MAGNETRON AS GENERATOR OF CENTIMETER WAVES 231 



quarter wavelength. Said another way, the electrical distance from the 

 back of a large resonator to its opening in the anode, across the segment face, 

 and to the back of the adjacent small resonator is an electrical half wave- 

 length along which the voltage and current vary approximately sinusoidally. 

 For this reason the maximum in the RF voltage and the corresponding cur- 

 rent node do not appear at the mouth of either cavity but at a point (M of 

 Fig. 28) somewhat inside the opening of the large cavity. This means that 

 the electric field across the mouth of the larger cavity is greater than that 

 across the mouth of the smaller cavity. The excess, since all the large 

 cavities are in phase, adds up around the anode to form an electric field 



Fig. 28. — .\ diagram illustrating the origin of the component independent of angle in the 

 TT mode interaction field of the "rising sun" resonator system. The length of the arrow 

 lying parallel to and just inside the resonator wall at any point is proportional to the magni- 

 tude of the RF current flowing there. The RF current node, and hence RF voltage maxi- 

 mum, occurs at M, inside the mouth of the larger cavity. Note that this gives rise to 

 currents flowing in the faces of the anode segments which are in the same direction around 

 the interaction space and that the RF field strength across the mouth of a larger cavity is 

 greater than that across the mouth of a smaUer cavity. This latter is indicated schemati- 

 cally by means of the dashed arrows. 



component independent of angle like the w = mode field in Fig. 23. 

 Further, it is seen in Fig. 28 that at any instant there are currents flowing 

 across the faces of the anode segments which are all in the same direction 

 around the anode. With this net circumferential current is associated the 

 unidirectional RF magnetic field component parallel to the axis shown 

 also in Fig. 23. 



The amount by which the two sets of mode frequencies of the "rising 

 sun" structure are separated increases with increasing ratio of resonator 

 sizes. Corresponding to this, the amount of ;i = like component in the 

 interaction field increases. 



The presence of the component independent of angle in the interaction 



