COUPLED WAVK THEORY AXD WAVEGUIDE APPLICATIONS 



(iS9 



figures a double logarithmic scale is used on the ordinate to represent 

 amplitude ^•ariations from 50 db below unity to amplitudes 50 db abo\'e 

 unit}'. An arbitrary break in the scale has been made at ±0.1 db which 

 for practical purposes will be assumed to correspond to amplitudes of 

 unity. With reference to Figure 27, small positive values of (ai — a-^jc 

 move the first null in isi** from ex = ir/2 toward lower \alues of ex. 

 For abscissa values greater than 7r/2, Ei** exceeds unity. For 

 (ai — aoj/c = 1, 7^1** again has a minimum in the vicinity of ex = 37r/2 

 but this second null has disapp(nu'ed for (ai — ao)/c = +2 and presum- 

 ably also for larger positive values. With reference to Figure 28, E^** 

 grows at a more rapid rate as a function of ex when (ai — a2)/c takes on 

 positive values. The null in the vicinity of ex = tt is still present for 

 (ai — a2)/e = 1 but has disappeared at (ai — a2)/c = 2. For (ai — a2)/c 

 equal to +2 (and presumably for larger positive values) the undriven 

 wave amplitude £"2** is greater than Ei** for ex larger than about 0.5. 

 The (luestion comes to mind in connection with this case in which the 



-30 



-20 



-10 



-6 



-4 



0.4 

 0.6 



4 

 6 



10 



20 



40 

 60 



too 



0.5 1.0 1.5 2.0 2.5 3.0 35 4.0 4.5 5.0 5.5 6.0 6.5 70 

 CX IN RADIANS 



Fig. 28 — Undriven line wave amplitude versus cz, for equal phase constants; 

 (ai — a2)/c as a parameter. 



