Design and fabrication of the Bosma stripline circulator in LTCC technology

Low temperature co-fired ceramics (LTCC) have shown to be one of the most admirable materials in high-frequency components design ([1], [2]). Low dielectric losses and the applicability of highly conductive materials are making them desirable in production of high quality passive components, most often capacitors and inductors. These are the reasons that made this technology attractive for the circulator fabrication, and present the core of this paper. Bosma type of the circulator with Y-junction configuration is the topic of this work and is intended to use at the 5 GHz. Field analysis and the design of the circulator was adopted from Bosma in [3] and Wu in [4]. Theoretical analysis from these works predicts the values of geometrical parameters and the COMSOL simulation was made to confirm its validity. The fabrication process included standard LTCC production procedure consisting of dielectric and ferrite tape preparation, laser cutting, photolithographic screen stencil preparation, screen printing, lamination and, finally, co-firing. Fabricated samples were magnetically polarized and characterized. To maintain magnetic polarization of the produced circulator, small disk shaped neodymium magnets were placed on top and bottom of the ferrite discs. Measurements and characterization were performed on vector network analyzer in range of 4.5 - 8 GHz.