Dielectric Constants and Power Factors at Centimeter 

 Wave-Lengths 



By CARL R. ENGLUND 



The theory underlying the measurement of dielectric constants and 

 power factors, by means of resonant lengths of coaxial transmission 

 line, is developed, apparatus used for such measurements is illustrated 

 and the measurement routine described. A table of typical results is ap- 

 pended together with an "-Y tan A'" table for aid in the calculations. 



Introduction 



THERE are two instrumentalities available for measuring dielectric 

 constants and power factors at centimeter wave-lengths. These are, 

 coaxial conductor lines and wave guides. Which one is, for any condition, 

 the more favorable one depends a great deal upon the wave-lengths used. 

 Under the conditions encountered in this work the coaxial line appeared to 

 have the practical superiority, down to something like 10 cms. wave-length, 

 anyway. Below this, the wave guide is ver}-- manageable and has several 

 advantageous features. 



When this work was begun, tlie most easily available and practicable 

 vacuum tube which would oscillate around 20 cms. wave-length was the W. 

 E. Co. 368A. This could be pushed down to something below 19 cms. 

 wave-length but was undependable there and as a practical compromise 

 22.5 cms. wave-length was finally chosen. Later another tube became 

 available and as it could be operated down to at least 9 cms. it was used in 

 the more recent work. Thus, while the bulk of the measurements made 

 were at 22.5 cms. wave-length, a good share of the samples investigated 

 were also measured at approximately 10 cms. wave-length. 



Any measurements made at these wave-lengths must be made in the form 

 of transmission line measurements and the dielectric must be physically part 

 of the coaxial line. There are various transmission line quantities definable 

 and measurable, such as series impedance per unit length, shunt admit- 

 tance per unit length, surge impedance, impedance transformation factor, 

 voltage and current step-up factors, resonance selectivity or "Q", etc. The 

 first two are measurable directly only at long wave-lengths, the last two are 

 properties of space resonant line elements. Of these the "Q" was the most 

 advantageous in the present instance. 



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