  This paper reports the first demonstration of a magnet-free, high performance
microelectromechanical system (MEMS) based circulator. An innovative circuit
based on the commutation of MEMS resonators with high quality (Q) factor using
RF switches is designed and implemented. Thanks to the high Q factor, a much
smaller modulation frequency can be achieved compared to the previous
demonstrations, reducing the power consumption and enabling the use of high
power-handling switches. Furthermore, the MEMS resonators greatly reduce the
required inductance value, guaranteeing much smaller form factor compared to
the previous LC demonstrations. The demonstrated circulator shows broad BW (15
dB-IX BW=34.7 MHz for an operational frequency around 2.5 GHz), low IL (4 dB),
high IX (30 dB), high linearity (P1dB=28 dBm; IIP3=40 dBm) and at the same time
low power consumption, addressing several of the current limitations hindering
the full development of magnet-free circulators.
