Method and modulation system for ambiguity reduction in pulsed radar

Claim 2

A modulation code generator for use in a pulsed radar system to shift some of the unwanted ambiguity peaks off of the time axis, including in combination: first oscillator means providing a pulse modulated signal at an output terminal thereof, said pulse modulated signal having a pulse repetition rate; second oscillator means providing a frequency modulated signal at an output terminal thereof, said frequency modulated signal having a frequency deviation which is a multiple of said pulse repetition rate of said pulse modulated signal; and signal combining means having an output terminal, a first input terminal connected to said output terminal of said first oscillator means and a second input terminal connected to said output terminal of said second oscillator means, said signal combining means combining said pulse modulated and said frequency modulated signals to provide an output signal at said output terminal thereof during the times that said pulse modulated and said frequency modulated signals simultaneously exist, said output signal being suitable for transmission by a radar system and for shifting some of the unwanted ambiguity peaks off of the time axis.

Claim 3

The modulation code generator of claim 1 wherein said frequency modulated signal changes in a substantially linear fashion between predetermined minimum and maximum frequencies at a modulation rate which is a submultiple of said pulse repetition rate.

Claim 4

The modulation code generator of claim 1 wherein: said first oscillator includes a control terminal and said second oscillator means includes a control terminal; and further including timing means having output terminals connected to said control terminal of said first oscillator means and to said control terminal of said second oscillator means, said timing means providing first control signals to said first oscillator means and second control signals to said second oscillator means to effect phase coherence between said pulse modulated signal and said frequency modulated signal.

Claim 5

The modulation code generator of claim 3 wherein said timing means includes: thIrd oscillator means providing a frequency stable oscillating signal at an output terminal thereof; divider means having an input terminal connected to said output terminal of said third oscillator means and an output terminal, said divider means providing a divided output signal in response to said frequency stable oscillating signal at said output terminal thereof; and multivibrator means having a first input terminal connected to said output terminal of said third oscillator means and a second input terminal connected to said output terminal of said divider means, said multivibrator means being responsive to said frequency stable oscillating signal and said divided output signal to remove leading edge jitter from said divided output signal.

Claim 6

The modulation code generator of claim 3 wherein said timing means includes: third oscillator means providing a frequency stable oscillating signal at its output terminal; first divider means having an input terminal connected to said output terminal of said third oscillator means and an output terminal, said first divider means providing a divided signal at said output terminal thereof which is frequency stable but has leading edge jitter; and first multivibrator means having a first input terminal connected to said output terminal of said third oscillator means and a second input terminal connected to said output terminal of said first divider means and an output terminal, said first multivibrator means providing said first control signals at said output terminal thereof for controlling said first oscillator means.

Claim 7

The modulation code generator of claim 5 further including: second divider means having an input terminal connected to said output terminal of said first divider means and an output terminal, said second divider means dividing said divided signal to provide a further divided signal at said output terminal thereof; and second multivibrator means having a first input terminal connected to said output terminal of said third oscillator means and a second input terminal connected to said output terminal of said second divider means and an output terminal, said second multivibrator means being responsive to said further divided output signal and said frequency stable oscillating signal to provide said second control signals at said output terminal thereof for controlling said second oscillator means.

Claim 8

The modulation code generator of claim 3 further including in combination: constant current source means having control and output terminals, said control terminal being connected to an output terminal of said timing means; integrating capacitor means having a terminal connected to said output terminal of said constant current source means; charging circuit means having a control terminal connected to an output terminal of said timing means and an output terminal connected to said terminal of said integrating capacitor means; and said charging circuit means being responsive to the existence of each of said second control signals to charge said integrating capacitor means to a predetermined voltage level, and said constant current source being responsive to the nonexistence of each of said second control signals to linearly discharge said integrating capacitor means so that a linear sawtooth waveform is thereby created at said terminal of said integrating capacitor means.

Claim 9

The modulation code generator of claim 7 wherein: said frequency of oscillation of said second oscillator means varies with variations in the magnitude of a voltage applied to a frequency control terminal of said second oscillator means; first circuit means connecting said frequency control terminal of said second oscillator means to said terminal of said integrating capacitor means so that the modulation rate and frequency deviation of said second oscillator means varies respectively with the repetition rate and amplitude change of said linear sawtooth waveform, said freQuency deviation being equal to said pulse repetition rate; said second oscillator means further having a reset terminal, said second oscillator means being responsive to a voltage of a particular polarity applied to said reset terminal to terminate oscillation; and reset circuit means connecting said reset terminal to an output terminal of said timing means.

Claim 10

The modulation code generator of claim 5 wherein said first oscillator means is responsive to each of said first control signals to provide a burst of sinusoidal signal having a constant frequency.

Claim 11

The modulation code generator of claim 1 further including a bandpass filter connected to said output terminal of said signal combining means for selecting the frequency components of said output signal which are equal to one of the sum and difference of the frequency components of said frequency modulated signal and said pulse modulated signal.

Claim 12

The modulation code generator of claim 1 wherein said frequency modulated signal has a frequency deviation which is equal to said pulse repetition rate of said pulse modulated signal.

Claim 13

In a radar system having a transmitter with a gated pulse amplifier which is responsive to a pulse repetition frequency signal applied to its control terminal to amplify a modulation code signal applied to its input terminal, and a receiver having a mixer operated by a demodulating signal having a center frequency which is a predetermined amount apart from the center frequency of the modulation code signal, a modulation code generator for providing the modulation code signal, the demodulating signal, and the pulse repetition frequency signal including in combination: pulse repetition frequency generator means providing a frequency stable pulse repetition frequency signal at an output terminal thereof, said output terminal being connected to the control terminal of the gated pulse amplifier; first divider means having an input terminal connected to said output terminal of said pulse repetition frequency generator means and an output terminal, said first divider means providing a divided signal at said output terminal thereof in response to said pulse repetition frequency signal; first multivibrator means having an input terminal connected to said output terminal of said first divider means and an output terminal, said first multivibrator means being responsive to each of said divided signals to provide a reset pulse at said output terminal thereof; frequency modulated oscillator means having a control terminal coupled to said output terminal of said first multivibrator means and an output terminal, said frequency modulated oscillator means being responsive to each of said reset pulses to provide a frequency modulated signal having an initial frequency immediately after the termination of a reset pulse, said frequency of said frequency modulated signal continuously changing until a subsequent reset pulse is applied thereto, said frequency modulated signal having a total frequency deviation which is a multiple of said pulse repetition frequency and a center frequency which is spaced the predetermined amount from the center frequency of the modulation code signal; apart from first circuit means connecting said output terminal of said frequency modulated oscillator means to the mixer of the receiver so that said frequency modulated signal can operate as the demodulating signal; second multivibrator means having an input terminal connected to said output terminal of said pulse repetition frequency generator menas and an output terminal, said second multivibrator means being responsive to each of said pulse repetition frequency signals to provide a gating pulse at said output terminal thereof; gated single frequency oscillator means having a control terminal connected to said output terminal of said second multivibrator means and an output terminal, said gated single frequency oscillator means being responsive to each of said gating pulses To provide a burst of sinusoidal signal of a constant frequency during the duration of each of said gating pulses to create a pulse modulated signal at said output terminal thereof, said bursts each formed by a sinusoidal signal having a frequency which is greater than said pulse repetition frequency and the repetition rate of said bursts being equal to said pulse repetition frequency; first mixer means having a first input terminal connected to said output terminal of said gated single frequency oscillator and a second input terminal connected to said output terminal of said frequency modulated oscillator means and an output terminal, said first mixer means mixing said pulse modulated signal and said frequency modulated signal to provide the modulation code signal at said output terminal thereof; and second circuit means connecting said output terminal of said first mixer means to the input terminal of the gated pulse amplifier.

Claim 14

In a radar system having a transmitter with a gated pulse amplifier which is responsive to a pulse repetition frequency signal applied to its control terminal to amplify a modulation code signal applied to its input terminal, and a receiver having a mixer operated by a demodulating signal having a center frequency which is a predetermined amount apart from the center frequency of the modulation code signal, a modulation code generator for providing the modulation code signal, the demodulating signal, and the pulse repetition frequency signal including in combination: pulse repetition frequency generator means providing a frequency stable pulse repetition frequency signal at an output terminal thereof, said output terminal being connected to the control terminal of the gated pulse amplifier; first divider means having an input terminal connected to said output terminal of said pulse repetition frequency generator means and an output terminal, said first divider means providing a divided signal at said output terminal thereof in response to said pulse repetition frequency signal; first multivibrator means having an input terminal connected to said output terminal of said first divider means and an output terminal, said first multivibrator means being responsive to each of said divided signals to provide a reset pulse at said output terminal thereof; frequency modulated oscillator means having a control terminal coupled to said output terminal of said first multivibrator means and an output terminal, said frequency modulated oscillator means being responsive to each of said reset pulses to provide a frequency modulated signal having an initial frequency immediately after the termination of a reset pulse, said frequency of said frequency modulated signal continuously changing until a subsequent reset pulse is applied thereto, said frequency modulated signal having a total frequency deviation which is a multiple of said pulse repetition frequency and a center frequency which is spaced the predetermined amount from the center frequency of the modulation code signal; apart from first circuit means connecting said output terminal of said frequency modulated oscillator means to the mixer of the receiver so that said frequency modulated signal can operate as the demodulating signal; second multivibrator means having an input terminal connected to said output terminal of said pulse repetition frequency generator menas and an output terminal, said second multivibrator means being responsive to each of said pulse repetition frequency signals to provide a gating pulse at said output terminal thereof; gated single frequency oscillator means having a control terminal connected to said output terminal of said second multivibrator means and an output terminal, said gated single frequency oscillator means being responsive to each of said gating pulses To provide a burst of sinusoidal signal of a constant frequency during the duration of each of said gating pulses to create a pulse modulated signal at said output terminal thereof, said bursts each formed by a sinusoidal signal having a frequency which is greater than said pulse repetition frequency and the repetition rate of said bursts being equal to said pulse repetition frequency; first mixer means having a first input terminal connected to said output terminal of said gated single frequency oscillator and a second input terminal connected to said output terminal of said frequency modulated oscillator means and an output terminal, said first mixer means mixing said pulse modulated signal and said frequency modulated signal to provide the modulation code signal at said output terminal thereof; and second circuit means connecting said output terminal of said first mixer means to the input terminal of the gated pulse amplifier.

Claim 15

The combination of claim 12 wherein said first circuit means includes a power splitter circuit.

Claim 16

The combination of claim 12 wherein said second circuit means includes a bandpass filter for selecting the sums of the frequency components of said pulse modulated signal and said frequency modulated signal.

Claim 17

The combination of claim 12 wherein said pulse repetition frequency generator means includes: master oscillator means providing a frequency stable signal at an output terminal thereof; and second divider means having an input terminal connected to said output terminal of said master oscillator means and an output terminal, said second divider means providing said pulse repetition frequency signal at said output terminal thereof in response to said frequency stable signal.

Claim 18

The combination of claim 12 wherein said frequency modulated signal changes in a substantially linear fashion between predetermined minimum and maximum values at a modulation rate, said modulation rate being a submultiple of said pulse repetition frequency.

Claim 19

The combination of claim 12 wherein said frequency modulated oscillator means further includes: constant current source means having control and output terminals, said control terminal being connected to said output terminal of said first multivibrator means; integrating capacitor means having a terminal connected to said output terminal of said constant current source means; charging circuit means having a control terminal connected to said output terminal of said first multivibrator means and an output terminal connected to said terminal of said integrating capacitor means; and said charging circuit means being responsive to the existence of each of said reset pulses to charge said integrating capacitor means to a predetermined voltage level, said constant current source means being responsive to the non-existence of each of said reset pulses to linearly discharge said integrating capacitor means so that a linear sawtooth waveform is thereby created at said terminal of said integrating capacitor means, said linear sawtooth waveform being adapted to control said frequency deviation of said frequency modulated oscillator means.

Claim 22

The method of claim 18 further including the step of using said frequency modulated, linear sawtooth signal to demodulate a returning radar signal.

Claim 25

The method of claim 20 including the additional step of: providing said pulse repetition frequency associated with said pulse modulation correlation function with a magnitude which optimizes the removal of velocity ambiguities from within possible target velocity limits of interest.

Claim 26

The method of claim 20 including the additional steps of: providing said deviation associated with said frequency modulation correlation function from a signal having a linear sawtooth nature and having a range equal to said pulse repetition frequency.

Claim 27

The method of claim 22 including the additional steps of: providing said linear sawtooth, frequency modulation correlation function with a peak corresponding to said desired range information peak and therefore said step of combining said pulse modulation correlation function with said frequency modulation correlation function together does not decrease the magnitude of the resulting range information peak.

Claim 30

The method of claim 24 including the additional steps of: controlling said deviation associated with said linear sawtooth, frequency modulation correlation function equal to said pulse repetition frequency.