1120 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



idized copper was next best while the steel line with a 20-mil inner copper 

 lining was the poorest. 



In the "J/ig" I-I^- oxygen-free high conductivity copper line the meas- 

 ured attenuation was 17 per cent higher than the calculated value (see 

 a meas/a: calc in Table I). This higher loss is attributed to spurious mode 

 conversion and to surface conductivity effects. In the %" line of the 

 same material the a meas/a calc = 1.29 which is an increase of 12 per 

 cent relative to the smaller waveguide. Since the %'' diameter line sup- 

 ports about four times the number of modes of the Jite" diameter line, 

 this increase in loss is attributed to mode conversion. In the other two 

 %'' diameter guides the added losses are believed to be increased mode 

 conversion which results from the poorer dimensional tolerances. These 

 data are listed in Table I together with dimensional tolerances. In this 

 table Q!meas is the measured attenuation averaged over the 5.2-5.7 mm 

 band together with the variations shown in Fig. 8; acaic is the average 

 theoretical attenuation for standard (I ACS) copper. The I.D. tolerances 

 are listed in two sets of rows A and B ; row A gives the fractional variation 



CARBON-LOADED 

 NEOPRENE 



END' 

 COUPLING 

 SECTION 



TYPE 



MEDIUM 

 SMALL 



O. P. 

 2" 



I.D. 



7/ a" 



7/16" 



o.oao" 



0.081" 



i 



Fig. 9 — Structure of spaced-disk mode filter. 



