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KU BAND FILTER
Courtesy Northrop Grumman
This is an edge coupled microstrip (ECM) filter designed on a Rogers TMM 10 substrate. Symmetry is used to simulate half of the filter in the "BPF_Half" sub-circuit. Two "BPF_Half" subcircuits are used to make the final "BPF" Filter.
The 3dB bandwidth measurement is accomplished with the markers on the "Filter Response" graph by first adding an auto-search marker to find the maximum and then adding two offset markers that reference the first marker that are 3dB below the reference. Finally the output equation document "3dB_Bandwidth" calculates the bandwidth from the values on the offset marker.
Activate the "BPF_Half" schematic by clicking on the title bar of the "BPF_Half" schematic. Notice the context sensitive tool bars along the top of Microwave Office change to present the available commands when a schematic window is active. Press the Tune icon to active the real-time tuner. The variables on the tuner (S1, S2, S3, S4) change the width of the gaps between the coupled line sections. Hold the CTRL key down while moving the slider and you can see the layout change while the Passband and Input Return Loss change in the "Filter Response" graph. Click Revert > Initial to go back to the initial stage of the tuning. to Press the V= icon along the top toolbar to activate the variable window. The variable window allows the user to sort and control all of the variables in the project.
Change the slider for variable "Linput" while holding the CTRL key down, one can see the layout update instantaneously. This is useful to see when the circuit is exceeding the limits of the module.
The optimization goals can be seen on the "Filter Response" graph. The optimization goals are added to the project by right clicking on "Optimizer Goals" in the project browser and selecting Add Opt. Goal... From the Optimization Goal dialog box, the user can select an existing measurement or add a new measurement to set an optimization goal. The frequency range, optimization goal, as well as slope over frequency can be specified. Once an optimization goal has been set, it can be modified from the graph by dragging the goal to a new location.
The Optimizer dialog box can be accessed from the Simulate menu along the top of the main window or press the F7 key. The user can select among many different optimizers including AWR's proprietary Pointer Optimizer. From the Optimizer dialog box the user can control all aspects of the optimization. By pressing the variable button in the lower left hand corner, the user can add or remove variables for optimization. By pressing the goals button, the user can change the optimization goals. Having all the optimization controls from one dialog box simplifies the optimization process. The equalize goals button is useful to make the amount each goal contributes to the cost uniform.
Open the Real-Time Tuner (Simulate > Tune) and move the first slider to the lower end of the range. The response of the Filter will now be out of spec. Open the Optimizer dialog box and press start. The Pointer optimizer will bring the filter response back into spec.
For further help on the Pointer Optimizer technology, please review the online Users Guide on The Pointer Optimization
The yield goals can be seen on the "Filter Response" Graph just above the optimization goals. The yield goals are added to the project by right clicking on "Yield Goals" in the project browser and selecting Add Yield Goal... From the Yield Goal dialog box, the user can select an existing measurement or add a new measurement to set a yield goal. The frequency range, yield goal, as well as slope over frequency can be specified. Once a yield goal has been set, it can be modified from the graph by dragging the goal to a new location. One can see that the yield and optimization setup is very similar.
In order to run a yield analysis, variables need to be selected and tolerances need to be added. Access to all of the project variables through the Variables dialog box that was shown in the the Optimizer and Real-Time Tuning section. Click on the V= hot button along the top of the AWR Design Environment in order to access the Variables dialog box. A variable is added to the yield analysis by checking the Use Statistics box. The tolerance and distribution(normal or uniform) can also be selected. An alternate way to adjust the statistical properties is to edit the properties of the variable or parameter directly in the schematic. In the "BPF_Half" schematic, select variable S1, right click, select properties... and a dialog box will appear to allow the user to edit the value, tuning, and statistical properties. This also works for elements. Double-click on the MSUB element. From the Element Options dialog box, select the Statistics tab to edit the statistical properties of the MSUB parameters.
The yield analysis can be started from the Simulate > Yield Analysis in the menu bar. From the Yield Analysis dialog box, the maximum iterations can be set and the yield analysis can be started. Press the Start button to see the yield analysis run, press stop button or let the yield analysis run until the max iterations is reached. In the "Filter Response" graph, the 1 standard deviation limit and mean can be seen. Different views of the yield data can be selected by editing the properties of the "Filter Response" graph. Right click in the "Filter Response" graph, select properties..., press the Yield data tab to acces the different yield data options.
Sensitivity analysis is obtained by adding a Ysens measurement to a graph. Double click on "Substrate Thickness" graph in the project browser to open the graph and see the sensitivity of the yield to the substrate thickness. Right click in the graph that was just opened and select Modify Measurement to see how the Ysens measurement was added to the "Substrate Thickness" graph. Move the cursor horizontally along the graph and watch the status window at the bottom of the program window to see the length values. Looking at the graph, one can see the yield drop off when the substrate thickness is greater than +/- 0.8 mils. By adding a simple Ysens measurement to a graph it is easy to see where component specs can be tightened or screens made on parts to increase manufacturing yield. There is no need to type complicated equations.