11-2] 



THE KLYSTRON 



593 



transmitted signal be unusually stable and free from sideband noise of a 

 character that might mask the doppler-shifted frequency that is returned 

 from the ground. The two-cavity klystron oscillator has been operated very 

 successfully in this application, and also in CW radar seekers for active 

 homing missiles, where similar requirements for high stability and low noise 

 are encountered. A typical example of a fixed-frequency two-cavity 

 klystron oscillator is shown in Fig. 11-19. 



Fig. 1 1-19 Two-Cavity Klystron Oscil- 

 lator. 



Flexible Diaphragm 

 for Tuning 



Fig. 1 1-20 Resonant Cavity for a High- 

 Power Klystron with a Gridless Gap. 



High-Power Klystron Characteristics. In the klystron that is 

 shown schematically in Fig. 11-16, the electron beam is focused through 

 grids that form the interaction gaps in each cavity. As the power level is 

 raised and the power density in the electron beam is increased, grids cannot 

 be built that will not be burned out by the beam. It is then necessary to have 

 ungridded apertures at the interaction gaps. If the dimensions of these gaps 

 are not too large, there will still be adequate interaction between the 

 electromagnetic fields in the cavity and the electron beam. A typical cavity 

 for high-power klystrons with a gridless gap is shown in Fig. 11-20. The 

 power level above which it is necessary to go to gridless gaps depends 

 upon the diameter of the electron beam, which in turn depends upon the 

 operating frequency. At 10,000 Mc, the klystron with gridded gaps is 

 limited to roughly 50 watts output; for high powers, gridless gaps must be 

 used. 



The two-cavity klystron amplifier of Fig. 11-16 will give roughly 10 db 

 gain. The gain can be greatly increased by spacing additional cavities along 

 the electron beam, as shown in Fig. 11-21. The cavities that are inter- 

 mediate between input and output cavity are coupled to the electron beam 



