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BELL SYSTEM TECHNICAL JOURNAL 



wave-length long and at optimum tilt. It will be observed that the 

 front-to-back ratio is not infinite but there still exists some directional 

 discrimination, due to the fact that the back wave has resulted in the 

 elementary currents tracing one and one-half rotations, thus obtaining 

 partial cancellation. It is important to notice that longer wires would 

 result in an increasing number of rotations and the resultant current of 

 the back wave would become smaller and smaller as compared with the 

 resultant of the front wave. This is a further argument for the use of 

 long tilted wires. The calculated front-to-back ratios obtained with 

 characteristic impedance terminations for various lengths of wires at 

 optimum tilt are plotted in Fig. 13. 



25 



> 13 



12 3 4 5 



WIRE LENGTH IN WAVE LENGTHS AT OPTIMUM TILT 



Fig. 13 — Front-to-back ratios for characteristic impedance termination. 



A very interesting feature about terminations is that, provided we 

 are willing to make slight readjustments in their value, it is possible to 

 obtain infinite front-to-back ratios at all frequencies within range. 

 This is accomplished by cancelling the residue of back signal by means 

 of a small reflection from the end termination obtained by departing 

 slightly from the characteristic impedance adjustment. It can be 

 shown that this results, for wires which are in length an even multiple, 

 greater than two, of one-quarter wave-length, when the termination is 

 the characteristic impedance times the cosine of the angle made by the 

 wire with the direction of wave propagation. 



