A Novel High-Linearity Ultrawideband Quasi-Circulator With 1.76-dB NF and 1.45-dB TX-ANT Insertion Loss

This article presents a novel high-linearity, ultrawideband (UWB) quasi-circulator that achieves a noise figure (NF) of 1.76 dB and a transmitter-antenna (TX-ANT) insertion loss of 1.45 dB, outperforming all prior designs. Additionally, it achieves more than 24.6-dB transmitter-receiver (TX-RX) isolation across a fractional bandwidth of 109%, spanning 0.5–1.7 GHz, with a maximum TX-RX isolation of 66 dB, demonstrating superior capability in minimizing signal leakage. The quasi-circulator leverages a low-noise impedance (LNI) termination at the isolation port of a directional coupler to significantly reduce the NF while maintaining wideband operation and notable linearity, with an input third-order intercept point (IIP3) of 45.6 dBm for antenna-receiver (ANT-RX) and 24.6 dBm for TX-ANT. This design, implemented with discrete components using a SiGe transistor, avoids digital circuitry and switching architectures, offering a simpler and more robust solution. It is fully compatible with IC technologies, including CMOS and SiGe, enabling scalability and compact designs, while GaAs and GaN technologies can further enhance power handling for high-power applications. Extensive simulations and measurements validate its stability, wideband performance, and noise reduction, positioning it as a high-performance solution for full-duplex communication systems and other modern RF applications.