Cooperative radar system

Claim 1

A cooperative interrogator-transponder pulse radar system adapted to measure long ranges with a high degree of accuracy comprising in combination: an interrogator radar and a transponder radar, both operable in both a CW and a pulse mode of operation including transmitter means for first transmitting CW signals of a first carrier frequency for initial lock up to a transponder radar and then transmitting radar pulses of said first carrier frequency and variable pulse repetition frequency (PRF) which is varied as a function of range separation between the interrogator and transponder and receiver means including circuit means for producing a predetermined IF frequency when receiving radar signals of a second carrier frequency transmitted from said transponder also generating first a CW and then a pulse signal of said second carrier frequency and having substantially the same variable PRF, said first and second carrier frequencies being separated by a predetermined frequency which is substantially equal to said IF frequency; said transponder radar including receiver means responsive first to CW and then pulses of the said first carrier frequency transmitted from said interrogator radar, and transmitter means for first transmitting first CW signals of said second carrier frequency for initial lock up to said interrogator and then transmitting radar pulses of said second carrier frequency back to said interrogator, said first and second carrier frequency at the respective interrogator and transponder radars additionally acting as respective local oscillators for producing an IF signal of the same frequency in both radars; a respective phase track loop included in both said interrogator and said transponder radars being responsive to CW signals and each having a variable frequency oscillator and a phase comparator circuit coupled together for phase locking the respective variable frequency oscillator to its IF frequency signal whereby said first and second carrier frequencies are locked together through the respective IF signal and said variable frequency oscillator operates at a predetermined substantially fixed frequency for the provision of a reference frequency signal; and a range track loop included in both said interrogator and said transponder radars, being responsive to the received radar IF pulse signals for controlling the respective PRFs of said radars after lock up in the CW mode of operation, each comprising PRF generator means coupled from said receiver means back to said transmitter means and being responsive to the pulse width of received IF pulse signals from the other radar to vary the PRF of the respective radar transmitter pulses and additionally generating a pair of adjacent range gates of predetermined variable equal pulse widths as a function of the range separation between said interrogator and said transponder radar, phase keyer circuit means coupled to said PRF generator means and said variable frequency oscillator in the respective phase trAck loop, being responsive to said pair of range gates to alternately invert the phase of said reference frequency signal applied thereto from said variable frequency oscillator, a second phase comparator circuit coupled to respective receiver means and said phase keyer circuit, being responsive to the respective IF pulse signals and the output of said phase keyer circuit and providing an output signal of a first polarity when said IF pulse signals and said reference frequency signal are in phase with one another and of the opposite polarity when said inputs are 180* out of phase, and integrator means coupled between said second phase comparator circuit and said PRF generator means, said integrator means averaging said output signals of said first and second opposite polarity and producing a control voltage to vary the frequency of said PRF generator means in a predetermined direction to produce the same PRF frequency and match the RF pulse widths in both the interrogator and transponder radars.