Methods and apparatus for obtaining positional information

• US 20030151541A1
• Filed: 01/24/2003
• Published: 08/14/2003
• Est. Priority Date: 02/08/2000
• Status: Active Grant

• Current Assignee: Aveillant Limited (Thales SA)
• Original Assignee: Cambridge Solutions Limited (DXC Technology Company)
• Inventors: Oswald, Gordon Kenneth Andrew, Toutoungi, Danielle Emma, Burchett, Michael Hugh, Clouston, Eric Nicol, Richardson, Alan Trevor
• Granted Patent: US 7,068,211 B2
• Time in Patent Office: Days
• US Class Current: 342/70
• CPC Class Codes: B60R 21/0134 responsive to imminent contact with an obstacle , e.g. using radar systems
• CPC Class Codes: B60R 21/01538 for image processing, e.g. cameras or sensor arrays
• CPC Class Codes: G01S 13/4454 phase comparisons monopulse, i.e. comparing the echo signals received by an interferometric antenna arrangement
• CPC Class Codes: G01S 13/46 Indirect determination of position data
• CPC Class Codes: G01S 13/888 through wall detection
• CPC Class Codes: G01S 13/931 of land vehicles
• CPC Class Codes: G01S 2013/468 by Triangulation, i.e. two antennas or two sensors determine separately the bearing, direction or angle to a target, whereby with the knowledge of the baseline length, the position data of the target is determined
• CPC Class Codes: G01S 2013/932 using own vehicle data, e.g. ground speed, steering wheel direction
• CPC Class Codes: G01S 2013/9322 using additional data, e.g. driver condition, road state or weather data
• CPC Class Codes: G01S 2013/9324 Alternative operation using ultrasonic waves
• CPC Class Codes: G01S 2013/93275 in the bumper area
• CPC Class Codes: G01S 2015/939 vertical stacking of sensors, e.g. to enable obstacle height determination
• CPC Class Codes: H01Q 1/3233 particular used as part of a sensor or in a security system, e.g. for automotive radar, navigation systems
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 21/065 Patch antenna array
• CPC Class Codes: H01Q 9/28 Conical, cylindrical, cage, strip, gauze, or like elements having an extended radiating surface; Elements comprising two conical surfaces having collinear axes and adjacent apices and fed by two-conductor transmission lines waveguide horns or mouths H01Q13/00; slot antennas H01Q13/00

Abstract

Apparatus for and methods of obtaining positional information about one or more objects in a detection field are disclosed. An array including a transmitting element and a plurality of receiving elements is provided. In one aspect a truncated cross-correlation function is applied to determine the interval between signals received by a plurality of the receiving elements, thereby to determine an angular position of an object. In another aspect a warning zone is defined and it is determined whether an object is within the warning zone. Also disclosed are techniques for stretching received signals, and techniques for obtaining positional information relating to an object using non-Doppler radar. Various implementations, modifications and applications of the techniques described are disclosed. Typical applications of the techniques described are with vehicles.

Claims

1. Apparatus for obtaining positional information relating to an object, the apparatus comprising:

an array comprising a transmitting element and a plurality of receiving elements;

a signal generating stage for applying a series of pulses to the transmitting element to cause it to transmit a signal, such that at least a portion of the signal can be reflected from the object to be received by the receiving elements;

a detection stage for detecting signals reflected to the receiving elements and for generating output signals representative of the received signals; and

a processing stage operable by application of a truncated cross-correlation function to detect the interval between signals received by a plurality of the receiving elements, whereby to determine an angular position of an object from which the transmitted signal has been reflected.

2. Apparatus according to claim 1 in which the truncated cross-correlation function is operable to shift one output signal with respect to another over a range which is less than the duration of the signals, and preferably less than the duration of a pulse.

3. Apparatus according to claim 1 or claim 2 in which the truncated cross-correlation function is operable to shift one output signal with respect to another over a range in which the maximum offset in either direction is less than 5 times the time that would be taken for the transmitted signal to travel directly from one receiving element to another, and preferably less than or equal to 3, 2 or 1 times this value.

4. Apparatus according to any of the preceding claims in which the signal has a characteristic wavelength λ

and the truncated cross-correlation function has an interval of correlation which is a small multiple of λ

.

6. Apparatus according to any preceding claim in which the receiving elements are spaced apart by a distance D and the truncated cross-correlation function has an interval that is less than a small multiple of D.

7. Apparatus according to claim 6 in which the interval of correlation is less than 5, 2, 1.5 or 1D, or, where the detection field of at least one element is less than 180 degrees, it may be 0.9D, 0.8D or 0.7D.

8. Apparatus according to any preceding claim in which the processing stage is operative to determine the distance from the array of an object from which a signal has been reflected.

9. Apparatus according to any preceding claim in which the processing stage is operative to identify a maximum value of the cross correlation function.

10. Apparatus for obtaining positional information relating to an object, preferably according to any preceding claim, in which the processing stage is operable to detect the interval between a signal being received by a first set of any two or more of the receiving elements and to determine a first angular position of an object from which the transmitted signal has been reflected;

and to determine the interval between a signal being received by a second set of any two or more of the receiving elements and to determine a second angular position of an object from which the transmitted signal has been reflected;

the processing stage being operable by application of a truncated cross-correlation function.

11. Apparatus according to claim 10 in which the first and second angular positions are measured in planes that are substantially not parallel to one another.

12. Apparatus according to claim 11 in which the said planes are approximately normal to one another.

13. Apparatus according to any preceding claim in which the processing stage is operative to determine the distance from the array of an object from which a signal has been reflected.

14. Apparatus according to claim 13 in which the processing stage is operable to determine a coordinate in three-dimensional space of an object from which the transmitted signal has been reflected.

15. Apparatus according to any one of claims 10 to 14 in which at least one of the first and second set of receiving elements includes three or more elements which are disposed such that the spacings between elements of at least two pairs of elements included in that set are unequal.

16. Apparatus according to claim 12 in which the spacing (D) between the elements of one pair is approximately equal to (for example between 50% and 200% or between 75 and 150% of) a characteristic wavelength λ

of the signal, and preferably the spacing between a second pair of elements is approximately equal to 3λ

/4, or 3 D/4, and preferably the ratio of the spacing of the elements in one of the first and second pairs to the spacing of the elements in the other of the first and second pairs is between 0.5 and 1 or 0.75 and 0.9.

17. Apparatus according to claim 10 or 16 in which the processing stage is operative to perform a truncated cross-correlation between the signals received by each pair of elements and to determine the product or otherwise compare of the result of the cross-correlations.

18. Apparatus according to any preceding claim further comprising an output stage operative to generate an output for presentation of positional information relating to the object to a user.

19. Apparatus according to claim 18 in which the output includes at least one of an audible and a visual signal.

20. Apparatus for obtaining positional information relating to an object, optionally in accordance with any preceding claim, the apparatus comprising:

a warning zone definition stage for defining a warning zone (in two or three dimensions) within a detection field of the apparatus; and

a discrimination stage for determining whether a detected object is within the warning zone;

in which the warning zone is defmed as a three-dimensional region within the detection field.

21. Apparatus according to claim 20 in which the warning zone is contained within and is smaller than the detection field of the apparatus.

22. Apparatus according to claim 20 or claim 21 in which the shape of the warning zone is dissimilar from the shape of the detection field of the apparatus.

23. Apparatus according to any one of claims 20 to 22 in which the shape of the warning zone is non-circular or non-spherical.

24. Apparatus according to claim any one of claims 20 to 23 in which the warning zone definition stage includes an algorithm that defines a warning zone as a function of a coordinate within the detection field.

25. Apparatus according to any one of claims 20 to 24 further comprising an object location stage for determining the position of a detected object within the detection field of the apparatus.

26. Apparatus according to any one of claims 20 to 25 in which the discrimination stage includes a coordinate generating stage for generating a coordinate of a detected object, which coordinate is then compared with the warning zone.

27. Apparatus according to claims 20 to 24 in which the discrimination stage is operable to determine the coordinates of the detected object and compare the determined coordinates with the coordinates of the warning zone to determine whether the object is within the warning zone.

28. Apparatus according to any one of claims 20 to 27 in which the warning zone definition stage defines at least a limiting value of one or more ordinates of a coordinate within the detection field.

29. Apparatus according to claim 28 in which the warning zone definition stage defines at least a limiting value of one or more angles of a polar coordinate within the detection field.

30. Apparatus according to claim 29 in which the warning zone definition stage defines at least a limiting value of a range of a polar coordinate within the detection field.

31. Apparatus according to any one of claims 20 to 30 in which the warning zone includes a plurality of discontinuous spatial regions.

32. Apparatus according to any one of claims 20 to 31 in which the discrimination stage is operative to generate an output signal indicative that the object is within the warning zone.

33. Apparatus according to any one of claims 20 to 32 further operative to issue a warning, for example at least one of an audible, a visual and a tactile warning to a user upon detection of an object in the warning zone.

34. Apparatus according to any one of claims 20 to 33 in which the warning zone definition stage defines a plurality of non-coextensive warning zones, and preferably in which the discrimination stage is operative to generate an output signal indicative of which of the plurality of warning zones contains the object.

35. Apparatus according to claim 34 in which the discrimination stage is operable to apply different logic to at least two of the zones.

36. Apparatus according to anyone of claims 20 to 35 in which the warning zone is limited in range and/or is approximately cuboid.

37. Apparatus according to any of claims 20 to 36 in which the discrimination stage is operative to analyse a characteristic of an object outside of the warning zone.

38. Apparatus according to claim 37 in which the discrimination stage is operative to track an object outside the warning zone and to predict its entry into the warning zone.

39. Apparatus according to any one of claims 20 to 38 for use on a vehicle, and optionally including the vehicle.

40. Apparatus according to claim 39 in which at least one of the shape and a relevant dimension of a warning zone is at least in part determined by a corresponding shape and dimension of the vehicle.

41. Apparatus according to claim 40 in which a warning zone has a width that is equal to the width of the vehicle plus a predetermined amount.

42. Apparatus according to claim 41 in which the predetermined amount is less than the width of the vehicle.

43. Apparatus according to any one of claims 39 to 42 in which the warning zone has a height that is equal to the height of the vehicle plus a predetermined amount.

44. Apparatus according to claim 43 in which the predetermined amount is less than the height of the vehicle.

45. Apparatus according to any one of claims 39 to 44 in which the warning zone has a lower surface that is substantially planar and spaced above a road surface upon which the vehicle is supported.

46. Apparatus according to any one of claims 39 to 45 in which at least one of the shape and a relevant dimension of the warning zone is changed in response to vehicle operating conditions.

47. Apparatus according to claim 46 in which the vehicle operating conditions include at least one of speed, direction of travel, and ambient environmental conditions.

48. Apparatus according to any preceding claim operative to transmit an electromagnetic signal.

49. Apparatus according to claim 48 in which the electromagnetic signal is microwave radiation.

50. Apparatus according to claim 49 in which the transmitted signal has a frequency of between 0.5 and 77 GHz.

51. Apparatus according to claim 50 in which the transmitted signal has a frequency of between 2 and 25 GHz.

52. Apparatus according to claim 51 in which the transmitted signal has a frequency of approximately one of 0.5 GHz, 1 GHz, 6 GHz, 10 GHz or 2-2.5 GHz.

53. Apparatus according to claim 52 in which the signal is approximately 2.45 GHz.

54. Apparatus according to any one of claims 48 to 53 in which the transmitted signal has a relative bandwidth with respect to the centre frequency of between 3 and 33%.

55. Apparatus according to claim 54 in which the transmitted signal has a relative bandwidth with respect to the centre frequency of between 5 and 25%.

56. Apparatus according to claim 55 in which the transmitted signal has a relative bandwidth with respect to the centre frequency of between 10 and 20%.

57. Apparatus according to claim 56 in which the transmitted signal has a relative bandwidth with respect to the centre frequency of approximately 15%.

58. Apparatus for obtaining positional information relating to an object according to any preceding claim, which is operative to transmit a signal into a detection field and to detect a signal reflected from an object in the detection field, in which the spatial length of the transmitted signal during its propagation is approximately the same as a dimension of the smallest objects that the apparatus is intended to resolve.

59. Apparatus for obtaining positional information relating to an object according to claim 58 in which the spatial length of the transmitted signal during its propagation is between 50 and 200% of the smallest objects that the apparatus is intended to resolve.

60. Apparatus for obtaining positional information relating to an object according to claim 58 in which the spatial length of the transmitted signal during its propagation is between 75 and 150% of the smallest objects that the apparatus is intended to resolve.

61. Apparatus according to any preceding claim in which the spatial length of the transmitted signal during its propagation is, in order of magnitude, not greater than 1.0 m, or preferably not greater than 0.3 m, 0.1 m, 0.03 m, or even 0.01 m.

62. Apparatus according to claim 48 or claim 49 in which the spatial length of the transmitted signal during its propagation is less than 10 wavelengths, or preferably less than 6, 5, 3, 2 or even 1 wavelengths.

63. Apparatus according to any preceding claim in which the signal is received at the apparatus at receiving elements spaced by a distance being of the same order of magnitude as a characteristic wavelength λ

of the signal.

64. Apparatus according to claim 63 in which the receiving elements are spaced apart by a distance nλ

where 0.5≦

n≦

10, preferably 1≦

n≦

5.

65. Apparatus according to any preceding claim, in which:

the signal generating stage applies a series of m pulses to the transmitting element to cause it to transmit a signal, at times t_n where n=1, 2 . . . m, such that at least a portion of the signal can be reflected from the object to be received by the receiving elements;

the detection stage detects a signal reflected to the receiving elements at times r_n and generates an output signal representative of the received signal;

wherein the value of r_n−

t_n varies as some function of n.

66. Apparatus according to claim 65 in which the value of r_n−

t_n changes linearly with n.

67. Apparatus according to claim 64 in which successive outputs of the detection stage are stored in a storage means, the storage means being operable to output a signal of substantially the same shape as the received signal, but with a duration that is increased in time.

68. Apparatus according to any preceding claim including a sampling stage operative under the control of a timing stage selectively to pass or to interrupt the passage of signals from the receiving elements to the detection stage.

69. Apparatus according to claim 68 in which, upon activation by the timing stage, the sampling stage passes signals to the detection stage for an aperture time ta.

70. Apparatus according to claim 69 comprising a respective sampling stage for each receiving element.

71. Apparatus according to claim 70 in which each sampling stage is connected to the timing stage by a respective signal delay line, within which delay line a signal is delayed by a time not less than t_a/2.

72. Apparatus for obtaining positional information relating to an object according to any preceding claim, contained within a single housing.

73. Apparatus according to claim 72 that is hand-holdable in use.

74. Apparatus according to claim 73 intended to provide information about the location of objects within or behind a wall.

75. Apparatus according to any preceding claim comprising an antenna array and processing means constructed as a single assembly.

76. Apparatus according to claim 75 in which the processing means operates to provide all functional electrical signals to and receive all functional electrical signals from the array.

77. Apparatus according to any one of claims 1 to 76 for use in a vehicle.

78. Apparatus for a land vehicle for obtaining positional information relating to an object, according to any preceding claim, comprising:

means for transmitting a probe signal towards the object;

means for receiving, at a plurality of spaced apart locations, the probe signal as returned by the object; and

detecting means, coupled to the receiving means, for detecting the relative timing of the returned probe signals as received at the plurality of locations;

whereby the positional information for the object can be determined from said relative timing.

80. Apparatus for obtaining positional information relating to an object, for use on a vehicle, optionally in accordance with any preceding claim, for resolving the angular position of an object using non-Doppler radar.

81. Apparatus optionally according to any preceding claim, for use on a vehicle, for obtaining positional information relating to an object external of or internal to the vehicle, the apparatus being operative to generate 3-dimensional positional data for the object.

82. Apparatus according to any one of claims 77 to 81 in which the apparatus has a detection field within a passenger compartment of the vehicle.

83. Apparatus according to any one of claims 77 to 82 in which the positional data includes at least one of the range, azimuth and elevation of the object.

84. Apparatus according to any one of claims 77 to 83 in which the antenna array is carried on a fixed location on the vehicle.

85. Apparatus according to any one of claims 77 to 84 in which the antenna array is located within a component of the vehicle, preferably a non-metallic component.

86. Apparatus according to any one of claims 77 to 85 in which the antenna array is located within a bumper of the vehicle.

87. Apparatus according to any one of claims 77 to 86 in which the antenna array is located within a non-metallic bumper.

88. Apparatus according to any one of claims 77 to 87 further comprising alerting apparatus for alerting a vehicle driver to the presence of a detected object.

89. Apparatus according to claim 88 in which the alerting apparatus is operative to generate an audible warning.

90. Apparatus according to claim 89 in which the audible warning includes a verbal warning.

91. Apparatus according to any one of claims 88 to 90 in which the alerting apparatus is operative to generate a visual warning.

92. Apparatus according to claim 91 in which the visual warning includes a visible representation of the position of an object detected by the apparatus.

93. Apparatus according to claim 92 further comprising a display upon which is presented a visual representation of a detection field of the apparatus and an object within the detection field.

94. Apparatus for obtaining positional information relating to an object, for use on a vehicle, optionally in accordance with any preceding claim, using preferably non-Doppler radar and being operative to determine a radar cross-section of an object.

95. Apparatus for obtaining positional information relating to an object, for use on a land vehicle optionally in accordance with any preceding claim, including a transmitting element for transmitting radiation into a detection field, a receiving element for receiving radiation reflected from an object in the detection field, and a processing stage, which is operative to analyse the signals from the receiving element to derive qualitative information relating to the object.

96. Apparatus according to claim 95 in which the processing stage is operative to compare information relating to an object at successive different angular positions against a look-up table.

97. Apparatus according to claim 95 or 96 in which the processing stage is operative to determine a radar cross-section of the object.

98. Apparatus according to claim 97 in which the processing stage is operative to compare the radar cross section with a threshold value of radar cross-section and to generate a warning signal in dependence upon the result of the comparison.

99. Apparatus according to any one of claims 95 to 98 in which the processing stage is operative to determine an evolution of angular position of the object.

100. Apparatus according to any of one claims 95 to 99 in which the processing stage is operative to predict a path of movement of the object.

102. A vehicle equipped with apparatus according to any preceding claim.

103. A motor road vehicle being equipped with a driver warning system, which system comprises apparatus according to any one of claims 1 to 100 for obtaining positional information relating to an object external of the vehicle, the apparatus being operative to generate 3-dimensional positional data for the object.

104. A road vehicle according to claim 103 in which the array of the apparatus is contained within a non-metallic bumper of the vehicle.

105. A road vehicle according to claim 104 comprising a display instrument operative to process information obtained by the apparatus and to generate a display therefrom for an operator of the vehicle.

106. A control system for air bags in a motor road vehicle, the control system comprising apparatus according to any one of claims 1 to 100 in which the apparatus has a detection field within a passenger compartment of the vehicle, and in which the processing stage is operational to determine the occupancy of a seat equipped with a passenger air bag, and to suppress deployment of the bag in dependence on the occupancy of the seat, for example, if the seat is unoccupied, the occupant is too close to the air bag, or if the occupant is determined to have violated a substantially planar surface or a substantially cuboid volume.

107. A device for obtaining information about objects within or behind a wall comprising a apparatus according to any one of claims 1 to 100.

108. A hand-held tool incorporating apparatus according to any one of claims 1 to 100.

110. An electromagnetic (optionally microwave) antenna array optionally for use in apparatus for obtaining positional information relating to an object in accordance with any one of claims 1 to 100, the array including a transmitting element and a plurality of receiving elements, the transmitting and receiving elements being disposed on a common substrate.

125. An electromagnetic antenna array according to any one of claims 109 to 124 for use in apparatus according to any one of claims 1 to 100.

126. An electromagnetic antenna array optionally in accordance with any one of claims 109 to 125, for use in apparatus for obtaining positional information relating to an object, which apparatus may be in accordance with any preceding claim, the array including a transmitting element and a plurality of receiving elements, in which the spacing of two pairs of the receiving elements in a common direction is unequal.

128. Apparatus for generating an image of objects within or through a solid object according to any one of claims 1 to 101.

129. Apparatus according to claim 128 in which the solid object is a wall.

130. Apparatus according to any one of claims 1 to 101 for providing an image of an environment in conditions that human vision is compromised.

131. Apparatus according to claim 130 in which vision is compromised by the physiological condition of a user.

132. Apparatus according to claim 130 or claim 131 in which vision is compromised by environmental conditions.

133. A method for obtaining positional information relating to an object, optionally in apparatus in accordance with any one of claims 1 to 100, comprising:

applying a series of pulses to a transmitting element of an (optionally fixed) array to cause it to transmit a signal, such that at least a portion of the signal is reflected from the object to be received by the receiving elements;

detecting signals reflected to receiving elements of the array and generating output signals representative of the received signals; and

applying a truncated cross-correlation function to the output signals to detect the interval between signals received by a plurality of the receiving elements, whereby to determine an angular position of an object from which the transmitted signal has been reflected.

134. A method according to claim 133 in which the truncated cross-correlation function comprises shifting one output signal with respect to another over a range which is less than the duration of the signals, and preferably less than the duration of a pulse.

135. A method according to claim 133 or 134 in which the truncated cross-correlation function comprises shifting one output signal with respect to another over a range in which the maximum offset in either direction is less than 5 times the time that would be taken for the transmitted signal to travel directly from one receiving element to another, and preferably less than or equal to 3, 2 or 1 times this value.

143. A method according to any one of claims 133 to 142 including the steps of:

determining the interval between a signal being received by a first set of any two or more of the receiving elements;

calculating a first angular position of an object from which the transmitted signal has been reflected;

determining the interval between a signal being received by a second set of any two or more of the receiving elements; and

calculating a second angular position of an object from which the transmitted signal has been reflected.

144. A method according to claim 143 in which the first and second angular positions are measured in planes that are substantially not parallel to one another.

145. A method according to claim 144 in which the said planes are approximately normal to one another.

146. A method according to claim 145 including determining a coordinate in three-dimensional space of an object from which the transmitted signal has been reflected.

147. A method according to any one of claims 143 to 146 in which at least one of the first and second set of receiving elements includes three or more elements which are disposed such that that set includes at least two pairs of elements, the spacing of elements in the two pairs being unequal.

148. A method according to claim 147 in which the spacing (D) between the elements of one pair is approximately equal to (for example between 50% and 200% or between 75 and 150% of) a characteristic wavelength λ

of the signal, and preferably the spacing between a second pair of elements is approximately equal to 3λ

/4, or 3 D/4, and preferably the ratio of the spacing of the elements in one of the first and second pairs to the spacing of the elements in the other of the first and second pairs is between 0.5 and 1 or 0.75 and 0.9.

149. A method according to claim 147 or 148 in which the truncated cross-correlation is performed between the signals received by each pair of elements and the product or another comparison of the result of the cross-correlations is determined.

225. A method of obtaining positional information relating to an object in apparatus in accordance with any one of claims 1 to 100, the method comprising an operating cycle having m steps in which n=1, . . . m, each step comprising:

(a) generating a signal at a given timing relationship with respect to a transmitting trigger instant t_n and transmitting it into a detection field; and

(b) receiving at a given timing relationship with respect to a receiving trigger instant r_n at least a portion of the signal reflected from the object;

wherein the interval r_n−

t_n varies as a function of n.

226. A method according to claim 225 in which the method further comprises:

c) providing at least two spaced receiving elements and identifying the values of n at which signals reflected from the object are received by the receiving elements.

227. A method according to claim 226 including in step c) a comparison of the amplitude of signals received by various of the receiving elements.

228. A method according to any one of claims 225 to 227 in which step c) includes comparison of characteristic features of the received signals, such features including at least one of zero-crossings, maxima and minima.

229. A method according to any one of claims 225 to 228 in which a truncated correlation is carried out in step c), and in which the correlation coefficient is approximately a cosinusoidal function of each offset angle (θ

-θ

₀), where θ

₀ is the angle offset of the object in the plane containing the relevant antenna pair in which the correlation coefficients are determined at a small sample of angles, separated by less than half the sinusoidal wavelength, to estimate the direction of the maximum, followed by further samples close to that direction to refine the estimate.

230. A method according to any one of claims 225 to 229 including a step of selecting reflections denoted by correlation maxima which exceed a predetermined signal threshold, and dividing each such correlation maximum by the gain of the transmitting and receiving antennas in the measured direction.

231. A method according to claim 230 in which each such correlation maximum is multiplied by the fourth power of the measured range, to obtain a value proportional to the radar cross-section of the object.

232. A method according to claim 231 in which the said value is compared to a cross-section threshold such that objects whose cross-section exceeds such threshold are subjected to further processing.

233. A method according to any one of claims 225 to 232 in which the range of values of r_n−

t_n for 1≦

n≦

m cover a range of time within which it is expected that a signal reflected from the object will be received.

241. An antenna array optionally for use in apparatus for obtaining positional information relating to an object in accordance with any one of claims 1 to 100, the array including a transmitting element and a plurality of receiving elements, the transmitting and receiving elements being disposed on a common substrate.

5. Apparatus according to claim 5 in which the interval of correlation is less than 10, 5, or 2λ

, or 1λ

.

79. Apparatus for obtaining positional information relating to an object, comprising:

a transmitting stage for transmitting a probe signal towards the object, the transmitting stage comprising;

a signal generating stage; and

at least one transmitting element;

a receiving stage for receiving, at a plurality of spaced apart locations, the probe signal as returned by the object, the receiving stage comprising;

at least one receiving element at the plurality of spaced apart locations; and

a detecting stage for detecting the relative timing of the returned probe signals as received at the plurality of locations, the detecting stage comprising;

a detection stage, coupled to the receiving stage;

whereby positional information for the object can be determined from the relative timing; and

wherein;

the signal generating stage applies a series of m pulses to the transmitting element to cause it to transmit a signal, at times t_n where n=1, 2 . . . m, such that at least a portion of the signal can be reflected from the object to be received by the receiving elements;

the detection stage detects a signal reflected to the receiving elements at times r_n and generates an output signal representative of the received signal; and

wherein the value of r_n−

t_n varies as some function of n.

101. Apparatus for obtaining positional information relating to an object substantially as herein described with reference to the accompanying drawings.

109. Apparatus for obtaining positional information relating to an object, comprising:

means for transmitting a probe signal towards the object, said transmitting means comprising a transmitting element;

means for receiving, at a plurality of spaced apart locations, the probe signal as returned by the object, said receiving means comprising a plurality of receiving elements; and

detecting means, coupled to the receiving means, for detecting the relative timing of the returned probe signals as received at the plurality of spaced apart locations;

whereby the positional information for the object can be determined from said relative timing; and

wherein the transmitting element and receiving elements are disposed on a common substrate.

111. An electromagnetic antenna array according to claim 109 or 110 including a single transmitting element.

112. An electromagnetic antenna array according to any one of claims 109 or 111 including three receiving elements arranged non-collinearly.

114. An electromagnetic antenna array according to claims 112 or 113 in which the receiving elements are arranged substantially at the vertices of a right-angled triangular locus.

115. An electromagnetic antenna array according to any one of claims 109 to 114 in which the receiving elements are spaced apart by a distance that is the same order of magnitude as the wavelength λ

of the radiation that it is intended to transmit and receive.

116. An electromagnetic antenna array according to claim 115 in which the receiving elements are spaced apart by a distance mλ

where m is less than 10, and preferably less than 8, 5, 3, or 2, and m is greater than 0.1 and preferably greater than 0.2, 0.3 or 0.5.

117. An electromagnetic antenna array according to claim 115 or 116 including four receiving elements arranged non-collinearly.

118. An electromagnetic antenna array according to any one of claims 115 to 117 including at least three receiving elements arranged non-collinearly such that there is an axis about which the array is asymmetrical.

120. An electromagnetic antenna array according to any of claims 109 to 119 in which the receiving elements are arranged substantially at the vertices of a quadrilateral.

121. An electromagnetic antenna array according to any of claims 109 to 120 in which the receiving elements are arranged substantially at the vertices of a trapezial locus.

122. An electromagnetic antenna array according to any of claims 109 to 121 in which the trapezial locus is rectangular.

123. An electromagnetic antenna array according to any of claims 109 to 121 in which the trapezial locus has long and short parallel sides and preferably the short side is between 0.5 and 1 times the length of the long side, or in which the quadrilateral has two opposing angles which are substantially right angles, the other two angles not being right angles.

124. An electromagnetic antenna array according to any of claims 109 to 122 in which the trapezial locus has long and short parallel sides, the length of the shorter side being approximately the wavelength λ

of the radiation that the array is intended to transmit and receive, and the length of the longer side is approximately 3λ

/2.

113. An electromagnetic antenna array optionally for use in apparatus for obtaining positional information relating to an object, the array including a transmitting element and at least three receiving elements arranged non-collinearly, the transmitting and receiving elements being disposed on a common substrate.

119. An electromagnetic antenna array including at least three receiving elements arranged non-collinearly such that there is an axis about which the array is asymmetrical.

127. Apparatus for obtaining positional information relating to one or more objects, the apparatus being operative in an operating cycle for each of m steps in which n=1, 2 . . . m, the apparatus including:

a signal generating stage operative, simultaneously with or at a fixed time after a transmitting trigger instant t_n to generate a signal, and a transmitting element to transmit said signal into a detection field;

a plurality of spaced receiving elements operative simultaneously with or at a fixed time after a receiving trigger instant r_n to receive a portion of the signal reflected from one or more objects in the detection field, the interval r_n−

t_n varying as a function of n and having a magnitude in a range corresponding to the times of travel of a signal reflected from an object within the detection field;

means for identifying the values of n at which signals reflected from one object are received at two or more receiving elements and thereby detecting the time taken, and therefore the distance travelled, by the signals from the transmitting element to the various receiving elements; and

means for calculating the position of the object from the various path lengths thereby identified.

136. A method according to any of the preceding method claims in which the signal has a characteristic wavelength λ

and the truncated cross-correlation function has an interval of correlation which is a small multiple of λ

.

137. A method according to claim 136 in which the interval of correlation is less than 10, 5, or 2λ

, or even λ

.

138. A method according to any of the preceding method claims in which the receiving elements are spaced apart by a distance D and the truncated cross-correlation function has an interval that is less than a small multiple of D.

139. A method according to claim 138 in which the interval of correlation is less than 5, 2, 1.5 or 1D, or, where the detection field of at least one element is less than 180 degrees, it may be 0.9D, 0.8D or 0.7D.

140. A method according to any of the preceding method claims further including determining the distance from the array of an object from which a signal has been reflected.

141. A method according to claim 140 in which determining the distance from the array includes a step of multiplying the time taken for the signal to be received by the speed of propagation of the signal.

142. A method according to any of the preceding method claims in which a maximum value of the cross correlation function is identified.

188. A method for obtaining positional information relating to an object, optionally according to any one of claims 142 to 187 comprising transmitting a signal into a detection field and detecting a signal reflected from an object in the detection field, in which the spatial length of the transmitted signal during its propagation is approximately the same as (say between 50 and 200% or 75 and 150% of) a dimension of the smallest objects that it is intended to resolve.

190. A method according to claim 188 or 189 in which the spatial length of the transmitted signal during its propagation is less than 10 wavelengths, or less than 6, 5, 3, 2 or even 1 wavelengths.

150. A method according to any preceding method claim further comprising generating an output for presentation of positional information relating to the object to a user.

151. A method according to claim 150 in which the output includes at least one of an audible and a visual signal.

152. A method for obtaining positional information relating to an object, optionally in accordance with any preceding method claim, comprising:

defining a warning zone (in two or three dimenstions) within a detection field; and

determining whether a detected object is within the warning zone;

wherein the warning zone is defined as a three-dimensional region within the detection field.

153. A method according to claim 152 in which the warning zone is contained within and is smaller than the detection field.

154. A method according to claim 152 or 153 in which the shape of the warning zone is dissimilar from the shape of the detection field.

155. A method according to any one of claims 152 to 154 in which the warning zone includes a region defined in two dimensions within the detection field, preferably in which the warning zone includes a planar surface within the detection field.

156. A method according to any one of claims 152 to 155 in which the warning zone is defined as a three-dimensional region within the detection field.

157. A method according to any one of claims 152 to 156 in which the warning zone is defined by an algorithm as a function of a coordinate within the detection field.

158. A method according to any one of claims 152 to 157 further including generation of a co-ordinate of a detected object.

159. A method according to claim 158 in which the generated co-ordinates are compared with co-ordinates of the warning zone to determine whether the object is within the warning zone.

160. A method according to any one of claims 152 to 159 in which the warning zone is defined by at least a limiting value of one or more ordinates of a coordinate within the detection field.

161. A method according to claim 160 in which the warning zone is defined by at least a limiting value of one or more angles of a polar coordinate within the detection field.

162. A method according to any one of claims 152 to 161 in which the warning zone is defined by at least a limiting value of a range of a polar coordinate within the detection field.

163. A method according to any one of claims 152 to 162 in which the warning zone includes a plurality of discontinuous spatial regions.

164. A method according to any one of claims 152 to 163 further comprising the step of generating an output signal indicative that the object is within the warning zone.

165. A method according to any one of claims 152 to 164 further comprising the step of issuing a warning to a user upon detection of an object in the warning zone.

166. A method according to any one of claims 152 to 165 in which there is defined a plurality of non-coextensive warning zones

167. A method according to claim 166 which includes a step of generating an output signal indicative of which of the plurality of warning zones contains the object.

168. A method according to claim 166 or claim 167 including a step of applying different logic to at least two of the zones.

169. A method according to any of claims 152 to 168 further comprising the step of analysing a characteristic of an object outside of the warning zone.

170. Apparatus according to claim 169 in which the step of analysing a characteristic comprises tracking an object outside the warning zone and predicting its entry into the warning zone.

171. A method according to any one of claims 152 to 170 further comprising the step of issuing at least one of an audible and a visual warning to a user upon detection of an object in a warning zone.

172. A method according to any one of claims 152 to 171 carried out on a vehicle, in which at least one of the shape and a relevant dimension of a warning zone is at least in part determined by a corresponding shape and dimension of the vehicle.

173. A method according to claim 172 which includes monitoring operating conditions of the vehicle and changing at least one of the shape and a relevant dimension of a warning zone in response to vehicle operating conditions.

174. A method according to claim 173 in which the vehicle operating conditions include at least one of speed, direction of travel, and ambient environmental conditions.

175. A method according to 173 or claim 174 in which the distance to which the warning zone extends in the direction of travel of the vehicle is increased with the speed of the vehicle.

176. A method according to any one of claims 173 to 175 in which the extent to which the warning zone extends to one side of a longitudinal axis of the vehicle is increased in a direction in which the vehicle is turning.

177. A method according to any one of the preceding method claims in which the signal is an electromagnetic signal.

178. A method according to claim 177 in which the electromagnetic signal is microwave radiation.

179. A method according to claim 178 in which the electromagnetic signal has a frequency of between 0.5 and 77 GHz.

180. A method according to claim 179 in which the electromagnetic signal has a frequency of between 2 and 25 GHz.

181. A method according to claim 179 in which the electromagnetic signal has a frequency of approximately one of 0.5 GHz, 1 GHz, 6 GHz, 10 GHz or 2-2.5 GHz.

182. A method according to claim 181 in which the electromagnetic signal has a frequency of approximately 2.45 GHz.

183. A method according to any one of claims 177 to 182 in which the transmitted signal has a relative bandwidth to the centre frequency between 10 and 20%.

184. A method according to claim 183 in which the transmitted signal has a relative bandwidth to the centre frequency between 5 and 25%.

185. A method according to claim 184 in which the transmitted signal has a relative bandwidth to the centre frequency between 3 and 33%.

186. A method according to claim 185 in which the transmitted signal has a relative bandwidth to the centre frequency of approximately 15%.

187. A method according to any one of claims 180 to 186 in which an angular position of an object is resolved with respect to a predetermined datum.

189. A method according to any preceding method claim in which the spatial length of the transmitted signal during its propagation is, in order of magnitude, not greater than 1.0 m, and preferably not greater than 0.3 m, 0.1 m, 0.03 m, or even 0.01 m.

191. A method according to any preceding method claim in which the signal is received at receiving elements spaced by a distance being of the same order of magnitude as a characteristic wavelength λ

of the signal.

192. A method according to claim 191 in which the receiving elements are spaced apart by a distance nλ

where 0.5≦

n≦

10, and preferably 1≦

n≦

5.

193. A method according to any preceding method claim in which

a series of pulses comprises m pulses to cause the transmitting element to transmit a signal, at times t_n where n=1, 2 . . . m;

and

reflected signals are detected by the receiving elements at times r_n;

comprising the steps of

generating an output signal representative of the received signal;

wherein the value of r_n−

t_n varies as some function of n.

194. A method according to claim 193 in which the value of r_n−

t_n changes linearly with n.

195. A method according to claim 193 or 194 further comprising storing values of the output signal corresponding to signals received at times r_n.

196. A method according to claim 195 further comprising outputting a signal of substantially the same shape as the received signal, but with a duration which is increased in time.

197. A method according to any preceding method claim for obtaining positional information relating to an object, performed on a vehicle.

198. A method according to claim 197 for resolving the angular position of an object using non-Doppler radar.

199. A method according to claim 197 or 198 for obtaining positional information relating to an object external of the vehicle, in which 3-dimensional positional data for the object is generated.

200. A method according to any one of claims 197 to 199 for obtaining positional information relating to an object internal to the vehicle, in which 3-dimensional positional data for the object is generated.

201. A method according to any one of claims 197 to 200 in which a detection field is within a passenger compartment of the vehicle.

202. A method according to any one of claims 197 to 201 in which the positional data includes at least one of the range, azimuth and elevation of the object.

203. A method according to any one of claims 197 to 202 which is carried out by apparatus including an antenna array that is carried on a fixed location on the vehicle.

204. A method according to any one of claims 197 to 203 in which the antenna array is located within a non-metallic component of the vehicle.

205. A method according to any one of claims 197 to 204 in which the antenna array is located within a non-metallic bumper of the vehicle.

206. A method according to any one of claims 197 to 205 further comprising a step of alerting a vehicle driver to the presence of a detected object.

207. A method according to claim 206 in which the alerting step includes generating an audible warning.

208. A method according to claim 207 in which the audible warning includes a descriptive verbal warning.

209. A method according to any one of claims 206 to 208 in which the alerting step includes generating a visual warning.

210. A method according to claim 209 in which the visual warning includes an image of the position of a detected object.

211. A method according to claim 209 further comprising a step of presenting a visual representation of a detection field and an object within the detection field.

212. A method for obtaining positional information relating to an object, performed on a vehicle optionally in accordance with any preceding method claim using non-Doppler radar, the method including determining a radar cross-section of an object.

213. A method for obtaining positional information relating to an object, in accordance with any preceding method claim, including transmitting radiation into a detection field, receiving radiation reflected from an object in the detection field, and analysing received signals to derive qualitative information relating to the object.

214. A method according to claim 213 in which a radar cross-section of the object is determined.

215. A method according to claim 213 or 214 in which the radar cross section is compared with a threshold value of radar cross-section and a warning signal is issued in dependence upon the result of the comparison.

216. A method according to any one of claims 213 to 215 in which an evolution of angular position of the object is determined.

217. A method according to any one of claims 213 to 216 in which a path of movement of the object is predicted.

218. A method according to any one of claims 213 to 217 in which in the analysis step the signals are modified to compensate for angular variation in sensitivity of the receiving element.

219. A method according to any one of claims 213 to 218 in which in the analysis step the signals are modified to compensate for the range of the object from which the signals are reflected.

220. A method according to any one of claims 213 to 219 in which the analysis step includes making a comparison between a received signal and a pattern corresponding to a signal from a known class of objects.

221. A method according to claim 220 in which the comparison includes identification of characteristic features of the received signal.

222. A method according to claim 221 in which the characteristic features include at least one of minima, maxima, and zero-crossings.

223. A method for obtaining positional information relating to an object substantially as herein described with reference to the accompanying drawings.

224. A method of controlling deployment of air bags in a vehicle, in which a method according to any preceding method claim is applied to determine the occupancy of a seat equipped with a passenger air bag, and deployment of the bag is suppressed in dependence on the occupancy of the seat, for example, if the seat is unoccupied or the occupant is too close to the air bag.

234. A method according to any one of the preceding method claims for providing an image of an environment in conditions that human vision is compromised.

235. A method according to claim 234 in which vision is compromised by the physiological condition of a user.

236. A method according to claim 234 or claim 235 in which vision is compromised by environmental conditions.

237. A method according to any preceding method claim for imaging within or through a solid object.

238. A method according to claim 237 in which the solid object is a wall.

239. Apparatus for obtaining positional information relating to an object, comprising:

transmitting means for transmitting a probe signal towards the object, the transmitting means comprising;

a signal generating stage; and

at least one transmitting element;

receiving means for receiving, at a plurality of spaced apart locations, the probe signal as returned by the object, the receiving means comprising;

at least one receiving element at the plurality of spaced apart locations; and

detecting means for detecting the relative timing of the returned probe signals as received at the plurality of locations, the detecting means comprising;

a detection stage, coupled to the receiving means,;

whereby positional information for the object can be determined from the relative timing;

and wherein;

the signal generating stage applies a series of m pulses to the transmitting element to cause it to transmit a signal, at times t_n where n=1, 2 . . . m, such that at least a portion of the signal can be reflected from the object to be received by the receiving elements;

the detection stage detects a signal reflected to the receiving elements at times r_n and generates an output signal representative of the received signal; and

wherein the value of r_n−

t_n varies as some function of n.

240. Apparatus for obtaining positional information relating to an object, comprising:

means for transmitting a probe signal towards the object, said transmitting means comprising a transmitting element;

means for receiving, at a plurality of spaced apart locations, the probe signal as returned by the object, said receiving means comprising a plurality of receiving elements; and

detecting means, coupled to the receiving means, for detecting the relative timing of the returned probe signals as received at the plurality of spaced apart locations;

whereby the positional information for the object can be determined from said relative timing; and

wherein the transmitting element and receiving elements are disposed on a common substrate.

242. A vehicle substantially as herein described and with reference to the accompanying drawings

243. A control system for air bags in a motor road vehicle substantially as herein described and with reference to the accompanying drawings.

244. Apparatus for a land vehicle substantially as herein described and with reference to the accompanying drawings.

245. A device for obtaining information about objects within or through a wall substantially as herein described and with reference to the accompanying drawings.

246. A hand-held tool substantially as herein described and with reference to the accompanying drawings.

247. An electromagnetic microwave antenna array substantially as herein described and with reference to the accompanying drawings.

248. Apparatus for generating an image of objects within or through a solid object substantially as herein described and with reference to the accompanying drawings.

249. Apparatus, optionally for use on a (for example, land) vehicle, for obtaining positional information relating to an object substantially as herein described with reference to the accompanying drawings.

250. A method for controlling deployment of air bags in a vehicle substantially as herein described.

251. Method of obtaining positional information relating to an object, comprising the steps of:

transmitting a probe signal towards the object;

receiving, at a plurality of spaced apart locations, the probe signal as returned by the object;

detecting the relative timing of the returned probe signals as received at the plurality of locations; and

determining positional information for the object from the relative timing;

wherein;

the transmitting step comprises applying a series of m pulses to a transmitting element to cause it to transmit a signal, at times t_n where n=1, 2 . . . m, such that at least a portion of the signal can be reflected from the object to be received at the plurality of spaced apart locations;

the detecting step comprises detecting a signal reflected to the receiving elements at times r_n and

generating an output signal representative of the received signal; and

wherein the value of r_n−

t_n varies as some function of n.

252. Method of obtaining positional information relating to an object using an apparatus comprising a transmitting element, a receiving means comprising a plurality of receiving elements and a detecting means, the method comprising:

transmitting a probe signal from the transmitting element towards the object;

receiving, at a plurality of spaced apart locations, the probe signal as returned by the object; and

detecting, at the detecting means, the relative timing of the returned probe signals as received at the plurality of spaced apart locations;

determining the positional information for the object from said relative timing;

wherein the detecting means is coupled to the receiving means and the transmitting element and receiving elements are disposed on a common substrate.

253. Use of an electromagnetic antenna array in a method according to claim 252 in which the receiving elements are spaced apart by a distance that is the same order of magnitude as the wavelength λ

of the radiation that it is intended to transmit and receive, the electromagnetic antenna array including at least three receiving elements arranged non-collinearly such that there is an axis about which the array is asymmetrical.

254. Use of an electromagnetic antenna array in a method of obtaining positional information relating to an object, the array including a transmitting element and at least three receiving elements arranged non-collinearly, the transmitting and receiving elements being disposed on a common substrate.

255. Use of an electromagnetic antenna array in a method of obtaining positional information relating to an object, the array including at least three receiving elements arranged non-collinearly such that there is an axis about which the array is asymmetrical.