WAVE PICTURE OF MICROWAVE TUBES 



1349 



distance L such that 



2 ^' L = r 



Uo 



we will find that the ac velocities of the two wa^'es cancel and their cur- 

 rents add. If at this point Ave put an output resonator, the current will 

 produce a Voltage across the resonator which will act on the electron 

 beam to set up new components of the slow and the fast waves. 



If the resonator is on tune, so that it acts as a resistive impedance, 

 the phase of the voltage is such with respect to the space-charge wave 

 producing it that the new component of the fast space-charge wave 



. r 



INPUT 

 RESONATOR 



2-— L = 77 

 Uo 



OUTPUT 

 RESONATOR 



Fig. 2 — In a klystron the input resonator sets up slow and fast space-charge 

 waves so phased that the velocities add and the currents cancel. At the output 

 resonator the currents add and the velocities cancel. The voltage across the output 

 resonator increases the amplitude of the slow, negative-power wave and decreases 

 the amplitude of the fast, positive-power wave. 



subtracts from the old component, while the new component of the slow 

 space-charge wave adds to the old component. Thus, while to the left 

 of the output resonator the two space-charge waves have equal magni- 

 tudes, so that the net power flow is zero, to the right of the output 

 resonator the slow space-charge wave has a greater magnitude than the 

 fast space-charge wave, so that the poAver flow in the beam is negative. 

 The missmg power appears as the output from the output resonator. 



Of course, klystrons are frequently used in the nonlinear range of 

 operation, and the distance L between resonators may be chosen differ- 

 ently from other considerations. 



THE RESISTIVE-WALL AMPLIFIER 



Consider a tube much like a klystron, but in which the electron beam 

 is surrounded by a glass tube coated Avith lossy material, such as graphite, 

 as shoAvn in Fig. 3. 



