Compact Self-biased Q-band Circulators

This article deals with the design and fabrication of compact self-biased $Q$ -band circulators. A pre-oriented substituted strontium hexaferrite that has a high anisotropy field was used to design a planar circulator at 38 GHz. The component has been measured in the 32–40 GHz frequency band at different temperatures. Measured insertion loss as low as 0.45 dB together with a high isolation level has been demonstrated. Moreover, the component demonstrated a quite stable temperature behavior. However, a slight shift toward low frequencies is observed compared to the simulation. Retro-simulations showed that small variations of the metallic strips’ dimensions induce significant S-parameters changes. These experimental results demonstrate that substituted strontium hexaferrites have a high potential for the realization of ultra-compact $Q$ -band circulator but also that the metallization process resolution is crucial for performance reproducibility.