Continuous wave correlation radar system

• US 4,078,234 A
• Filed: 05/19/1976
• Issued: 03/07/1978
• Est. Priority Date: 04/25/1975
• Status: Expired due to Term

• Current Assignee: The United States Of America As Represented By The Secretary Of The Army
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Fishbein, William, Rittenbach, Otto E.
• Primary Examiner(s): Tubbesing, T.H.
• Application Number:
  US05/687,783
• Time in Patent Office: 657 Days
• Field of Search: 343/9, 343/17.2 R, 343/17.5
• US Class Current: 342/110
• CPC Class Codes: G01S 13/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 13/325 using transmission of coded signals, e.g. P.S.K. signals
• CPC Class Codes: G01S 13/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal

Abstract

A CW radar transmitter is simultaneously frequency modulated with a sinusal wave and phase-modulated with a pseudorandom binary code. Both the frequency of the FM signal and the bits and bit duration in the binary code can be varied to change the resolution and range of the system.

Claims

1. A radar system comprising:

a signal transmitter source of continuous wave electromagnetic energy of a single frequency;

means for generating a sinusoidal signal for frequency modulating said source;

code means for generating a p-bit pseudo-random binary code; and

means for phase-modulating said frequency modulated source with said pseudo-random code.

2. A radar system comprising:

antenna means;

a signal transmitter source of continuous wave electromagnetic energy coupled to said antenna means;

means for generating a sinusoidal signal of a first frequency f₁ for frequency modulating said source;

code means for generating a p-bit pseudo-random binary code of repetition frequency f_r which remains fixed in phase and provides a zero range timing reference for the radar system;

means for phase-modulating said source with said pseudo-random code;

a receiver including means coupled to said antenna means and to said source for deriving from each target echo received by said antenna means and delayed by the round trip time and frequency translated by the Doppler shift f_d owing to target motion relative to said antenna means a video frequency signal comprising the target doppler signal f_d modulated upon a coded signal of frequency f₁ ;

reference code producing means for providing n distinct reference codes which are replicas of said p-bit code but delayed in time with respect thereto by n different amounts representing n corresponding range slots; and

n correlation means for each of said n range slots coupled to said video frequency signal deriving means and receptive of a corresponding one of said reference codes for correlating said video frequency signals with said reference code,

each of said n correlation means including phase sensitive demodulator means for extracting for each target within a given range slot the target doppler signal f_d from said video frequency signal.

3. A radar system according to claim 2 further comprising range switching means connected in circuit with selectable ones of said n correlation means for monitoring target doppler signals associated with targets within the corresponding range slot.

4. A radar system according to claim 3 further comprising means for rendering said target doppler signals audible to an operator.

5. A radar system according to Claim 2 wherein each of said correlation means include doppler filter means wherein the difference frequencies N /f₁ - f_r / generated within the receiver with N being any positive integer are at least twice the largest doppler frequency f_d unattenuated by the doppler filters.

6. A radar system according to claim 5 further comprising n filter means each responsive to a corresponding correlation means for suppressing from the output of that correlation means all frequencies other than a band of frequencies lying between f₁ - f_d and f₁ + f_d.

7. A radar system according to claim 5 further comprising means for supplying dc power to the components of said system and including ac sources for supplying only /f₁ - f_r / harmonics thereof.

8. A radar system according to claim 2 wherein said receiver means for deriving a video signal includes mixer means for multiplying the transmitted signal and the received target echo, each of said reference code producing means including a delay code generator and means for multiplying the generated delay code by said binary code.

9. A radar system according to claim 8 further comprising adjustable phase shifting means coupled between said means for generating and said demodulator means for adjusting the phase of the transmitted frequency modulation signal to attenuate the output of said demodulator means for close-in targets.

10. A radar system according to claim 2 further comprising adjustable phase shifting means coupled between said means for generating and said demodulator means for adjusting the phase of the transmitted frequency modulation signal to attenuate the output of said demodulator means for close-in targets.

11. A radar system according to claim 2 further comprising n filter means each responsive to a corresponding correlation means for suppressing from the output of that correlation means all frequencies other than a band of frequencies lying between f₁ - f_d and f₁ + f_d.

12. A radar system according to claim 2 further comprising variable clock means connected to said code means for selectively altering the value of p and the duration of each pulse in said binary code to alter the system resolution.

13. A radar system according to claim 2 further comprising a generator of sinusoidal signal energy of frequency f₂ and means for frequency modulating said source with said frequency f₂ in addition to said modulation of the source with said frequency f₁ whereby fixed stationary targets can be detected.

14. A radar system according to claim 2 wherein said means for phase modulating said source comprises a microwave circulator having an input port and an output port interposed between said source and said antenna means, a diode switch disposed in said input port and connected to the output of said code means whereby said diode switch is switched from a conducting to a non-conducting state in accordance with the polarity of the bits in said binary code to alter selectively the phase of the signal emerging from said circular output port by π

/2 radians.