In this tutorial you will learn how to design and use microstrip lines and components. You will analyze a microstrip double-step and will utilize microstrip discontinuity models to improve the accuracy of your analysis.
[[File:RF40.png|thumb|360px|The RF.Spice Microstrip Designer dialog.]]
== Designing Microstrip Lines ==
[[RF.Spice A/D]] has a large number of physical line calculators and designers. You can access these tools from the Device EditorManager. Open [[RF.Spice]]'s Device Editor Manager either from its '''File Menu ''' or using the keyboard shortcut "{{key|Ctrl+D"}}. At the top of Device EditorManager's RF '''Tools Menu''', find "'''Microstrip Designer" ''' and open it. For this project, you will use an FR-4 substrate of thickness h = 1.2mm, relative permittivity er = 4.5 and loss tangent tand = 0.02. To design a 50Ω microstrip line, enter these values into the designer dialog and set Z0 = 50. The corresponding width value is computed to be 2.3mm. <table><tr><td>[[File:RF40.png|thumb|360px|The RF.Spice A/D Microstrip Designer dialog accessible from the Device Manager.]]</td></tr></table> == Verifying a Simple Microstrip Circuit == {| border="0"|-| valign="top"||-{| class="wikitable"|-! scope="col"| Part Name! scope="col"| Part Type! scope="col"| Part Value|-! scope="row"| AC1| AC Voltage Source| 1V|-! scope="row"| XTL1| Microstrip Line| Defaults: w = 2.3, h = 1.2, er = 4.5, len = 50, tand = 0.02|-! scope="row"| R1| Resistor| 50 |-! scope="row"| R2| Resistor| 50 |} Place and connect the parts as shown in the figure below: <table><tr><td>[[File:RF42.png|thumb|300px|left|A simple microstrip circuit with a load termination.]]</td></tr></table>
In order to verify your design, go back to the [[RF.Spice]] Workshop and place a "Microstrip Line" part on the schematic either using the RF Menu of [[Schematic Editor]] or using the keyboard shortcut "Alt+T". Open the part's property dialog and enter the [[parameters]]: w = 2.3mm, h = 1.2mm, er = 4.5, len = 20mm, tand = 0.02, as shown in the figure below. Terminate the line segment in a 50Ω resistor and ground both negative pins of the microstrip. Place a "Net" Marker called "IN" (keyboard shortcut: Alt+N) at the input of the microstrip segment. Run a Network Analysis of this simple circuit, with Port 1 defined between node IN and the ground. Set the frequency sweep to go from 100MHz to 6GHz with the linear steps of 100MHz. Choose the Smith Chart for your output data and run the test. You will see a Smith chart like the one shown below with all the frequency points overlaid at the center of the chart. This means that the input impedance of your circuit at Port 1 is Z<sub>in</sub> = 50Ω at all frequencies. This can happen only if the characteristic impedance of you transmission line segment perfectly matches your termination load.
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[[File:RF42.png|thumb|300px|left|A simple microstrip circuit with a load termination.]]
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[[File:RF44.png|thumb|400px|left|The property dialog of the Microstrip Line device.]]
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[[File:RF41.png|thumb|360px|The RF.Spice Microstrip Calculator dialog.]]
== Calculating Microstrip Line Parameters ==
[[File:RF41.png|thumb|360px|The RF.Spice Microstrip Calculator dialog.]]
Next, you will use the Device Editor's "Microstrip Calculator" to find the effective permittivity of your 50Ω microstrip line and its guide wavelength at 2GHz. Open the Line Calculator from the RF Menu of Device Editor. Enter the [[parameters]]: w = 2.3mm, h = 1.2mm, er = 4.5, len = 20mm, tand = 0.02, as shown in the opposite figure. In the other parts of this tutorial lesson you will use very wide and very narrow microstrip line segments. Repeat the same calculations for microstrip width values of 0.5mm and 5mm. The results are summarized in the table below.