Bandwidth Optimization of an Integrated Microstrip Circulator and Antenna Assembly: Part 2

The integration of a ferrite circulator with an arbitrary load - such as a wideband antenna - is considered by examining the conditions for perfect circulation over large bandwidths. These conditions relax the requirements of the loading impedance from being purely real (e.g., 50 ohms) to being complex, per a circulation impedance equation. The impedance equation is couched in terms of open-circuit impedance parameters, which are the natural parameters for describing an embedded microstrip circulator. By means of a rigorous field analysis, the impedance parameters are computed by modeling the microstrip ferrite circuit as a closed PEC/PMC cavity. The justification, features, and limitations of this model are discussed in detail, it is shown herein how the Z parameters can be invoked in some search algorithm to optimize the parameters of the ferrite, to achieve either superb circulator bandwidth or isolation performance. An example of a wideband circulator is given for which both simulation and experimental data are provided. The high degree of correlation between these two data sets corroborates the methodology