Bandwidth optimization of an integrated microstrip circulator and antenna assembly. 1

A methodology for integrating a wideband circulator with a wideband antenna is considered herein. To accomplish this integration effectively, the conditions for perfect circulation are examined, whereby the port impedances of the circulator are allowed to be complex, treated as part of the design of the circulator, and couched in terms of network-scattering parameters. This approach allows for the design of a single matching network that interfaces between the circulator and the antenna, and effects a complex-to-complex impedance match for maximum power transfer. Simulation and experimental data for a stand-alone circulator and a compact circulator/antenna assembly are presented to validate the design methodology. The data shows that return loss and isolation on the order of 20 dB over a 4 GHz bandwidth about a 14 GHz center frequency was achievable, without the need of any post-fabrication adjustments