Coherent-angle tracking system incorporating target-velocity tracking apparatus

Claim 2

In a moving target indicating system of the character described wherein a composite signal containing both target echo and clutter return signals is received in response to exploratory pulses radiated at a predetermined pulse-repetition frequency from an antenna tracking a target and mixed with local oscillations from a stable oscillator to provide a composite intermediate-frequency signal, said system also including means for producing a reference signal of a frequency substantially equal to that of said stable oscillations and that is capable of being shifted in frequency, means for vectorially adding said intermediate-frequency signal to said reference signal to produce a resultant signal, means for generating a video signal of an amplitude representative of the phase difference between said reference and resultant signals, means for taking a sequence of samples from said video signal which include intervals concurrent in time with corresponding range elements from each sweep of said intermediate-frequency signal that include the target echo component, a first filter responsive to said sequence of samples taken from said video signal having a pass band from n to (n + 1) times one-half the predetermined pulse-repetition frequency of said exploratory pulses wherein n 0, 1, 2, 3, 4 . . . , means coupled to the output of said first filter for shifting the frequency of said reference signal to maintain the spectral distribution of the frequency components of said clutter return signal disposed about the mid-frequencY of said pass band, and a target-velocity tracking unit, said tracking unit comprising: a second filter coupled to the output of said first filter for rejecting said spectral distribution of frequency components of said clutter return signal, means for producing oscillations which are frequency-modulated through a band of frequencies at least as wide as said pass band, a mixer coupled to the output of said second filter for mixing said frequency-modulated oscillations with the frequency components of said target echo signal remaining within said pass band thereby to periodically shift the frequency components of said target echo signal through a selected range of frequencies, a third filter coupled to the output of said mixer having a narrow pass band centered about a predetermined frequency within said selected range, a frequency discriminator coupled to the output of said third filter, said frequency discriminator being adapted to produce a direct-current null output at the center frequency of said narrow pass band, means for integrating the direct-current null-output signal from said frequency discriminator to produce a control signal, and means for replacing said frequency-modulated oscillations with oscillations of a frequency determined by said control signal upon the appearance of said target echo signal at the output of said third filter thereby to maintain the frequency components of said target echo signal centered within the narrow pass band of said third filter.

Claim 3

In a moving target indicating system of the character described wherein a composite signal containing both target echo and clutter return signals is received in response to exploratory pulses radiated at a predetermined pulse-repetition frequency from an antenna tracking a target and mixed with local oscillations from a stable oscillator to provide a composite intermediate-frequency signal, said system also including means for producing a reference signal of a frequency substantially equal to that of said stable oscillations and that is capable of being shifted in frequency, means for vectorially adding said intermediate-frequency signal to said reference signal to produce a resultant signal, means for generating a video signal of an amplitude representative of the phase difference between said reference and resultant signals, means for taking a sequence of samples from said video signal which include intervals concurrent in time with corresponding range elements from each sweep of said intermediate-frequency signal that include the target echo component, a first filter responsive to said sequence of samples taken from said video signal having a pass band from n to (n + 1) times one-half the predetermined pulse-repetition frequency of said exploratory pulses wherein n 0, 1, 2, 3, 4 . . . , means coupled to the output of said first filter for shifting the frequency of said reference signal to maintain the spectral distribution of the frequency components of said clutter return signal disposed about the mid-frequencY of said pass band, and a target-velocity tracking unit, said tracking unit comprising: a second filter coupled to the output of said first filter for rejecting said spectral distribution of frequency components of said clutter return signal, means for producing oscillations which are frequency-modulated through a band of frequencies at least as wide as said pass band, a mixer coupled to the output of said second filter for mixing said frequency-modulated oscillations with the frequency components of said target echo signal remaining within said pass band thereby to periodically shift the frequency components of said target echo signal through a selected range of frequencies, a third filter coupled to the output of said mixer having a narrow pass band centered about a predetermined frequency within said selected range, a frequency discriminator coupled to the output of said third filter, said frequency discriminator being adapted to produce a direct-current null output at the center frequency of said narrow pass band, means for integrating the direct-current null-output signal from said frequency discriminator to produce a control signal, and means for replacing said frequency-modulated oscillations with oscillations of a frequency determined by said control signal upon the appearance of said target echo signal at the output of said third filter thereby to maintain the frequency components of said target echo signal centered within the narrow pass band of said third filter.

Claim 4

In a moving target indicating system of the character described wherein a composite signal containing both target echo and clutter return signals is received in response to exploratory pulses radiated at a predetermined pulse-repetition frequency from an antenna tracking a target and mixed with local oscillations from a stable oscillator to provide a composite intermediate-frequency signal, said system also including means for producing a reference signal of a frequency substantially equal to that of said stable oscillations and that is capable of being shifted in frequency, means for vectorially adding said intermediate-frequency signal to said reference signal to produce a resultant signal, means for generating a video signal of an amplitude representative of the phase difference between said reference and resultant signals, means for taking a sequence of samples from said video signal which include intervals concurrent in time with corresponding range elements from each sweep of said intermediate-frequency signal that include the target echo component, a first filter responsive to said sequence of samples taken from said video signal having a pass band from n to (n + 1) times one-half the predetermined pulse-repetition frequency of said exploratory pulses wherein n 0, 1, 2, 3, 4 . . . , means coupled to the output of said first filter for shifting the frequency of said reference signal to maintain the spectral distribution of the frequency components of said clutter return signal disposed about the mid-frequencY of said pass band, and a target-velocity tracking unit, said tracking unit comprising: a second filter coupled to the output of said first filter for rejecting said spectral distribution of frequency components of said clutter return signal, means for producing oscillations which are frequency-modulated through a band of frequencies at least as wide as said pass band, a mixer coupled to the output of said second filter for mixing said frequency-modulated oscillations with the frequency components of said target echo signal remaining within said pass band thereby to periodically shift the frequency components of said target echo signal through a selected range of frequencies, a third filter coupled to the output of said mixer having a narrow pass band centered about a predetermined frequency within said selected range, a frequency discriminator coupled to the output of said third filter, said frequency discriminator being adapted to produce a direct-current null output at the center frequency of said narrow pass band, means for integrating the direct-current null-output signal from said frequency discriminator to produce a control signal, and means for replacing said frequency-modulated oscillations with oscillations of a frequency determined by said control signal upon the appearance of said target echo signal at the output of said third filter thereby to maintain the frequency components of said target echo signal centered within the narrow pass band of said third filter.

Claim 5

In a moving target indicating system as defined in claim 1 wherein said third filter is of the envelope-type adapted to pass a carrier signal and two sideband components corresponding to a frequency equal to the effective spinfrequency of the antenna.

Claim 6

In a moving target indicating system of the character described wherein a composite signal containing both target echo and clutter return signals is received in response to exploratory pulses radiated at a predetermined pulse-repetition frequency from an antenna tracking a target and mixed with local oscillations from a stable oscillator to provide a composite intermediate-frequency signal, said system also including means for producing a reference signal of a frequency substantially equal to that of said stable oscillations and that is capable of being shifted in frequency, means for vectorially adding said intermediate-frequency signal to said reference signal to produce a resultant signal, means for generating a video signal of an amplitude representative of the phase difference between said reference and resultant signals, means for taking a sequence of samples from said video signal which include intervals concurrent in time with corresponding range elements from each sweep of said intermediate-frequency signal that include the target echo component, a first filter responsive to said sequence of samples taken from said video signal having a pass band from n to (n + 1) times one-half the predetermined pulse-repetition frequency of said exploratory pulses wherein n 0, 1, 2, 3, 4 . . . , means coupled to the output of said first filter for shifting the frequency of said reference signal to maintain the spectral distribution of the frequency components of said clutter return signal disposed about the mid-frequency of said pass band, and a target-velocity tracking unit, said tracking unit comprising: a second filter coupled to the output of said first filter for rejecting said spectral distribution of frequency components of said clutter return signal, means for producing oscillations which are frequency-modulated through a band of frequencies at least as wide as said pass band, a mixer coupled to the output of said second filter for mixing said frequency-modulated oscillations with the frequency components of said target echo signal remaining within said pass band thereby to periodically shift the frequency components of said target echo signal through a selected range of frequencies, a third filter coUpled to the output of said mixer having a narrow pass band centered about a predetermined frequency within said selected range, a frequency discriminator coupled to the output of said third filter, said frequency discriminator being adapted to produce a direct-current null output at the center frequency of said narrow pass band, means for integrating the direct-current null-output signal from said frequency discriminator to produce a control signal, and means for replacing said frequency-modulated oscillations with oscillations of a frequency determined by said control signal upon the appearance of said target echo signal at the output of said third filter thereby to maintain the frequency components of said target echo signal centered within the narrow pass band of said third filter; and additional means responsive to a signal appearing at the output of said third filter, for by-passing said second filter after said frequency-modulated oscillations have been replaced with said oscillations of a frequency determined by said control signal.

Claim 7

In a moving target indicating system of the character described wherein a composite signal containing both target echo and clutter return signals is received in response to exploratory pulses radiated at a predetermined pulse-repetition frequency from an antenna tracking a target and mixed with local oscillations from a stable oscillator to provide a composite intermediate-frequency signal, said system also including means for producing a reference signal of a frequency substantially equal to that of said stable oscillations and that is capable of being shifted in frequency, means for vectorially adding said intermediate-frequency signal to said reference signal to produce a resultant signal, means for generating a video signal of an amplitude representative of the phase difference between said reference and resultant signals, means for taking a sequence of samples from said video signal which include intervals concurrent in time with corresponding range elements from each sweep of said intermediate-frequency signal that include the target echo component, a first filter responsive to said sequence of samples taken from said video signal having a pass band from n to (n + 1) times one-half the predetermined pulse-repetition frequency of said exploratory pulses wherein n 0, 1, 2, 3, 4 . . . , means coupled to the output of said first filter for shifting the frequency of said reference signal to maintain the spectral distribution of the frequency components of said clutter return signal disposed about the mid-frequency of said pass band, and a target-velocity tracking unit, said tracking unit comprising: a second filter coupled to the output of said first filter for rejecting said spectral distribution of frequency components of said clutter return signal, means for producing oscillations which are frequency-modulated through a band of frequencies at least as wide as said pass band, a mixer coupled to the output of said second filter for mixing said frequency-modulated oscillations with the frequency components of said target echo signal remaining within said pass band thereby to periodically shift the frequency components of said target echo signal through a selected range of frequencies, a third filter coUpled to the output of said mixer having a narrow pass band centered about a predetermined frequency within said selected range, a frequency discriminator coupled to the output of said third filter, said frequency discriminator being adapted to produce a direct-current null output at the center frequency of said narrow pass band, means for integrating the direct-current null-output signal from said frequency discriminator to produce a control signal, and means for replacing said frequency-modulated oscillations with oscillations of a frequency determined by said control signal upon the appearance of said target echo signal at the output of said third filter thereby to maintain the frequency components of said target echo signal centered within the narrow pass band of said third filter; and additional means responsive to a signal appearing at the output of said third filter, for by-passing said second filter after said frequency-modulated oscillations have been replaced with said oscillations of a frequency determined by said control signal.

Claim 8

In a moving target indicating system wherein an antenna follows a moving target in response to an antenna positioning and scanning apparatus comprising: search radar means to receive clutter and target echo signals from said moving target; coherent Doppler angle tracking means connected to said search radar means to produce signal components of a target echo signal, and of the clutter return signal located at the center of a fixed frequency band width; a first filter means to eject said clutter signals at the center frequency of the fixed band width; a second filter means with a desired pass band in said fixed frequency band width to pass the target echo signal from said first filter; a mixer connected between said first and said second filter; an oscillator connected to said mixer to shift the frequencies of said signal components when passing from said first filter to said second filter; a switch with a first, second and Third input and with its output connected to control the frequency of said oscillator; a sweep generator connected to said first input of said switch to provide frequency modulation of said oscillator; discriminator and signal forming means connected to said second input of said switch to form a control signal upon the appearance of said target echo signals at the output of said second filter; said third input of said switch connected to the output of said second filter to pass said control signal through said switch to said oscillator to disconnect said sweep generator to maintain the frequency of said oscillator upon the appearance of said target echo signals at the output of said second filter; by-pass means connected between said coherent Doppler angle tracking means and said mixer to by-pass said first filter in response to target echo signals at the output of said second filter; and detector means connected between the output of said second filter and said antenna positioning and scanning apparatus to control said antenna in response to said target echo signal.

Claim 9

In a moving target indicating system wherein an antenna follows a moving target in response to an antenna positioning and scanning apparatus comprising: search radar means to receive clutter and target echo signals from said moving target; coherent Doppler angle tracking means connected to said search radar means to produce signal components of a target echo signal, and of the clutter return signal located at the center of a fixed frequency band width; a first filter means to eject said clutter signals at the center frequency of the fixed band width; a second filter means with a desired pass band in said fixed frequency band width to pass the target echo signal from said first filter; a mixer connected between said first and said second filter; an oscillator connected to said mixer to shift the frequencies of said signal components when passing from said first filter to said second filter; a switch with a first, second and Third input and with its output connected to control the frequency of said oscillator; a sweep generator connected to said first input of said switch to provide frequency modulation of said oscillator; discriminator and signal forming means connected to said second input of said switch to form a control signal upon the appearance of said target echo signals at the output of said second filter; said third input of said switch connected to the output of said second filter to pass said control signal through said switch to said oscillator to disconnect said sweep generator to maintain the frequency of said oscillator upon the appearance of said target echo signals at the output of said second filter; by-pass means connected between said coherent Doppler angle tracking means and said mixer to by-pass said first filter in response to target echo signals at the output of said second filter; and detector means connected between the output of said second filter and said antenna positioning and scanning apparatus to control said antenna in response to said target echo signal.