Virtual noise radar waveform for reduced radar detectability

• US 5,861,834 A
• Filed: 02/14/1998
• Issued: 01/19/1999
• Est. Priority Date: 05/30/1996
• Status: Expired due to Term

• Current Assignee: Hazeltine Corporation (BAE Systems Plc), Micron Technology, Inc., Systems & Electronics Incorporated (Xerox Holdings Corp.)
• Original Assignee: ESCO Electronics Corporation
• Inventors: Kremer, Larry R., Ziegler, John A., Sauer, Mark F.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US09/024,003
• Time in Patent Office: 339 Days
• Field of Search: 342/13, 342/194, 342/130, 342/200
• US Class Current: 342/13
• CPC Class Codes: G01S 13/222 using random or pseudorandom pulse repetition frequency
• CPC Class Codes: G01S 13/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 2013/0281 LPI, Low Probability of Intercept radar
• CPC Class Codes: G01S 7/282 Transmitters
• CPC Class Codes: G01S 7/285 Receivers
• CPC Class Codes: G01S 7/35 Details of non-pulse systems
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures

Abstract

Apparatus (10) for generating a radar waveform (W). A noise generator (20) generates a series of pulses in a pseudo-random pattern, and a frequency generator (16) generates a carrier wave having a frequency within a predetermined band of frequencies. The carrier wave is modulated with the pseudo-random pattern of pulses, and the resulting modulated carrier wave passed through both a filter (30) and an attenuator (32) to suppress any discernible feature or signal characteristics of the resulting waveform. The modulated carrier is transmitted by an antenna (42) and a received return signal is processed by a signal processor (100) to obtain pertinent information about a target. The transmitted waveform has no discernible attributes by which the waveform, if processed and analyzed by someone else'"'"'s radar detector (E) would convey any intelligence as to the presence or source of the transmitted waveform.

Claims

1. In apparatus generating a radar waveform and including a psuedo-random noise generator generating pulses in a pseudo-random pattern which are combined to produce an offset frequency signal, means generating a carrier wave having a frequency within a predetermined band of frequencies, and a modulator modulating the carrier wave with the offset frequency signal, the improvement wherein said psuedo random noise generator includes a pulse shaping filter suppressing modulation characteristics of said psuedo-random noise generator, said filter having a spectral response characteristic including raised cosine shapes;

and, a propagation means transmitting the modulated waveform and for receiving a return waveform, the transmitted waveform having no discernible attributes by which the waveform, if received and analyzed by a detector other than the propagation means, would convey any intelligence as to the presence of the transmitted waveform or the source thereof.

2. The improvement of claim 1 wherein said pulse shaping filter is a truncated Nyquist filter.

3. The improvement of claim 1 wherein said psuedo-random noise generator generates in-phase and quadrature-phase code sequences at a code rate substantially greater than that required for radar range resolution.

4. The improvement of claim 1 wherein said carrier wave is supressed in an n^th order detector in which n is equal to one-half the ratio of the overall code rate to the bandwidth of said filter.

5. The improvement of claim 2 further including processing means processing a received, return waveform to obain pertinent information about a target at which a transmitted waveform is directed, said processing means performing a cross-correlation on the received waveform using as a reference an unfiltered output of said psuedo-random noise generator.

6. The improvement of claim 1 wherein said psuedo random pattern is based upon complementary code sequences.

7. The improvement of claim 6 wherein said complementary sequence is a member of the Golay family of complementary code pairs.

8. The improvement of claim 7 wherein said code pairs are members of the Welti-D class of Golay codes.

9. The improvement of claim 6 wherein said complementary sequence is transmitted in sets of Hadamard codes.

10. In apparatus for generating a virtual noise waveform and including a generator generating a series of coded digital electrical pulses in a pseudo-random pattern, means modulating a carrier wave with the pulses to produce a modulated waveform, a filter filtering the resulting modulated waveform for an output waveform from the filter to fall within a null portion of the filter for the waveform energy of the output from the filter to be at a minimum level, the bandwidth of the filtered waveform being sufficient to enable the waveform to obtain desired information when directed at an area of interest, and an attenuator attenuating the filtered waveform to sufficiently suppress any remaining features of the waveform so to produce a virtual noise waveform which appears as a random noise signal having no discernible attributes and conveying no information about the waveform or its source, the improvement comprising a pulse shaping filter suppressing modulation characteristics of said electrical pulse generator, said filter having a spectral response characteristic including raised cosine shapes.

11. The improvement of claim 10 wherein said pulse shaping filter is a truncated Nyquist filter.

12. The improvement of claim 10 wherein said coded digital electrical pulses are generated in a psuedo random pattern using complementary code sequences.

13. The improvement of claim 12 wherein said complementary sequence is a member of the Golay family of complementary code pairs.

14. The improvement of claim 13 wherein said code pairs are members of the Welti-D class of Golay codes.

15. The improvement of claim 12 wherein said complementary sequence is transmitted in sets of Hadamard codes.

16. The improvement of claim 10 wherein said psuedo-random noise generator generates in-phase and quadrature-phase code sequences at a code rate substantially greater than that required for radar range resolution.

17. In a method of generating a virtual noise waveform including the steps of generating two series of digital pulses in a pseudo-random pattern, combining the respective series of pulses to produce an offset frequency, modulating a carrier wave with the offset frequency to produce a modulated waveform, and suppressing the characteristics of the resulting modulated waveform for the waveform to have no discernible attributes which would convey any information about the existence of the waveform or its source, the improvement comprising filtering said digital pulses with a pulse shaping filter to suppress modulation characteristics of said waveform, said filter having a spectral response characteristic including raised cosine shapes.

18. The improvement of claim 17 wherein said filtering of said digital pulses is performed with a truncated Nyquist filter.

19. The improvement of claim 17 wherein said two series of pulses are generated in a psuedo random pattern using complementary code sequences.

20. The improvement of claim 19 wherein said complementary sequence is a member of the Golay family of complementary code pairs.

21. The improvement of claim 20 wherein said code pairs are members of the Welti-D class of Golay codes.

22. The improvement of claim 20 wherein said complementary sequence is transmitted in sets of Hadamard codes.

23. The improvement of claim 17 wherein said two series of pulses are generated at a code rate substantially greater than that required for radar range resolution.

24. In a method of generating a radar waveform including generating an in-phase series and a quadrature-phase series of coded pulse sequences in a pseudo-random pattern, combining the two series of coded pulse sequences into an offset frequency, generating a carrier wave having a frequency within a predetermined frequency band, modulating said carrier wave with said offset frequency, filtering the modulated waveform so the waveform energy is concentrated within a narrow bandwidth corresponding to the bandwidth required for information gathering, the energy of the resulting filtered waveform being substantially less than that of the unfiltered modulated waveform, attenuating the filtered waveform to suppress any features therein and to eliminate any discernible features of the filtered waveform, and transmitting the resulting waveform and receiving a return waveform, said transmitted waveform, if received and analyzed by a detection means other than that associated with the source of the waveform, appearing as a random noise signal having no discernible attributes and conveying no information about the waveform or its source, the improvement comprising filtering said coded pulse sequences with a pulse shaping filter to suppress modulation characteristics of said waveform, said filter having a spectral response characteristic including raised cosine shapes.

25. The improvement of claim 24 wherein filtering of said coded pulse sequences is performed with a truncated Nyquist filter.

26. The improvement of claim 24 wherein said two series of pulses are generated in a psuedo random pattern using complementary code sequences.

27. The improvement of claim 26 wherein said complementary sequence is a member of the Golay family of complementary code pairs.

28. The improvement of claim 27 wherein said code pairs are members of the Welti-D class of Golay codes.

29. The improvement of claim 27 wherein said complementary sequence is transmitted in sets of Hadamard codes.

30. The improvement of claim 24 further including processing said received, return waveform to obtain pertinent information about a target at which said modulated waveform is transmitted, said processing including performing a cross-correlation on the received waveform using as a reference an unfiltered output of said coded electrical digital pulses.