Low NF Active Quasi‐Circulator Design Based on Noise Suppression Technique

ABSTRACT In this paper, an active quasi‐circulator (QC) exhibiting a low noise figure (NF) of 1.1 dB is presented, which is composed of two couplers, three connecting transmission lines (TLs) and a nonreciprocal stage. High isolation between transmitter (Tx) and receiver (Rx) ports can be obtained through two‐path signal cancelation by precisely designing the amplitude and phase of the nonreciprocal stage, which is realised by an amplifier. To reduce the additional noise introduced by the amplifier, a noise suppression technique that exploits the inherent isolation of the coupler is employed. A QC is designed to validate our design approach, which achieves an operating bandwidth of 1.82–1.96 GHz with > 20‐dB Tx–Rx isolation, a minimum in‐band Tx‐antenna (Ant) IL of 2.6 dB, an Ant‐Rx IL of 0.9 dB and a NF of 1.1 dB.