Active RF Circulators

The development of broadband high-isolation active circulators with simultaneous transmit and receive (STAR) capabilities would enable increased persistence in intelligence, surveillance and reconnaissance (ISR) systems and allow multiple simultaneous radar modes including SAR, GMTI and AMTI for global and local multifunction and multi-task operations. Previous works in MMIC active circulators demonstrated the concept and feasibility to realize the devices with stringent design requirements in order to achieve broadband and high isolation operation. Various active circulator configurations which are capable of STAR applications have been studied in our Phase I R&D, including a compilation of desired specifications for STAR radar application. The Phase I investigation also considered available device technologies and substrate materials in terms of power handling, frequency, bandwidth, isolation and interface matching. The Phase II effort will extend this work to implement and realize a broadband high-isolation active circulator with STAR and MMIC capabilities. The proposed work will include a trade-space study on the performance sensitivity of the active circulator based on power-to-noise and bandwidth-to-isolation requirements, development of active matching circuitry at antenna interface, development of feedforward cancellation circuits, final selection of foundry technology for device fabrication in terms of high power and low noise Figure (NF) applications, and finally device fabrication and testing. The development of a high-performance MMIC-based circulator will enable system-on-a-chip architectures with high isolation over a relatively wide bandwidth, while minimizing size and cost for phased array radar application.