Highly Linear Magnetic-free Isolator Based on a Time-Modulated Differential RF MEMS Lattice Filter

This paper experimentally demonstrates the first time-varying magnetic-free RF MEMS isolator. For the first time, magnetic-free non-reciprocity is achieved by periodic modulation of an individual differential Aluminum Nitride (AlN) thin-film bulk acoustic resonator (FBAR) based lattice filter. The fabricated FBAR lattice filter is used as an ultra-compact and low-loss frequency selective delay network and it is periodically modulated by RF switches. By taking advantage of the differential nature of the designed lattice architecture, only one MEMS filter is required to achieve non-reciprocity, significantly reducing the system complexity. Due to the high figure of merit (FoM) of the FBARs, large group delay (30 ns) is achieved with low insertion loss (IL) leading to the demonstration of a miniaturized RF isolator characterized simultaneously by low IL (5.8 dB), strong isolation ( dB), broad bandwidth (20 dB isolation bandwidth ~20 MHz), and with an ultra-low modulation frequency (4.5 MHz). This modulation frequency is significantly lower compared to conventional magnetic-free non-reciprocal networks based on transmission lines and lumped elements. Furthermore, such a low modulation frequency allows the use of GaAs SPDT RF switches with large power handling performances, resulting in an isolator with the highest power handling performance and highest linearity ( P1dB=27.8 dBm; IIP3=51 dBm) ever demonstrated among time-modulated magnetic-free non-reciprocal networks.