Pseudonoise radar system

Claim 2

A radar system comprising: first means for transmitting a carrier wave having a digital code modulation with all words in the code being identical, said words being generated at a rate, fw, larger than the maximum expected Doppler shift, fd, to be encountered in reflection of said wave from a target; second means for reducing a wave reflected from a target to its Doppler shift frequency; and a low-pass filter adapted to receive the output of said second means, said filter having a cutoff frequency less than fw.

Claim 3

The invention as defined in claim 1, wherein said code is a binary code, said first means including a carrier oscillator, a first modulator, a range tone oscillator, said first modulator modulating the output of said carrier oscillator in accordance with the output of said range tone oscillator, the wavelength of the output of said range tone oscillator being larger than 2Rm/C, where Rm is the maximum range desired and C is the velocity of light, a second modulator connected to receive the output of said first modulator, a code generator to operate said second modulator in a manner to maintain and to reverse the phase of said carrier in accordance with said binary code, said first means including a transmitting antenna, a receiving antenna located a predetermined distance, D, from said transmitting antenna, a first demodulator connected from said receiving antenna, a first delay device connected from said code generator to said first demodulator to decode spillover, said first delay device providing a delay approximately equal to D/C, a notch filter having a center frequency of about fo connected from said first demodulator, a second demodulator connected from said notch filter, third means to provide a delayed code input to said second demodulator to remove the coding of a reflected wave provided by said first demodulator, said third means providing a delay of about D/C+ d, where d is the delay of said notch filter, a variable delay device connected from said code generator, a low-pass filter, said second means including first and second mixers, said first mixer being connected from said second mixer and said second demodulator to said low-pass filter, said second mixer being connected from said carrier oscillator and said variable delay device, fourth means calibrated in range to provide an indication of the delay setting of said variable delay device, a voltmeter connected from said low-pass filter, an amplitude demodulator connected from said low-pass filter to derive said range tone from said Doppler shift, a band-pass filter connected from said amplitude demodulator to pass said range tone, a phase detector connected from said range tone oscillator and said band-pass filter, and a course range indicator for producing a range indication directly proportional to the output of said phase detector, said low-pass filter having a coupling capacitor connected therefrom to said voltmeter and to said amplitude demodulator.

Claim 4

The invention as defined in claim 1, wherein said code is a serial binary code, said code including a series of binary bits for each word, each word having the same number of bits, the coding of said series being identical for each word, said first means including a code generator and a modulator connected to modulate said carrier, said modulator maintaining and reversing the phase of said carrier according to said code.

Claim 5

The invention as defined in claim 1, including a transmitting antenna and a receiving antenna and a spillover rejector connected between said receiving antenna and said second means, said spillover rejector comprising a first demodulator connected from said antenna, a code generator to supply the code for said first means, a first delay device connected from said code generator to said first demodulator to decode the spillover, said first delay device providing a delay of said code of about D/C, where D is the distance between said antennas and C is the velocity of light, a second demodulator, a notch filter connected between said first and second demodulators, said notch filter having a center frequency of about fo, and means to introduce said code to said second demodulator with a delay from said code generator equal to the delay of said first delay device plus the delay of said notch filter.

Claim 6

The invention as defined in claim 1, including means to produce an output proportional to the misalignment of the codes of the transmitted and reflected waves, said misalignment being proportional to a portion of the range of a target, means to modulate said carrier with a range tone before broadcast, means to derive said range tone from the received signal, and means for producing an output signal proportional to the difference between the phases of the transmitted and received range tones, said range tone having a wavelength longer than twice the maximum range desired.

Claim 7

The invention as defined in claim 5, including means calibrated in range to indicate the said misalignment of said codes, and means calibrated in range to indicate said difference in phases.

Claim 8

The invention as defined in claim 1, wherein a DC blocking capacitor is connected at a position after said second means to block the DC output thereof.

Claim 9

The invention as defined in claim 1, wherein the passband of said filter minus fw is small in comparison to fw.