DEVELOPMENTS IN SHORT-WAVE DIRECTIVE ANTENNAS 679 



Fig. 18 is a plot similar in character to that of Fig. 16, giving the 

 location of nulls and maxima in the same manner. In our previous 

 example, vertical plane considerations indicated that a tilt angle of 65 

 degrees was desirable. An examination of Fig. 18 gives a rapid esti- 

 mate of the approximate plan view of the directive diagram and Fig. 19 

 is the more complete plan diagram for this tilt angle. It will be noted 

 in Fig. 18 that the lines indicating factor maxima and minima fre- 

 quently intersect. This property can be utilized for the suppression of 

 particular minor lobes of the directive diagram by a proper selection of 

 the tilt angle. 



Frequency Range 

 Previously, it was stated that the V form of antenna counteracts the 

 slight tendency for a change in optimum direction when the frequency 



90* 



60* 



30* 



NOTE: GROUND CANCELLATION IS IGNORED 

 Fig. 19 — Plan view directive diagram. 



NOTE: GROUND CANCELLATION IS IGNORED 



Fig. 20 — Plan view directive diagram. 



is altered. The correctness of this statement is verified in Figs. 19, 

 20, and 21. The linear dimensions and tilt angle were unaltered as 

 the wave-length was varied over a two-to-one range. The optimum 



