MAGNETRON AS GENERATOR OF CENTIMETER WAVES 



249 



however, that with reasonable tightness of strapping difficult is encountered 

 with mode frequency separation. 



Variation of the capacitance may be accomplished by moving a member 

 in the vicinity of the region of large distributed capacitance of the reso- 

 nators. One such tuning scheme is that shown in Fig. 36 (b) in which a 

 member shaped like a "cookie cutter" is moved in and out of annular grooves 

 in one end of the resonator block, the other end of which is usually strapped. 

 As the member is inserted the mode frequencies decrease. The frequency 

 range available for tt mode operation is limited by the fact that the fre- 



Fig. 36.— Schematic diagrams showing three types of tuning schemes which have been 

 used in magnetron resonator systems. The views represent sections on a diametral plane 

 through the anode structure. The cathode is shown in the center of each part of the 

 figure. The resonators are of the hole and slot type, (a) shows the scheme involving 

 variation of the inductance by means of tuning pins, (6), the scheme involving variation of 

 resonator capacitance, and ic), that involving variation of strap capacitance. Each of the 

 last two schemes is accomplished with a "cookie cutter" shaped member. 



quencies of modes of smaller n, which are normally higher than that of the 

 ■K mode, change faster and eventually cross the tt mode frequency. 



To understand what determines the frequency of resonance in any mode, 

 it is sufficient to consider the inductances and capacitances present in the 

 average sector of the resonator system across which there is a half wavelength 

 azimuthal variation of RF potential with an extremum at either end. In 

 the TT mode of an N = 8 resonator system, one may thus consider one eighth 

 of the system, namely, a single resonator; in the n = \ mode, one may con- 

 sider half of the resonator system. In the case of the half wavelength 

 sector for the n = \ mode, across which the potential varies monotonically 

 (see Fig. 23), the four resonators may be considered as connected essen- 



