TARGETS FOR MICROWAVE RADAR NAVIGATION 869 



the source. The "Biconical" reflector may perhaps be likened to a cylinder 

 which automatically orients itself so that the impinging rays are always 

 perpendicular to the axis. 



A biconical reflector was constructed of sheet metal having the dimensions 

 indicated in Fig. 17. The vertical response pattern was measured and is 

 plotted in the lower portion of the figure. Because of the circular symmetry 

 of the reflector, the vertical response curve shown will be equally valid for all 

 angles of azimuth. At </> = 0° the reflector exhibited an effective area of 

 0.16 square feet. The measurements were made at a wavelength of 1.25 

 centimeters. 



In the above experiment the incident radiation was polarized in the plane 

 of the axis of the cones. In another test with the polarization perpendicular 

 to the axis the received echo was reduced by four decibels. This effect is not 

 as yet entirely explained. It probably results from a depolarizing effect 

 similar to that encountered in the dihedral corner reflector, complicated 

 however by the curvature of the cones. 



Only a limited amount of data is available for predicting the effective area 

 of a biconical reflector over a wide range of sizes and wavelengths. The 

 available data indicate that to a rough approximation and for a given polari- 

 zation the effective area varies directly as the square root of the wavelength 

 and as the three-halves power of the diameter of the cones, assuming that 

 the height of the reflector is approximately equal to the diameter. 



