CIRCULAR ELECTRIC WAVE IN SERPENTINE BENDS 



1289 



01 



< 



a. 

 u 



z 



z 

 o 



I- 

 < 



3 

 Z 



UJ 



t- 

 < 



LU 



1.0 

 0.8 



0.6 

 0.4 



0.2 



0.1 

 0.08 



0.06 



0.04 



0.02 



0.0 1 

 0.008 



0.006 

 0.004 



0.002 



0.001 



10 20 40 60 100 200 400 600 1000 2000 



SPACING OF MODE FILTERS IN FEET 



4000 6000 10,000 



Fig. 2 — TEoi attenuation increase of TE01-TE12 coupling in serpentine bends 

 with mode filters; 2-inch I.D. 2f-inch O.D., X = 5.4 mm. Serpentine bends are 

 caused by equally spaced supports and the elasticity of the copper pipe. The sup- 

 porting distance is a multiple of the beat -wavelength between TEoi and TE12 . 



An alternative to control the coupling effects is insertion of mode 

 filters into the line. Mode filters which pass the TEo„ waves ^nthout loss 

 but attenuate all other modes have been developed in various forms. 

 To estimate the amount of mode conversion control that can be achieved 

 by mode filters, we make two different assumptions. Only the critical 

 case of the supporting distance ecjual to a multiple of the beat wave- 

 length is considered here. 



A. The mode filters are ideal; they present infinite attenuation to all 

 unwanted modes. At the input of a section between two mode filters we 

 have a TEoi wave only and at the output the spurious mode level has 

 risen to 





w 



Co 



EI (2A/5)2 



(34) 



