Observed 5-6 mm Attenuation for the 



Circular Electric Wave in Small and 



Medium-Sized Pipes 



By A. P. KING 



(Manuscript received March 20, 1956) 



At frequencies in the 50-60 kmc region the use of circular electric wave 

 transmission can provide lower transmission losses than the dominant 

 mode, even in relatively small pipes. 



The performance of two sizes of waveguide was investigated. In the small 

 size (Kg" ^•^- X Me" wall) the measured TEoi attenuation was approxi- 

 mately 5 db/100 ft and is appreciably less than that of the dominant mode. 

 The measured attenuation for the medium sized (%" I.D. X }^i'^ wall) 

 waveguide was 0.5 dh/100 ft which is about one-fourth that for the dominant 

 mode. 



This paper also considers briefly some of the spurious mode conversion- 

 reconversion effects over the transmission band and their reduction when 

 spurious mode filters are distributed along the line. Allowance has been 

 made for the added losses due to oxygen absorption when air is present. 



INTRODUCTION 



Since 5.4-mm dominant-mode rectangular waveguide has attenuations 

 of the order of 60 db/100 ft, another transmission technique is required 

 in applications which involve appreciable line lengths. Losses may be 

 reduced by the use of oversize waveguide ; some earlier work with domi- 

 nant mode transmission in slightly oversize round waveguide (two or 

 three propagating modes) has been reported.^ The possibility of still 

 lower losses exists with circular electric wave transmission in an over- 

 size round waveguide. Miller and Beck- have computed the theoretical 

 relative transmission losses of the TEoi and TEn modes as functions of 



' A. P. King, Dominant Wave Transnaission Characteristics of a Multimode 

 Round Waveguide, Proc. I.R.E., 40, pp 966-969, Aug., 1952. 



2 S. E. Miller and A. C. Beck, Low Loss Waveguide Transmission, Proc. I.R.E., 

 41, pp 348-358, March, 1953. 



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