GPS receivers with adaptive antenna systems for suppressing interference signals

• US 6,175,327 B1
• Filed: 01/16/1999
• Issued: 01/16/2001
• Est. Priority Date: 01/16/1999
• Status: Expired due to Term

• Current Assignee: Sensor Systems
• Original Assignee: Sensory Systems
• Inventors: Lin, Zhen-biao, Robin, Seymour
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/232,573
• Time in Patent Office: 731 Days
• Field of Search: 342/357-1-3, 342/378-384, 342/13-19, 342/362, 342/368, 342/363-367
• US Class Current: 342/357.64
• CPC Class Codes: H01Q 21/06 Arrays of individually energised antenna units similarly polarised and spaced apart
• CPC Class Codes: H01Q 21/24 Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction circularly polarised patch antennas H01Q9/0428; circularly polarised horns H01Q13/0241; cross-polarised horns H01Q13/0258; polarisation converters H01Q15/242; cross-polarised rear feeds H01Q19/136; crossed polarisation dual antenna H01Q25/001
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 7/084 Equal gain combining, only phase adjustments antenna beam scanning or forming by phase or amplitude control H01Q3/26, e.g. phased arrays

Abstract

GPS receivers are provided that reduce all types of interference signals with a simple receiver structure that includes an antenna system having a reference antenna element and a plurality of auxiliary antenna elements, a plurality of phase shifters and a power combiner. The receiver also includes a downconverter, a digital GPS processor and an analog-to-digital converter (ADC). Each antenna element generates a single output signal in response to all polarization components of a GPS signal. In response to a composite signal of interference signals and GPS signals, the reference antenna element provides a reference signal and the auxiliary antenna elements provide auxiliary signals which each has a phase difference from the reference signal that is a function of its respective auxiliary antenna element'"'"'s location in an antenna array space and of paths of the interference signals. The phase shifters facilitate phase adjustment of at least one of the auxiliary signals to thereby reduce the amplitude of the combined signal and thereby reduce the contribution of the interference signal below a selected threshold. The reference signal has a reference signal gain and each of N auxiliary signals has an auxiliary signal gain substantially equal to 1/N times the reference signal gain. This fixed amplitude relationship further reduces the contribution of the interference signal while simplifying the receiver structure and lowering its cost. Preferably, a signal processor is responsive to the ADC and is programmed to adjust the phase shifters to reduce the combined signal.

Claims

1. A global positioning system (GPS) receiver for reducing a contribution of an interference signal while receiving a composite signal that includes said interference signal and at least one circularly-polarized GPS signal wherein said interference signal propagates along an associated interference signal path, the receiver comprising:

an antenna having a reference antenna element and a plurality of auxiliary antenna elements arranged across an antenna array wherein each antenna element generates a single output signal in response to all polarization components of said GPS signal and, in response to said composite signal, said reference antenna element provides a reference signal and said auxiliary antenna elements provide auxiliary signals which each has a phase difference from said reference signal that is a function of its respective auxiliary antenna element'"'"'s location in said antenna array and of said interference signal path;

a plurality of phase shifters that are each coupled to vary the phase of a respective one of said auxiliary signals;

a power combiner coupled to said reference antenna element and to said phase shifters to combine said reference signal and said auxiliary signals into a combined signal;

a downconverter that reduces the frequency of said combined signal;

a digital GPS processor; and

an analog-to-digital converter (ADC) that couples said downconverter to said GPS processor;

said phase shifters facilitating phase adjustment of at least one of said auxiliary signals to thereby reduce the amplitude of said combined signal and thereby reduce said contribution of said interference signal.

2. The GPS receiver of claim 1, further including:

a low-noise amplifier that couples said reference antenna element to said power combiner; and

a plurality of low-noise amplifiers that each couple a respective one of said auxiliary antenna elements to its respective phase shifter.

3. The GPS receiver of claim 1, wherein each of said reference antenna element and said auxiliary antenna elements is a patch antenna.

4. The GPS receiver of claim 1, wherein each of said auxiliary antenna elements is positioned on a respective one of a plurality of imaginary concentric circles centered on said reference element.

5. The GPS receiver of claim 1, wherein each of said auxiliary antenna elements is positioned on an imaginary circle centered on said reference element.

6. The GPS receiver of claim 5, wherein said plurality of auxiliary antenna elements is three auxiliary antenna elements that are spaced substantially 120°

apart.

7. The GPS receiver of claim 1, wherein said antenna array is a planar array.

8. The GPS receiver of claim 1, wherein said antenna array is a three-dimensional array.

9. The GPS receiver of claim 1, wherein said digital GPS processor includes at least one digital receiver channel that has a code tracking loop and a carrier tracking loop for tracking the frequency and ranging codes of said GPS signal.

10. The GPS receiver of claim 1, further including a signal processor responsive to said ADC, said signal processor facilitating adjustment of said phase shifters to reduce said combined signal.

11. A global positioning system (GPS) receiver for reducing a contribution of an interference signal while receiving a composite signal that includes said interference signal and at least one circularly-polarized GPS signal wherein said interference signal propagates along an associated interference signal path, the receiver comprising:

an antenna having a reference antenna element and N auxiliary antenna elements arranged to define an antenna array wherein each antenna element generates a single output signal in response to all polarization components of said GPS signal and, in response to said composite signal, said reference antenna element provides a reference signal and said auxiliary antenna elements provide auxiliary signals which each has a phase difference from said reference signal that is a function of its respective auxiliary antenna element'"'"'s location in said antenna array and of said interference signal path;

N phase shifters that are each coupled to vary the phase of a respective one of said auxiliary signals;

a power combiner coupled to said reference antenna element and to said phase shifters to combine said reference signal and said auxiliary signals into a combined signal;

a downconverter that reduces the frequency of said combined signal;

a digital GPS processor;

an analog-to-digital converter (ADC) that couples said downconverter to said GPS processor; and

a signal processor that is responsive to said ADC and facilitates adjustment of said phase shifters to reduce said combined signal and thereby reduce said contribution of said interference signal.

12. The GPS receiver of claim 11, wherein, prior to their combination in said power combiner, said reference signal has a reference signal gain and each of said auxiliary signals have an auxiliary signal gain substantially equal to 1/N times said reference signal gain.

13. A global positioning system (GPS) antenna system for reducing a contribution of an interference signal while receiving a composite signal that includes said interference signal and at least one circularly-polarized GPS signal wherein said interference signal propagates along an associated interference signal path, the receiver comprising:

an antenna having a reference antenna element and a plurality of auxiliary antenna elements arranged to define an antenna array wherein each antenna element generates a single output signal in response to all polarization components of said GPS signal and, in response to said composite signal, said reference antenna element provides a reference signal and said auxiliary antenna elements provide auxiliary signals which each has a phase difference from said reference signal that is a function of its respective auxiliary antenna element'"'"'s location in said antenna array and of said interference signal path;

a plurality of phase shifters that are each coupled to vary the phase of a respective one of said auxiliary signals; and

a power combiner coupled to said reference antenna element and to said phase shifters to combine said reference signal and said auxiliary signals into a combined signal;

said phase shifters facilitating phase adjustment of at least one of said auxiliary signals to thereby reduce the amplitude of said combined signal and thereby reduce said contribution of said interference signal.

14. The GPS antenna system of claim 13, wherein each of said reference antenna element and said auxiliary antenna elements is a patch antenna.

15. The GPS antenna system of claim 14, wherein each of said reference antenna element and said auxiliary antenna elements includes:

a patch;

first and second tap points on said patch arranged to detect first and second orthogonally-polarized signals; and

a feed-line structure arranged to combine said first and second orthogonally-polarized signals into a single signal.

16. The GPS antenna system of claim 13, wherein each of said auxiliary antenna elements is positioned on a respective one of a plurality of imaginary concentric circles centered on said reference element.

17. The GPS antenna system of claim 13, wherein each of said auxiliary antenna elements is positioned on an imaginary circle centered on said reference element.

18. The GPS antenna system of claim 17, wherein said plurality of auxiliary antenna elements is three auxiliary antenna elements that are spaced substantially 120°

apart.

19. The GPS antenna system of claim 13, wherein said antenna array is a planar array.

20. The GPS antenna system of claim 13, wherein said antenna array is a three-dimensional array.

21. A method of reducing a contribution of an interference signal to a received composite signal that includes said interference signal and at least one global positioning system (GPS) signal wherein said interference signal propagates along an associated interference signal path, the method comprising the steps of:

providing a reference antenna element and a plurality of auxiliary antenna elements wherein each antenna element generates a single output signal in response to all polarization components of said composite signal;

arranging said reference antenna element and said auxiliary antenna elements to define an antenna array;

receiving said composite signal with said reference antenna element and said auxiliary antenna elements to thereby provide a reference signal and also provide a plurality of auxiliary signals which each has a phase difference from said reference signal that is a function of its respective location in said antenna array and of said interference signal path;

combining said reference signal and said auxiliary signals to form a combined signal; and

adjusting the phase of at least one of said auxiliary signals to reduce said combined signal and thereby reduce said contribution of said interference signal.

22. The method of claim 21, wherein said reference signal has a reference amplitude, said auxiliary signals have auxiliary amplitudes and the sum of said auxiliary amplitudes differs from said reference amplitude by an amplitude difference;

and

further including the step of selecting the amplitude of at least one of said reference signal and said auxiliary signals to reduce said amplitude difference and thereby reduce said contribution of said interference signal.

23. The method of claim 21, wherein each of said reference antenna element and said auxiliary antenna elements is a patch and further including the steps of:

arranging tap points on said patch to detect first and second orthogonally-polarized signals; and

coupling said tap points with a feed-line structure that is arranged to combine said first and second orthogonally-polarized signals into a single signal.

24. The method of claim 21, wherein said arranging step includes the step of positioning each of said auxiliary antenna elements on a respective one of a plurality of imaginary concentric circles centered about said reference element.

25. The method of claim 21, wherein said arranging step includes the step of positioning each of said auxiliary antenna elements on an imaginary circle centered about said reference element.

26. The method of claim 25, wherein said plurality of auxiliary antenna elements is three auxiliary antenna elements and said positioning step includes the steps of spacing each of said auxiliary antenna elements substantially 120°

apart.

27. The GPS antenna system of claim 21, wherein said antenna array is a planar array.

28. The GPS antenna system of claim 21, wherein said antenna array is a three-dimensional array.

29. The method of claim 21, further including the step of establishing a threshold signal level and wherein said adjusting step includes the step of reducing the amplitude of said combined signal below said threshold signal level.