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Double Stub EM Optimization Example
This example demonstrates MWO's ability to perform optimization on an EM structure. In the interest of simulation speed and simplicity, and relatively basic structure, a double stub microstrip filter, is being optimized.
There are two schematics in this project, "New_Discrete_Optimization" and "Old_Discrete_Optimization". The "Old_Discrete_Optimization" schematic uses the old optimization method for EM which is more complicated and time consuming. In the old method, you had to define a variable in the schematic and then optimize the variable. As you can see in the "Old_Discrete_Optimization" schematic, there are two different variables, L1 and L2. These variables have been assigned to the length parameters of the MLEF elements. The reason for using variables instead of simply choosing those two parameters to be optimizable is so we can use discrete optimization. The benefit of using discrete optimization when optimizing an EM structure is that we can set the step size of the discrete variable list to be the same as the cell size of the extracted EM structure. The "L_VECT" vector is defined to set up for discrete optimization. Finally you set L1 and L2 to be optimized.
However in the new method, using the Discrete Local Search Optimizer, all the set up can be done in the Variable Browser. Go to View > Variable Browser and look at the L values for MLEF elements in the "New_Discrete_Optimization" schematic. The Lower, Upper, and Step Size columns are set and the Constrained box is checked.
An optimization goal has been set so that S21 must be less than -10 dB from 4.5 GHz to 8.5 GHz.
Simulation and Optimization
After simulating the schematic, it is clear the filter in its current state is not meeting the optimization goal. At this point the circuit can either be optimized to achieve the goal.
To optimize the circuit, bring up the Optimization window and click the "Start" button. Note that the optimization method is set to "Discrete Local Search". Unlike other optimizers, this optimizer will only search over the discrete set of values determined by the Lower, Upper, and Step Size properties of the optimization variables. While the circuit is being optimized, you can see the layout of the extracted portion of the filter (2D and 3D) changing. Because of the number of frequency points and the nature of EM simulation, it may take up to a minute for the optimizer to reach its goal.
Note: In order to utilize this feature, the user must have a license that includes ACE
To change the solver from AXIEM to ACE, simply change the Simulator parameter of the EXTRACT block to "ACE". Also, disable the EM_MESH annotation and enable the EXT_CKT3D annotation.
In the Optimizer window, click on Revert > Initial to reset the dimensions of the filter. Now click "Start" in the Optimizer window or use the tuner to manually tune the circuit. ACE simulation will be much faster than using a standard EM solver.
Tuning on Dielectric Height
One other feature to try is tuning on the dielectric height. In the Global Definitions window, you can see that the parameter for the substrate height in the STACKUP has been defined as a variable, T, which is tunable. If you tune this variable, you can see the change in the filter response and see the dielectric height change in the 3D view of "EM_Extract_Doc".
Schematic - Old_Discrete_Optimization
Schematic - New_Discrete_Optimization
EM Structure 3D - EM_Extract_Doc
Graph - Filter Response