Abstract In a coherent pulsed laser radar system employing state-of-theart laser technology, optical technology and microwave radar video signal processing technology, the radar receiver is provided with a bandwidth which is commensurate with doppler frequencies in radar return signals resulting from unresolved target return signal doppler shifts. These unresolved doppler shifts are on the order of magnitude of those resulting from targets having ground speeds on the order of tens of miles per hour. The above said bandwidth being orders of magnitude larger than that required for the data rate of return signals. The pulsewidth of the transmitter is designed to be matched (substantially the reciprocal) to the aforementioned large bandwidth, whose function is determined by the shape of the transmitted pulse. The PRF is chosen to be the lowest possible commensurate with the data rate. In one embodiment, a 10.6 micron carbon dioxide laser transmitter is passively Q-switched by a low pressure gas saturable absorber, such as a sulfer hexafluoride cell, giving an output pulse having a pulsewidth on the order of roughly one tenth microsecond to one microsecond, and the receiver has bandwidth of approximately one half to three MHz, operating at a nominal IF center frequency of 30 MHz, with receiver information rates on the order of 20-50 KHz, the local oscillator being adjusted with respect to the ground velocity of the laser radar so as to provide radar video at substantially the IF frequency falling within the bandwidth, as described hereinbefore.
A laser radar system having a radar return signal data rate on the order of 20-50 KHz, and adapted to be disposed for use upon a moving vehicle, comprising: a pulsed CO2 laser transmitter passively Q-switched with a low pressure sulfer hexafluoride gas saturable absorber producing a Gaussian output pulse having a half power pulsewidth on the order of from 0.1 microsecond to 1.0 microsecond and transmitting at a PRF as low as will accomodate said data rate, on the order of 20-50 KHz; a cw laser local oscillator; a laser signal heterodyning means optically responsive to said local oscillator; laser antenna means includinG means optically connected with the laser transmitter and with said heterodyning means and including means for transmitting energy supplied thereto by said transmitter and for receiving laser energy incident thereupon from outside of said system and applying said received laser energy to said heterodyning means; said heterodyning means including a detector responsive to laser energy applied thereto for providing an electrical signal at a frequency equal to the difference between the frequencies of the received laser signal and the laser signal from said local oscillator; means providing a signal as a function of the velocity of said vehicle for adjusting the frequency of said local oscillator in a manner to provide an IF frequency which is substantially constant independently of doppler shifts which occur in return signals as a result of the relative velocity of the vehicle with respect to earth at the carrier frequency of said transmitter; and receiver amplifier means responsive to said detector means, said receiver amplifier means having a center frequency which is substantially equal to said substantially constant IF frequency, said receiver amplifier means having a bandwidth on the order of 1 MHz to 3 MHz which is substantially equal to the doppler shift in received laser signals resulting from targets having velocity components along the velocity vector of the vehicle on the order of tens of miles per hour at the carrier frequency of said transmitter.
Claim 2
Dependent Claim
336 words
A laser radar system having a radar return signal data rate on the order of 20-50 KHz, and adapted to be disposed for use upon a moving vehicle, comprising: a pulsed CO2 laser transmitter passively Q-switched with a low pressure sulfer hexafluoride gas saturable absorber producing a Gaussian output pulse having a half power pulsewidth on the order of from 0.1 microsecond to 1.0 microsecond and transmitting at a PRF as low as will accomodate said data rate, on the order of 20-50 KHz; a cw laser local oscillator; a laser signal heterodyning means optically responsive to said local oscillator; laser antenna means includinG means optically connected with the laser transmitter and with said heterodyning means and including means for transmitting energy supplied thereto by said transmitter and for receiving laser energy incident thereupon from outside of said system and applying said received laser energy to said heterodyning means; said heterodyning means including a detector responsive to laser energy applied thereto for providing an electrical signal at a frequency equal to the difference between the frequencies of the received laser signal and the laser signal from said local oscillator; means providing a signal as a function of the velocity of said vehicle for adjusting the frequency of said local oscillator in a manner to provide an IF frequency which is substantially constant independently of doppler shifts which occur in return signals as a result of the relative velocity of the vehicle with respect to earth at the carrier frequency of said transmitter; and receiver amplifier means responsive to said detector means, said receiver amplifier means having a center frequency which is substantially equal to said substantially constant IF frequency, said receiver amplifier means having a bandwidth on the order of 1 MHz to 3 MHz which is substantially equal to the doppler shift in received laser signals resulting from targets having velocity components along the velocity vector of the vehicle on the order of tens of miles per hour at the carrier frequency of said transmitter.