Active RF Circulators

Applied Radar Inc. proposes the development of active MMIC-based circulators in order to achieve high isolation between transmit and receive paths for simultaneous transmit and receive (STAR) phased-array radar system architectures. This technology will enable increased persistence in intelligence, surveillance and reconnaissance (ISR) systems and allow multiple simultaneous radar modes including SAR, GMTI and AMTI. The different pulse widths required by these various radar modes often precludes simultaneous multi-mode radar operation. Previous work in active MMIC circulators in the early 1990's demonstrated the concept of active circulator, but did not achieve the required performance. Recent advances in chip-level RF modeling, advances in device processes and new materials such as SiGe, GaN, and SiC show promise of achieving an active circulator with up to 40 dB of T/R isolation with less than 0.5 dB of loss, while handling 1 Watt or more of CW power. There is also a growing trend towards the integration of multiple RF components in a single chip. The development of a high-performance MMIC-based circulator will enable system-on-a-chip architectures, enabling increased phased-array functionality, while reducing size and cost.