The ferrite-embedded drop-in circulator for millimeter wave communication systems

We have developed a ferrite-embedded drop-in circulator (FEC) that operates on the W-band for millimeter wave communication systems. The FEC is taken as the composite structure, that is, the Sr-ferrite disc is embedded in a dielectric layer which is formed on an alumina substrate. The FEC does not require a magnet by using the large anisotropy field, H/sub a/ of Sr-ferrite. And the FEC has a high flexural strength and has a coefficient of thermal expansion (CTE) similar to that of ceramic materials which are used for a multi-chip radio frequency (RF) module. As a result, the FEC can be assembled directly on multi-chip RF module. Moreover, benzocyclobutene (BCB), an organic resin, is the material used in the dielectric layer of the FEC. Using organic resins like BCB in the dielectric layer makes the process of embedding ferrite easy and simplifies fabrication. BCB also offers other advantages such as low dielectric loss, low moisture absorption, and excellent planarization. The optimumly configured FEC performed well, demonstrating an insertion loss of less than 2 dB, a return loss of more than 20 dB, and an isolation of more than 25 dB at 60 GHz. Using the MCM with the FEC directly assembled. Millimeter wave communications equipment are expected to have less than a tenth volume of conventional equipment and also to decrease in cost.