RF MODULE

Computing the Solution Using a Parametric Sweep—Brass
1 From the Solve menu, choose Parametric Sweep.
2 In the Parameters area, enter the following settings:
Parameter names T1
Parameter values range(273.15,10,373.15)
To compute the thermal drift of the filter’s lowest eigenfrequency, you want to
record the value of nu_rfw for each operating temperature in the sweep. However,
for this particular case you need not enter this variable in the Output area because
for output from the eigenvalue solver, COMSOL Multiphysics by default logs the
eigenvalue, lambda, in the second data column after the parameter value. Thus,
leave the Global variables to evaluate edit field empty and specify only a log file name.
3 Click the Browse button, navigate to a directory where you have writing
permissions, and then type mw_filter_freqs_brass.txt in the Log file name edit
field.
4 Click the Solve button to start the parametric sweep.
5 When the solver has finished, click OK to close the dialog box.
Boundary Conditions—Shell
Change the material in the post from brass to steel.
1 From the Multiphysics menu, select Geom1: Shell (smsh).
2 From the Physics menu, open the Boundary Settings dialog box.
3 Select Boundaries 6–10, then change the Group from Brass to Steel.
4 Click OK.
Computing the Solution Using a Parametric Sweep—Steel
1 From the Solve menu, choose Parametric Sweep.
2 In the Output area, change the Log file name to mw_filter_freqs_steel.txt.
3 Click the Solve button.
4 When the solver has finished, click OK to close the dialog box.
Importing the Frequency-Temperature Data
The next step is to import the eigenfrequency versus temperature data to the model.
Do this by creating two interpolation functions.
1 From the Options menu, choose Functions.
2 In the Functions dialog box, click the New Function button.
THERMAL DRIFT IN A MICROWAVE FILTER | 107