Sensor system

• US 6,542,121 B1
• Filed: 12/17/2001
• Issued: 04/01/2003
• Est. Priority Date: 03/03/1999
• Status: Expired due to Term

• Current Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Beale, Dean A R, Blake, Alan P, Slade, Ian R, Trafford, Keith
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/914,727
• Time in Patent Office: 470 Days
• Field of Search: 342/357.01, 342/357.06, 342/442, 342/457, 342/444, 701/213, 701/215
• US Class Current: 342/442
• CPC Class Codes: G01S 1/045 Receivers
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G01S 19/43 using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry
• CPC Class Codes: G01S 5/0278 involving statistical or probabilistic considerations G01S5/0252, G01S5/0294 take precedence
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence

Abstract

A sensor system (10) for locating transmitters incorporates three vehicle-mounted patch antennas (30 to 34), a signal processing unit (40), a navigation unit (50) and a computer (60). The navigation unit (50) measures sensor system position using the Global Positioning System. The antennas (30 to 34) receive radiation from a transmitter (210) to be located and respond by generating output signals which are frequency downconverted and processing coherently by a digital signal processing unit (230). This produces elevation and azimuth phase data for the computer (60), which determines measured phase differences. The computer (60) also calculates expected phase differences from antenna positions and trial transmitter positions. It determines transmitter location from correlation between measured and expected phase differences. The position of a transmitter (210) is determined for a number of sensor system positions.

Claims

1. A sensor system for transmitter location incorporating:

a) two receiver elements (30, 34) responsive to incident radiation by generation of respective signals,

b) a processing system (40) for determining phase difference data for pairs of element signals,

c) means (50) for measuring sensor system position in terms of position data;

d) computer apparatus (60) for determining transmitter position from phase difference data measured from processed element signals and calculated from trial transmitter locations,

characterised in that the computer apparatus (60) is arranged to locate transmitters from magnitude or phase of circular functions of differentials between measured and calculated phase difference data.

2. A sensor system according to claim 1 characterised in that the processing system (40) is arranged to process a pair of element signals or a pair of frequency downconverted signals equivalent thereto by multiplying one signal of each pair in either case by a complex conjugate of the other to enable their phase difference to be measured.

3. A sensor system according to claim 2 characterised in that the processing system (40) is arranged to determine phase difference by:

a) mixing each signal of a pair with sine and cosine reference signals to determine in-phase and quadrature components,

b) multiplying each component of one signal by both components of the other to produce an in-phase component product, a quadrature component product and two products of in-phase and quadrature components,

c) adding the in-phase component product to the quadrature component product, and

d) subtracting one product of in-phase and quadrature components from the other.

4. A sensor system according to claim 3 characterised in that the processing system (40) is arranged to digitise signals at a sampling rate prior to mixing with reference signals, the reference signals have a frequency of one quarter of the sampling rate, and mixing is implemented by multiplication of alternate samples by 0 and one other sample in four by −

1.

5. A sensor system according to claim 1 characterised in that the circular functions are complex exponents.

6. A sensor system according to claim 5 characterised in that the computer apparatus (60) is arranged to determine actual transmitter location by summing exponents over a range of system positions and to indicate transmitter location from the magnitude or phase of this summation.

7. A sensor system according to claim 5 characterised in that the computer apparatus (60) is arranged to determine actual transmitter location by producing summations of exponents over a range of system positions, to multiply the summations together to form a product and to indicate transmitter location as that corresponding to a predetermined magnitude or phase of this product.

8. A sensor system according to claim 1 characterised in that the measuring means comprises a GPS base station (160) and co-located with the receiver elements a GPS subsidiary station (50) for co-operation with the base station (160) and provision of position data.

9. A sensor system according to claim 8 characterised in that:

a) it is movable relative to a transmitter (210) to be located,

b) the base and subsidiary GPS stations (50, 160) are arranged to provide position data,

c) the computer apparatus (60) is arranged to subtract calculated phase differences from those of processed element signals for a series of sensor system positions.

10. A sensor system according to claim 1 characterised in that the measuring means (50) is arranged to implement inertial navigation.

11. A sensor system according to claim 1 characterised in that it incorporates at least three receiver elements (30, 32, 34) disposed to define a plurality of measurement dimensions in which to locate a transmitter (210).

12. A system according to claim 1 characterised in that the receiver elements are patch antennas (30, 32, 34).

13. A method of locating a transmitter having the steps of:

a) providing two receiver elements (30, 34) responsive to incident radiation by generation of respective signals,

b) determining phase difference data for pairs of element signals,

c) measuring sensor system position in terms of position data;

d) determining transmitter position from phase difference data measured from processed element signals and calculated from trial transmitter locations,

characterised in that transmitter position is determined from magnitude or phase of at least one circular function of a differential between measured and calculated phase difference data.

14. A method according to claim 13 characterised in that determining phase difference data for pairs of element signals is carried out by multiplying one signal of each pair in either case by a complex conjugate of the other to enable their phase difference to be measured.

15. A method according to claim 14 characterised in that determining phase difference data is carried out by:

a) mixing each signal of a pair with sine and cosine reference signals to determine in-phase and quadrature components,

b) multiplying each component of one signal by both components of the other to produce an in-phase component product, a quadrature component product and two products of in-phase and quadrature components,

c) adding the in-phase component product to the quadrature component product, and

d) subtracting one product of in-phase and quadrature components from the other.

16. A method according to claim 15 characterised in that signals are digitised during processing at a sampling rate prior to mixing with reference signals, the reference signals have a frequency of one quarter of the sampling rate, and mixing is implemented by multiplication of alternate samples by 0 and one other sample in four by −

1.

17. A method according to claim 13 characterised in that calculated phase differences are produced for a plurality of possible transmitter locations and actual transmitter location is determined from correlation between calculated and measured phase differences.

18. A method according to claim 13 characterised in that the at least one circular function is at least one complex exponent.

19. A method according to claim 18 characterised in that the at least one complex exponent is a plurality of complex exponents, actual transmitter location is determined by producing a summation of exponents over a range of system positions and indicating transmitter location to be that corresponding to a predetermined magnitude or phase of this summation.

20. A method according to claim 18 characterised in that the at least one complex exponent is a plurality of complex exponents, actual transmitter location is determined by producing a plurality of summations of exponents over a range of system positions and corresponding to respective dimensions of transmitter location, multiplying the summations together to form a product and indicating transmitter location to be that corresponding to a predetermined magnitude or phase of this product.

21. A method according to claim 13 characterised in that position data is provided by means of a GPS base station (160) co-operating with a GPS subsidiary station (50) co-located with the receiver elements.

22. A method according to claim 20 characterised in that:

a) the receiver elements (30, 32, 34) are movable relative to a transmitter (210) to be located,

b) position data are provided by base and subsidiary GPS stations (50, 160),

c) calculated phase differences are subtracted from those of processed element signals for a series of sensor system positions.

23. A method according to claim 13 characterised in that position data are obtained using inertial navigation.

24. A method according to claim 13 characterised in that it employs at least three receiver elements (30, 32, 34) disposed to define a plurality of measurement dimensions in which to locate a transmitter (210).

25. A method according to claim 13 characterised in that the receiver elements (30, 32, 34) are patch antennas.