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    Tabulating Input Impedances, VSWR, and S11

    Created On
    Updated On
    By:Tony Golden

    To analyze the impedance matching and power efficiency of your antenna across the simulated frequency range, use the following procedure:

    1. Select the Source Wire: Right-click on the wire containing the source to open the pop-up menu.
    2. Activate the Toolbar: Click the Current vs. Freq… command to bring up the Current vs. Freq. toolbar (Fig. 1).
    3. Target the Source Segment: Use the slider to select the specific segment where the source is located. If you positioned the source at the exact center, the 50% button will jump there instantly.
    4. Access the Input List: Click the Input List button. This opens the Input List dialog box containing:
      • Input Impedance: Real and imaginary parts.
      • Source Data: Input current, voltage, and power.
      • Matching Parameters: Reflection coefficient, VSWR, and S11 (Return Loss) in decibels.
    5. Visualize the Data:
      • XY Plot: Select a parameter (like VSWR or S11) from the list in the upper right corner and press Plot to see its frequency response.
      • Smith Chart: Press the Smith button to visualize how the input impedance moves across the complex plane relative to the characteristic impedance.
    Fig. 1: Accessing the “Current vs. Freq.” toolbar to tabulate and plot the input impedance, VSWR, S11, etc., versus frequency at an antenna feed point.

    To ensure your reflection data (VSWR, S11, and Return Loss) aligns with your specific system, you can customize the reference impedance and use shortcuts to access source data.

    Setting the Reference Impedance

    By default, calculations are referenced to $50\ \Omega$, but you can adjust this value to match your specific feedline or connector:

    1. Navigate to the Setup tab in the main workspace.
    2. Locate the Settings panel (Fig. 2).
    3. Enter your desired value in the VSWR Ref. Impedance field.
    Fig. 2: “VSWR Ref. Impedance” option in the Settings panel.

    Quick Access to Source Data

    If your antenna has multiple sources, you can bypass the segment selection slider and access the input data directly (Fig. 3):

    1. Go to the Metrics tab and select the source index from the drop-down menu. Source indexes are displayed next to each source in the workspace when the model contains two or more sources.
    2. Go to the main menu and select Results > Input Impedance Table (or click the Input Impedance Table button, ZIN, on the toolbar).
    Fig. 3: Selecting a source index in the Metrics tab to tabulate its feed point impedance data.
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