MAGNETRON AS GENERATOR OF CENTIMETER WAVES 269 



changeable. Finally, in Fig. 44 are shown two magnetron oscillators, the 

 720A and 725 A, mounted in their magnets. By comparison with Fig. 42, 

 the space and weight saved by packaging may be seen. A fair comparison 

 is that between the 725A and magnet of Fig. 44 and the 4J52, number 2 

 in Fig. 42. Both are 3.2 cm. models, the latter, moreover, being capable 

 of generating higher power. 



The designer of a magnetron oscillator is faced with a variety of tasks. 

 If the magnetron is to be used in a specific application he has at his disposal 

 data concerning the amount of power available to drive the magnetron, 

 the nature of the pulsing if such is to be used, the frequency of operation, 

 mechanical features having to do with form and weight, and an idea of what 

 the user hopes or expects to obtain in the way of output power, frequency 

 stabiUty, and operating efficiency. It is the problem of magnetron design 

 to arrange the resonator system, output circuit, cathode, magnetic circuit, 

 and mechanical features to meet these requirements if possible. 



In the design of the resonator system it must be arranged to achieve the 

 proper frequency of operation, proper characteristics regarding modes, the 

 proper size of interaction space, and other characteristics which have a 

 bearing on the electronic operation. In special cases a tunable resonator 

 system must be provided. 



In the design of the output circuit it is necessary to arrange the type of 

 coupling to the resonator system, the necessary impedance transformation 

 from resonator to load, the type of external coupling, a vacuum seal, and 

 generally to take into account the possibility of electrical breakdown when 

 the power delivered is high. , 



In the design of the magnetron cathode, attention must be paid to its 

 surface and how it is equipped to meet the rigorous demands made of it. 

 The cathode mounting and input leads must be designed for proper geom- 

 etry at the cathode ends, heat dissipation, mechanical strength, and DC 

 voltage breakdown strength. 



The requirements placed on the magnetic circuit of a magnetron must be 

 borne in mind throughout the design of the magnetron itself. Considerable 

 efifort may be expended in arranging for the magnet gap, and hence the re- 

 quired magnet, to be as small as possible. In "packaged" magnetrons the 

 magnet pole pieces, which are built into the magnetron structure, must be 

 designed to produce a field of proper configuration and to make the neces- 

 sary external magnets feasible. 



Generally, the design of the mechanical features of a device as complicated 

 as the multiresonator magnetron oscillator is extremely important and must 

 provide for structural strength under a variety of conditions, as well as 

 cooling facilities and external protection of relatively fragile parts. 



