DEVELOPMENTS IN SHORT-WAVE DIRECTIVE ANTENNAS 667 



rents propagated to the far end in appropriate terminating impedances. 

 In many of the diagrams, the load currents which would arrive from 

 open-end reflections have been included merely as of general interest. 

 The above stated principle permits us to remedy the null situation 

 of Fig. 7 by tilting the wire as shown in Fig. 8. Notice that point 1 has 

 been advanced into the wave propagation so that, at any given instant, 

 point 1 is later in phase than for instance, point 5. The directly propa- 

 gated currents of Fig. 8 trace a semicircumference and, therefore, the 

 wire length ^ appears to be an optimum for the tilt selected. 



RMS CURRENT RMS CURRENT 



AT R-DIRECT AT R VIA END 



PROPAGATION REFLECTION 



/ 



/ 



\ 



PERFECT GROUND 



RESULTANTS 



V " 



\ 



© 



Fig. 8 — Vector relations in a tilted wire antenna. 



For any wire tilt angle, there exists a wire length which will trace a 

 semicircumference similar to the above. This occurs when the tilt is 

 such that the wire length is one-half wave-length longer than its pro- 

 jection upon the wave direction of propagation. Using appropriate tilt 

 angles, as the wire length increases, output gains are achieved through 

 increased effective induced voltage in the wire. vStill further gain in 

 output is available through the increasing directivity that is bound to 

 result from the increasing dimensions. 



One of the chief features of the tilted wire antenna is that in its 



* For rigid accuracy in determining optimum dimensions, a small correction must 

 be applied to these rules. This correction occurs in cases where, upon changing the 

 wire tilt angle, the rate of change of induced voltage is comparable to the rate of 

 change of load current as described above. 



