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Iris Filter Simulation
Description
We present in this example a validated 5 pole H-plane Iris Filter (WR75) : We compared the simulated results from HFWorks to those measured and plotted in [1]. The bandpass filter is composed of five Irises of 0.05 inch thickness. The dimensions of the cavities and Irises' windows are shown in the next figure. The filter was implemented inside a WR75 waveguide and it has shown good performances over the 11.5 to 12.5 GHz frequency band (Satellite communications).
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Figure 1 - the structure's 3D view in SolidWorks
Figure 2 - Mesh of the structure
Simulation
The Scattering Parameters solver of HFWorks is suitable for filters' analysis. The study computes several parameters in different formats and outputs different plots. In the results folder, we will be most interested in the return and insertion loss of the filter. We can specify a fast sweep frequency plan as it is suitable for almost all filters' studies. The PEC waveguide is plunged in an air box and two ports are assigned to the lateral faces of the structure.
The simulated study provides multiple choices and options to plot. They also offer the exploitation of electrical parameters calculated in Scattering Parameters simulations (insertion, return losses...etc).
Loads/ Restraints
The ports can be calibrated (i.e. polarized) using an integration line to specify the electric field orientation. the Irises are treated as Perfect Electric Conductors. A fine mesh is preferably applied to these Irises because their dimensions are critical.
Results
To validate the simulation's accuracy, we can have a look at the return loss and insertion loss curve. The curve shows that the simulator captures perfectly the stopped band. As mentioned in the beginning of the report, the fast sweep plan was used in this example; Nevertheless, The discrete sweep gives more accurate results but requires longer simulation. The following figures show the simulated and measured curves:
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Figure 3 - Insertion and return losses (2D and Smith Chart)
For Scattering Parmeters viewing, we use the Electical Parmeters results folder. We choose either a 2D or Smith Chart plot. We can explore the curve using a marker. We can plot other predefined curves like a circle (VSWR = constant) on the Smith Chart. The previous figure shows the return loss and insertion loss of the filter.
Figure 4 - Electric field distribution
The electric field distribution is spotted on the this figure; when animated, we can see clearly electromagnetic waves going through the circuit and reach the second second port.
References
[1] Power-Handling Capability for RF Filters Ming Yu IEEE Microwave Magazine -October 2007 [link]