Real-time, cross-correlating millimetre-wave imaging system

Abstract

A method and apparatus are disclosed for forming an image from millimetre waves. A field of view scanned using two geometrically orthogonal, intersecting copolarized fan beams ( 110, 120 ) to receive millimetre wave radiation. The received millimetre wave radiation from said fan beams are then cross-correlated ( 250, 650 ). Also, a method and antenna ( 400, 610 ) for receiving millimetre wave radiation are disclosed. The antenna includes first and second fan beam antennas ( 410, 420 ) for receiving millimetre wave radiation and a filter ( 430, 440 ) for rotating polarization of incident millimetre wave radiation through 90 degrees received by the second fan beam antenna ( 410 ). The respective first and second beams ( 110, 120 ) intersect and are co-polarized and geometrically orthogonal to each other. Still further, a millimetre wave imaging system ( 600 ) and method are also disclosed, which utilise an antenna ( 610 ) for receiving millimetre wave radiation, process the received millimetre wave radiation from the antenna ( 610 ), and build up the image ( 682 ) using a filtered, cross-correlated signal.

1 . A method of forming an image from millimetre waves, said method including the steps of:
 scanning a field of view using two geometrically orthogonal, intersecting co-polarized fan beams to receive millimetre wave radiation; and   cross-correlating components of said received millimetre wave radiation from said fan beams.   
   
   
       2 . The method according to  claim 1 , wherein polarizations of the electric fields of said two fan beams are arranged to be substantially parallel in alignment. 
   
   
       3 . The method according to  claim 2 , further including the step of polarization rotation filtering of said millimetre wave radiation received in one of said fan beams. 
   
   
       4 . The method according to  claim 1 , wherein said scanning step is performed in azimuth and elevation defining a scan range, and an intersection region of said two fan beams is able to cover any point in said scan range. 
   
   
       5 . The method according to  claim 4 , wherein said scan range determines said field of view and a beam width of each fan-beam in a narrow direction determines an angular resolution of said image. 
   
   
       6 . The method according to  claim 1 , further including the step of measuring said cross-correlated output at each point in said field of view to produce a map of brightness. 
   
   
       7 . The method according to  claim 6 , further including the step of controlling said two geometrically orthogonal, intersecting fan beams to generate said cross-correlated output at each fan beam intersection point in said field of view. 
   
   
       8 . The method according to  claim 1 , wherein said scanning step is implemented using a dual fan-beam antenna. 
   
   
       9 . The method according to  claim 8 , wherein said dual fan-beam antenna has two modified pill-box antennas and a polarization rotator to change the direction of incident polarization for one of said modified pill-box antennas. 
   
   
       10 . An apparatus for forming an image from millimetre waves, said apparatus including:
 an antenna for scanning a field of view using two geometrically orthogonal, intersecting co-polarized fan beams to receive millimetre wave radiation; and   a receiver for cross-correlating components of said received millimetre wave radiation from said fan beams.   
   
   
       11 . The apparatus according to  claim 10 , wherein polarizations of the electric fields of said two fan beams is arranged to be substantially parallel in alignment. 
   
   
       12 . The apparatus according to  claim 11 , further including a polarization rotation filter for said millimetre wave radiation received in one of said fan beams. 
   
   
       13 . The apparatus according to  claim 10 , wherein scanning by said antenna is performed in azimuth and elevation defining a scan range, and an intersection region of said two fan beams is able to cover any point in said scan range. 
   
   
       14 . The apparatus according to  claim 13 , wherein said scan range determines said field of view and a beam width of each fan-beam in a narrow direction determines an angular resolution of said image. 
   
   
       15 . The apparatus according to  claim 10 , further including a processor for measuring said cross-correlated output at each point in said field of view to produce a map of brightness. 
   
   
       16 . The apparatus according to  claim 15 , further including a controller for controlling said two geometrically orthogonal, intersecting fan beams to generate said cross-correlated output at each fan beam intersection point in said field of view. 
   
   
       17 . The apparatus according to  claim 10 , wherein said antenna is a dual fan-beam antenna. 
   
   
       18 . The apparatus according to  claim 17 , wherein said dual fan-beam antenna has two modified pill-box antennas and a polarization rotator to change the direction of incident polarization for one of said modified pill-box antennas.