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Ansoft Designer / Ansys Designer 在线帮助文档：

Filter Design Tool >
   Filter Design Wizard >
       Wizard Step 1 Properties >
           Ripple, Corners and Load Dialog Box

Ripple, Corners and Load Dialog Box

There are several conventions in specifying the passband ripple of a filter:

• Ripple [absolute magnitude]

• Ripple [dB]

• Return loss [dB]

• VSWR [absolute magnitude]

• VSWR [dB]

Given any of these parameters, others can be computed. Among them, Ripple[dB] is the most popular approach and Filter Design Tool uses this type of specification.

If you have a passband ripple in a format other than Ripple[dB], you can specify it in this dialog box and Filter Design Tool will convert it into Ripple[dB] automatically and use it internally.

Note

Absolute magnitude ripple is the most rarely used and therefore ignored in conversions.

To specify a passband ripple in a format other than Ripple[dB]:

1. Bring up the dialog box by clicking Ripple/Corners in the Properties page of the design wizard.

2. Type in the value in the desired edit box under Passband Ripple vs. VSWR.

3. Click OK.

Converting Chebyshev Ripple Corners

Filter Design Tool uses ripple corners for Chebyshev type filters. This means the insertion loss at the specified frequency corners will have the specified amount of ripple. Beyond that, the response starts to have more insertion loss. In some literature however, passband corners are given coupled with a specified loss specification.

Example: bandpass filter, 0.1dB passband ripple, 3-dB IL at 100 and 200 MHz.

You may specify your desired values at desired corners in The Ripple, Corners and Load dialog box. Filter Design Tool will then do the conversion and use ripple corners internally.

To specify desired insertion loss:

1. Bring up the dialog box by clicking Ripple/Corners in the Properties page of the design wizard.

2. In the dialog box, type in Order field.

3. Type in Desired loss field in dB format. Example: 3.0103

4. Type in the Desired fp1 and/or Desired fp2 field(s).

5. Ripple corners are automatically calculated and updated.

6. Click 3-dB corner setting if you want to enter 3-dB desired loss.

7. Check Desired loss = Ripple if you do not want to change the default ripple corner method. Each time you change the ripple the desired loss will be updated to be the same as ripple yielding the ripple corners to be the same as desired corners.

8. Click OK.

Matched Load Values for Chebyshev Filters

In Filter Design Tool, you may specify unequal terminations for Maximally Flat and Chebyshev filters. For odd-order filters, there is no constraint on the value of load termination. The filter will have a prescribed DC loss and ripple will fluctuate under that value.

For even-order filters, the ripple and load termination have a strong interdependence although the DC loss is the same as in odd-order case. This time, ripple will fluctuate above DC-loss. Given ripple or load, you can still specify a wide range of values for the other factor. Two of these combinations will produce exactly matched filters, i.e., at some points in passband, full transmission of power can be realized.

On the bottom left, the exact matched values of load termination are given. You may specify the load either smaller than or larger than the source termination. Both specifications yield the same response but the element of the equivalent circuit will be different.

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