Optical and electrical studies of novel ferroelectric composites for use in phased array antennas

Abstract

Ceramic composites of barium strontium titanate and other non-ferroelectric oxides have been fabricated for use in phased array antennas. These composites have shown superior electronic properties at low and microwave frequencies in that they have reduced dielectric constants, low loss tangents and high tunabilities. However, minimal work (other than x-ray powder diffraction) has been reported on the correlation of these electronic properties to the site substitutions and the sample topography. Raman and FTIR spectroscopy has been used to study the structural properties related to the additions of both strontium to the barium titanate crystal structure as well as the effect of the additions of oxide 111 on Bal.xSrxTi03 (1-x = 0.00, 0.15, 0.30, 0.40, 0.45, 0.50, 0.55, 0.6,0.7,0.80, and 1.0). The optical properties of the ceramic composites have been correlated to the electrical properties of the materials such as the Curie temperatures and these results will be discussed in detail. I. IhTRODUCTlONPhased array antennas can steer transmitted or received signals either linearly or in two lmensions without mechanically oscillating the antenna. In order to make these devices available for many other commercial and militaTy uses, the basic concept of the antem must be improved. If ferroelectric materials could be used for the phase shifting element instead of ferrites, phased array antennas would be totally revolutionized.A ceramic Barium Strontium Titanate, Bal,SrxTi03, (BSTO), phase shifter using a planar microstrip construction has been demonstrated at 5-10 GHz. [1,2] BSTO/Oxide E l (designated as oxide III as the materials are undergoing the patent filing process) composites have shown greatly improved electronic properties at both low (KKz-MHz) to microwave frequency regions (10 GHz).[3] Most notably the loss tangents have been reduced to less than 0.002. [4] However, in order to improve the already adequate performance of the antennas, we have investigated composites with even lower loss tangents. We have therefore fabricated Bal-,SrxTi03 (BSTO) ceramics with a various molar ratios 0.55, 0.60, 0.70, and 1.00. The electronic properties of all of the above named compositions were then examined Additionally, Fourier transfm Raman and irhared spectroscopy was utilized to characterize . the BSTO composite as a function of the Ba / ratio and the site substitution of oxide JJI. Subsequently it was found that the materials containing barium content, 0.45, 0.50, 0.55 and U.S. Government work n o t p r o t e c t e d by U.S. copyright. O f barium, including, 1-x = 0.00, 0.30, 0.40 ,0.45, 0.50, 0.60 were the most promising in terms of the electronic properties appropriate for use in phased array antennas. Therefore, composites of B%.45Sr0.55Ti03, BW.50Sr0.50Ti03, B%.55Sr0.45Ti03, and B%.60Sr0.40Ti03/ Oxide III were fabricated and the electrical properties and optical properties were obtained. II. EXPERIMENTAL A. Ceramic Processing Powder forms of Barium Titanate and StrontiumTitanate were obtained fiom Ferro Corporation, Tran...

Sinterability and dielectric properties of Ba0.55Sr0.4Ca0.05TiO3–CaTiSiO5–Mg2TiO4 composite ceramics

“…In recent years, (Ba, Sr)TiO 3 (BST) solid solutions have attracted great attention as tunable materials in microwave tunable filed [1]. The dielectric properties of BST ceramics are required to be relatively low dielectric constant (<600), low dielectric loss (<6 × 10 −3 ), less temperature dependence and high electric field tunability [2].…”

Application of Ferroelectrics in Low-Cost Microwave Phased-Array Antennas

“…VTDs that we used are bulk composite ceramics of tunable ferroelectrics in the paraclectric phase and non-tunable materials [1,3]. In addition to providing bulk phase shift, VTDs offer reciprocal phase shift; i.e., the transmission coefficient through devices that use these materials is the same for different directions of propagation.…”

Magnetic and Dielectric Properties of BST/BF Multiferroic Ceramic Materials

“…When barium atoms are replaced by strontium atoms at A site in perovskite barium titanate matrix, the phase transition temperature of paraelectric to ferroelectric decreases and the phase transition behavior changes from sharp to diffuse [5][6][7]. Among the perovskites mixed systems, Ba 1-x Sr x TiO 3 (BST) is an interesting series due to its unique ferroelectric properties which are suitable for various potential applications [8].…”