Frequency modulated doppler distance measuring system

A frequency modulated doppler distance measuring system comprising in combination:

• means for transmitting frequency modulated radiofrequency energy towards a target, said radiofrequency energy being frequency modulated at a modulation frequency which is considerably lower than the doppler frequency, means for receiving energy reflected from the target, means for mixing a portion of said transmitted energy with said received energy to produce a detected signal comprising a frequency modulated wave having a carrier frequency equal to the doppler frequency and sidebands equal, respectively, to the sums and differences of said carrier frequency and said modulation frequency and its harmonics, said frequency modulated wave having a frequency deviation which is dependent upon target distance, an amplifier to which said detected signal is fed, said amplifier being tuned to the doppler frequency and having a bandwidth which includes a significant portion of the frequency spectrum of said frequency modulated wave over the range of distances being measured, a limiter to which the output of said amplifier is fed for producing an essentially constant amplitude signal, a frequency discriminator to which the output of said limiter is fed, said discriminator producing an output voltage which is substantially proportional to target distance, and indication means to which the output of said discriminator is fed for providing an indication of target distance.

A frequency modulated doppler distance measuring system comprising in combination:

• means for transmitting frequency modulated radiofrequency energy towards a target, said radiofrequency energy being frequency modulated at a modulation frequency which is considerably lower than the doppler frequency, means for receiving energy reflected from the target, means for mixing a portion of said transmitted energy with said received energy to produce a detected signal comprising a frequency modulated wave having a carrier frequency equal to the doppler frequency and sidebands equal, respectively, to the sums and differences of said carrier frequency and said modulation frequency and its harmonics, said frequency modulated wave having a frequency deviation which is dependent upon target distance, a mixer having first and second inputs, said detected signal being fed to the first input of said mixer, a local oscillator having its output fed to the second input of said mixer, means to which said detected signal is also fed for changing the oscillation frequency of said local oscillator in response to changes in the doppler frequency so that the sum of the doppler frequency and said oscillation frequency remains substantially constant, an amplifier to which said detected signal is fed, said amplifier being tuned to a frequency equal to the sum of the doppler frequency and said oscillation frequency and having a bandwidth which includes a significant portion of the frequency spectrum of said frequency modulated wave over the range of distances being measured, a limiter to which the output of said amplifier is fed for producing an essentially constant amplitude signal, a frequency discriminator to which the output of said limiter is fed, said discriminator producing an output voltage which is substantially proportional to target distance, and indication means to which the output of said discriminator is fed for providing an indication of target distance.

A single antenna missile fuzing system adapted to function at a predetermined distance from a target, said system comprising in combination:

• a microwave oscillator, a frequency modulator for modulating said oscillator at a frequency which is considerably lower than the doppler frequency occurring when the missile is falling at terminal velocity, a magic tee having first and second side arms, an H-arm and an E-arm, the output of said microwave oscillator being fed to said H-arm, an antenna connected to said first side arm and adapted to radiate energy towards a target and receive energy reflected therefrom, a load connected to said second side arm, a crystal detector disposed in said E-arm, said load being chosen so that only a relatively small portion of the energy from said microwave oscillator passes to said crystal detector to mix with the received energy passing to said detector from said first side arm, the output of said detector comprising a frequency modulated wave having a carrier frequency equal to the doppler frequency and sidebands equal, respectively, to the sums and differences of said carrier frequency and said modulation frequency and its harmonics, said frequency modulated wave having a frequency deviation which is dependent upon target distance, an amplifier to which said detected signal is fed, said amplifier being tuned to the doppler frequency and having a bandwidth which is equal to at least twice said modulation frequency, a limiter to which the output of said amplifier is fed for producing an essentially constant amplitude signal, a frequency discriminator to which the output of said limiter is fed, said discriminator producing an output voltage which is substantially proportional to target distance, and means connected to the output of said discriminator for functioning said fuze when the output of said discriminator is a predetermined value corresponding to said predetermined distance.