Batch-Fabricated Substrate-Embedded Ka Band Self-Biased Circulators Using Screen-Printed Strontium Hexaferrite/PDMS Composite

In this work, we report a Ka band self-biased microwave circulator using a strontium hexaferrite (SrM) / polydimethylsiloxane (PDMS) nanocomposite fabricated with a low-temperature (70 °C), packaging-compatible, screen-printing process. The magnetic composite shows a ferromagnetic resonance frequency (FMR) of 44.3 GHz. A millimeter wave circulator completely embedded in a Rogers 5880 substrate with a thickness of 254 µm and a total area of 33 mm² is designed, fabricated, and characterized. At an operational frequency of 37.2 GHz, the measured insertion loss (IL) and isolation (IS) of the circulator are 5.4 dB and 22.2 dB, respectively. The measurement results match with the simulation results from High Frequency Structure Simulator (HFSS) and compare favorably with those of other magnetic circulators from literature.