Plotting the Far-Field Spectrum

Far-field frequency spectra are generated when a simulation is executed using a specified list of frequencies or a frequency sweep. At each frequency point, the far field is calculated over the angular range (Theta and Phi) and observation distance defined in the Field panel of the Setup tab. To visualize the far field as a function of frequency, a fixed observation direction, defined by specific Zenith (Theta) and Azimuth (Phi) angles, must be selected.

Generating the Spectrum Plot

To visualize the spectrum, navigate to Results > Plot Far-Field Spectrum in the main menu. This action opens the Select Far-Field Point dialog box (Fig. 1), where the target Theta and Phi coordinates are specified. Upon clicking OK, the AN-XY Chart application displays the far-field spectrum relative to frequency (Fig. 2).

Available Metrics and Polarization Analysis

The Plot menu in the AN-XY Chart application provides access to several critical far-field metrics, including:

• Power Density, Directivity, and Gain.
• Radiation Pattern and E-Field.
• Axial Ratio.

Most metrics can be toggled between linear units and decibels. Furthermore, the software supports polarization decomposition into VP (Vertical), HP (Horizontal), RHCP (Right-Hand), and LHCP (Left-Hand) components. The application toolbar allows for rapid switching between these polarization states (Fig. 3).

Electric Field Components and Axial Ratio

Users can plot the linearly polarized electric field components ($E_\theta$ and $E_\phi$) or circularly polarized components ($E_{\text{Right}}$ and $E_{\text{Left}}$) against frequency. Each component can be analyzed through:

• Amplitude and Phase.
• Real and Imaginary parts.

The Axial Ratio, representing the ratio of the minor to major axes of the polarization ellipse, is also available as a function of frequency. This is a vital tool for verifying the circular polarization bandwidth of an antenna, plottable in both linear and dB scales.

Tabular Data and Visualization

The far-field spectrum for a selected observation point can also be reviewed in a tabular format. By selecting Results > List Far-Field Spectrum from the main menu and specifying the Theta and Phi coordinates, a table is generated listing all field components versus frequency. From this view, clicking the Plot button provides an alternative route to visual data analysis (Fig. 4). This suite of tools is essential for evaluating the wideband performance and stability of an antenna design.