Notched-spectrum swept-frequency generator and method therefor

• US 5,852,418 A
• Filed: 11/12/1997
• Issued: 12/22/1998
• Est. Priority Date: 11/12/1997
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Woody, William C., Ferrell, Bruce H.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/967,840
• Time in Patent Office: 405 Days
• Field of Search: 342/202, 342/21, 342/101, 342/132, 342/134, 342/135
• US Class Current: 342/202
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: H03B 23/00 Generation of oscillations periodically swept over a predetermined frequency range angle-modulating circuits in general H03C3/00

Abstract

A notched-chirp generator (20), utilizing first and second chirp generators (28, 30), a functional conversion element (40), an antichirp generator (42), a summing element (64), and a translation element (66), generates a notched-chirp signal (24). The second chirp generator (30) generates a second chirp phase signal (φ_C1), is translated by the functional conversion element (40) into an oscillating antichirp signal (A_O1). The antichirp generator (42) generates an antichirp signal (A₁) by scaling, weighting, and cyclically positioning the oscillating antichirp signal (A_O1). The summing element (64) sums the antichirp signal (A₁) with a first chirp phase signal (φ_C0), generated by the first chirp generator (28), to produce a notched-chirp phase signal (φ_N), which is converted by the translation element (66) into a notched-chirp signal (24) having a notch (26) positioned at a specific frequency (f_N) determined by the antichirp signal (A₁)

Claims

1. A method for generating a notched-chirp signal, said method comprising the steps of:

generating a chirp phase signal which progresses quadratically over time;

generating an antichirp signal as a function of said chirp phase signal;

modulating said chirp phase signal by said antichirp signal; and

translating said chirp phase signal into said notched-chirp signal.

2. A method as claimed in claim 1 wherein:

said modulating step modulates said chirp phase signal by said antichirp signal to produce a notched-chirp phase signal; and

said translating step translates said notched-chirp phase signal into said notched-chirp signal.

3. A method as claimed in claim 2 wherein said modulating step comprises the step of scaling said antichirp signal so that said chirp phase signal experiences perturbations away from said quadratic progression.

4. A method as claimed in claim 2 wherein said modulating step causes said chirp phase signal to experience excursions of less than 0.04 radians.

5. A method as claimed in claim 2 wherein:

said chirp phase signal has a chirp duration; and

said modulating step causes said chirp phase signal to experience excursions which vary in frequency throughout said chirp duration.

6. A method as claimed in claim 5 wherein said modulating step modulates said chirp phase signal with a modulation envelope having an envelope cycle extending over said chirp duration, said modulation envelope having a maximum excursion within said envelope cycle.

7. A method as claimed in claim 6 wherein said excursions vary linearly in frequency throughout said envelope cycle.

8. A method as claimed in claim 6 wherein said modulating step comprises the step of cyclically shifting said envelope cycle relative to said chirp duration.

9. A method as claimed in claim 1 wherein:

said translating step translates said chirp phase signal into a chirp signal; and

said modulating step modulates said chirp signal by said antichirp signal to produce said notched-chirp signal.

10. A notched-chirp generator configured to generate a notched-chirp signal and comprising:

a chirp generator configured to generate a chirp phase signal which is a quadratic function of time;

an antichirp generator configured to generate an antichirp signal having excursions which vary in frequency over time; and

a modulating element configured to modulate said chirp phase signal by said antichirp signal to produce a notched-chirp signal.

11. A notched-chirp generator as claimed in claim 10 additionally comprising a functional conversion element coupled to said antichirp generator and configured to generate an oscillating signal which varies in frequency over time.

12. A notched-chirp generator as claimed in claim 10 wherein said antichirp generator receives an oscillating signal which varies in frequency over time, and comprises a scaling element configured to scale said oscillating signal.

13. A notched-chirp generator as claimed in claim 10 wherein said antichirp generator receives an oscillating signal which varies in frequency over time, and comprises a weighting element configured to weight said oscillating signal with a weighting function.

14. A notched-chirp generator as claimed in claim 10 wherein said antichirp generator receives an oscillating signal which varies in frequency over time, and comprises a shift element configured to cyclically position said oscillating signal so as to produce a signal notch at a specific frequency within a spectrum of said notched-chirp signal.

15. A notched-chirp generator as claimed in claim 10 wherein said antichirp generator receives an oscillating signal which varies in frequency over time, and comprises:

a scaling element configured to scale said oscillating signal;

a weighting element configured to weight said oscillating signal; and

a shift element configured to cyclically position said oscillating signal so as to produce a signal notch at a specific frequency within said notched-chirp signal.

16. A notched-chirp generator as claimed in claim 10 wherein:

said chirp generator is a first chirp generator; and

said notched-chirp generator additionally comprises a second chirp generator, said second chirp generator being coupled to said antichirp generator.

17. A notched-chirp generator as claimed in claim 10 wherein:

said antichirp generator is one of a plurality of antichirp generators;

said antichirp signal is one of a plurality of antichirp signals, each of said antichirp signals being generated by a different one of said plurality of antichirp generators and being configured to produce a signal notch at a different frequency within a spectrum of said notched-chirp signal; and

said modulating element is configured to modulate said chirp phase signal and each of said plurality of antichirp signals to produce said notched-chirp phase signal.

18. A notched-chirp generator as claimed in claim 10 additionally comprising means for translating said notched-chirp phase signal into said notched-chirp signal.

19. A method for the generation of a notched-chirp radar transmission signal wherein said method comprises the steps of:

producing first and second chirp phase signals;

converting said second chirp phase signal into an oscillating signal;

generating an antichirp signal from said oscillating signal;

modulating said first chirp phase signal by said antichirp signal to produce a notched-chirp phase signal; and

translating said notched-chirp phase signal to produce said notched-chirp signal.

20. A method as claimed in claim 19 wherein said generating step comprises the step of multiplying said oscillating signal by a scaling signal.

21. A method as claimed in claim 20 wherein said generating step comprises the step of multiplying said oscillating signal by a weighting function.

22. A method as claimed in claim 21 wherein said generating step comprises the step of cyclically positioning said oscillating signal to produce said antichirp signal.

23. A method as claimed in claim 19 wherein:

said method additionally comprises the step of repeating said generating step to generate a plurality of antichirp signals, each of which is configured to produce a signal notch at a different frequency within said notched-chirp signal; and

said modulating step sums said plurality of antichirp signals and said first chirp phase signal to produce said notched-chirp phase signal.