A MULTIPLE UNIT STEERABLE ANTENNA 



365 



tenna does not suppress the second lobe of the array factor as well as 

 could be desired. By design, it does so for the short waves but in- 

 herently fails to do so for the longer waves. Second, the principal lobe 

 of the unit antenna shifts bodily towards higher angles with increasing 

 wave-length, whereas it is desirable to have only the upper cutoff move 



MUSA PATTERNS (O = l) 



q MW wy I 



$ = 0° 



\ olAjwa. 



(D= 60° 



0.5 



< 

 u 1.0 



10 20 30 40 50 60 70 10 20 30 40 50 60 70 

 EARTH ANGLE, S IN DEGREES 



Fig. 20 — ^Vertical directional patterns of the experimental MUSA. Note that the 

 angle scale is half of that in Fig. 19. 



upward while retaining low-angle response. Both of these short- 

 comings restrict the steering range through which the MUSA is 

 essentially single lobed. The upward shift with wave-length of the 

 unit antenna response is in fair agreement with the way in which the 

 mean angle of arrival has been found to vary with wave-length and is, 



