COUPLKD WAVE THEOKY AXD WAVKOnOK APl'LICATIOXS 



715 



"A 10 



< 4 



1.00 



Fig. 53 — The transfer loss E2* versus normalized frequency for two coupled 

 hollow conductor waveguides, one of which is air filled and has a guide wavelength 

 ■y/2 times the free space wavelength at/,,, , and the other of which is filled with a 

 material of dielectric constant 2.55 with dimensions chosen for equality of phase 

 constant with the air-filled guide at /„, . Coui)ling ex assumed constant at ir/2. 



characteristic applies regardless of the shapes of the hollow conductor 

 waveguidess (which may be dissimilar) and regardless of the modes 

 selected. 



It is apparent that frequency selectivity in the transfer characteristic 

 E2* can also be obtained without recjuiring that the phase constants be 

 unequal by using coupling elements which are freriuency sensitive. 



DIELECTRIC WAVECiUIDE CONFIGURATIONS 



The coupled-wave approach to circuit design is applicable using any 

 form of transmission line, the only important variant associated with 

 different forms of line being the physical structure associated with intro- 

 ducing the desired coupling between lines. In a recent publication*' A. G. 

 Fox showed that dielectric waveguides are very attractive for use in the 

 millimeter wavelength range, and this section points out how dielectric 

 waveguides can be used in various forms of coupled wa\'e devices. Fox 

 showed that dielectric waveguides arranged in the configuration sketched 

 in Fig. 54 are coupled by the electric field components only, and that 



