232 BELL SYSTEM TECHNICAL JOURNAL 



field is thus an inherent characteristic of the "rising sun" resonator system. 

 One is faced with the problem of designing for sufficient mode separation 

 without unduly increasing this component. How the presence of this com- 

 ponent in the interaction field perturbs the electronic interaction with the 

 TT mode, resulting in a performance characteristic like that of Fig. 20, has 

 already been discussed. 



8. Output Circuit and Load 



8.1 Output Circuit: In the general physical description of the centimeter 

 wave magnetron whose constituent parts are shown in Fig. 1 there remains 

 the discussion of the output circuit. The output circuit is the means of 

 coupling the fields of the magnetron resonator to the load and as such it 

 must contrive to induce a voltage across a coaxial line or a waveguide to 

 which the load circuit is connected. Several types of coupling are involved 

 in magnetron construction. These are illustrated schematically in Fig. 29. 

 Here the resonator of the magnetron is represented by a simple L— C cir- 

 cuit and any transformer action of the output circuit between the resonator 

 and the load is to be accounted for by the unspecified network T. The 

 scheme of Fig. 29 (a) involves magnetic coupling, that of (b), electrostatic 

 coupling, those of (c) and (d), two forms of direct coupling. 



Type (a), it is clear, corresponds to the output coupling accomplished 

 by a loop, like that shown in Fig. 1, feeding a coaxial line. The loop may 

 be placed inside the cavity as in Fig. 1, may be placed above the resonator 

 in the end space as in the case of the so-called "halo" loop, or may be placed 

 with its plane parallel to the axis of the anode between the resonators in 

 the end space. In each case the coupling is eflfected mainly by linking of 

 magnetic lines of force by the loop. The coupHng is not entirely magnetic, 

 however. There is electrostatic induction in the loop by the anode seg- 

 ments near it, corresponding to coupling of type (b) of Fig. 29, and in the 

 case of the third possible placement of the loop listed above, there is in- 

 volved some direct coupling of the type (c) of Fig. 29 since the loop is termi- 

 nated on an anode segment on which there is RF potential. 



In most cases the coaxial line must expand in dimensions from the loop 

 extremity, pass through the vacuum envelope, and be provided with a 

 means of coupling to the coaxial load line of the system in which the mag- 

 netron is used. The output circuit from the loop to the smooth fine of the 

 system must provide the transformer action necessary to load the loop by 

 an admittance which gives the desired Q [see equation (23)]. What this 

 admittance must be is dependent, to be sure, on the size and position of 

 the loop, that is, upon the degree to which it couples the magnetic lines in 

 the resonator. Generally, the attempt is made to build the transformer 



