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    Plotting the Far Field Spectrum

    Created OnOctober 13, 2022
    Updated OnJuly 28, 2025
    By:Tony Golden

    Far-field frequency spectra are generated when a simulation is run using either a specified list of frequencies or a frequency sweep. At each frequency, the far field is calculated over a range of directions defined by the zenith (Theta) and azimuth (Phi) angles, as well as the observation distance set in the Far-Field panel of the Setup tab. To plot the far field as a function of frequency, you must first choose a fixed direction—i.e., specific Theta and Phi angles.

    To generate the far-field spectrum plot, go to Results > Plot Far-Field Spectrum in the main menu. This will open the Select Far-Field Point dialog box (see Fig. 1), where you can specify the desired Theta and Phi angles. After clicking OK, the AN-XY Chart application will display the far-field spectrum versus frequency (see Fig. 2).

    Fig. 1: “Select Far-Field Point” dialog box for choosing a fixed observation direction (Theta, Phi).
    Fig. 2: Far-field frequency spectrum plotted in AN-XY Chart, showing the LHCP component of the Gain in dBi.

    In the Plot menu of the AN-XY Chart application, various far-field metrics are available, including Power Density, Directivity, Gain, Radiation Pattern, E-Field, and Axial Ratio. Most of these metrics can be displayed in decibels and support polarization decomposition into VP (Vertically Polarized), HP (Horizontally Polarized), RHCP (Right-Hand Circularly Polarized), and LHCP (Left-Hand Circularly Polarized) components. The toolbar offers quick access to toggle between these polarization components (see Fig. 3).

    Fig. 3: Selecting VP, HP, RHCP, and LHCP polarization components using the toolbar buttons in the AN-XY Chart application.

    You can also plot the linearly polarized electric field components (E-Theta and E-Phi) and the circularly polarized components (E-Right and E-Left) versus frequency. Each component can be displayed in terms of amplitude, phase, or real and imaginary parts. Additionally, the Axial Ratio—defined as the ratio of the minor to major axes of the polarization ellipse—can be plotted as a function of frequency, in both linear scale and decibels.

    The far-field spectrum at a selected observation point can also be displayed in tabular form. To do this, go to Results > List Far-Field Spectrum in the AN-SOF main menu. This will open the Select Far-Field Point dialog box, where you can specify fixed values for Theta and Phi. Once selected, a table listing the far-field components versus frequency will be displayed. You can then click the Plot button to visualize the data (see Fig. 4). This set of tools offers valuable capabilities for analyzing far-field behavior across frequencies.

    Fig. 4: Table listing far-field components as a function of frequency.
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