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Curved Wilkinson Combiner
This example demonstrates how to layout a curved Wilkinson divider.
It uses schematic equations to calculate the radius of the curves forming the loops so that they remain closed during tuning and optimization.
Try using the tuner to change the lengths and widths of the transmission lines, and watch how the layout and S-parameters update (hint: hold down the ctrl key to see the layout update as you tune). As saved, the performance of the combiner is poor so that you can tune or optimize to see the improvement. Tuning is effective to give you a feel for how parameters affect performance. However, many times you want to change several values to achieve some simulation goal, this is where you should use optimization.
The default TFR layout cell is 1 mil larger on each end than what is specified in the element. To offset this difference each face has an offset that is specified in the shape properties.
The layout was constructed using the MCURVE element with equations that determine the radii of the curves given the width and lengths of the microstrip lines.
Displaying Variable Values
The value of any equation can be displayed easily by adding an equation and typing in a variable name followed by the ":" character. Please see the schematic near the equations to see the the evaluated values for each variable is displayed.
Most of the optimizers will work well on this project. Try the Pointer - Robust, Pointer - Gradient, Simplex Optimizer, or Random (Local). Start the optimizer by selecting Simulate > Optimize (or hit the F7 key). The Optimizer dialog box will open. You select your optimizer type from the Optimization Methods pull down, set the Maximum Iterations, and then click the Start button. You can stop the optimization at any time. Before you optimize, it is a good idea to tile your windows (select Window > Tile Vertical or Window > Tile Horizontal) so you can see the optimization progress as well as all your open windows. As you optimize watch the layout change, the graphs change and in the Optimizer window watch as the Cost value continues to get smaller.
This Wilkinson Combiner schematic is setup for Axiem extraction. This example will not cover the basics of how extraction works. Please use the User’s Guide or other extraction examples to understand these concepts.
First Freeze the traces in both the graphs from the menu by choosing Graph > Freeze Traces so you can compare the Axiem results vs schematic results. Enable the EXTRACT block in the Wilkinson schematic and simulate. This will simulate the entire layout of Wilkinson schematic in the EM structure named EM_Extract_Wilkinson and use the EM results back in the schematic. You can also toggle this block on and off to see the results with and without extracting this part of the design.