32 



ANTENNAS 



value for angle a is equal to the angle between each 

 element and its maximum lobe (see Figure 11). 

 Figure 19 gives the (power) radiation pattern for 

 11 = 16 half-wavelengths. 



The directivity of this antenna system may be 

 improved by adding one or more reflectors (see 

 Section 3.4.6). The reflector is a V antenna of 

 identical type. The legs of the reflector are placed 

 parallel to those of the primary V and lie in the same 

 plane as the original V. The reflector is set approxi- 

 mately X/4 behind the primary V. 



3.3 TRAVELING-WAVE ANTENNAS 



^^^ Field and Pattern 



A traveling-wave antenna is one in which only 

 progressive (or traveling) waves are allowed. Re- 

 flected waves are eliminated by terminating the end 

 opposite the input point in the characteristic imped- 

 ance. See Figure 20. 



The major lobes given by this eciuation are plotted 

 in Figure 21, and the major lobe angles with the 

 wire dm are plotted in Figure 22. Angle d,„, it will be 

 noted, decreases with increasing wire length. 



3.3.2 



Traveling-Wave V Antenna 



As in the case of the standing-wave antenna a 

 pair of lines arranged at a suitable angle with each 



<g TRAVELING WAVE 

 PmSIINGLE WIRE 



CHARACTERISTIC 

 IMPEDANCE 



FiGi'RE 20. Lobe structure for L = 2X traveling-wave 

 antenna in free space. 



1.0 2,0 3.0 4.0 



Figure 21. Major lobes (relative field strength) for traveling-wave antenna. 



The ec|uation of the radiation field, neglecting other, and carrying traveling waves, can be made to 

 wire losses, is produce a directional pattern with fairl.y high gain. 



The traveling- wave Y antenna can be designed 



Ee = 



607i sin B 



d 1 



sm 



tL 

 L X 



(1 - cose) . (19) 



so that the plane of the V is horizontal and the 

 maximum lies in the direction of the axis of sym- 



