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RF Circuit Objects

This example shows how to create and use RF Toolbox™ circuit objects. In this example, you create three circuit (rfckt) objects: two transmission lines and an amplifier. You visualize the amplifier data using RF Toolbox™ functions and retrieve frequency data that was read from a file into the amplifier rfckt object. Then you analyze the amplifier over a different frequency range and visualize the results. Next, you cascade the three circuits to create a cascaded rfckt object. Then you analyze the cascaded network and visualize its S-parameters over the original frequency range of the amplifier. Finally, you plot the S11, S22, and S21 parameters and noise figure of the cascaded network.

Create rfckt Objects

Create three circuit objects: two transmission lines, and an amplifier using data from default.ampdefault.amp data file.

FirstCkt = rfckt.txline;
SecondCkt = rfckt.amplifier('IntpType', 'cubic');
read(SecondCkt, 'default.amp');
ThirdCkt = rfckt.txline('LineLength', 0.025, 'PV', 2.0e8);

View Properties of rfckt Objects

You can use the get function to view an object's properties. For example,

PropertiesOfFirstCkt = get(FirstCkt)
PropertiesOfFirstCkt = 

        LineLength: 0.0100
          StubMode: 'NotAStub'
       Termination: 'NotApplicable'
              Freq: 1.0000e+09
                Z0: 50.0000 + 0.0000i
                PV: 299792458
              Loss: 0
          IntpType: 'Linear'
             nPort: 2
    AnalyzedResult: []
              Name: 'Transmission Line'

PropertiesOfSecondCkt = get(SecondCkt)
PropertiesOfSecondCkt = 

         NoiseData: [1x1 rfdata.noise]
     NonlinearData: [1x1 rfdata.power]
          IntpType: 'Cubic'
       NetworkData: [1x1 rfdata.network]
             nPort: 2
    AnalyzedResult: [1x1 rfdata.data]
              Name: 'Amplifier'

PropertiesOfThirdCkt = get(ThirdCkt)
PropertiesOfThirdCkt = 

        LineLength: 0.0250
          StubMode: 'NotAStub'
       Termination: 'NotApplicable'
              Freq: 1.0000e+09
                Z0: 50.0000 + 0.0000i
                PV: 200000000
              Loss: 0
          IntpType: 'Linear'
             nPort: 2
    AnalyzedResult: []
              Name: 'Transmission Line'

List Methods of rfckt Objects

You can use the methods function to list an object's methods. For example,

MethodsOfThirdCkt = methods(ThirdCkt);

Change Properties of rfckt Objects

Use the set function to change the line length of the first transmission line.

DefaultLength = get(FirstCkt, 'LineLength')
DefaultLength =

    0.0100

set(FirstCkt, 'LineLength', .001);
NewLength = get(FirstCkt, 'LineLength')
NewLength =

   1.0000e-03

Plot the Amplifier S11 and S22 Parameters

Use the smithsmith method of circuit object to plot the original S11 and S22 parameters of the amplifier (SecondCkt) on a Z Smith chart. The original frequencies of the amplifier's S-parameters range from 1.0 GHz to 2.9 GHz.

fig = figure;
smith(SecondCkt, 'S11', 'S22');
legend show;

Plot the Amplifier Pin-Pout Data

Use the plotplot method of circuit object to plot the amplifier (SecondCkt) Pin-Pout data, in dBm, at 2.1 GHz on an X-Y plane.

plot(SecondCkt, 'Pout','dBm');
legend show;
set(legend, 'Location', 'NorthWest');

Get the Original Frequency Data and the Result of the Analyzing the Amplifier over the Original Frequencies

When the RF Toolbox reads data from default.amp into an amplifier object (SecondCkt), it also analyzes the amplifier over the frequencies of network parameters in default.amp file and store the result at the property AnalyzedResult. Here are the original amplifier frequency and analyzed result over it.

f = SecondCkt.AnalyzedResult.Freq;
data = SecondCkt.AnalyzedResult
data = 

   rfdata.data with properties:

            Freq: [191x1 double]
    S_Parameters: [2x2x191 double]
      GroupDelay: [191x1 double]
              NF: [191x1 double]
            OIP3: [191x1 double]
              Z0: 50.0000 + 0.0000i
              ZS: 50.0000 + 0.0000i
              ZL: 50.0000 + 0.0000i
        IntpType: 'Cubic'
            Name: 'Data object'

Analyze the Amplifier over a New Frequency Range and Plot Its New S11 and S22

To visualize the S-parameters of a circuit over a different frequency range, you must first analyze it over that frequency range.

analyze(SecondCkt, [1.85e9:1e7:2.55e9]);
smith(SecondCkt, 'S11', 'S22', 'zy');
legend show;

Create and Analyze a Cascaded rfckt Object

Cascade three circuit objects to create a cascaded circuit object, and then analyze it at the original amplifier frequencies which range from 1.0 GHz to 2.9 GHz.

CascadedCkt = rfckt.cascade('Ckts', {FirstCkt, SecondCkt, ThirdCkt});
analyze(CascadedCkt, f);

Figure 1: The cascaded circuit.

Plot the S11 and S22 Parameters of the Cascaded Circuit

Use the smith method of circuit object to plot S11 and S22 of the cascaded circuit (CascadedCkt) on a Z Smith chart.

smith(CascadedCkt, 'S11', 'S22', 'z');
legend show;

Plot the S21 Parameters of the Cascaded Circuit

Use the plot method of circuit object to plot S21 of the cascaded circuit (CascadedCkt) on an X-Y plane.

plot(CascadedCkt, 'S21', 'dB');
legend show;

Plot the Budget S21 Parameters and Noise Figure of the Cascaded Circuit

Use the plot method of circuit object to plot the budget S21 parameters and noise figure of the cascaded circuit (CascadedCkt) on an X-Y plane.

plot(CascadedCkt, 'budget', 'S21', 'NF');
legend show;

close(fig);
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