In some passive microwave devices, ferrite cores are used to provide the rotation of the field required to achieve the phase shifting that makes the device work. Devices such as circulators, isolators, gyrators and phase shifters work on a range of frequencies based on the properties and size of the ferrite material and the size of the waveguide in which it is contained. Software based analysis tools are a necessary part of the design and optimization process of such devices. INTEGRATED is now working on the capability to analyze anisotropic materials using FEM method in SINGULA so it can be used to investigate the aforementioned devices.
To demonstrate this capability, we will use an example in the literature to base our model on and compare results to. The model is a microwave circulator found in the IEEE Transactions on Microwave Methods and Techniques, January 1986, pages 103-106.
Figure 1. Cut-plane solid view of the microwave circulator (left) and tetrahedral mesh used to solve (right).
The circulator has three ports, with a cylindrical ferrite rod in the center as shown above.
A mesh with approximately 100 000 tetrahedral volume elements is used to solve as shown above on the right. Each frequency step takes less than 30 seconds to solve on a 3.2 GHz, Pentium D based computer with 3.2 GB of memory.
Figure 2 shows the general agreement of the SINGULA analysis with published results. The insertion loss at the top of the published results correspond to the red line of the Singula plot, the reflection in the middle corresponds to the blue line and the isolation at the bottom corresponds to the green plot. (Note that Singula expresses these as a scattering parameter and the paper gives them as a positive loss and so the correponding plots are negatives of each other.) Both plots show the ideal frequency of operation slightly less than 10GHz.
Figure 2. Singula results (left) and published results (right) for a single port of the circulator.
In Figure 3, arrow plots are used to demonstrate the power flow when each of the ports is excited separately. Qualitatively, we can see that the power flows to the next port as it should.
Figure 3. Arrow plots demonstrating the function of the circulator; in each plot, the port from which the arrows emerge is excited separately.
The anisotropic analysis addition to Singula is currently in the testing stage and should be available to users in the spring of 2009. For more information, please contact us.