HVPER-FREQUENCY WAVE GUIDES 



299 



the form of a movable piston. Another form is a resonant chamber 

 containing some dissipative material. C'onditions for termination 

 may be calculated in so far as the properties of materials are known 

 or the>- may be determined e.xperimentally by successive adjustments 

 of film density and piston adjustments until standing waves have been 

 eliminated. Figure 10 shows graphically a typical series of experi- 



50 



4.5 



;4.o 



3.5 

 3.0 

 2.5 



2.0 



150 200 250 

 RESISTIVIT 



Fig. 10 — T\-pical set of experimen 



PROPAGATED 

 WAVE 



_ \/\ 



FREQUENCY = 1900 MEGACYCLES 

 WAVELENGTH IN AIR = 15.79 CENTIMETERS 



300 350 400 450 500 550 600 650 700 

 OF FILM IN ARBITRARY UNITS 



al data as various degrees of impedance match 

 are obtained. 



mental data of the magnitudes of standing waves as various degrees 

 of impedance match are obtained. 



Frequency Selectivity 



It is evident from Fig. 7 above that wave guides are inherenth" 

 high-pass filters. There is still another property of a wave guide 

 that may also provide selectivity. It depends on the principle of 

 standing waves. By this means, resonance effects may be produced 

 that make a short section of guide behave somewhat as if it were a 

 simple series circuit consisting of an inductance and a capacity in series 



