Ferroelectric materials for phased array applications

Ferroelectric materials have the unique property of variable dielectric constant with applied DC bias voltage. This property can, in principle, be used to develop phase shifters for phased arrays. However, the high dielectric constant and the high loss of pure ferroelectric materials have limited their applications in phased arrays. Improvements in ferroelectric composite materials prompted renewed interest in developing phase shifters at microwave frequencies. A typical phased array uses several thousand radiating elements and phase shifters, and hence it is very expensive. The Naval Research Laboratory (NRL) is developing a lens antenna that incorporates bulk phase shifting using ferroelectric material. The ferroelectrics were developed at the Army Research Laboratory (ARL); they are low-cost, bulk oxide-ceramic composites of barium strontium titanate oxide (BSTO). The lens approach reduces the number of phase shifters, phase shifter drivers and controls resulting in a low-cost phased array. This paper describes the ferroelectric lens concept and methods of using this lens in developing low-cost phased arrays. The properties of ferroelectric materials and the improvements at the ARL, in reducing the dielectric constant and the loss tangent are then discussed. This is followed by the presentation of the theoretical and experimental results and conclusions.