35-GHz Barium Hexaferrite/PDMS Composite-Based Millimeter-Wave Circulators for 5G Applications

We report a self-biased, low-profile circulator operating in the Ka-band fabricated by an entirely low-temperature (70 degrees C) screen-printing approach on printed circuit board (PCB). The magnetic material for the circulator is a barium hexaferrite BaFe12O19 (BaM)/polydimethylsiloxane (PDMS) nanocomposite that exhibits a zero-bias ferromagnetic resonance frequency (f(FMR)) at 46.6 GHz. Using this material, a microstrip-based circulator operating at 35 GHz is designed, fabricated, and characterized. A combination of mechanical milling, screen printing, photolithography, and electroplating is used for fabricating the circulator, in which the circulator disk (diameter of 2 mm and thickness of 250 mu m) is completely embedded in the PCB, realizing a packaging compatible low-profile architecture with the total device area of 33 mm(2). The measured isolation (IS) and insertion loss (IL) of the fabricated circulator at 35 GHz is 3.9 and 8.7 dB, respectively. When the additional magnetic bias is applied to the circulator using external permanent magnets, the IS and IL performance is improved to be 7.4 and 8.4 dB, respectively. The impact of the loss factors associated with dielectric loss and surface roughness on the device performance is analyzed using High Frequency Structural Simulator (HFSS).