Ultra-Wide Band On-Chip Circulator With Sequentially Switched Delay Lines (SSDL)

The Sequentially-Switched Delay Lines (SSDL) consists of a set of RF switches and transmission lines of equal length which provides magnetless nonreciprocity with no theoretical bandwidth limit. SSDL circulator architectures are presented in this paper on a GaN MMIC. The SSDL circulators presented here demonstrate nonreciprocity from 10 MHz to 1.2 GHz with isolation between the transmitter and receiver which is greater than 20 dB for most of the measured frequency range. The insertion loss of the GaN MMIC SSDL circulator is reduced to below 3 dB from 10 MHz to 800 MHz, by using matching circuits at the gates of the switching transistors. The spurious-free operation of the SSDL circulator is also verified from 10 MHz to 1 GHz. It is also demonstrated that with passive bootstrapping, SSDL insertion loss is further reduced to about 2 dB and P1 dB performance can be significantly enhanced by an additional 10 dB. The time-modulation/switching strategy to achieve broadband magnetless nonreciprocity has the potential to be used in future STAR and full duplex communication systems.