基于ADS的微带天线的设计与仿真(9)

Momentum RF provides accurate electromagnetic simulation performance at RF frequencies. At higher frequencies, as radiation effects increase, the accuracy of the Momentum RF models declines smoothly with increased frequency. Momentum RF addresses the need for faster, more stable simulations down to DC, while conserving computer resources. Typical RF applications include RF components and circuits on chips, modules, and boards, as well as digital and analog RF interconnects and packages.

When compared to the Momentum mode, the Momentum RF mode uses new technologies enabling it to simulate physical designs at RF frequencies with several useful benefits. The RF mode is based on quasi-static electromagnetic functions enabling faster simulation of designs. Momentum RF has the same use-model as Momentum in ADS, and works with Momentum Visualization and Optimization. Figure 1-1 shows how each mode supports Momentum product features. For a detailed comparison of the two simulation modes, see Comparing the Microwave and RF Simulation Modes.

Selecting the Correct Mode

In the Layout window, the Momentum menu label displays the current simulation mode. To select the mode, toggle the mode setting.

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To switch the mode from Momentum to Momentum RF, choose Momentum > Enable RF Mode.

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To switch the mode from Momentum RF to Momentum, choose Momentum RF > Disable RF Mode.

In each case, the menu label in the Layout window changes to the current mode. Deciding which mode to use depends on your application. Each mode has its advantages. In addition to specifically RF applications, Momentum RF can simulate microwave circuits. The following graph identifies which mode is best suited for various applications. As you can see, some applications can benefit from using either mode depending on your requirements. As your requirements change, you can quickly switch modes to simulate the same physical design. As an example, you may want to begin simulating microwave applications using Momentum RF for quick, initial design and optimization iterations, then switch to Momentum to include radiation effects for final design and optimization.

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Figure 1-1. Choose the mode that matches the application.

Momentum RF is usually the more efficient mode when a circuit

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is electrically small is geometrically complex does not radiate

For descriptions about electrically small and geometrically complex circuits, see Matching the Simulation Mode to Circuit Characteristics.

Note For infinite ground planes with a loss conductivity specification, the MW mode of Momentum incorporates the HF losses in ground planes, however, the RF mode of Momentum will make an abstraction of these HF losses.

Choose Momentum > Mesh > Setup to set up mesh parameters, which enable you to control the number of cells that are used to create the mesh. The more cells, the more accurate the simulation will be, but too many cells will slow down a simulation and provide little improvement in accuracy. You can choose not to set up mesh parameters, and default values will be used to create the mesh.

If you choose to define mesh parameters, you can set them for:

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The entire circuit

The objects on a layout layer A single object

It is not necessary to specify parameters for all levels. You can, for example, specify mesh parameters for a single object, and use default values for the rest of the circuit.

For more information about how a mesh is generated, refer to About the Mesh Generator. For suggestions to consider when setting mesh parameters, refer to Guidelines for Meshing.

Procedures for setting up mesh parameters follow.

Defining Mesh Parameters for the Entire Circuit

Global mesh parameters affect the entire circuit. To set up global parameters:

1. 2. 3.

Choose Momentum > Mesh > Setup. The Global parameters are displayed.

Enter the mesh frequency in the Mesh Frequency field and select the units. The

wavelength of this frequency will be used to determine the density of the mesh. In general, set the value of the mesh frequency to the highest frequency that will be simulated. For more information, refer to Adjusting Mesh Density.

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Enter the Number of Cells per Wavelength. This value will also be used to determine

the density of the mesh. The relationship between wavelength and cells per wavelength can be described by the following example:

If the circuit is 3 wavelengths long and the number of cells per wavelength is 20, the length of the circuit will be divided into 60 cells. For more information, refer to Adjusting Mesh Density.

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Any curved areas in the circuit will be meshed using facets. In the Arc Facet Angle field,

enter the number of degrees that will be included in a single facet. The maximum is 45 degrees per facet. The lower the value, the better the resolution and the denser the mesh will be. The minimum value is equal to the Arc/Circle Resolution which is set when the object is drawn. For more information, refer to Processing Object Overlap.

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6.

Enable Edge Mesh to add a relatively dense mesh along the edges of objects. Since

most current flows along the edges of objects, the edge mesh can improve the accuracy and speed of a simulation.

If you want the edge mesh to be sized automatically, leave the Edge Width field blank. Otherwise, specify the edge width and select the units. For more information about the edge mesh, refer to About the Edge Mesh.

Note An edge mesh that is specified with a width larger than the cell size set by the wavelength/number of cells wavelength, will be ignored. This is because such edge meshes w …… 此处隐藏：5686字，全部文档内容请下载后查看。喜欢就下载吧 ……