Patent ID: 7154590

Claim:
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.