Ferroelectric Phase Shifters for VHF and UHF

An electric field controlled ferroelectric phase shifter has been developed which provides a differential phase shift of approximately 100/spl deg/ per centimeter at a frequency of 200 Mc /s. The attenuation varies from 1.1 to 1.5 db per centimeter. The phase shifter, shown in figure1, was constructed in dielectric loaded parallel plane waveguide in which the dominant TE/sub10/ surface wave mode is excited. This transmission line is inherently suited to the construction of devices requiring control by a uniform electric field. As shown in figure 1, the surface wave is launched onto and collected from the ferroelectric loaded line by means of a coaxial line feeding through the upper plate. The center conductor traverses the space between the parallel plates and contacts the lower plate. Prior analysis 2 has shown that this method of surface wave launching is extremely efficient and broadbanded when the dielectric constant (K) of the dielectric slab is very high. In addition it has been found that if the dielectric constant is very high, as it is in the case of ferroelectric materials (K>1000), then the launching efficiency is independent of the dielectric constant. Thus changes in the dielectric constant due to electric field and temperature changes do not affect the launching efficiency. It has been analytically and experimentally determined that the impedance of the ferroelectric loaded parallel plane waveguide is very low compared to the impedance of the unloaded parallel plane regions beyond the extremities of the ferroelectric slab. Hence, very little power radiates from the ends of the slab.