Dielectric Constants and Power Factors at Centimeter Wave-Lengths

T H E R E 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 very manageable and has several advantageous features. When this work was begun, the 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 admittance per unit length, surge impedance, impedance transformation factor, voltage and current step-up factors, resonance selectivity or "Q", etc.