714 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1954 



12345678 



A-/^2 



2C 



Fig. 51 — Transfer loss E-2* versus (0i — 02)/2c for coupling strength ex = 

 7r/2, the value required for complete power transfer. 



of which is air-filled and the other of which is filled with a material of 

 dielectric-constant e. The phase constants for these waveguides have the 

 form sketched in Fig. 52, in which /3o is the phase constant in free space. 

 At the frequency /,„ the two waveguides have identical phase constants 

 and, in a typical case, negligible loss constants so that complete power 

 transfer can be obtained. For the case e = 2.55, Fig. 53 shows the com- 

 puted frequency characteristic on the assumption that the integrated 

 coupling is set for complete transfer (ex = 7r/2) and is independent of 

 frequency. (Actually the usual coupling mechanisms are somewhat fre- 

 quency sensitive and would increase the selectivity somewhat.) This filter 



'Cl 'C2 



FREQUENCY — »• 



Fig. 52 — The general form of the phase constants for two hollow conductor 

 waveguides, one of which is filled with a dielectric. 



