MICROWAITE PROPERTIES OF COMPOSITE CERAMIC PHASE SHIFTER MATERIALS Richard G. Geyerc, Jerzy Krupkab, Louise Senguptac, Somnath Sengupta" "National Institute of Standards and Technology 325 Broadway, Boulder, CO 80303 U.S.A. bInstytut Mikroelektroniki i Optoelektroniki Politechniki Warszawsliej Koszykowa 75, 00-662 Warszawa, Poland, "U.S. Army Research Laboratory Aberdeen Proving Ground, MD 21005 zyxw Abstract The microwave properties of bulk ceramic barium strontium titanate and non-ferroelectric oxide com- posites are measured at X-band with a cylindrical mode-filtered resonant cavity. A helical wire-wound waveguide makes up the cavity's cylindrical wall, which permits the use of high-purity TEolp reso- nant modes for high accuracy permittivity measure- ments. Measurement results at 300K show that mi- crowave dielectric losses increase as the stoichiomet- ric percentage of barium increases. The real relative permittivity increases with decreasing weight percent of added non-ferroelectric low-loss oxide. Dielectric losses rapidly decrease with the addition of a rela- tively small amount of non-ferroelectric oxide. 1 Introduction Recent advances in ceramic composites and thin- film deposition technologies have resulted in new fer- roelectrics with voltage-tunable dielectric constants at room temperature and improved dielectric loss properties. These new ferroelectrics, whether in bulk or thin-film form, have potential uses in microwave circuit applications. One application is in phased- array antennas. These antennas are currently con- structed using ferrite phase-shifting elements. The ferrite phase-shifting elements are relatively large and heavy. Because of the circuit requirements necessary to operate phased-array antennas, they are also ex- pensive. Ferroelectric materials offer the promise of reduced sue zyxwvut and weight, at a fraction of the cost. Therefore they could revolutionize phased-array an- tennas and could make these devices available for many commercial uses. One figure of merit of phase- shifting elements is that of maximum, temperature- stable phase shift consistent with minimum insertion loss. In this paper we report microwave dieIectric property measurements of various bulk composites of Ba,Srl-,TiO~ and low-loss non-ferroelectric oxides. These properties can be directly related to insertion losses and can be used as tests of previous effective medium theory formulations for two-phase compos- ites [l]. A very sensitive method was used to mea- sure permittivity and dielectric loss tangent of disk samples. This method allows the accurate measure- ment of high permittivity materials whose dielectric loss tangents range from to io-'. 2 Experimental Procedure The 50-millimeter X-band mode-filtered cavity which was used to measure permittivity and dielec- tric loss tangent is shown in Fig. 1. The cavity is constructed with a helix waveguide to filter all modes resulting from current flow other than that flowing circumferentially about the cavity wall (Fig. 2). For a cylindrical cavity that is not mode-filtered, both TEolp and irherfering TMllp modes occur, which re- sults from both azimuthal and radial current flow in the cavity end plates and axial current flow in the cylinder wall (Fig. 3). The use of helical guide yields a high-Q cavity with very pure TE-mode structure for precision electrical property measurements. No capacitive coupling be- tween sample and cavity end plate occurs with TEmp mode structure, and the quality factor for this mode U.S. Government work not protected by U.S. copyright. zyxwv 851