Research on ferroelectric materials for millimeter wave application

A one-year research program has been undertaken to determine whether certain selected ferroelectric materials can be used to obtain effective phase control in millimeter wave radar systems. This investigation is an outgrowth of earlier work at Rockwell which included the first demonstration of microwave phase modulation in strontium barium niobate (SBN) single crystals. The present study combines materials development and millimeter wave characterization to investigate the feasibility of achieving sensitivity of the microwave refractive index to an applied electric field, dn/dE, in excess of 1/10,000 meters/volt, while maintaining absorptive loss in the material below a few dB per millimeter. Because measurements early in the program revealed high absorptive losses in the available strontium barium niobate crystals, the first six months have been devoted to expanding the materials base. In addition to the development of growth techniques for other tungsten bronze ferro-electrics, measurements of millimeter wave dielectric properties have been carried out on these ferroelectric and other systems obtained from the Penn State Materials Research Laboratory, including an antiferroelectric ceramic lead-lantanum zirconate-titanate (PLZT). These measurements generally show large decreases in polar axis permittivity from their dc values, suggesting an extrinsic origin for the bulk of the dc permittivity. The material factors controlling this phenomenon should be explored, since they will determine to what extent the observed high losses can be reduced over the frequency range of interest.