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Where Γ L is the load reflection coefficient, ζ L = Z L/Z 0 is the normalized load value, L is the length of the line segment (same as the len parameter), and β = 2π/λ g = 2π√(ε eff)/λ 0. The 2GHz point is located at the center of the Smith chart.Įxploring the Effect of Varying the Line Segment Lengthįrom the transmission line theory, the input impedance of your basic transmission live circuit can be expressed as: On the Status Bar, you can view the frequency associated with each data point as well as the real and imaginary parts of the reflection coefficient at that point. A tracking bar appears on the graph that connects the current cursor position to the data points. For this purpose, click the Track Selected Plot button of the Graph Toolbar and then move the mouse onto the surface of the Smith Chart. You can read the values of the data points on the Smith chart using the "Tracking Crosshairs" feature. However, it causes a phase shift in the signal, which can also be interpreted as a time delay. Since your T-Line segment is lossless (alpha = 0), its delivers the input signal to the load without attenuation. The distance from the center is the magnitude of the reflection coefficient S11 (also known as the return loss). The S11-parameter data points over the frequency range 1-5GHz form a perfect circle around the center of the circular chart. Let's analyze the S11-parameter data plotted on the Smith chart in a little bit more detail. The tracking bar shows the points corresponding to 2GHz. The S11-parameter plotted on a Smith Chart. The Smith chart is available for the S-parameter set only. Then check box labeled Plot Circular Chart (Not Elliptical). Then open the Edit Graph tab of the Toolbox and press the Circle button/tab at the top of the panel. To make it circular, click on the graph window's title tab to make it active. If your graph window is elongated, the Smith chart will look elliptical. Sometime, the program tries to fit the graph to the size of the graph window.
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Run a network analysis of your RF circuit with the following parameters:Īt the end of the simulation, view the resulting Smith chart. In order to better view the data points on the Smith chart, change the step size to 500MHz in the Sweep tab of the test panel. For the "Graph Type", check the "Smith" checkbox. For this purpose, open the Network Analysis Test Panel of the Toolbox once again, and this time choose the S radio button in the "Parameter Set" section of the Output tab. RF.Spice A/D allows you to plot the S-parameters of your circuit on the Smith Chart. The Smith chart is a very useful graphical tool for RF engineers. Check the checkboxes labeled Decibels and Degrees for magnitude and phase, respectively.Ĭartesian graph of the real and imaginary parts of the Z11-parameter.
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From the top "Graph Type" options, choose Cartesian (Mag/Phase). Since your circuit is a one-port, you will have the S11-parameter only. In the third tab of the dialog, Output, go to the "Parameter Set" section and choose the S radio button to compute the scattering parameters. This will provide a smooth graph of the port characteristics. Select a linear scale interval and set the step size to 10MHz. In the second tab, Sweep, set the start and stop frequencies to 1GHz and 5GHz, respectively. Accept the default value of 50Ω for the "Reference Impedance". In this case, Port 1 is defined between Node 2 and the ground. In the first tab, Connections, you define the port(s) of your circuit. It has three tabs at the top: Connections, Sweep and Output. In the Toolbox, select the Test Panel and check the "Network Analysis" checkbox. In this case, you will define a one-port network with an input port established at the input of the T-Line between Node 2 and ground. Network analysis calculates the S/Z/Y parameters of your circuit based on the port(s) you define for your RF circuit. Running a Network Analysis of Your RF CircuitĪs a first step, you will run a "Network Analysis" test of your RF circuit. The quarter-wave impedance transformer circuit tuned for f 0 = 2GHz.