MAGNETRON AS GENERATOR OF CENTIMETER WAVES 247 



values of p and ( which if exceeded makes oscillation possible at more than 

 one frequency at all phases of the load reflection coefficient. The second 

 specifies the values of p and ( which must not be exceeded if oscillation is 

 to be possible at only one frequency for all phases of the load reflection co- 

 efficient. This latter relation between p and t is that for which the slope 

 of the load line is equal to the slope of the magnetron characteristic at its 

 point of inflection. 



From what has been said it would appear that the use of long load lines 

 is to be avoided if at all possible. If the magnetron is pulsed and the line 



Fig. 35. — Plots of the frequency characteristics of a magnetron and a frequency sen- 

 sitive load for two magnitudes of reflection coefficient, p, and two line lengths, (. The 

 ordinates are frequency and the abscissas are phase angle of the reflection coefficient in the 

 fundamental period to tt radians. Stable oscillation occurs at the intersections indicated 

 by hlled circles. The open circle indicates a point of unstable operation for the three 

 conditions p = 0.5 and ^ = A , p = 0.5 and t = (2 , and p = 0.2 and ( — fn, In addition, 

 it indicates a point of stable operation forp = 0.2 and ( = (-i. These four points are coa- 

 lesced on the figure for simplicity. The lines A' and h' indicate how stable operation at 

 both p = 0.2 and 0.5 may be attained by an increase of Une length of approximately a 

 quarter wavelength. 



is sufficiently long, however, it is possible for the oscillation in a pulse to 

 have been completed before any energ}' reflected from the termination has 

 arrived back at the magnetron. ' Under these circumstances the magnetron 

 operates into an effectively infinite line which presents its characteristic 

 admittance to the magnetron output. For a pulse of one microsecond 

 duration this w^ould require a line length of about 150 meters. Usually such 

 lengths are not possible or are undesirable by virtue of attenuation, and 

 either the line is made sufficiently short or its length critically adjusted or 

 the standing wave on it reduced so as to cause operation to occur at a single 



