210 



REFLECTION AND TRANSMISSION OF RADIO WAVES 



radar area and its rms spread may be calculated quite easily. In this way, 

 these quantities may be determined over the range of aspect angles of interest. 

 In addition to the average areas, it is possible to predict the target noise. 

 After having replaced the aircraft by a finite number of simple shapes at 

 fixed locations, the doppler frequencies generated by a known variation of 

 angular velocity can be calculated in the manner described in Paragraph 

 4-4, and the spectrum can be determined. This calculation can be expedited 

 by the use of a target simulator. ^^ As an example, Fig. 4-32 shows the 



1.2 



4.8 6.0 7.2 



FREQUENCY (cps) 



8.4 



9.6 



10.8 



Fig. 4-32 Spectral Distribution of Angle Noise from a B-17 (Four-Engine Bomb- 

 er) Aircraft (Actual Measurement). 



1.2 2.4 3.6 4.8 6.0 7.2 8.4 9.6 10.8 



FREQUENCY (cps) 



Fig. 4-33 Spectra! Distribution of Simulated Angle Noise from a B-17 Target 



Simulator. 



measured angle noise spectrum of a B-17, while Fig. 4-33 shows the simu- 

 lated spectrum. The latter was obtained with a "target motion" composed 

 of a random oscillation having a Gaussian distribution of velocities about 

 zero mean, with a standard deviation of 0.3° /sec. 



22See footnote 17, NRL Reports 4694, 4770, 4796. 



