MAGNETRON AS GENERATOR OF CENTIMETER WAVES 295 



ability that these effects do not exactly cancel one another and that a net 

 improvement in performance could be effected. 



The design of the 5 J26 was accomplished in the following way : The slot 

 type resonator was chosen as it possesses a low value of inductance needed 

 to give a high value of Ga for a given value of loaded Q}^ The number of 

 resonators was chosen to be eight, the anode length of the 4J2 1-30 retained, 

 and the design carried out at Ql = 150 and/ = 1220 mc/s. The empirical 

 relations used were that relating Ic/h to GjGo , that relating jje to GJG^ , 

 and the equation of a constant B line on the performance chart obtained for 

 the 4J21-30. In addition to the definitions of Gs , ^o , ^o , and Go, there were 

 to be met the operating conditions of F = 27 kv., / = 46 amps., and B = 

 1400 gauss, as well as a maximum value for the over-all diameter of the 

 resonator system dictated by interchangeability. The value of resonator 

 inductance was calculated for a terminated parallel plate line. With the 

 choice of h = 60 amps., the above mentioned conditions could be solved 

 numerically to give a definite set of design parameters. The anode and 

 cathode radii, resonator length, and thus unstrapped wavelength were 

 determined. The straps were designed to achieve the proper frequency 

 and to provide sufficient tuning range with the tuning means employed. The 

 ratio rc/ra was determined as 0.546, considerably in excess of the value 

 0.375 in the 4J21-30 magnetrons. 



The output circuit of the 5J26 magnetron was similar to that used in the 

 other tunable magnetrons of long wavelength. It employed the broad band 

 design of external coupling and transition section to the coupling loop. The 

 size of the loop was dictated by the coupling required to provide a Ql of 

 approximately 150. It may be seen in Fig. 58. 



The input leads of the 5J26 magnetron were of new design, incorporating 

 chokes in the leads to prevent leakage of RF energy picked up on the cath- 

 ode, and large size center conductor to minimize RF voltage breakdown on 

 the input leads. 



The significant design and operating data for the 5J26 magnetron are 

 included in Table I. This magnetron design provided a single tunable 

 replacement of superior performance for the entire 4J21-30 series. In Fig. 

 59 are shown curves of mode frequency tuning throughout the w mode tuning 

 range, indicating that in the strap tuning method difficulties with mode 

 frequency interference are avoided. 



15. Magnetrons for Wavelengths near 10 Centimeters — 

 UNDER 200 Kilowatts 



15.1 The 706 A-C and 7 MA Magnetrons: The work in the wavelength 

 region near 10 cm., described in Section 12, was continued in the study 

 of variations from the British design. For the most part these early studies 



