Method for Measuring the Dielectric Constant of Ferroelectric Ceramics at S‐Band Frequencies

Abstract

A method is presented for measuring the complex dielectric constant of ferroelectric ceramics at microwave frequencies. The method employs a disk‐shaped sample in a radial‐line configuration at the end of a coaxial‐line structure. An equivalent circuit, established by admittance measurements, is used to relate the radial admittance at the sample face to the measured admittance on the slotted line preceding the coaxial sample holder. The nonuniform variation of electric field over the face of the sample is taken into account by means of a continued fraction expansion of x J t ( x )/ J 0 ( x ) in terms of x = k′a , where k′ is the wave number in the ferroelectric sample and a is its radius. Representative data on the variation of the complex dielectric constant with temperature at 3 kmc. are given for two samples of BaTiO 3 fired under atmospheric pressure and 5000 lb. per sq. in. The frequency spectrum of hot‐pressed Cd 2 Nb 2 O 7 in the range 1.8 to 4.0 kmc. is also presented.