MAGNETRON AS GENERATOR OF CENTIMETER WAVES 



273 



■difficulty lay not in the actual measurement of power or voltage but in the 

 fact that the magnetrons were not loaded in a reproducible fashion. It was 

 considerably later that load impedance measurements were made and used 

 in evaluating magnetron performance. In many early studies the effect 

 of load on operation was not sufficiently disentangled from the efifects of 

 other things. In spite of these inadequacies, however, it was generally 

 possible to distinguish a good design change from a bad one, and much of 

 value was gained in early work. 



The cathode diameter used in the 700A-D magnetrons is given in Table 

 I along with other data on these and other magnetrons in the 20 to 45 cm. 



Fig. 46— An internal view of a 700A-D magnetron (40 kw., ^^700 mc/s) showing the 

 unstrapped resonator system of six hole and slot circuits, the cathode, the cathode end 

 disks and support leads, and the output coupling loop and lead. 



wavelength range. It should be noted that the optimized ratio fc/r^ is 

 0.300 as compared to 0.375 in the British magnetron having eight resonators. 

 Plain oxide coating is used on the cathode. Life expectancy is thousands 

 of hours. 



As may be seen in Fig. 46, the output coupling is accomplished by means 

 of a loop in the end space of the structure. The loop is connected to an 

 anode segment. It is driven by direct coupling to the anode segment and 

 by coupling to the magnetic flux linking the two adjacent resonators. 

 The output circuit was not designed to operate into a matched output line, 

 however, and external impedance transformation must be incorporated 

 into the load line. 



