MAGNETRON AS GENERATOR OF CENTIMETER WAVES 321 



output power and pulling figure against frequency could be obtained with 

 it. The fundamental mechanical problems of "packaging" the magnetron 

 and providing facilities for driving the tuning head were shown to be feasible 

 and a smooth working and resettable driving mechanism designed and 

 constructed. 



The Columbia Radiation Laboratory built a series of these magnetrons, 

 several of which were used in the development of tunable radar systems. 

 The Bell Laboratories had cooperated from the start by supplying 725A 

 magnetron parts, and by making anode inserts of special dimensions to raise 

 the maximum attainable wavelength of the resonator system. It was 

 decided that the Bell Laboratories should take over the main burden of 

 further development of the magnetron for manufacture by the Western 

 Electric Co. By this time its specifications had been quite definitely estab- 

 lished. It was to be a magnetron with the general power output capabilities 

 of the 725A, tunable over the frequency range from 8500 to 9600 mc/s 

 (approximately 3.13 to 3.53 cm.). It was to be interchangeable with the 

 725A magnetron in the sense that it could be installed directly in any radar 

 system using the 725A when the magnetron and its magnet were removed. 

 Interchangeability, as usual, was one of the most annoying requirements. 

 The magnetron was to be "packaged" and provided with magnetic shunts 

 so that the magnetic fields necesssfty for operation at 10 kv. and 10 amps., 

 12 kv. and 12 amps., and 14 kv. and 14 amps, could be attained with a 

 single magnet design. No specific requirements on variation of output 

 characteristics were made at that time, but it was understood that only a 

 magnetron whose pulling figure varied by an amount of the order of 3 mc/s 

 or less over the entire frequency band would be acceptable. Similarly, it 

 was understood that the tuning mechanism should provide smooth varia- 

 tion in frequency with a minimum of backlash and of such resettability that 

 the use of a wavemeter would not be required in setting the radar system to a 

 new frequency. 



During the course of the development at the Bell Laboratories it became 

 necessar>^ to redesign the magnetron in a number of important respects. 

 The requirement that the magnetron operate at 14 kv. and 14 amps, de- 

 manded a magnetic field for which the magnet weight would be prohibitive. 

 Consequently, anode and cathode radii were scaled from those of the 725A 

 magnetron by the factor 1.2. The larger cathode resulting from this re- 

 design made easier the problem of attaining the maximum of 200 kw. peak 

 input power required by the specifications. However, it caused a recurrence 

 of the difficulty with a resonance of the tuning pin structure appearing in the 

 8500 to 9600 mc 's range. This had been found at the Columbia Laboratory 

 to be a resonance of the capacitance between the pins and anode structure 



