Waveform generator

• US 5,055,850 A
• Filed: 09/04/1990
• Issued: 10/08/1991
• Est. Priority Date: 09/04/1990
• Status: Expired due to Term

• Current Assignee: DRS Sustainment Systems, Inc (Leonardo S.p.A.)
• Original Assignee: Electronics and Space Corp (Leonardo S.p.A.)
• Inventors: Grettenberg, Thomas L., Lamper, David
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US07/576,996
• Time in Patent Office: 399 Days
• Field of Search: 342/25, 342/201
• US Class Current: 342/201
• 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

Abstract

A waveform generator (12'"'"') is responsive to a reference clock signal input for producing an output waveform which is a linear FM waveform. A reference clock signal is supplied to the generator which performs a double integration to obtain the phase of the output signal. The phase resulting from the double integration is used to obtain the sine of the phase using a lookup table. The sine of the phase is input to digital-to-analogue (D/A) converter, and the output from the D/A converter is filtered using a bandwidth matched to the bandwidth of the transmitted signal. The generator is useful in radar systems for area mapping and target identification.

Claims

1. In a radar system in which a coherent clock reference signal is used to generate a linear FM signal which is radiated from a transmitter located on a radar system platform, strikes an object, and has a portion thereof reflected back toward the platform, received by the system and thereafter processed to obtain information about the object, this processing including periodically sampling the received signal, a waveform generator whose output signal automatically compensates the received signal both with respect to any difference between the leading edge of the sampled portion of the signal and the leading edge of a sampling window (i.e., range walk) and any change in the received pulse-to-pulse phase and frequency due to motion of the platform occurring between transmission of one pulse and the next (i.e. "focusing"), the generator having means for generating a linear FM reference signal whose signal characteristics account for both any time difference between the leading edge of a sampling window and the leading edge of the sampled portion of the signal and any change in the received pulse-to-pulse phase and frequency due to motion of the platform occurring between the transmission of one pulse and the next.

2. The generator of claim 1 wherein the waveform generator includes integration means for performing a multiple integration to obtain the phase of an output signal supplied by it.

3. The generator of claim 2 wherein the integration means includes means for performing a first integration and a second integration of the second derivative of the phase of the output signal.

4. The generator of claim 3 further including means for combining an initial phase, a first integrated phase rate phase, and a second integrated signal phase, in any combination, to produce a resultant signal.

5. The generator of claim 4 further including output means responsive to the resultant signal for producing a linear FM reference signal.

6. The generator of claim 5 wherein the output means includes a look-up table having as an input the signal output of the combining means the output means producing a digital signal representing a modulated sine wave whose signal characteristics are a function of the input.

7. The generator of claim 6 wherein the output means further includes a digital-to-analog converter for converting the digital signal to the modulated sine wave.

8. The generator of claim 7 wherein the output means further includes filter means for matching the bandwith of the modulated sine wave with that of the transmitted signal.

9. A waveform generator responsive to a reference signal input for producing an output waveform comprising:

means to which the reference signal is supplied;

means for performing a multiple integration to obtain the phase of the output waveform; and

,

means for combining the results of the integration with a starting phase to produce the resultant waveform.

10. The generator of claim 9 wherein the integration means performs a first integration and a second integration to obtain the phase of the output waveform.

11. The generator of claim 10 wherein the combining means includes means for combining an initial phase, a first integrated signal phase rate, and a second integrated signal phase second derivative, in any combination thereof.

12. The generator of claim 11 further including output means comprising a look-up table having as an input the output of the combining means and as an output a digital signal representing a sine wave whose signal characteristics are a function of the input.

13. The generator of claim 12 wherein the output means further includes a digital-to-analog converter for converting the digital signal to the sine wave, and filter means for bandwidth matching the sine wave with a using system'"'"'s requirements.

14. A method of generating a waveform comprising:

supplying to a waveform generator an initial phase;

performing a multiple integration of the phase'"'"'s first and second derivatives;

combining, in any combination, the initial phase, and the derivative'"'"'s from each stage of the integration to produce a resultant signal; and

,

deriving from the resultant signal an output waveform by providing the resultant signal to a sine wave look-up table, locating in the table a digital value representing a sine wave having a specified set of characteristics, converting the digital value representing the sine wave to an analog sine wave signal, and passing the resultant waveform through a bandpass for bandwidth matching with a signal transmission system.

15. The method of claim 14 wherein performing the multiple integration of the reference phase includes performing respective first and second integrations thereof.

16. The method of claim 14 for generating a linear FM waveform.

17. In a radar system in which a coherent clock reference signal is used to generate a linear FM signal which is radiated from a transmitter located on a radar system platform, strikes an object, and has a portion thereof reflected back toward the platform, received by the system and thereafter processed to obtain information about the object, this processing including periodically sampling the received signal, a waveform generator whose output signal automatically compensates the received signal both with respect to any difference between the leading edge of the sampled portion of the signal and the leading edge of a sampling window (i.e., range walk) and any change in the received pulse-to-pulse phase and frequency due to motion of the platform occurring between transmission of one pulse and the next (i.e. "focusing"), the generator having means for generating a linear FM reference signal whose signal characteristics account for both any time difference between the leading edge of a sampling window and the leading edge of the sampled portion of the signal and any change in the received pulse-to-pulse phase and frequency due to motion of the platform occurring between the transmission of one pulse and the next.

18. The improvement of claim 17 further including means for supplying a reference signal to the generator means, the generator means including integration means for obtaining the phase of the output signal.

19. The improvement of claim 18 wherein the integration means includes means for performing a first integration and a second integration to obtain the phase of the output signal.

20. The improvement of claim 19 further including means for processing the received, automatically compensated signal.