COUPLED WAVE THKOPvY AND WAVKOT'IDE APPLTCATIOXS 



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FREQUENCY IN KMC 



Fig. 49 — Impedance characteristic of the transducer of Fig. 42. 



smoothly according to a cosine amplitude function as would be expected 

 for two coupled waves of identical phase constant, but instead exhibited 

 ripples. The remarkable thing about the data of Figs. 45 and 4G is that 

 it agrees with the theory for two coupled waves as well as it does. 



The coupling per individual orifice decreases with increasing frequency 

 and this is verified hy the observation (Fig. 46) that a greater number of 

 couphng elements are required to reach the maximum insertion loss in 

 the rectangular guide at the higher frequency. 



Some indication of the overall bandwidth of this first experimental 

 model is given in Figs. 47, 48 and 49 which show respectively the TEio° — 

 TEoi° transfer loss, the insertion losses in the TEio° and TEoi° modes, 

 the TEio° - TEuO and TEio° - backward wave TEoi° transfer losses, 

 and the TEio° and TEm^ return losses in the frequency range 20,000 to 

 30,000 mc. Xo one of these characteristics represents the degree of ex- 

 cellence which is achie\'able but they do demonstrate that good im- 

 pedance match, low transfer losses to the desired mode, and appreciable 

 discrimination against unwanted modes, can be achieved over frequency 

 ratios on the order of 1.5. 



FREQUENCY SELECTIVITY 



In the case wherein the coupling is so weak as to not affect the total 

 phase constant appreciably, all modes of hollow conductor waveguides 

 of any cross section have the same phase constant at all frequencies pro- 

 vided that these modes have the same cut-off frequency. This results 



