1256 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 



of transducer has the same geometric appearance (aside from exact 

 dimensions) for any mode in the round guide and is attractive in that 

 it presents a matched impedance to all the modes of propagation. This 

 property may be used to combine a series of signals onto different modes 

 in a single transmission line. The coupled wave transducer may also be 

 employed to multiplex a series of frequency bands into one pipe. We 

 may wish to employ the long-distance waveguide over the frequency 

 band from perhaps 35,000 mc to 75,000 mc and will require a series of 

 transducers to go from dominant mode guides in various portions of this 

 band to the circular-electric wave in the round guide. Frecjuency-selec- 

 tive coupled-wave transducers may be employed in the manner sketched 

 in Fig. 30 to multiplex these frequency bands into the pipe for the long 

 distance transmission. 



A. G. Fox'* has shown that dielectric waveguides are attractive as a 

 flexible connecting link for terminal equipment in the millimeter wave 

 region and may also be employed in circuits such as hybrids. 



On all of these items of millimeter wave technique and multimode 

 waveguide technique, individual publications will appear as soon as the 

 work has reached the point where this becomes possible. 



MODULATION METHODS 



The modulation method to be used for the transmission of intelligence 

 on a waveguide system will probably be dominated by the conversion- 

 reconversion phenomenon already discussed. In order to evaluate the 



,-z 



COUPLING 

 APERTURE 



Fig. 29 ■ — Coupled-wave transducer for generating circular-electric or other 

 .veeruide modes. 



waveguide modes. 



