178 REFLECTION AND TRANSMISSION OF RADIO WAVES 



1 



then, neglecting the slight effect of variations in the — term, the total field 

 received will be 



R" 



e-^^'^ dl 





ILR" ' 



(4-13) 



where u = ILKXRy^, and C(u) and S(u) are the Fresnel integrals 

 C(u) = / cos (x2V2) dz, 



S(u) = / sin (7r2V2) dz. 

 Hence the effective radar length is 



/' = /[C^_,^]. (4.U) 



From Equations 4-2 and 4-14 the effective radar area a' may be derived as 



(4-15) 



C~{u) + S%u) 



Thus the radar length (and radar area a) becomes a function of range, 

 especially for targets of great width at short range, the measurements being 



10^ 2 4 7 10'' 2 4 



Fig. 4-2 Radar Cross Section as a Function of Range. 



