Digital polarimetric system for generating polarization agile signals

• US 6,608,587 B1
• Filed: 07/24/2001
• Issued: 08/19/2003
• Est. Priority Date: 07/24/2001
• Status: Expired due to Fees

• Current Assignee: Exelis Incorporated (L3Harris Technologies, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: Sparrow, Mitchell S., Cikalo, Joseph
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/910,948
• Time in Patent Office: 756 Days
• Field of Search: 342/13-20, 342/82, 342/83, 342/175, 342/188, 342/195, 342/361, 342/362-367, 342/95, 356/364-370
• US Class Current: 342/188
• CPC Class Codes: G01S 7/024 using polarisation effects in waveguides H01P1/165; for aerials H01Q, e.g. H01Q15/22, H01Q15/24, H01Q19/195
• CPC Class Codes: G01S 7/282 Transmitters
• CPC Class Codes: G01S 7/38 Jamming means, e.g. producing false echoes

Abstract

A digital polarimeter employs a signal time stretching technique to apply polarization phase shift characteristics to digitally generated polarization agile signal components. An RF signal to be transmitted is down-converted to an intermediate frequency and digitally sampled at a rate feasible with currently-available analog-to-digital converters. Horizontal and vertical signal components of the sampled IF signal are generated by processing the digital signal samples. Each digital signal sample is “time stretched” by storing each sample in M memory locations, such that N samples occupy M×N memory locations. Because each sample is stored in M memory locations, each incremental phase shift from one memory location to the next corresponds to 1/M^th of the actual sampling interval. The stretching process effectively increases the digital sampling frequency, yielding sufficient phase resolution. The time-stretched signal components are subsequently compressed, converted to analog signals and up-converted for transmission.

Claims

1. A method for generating a polarization agile signal, comprising:

(a) time stretching a digital input signal by representing each of a number of samples of the digital input signal as a plurality of time-stretched samples to produce a time-stretched signal;

(b) generating digital time-stretched signal components of the polarization agile signal from the time-stretched signal and polarization data;

(c) time compressing the digital time-stretched signal components to produce digital signal components of the polarization agile signal; and

(d) generating the polarization agile signal from the digital signal components.

2. The method of claim 1, wherein an effective phase resolution of the time-stretched signal is greater than that of the digital input signal.

3. The method of claim 1, wherein (a) includes storing each of said number of samples in plural memory locations.

4. The method of claim 1, wherein the digital input signal comprises N samples per signal cycle, where N is a positive number, and wherein (a) includes storing each of the N samples in M memory locations, such that M×

N samples are stored for each signal cycle, where M is a positive integer.

5. The method of claim 1, wherein the polarization data includes first and second polarization phase data and (b) includes:

(b1) inverting samples of the time-stretched signal to produce an inverted signal;

(b2) shifting samples of the inverted signal by a number of sample positions in accordance with the first polarization phase data to produce a shifted signal;

(b3) adding the time-stretched-signal and the shifted signal to produce a first digital time-stretched signal component of the polarization agile signal;

(b4) adding the inverted signal and the shifted signal to produce a sum signal; and

(b5) shifting samples of the sum signal by a number of sample positions in accordance with the second polarization phase data to produce a second digital time-stretched signal component of the polarization agile signal.

6. The method of claim 5, wherein the first and second digital time-stretched signal components respectively correspond to the horizontal and vertical polarization components of the polarization agile signal.

7. The method of claim 1, wherein the polarization data comprises phase values representing polarization phase and amplitude information.

8. The method of claim 1, wherein the polarization data comprises integer values representing numbers of memory location shifts.

9. The method of claim 1, further comprising:

(e) sampling an input analog signal to generate the digital input signal, wherein a phase resolution of the time-stretched sequence of digital samples is a function of a sampling rate of the digital input signal and a number of memory locations in which each of said number of samples is stored.

10. The method of claim 9, further comprising:

(f) down converting an input radio frequency signal to produce the input analog signal at an intermediate frequency.

11. The method of claim 1, wherein (d) includes:

(d1) converting the digital signal components to analog intermediate frequency signal components; and

(d2) up-converting the analog intermediate frequency signal components to radio frequency signal components.

12. An apparatus for generating a polarization agile signal, comprising:

an analog-to-digital converter configured to digitally sample an input signal to produce a digital input signal;

a processor configured to generate a time-stretched signal by representing each of a number of samples of the digital input signal as a plurality of time-stretched samples, said processor generating digital time-stretched signal components of the polarization agile signal from the time-stretched signal and polarization data, and time compressing the digital time-stretched signal components to produce digital signal components of the polarization agile signal; and

a digital-to-analog converter device configured to receive the digital signal components and generate corresponding analog signal components of the polarization agile signal.

13. The apparatus of claim 12, further comprising a memory device coupled to said processor and configured to store samples of the digital input signal and the time-stretched signal.

14. The apparatus of claim 13, wherein:

said analog-to-digital converter samples the input signal at a sampling rate of N samples per signal cycle, where N is a positive number; and

said memory device stores each of the N samples in M memory locations, such that M×

N samples are stored for each signal cycle, where M is a positive integer.

15. The apparatus of claim 14, wherein a phase resolution of the time-stretched signal is a function of the sampling rate and the number of memory locations M in which each of said number of samples is stored.

16. The apparatus of claim 12, wherein an effective phase resolution of the time-stretched signal is greater than that of the digital input signal.

17. The apparatus of claim 12, wherein the polarization data includes first and second polarization phase data and said processor includes:

a signal inverter configured to inverter values of samples of the time-stretched signal to produce an inverted signal;

a first data shifter configured to shift samples of the inverted signal by a number of sample positions in accordance with the first polarization phase data to produce a shifted signal;

a first adder configured to add the time-stretched signal and the shifted signal to produce a first digital time-stretched signal component of the polarization agile signal;

a second adder configured to add the inverted signal and the shifted signal to produce a sum signal; and

a

second data shifter configured to shift samples of the sum signal by a number of sample positions in accordance with the second polarization phase data to produce a second digital time-stretched signal component of the polarization agile signal.

18. The apparatus of claim 17, wherein the first and second digital time-stretched signal components respectively correspond to the horizontal and vertical polarization components of the polarization agile signal.

19. The apparatus of claim 12, wherein the polarization data comprises phase values representing polarization phase and amplitude information.

20. The apparatus of claim 12, wherein the polarization data comprises integer values representing numbers of memory location shifts.

21. The apparatus of claim 12, wherein said digital-to-analog converter device comprises plural digital-to-analog converters.

22. The apparatus of claim 12, further comprising:

a down converter configured to convert an input radio frequency signal to an intermediate frequency to produce the input signal.

23. The apparatus of claim 12, further comprising:

an up converter configured to convert the analog signal components of the polarization agile signal from an intermediate frequency to a transmission frequency.

24. The apparatus of claim 23, further comprising a dual-polarization antenna configured to receive the analog signal components and transmit the polarization agile signal at the radio frequency.

25. An apparatus for generating a polarization agile signal, comprising:

means for time stretching a digital input signal by representing each of a number of samples of the digital input signal as a plurality of time-stretched samples;

means for generating digital time-stretched signal components of the polarization agile signal from the time-stretched signal and polarization data;

means for time compressing the digital time-stretched signal components to produce digital signal components of the polarization agile signal; and

means for producing the polarization agile signal from the digital signal components.

26. The apparatus of claim 25, wherein an effective phase resolution of the time-stretched signal is greater than that of the digital input signal.

27. The apparatus of claim 25, wherein said means for time stretching includes means for storing each of said number of samples in plural memory locations.

28. The apparatus of claim 25, wherein the digital input signal comprises N samples per signal cycle, where N is a positive number, and wherein means for time stretching includes means for storing each of the N samples in M memory locations, such that M×

N samples are stored for each signal cycle, where M is a positive integer.

29. The apparatus of claim 25, wherein the polarization data includes first and second polarization phase data and said means for generating includes:

means for inverting samples of the time-stretched signal to produce an inverted signal;

means for shifting samples of the inverted signal by a number of sample positions in accordance with the first polarization phase data to produce a shifted signal;

means for adding the time-stretched signal and the shifted signal to produce a first digital time-stretched signal component of the polarization agile signal;

means for adding the inverted signal and the shifted signal to produce a sum signal; and

means for shifting samples of the sum signal by a number of sample positions in accordance with the second polarization phase data to produce a second digital time-stretched signal component of the polarization agile signal.

30. The apparatus of claim 29, wherein the first and second digital time-stretched signal components respectively correspond to the horizontal and vertical polarization components of the polarization agile signal.

31. The apparatus of claim 25, wherein the polarization data comprises phase values representing polarization phase and amplitude information.

32. The apparatus of claim 25, wherein the polarization data comprises integer values representing numbers of memory location shifts.

33. The apparatus of claim 25, further comprising:

means for sampling an input analog signal to generate the digital input signal, wherein a phase resolution of the time-stretched sequence of digital samples is a function of a sampling rate of the digital input signal and a number of memory locations in which each of said number of samples is stored.

34. The apparatus of claim 33, further comprising:

means for down converting an input radio frequency signal to an intermediate frequency to produce the input analog signal.

35. The apparatus of claim 25, wherein said means for producing includes:

means for converting the digital signal components to analog intermediate frequency signal components; and

means for up-converting the analog intermediate;

frequency signal components to radio frequency signal components.

36. A digital polarimetric system for generating a polarization agile signal, comprising:

an analog-to-digital converter configured to digitally sample an input signal;

a memory device configured to receive digital samples from said analog-to-digital converter and store each of the digital samples in a plurality of memory locations to form a time-stretched sequence of digital samples;

a digital signal processor configured to generate digital time-stretched signal components of the polarization agile signal from the time-stretched sequence of digital samples and polarization data, and time compress the digital time-stretched signal components to produce digital signal components of the polarization agile signal;

a digital-to-analog converter device configured to receive the digital signal components and generate corresponding analog signal components of the polarization agile signal;

a frequency converter configured to convert a frequency of the analog signal components to a transmission frequency; and

a dual-polarization antenna configured to receive the analog signal components and transmit the polarization agile signal.

37. The system of claim 36, wherein a phase resolution of the time-stretched signal is a function of a sampling rate of said analog-to-digital converter and a number of memory locations in which each of the digital samples is stored in said memory device.

38. A digital transmit polarimeter, comprising:

a signal time-stretching processor configured to produce a time-stretched signal by representing each of a number of samples of a digital input signal as a plurality of time-stretched samples;

a data inverter configured to invert-samples of the time-stretched signal to produce an inverted signal;

a first data shifter receiving first polarization data and delaying samples of the inverted signal by a number of sample, positions in accordance with first polarization data to produce a shifted signal;

a first signal combiner configured to add the time-stretched signal and the shifted signal to produce a first digital time-stretched signal component of the polarization agile signal;

a second signal combiner configured to add the inverted signal and the shifted signal to produce a sum signal;

a second data shifter receiving second polarization data and delaying samples of the sum signal by a number of sample positions in accordance with second polarization data to produce a second digital time-stretched signal component of the polarization agile signal; and

first and second signal time-compressing processors configured to respectively compress the first and second digital time-stretched signal components to produce first and second digital signal components of the polarization agile signal.

39. The polarimeter of claim 38, wherein an effective phase resolution of the time-stretched signal is greater than that of the digital input signal.