CST MICROWAVE STUDIO® (CST MWS) features two specialized frequency domain techniques for resonant structures.
The Resonant: Fast S-parameter Solver (also known as MOR solver) is an advanced mathematical approach which directly calculates the S-parameters without calculating the fields. The principal application is filter design, where tremendous speed-ups can be achieved; field patterns, however, cannot be visualized.
The Resonant: S-Parameter, Fields Solver (extended Modal Analysis) can be reached through the Frequency Domain Solver menu, as option for highly resonant structures. It is applicable to hexahedral grids. After the modes of a device have been calculated, this very efficient technique can derive the S-parameters of the filter with little additional simulation time. In addition, the calculation of field patterns at arbitrary frequencies inside the range is possible.