Circulators for microwave and millimeter-wave integrated circuits

The requirements for circulators for use in combination with microwave and millimeter-wave integrated circuits are reviewed, with special emphasis on modules for phased-array antennas. Recent advances in broadbanding and in miniaturization are summarized. Novel types of circulators that are fabricated by attaching a ferrite disc and a suitable coupling structure to the surface of a dielectric of semiconductor substrate (quasimonolithic integration) are described. Methods for achieving complete monolithic integration are also discussed