MAGNETRON AS GENERATOR OF CENTIMETER WAVES 227 



in the manner already discussed in Section 4.5 EJfect of Other Components in 

 the Interaction Field. It can be removed by shielding the straps as shown 

 for the case of the double ring straps in the section A-A of Fig. 24 (d). The 

 shields, being parts of the anode segments, maintain the proper potential 

 distribution in the interaction space. The echelon straps of Fig. 24 (c), 

 since they overlap, need not be shielded. 



Secondly, the location of the straps at the ends of the resonator system has 

 an effect on the amount of variation of RF voltage along the length of the 

 anode in the tt mode. For anodes of length approaching a half wavelength 

 or greater, this may become great enough to warrant attention. It is in- 

 structive, in this connection, to consider the anode structure as being made 

 up of two circular strip transmission lines, the straps at the ends of the 

 structure, between which there are connected at intervals N "half-section" 

 wave guides, the N resonators of the system. Since the resonant frequency 

 of the system is less than that of an individual resonator, the resonators act 

 as inductances connected across each set of straps and as wave guide con- 

 nections between the sets of straps operating beyond cut-off, the RF voltage 

 var>ang hyperbolically along their lengths. Since the two ends of the anode 

 structure are in phase, the mode is symmetric about the median plane and 

 the variation of RF voltage along the axis is expressed by the hyperbolic 

 cosine. 



7.4 The "Rising Sun" Resonator System: The second type of magnetron 

 resonator system in which the mode frequencies may be separated sufficiently 

 well to allow "clean" operation in the ir mode is an unstrapped structure 

 involving the use of resonant cavities of two sizes so arranged that adjacent 

 cavities are alternately large and small. This resonator system, called the 

 "rising sun" system, accomplishes mode frequency separation by a means 

 analogous to the increase in separation of the mode frequencies of a system 

 of two coupled resonators achieved by relative detuning of the individual 

 resonators. At the Columbia Radiation Laboratory during a series of 

 experiments with asymmetries in an unstrapped resonator system, designed 

 to achieve good operation in a harmonic of one of its doublet modes rather 

 than in the w mode, it was observed that as the natural frequencies of the 

 two sets of resonators were separated the mode frequencies diverged in two 

 groups as though each group corresponded to one of the two sets of resona- 

 tors and that in this configuration the t mode was quite well separated 

 from the other modes. Thus the system appeared to be well suited for 

 TT mode operation, providing a means of mode separation without the use 

 of straps. As such it is particularly adaptable to use in magnetrons of 

 short wavelength where straps become very small and extremely difficult to 

 construct. 



