, each photomixer being adapted to receive a portion of the thus combined Doppler shifted and local oscillator beams, each photomixer for photomixing the combined Doppler shifted and local oscillator beams, each photomixer for generating a respective photomixed signal; at least four phase shifting elements, each phase shifting element for phase shifting a corresponding one of the photomixed signals, the at least four phase shifting elements for outputting corresponding shifted photomixed signals; at least eight A/D converters, each A/D converter for converting a corresponding one of the photomixed or shifted photomixed signals, the at least eight A/D converters for outputting digital data; a Doppler bin array for receiving the digital data, the Doppler bin array for storing the digital data by Doppler frequency; an angle processor for processing the digital data from the Doppler bin array to determine azimuth, elevation, and summation signals for the target at each Doppler frequency, the angle processor thereby discriminating the target from a background at a corresponding azimuth and elevation based upon Doppler frequency, the angle processor being adapted to generate guidance signals based upon the azimuth and elevation signals. 52. A guidable munition in accordance with claim 51, further comprising a radial speed processor for determining a radial speed of the target based upon a magnitude of the Doppler frequency, the radial speed processor being adapted to generate guidance signals based upon the radial speed. 53. A guidable munition in accordance with claim 51, further comprising a range processor for determining a distance from the guidable munition to the target, the range processor being adapted to generate guidance signals based upon the distance. 54. A guidable munition in accordance with claim 51, further comprising an acousto-optic modulator, the acousto-optic modulator for modulating a frequency of the laser beam. 55. A guidable munition in accordance with claim 51, further comprising an acousto-optic modulator, the acousto-optic modulator for modulating a frequency of the local oscillator beam. 56. A guidable munition for striking a target, the guided munition comprising: a body; control means for controlling a direction of the guidable munition, the control means being responsive to guidance signals, the control means being attached to the body; a radome attached to a forward portion of the body; and a guidance apparatus, the guidance apparatus including: a laser source for emitting a laser beam; a beamsplitter for splitting the laser beam into first and second portions, the first portion being a transmit beam, the second portion being a first local oscillator beam; a transmitting window system for transmitting the transmit beam toward the target; a receiving window system for receiving a Doppler shifted beam, the Doppler shifted beam being a portion of the transmit beam reflected by the target, a wavelength of the Doppler shifted beam being Doppler shifted due to a radial speed of the target, the receiving window system having an optical axis, the receiving window system having Fresnel transmittance properties, the receiving window system being configured such that if the Doppler shifted beam is parallel to the optical axis, the Doppler shifted beam is incident upon a surface of the receiving window system at a boresight incidence angle such that an instantaneous rate of change of the Fresnel transmittance as a function of angle of incidence at the boresight incidence angle is significantly different from zero; at least four beam combiners for combining the Doppler shifted and first local oscillator beams; at least four photomixers, each photomixer being adapted to receive a portion of the thus combined Doppler shifted and first local oscillator beams, each photomixer for photomixing the combined Doppler shifted and first local oscillator beams, each photomixer for generating a respective photomixed signal; an oscillator for generating a second local oscillator signal; a phase shifting element for phase shifting the second local oscillator signal, the phase shifting element for outputting a thus shifted second local oscillator signal; at least four first mixers, each of the at least four first mixers for mixing the second local oscillator signal with a corresponding one of the photomixed signals, the at least four first mixers for outputting corresponding mixed photomixed signals; at least four second mixers, each of the at least four second mixers for mixing the shifted second local oscillator signal with a corresponding one of the photomixed signals, the at least four second mixers for outputting corresponding shifted mixed photomixed signals; at least eight A/D converters, each A/D converter for converting a corresponding one of the mixed photomixed or shifted mixed photomixed signals, the at least eight A/D converters for outputting digital data; a Doppler bin array for receiving the digital data, the Doppler bin array for storing the digital data by Doppler frequency; and an angle processor for processing the digital data from the Doppler bin array to determine azimuth, elevation, and summation signals for the target at each Doppler frequency, the angle processor thereby discriminating the target from a background at a corresponding azimuth and elevation based upon Doppler frequency, the angle processor being adapted to generate guidance signals based upon the azimuth and elevation signals. 57. A guidable munition in accordance with claim 56, further comprising a range processor for determining a distance from the guidable munition to the target, the range processor being adapted to generate guidance signals based upon the distance. 58. A guidable munition in accordance with claim 56, further comprising an acousto-optic modulator, the acousto-optic modulator for modulating a frequency of the laser beam. 59. A guidable munition in accordance with claim 56, further comprising an acousto-optic modulator, the acousto-optic modulator for modulating a frequency of the first local oscillator beam.