Self-Biased Microstrip Junction Circulator Based on Barium Ferrite Thin Films for Monolithic Microwave Integrated Circuits

Barium hexaferrite thin films with thickness of 8 μm had been deposited on a sapphire substrate by radio-frequency magnetron sputtering. The results show that the grain size is about 2 μm in diameter. The coercivity is about 2.2 kOe and the saturation magnetization is about 4000 Gs with remanence ratio of 0.58. Based on the sputtered thin films, a self-biased microstrip junction circulator had been developed. The measured S-parameters indicate that a nonreciprocal effect greater than 10 dB occurs at about 26 GHz. The maximum isolation is 44 dB and the minimum insertion loss is 27 dB. The origins of the large insertion losses have been discussed.