Unambiguous range-doppler processing method and system

• US 5,657,022 A
• Filed: 11/17/1992
• Issued: 08/12/1997
• Est. Priority Date: 11/17/1992
• Status: Expired due to Term

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Wicks, Michael C., Van Etten, Paul
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US07/985,071
• Time in Patent Office: 1,729 Days
• Field of Search: 342/104, 342/13, 342/107, 342/112, 342/115, 342/132, 342/134, 342/137, 342/145, 342/201, 342/203
• US Class Current: 342/104
• CPC Class Codes: G01S 13/0209 Systems with very large relative bandwidth, i.e. larger than 10 %, e.g. baseband, pulse, carrier-free, ultrawideband
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 13/30 using more than one pulse per radar period
• CPC Class Codes: G01S 13/582 adapted for simultaneous range and velocity measurements

Abstract

Range-Doppler ambiguity is eliminated from an ultra-wideband radar system by transmitting an ultra-wideband chirped pulse towards a moving target, and mixing it with the doppler-shifted chirped pulse which is received as a target echo return signal. Multioctave radar tracing systems can potentiality track stealth aircraft without ambiguity since pulses containing many frequencies can defeat narrow-band radar absorbing material coatings. The unambiguous range-doppler signal processing method mixes the chirped pulse to yield an instantaneous Doppler frequency (which indicates target velocity) and a rate of change in the instantaneous Doppler frequency (which indicates target acceleration).

Claims

1. A process for use with a radar system for measuring an unambigiuous Range-Doppler measurement of a target'"'"'s velocity, said process comprising the steps of:

transmitting an ultra-wideband chirped pulse from said radar system;

receiving a Doppler-shifted chirped pulse as a target echo return signal from said target; and

determining said target'"'"'s velocity using both said chirped pulse and said Doppler shifted chirped pulse to determine said measurement thereby.

2. A process, as defined in claim 1 wherein said ultra-wideband chirped pulse spectrum covers the frequency rouge from frequency f₁, to frequency f₂, and wherein said baseband doppler-shifted chirped pulse spectrum covers its frequency fd₁, to frequency fd₂, and wherein said detemining step is performed by:

V=C (f_d2 -f_d1)/4B where;

V is the velocity of the target,

B equals bandwidth given by f₂ -f₁ ; and

C equals the velocity of light.

3. A process, as defined in claim 1, wherein said ultra-wideband chirped waveform comprise a pulse with a frequency sweeping from f₁, to frequcy f₂, and wherein said baseband Doppler-shifted pulse with a frequency sweeping from fd₁ to fd₂, and wherein said determining step is performed by mixing said ultra-wideband chirped pulse with said Doppler-shifted chirped pulse to obtain an output signal with an instantaneous frequency f;

and wherein said velocity is determined by a mathematical relationship comprising;

f_i =2RB/CT+2VBt/CT where;

V equal the velocity of the target;

B equals a bandwidth given by f₂ -f₁ ;

C equals the velocity of light;

T equals a time duration of said ultra-wideband chirped pulse pair; and

t equals a time delay below reception of the Doppler-shifted chirped pulse.

4. A process, as defined in claim 3, wherein said pulse is taken from a radar frequency band.

5. A process, as defined in claim 2, wherein said pulse has frequencies f1 and f2 which are selected from a radar frequency range which extends from about 300 Mc to 40 Gc such that said second pulse has its frequency f₂ greater than the frequency f₁ by about 25 percent of said radar frequency range.

6. A process, as defined in claim 4, wherein said first pulse and said second pulse each have frequencies which are selected from a radar frequency range which extends from about 300 Mc to 40 Gc such that said second pulse has its frequency f₂ greater than the frequency f₁ by about 25 percent of said radar frequency range.

7. A process, as defined in claim 5, wherein said first pulse and said second pulse each have frequencies which are selected from a radar frequency range which extends from about 300 Mc to 40 Gc such that said second pulse has its frequency f₂ greater than the frequency f₁ by about 25 percent of said radar frequency range.

8. A process, as defined in claim 6, wherein said target is accelerating with an acceleration which has a value A which may be determined by a mathematical relationship comprising:

dfi/dt=4VB/CT+2AB/CT where;

dfi/dt is a derivative of the instantaneous frequency with respect to time.

9. A process, as defined in claim 8, wherein said first pulse is taken from a first radar frequency band, and said second pulse is taken from a second radar frequency band.

10. A process, as defined in claim 9, wherein said first pulse and said second pulse each have frequencies which are selected from a radar frequency range which extends from about 300 Mc to 40 Gc such that said second pulse has its frequency f₂ greater than the frequency f₁ by about 25 percent of said radar frequency range.

11. An ultra-wideband radar system for tracking a moving target, and which comprises:

a means for transmitting an ultra-wideband chirped pulse pair towards said moving target;

a means for receiving a Doppler-shifted chirped pulse pair, said Doppler-shifted chirped pulse pair being a target echo return signal which occurs when said ultra-wideband chirped pulse pair is reflected off of said moving target; and

a means for processing signals which receives said Doppler-shifted chirped pulse pair from said receiving means, and measures said moving target'"'"'s velocity, range and position therefrom.

12. An ultra-wideband radar system, as defined in claim 11, wherein said transmitting means comprises:

a first signal generator which produces an output signal by generating said ultra-wideband chirped pulse pair which comprises a first pulse with a frequency f₁, and a second pulse with a frequency f₂, and wherein said Doppler-shifted chirped pulse pair has a first Doppler-shifted pulse with a frequency f_d1, and a second Doppler-shifted pulse with a frequncy f_d 2;

a transmitting antenna which receives the output signal of said first signal generator and transmits said ultra-wideband chirped pulse pair thereby.

13. An ultra-wideband radar system, as defined in claim 12, wherein said signal processing means comprises:

a data processor which measures said moving target'"'"'s velocity, range and position using both said ultra-wideband chirped pulse pair and said Doppler shifted chirped pulse pair; and

a signal processing circuit which is electrically connected between said transmitting means, said receiving means and said data processor to conduct said ultra-wideband chirped pulse pair and said Doppler-shifted chirped pulse pair to said data processor.

14. An ultra-wideband radar system, as defined in claim 13, wherein said data processor comprises a computer which is programmed to calculate said moving target'"'"'s velocity using:

V=C (f_d2 -f_d1)/4B where;

V equals the velocity of the target;

B equals a bandwidth given by f₂ -f₁ ; and

C equals the velocity of light.

15. An ultra-wideband radar system, as defined in claim 14, wherein said signal processing circuit comprises:

a first mixer which produces an output signal by receving and mixing the ultra-wideband chirped pulse pair from the transmitting means, with the Doppler-shifted chirped pulse pair from the receiving means;

a second generator which outputs a Doppler deramping chirp signal;

a second mixer which produces an output signal by receiving and mixing the output signal of the first mixer with the Doppler deramping chirp signal of the second signal generator;

an amplifier which produces output signal by amplitude weighing the output signal of the second mixer;

a spectrum analyzer which produces an output signal to display processed target echo return signals by processing the output signal of the analyzer, and

a data processor which determines the velocity of the moving target by a mathematical relationship comprising;

f₁ =2Rb/CT+2VBt/CT where;

V equals the velocity of the target;

B equals a bandwidth given by f₂ -f₁ ;

C equals the velocity of light;

T equals a time duration of said ultra-wideband chirped pulse pair; and

t equals a time delay before reception of the doppler-shifted chirped pulse pair.

16. An ultra-wide radar system, as defined in claim 15, wherein said first pulse is taken from a first radar frequency band, and said second pulse is taken from a second radar frequency band.

17. An ultra wide radar system, as defined in claim 16, wherein said first pulse and said second pulse each have frequencies which are selected from a radar frequency range which extends from about 300 Mc to 40 Gc such that said second pulse has its frequency f₂ greater than the frequency f₁ by about 25 percent of said radar frequency range.