RADAR ANTENNAS 



241 



We therefore obtain 



, . sin ^ C2 



F{a) = aCx — ^ + ^ y 



sin 



(.+i)^ sin(,--y 



U^-^d (*-^) 



(42) 



The patterns resulting from two possible tapers are given by substi- 

 tuting Ci == 0, C2 = 1 and Ci = 1/3, C2 = 2/3 in (42). These patterns are 



sin a 



evidently calculable in terms of the known function . They are plotted 



a 



in Figs. 12 and 13. 



0.8 



< 0.2 



- 5n -4TT 



■3n -2n 



-non 

 ... no sma 



3TT 4-n 



Fig. 12 — Pattern of Tapered Rectangular Antenna. 



It will be observed that minor lobe suppression through tapering is ob- 

 tained at the expense of beam broadening. In addition to this the gain is 

 reduced by tapering, as could have been calculated from 28. These unde- 

 sirable effects must be contended with in any practical antenna design. 

 The choice of taper must be made on the basis of the most desirable com- 

 promise between the conflicting factors. 



3.8 Efect on Pattern of Linear Phase Variation 



If we assume a constant amplitude and a linear phase variation 



4>'{x) = —k\x 



