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BELL SYSTEM TECIIMCAL JOURNAL 



"suppression of the extraneous modes". In this process, an exact knowledge 

 of the distribution of the currents in the cavity walls has been found highly 

 useful. 



For example, it has been found experimentally that annular cuts in the 

 end pliUes of the cylinder give a considerable amount of suppression to many 

 types of extraneous modes with very little effect on the performance of the 

 desired TE Oln mode. These cuts are narrow slits concentric with the axis 

 of the cylinder and going all the way through the metallic end plates into a 

 dielectric beyond.- The physical explanation is that an annular slit cuts 

 through the lines of current fiow of the extraneous modes, and thereby 

 interrupts the radial component of current and introduces an impedance 

 which damps, or suppresses, the mode. For the TE Oln mode, the slits 



k = ^ ^ kl-^ kl 



A 



^1 



2r , _ nv 



D ' ~ L 



r = ;;;"' root of J f{x) = for TM Modes. 

 = m"' root of /;.(.v) = for TE Modes. 

 D = cavity diameter 

 L = cavity length 

 Fig. 1 — Components of H vector at walls of circular c_\ Under cavity resonator. 



are parallel to the current streamlines and there is no such interruption; 

 presumably there is a slight increase in current density alongside the slit, 



2 Similar cuts through the side wall of tlie cylinder in planes i)erpendicular to the 

 cylinder axis are also henctkial, hut are more troublesome mechanically. 



