Phase coherent radar system using fast frequency agile waveform synthesis

• US 5,726,657 A
• Filed: 03/22/1996
• Issued: 03/10/1998
• Est. Priority Date: 03/22/1996
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: O'Donnell, Daniel J., Sabin, Albert S., Pergande, Albert N.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/620,363
• Time in Patent Office: 718 Days
• Field of Search: 342/202, 342/62, 342/90, 342/97, 342/131, 342/137, 342/140, 342/141, 342/162, 342/188, 342/194, 342/195, 342/196, 342/201, 342/203
• US Class Current: 342/202
• CPC Class Codes: G01S 13/24 using frequency agility of carrier wave
• CPC Class Codes: G01S 13/288 phase modulated
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 7/288 Coherent receivers
• CPC Class Codes: G01S 7/2883 using FFT processing

Abstract

A radar system in which a frequency agile synthesizer is used to provide rapid frequency shifts and in which measures are taken to maintain phase coherency. The system is fully coherent such that all signals are derived from a common source and are capable of high pulse repetition rates in excess of 1 MHz. There are no inherent transmit duty cycle restrictions and the system is able to transmit complex phase and frequency modulated waveforms. A frequency interleaving scheme is used to resolve range ambiguities at high pulse repetition frequencies and the use of a complementary phase coding scheme allows a high range resolution processing with the transmitted waveforms.

Claims

1. Apparatus comprising:

a waveform generator for generating an interleaved waveform and a second output coherent with said waveform, said waveform generator including a frequency agile synthesizer capable of changing its output frequency to produce said interleaved waveform using multiple frequencies, a frequency and phase of said waveform, and said second output, being based on said output of said frequency synthesizer;

an antenna coupled to said waveform generator for transmitting said waveform, for receiving a return signal, and for generating at least one antenna output signal on the basis of said return signal;

a receiver coupled to said antenna and to said waveform generator to detect said return signal as a frequency interleaved signal, an interleaving of said frequency interleaved signal being selected to define an unambiguous range of said antenna, said receiver receiving said antenna output signal and said second output and converting said return signal on the basis of said second output signal to produce a converted signal; and

a processor for processing said converted signal to derive target data.

2. Apparatus as claimed in claim 1 wherein said frequency agile synthesizer is capable of changing its output frequency in a psuedorandom manner.

3. Apparatus as claimed in claim 1 wherein said frequency agile synthesizer is capable of changing its output pulse width.

4. Apparatus as claimed in claim 1 wherein said frequency agile synthesizer is capable of changing its pulse repetition frequency.

5. Apparatus as claimed in claim 1 wherein said frequency agile synthesizer is capable of impressing an arbitrary phase code on each pulse transmitted and wherein said processor performs pulse compression on the basis of said phase code.

6. Apparatus as claimed in claim 1 wherein said waveform generator further includes:

a millimeter wave phase locked oscillator connected to said frequency agile synthesizer for generating a millimeter wave oscillator output which is phase coherent with said frequency agile synthesizer output frequency, and

a frequency upconverter connected to said frequency agile synthesizer and to said phase locked oscillator for generating an upconverted output signal which is a millimeter wave multiple of and phase coherent with said frequency agile synthesizer output.

7. Apparatus as claimed in claim 6 wherein said waveform generator further includes:

a first frequency multiplier having said waveform as its output;

a second frequency multiplier having said second output as its output; and

a switch connected to the frequency upconverter for selectably connecting said upconverted output signal to said first frequency multiplier or said second frequency multiplier under control of said frequency agile synthesizer.

8. Apparatus as claimed in claim 7 wherein said frequency agile synthesizer controls said switch to connect said upconverted output signal to said first frequency multiplier during a transmit operation and controls said switch to connect said upconverted output signal to said second frequency multiplier during a receive operation.

9. A millimeter wave seeker system according to claim 1, wherein said antenna comprises a Cassegrainian dual-reflector antenna having a plurality of subassemblies for providing monopulse returns in both azimuth and elevation.

10. A millimeter wave seeker system according to claim 9, wherein said plurality of subassemblies comprise a collimator, a circular polarizer and an amplitude monopulse feed.

11. Apparatus as claimed in claim 1 wherein said receiver comprises at least one frequency downconverter connected to said antenna for converting said antenna output signal m a lower frequency signal, said downconverter being connected to receive said second output and generating said lower frequency signal to be phase coherent with said second output.

12. Apparatus as claimed in claim 11 wherein said receiver includes at least one IF receiver connected to said frequency downconverter for converting the lower frequency signal to baseband in-phase and quadrature outputs.

13. Apparatus as claimed in claim 1 wherein said antenna produces a first antenna output signal and a second antenna output signal, wherein said receiver comprises a first frequency downconverter connected to said antenna for converting said first antenna output signal to a first lower frequency signal and a second frequency downconverter connected to said antenna for converting said second antenna output signal to a second first lower frequency signal.

14. Apparatus as claimed in claim 13 wherein said receiver includes at least one IF receiver connected to said first frequency downconverter and said second frequency downconverter for converting the first and second lower frequency signals to baseband in-phase and quadrature outputs.

15. Apparatus as claimed in claim 1 wherein said processor processes said converted signal to derive target detection data.

16. Apparatus as claimed in claim 1 wherein said processor processes said converted signal to derive target tracking data.

17. Apparatus as claimed in claim 1, wherein said processor sends phase codes to transmit to the frequency agile synthesizer, such that said phase codes may be compressed when received by said processor.

27. Apparatus as claimed in claim 1, wherein said antenna transmits said waveform at a first transmit frequency while said return signal is received at a second receive frequency, different from said transmit frequency.

18. A method comprising the steps of:

generating an interleaved waveform and a second output coherent with said waveform by using a frequency agile synthesizer capable of changing its output frequency to produce said interleaved waveform using multiple frequencies, a frequency and phase of said waveform, and said second output, being based on said output frequency of said frequency synthesizer;

transmitting said waveform;

receiving a frequency interleaved return signal, an interleaving of said frequency interleaved return signal being selected to define an unambiguous range of said antenna;

generating at least one antenna signal on the basis of said return signal;

converting said return signal on the basis of said second output signal to produce a converted signal; and

processing said converted signal to derive target data.

19. A method as claimed in claim 18 wherein said frequency agile synthesizer changes its output frequency in a psuedorandom manner.

20. A method as claimed in claim 18 wherein said frequency agile synthesizer changes its output pulse width.

21. A method as claimed in claim 18 wherein said frequency agile synthesizer changes its pulse repetition frequency.

22. A method as claimed in claim 18 wherein said frequency agile synthesizer impresses an arbitrary phase code on each pulse transmitted and wherein said processing includes pulse compression on the basis of said phase code.

23. A method as claimed in claim 18 wherein said waveform generating step comprises the steps of:

upconverting the output of the frequency agile synthesizer to produce an upconverted output signal which is a millimeter wave multiple of and phase coherent with said frequency agile synthesizer output, and

selectably connecting said upconverted output signal under control of said frequency agile synthesizer to a first frequency multiplier to produce said waveform or a second frequency multiplier to produce said second output.

24. A method as claimed in claim 18 wherein said converting step comprises converting said antenna output signal to a lower frequency signal which is phase coherent with said second output.

25. A method as claimed in claim 18 wherein said processor processes said converted signal to derive target detection data.

26. A method as claimed in claim 18 wherein said processor processes said converted signal to derive target tracking data.