Getting Started: An HFSS Optimetrics Problem

Ansoft Optimetrics

NSOFT Getting Started: An HFSS Optimetrics Problem

January 2001

Notice The information contained in this document is subject to change without notice. Ansoft makes no warranty of any kind with regard to this material, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose. Ansoft shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material. This document contains proprietary information which is protected by copyright. All rights are reserved. Ansoft Corporation Four Station Square Suite 200 Pittsburgh, PA 15219 (412) 261 - 3200 Motif is a trademark of the Open Software Foundation, Inc. UNIX is a registered trademark of UNIX Systems Laboratories, Inc. Windows is a trademark of Microsoft® Corporation OpenWindows is a trademark of Sun Microsystems, Inc.

© Copyright 1994-2001 Ansoft Corporation ii

Printing History New editions of this manual will incorporate all material updated since the previous edition. The manual printing date, which indicates the manual’s current edition, changes when a new edition is printed. Minor corrections and updates which are incorporated at reprint do not cause the date to change. Update packages may be issued between editions and contain additional and/or replacement pages to be merged into the manual by the user. Note that pages which are rearranged due to changes on a previous page are not considered to be revised. Edition

Date

Software Revision

1.0

October 1999

1.0

2.0

January 2001

2.0

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Welcome! This manual is a tutorial guide for setting up a simulation problem using Ansoft Optimetrics, a software package for varying basic design parameters that are to be varied during a simulation and finding the minimum of a userdefined cost function.

Ansoft HFSS Guides There are several companion guides for Ansoft HFSS:

Getting Started: An Eigenmode Problem Getting Started: An Antenna Problem Getting Started: A Full-Wave Spice Problem Introduction to the Ansoft Macro Language

For information on all of the Ansoft Optimetrics and Ansoft HFSS commands, refer to the online documentation.

Installation Guide Before you use Ansoft Optimetrics, you must: 1. 2.

Set up your system’s graphical windowing system. Install the Maxwell software, using the directions in the installation guide.

If you have not yet done these steps, refer to the installation guides and the documentation that came with your computer system, or ask your system administrator for help.

Other References For detailed information on the Ansoft Optimetrics commands, refer to the online help provided with Ansoft Optimetrics. For detailed information on the Control Panel commands, refer to the online help for the Maxwell Control Panel.

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Typeface Conventions Computer type is used for on-screen prompts and messages, for field names, and for keyboard entries that must be typed in their entirety exactly as shown. For example, the instruction “copy file1” means to type the word copy, to type a space, and then to type file1. Menu/Command Computer type is also used to display the commands that are needed to perform a specific task. Menu levels are separated by forward slashes (/). For example, the instruction “Choose File/Open” means to choose the Open command under the File menu. Italics Italic type is used for emphasis and for the titles of manuals and other publications. Italic type is also used for keyboard entries when a name or a variable must be typed in place of the words in italics. For example, the instruction “copy filename” means to type the word copy, to type a space, and then to type the name of a file, such as file1. Keys Helvetica type is used for labeled keys on the computer keyboard. For example, the instruction “Press Return” means to press the key on the keyboard that is labeled Return. Computer

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Using a Graphical User Interface If you are familiar with the concepts of using a hand-held mouse, menus, and other graphical user interface (GUI) tools, skip to Chapter 1, “Introduction.” If you have not used a GUI before, this section will help you understand some of the terminology used in this guide. Since GUIs are basically visual, the best way to learn to use them is by practicing on your system. Most GUI systems use a “mouse” as a pointing device, with which you can select areas on the screen for command execution and moving from one program to another. Your mouse may have 2 or 3 buttons; Ansoft Optimetrics ignores the middle button on 3-button models, since Ansoft products do not use this button. You can program mouse buttons to work in non-standard ways, as you might want to if you are left-handed. For simplicity, the left-hand button (under your forefinger if you are right-handed) is referred to as the left mouse button, and the one on far right as the right mouse button. You will probably find the terms intuitive once you use these buttons a few times. Point and Click; Right Click To choose an item with the mouse, first move it on your desk until the arrow cursor is on that item; you are now “pointing” at the item. Next, press and release the left mouse button; this is called “clicking.” Point-and-click is the most common action you will make with your mouse. Generally, “click” refers to a left mouse button click. Sometimes, you can use your right mouse button to access commands. In the 3D Modeler, a right mouse button click causes a menu of commands to appear. Generally, “right click” refers to a right mouse button click. Double-Click Occasionally you may want to select all of the text in a box, or perform a special task (say, indicating the end of drawing a line). You can do this by quickly clicking twice with your left mouse button — a “double-click.” Dragging Objects; Click and Hold When you are drawing in the 3D Modeler, you can often use your mouse to enter objects and move around the screen. Frequently, you will click the mouse button and hold it down until the next part of the command is reached (the object is moved, the next point is entered, and so forth). If you click and hold on the edge of a window, you can position, or drag, the window on your screen. You can often drag objects in the 3D Modeler; experiment to see what will move. vi

Menus Within some screens of Ansoft Optimetrics are areas which list subsets, or “menus,” of commands. You can access a menu by clicking your mouse on the word or button that indicates the menu. The menu is “pulled down”, and lists the commands available on that menu. Usually, the menu will remain displayed until you choose a command, or click on the desktop to exit. If the menu does not remain displayed, click and hold the mouse button, then release the button to make your choice.

An arrow on the right side of a command indicates that there is a submenu for that command. An ellipsis (. . .) indicates that a pop-up window appears after choosing this command. When you are asked to use a menu command, each level is separated by a “/”. For example, to zoom in on a drawing, you would choose the View/Zoom In menu command. There are also pop-up menus, which appear when you right-click on a Maxwell modeler window. Choose commands from these menus in the same way as from menu bars. For more information on using GUIs, refer to the online help for the Maxwell Control Panel.

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Tool Bars Tool bars are shortcut methods for entering commands. There are tool bars in many of the Ansoft Optimetrics modules for several commands. To use a tool bar, click the mouse cursor on the button you want to use. Here is an example of a tool bar:

Note:

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To execute a command, click on the appropriate button. To display a brief description of the command in the message bar, move the cursor to the toolbar icon and hold down the mouse button. If a tool bar icon appears to do nothing when you click on it, the command may not be available at the time.

Table of Contents

1.

Introduction Nominal and Parametric Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 Nominal Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 Parametric Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

The Sample Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

2.

Creating the Optimetrics Project Access the Project Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 Create a Project Directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4 Create the Nominal Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6 Access the Project Directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6 Add the New Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6 Save Project Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

3.

Run Ansoft Optimetrics Open the New Project and Run the Simulator . . . . . . . . . . . . . . . . . . 3-2 Executive Commands Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 Commands Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 Display Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

General Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

Contents - 1

4.

Set Up the Nominal Problem Select the Nominal Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 Set Up the Nominal Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 Select the Solver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 Driven Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 Eigenmode Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

Draw the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 The Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6 Draw the Three Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 Draw the First Waveguide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 Draw the Quarter-wave Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9 Draw the Final Waveguide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9

Edit the Modeler Macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10 Exit the Modeler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

Assign Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13 Start the Material Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13 Assign Vacuum to wg1 and wg2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14 Create and Assign a Custom Material to wg3 . . . . . . . . . . . . . . . . . 4-14 Create the New Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14 Assign Material80 to wg3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15

Exit Setup Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15

Set Up Ports and Boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16 Start the 3D Boundary Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16 Define the Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17 Define Port1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17 Define Port2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

Define the Symmetry Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18 Define the Perfect H Symmetry Plane . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19 Define the Perfect E Symmetry Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20

Exit the Boundary Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20

Contents - 2

5.

Set Up the Optimization Problem Specify Solution Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 Select the Output Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4 Exit Ansoft HFSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 Check the Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 Create the Cost Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 Set Up the Optimization Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 Add the Cost Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 Generate the Optimization Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 Analyzing the Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14 Viewing the Table from the Executive Commands Menu . . . . . . . 5-16 Viewing Solved Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16

6.

Set Up the Parametric Problem Set Up the Parametric Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 Selecting Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 Specify the Sweep Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 Exit the Parametric Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

Generate the Parametric Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4 Analyzing the Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 Exit the Post Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9 Exit Ansoft Optimetrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

Contents - 3

Contents - 4

1 Introduction

Ansoft Optimetrics is an analytical tool that enables you to conveniently perform variable (optimization and parametric) analyses of models. It allows you to simulate design variations using a single model, instead of having to explicitly set up and solve a series of models. Ansoft Optimetrics allows you to:

Identify the basic design parameters that are to be varied during the simulation — such as geometric dimensions, material properties, boundary conditions, excitations, and solution frequency. Define a cost function for which the optimizer will attempt to find the minimum value, using a quasi-Newton method for optimization. Specify the values to which each design parameter is set during the solution, generally by “sweeping” them through a range of values. This lets you define a series of variations on the original, “nominal” model, each of which will be solved during the parametric sweep.

The software then automatically sets the design parameters to the values you specified, and computes a solution for each variation on the nominal model. After the parameter sweep is completed, you can analyze the results using the software’s post-processing functions. This Getting Started guide demonstrates how to use Ansoft Optimetrics in conjunction with Ansoft HFSS.

Introduction

1-1

Nominal and Parametric Models

Nominal and Parametric Models Ansoft Optimetrics breaks a project down into two parts — a nominal model and a parametric model.

Nominal Model To perform a parametric analysis, you must first create a nominal model. Essentially, it is an ordinary model that has been parameterized, and serves as the model on which the parametric analysis is based. The nominal model is created much like any other model, except that the design parameters that will be changed during a parametric sweep must be defined as variables. The methods for doing this depend on the type of variable. No variables need to be defined if you do not plan to run a parametric analysis on a model. The nominal model’s field solution is computed independently of any parametric solutions, although both may use the same set of solution criteria. When computing solutions, the simulator uses the original values for all design variables that were specified when the model was created, ignoring any values they might be set to during a parametric sweep.

Parametric Model The parametric model consists of a series of variations on the nominal model, in which the design variables are assigned a range specified when you set up the parametric sweep. The number of variations that can be defined is limited only by your computing resources and imagination. Each variant on the nominal model is known as a “parametric setup.” It represents the model corresponding to the changing value of each variable. During the solution process, field solutions are computed for each setup, and post-processing macros are executed using the results of the setup’s field solution. You can then compare the results obtained for each setup to determine how each design change affects the model’s performance. (If there is a large number of solved setups, changing the values of more than one or two variables at a time may make it difficult to isolate the effects of an individual design variation.) Ansoft Optimetrics allows you to define a cost function and run an optimization analysis, or to define your own table of setups in which you explicitly control the values of the variables. During the optimization process, the optimizer creates its own setups in order to find the minimum of the user-defined cost function.

1-2

Introduction

The Sample Problem

The Sample Problem In this problem, you will optimize a junction between standard WR90 and WR137 rectangular waveguides. The two waveguides are connected with a custom-made intermediate waveguide that serves as an impedance transformer. The design of the waveguide junction is based on a quarter-wave transformer. The example given in this guide attempts to find the smallest reflection between the two waveguides by varying the length and height of the quarterwave transformer. Therefore, you will set up the optimizer to find the minimum value for a cost function based on S11.

Introduction

1-3

The Sample Problem

1-4

Introduction

2 Creating the Optimetrics Project

This guide assumes that Ansoft HFSS and Ansoft HFSS Optimetrics have already been installed as described in the Installation Guide. If you have not installed the software or you are not yet set up to run the software, STOP! Follow the instructions in the Installation Guide.

Note:

Your goals in this chapter are as follows:

Time:

Create a project directory in which to save the projects. Create a new project in that directory in which to save the Optimetrics problem.

The total time needed to complete this chapter is approximately 10 minutes.

Creating the Optimetrics Project

2-1

Access the Project Manager

Access the Project Manager To access Ansoft HFSS Optimetrics and Ansoft HFSS, you must first access the Project Manager, which allows you to create and open projects for all Ansoft products.

Access the Project Manager: 1. Do one of the following to access the Maxwell Control Panel: On a UNIX workstation, enter the following command at the UNIX prompt: maxwell & On the PC, click the left mouse button twice on the Maxwell icon. The Maxwell Control Panel appears as shown below:

2.

Note:

2-2

Refer to the Maxwell Control Panel online documentation for a detailed description of the other options in the Maxwell Control Panel. If the Maxwell Control Panel doesn’t appear, refer to the installation guide for possible reasons. Click the left mouse button on the Projects button in the Maxwell Control Panel to access the Project Manager.

From now on, when you are asked to “choose” a button or a command, click the left mouse button on it.


Access the Project Manager

The Project Manager appears as shown below:


2-3

Create a Project Directory

Create a Project Directory The first step in using Ansoft HFSS Optimetrics to solve a problem is to create a directory and a project in which to save all the data associated with the problem. A project directory is a directory that contains a specific set of projects created with the Ansoft software. You can use project directories to categorize projects any number of ways. For example, you might want to store all projects related to a particular facility or application in one project directory. You will now create a project directory in that default directory.

The Project Manager should still be on the screen. You will add the getstart directory for the Ansoft HFSS Optimetrics project you are creating using this Getting Started guide.

Note:

If you’ve already created a project directory while working through another Getting Started guide, skip to the “Create the Nominal Project” section.

Add a project directory for the sample problem: 1. Choose Add in the Project Directories box at the bottom left of the window. The following window appears, listing directories and subdirectories:

2.

Type the following in the Alias field:

3. 4.

Choose Make New Directory. Choose OK.

getstart

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Create a Project Directory

Note:

The directory getstart is created under the current default project directory, and getstart now appears in the Project Directories box. You return to the Project Manager window. Ansoft HFSS Optimetrics projects are generally created in directories which have aliases — that is, directories that have been identified as project directories using the Add command. To change directories to look at another’s contents: 1. Choose Change Dir from the Project Directories box. 2. Double-click the left mouse button on the desired directory. (Choose ../ to move up a level in the directory structure.) 3. After you are done, choose OK. Refer to the online documentation for the Maxwell Control Panel for more information on changing directories and other Project Manager functions.


2-5

Create the Nominal Project

Create the Nominal Project Now you are ready to create a new project named param in the project directory getstart.

Access the Project Directory Before you create the new project, access the project directory getstart.

Access the project directory: Choose getstart in the Project Directories box at the bottom left. The current directory displayed at the top of the Project Manager menu changes to show the pathname of the directory associated with the alias getstart. If you have previously created a model, it will be listed in the Projects box. Otherwise, the Projects box is empty — no projects have been created yet in this project directory.

Add the New Project

Add a new project: 1. Choose New in the Projects box at the top left of the menu. A window like the one shown below appears:

2. 3.

Note:

4.

If you are running the software on a workstation, or on a PC using Microsoft Windows NT, the name of the person who logged onto the system appears. 5. 6.

2-6

Type param in the Name field. Use the Back Space and Delete keys to correct typos. To select the type of project to be created, click the left mouse button on the button next to the software package listed in the Type field. A menu appears, listing all of the Ansoft software packages you purchased. Click on Ansoft HFSS Optimetrics 2 to select it as the project type. Optionally, enter your name in the Created By field.

Deselect Open project upon creation. When selected, this option opens the project after you choose OK. However, don’t open the project quite yet. Choose OK to create the project.



The information that you just entered is now displayed in the corresponding fields in the Selected Project box. Writable is selected, showing that you have access to the project.

Save Project Notes It is a good idea to save the notes about your new project so that the next time you use Ansoft HFSS Optimetrics, you can view information about a project without opening it.

Enter notes for the param problem: 1. Leave Notes selected by default. 2. Click the left mouse button in the area under the Notes option. A cursor appears, indicating that you can now enter text. 3. Enter your notes on the project, such as the following: This Ansoft HFSS Optimetrics problem was created using the Ansoft HFSS Optimetrics Getting Started guide.

4.

Note:

When you start entering project notes, the text of the Save Notes button (which is located below the Notes box) becomes enabled. Before you began typing in the Notes box, Save Notes was grayed out, or disabled. When you are done entering the description, choose Save Notes to save it. After you do, the Save Notes option is grayed out again.

Grayed out text on commands or buttons means that the command or button is temporarily disabled.

Now, you are ready to open the project and run Ansoft HFSS Optimetrics.


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2-8


3 Run Ansoft Optimetrics

In the last chapter, you created the directory getstart, and created the project param within that directory. This chapter describes:

Time:

How to open the project you just created and run Ansoft Optimetrics. The Ansoft Optimetrics Executive Commands window. The general procedure for creating an Ansoft HFSS problem in Ansoft Optimetrics.

The total time needed to complete this chapter is approximately 10 minutes.

Run Ansoft Optimetrics

3-1

Open the New Project and Run the Simulator

Open the New Project and Run the Simulator The newly created project param should still be selected in the Projects box. (If it is not, move the cursor on it and click the left mouse button.)

Run Ansoft Optimetrics: Choose Open from the Project Manager. The Executive Commands window of Ansoft Optimetrics appears as shown below:

3-2


Executive Commands Window

Executive Commands Window The Executive Commands window of Ansoft Optimetrics acts as a path to each step of creating and solving the parametric problem. This window is divided into two sections: the commands area and the display area.

Commands Area The commands in the Ansoft Optimetrics Executive Commands area are: Creates, selects, or edits the nominal problem on which to perform a parametric analysis. Setup Solution Options Accesses the Solution Options panel of the software package used to create the nominal problem. From here you can specify the solution options that will be used during the parametric analysis. Setup Output Creates and runs post-processor macros. These Parameters macros allow you to extract solution information from the nominal problem and use them in the parametric analysis or to create a post-processor macro to run for each solved parametric setup. Edit Functions Edits the variables for the problem and defines the cost function. Setup Analysis Allows you to create the parametric table and set up the optimization analysis. Add/Remove Output Adds solution variables to the parametric table. Columns Nominal Project

Run Post Process Table

Generates a solution for the parametric table or starts the optimization analysis. Plots columns of the parametric table versus other columns.

Display Area The display area is blank for now, but once the nominal model is drawn, a picture of the structure appears. After the solution process is finished, you may use this area to switch between a display of the model, a table of each setup, or the profile of system resources used during solution.


3-3

General Procedure

General Procedure

To set up a model for Optimetrics analysis: 1. Select the Ansoft software to use to create the nominal problem or import an existing problem. 2. Create your model using an Ansoft software product that supports Ansoft’s macro language. Keep the following points in mind: Ansoft Optimetrics requires a geometry macro in order to vary the geometric parameters of your objects. A geometry macro is automatically created and recorded to projectname.mac in the projectname.pjt/mod3 directory when you open the software’s modeler. When you exit the modeler, macro recording automatically ends. The parametric module looks for this modeler macro in the project directory of the nominal problem. Materials and boundaries can be defined using functions, and do not require macros. 3. Edit the nominal problem’s macros and create variables to change during a parametric sweep. Assign the variables the values used in the nominal problem as the default values. 4. Assign material properties to the model objects. Define each material to be varied during the parametric sweep as a function with a constant value. This value is used during the nominal solution. 5. Assign boundary and source values to your model. Define each boundary or source property to be varied during the parametric sweep as a function with a constant value. This value is used during the nominal solution. 6. Define the solution options (Setup Solution Options). 7. Define the variables on which to base the cost function. These variables will be added later as columns to the parametric table. 8. Define the cost function for optimization. 9. Set up an optimization and/or parametric analysis, with ranges for design variables or parametric sweeps. 10. Add the cost function and the variables on which it is based as columns of the parametric table. 11. Run the optimization analysis. Ansoft Optimetrics creates the parametric table that sweeps through the design variables, with the values of the cost function as one of the output columns. 12. Generate the parametric solution. 13. View and plot parametric solution results. Analyze nominal and parametric field solutions. The way you use Ansoft Optimetrics depends upon the Ansoft software used to create the nominal problem and the type of problem you wish to solve.

3-4


4 Set Up the Nominal Problem

In the last chapter, you started Ansoft Optimetrics. Before you can begin to solve the parametric problem, you must create the nominal problem using Ansoft HFSS. This chapter describes:

Time:

How to access Ansoft HFSS from Ansoft Optimetrics and create an Ansoft HFSS problem to use for optimization. How to draw the geometry. How to define functional material properties.

The total time needed to complete this chapter is approximately one hour.

Set Up the Nominal Problem

4-1

Select the Nominal Problem

Select the Nominal Problem Before starting a parametric problem, you must select or create the nominal problem to use for parametric analysis. Because Ansoft Optimetrics can be used with several Ansoft products, you must specify the nominal project to use. Using the Nominal Project menu, you can either select a pre-existing nominal problem or create a new one. For this Getting Started guide, create a new Ansoft HFSS problem.

Select the nominal project: 1. Choose Nominal Project/Create. A window like the one shown below appears:

2. 3.

4.

Type nominal in the Name field. Use the Back Space and Delete keys to correct typos. To select the type of project to be created, click the left mouse button on the button next to the software package listed in the Select product field. A menu appears, listing all of the Ansoft software packages for which you have licenses and can use with Ansoft Optimetrics. Click on Ansoft High Frequency Structure Simulator 8 to select it as the project type. Choose OK to create the project. The Executive Commands window for Ansoft HFSS appears. This project will be used as the nominal project. It is saved in the template directory in the Ansoft Optimetrics project directory, which in this case is param.pjt/template/.

After Ansoft HFSS appears, draw the geometric model, assign materials, assign boundary and source conditions, and set up the solution options. Rather than solving the problem as you usually would, you will exit from Ansoft HFSS and return to Ansoft Optimetrics.

4-2


Set Up the Nominal Project

Set Up the Nominal Project The Executive Commands window of Ansoft HFSS appears as shown below:


4-3

Select the Solver

Select the Solver Leave the solver set to Driven Solution.

Driven Solution Select Driven Solution to use the finite element-based solver to generate a solution for a structure that is “driven” by a source. Ansoft HFSS calculates the S-parameters of passive, high-frequency structures such as microstrips, waveguides, and transmission lines. The software also includes post-processing commands for analyzing the electromagnetic behavior of a structure in more detail. Using the Driven Solution, you can compute:

Basic electromagnetic field quantities and, for open boundary problems, radiated near and far fields. Characteristic port impedances and propagation constants. Generalized S-parameters and S-parameters renormalized to specific port impedances.

Eigenmode Solution Select Eigenmode Solution to calculate the eigenmodes, or resonances, of a structure. The eigenmode solver finds the resonant frequencies of the structure and the fields at those resonant frequencies. The Ansoft HFSS eigenmode solver can find the eigenmodes of lossy as well as lossless structures, and can calculate the unloaded Q of a cavity. Q is the quality factor, and is a measure of how much energy is lost in the system. Unloaded Q is the energy lost due to lossy materials. Because ports and other sources are unavailable for eigenmode problems, the calculated Q does not include losses due to those sources. The following restrictions apply to Eigenmode solutions:

4-4

Emissions may not be calculated. The following boundary conditions may not be defined: Port Incident Wave Voltage Drop Current Magnetic Bias Radiation Fast frequency, interpolating, and discrete frequency sweeps are not available. Nonlinear materials may not be used. Matrix Data and Matrix Plot are not available, and the Matrix button on the Executive Commands window changes to Eigen Modes.


Draw the Model

Draw the Model To draw the geometric model, use the 3D Modeler, which is the portion of Ansoft HFSS that allows you to create objects.

Start the 3D Modeler: 1. Choose Draw from the top of the Executive Commands menu. The 3D Modeler window appears. 2. You are prompted to choose the units of length. Select inches as the units, and choose OK. These units are shown at the Absolute/Relative coordinates menu. The 3D Modeler window is divided into several parts:

Menu Tool bar

Absolute/Relative Coordinates

xyz

xy

xyz

xy “Snap to” settings

Side window yz

xz yz

Status bar

Note:

xz

If you require further information on any topic in Ansoft HFSS, such as the 3D Modeler commands or windows, there are several options for displaying context-sensitive help: Choose Help in a window. Press F1, see the cursor change to ?, then click on the item on which you need help. Use the commands from the Help menu.


4-5

Draw the Model

The Geometry The geometry for the nominal problem consists of three boxes: two rectangular waveguides between which the quarter-wave transformer sits. The geometry of the boxes is shown below: wg2

wg3 H Plane Cross-section

wg1

E Plane Cross-section

l2

l2

w2

w3

w1

H Plane Cross-section

h3

h2

h1


Since you are taking advantage of the two planes of symmetry in the problem, you are only drawing one-quarter of the geometry. The dimensions of the geometry are shown below, along with the names of the variables used for the dimensions: wg3Length = 0.3

wg3HalfWidth = 0.685

wg2Length = 0.504

wg1Length = 0.3

wg1HalfWidth = 0.45

wg2HalfWidth = 0.515

H Plane Cross-section 4-6


wg3Length = 0.3

wg2Length = 0.504

wg3HalfHeight = 0.311

wg1Length = 0.3

wg1HalfHeight = 0.2

wg2HalfHeight = 0.45 x wg2HalfWidth


Draw the Model

Draw the Three Boxes Draw the three boxes that represent the two waveguides and quarter-wave transformer. As you are creating the three boxes, note the coordinates used for the base vertex of each box. The base vertices lie along the y-axis. Because you will be varying the size of the quarter-wave transformer, the dimensions of the other two objects must have a dependency upon the dimensions of the quarterwave transformer. You accomplish this by relating the base vertex of the waveguide objects to the dimensions of the quarter-wave transformer. You will relate the base vertex coordinates of the two waveguides when you are editing the macro. Draw the First Waveguide Draw the first box, which corresponds to wg1 and represents a section of WR90 waveguide tubing.

Draw the first box: 1. Choose Solids/Box to create a rectangular box. The controls for entering the base vertex of the box appear in the side window. 2. Leave the base vertex coordinates set to the origin. If they are not set to the origin, enter 0 for the X, Y, and Z fields. 3. Choose Enter to set this point as the box’s base vertex. The 3D Modeler accepts the point, and fields for entering the box information appear in the side window. 4. Enter 0.45 in the X field under Enter box size. 5. Enter 0.3 in the Y field. 6. Enter 0.2 in the Z field. 7. Enter wg1 as the name of the box. 8. Select red as the color. 9. Choose Enter. Initially, the box is so small it is not visible on the screen. 10. Choose View/Fit All/All Views (or hotkey f) to expand the box so it fills the view windows.


4-7

Draw the Model

The box appears in all the windows:

4-8


Draw the Model

Draw the Quarter-wave Transformer Draw the second box, which corresponds to wg2 and represents the quarterwave transformer. The base vertex for this box is the y-coordinate of the base vertex of the first box wg1 plus the length of the first box. Initially, it is 0.3. Since the base vertices are along the y-axis, the x- and z-coordinates are 0.

Create the quarter-wave transformer: 1. Choose Solids/Box. 2. Define the base vertex coordinates in the following manner: a. Enter 0 in the X field. b. Enter 0.3 in the Y field. It may already be set to 0.3 from the previous procedure. c. Enter 0 in the Z field. If the Z field is not enabled, select the checkbox next to it. d. Choose Enter to set this point as the box’s base vertex. 3. Enter 0.515 in the X field under Enter box size. 4. Enter 0.504 in the Y field. 5. Enter 0.23175 in the Z field. 6. Enter wg2 as the name of the box. 7. Select red as the color. 8. Choose Enter. The box appears in all the windows. 9. Choose View/Fit All/All Views to expand the boxes so they fill the view windows. You are now ready to draw the final waveguide.

Draw the Final Waveguide Draw the third box, which corresponds to wg3 and represents a section of WR137 waveguide. The base vertex for this box is the y-coordinate of the base vertex of the second box wg2 plus the length of the second box. Initially, it is 0.804.

Create the final waveguide: 1. Choose Solids/Box. 2. Define the base vertex coordinates in the following manner: a. Enter 0 in the X field. b. Enter 0.804 in the Y field. It may already be set to 0.804 from the previous procedure. c. Enter 0 in the Z field. d. Choose Enter to set this point as the box’s base vertex. 3. Enter 0.685 in the X field under Enter box size. 4. Enter 0.3 in the Y field. 5. Enter 0.311 in the Z field. 6. Enter wg3 as the name of the box. 7. Select red as the color. 8. Choose Enter. The box appears in all the windows. 9. Choose View/Fit All/All Views. Set Up the Nominal Problem

4-9

Draw the Model

Edit the Modeler Macro You are now finished drawing the model. In order to perform an analysis in which you vary geometric parameters, you must add appropriate variables to the macro file that was automatically generated while creating the model. This macro file was named nominal.mac and was stored in the nominal.pjt/mod3 directory by default. Because this problem involves varying the size of the quarter-wave transformer, you are going to first create and then add variables for the three boxes that compose the transformer and waveguides. Do this using the Ansoft Macro Editor.

Access the Macro Editor and change the variables: 1. Choose File/Macro/Edit Macro. A message appears asking if you want to edit the command list automatically recorded in this session. Choose Yes. The following window appears, with the macro text displayed:

The parameter boxes on the right side only appear if you click on a line with parameters on the left side.

4-10


Draw the Model

2.

Choose Edit/All Parameters. The Edit Parameters window appears, allowing you to add new parameters:

3. 4. 5. 6. 7.

In the field on the left of the = symbol, enter wg1HalfWidth. Press TAB to move to the field on the right of the = symbol. In this field, enter 0.45. Choose Add or press Return to add the new parameter to the list. Enter the following parameters in the same way: wg1Length

0.3

wg1HalfHeight

0.2

wg1BaseY

0

wg2HalfWidth

0.515

wg2Length

0.504

wg2HalfHeight

wg2HalfWidth * 0.45

wg2BaseY

wg1BaseY + wg1Length


4-11

Draw the Model

The quantities wg2HalfWidth and wg2Length are the design variables. Here you are using the initial values, which the optimizer can change later. The other variables allow the entire structure to adjust itself to make room as these two parameters change. Now enter the following parameters for the third box:

8. 9. 10.

11. 12. 13. 14. 15. 16.

wg3HalfWidth

0.685

wg3Length

0.3

wg3HalfHeight

0.311

wg3BaseY

wg2BaseY + wg2Length

Choose Done to exit the Edit Parameters window. You can now assign these parameters within the macro. Click on the line for box wg1. The parameters for wg1 appear on the right-hand side of the Macro Editor. Edit the box parameters: a. Enter wg1BaseY in the Y field for the Base vertex. b. Press TAB twice to move to the fields for the Size. c. Enter wg1HalfWidth in the X field, and TAB to the next field. d. Enter wg1Length in the Y field, and TAB to the next field. e. Enter wg1HalfHeight in the Z field. Choose Accept to enter the new parameters. Click on the line for box wg2. The parameters for wg2 appear on the right-hand side of the Macro Editor. Edit the box parameters in the same way, except use the wg2 parameters (that is, wg2BaseY and so forth) instead of the wg1 parameters. Choose Accept to enter the new parameters. Repeat the procedure for wg3, using the wg3 parameters. Choose File/Exit, and choose Yes to apply the changes in the 3D Modeler.

Exit the Modeler You are now finished drawing the model.

Exit the 3D Modeler: 1. Choose File/Exit. You are prompted to save the model. 2. Choose Yes to save the model. You return to the Executive Commands window and are now ready to assign materials and define boundaries.

4-12


Assign Materials

Assign Materials To completely set up this problem, you must assign material characteristics to each 3D object in the geometric model. To set material properties for the objects in this problem, you will assign vacuum to two of the boxes and a custom material to the third box. The custom material is included to demonstrate how to use functional material properties in Ansoft Optimetrics. The custom material will be identical to vacuum, but one of the properties will be a function.

Start the Material Manager

Start the Material Manager: Choose Setup Materials. The Material Setup window appears:

All objects — in this case wg1, wg2, and wg3 — are listed in the Object box, and the materials in the material database provided with the software are listed in the Material box. The characteristics of the materials are listed under Material Attributes.


4-13

Assign Materials

Assign Vacuum to wg1 and wg2 Assign vacuum to wg1 and wg2. You will use a perfect E boundary to simulate a perfect conductor on the waveguides and the quarter-wave transformer.

Assign vacuum to wg1 and wg2: 1. Select wg1 and wg2 from the Object list. On the PC, hold down the Ctrl key to select multiple objects. 2. The material vacuum should be selected in the Material list by default. If it is not, select it. 3. Choose Assign. The material is assigned to wg1 and wg2 and its name appears under Material.

Create and Assign a Custom Material to wg3 For the last waveguide, derive a material from vacuum and assign it to wg3. Create the New Material To create the new material, derive it from vacuum. This gives the new material all the material attributes of vacuum. You can then change one of the attributes to a function that you can vary using Ansoft Optimetrics. Because this is a demonstration, this function will have the same value as the corresponding vacuum property and will not be varied in the parametric problem.

Create the new material: 1. The material vacuum should still be selected. If it is not, select it. 2. Choose Material/Derive. A new material called Material80 is created, with the same properties as vacuum. 3. Choose Functions to create a function. The Function Definitions window appears allowing you to specify the function. 4. In the field on the left of the = symbol, enter permittivity. 5. In the field on the right of the = symbol, enter 1. 6. Choose Add to add the new function to the function list. 7. Choose Done to exit the Function Definitions window. 8. Choose Options to specify which material property to make functional. A window appears allowing you to toggle between constant and functional. 9. Select Function under Rel. Permittivity and choose OK. Notice that the Rel. Permittivity field now displays UNDEFINED. This indicates that a function needs to be entered in the field. 10. Enter permittivity in the Rel. Permittivity field. The relative permittivity of the material can now be varied by changing the value of the variable permittivity. 11. Choose Enter to finish creating the new material. You are now ready to assign this material to wg3.

4-14


Assign Materials

Assign Material80 to wg3 Assign the material you just created to the last waveguide.

Assign Material80 to wg3: 1. Select wg3 from the Object list. 2. The material Material80 should still be selected. If it is not, select it. 3. Choose Assign. The material is assigned to wg3 and its name appears under Material.

Exit Setup Materials

Exit the Material Manager: 1. Choose Exit. You are prompted to save the material assignments. 2. Choose Yes. The material assignments are saved. You return to the Executive Commands window, and a checkmark is displayed next to Setup Materials, indicating that all objects have been successfully assigned material characteristics.


4-15

Set Up Ports and Boundaries

Set Up Ports and Boundaries After assigning material properties, you must define ports and boundary conditions. This specifies the excitation signals entering the structure, the behavior of electric and magnetic fields at various surfaces in the model, and any special surface characteristics.

Start the 3D Boundary Manager

4-16

Start the 3D Boundary Manager: Choose Setup Boundaries/Sources. The 3D Boundary/Source Manager window appears as shown below:



Define the Ports The ports for this problem cover the end faces of the two waveguides. Define Port1 Select the end surface of wg3 and define it as the location of port1.

Create port1: 1. Click on the end face of wg3 to select it:

2. 3. 4.

By default, Port should be selected as the Source type. Leave Source and Port selected. Leave all the parameters set to their defaults. Choose Assign.

The new port appears in the boundary list under Name and the type of boundary or source appears under Assigned. You are now ready to create the second port. Define Port2 Select the end face of wg1 and define it as the location of port2.

Note:

Create port2: 1. Select the end face of wg1. This face is on the opposite end from port1.

2.

Port should be selected as the Source type. If it is not, select it.

If you are unable to select this face directly, click on a face that covers it, then click the right mouse button and choose Next Behind. You can also press the Ctrl and left mouse buttons at the same time to rotate the model within the display area, making this face easier to select. Set Up the Nominal Problem

4-17


3. 4.

Leave all the parameters set to their defaults. Choose Assign.

The new port appears in the boundary list under Name and the type of boundary or source appears under Assigned. You are now ready to create the symmetry boundaries.

Define the Symmetry Plane When you are defining a symmetry plane, you must decide which type of symmetry boundary should be used, a perfect E or a perfect H. In general, use the following guidelines to decide which type of symmetry plane to use:

If the symmetry is such that the E-field is normal to the symmetry plane, use a perfect E symmetry plane. If the symmetry is such that the E-field is tangential to the symmetry plane, use a perfect H symmetry plane. The faces to which you don’t explicitly assign a port or boundary have a perfect E boundary automatically assigned to them. Any surface exposed to the background object automatically has a perfect E boundary assigned to it.

Note:

The simple two-port rectangular waveguide shown below illustrates the differences between the two types of symmetry planes. The E-field distribution in an arbitrary waveguide is shown. The waveguide has two planes of symmetry, one vertically through the center and one horizontally.

The horizontal plane of symmetry is a perfect E surface. The E-field is normal and the H-field is tangential to that surface. The vertical plane of symmetry is a perfect H surface. The E-field is tangential and H-field is normal to that surface. Electric field distribution

Perfect H symmetry plane

Perfect E symmetry plane

This problem has two planes of symmetry: a perfect H symmetry plane in the xy plane, and a perfect E symmetry plane in the yz plane. 4-18



Define the Perfect H Symmetry Plane Define the perfect H symmetry plane: 1. Select the three side faces that make up the symmetry plane. These faces lie in the yz plane along the y-axis:

You can also choose Edit/Select/By Name to select the appropriate face on each object.

Note:

2. 3.

4. 5. 6.

Select Boundary as the condition type. Select Symmetry from the boundary type menu. Selection checkboxes appear in the area below this menu, allowing you to choose the type of boundary for the symmetry plane. Select Perfect H as the type of symmetry plane. Change the name to Hsymm. Choose Assign. The boundary appears in the boundary list.


4-19


Define the Perfect E Symmetry Plane Define the perfect E symmetry plane: 1. Select the three bottom faces that make up the symmetry plane. These faces lie in the xy plane:

2. 3. 4.

You may also choose Edit/Select/By Name to select the appropriate face on each object. Boundary and Symmetry should still be selected, if they are not, select them. Select Perfect E as the type of symmetry plane. Change the name to Esymm. Choose Assign. The boundary appears in the boundary list.

The new boundary appears in the boundary list.

Exit the Boundary Manager

Exit the Boundary Manager: 1. Choose File/Exit. You are prompted to save your boundary settings. 2. Choose Yes. A window appears, reminding you that the impedance multiplier needs to be set when using symmetry boundaries. 3. Leave 1 as the impedance multiplier, and choose OK. You return to the Executive Commands window.

4-20


5 Set Up the Optimization Problem

Now, set up the optimizer to minimize reflection. Your goals for this chapter are as follows:

Time:

Set up the solution parameters for the problem. Select the solution parameters to use for the cost function. Define the cost function to use as a stopping criterion for the optimization analysis. View the parameters you can vary. Specify the variables to vary during the optimization analysis. Start the optimization analysis and generate a solution.

The total time needed to complete this chapter is approximately one hour and 45 minutes.

Set Up the Optimization Problem

5-1

Specify Solution Parameters

Specify Solution Parameters The solution parameters control how the software computes the requested field solution and the frequency at which the solution is computed. For the nominal problem, specify the following solution criteria:

Perform 5 adaptive passes at a frequency of 8.2 GHz. Specify that the maximum change in the S-parameters from one pass to the next be equal to or less than 0.00001.

You should still be in Ansoft HFSS.

Set up the solution criteria for the problem: 1. Choose Setup Solution. The HFSS Solution Setup window appears:

2. 3.

5-2

Leave Single Frequency selected and enter 8.2 as the frequency value. Leave the frequency units set to GHz.


Specify Solution Parameters

4.

Note:

Leave Adaptive selected and enter the following solution criteria: Enter 5 in the Requested Passes field. The simulator generates five successive solutions for the problem, refining the mesh before it generates the next solution. Leave the Tet. Refinement field set to 20. This determines how many tetrahedra are added after each iteration of the adaptive refinement process. Enter 0.00001 in the Max Delta S field.

The solution process stops if either the Requested Passes or Max Delta S is reached. The Max Delta S for this problem was set very low in order to force the simulator to complete five passes. Waveguides tend to converge quickly, and setting the Max Delta S very low ensures that the mesh is refined to a much greater degree. 5. 6.

Leave the other parameters set to their defaults. For an explanation of these parameters, refer to the Ansoft HFSS online documentation. Choose OK. The criteria are saved and you return to Ansoft HFSS.

You can now identify the circuit parameters that will be used in the cost function.


5-3

Select the Output Parameters

Select the Output Parameters When performing an optimization analysis, you must select the solution variables (the circuit parameters which are output by HFSS) on which to base the cost function. The optimizer attempts to find the minimum of the cost function. For this problem, the cost function is based on the magnitude of S11.

Select the output parameters: 1. Choose Post Process/Extract Circuit Parameter. The following window appears:

2. 3. 4. 5.

6.

Leave port1:m1, port 1:m1 selected. This indicates that the S-parameter for port 1, mode 1 (S11) will be used. Leave the Component and Frequencies set to Magnitude and 8.2. Enter S11_mag in the Parameter Name field. Choose Add Circuit Parameter to add the solution variable to the Selected Quantities list. The solution variables appearing in this list are available for use in Ansoft Optimetrics. Leave the other options set to their defaults and choose OK. You return to Ansoft HFSS.

You are now ready to set up the Optimetrics problem.

5-4


Exit Ansoft HFSS

Exit Ansoft HFSS

Exit Ansoft HFSS: 1. Choose Exit. The following message appears: Exit HFSS? 2.

Choose Yes.

You return to Ansoft Optimetrics. There is now a checkmark next to Nominal Project, indicating that the nominal problem has been defined.

Check the Variables You may now view the parameters that are available for varying using the Edit Functions command. This command also allows you to add functions, such as the cost function generally defined for optimization.

Check which parameters Ansoft Optimetrics can currently vary: 1. Choose Edit Functions. The following window appears:

Notice that parameters listed are those you defined in the 3D Modeler macro, frequency (which is always a variable for Ansoft HFSS), permittivity, and S11_mag. You are now ready to specify the cost function.


5-5

Create the Cost Function

Create the Cost Function To define an optimization analysis, you must create a cost function out of the appropriate solution output variables. Ansoft Optimetrics manipulates the input parameters to find the user-specified goal value for the cost function, which is generally at or near the minimum value. Because Optimetrics tries to minimize the cost function, you must define the function so that the minimum value is the optimum value. Ansoft Optimetrics uses a quasi-Newton method for optimization. The cost function should therefore be a smooth, twice-differentiable function that can be approximated well by quadratics in the vicinity of the minimum. In other words, the slope of the cost function should decrease as you approach the optimum value. In particular, the cost function should not have a sharp dip or pole near the minimum, and should have a value that ranges from 0 to 1, although ranges of greater magnitude are possible. For this problem, define the cost function as the square of S11_mag. This prevents the software from missing discontinuities that would be more sharply defined by S11_mag. Ansoft Optimetrics changes the indicated variables until the solution of one setup satisfies the cost function. Following are examples of cost functions:

When varying a model to find the maximum reflection for port1 (S11 → 1), the cost function is defined to be -mag(S11)2. When optimizing towards a resonant frequency in an eigenmode solution, the cost function is defined to be:

fo – fr 2 ------------fr

where: fo is the resonant frequency solved for any given setup. fr is the desired resonant frequency. When achieving multiple goals in a single project, where one cost has more weight than another, the cost function is defined to be:

cos t1 + ( 1.5 × cos t2 )---------------------------------------------------2.5 where cost2 has more weight than cost1.

5-6


Create the Cost Function

Define the cost function: 1. You should still be in the Project parameters window; if not, choose Edit Functions. The window that appears displays the variables that are currently defined, and allows you to create new variables or functions. 2. Enter cost in the field to the left of the = sign. This is the name of the new cost function. You will use this later when identifying its stopping value. 3. Enter S11_mag * S11_mag in the field to the right of the = sign. This defines the cost function as the square of S11_mag. For each solution, the value of S11 is calculated, then Ansoft Optimetrics uses that value to calculate the cost function (or any function that uses S11_mag). 4. Choose Add to add the new function to the list of variables. Unlike the other variables, which are constants, a function depends on the values of the other variables. 5. Choose Done to accept the new cost function. Now that you have created the cost function, you need to specify the value at which the solution process stops.


5-7

Set Up the Optimization Analysis

Set Up the Optimization Analysis After creating the cost function, specify the variables the optimization process changes, and the value of the cost function at which the optimization process stops. To set up an optimization analysis, you must specify:

the value below which the cost function must fall and the cost function noise.

The goal of this guide is to optimize the dimensions of the quarter-wave transformer so the reflection loss at 8.2 GHz is below 1%; that is, ïS11(8.2 GHz)ï < –40 dB. Therefore, the acceptable cost for the cost function is 0.012 = 10-4. The cost function noise is the approximate error in the cost function in the vicinity of its minimum. It is not used explicitly as a stopping criterion. It indicates if a change during the solution process is significant enough to support achievement of the cost function. At the permissible return loss, the error in the cost function is: error = perturbed cost – nonperturbed cost = (ïS11ï + 0.005)2 – 0.012 = (0.01 + 0.005)2 – 0.012 = 0.000125 where 0.005 is the estimated error in the S11 calculation after 5 passes. This value varies depending on the type of problem, number of passes, amount of mesh refinement, and so forth.

5-8



Define the optimization analysis: 1. Choose Setup Analysis/Optimization. The following window appears:

2.

3.

4. 5.

Select Quasi Newton Optimizer from the Quasi Newton Optimizer/ Pattern Search Optimizer pull-down menu. This enables you to define the cost function noise. Select cost (which you previously defined) from the Cost Function menu. Any solution variable defined using the Setup Output Parameters commands may be used as a cost function. Leave the Cost Function Noise set to 0.0001. The Cost Function Noise is given by the estimated error in the cost function near the minimum. Specify the variables to vary during the optimization process: Choose Add from the Design Variables buttons. A window appears prompting you to select the variable and specify the variable and minimum and maximum values for the variable.


5-9


6.

Note:

If the variables used in the nominal problem lie outside the range specified when you set up the analysis, an error will appear when you attempt to use the Run command from the Executive Commands menu. You can correct this in one of the following ways: Return to Setup Analysis/Optimization and edit the Maximum and Minimum values for the variables so they are within the specified range. Change the value of the variable: 1. Return to Setup Analysis/Parametrics. 2. Choose Variables/Add to insert the variables you want to change into the parametric table. 3. Choose Edit/Insert Row. A single row is added to the setup. 4. Click in the cell for the variable you want to change. 5. Enter the new value in the Value box at the bottom of the table. 6. Choose Enter to accept the new value. 7. Choose File/Exit, and save the changes as you exit. 7.

5-10

Select wg2HalfWidth from the Select Variable menu. You must now specify the bounds between which Ansoft Optimetrics searches for the minimum. For this problem, the optimum width of the quarterwave transformer will certainly be somewhere between the widths of the two waveguides. Enter 0.45 in the Minimum field. Ansoft Optimetrics will not create a setup where the value of wg2HalfWidth is below 0.45. Enter 0.685 in the Maximum field. Ansoft Optimetrics will not create a setup where the value of wg2HalfWidth is above 0.685. Leave the default set to 0 in the Min. Step field. Enter 0.34 in the Max. Step field. Choose OK. The variable appears in the variables list, displaying the minimum and maximum values. Select wg2Length as the second variable to vary: Choose Add from the Design Variables buttons. Select wg2Length from the menu. Enter 0.2 in the Minimum field. Enter 0.8 in the Maximum field. Leave the default set to 0 in the Min. Step field. Enter 0.4 in the Max. Step field. Choose OK.

Enter 0.0001 in the Acceptable Cost field. This is the value at or below which the cost function must be before the optimization process stops. For this problem, the amount of reflection should be as low as possible.



8.

Note:

Enter 30 in the Max Iterations field. This stops the optimization process at 30 iterations, and allows you to put an upper limit on the number of setups that Ansoft Optimetrics creates when trying to minimize the cost function.

There is an additional stopping criterion that may halt the optimization process. The software uses several algorithms to determine what is the best path for determining the minimum value for the cost function. If the software determines that it cannot further improve the value of the cost function, the optimization process stops. This is effective for situations where the minimum for the problem is found relatively early, but the Acceptable Cost is not satisfied. 9.

Leave Save Fields unselected. You may use this to save the field solution for each setup created during the optimization process. Since this problem doesn’t require field solutions after the optimization is finished, leave it unselected to save disk space. 10. Choose OK to accept the optimization parameters. A checkmark appears next to Setup Analysis/Optimization, indicating that the optimization process has been defined and is ready to be solved. When you generate a solution for the optimization setup, a table is created with each row representing a separate problem with unique variable values. The variables defined for the optimization process are automatically defined as columns in the table. Now that you have defined the cost function and set up the optimization process, add the cost function to the table.


5-11

Add the Cost Function

Add the Cost Function To view the cost function and solution variable as each setup is solved, add the cost function and S11_mag to the setup table.

Add the cost function to the setup table: 1. Choose Add/Remove Output Columns to add functions or variables based on the solution of the nominal problem. The following window appears:

2. 3.

4.

Select cost and S11_mag from the Available Entries list. On the PC, hold down the Ctrl key to select multiple objects. Choose Add to move the cost function and S11_mag to the Table Entries list. All values listed in the Table Entries list are columns in the setup table. Choose OK to accept this.

The cost function and S11 will be displayed in the setup table as it is created for the optimization process. You are now ready to start the optimization process.

5-12


Generate the Optimization Solution

Generate the Optimization Solution Now that you have entered the optimization parameters, the problem is ready to be solved. Ansoft Optimetrics invokes Ansoft HFSS to generate a solution for each setup. The S11 value is displayed under the S11_mag column. The software calculates the cost function from the S11 value and displays that under the cost column. If a parametric table has been defined, Ansoft Optimetrics first solves all the setups in the table for which no solution exists. Ignoring any rows outside the range specified by the user, it selects the setup within that range which yields the lowest value for the cost function, and uses it as the starting point for the optimization analysis. If none of the setups are within the range, the software uses the nominal model. The starting point must be within the specified range, or an error appears during the solution process.

Note:

Note:

For this problem, a parametric table has not been defined. Depending on how closely you followed the guide, the results that you obtain should be approximately the same as the ones given in this guide. However, there may be a slight variation between platforms. Start the optimization process: 1. Choose Run/Optimization Analysis from the Executive Commands window to perform an optimization analysis. Ansoft HFSS starts and generates a solution for each setup project, and adds it to the table. 2. Once the optimization analysis is finished, a message appears informing you that it completed successfully. Choose OK to dismiss the window. 3. Choose Table from above the display area to view the table of results. Any setups from the parametric table that the optimizer solves are not considered part of the optimization process, and do not count towards the number of iterations you specified when defining the optimization parameters.


5-13

Analyzing the Results

Analyzing the Results The ideal values for the dimensions of the quarter-wave transformer are a length of 0.504 inches and a width of 1.030 inches as suggested by circuit theory. However, this does not take into account the effects of discontinuities. On the computer used for the following screen capture, the optimization process created 16 setups before reaching the Acceptable Cost value. The values for which the optimizer found a minimum for the length and width of the quarter-wave transformer were 0.34215 and 0.50771 inches, respectively.

5-14

Post process the parametric table: 1. Choose Post Process Table to access the Parametrics Post Processor. The post processor allows you to sort the data using a variety of sorting criteria and to create plots of the columns. The Post Process Variables window appears:



The following fields appear for all parametric sweeps: Displays the parametric setups that have been defined for that particular model. Initially, this column is blank because setups have not been defined. Each variation is automatically assigned a name (setup1, setup2, and so forth). Solved Indicates whether a solution has been generated. Sensitivity Indicates whether a sensitivity analysis was performed. A Done sensitivity analysis determines the permissible tolerance in a range of values for a particular setup. Save Fields Indicates whether the field solutions have been saved. By default this field is set to N (no). If you wish to view the fields for each solution or if you are planning on running a post-processor macro that requires the field solution, turn this on. If you do not need to view the field solutions for each setup, turn this off to conserve disk space. Solve Lets you select which parametric setups to solve during a parametric sweep. By default, this field is set to Y (yes). Setup

2. 3.

4. 5. 6.

In addition to the default columns, the variables you added to the table are also displayed. In this case, wg2halfwidth, wg2length, S11_mag, and cost also appear as columns. The next steps sort the rows so that the optimal values of the cost function are listed at the top of the table. Select all the rows in the table by clicking on the Setup cell at the upperleft corner of the table. Choose Data/Sort to specify the sorting criteria. The following window appears:

Select cost from the Variables list. Choose Add to add cost to the Sort Keys list. Any column listed in the Sort Keys list will be sorted in either ascending or descending order. Leave the sorting criterion set to Ascending. This displays the smallest values of the cost function results at the top of the table.


5-15


7.

8.

Choose OK to sort the table. The smallest cost values (the optimal values of the cost function) are listed at the top of the table, with the associated length and width values in the same rows. Choose File/Exit to exit the Parametric Post Processor.

Viewing the Table from the Executive Commands Menu If you simply want to view the table, but do not want to use any post-processing functions, choose Table from above the model display. The table appears much as it does in the Parametric Post Processor, but without the toolbar or menu commands.

Viewing Solved Projects You may view any project in the setup table by selecting the setup you wish to view. The Executive Commands menu is replaced by the following window:

Displays the value for the design variables in the selected setup.

Starts Ansoft HFSS in view-only mode and allows you to view the project using Ansoft HFSS. Returns you to the Executive Commands view.

5-16


6 Set Up the Parametric Problem

This chapter shows you how to set up a parametric problem for the nominal problem. Since you have already optimized this problem, you do not need to set up a parametric problem. This chapter is provided strictly as a demonstration on creating a parametric setup. Your goals are as follows:

Time:

Add three new solution variables. Specify which parameters you are going to vary and the values to sweep these parameters through. Generate a solution for the parametric setup. Post process the parametric table to determine a suitable range to use for an optimization process.

The total time needed to complete this chapter is approximately one hour.

Set Up the Parametric Problem

6-1

Set Up the Parametric Analysis

Set Up the Parametric Analysis Use the Setup Analysis/Parametrics command to set up the table of variables in the table editor. In general, use the parametric table when you don’t have a good idea for a starting point for optimization. After generating the solution for the parametric table, you can determine a reasonable range for your problem in which to perform optimization.

Access the table editor: Choose Setup Analysis/Parametrics. The Setup Variables window appears as shown below:

Selecting Cells You can select cells in a variety of ways: Selects a single cell. Selects a rectangular region of cells. Extends the rectangular selection to include the target cell. Control-click Adds a disconnected cell to the selection. Control-click & Drag Adds a disconnected rectangular region to the selection. Click Click & Drag Shift-click

Performing these actions on a column or row heading selects those columns or rows. When working with the table, commands are only executed on the current selection. For instance, if you select the Edit/Clear command with five rows selected, only those five rows are cleared.

6-2


Set Up the Parametric Analysis

Specify the Sweep Values

Note:

Unlike the optimization analysis, where you specified the upper and lower bounds for the variables, you must explicitly define the values through which the variables will be swept for a parametric table. The range chosen for these variables is meant to demonstrate how you would use the parametric table to select a feasible range for optimization when you do not know what to expect from the model. Define the values to sweep the variables through: 1. Choose Data/Sweep to specify the sweep values. The following window appears:

2. 3. 4. 5. 6.

Note:

7. 8.

Select wg2HalfWidth from the variable list. Notice that it is currently defined with the value you specified when creating the nominal problem. Enter 0.1 in the t_start field. This is the value at which wg2HalfWidth will start. Enter 0.85 in the t_end field. Enter 5 in the #samples field. This defines the number of parametric setups to create between the start and end parameters. Choose Accept to assign the start, end, and number of samples to wg2HalfWidth. Select wg2Length to specify its sweep values. Enter 0.1 for t_start, 1.25 for t_end, and 5 for #samples.

When you vary two or more variables, the number of total setups created is equal to the #samples for each variable multiplied together. For this problem, there are 25 rows. 9.

Choose Accept to assign the sweep values to wg2Length. Set Up the Parametric Problem

6-3

Generate the Parametric Solution

10. Leave Append to table selected. This adds the rows to the existing table created during the optimization process. If you deselect Append to table, the current rows (if any) are replaced with the new rows. 11. Choose OK to accept these sweep values. A parametric setup is created for each variation of the variables and these are added at the end of the table created during the optimization analysis. For this problem, there should be 25 additional setups added to the table.

Exit the Parametric Table Now that you have finished setting up the parametric table, save and exit.

Save your parametric table and exit: 1. Choose File/Exit. You are prompted to save your changes before exiting. 2. Choose Yes to save your setup information and exit. You return to Ansoft Optimetrics. Now you are ready to generate a solution for the parametric table.

Generate the Parametric Solution

Note:

6-4

Now that you have created the parametric table, the problem is ready to be solved. Ansoft Optimetrics invokes Ansoft HFSS to generate a solution for each row in the parametric table. The solution variable values are displayed under their respective columns. Depending on how closely you followed the guide, the results that you obtain should be approximately the same as the ones given in this guide. However, there may be a slight variation between platforms. Start the optimization process: Choose Run/Parametric Analysis from the Executive Commands window to start the parametric solution. Ansoft HFSS starts and generates a solution for each row in the parametric table. The solved rows for the optimization process do not get re-solved. The results are displayed in the table.



Analyzing the Results Once a solution has been generated for each row in the parametric table, use the variable post processor to analyze the results and determine a good range to use for optimization. To do this, sort the S11_mag column in ascending order. Because you are trying to minimize the magnitude of S11, the range that produces the smallest S11 values is of greatest interest. Using a parametric table in this way allows you to examine a broad range of values and narrow down the range to use for optimization. In general, if you do not know what behavior to expect from your model, set up a parametric table with a broad range before doing optimization.

Post process the parametric table: 1. Choose Post Process Table to access the Ansoft Optimetrics post processor. The post processor allows you to sort the data using a variety of sorting criteria and to create plots of the columns. The Post Process Variables window appears:


6-5


First examine how the magnitude of S11 (S11_mag) varies as the width of the quarter-wave transformer (wg2HalfWidth) changes. 2.

3.

4. 5.

6. 7. 8.

Click on the first setup containing an Acceptable Cost value to select that row, then hold down the Shift key and click on the last setup. (On the computer used for the previous screen capture, this selection would begin with setup 17.) This selects all the intervening rows, and selects only those rows for the parametric sweep, ignoring those generated from the optimization. Choose Data/Sort to specify the sorting criteria. The following window appears:

Select wg2Length from the Variables list. Choose Add to add wg2Length to the Sort Keys list. Any column listed in the Sort Keys list will be sorted in either ascending or descending order. Add wg2HalfWidth, then S11_mag, to the Sort Keys list in the same way. Leave the sorting criterion set to Ascending. This displays the smallest values on the list first. Choose OK to sort the table.

The sorting procedure above sets up the table by first sorting wg2Length in ascending order. Then, while maintaining the ordering of wg2Length, wg2HalfWidth and finally S11_mag are sorted. This is the first step in creating reasonable plots.

6-6



9.

Choose Plot/New. The following window appears:

10. Select wg2HalfWidth from the Abscissa (x-axis) column on the left. 11. Select S11_mag from the Ordinate (y-axis) column on the right. 12. Select Family of Curves. This results in a plot consisting of several separate lines without connecting their ends, which would result in a zig-zag plot. (Values corresponding to each value of S11 are plotted on their own curve.)


6-7


13. Choose OK. The plot is displayed in a new view window:

Now repeat this process to see how |S11| varies with the length of the quarter-wave transformer. 14. Display the table (partially hidden under the plot) by clicking within its window. 15. Select the first setup row with an Acceptable Cost value (on the computer used for the previous screen capture, this selection would begin with setup 17) through the last setup. 16. Choose Data/Sort to specify the sorting criteria. The Sort Setup window appears. 17. Select wg2HalfWidth from the Variables list. 18. Choose Add to add wg2HalfWidth to the Sort Keys list. 19. Add wg2Length, then S11_mag, to the Sort Keys list in the same way. 20. Leave the sorting criterion set to Ascending and choose OK to sort the table. The sorting order is different from the last time, giving priority to wg2Length. 21. 22. 23. 24.

6-8

Choose Plot/New. The Select Data to Plot window appears. Select wg2Length from the Abscissa (x-axis) column on the left. Select S11_mag from the Ordinate (y-axis) column on the right. Select Family of Curves to plot values corresponding to each value of S11 on their own curve.


Exit the Post Processor

25. Choose OK. The plot is displayed in a new view window:

26. Choose Window/Tile/Subwindows to view the table and the two plots together:

Exit the Post Processor Now that you have finished post processing the parametric table, exit the post processor.

Exit the post processor: Choose File/Exit. You return to Ansoft Optimetrics.

Exit Ansoft Optimetrics To exit Ansoft Optimetrics, follow the steps below:

Exit Ansoft Optimetrics: 1. Choose Exit. The following message appears: Exit Ansoft Optimetrics? 2.

Choose Yes.

You return to the Maxwell Control Panel.


6-9

Exit Ansoft Optimetrics

6-10


Index

Numerics

B

3D Modeler, starting 4-5

boundaries about 4-16 assigning 4-17 radiation 4-7 selecting surfaces 4-17 Symmetry 4-18 Boundary Manager, starting 4-16 boxes, drawing 4-7

A absolute coordinates 4-5 accessing Ansoft HFSS 4-2 Ansoft Optimetrics 3-2 online help 4-5 Parametric Post Processor 6-5 adaptive solution 5-2 alias 2-6 Ansoft HFSS Executive Commands window 4-3 exiting 5-4 starting 4-2 Ansoft Optimetrics Executive Commands window 3-2 exiting 6-9 general procedure 3-4 starting 3-2 assigning boundaries 4-17 materials 4-14

C cells, selecting 6-2 changing project directories 2-5 click click and hold vi double-click vi point and click vi right click vi columns, selecting 6-2 commands disabled 2-7 Executive Commands menu 3-2 context-sensitive help 4-5 coordinates absolute 4-5 Index-1

relative 4-5 cost function, adding 5-12 creating boxes 4-7 geometric model 4-5 projects 2-6 radiation boundary 4-7

D database, material 4-13 disabled commands 2-7 dragging objects vi drawing units, selecting 4-5 Driven Solution 4-4

E

starting the 3D Modeler 4-5 graphical user interface vi grayed-out commands 2-7 GUI, see graphical user interface

H help accessing 4-5 context-sensitive 4-5

I installing Maxwell software iv

M

F1 key 4-5 finite element analysis 1-1 fitting model in display window 4-7

macros automatically recorded 3-4 editing 4-10 Material Manager, starting 4-13 materials assigning 4-14 material database 4-13 Maxwell Control Panel accessing from a PC 2-2 accessing from a workstation 2-2 opening projects from 2-2 menus about vii pop-up vii pull-down vii mesh, refining adaptively 5-3 modeler, see 3D Modeler mouse vi

G

N

geometric model creating 4-5 sample problem 4-6 saving 4-12 solution parameters 5-2

names, selecting by 4-17 nominal model definition of 1-2 relationship to parametric model 1-2 notes describing project 2-7

Eigenmode Solution 4-4 electric field, on a symmetry plane 4-18 Executive Commands Add/Remove Output Columns 5-12 Edit Functions 5-5 Nominal Project 4-2 Post Process Table 6-5 Run 5-13, 6-4 Setup Analysis 5-9 Setup Output Parameters 5-4 Setup Solution Options 5-2

F

Index-2

O objects dragging vi in the nominal problem 4-6 opening Project Manager 2-2 projects 3-2 optimization analysis about 5-8 setting up 5-9

P parametric model analysis 6-5 definition of 1-2 relationship to nominal model 1-2 ports, defining 4-17 post processor, accessing 6-5 project directory creating 2-4 definition of 2-4 Project Manager commands Add 2-4 Change Dir 2-5 New 2-6 Open 3-2 Save Notes 2-7 Project Manager, opening 2-2 projects Ansoft Optimetrics 2-6 changing directories 2-5 creating 2-6 describing (notes) 2-7 displaying geometry of 2-7 opening 4-3 saving notes on 2-7 specifying name of 2-6

R

and virtual objects 4-7 creating 4-7 distance from source 4-7 drawing 4-7 relative coordinates 4-5 rows, selecting 6-2

S sample problem 1-3 saving geometric model 4-12 notes 2-7 selecting by name 4-17 cells 6-2 columns 6-2 drawing units 4-5 faces 4-17 rows 6-2 solver type 4-4 solution changing problem after 5-13, 6-4 criteria 5-2 frequency 5-2 general procedure 5-13, 6-4 setting solution parameters 5-2 viewing 5-16 solver types Driven 4-4 Eigenmode 4-4 selecting 4-4 starting Ansoft Optimetrics 3-2 status bar 4-5 symmetry boundaries defining 4-18 perfect E vs. perfect H 4-18 restrictions 4-18

T tool bar, about viii

radiation boundary Index-3

U units, selecting 4-5

V view windows 4-5 viewing solutions 5-16 virtual objects and radiation boundaries 4-7

W windows 3D Modeler 4-5 view windows 4-5

Index-4

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Getting Started: An HFSS Optimetrics Problem

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