604 THE GENERATION OF MICROWAVE POWER 



\ ^ci VA/ ct * Cathode 



Slow Wave Structure ^ ^ Slow Wave Structure 



Magnetron Platinotron 



Fig. 11-31 Basic Structure of the Platinotron as Compared with the Magnetron. 



wave structure in the anode is not re-entrant. It extends most of the way 

 around the circumference of the anode, but has an input and output and is 

 a nonresonant rather than a resonant structure. 



If both input and output are externally terminated in matched termi- 

 nations, there is no mechanism to determine the frequency of operation of 

 the platinotron. If it is pulsed like a magnetron, the output will consist of 

 noise and random frequencies of oscillation, spread over a considerable band 

 of the spectrum. For useful operation it is necessary to add to the basic 

 platinotron some means of determining its frequency of operation. This 

 can be done by coupling a high-^ resonant cavity to the input end. The 

 frequency of oscillation will then lock to the frequency of the added cavity. 

 To the device operated in this form the term stabilotron is applied. The 

 stabilotron is a relatively stable self-excited oscillator, many times more 

 stable than the ordinary self-excited, unstabilized magnetron. Higher 

 circuit efficiency is obtained than with the cavity-stabilized magnetron 

 because the stabilizing cavity placed at the input to the circuit absorbs 

 relatively little power. 



The frequency of operation of the platinotron can also be established by 

 injecting a signal into the input. The output signal will be affected only 

 slightly until the strength of the input signal exceeds a threshold level. 

 Above this threshold level, the output signal will be locked in frequency to 

 the input signal, and the device will act as a saturated amplifier. To the 

 device operated in this manner the term amplitron is applied. The input 

 signal is also transmitted through the amplitron to the output, so that 

 as the input is increased above the threshold level, the increase in input 

 signal will be added to the output signal. A signal which is reflected from 

 the load under these conditions of operation is transmitted in a reverse 

 direction through the amplitron, and comes out of the input end with little 

 attenuation. 



