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BELL SYSTEM TECHNICAL JOURNAL 



The situation in the immediate vicinity of the antenna is more 

 clearly represented in Fig. 3A in which the attenuation factor is plotted 

 against distance in wave-lengths. This allows inclusion of curves for 

 € = 1 (i.e. for the earth replaced by air) and e = oo (which is equiva- 

 lent to perfectly conducting earth). Comparison of these curves with 

 the broken lines which are replotted from Fig. 2 shows that for dis- 



0.02 0.05 0.1 0.2 0.5 1 2 3 4 



DISTANCE IN WAVELENGTHS, d/\ 



Fig. 3A — Variation of attenuation factor with distance in wave-lengths for trans- 

 mission over a dielectric plane. For d/\ small, 



^/-. = C-iT)/(W- 



The broken curves are replots of the curve for ()= oo from Fig. 2. 



tances greater than a wave-length the main effect of using the curves 

 of Fig. 2 is to ignore the presence of the oscillations in the curves. For 

 a perfect dielectric the amplitudes of these oscillations do not decrease 

 below ± l/e^/2 even at great distances as can be seen from equation 

 (19). The presence of some conductivity causes these oscillations to 

 be damped out. For example, a ^ of 5 reduces the amplitudes of these 

 oscillations within the first four wave-lengths to a value too small to 

 show on the figure. 



