Packaged Quasi-Circulators With Low NF and High Isolation Considering the Fabrication Tolerance

A packaged quasi-circulator (QC) with low noise, low insertion loss (IL), high isolation, and ease of manufacturing is proposed in this letter. The proposed QC is constructed by two couplers, three connecting transmission lines (TLs), and a common-emitter amplifier. High isolation between transmitter (TX) and receiver (RX) ports can be obtained using two-way signal cancellation by designing the amplitude and phase of the amplifier, while the noise from the amplifier is suppressed by the isolation of the coupler. The negative group delay (NGD) technique is introduced to change the slope of the loop phase to improve the TX-ANT transmission bandwidth. Furthermore, a reconfigurable load is employed to ensure high isolation within a wide frequency range since the isolation performance is sensitive to the fabrication tolerance. For design validation, a QC is designed and fabricated, which achieves the in-band TX-ANT IL of 2.1 dB, ANT-RX IL of 1.7 dB, and noise figure (NF) of 2.3 dB. By tuning two controlling voltage of varactors, the proposed circulator can obtain >40 dB isolation in the frequency range of 1.925–2.09 GHz.