{{projectinfo|Tutorial| Designing a Microstrip MESFET Amplifier |RF150.png|In this project, the basic concepts of RF.Spice A/D are demonstrated, you will build and test a simple voltage divider is modeled and examineddistributed RF amplifier using your own S-parameter-based MESFET model.|
*[[CubeCAD]]RF Amplifier*VisualizationS-Parameter-Based MESFET Model*[[EM.Tempo#Lumped Sources | Lumped Sources]]Maximum Gain Design*[[EM.Tempo#Scattering Parameters and Port Characteristics | S-Parameters]] Microstrip Line Segment*[[EM.Tempo#Far Field Calculations in FDTD | Far Fields]] AC Frequency Sweep*[[Advanced Meshing in EM.Tempo]] Power Gain|All versions|{{download|http://www.emagtech.com/contentdownloads/project-file-download-repository|EMProjectRepo/RFLesson11.Tempo zip RF Lesson 1|[[EM.Cube]] 14.811}} }}
=== What You Will Learn ===
In this tutorial you will learn how to import an RF FET model from a text file and will build a distributed RF amplifier using a unilateral MESFET along with physical microstrip components for the input and output matching networks.
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Open [[RF.Spice]]'s Device Manager and select "Create New RF Device from S-Parameter Test File..." from its File Menu. Follow the program's prompts step by step and create your new MESFET devices according to the table below:
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The figure below shows the results for S11, S21, S12 and S22 [[parameters]]. Note that since S<sub>12</sub> = 0, its dB-scale plot falls at a very large negative number. Therefore, you need to adjust the scale of the vertical axis. Or you can deselect S12 from the graph's legend and zoom to fit. The insertion gain |s<sub>21</sub>| is almost 11dB as expected from the design. However, the value of the return loss |s<sub>11</sub>| is only -5dB and certainly not very good. This is due to the fact that you had to deliberately introduce a mismatch in the input and output matching networks to achieve the specified gain of 11dB.
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== Running an AC Frequency Sweep to Compute Power Gain ==
Next, connect the AC voltage source and the source and load resistors and place two ammeters at the source and load ammeters in a similar manner as in the last part of this tutorial lesson. Similarly, define a custom output plot called G<sub>P</sub> for the power gain of your amplifier. Use the same definition: G<sub>P</sub> = 20*log10(abs(i(am2)/i(am1))). Run an AC Frequency Sweep Test of your amplifier from 3GHz to 5GHz with linear frequency steps of 10MHzTutorial Lesson 10. The figure below shows the graph of power gain vs. frequency. circuit with the source, load and ammeters:
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Run an AC Frequency Sweep Test of your amplifier according to the table below:
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| valign="bottomtop"|[[File:RF153.png|thumb|900px|left|The graph of the power gain of the MESFET amplifier vs. frequency.]]
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! scope="row"| Start Frequency
| 3G
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! scope="row"| Stop Frequency
| 5G
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! scope="row"| Steps/Interval
| 10Meg
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! scope="row"| Interval Type
| Linear
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! scope="row"| Preset Graph Plots
| i(iam1), i(iam2)
|}
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<td>
[[File:RFTUT11_7.png|thumb|750px|The graph of variation of input source current and output load current as a function of frequency.]]
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Also define a custom output plot called "Power_Gain" for your amplifier using the same definition: G<sub>P</sub> = 20*log10(abs(i(am2)/i(am1))).
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| valign="top"|
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{| class="wikitable"
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! scope="row"| Start Frequency
| 3G
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! scope="row"| Stop Frequency
| 5G
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! scope="row"| Steps/Interval
| 10Meg
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! scope="row"| Interval Type
| Linear
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! scope="row"| Preset Graph Plots
| Custom: Power_Gain
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The figure below shows the graph of power gain vs. frequency. Using the crosshairs you can read the value of the power gain at 4GHz to be 11.148dB, which agrees well with the value of insertion gain calculated in the previous part.
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<td>
[[File:RFTUT11_8.png|thumb|750px|The graph of the power gain of the MESFET amplifier vs. frequency.]]
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</table>
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