Design of microstrip antenna/ferrite circulator systems

Circulators are commonly used in antenna systems to route microwave signals in a convenient manner. This paper presents a methodology wherein both the antenna impedance and the circulator scattering parameters are considered together in the system design. Two integrated antenna/circulator systems are presented to validate the approach. The planar antenna considered for this study is a modified version of the Yagi-Uda antenna presented by Kaneda et. al. (2002). Kaneda´s antenna provides a narrow beamwidth in the E-plane but, due to the planar structure, it presents a very wide beamwidth in the H-plane. It was shown in this work that the antenna geometry of Kaneda et. al. can be extended to provide a narrower beamwidth in the H-plane and corresponding improvements in antenna gain. When used in communication or radar systems, this additional gain can be used to offset the insertion losses associated with the circulator in the integrated system.