MICROWAVE REPEATER RESEARCH 



237 



of a window in the side of the cavity when a waveguide line is used, and by 

 means of a wire loop projecting within the cavity when a coaxial line is used. 

 Amplifiers employing both types of coupling were designed and tested. The 

 coaxial coupling type with links approximately one-half wavelength long 



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Fig V-15 —A single stage of a coaxial-coupled amplifier using the velocity modulated 



tube of Fig. V-14. 



proved the easier to adjust. Variation of the coupHng from zero to a maxi- 

 mum is accompHshed by rotating the plane of the coupling loop through 

 90°. Each cavity is provided with a small plate of resistance fihn pro- 

 jecting into the field in such a way that rotation of the plate about an axis 

 lying in the plane of the plate will vary the resistive loading present in the 

 cavity from zero to a maxunum. Finally, the input and output cavities of 



