594 



THE GENERATION OF MICROWAVE POWER 



-Input Cavity 



Output Cavity 



3::^5R 



RF Input 



RF Output 



Fig. 11-21 Schematic Diagram of a Multicavity Klystron Amplifier with Higher 

 Gain than a Two-Cavity Amplifier. 



at the gaps, but are not coupled to any external sources or sinks of power. 

 Each additional cavity that is added gives effectively another stage of gain. 

 The exact amount of gain that can be obtained depends substantially upon 

 the details of design, but the following data are typical: 



NO. OF CAVITIES 



2 

 3 

 4 



5 



GAIN IN DECIBELS 



10 



30-35 

 50-60 

 70-80 



If possible sources of feedback, such as external leakage or internal second- 

 ary electrons, are avoided, the high values of gain shown can be obtained 

 stably and reproducibly. This is often of great value to a system designer, 

 as he can obtain kilowatts of output power with milliwatts of drive power. 



For various reasons it may be desirable to limit the gain in the power 

 klystron amplifier to something less than the maximum value. For example, 

 the signal-to-noise ratio of the amplifier becomes poorer as the gain becomes 

 higher. Also, the physical size and weight may become excessive. Another 

 alternative that is available is to use several cavities in the klystron and 

 then stagger-tune them for wide bandwidth. In a manner somewhat 

 analogous to the well-known stagger-tuning techniques of IF amplifiers, 

 it is also possible to stagger-tune the cavities of a klystron amplifier and 

 trade gain for bandwidth. 



In a multicavity klystron amplifier, the electron beam is necessarily 

 rather long. The electron-optical system of the cathode and anode are 

 normally designed to form a dense, small-diameter electron beam where 

 the beam enters the aperture in the anode. The forces of mutual repulsion 



