MAGXETROX AS GEXERATOR OF CEXTI METER WAVES 259 



these have been aimed at meeting requirements (3) to (5) above. The con- 

 structions liave made use of wire meshes and of sintered nickel matrices both 

 to reduce the coating resistance and to hold sufficient material on the cathode 

 in a manner such that it may be dispensed gradually during life. 



10.8 The Magnetic Circuit: The magnetic field required for operation of 

 the magnetron oscillator is generally obtained, e.xcept in laboratory e.xperi- 

 ments, by means of a permanent magnet. At long wavelengths and in 

 early models at shorter wavelengths, the magnetron and permanent magnet 

 are separable. Building the magnetic pole faces into the magnetron struc- 

 ture itself and attaching the magnetic material to it has made possible the 

 reduction of the over-all magnet gap, and hence total magnet weight, as 

 well as the use of mechanically superior axial cathode mountings. The 

 resulting so-called "packaged" magnetron design has been used at shorter 

 wavelengths where the magnetic fields are high but need not extend over a 

 large area. The total magnet weight under these conditions is much less 

 than that required in a separate magnet. Needless to say, the possession of 

 good permanent magnet material and the work done on magnet design have 

 contributed materially to the success of the centimeter wave magnetron. 



10.9 Magnetron Measurements: The fundamental measurements made 

 on the magnetron oscillator have already been discussed or alluded to where 

 the performance characteristics of the magnetron and its circuit theor}- are 

 described. Here will be described briefly the technique of measurement. 



Magnetron measurements are of two general types. One is made on the 

 oscillating magnetron and the other on the non-oscillating magnetron. 

 The latter may be made at any stage in the fabrication of the magnetron 

 after its anode structure and output circuit are completed. Figs. 39 and 

 40 illustrate schematically the apparatus employed in these tests. 



Perhaps the best way of describing the techniques of magnetron measure- 

 ments is to list all of the parameters, quantities, or characteristics asso- 

 ciated with such measurements and for each to give the definition, method 

 of measurement or calculation, or the way it is put together from other 

 data, as the case may be. In any event, the list given below permits of 

 ready reference. Although the text applies directly to pulsed magnetrons 

 the simplifications for CW magnetrons are obvious. 



The DC magnetic f eld, B, in w'hich the magnetron operates is generally 

 supplied in the laboratory by an electromagnet, the field in the gap generally 

 being calibrated in terms of the current passed through the magnet coils. 



The peak DC voltage, V, applied to the magnetron cathode is measured by 

 means of a peak voltmeter or by observing a known fraction of the voltage 



