Plotting the Near Field Spectrum

While spatial plots show you how fields vary across a region at a single frequency, the Near Field Spectrum allows you to observe how the field intensity changes at a single, fixed point across a range of frequencies. This is essential for identifying resonant frequencies or ensuring field limits are not exceeded over a wide bandwidth.

Step 1: Selecting the Observation Point

Since a spectrum requires a stationary point, executing the plot command will first prompt the Select Near-Field Point dialog box (Fig. 1).

• To start, navigate to Results > Plot Near [E-Field/H-Field/Power Density] Spectrum.
• In the dialog box, select one of the points from the grid you previously defined in the Near-Field panel of the Setup tab.

Step 2: Analyzing the Spectrum in AN-XY Chart

Once a point is selected, AN-XY Chart launches to display the magnitude of the field vs. frequency (Fig. 2).

To perform a deeper analysis of the vector components, you can use the Plot menu in the AN-XY Chart main menu to view:

• Components: Isolate $E_x, E_y, E_z$ (or the corresponding components for your chosen coordinate system).
• Data Types: Switch between Amplitude, Phase, Real, and Imaginary parts.

Practical Application

This feature is particularly useful when checking for Electromagnetic Interference (EMI). For instance, if you have sensitive electronics located at a specific distance from an antenna, you can plot the Power Density Spectrum at that exact coordinate to ensure it stays below a safe threshold across the entire operating frequency range.