T. MORENO 



CHAPTER 11 



THE GENERATION OF MICROWAVE POWER 



11-1 THE MAGNETRON 



The magnetron has been the source of transmitted microwave power 

 in nearly all of the airborne radar equipment constructed in recent years. 

 It is a self-excited power oscillator that in its more modern versions can be 

 tuned mechanically over moderate frequency ranges, typically 10 per cent. 



At the present time other types of 



RF Output 



Cathode 



Fig. 11-1 Physical Configuration 

 Typical Microwave Magnetron. 



of 



tubes that permit more sophisti- 

 cated systems are being given in- 

 creasingly serious consideration by 

 designers of modern radar systems. 

 However, the primary virtues of the 

 magnetron that have led to its 

 present dominant role have yet to be 

 excelled by other types of tubes. 

 These virtues are small size, light 

 weight, high efficiency, and low 

 operating voltage. All of these 

 virtues are important to the designer 

 of airborne radar equipment. 



The physical configuration of a 

 typical microwave magnetron is 

 shown in Fig. 11-1. The magnetron 

 is basically a cylindrical diode, with 

 a central cathode enclosed in a 

 larger, cylindrical anode. The mag- 

 netron is immersed in a strong 



magnetic field parallel to the cylindrical axis. 



Electron Motion. To understand the operation of a magnetron, it is 

 necessary first to understand the nature of the electron trajectories in a 

 static, nonoscillating magnetron. When an electron leaves the cathode and 

 is accelerated toward the anode by a small anode potential, its trajectory is 

 curved by the action of the magnetic field. The electron follows a quasi- 



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