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CirculatorTransient Analysis Examples - S-Parameter Calculations: Waveguide Devices
General Description
In this example the characteristic behavior of an H-plane three port circulator is presented by the calculation of the corresponding S-parameters with the transient solver. The structure is given by the rotation domain, containing two ferrite disks embedded in a teflon cylinder, as well as three rectangular waveguides for the in and out coupling of the fundamental TE mode. In case that the ferrite material is biased by a static magnetic field, the circulator shows a non-reciprocal behavior, which is typical for microwave devices using gyrotropic media. The resulting asymmetric field distribution is visualized by help of 3D field monitors, in particular the powerflow and current density. The same structure has also been simulated with the Frequency Domain General Purpose Tetrahedral solver.
Structure Generation
The main part of the circulator is constructed with the definition of a curve and its extrude functionality, while all other elements are modelled as solid shapes, applying mirror and rotation transformations. Using the local coordinate system offers the possibility to create the different parts relative to each other. The anisotropic and dispersive material character of the biased ferrite is defined by the corresponding material parameters, here referred to the Gauss system.
Solver Setup
Three waveguide ports are defined at the ends of the given waveguides to perform the S-parameter calculation. The excitation signal at port No.1 is a Gaussian shaped pulse referring to the frequency range from 13 to 17 GHz. The adaptive mesh refinement is activated to ensure a good mesh resolution and you can see that only two passes are needed to obtain the desired accuracy. In order to get an additional visualization of the non-reciprocal wave propagation several 3D field monitors (electric and magnetic field, powerflow) are defined at the operation frequency of 15 GHz.
Post Processing
The resulting time signals and the corresponding scattering parameters of the transient calculation are listed in the navigation tree in the folder 1D Results. Regarding the absolute value of the S-parameters the asymmetric coupling of the field energy from port No.1 to port No.2 is obvious. This result can be visualized more impressively by plotting the monitored 3D fields, which can be found in the folder 2D/3D Results.
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