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# Plotting Near Field Patterns

The grid of points where the near field is calculated can be specified in the **Near-Field panel** of the **Setup** **tab**. There, the points can be entered in **Cartesian**, **Cylindrical**, or **Spherical Coordinates**. The near electric (**E**) and magnetic (**H**) fields **can be calculated separately**. Of course, the near fields can be calculated in any region of an antenna, very close to it or far away. In the far-field region, the near fields will tend to the known behavior of far-fields: **E** and **H** are perpendicular to each other and perpendicular to the radial direction from the antenna, they oscillate in phase, and their magnitudes have a constant ratio: E/H ≈ 377 Ohms (often also approximated as 120π Ohms) in free space. This behavior can be verified by performing calculations of the “near” E and H fields far from an antenna.

When both E and H fields have been calculated, the power density (S) will also be available in tables and plots. The total rms power density is calculated as S = |**E** x **H**^{*}|. This metric is particularly important for assessments to evaluate **electromagnetic field compliance** with radiation exposure limits published by regulatory authorities.

To plot the near electric field as a 3D graph with a color scale, go to **Results > Plot Near E-Field Pattern > 3D Plot** in the main menu. This command executes the **AN-3D Pattern** application (Fig. 1). To display a 3D plot of the near magnetic field or power density, respectively, go to **Results > Plot Near H-Field Pattern > 3D Plot** or **Results > Plot Power Density Pattern > 3D Plot**.

Near-field 3D plots will be shown according to the type of coordinate system chosen in the **Near-Field panel** of the **Setup** tab: **Cartesian**, **Cylindrical**, or **Spherical**. If near-fields were calculated for more than one frequency, a dialog box asking for a fixed frequency will be shown before plotting the near-field pattern.

The near electric field can also be plotted as a 2D rectangular plot by going to **Results > Plot Near E-Field Pattern > 2D Plot** in the main menu. The near magnetic field can be plotted by going to **Results > Plot Near H-Field Pattern > 2D Plot**, and the power density by going to **Results > Plot Power Density Pattern > 2D Plot**. These commands execute the **AN-XY Chart** application, where the total rms electric field, magnetic field, or power density is plotted in a 2D chart (Fig. 2). The components of the near E and H fields can be plotted individually by going to the **Plot** menu in the **AN-XY Chart** and selecting the desired component.

The near-field patterns for a given frequency can also be tabulated by going to **Results > List Near E-Field Pattern**, **Results > List Near H-Field Pattern**, or **Results > List Power Density Pattern** in the AN-SOF main menu.

**Regarding the E and H Field Components**

- If
**Cartesian coordinates**have been set in the**Near-Field**panel of the**Setup**tab, the**E**,_{x}**E**, and_{y}**E**electric field components and the_{z}**H**,_{x}**H**, and_{y}**H**magnetic field components will be calculated in a rectangular grid of points in space with coordinates (x, y, z)._{z}

- If
**Cylindrical coordinates**have been set in the**Near-Field**panel of the**Setup**tab, the**E**,_{r}**E**, and_{phi}**E**electric field components and the_{z}**H**,_{r}**H**, and_{phi}**H**magnetic field components will be calculated in a cylindrical grid of points in space with coordinates (r, phi, z)._{z}

- If
**Spherical coordinates**have been set in the**Near-Field**panel of the**Setup**tab, the**E**,_{r}**E**, and_{theta}**E**electric field components and the_{phi}**H**,_{r}**H**, and_{theta}**H**magnetic field components will be calculated in a spherical grid of points in space with coordinates (r, theta, phi)._{phi}