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BELL SYSTEM TECHNICAL JOURNAL 



and with the same polarization as the incident ray. The path of a typical 

 ray is shown by line 1, 2, 3, the particular ray chosen having entered the 

 reflector along a line perpendicular to the plane of the paper. Points 1 and 

 3 represent the initial and linal points of reflection, respectively, whereas 

 point 2 represents the intermediate reflection point. 



Two important conclusions can be drawn from a careful inspection of the 

 path 1,2,3 ; namely, the projections of points 1 and 3 are diametrically oppo- 

 site on a circle drawn about point O as a center, and points 1 and 3 appear 

 to be images of point 2 ; i.e., the ingoing ray at 1 appears to be directed toward 



Fig. 4— Trihedral corner reflector showing the paths of typical rays. 



the image of point 2 in plane AOB, and the outcoming ray at 3 appears to 

 come from the image of point 2 in plane AOC. 



Not all rays falling upon a corner reflector of tinite dimensions will be re- 

 flected in the direction of the source. For example, a ray striking point 4 in 

 Fig. 4 may be reflected successively at points 4 and 5, but if the plane BOC 

 is not sufficiently extended it will not undergo the necessar>^ third reflection 

 required to return the ray in the incident direction. 



'J'he portion of the ])rojccted cross-section of a corner reflector which is 

 able to return incident radiation to the source is called the ''effective area." 

 It is, of course, a function of the aspect, that is to say, the angle at which the 



