A balun can be modeled in AN-SOF using an equivalent generator, as the figure below shows. Since voltage sources admit an internal impedance, we can adjust its resistive part to match the antenna input resistance.

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The Scilab script shown in this video, Isocontours script, is ready to use together with AN-SOF. It allows us to plot level curves or isocontours of a field pattern. The example shows the electric field pattern at the soil level just below an Inverted-V antenna.

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Did you know that AN-SOF data can be exported to Excel?

It is important to be able to export data so we can write reports and share our progress with colleagues. Simulation results can be exported to CSV (Comma Separated Values) files, where data are saved in tabular format. CSV files can then be opened with a spreadsheet program, such as Microsoft Excel or Google Sheets.

We will find the “Export” button next to the following tables:

1. Select a wire in AN-SOF, go to Main menu > Results > List Currents. Move the slider to choose a segment and click on the Current on Segment button or Input List button (it is enabled if there is a source there). A table of current/input impedance vs. frequency will be shown.
2. Go to Main menu > Results > Power Budget/RCS to display the table of input power, radiated power, directivity, gain and efficiency.
3. The far-field can be tabulated as a function of the direction (far-field pattern) for a chosen frequency or as a function of frequency for a selected direction (theta,phi). Go to Main menu > Results > List Far-Field Pattern for the first option or Results > List Far-Field Spectrum for the second one.
4. Regarding the near field, we can say the same as in 3). Go to Main menu > Results > List Near E-Field (H-Field) Pattern or Results > List Near E-Field (H-Field) Spectrum.

Regarding plots, after plotting some result in AN-XY Chart, AN-Polar or AN-Smith, go to the main menu of any of these applications > File > Export to export a CSV file.

In addition, there is a Copy Plot (Ctrl+C) command in the Edit menu of these applications. This option is called Copy Workspace in the File menu of AN-SOF. It sends the graphic to the clipboard as a bitmap, which can then be pasted elsewhere (Ctrl+V), e.g. in Microsoft Word, Power Point or their Google-equivalents, in an image editor, in an email body, etc.

To discover errors in the wire structure we can use the following functions in the AN-SOF main menu > Tools option:

• Check Individual Wires: It will be checked that the length of each segment and its radius are short compared to the wavelength. If the Exact Kernel is not set in Setup tab > Settings, then the segment diameter/length ratio will also be checked (the so-called thin-wire ratio).
• Check Wire Spacing: It will be checked that each wire does not overlap with the others. Two wires can be as close as their radii allow, without overlapping.
• Delete Duplicate Wires: It will be checked that each wire is unique, in other words, that an identical wire has not been superimposed on it. Duplicate wires will be automatically deleted.

Those wires in error will be highlighted in red and those in warning in yellow.

Keep in mind that we can still run a simulation with wires in warning if we check the validity of the model using an Average Gain Test (AGT). On the other hand, at a point where several wires are connected, slight overlaps may occur that do not generate errors in the results since Kirchhoff’s current law is fulfilled there.

It is important to have control over the scales of the graphs for a better presentation and interpretation of the results. We can adjust the maximum and minimum values of the color bar in AN-3D Pattern to obtain increments in multiples of 5 or the value we want.

Go to the AN-3D Pattern main menu > Edit > Preferences and set the Max and Min values of the color scale.

From the far field point of view, the whole structure of an antenna and its surroundings is reduced to a single point at the origin (X,Y,Z) = (0,0,0). So the standard practice of superimposing the 3D radiation pattern to the antenna structure is just a means to facilitate the interpretation of the directional characteristics of an antenna.

For this reason, you can move the phase origin of the 3D radiation pattern to the desired point in order to get a better view of the antenna orientation versus its radiation pattern. Go to the Setup tab > Far Field > Origin and set the X0, Y0, Z0 coordinates of the radiation pattern center (see Section “4.3 Far-Fields” in AN-SOF user’s guide).

Wires can be imported into AN-SOF from another AN-SOF project, so wire structures of different projects can be merged in a single project.

When a project is saved, a file having extension .wre will also be saved. This file contains the geometrical description of the wires. To import wires to a project, go to File menu > Import Wires > AN-SOF Format and just find and select the .wre file that you want to import.

For instance, this feature allows us to analyze the electromagnetic response of an antenna and its supporting structure separately, and then to combine them in a new project to analyze the response of the whole structure.

Radiating towers or radio masts can be modeled in AN-SOF with a high degree of detail, as shown in this figure. Since we already know the omnidirectional shape of the radiation pattern, what interests us is to calculate electric field values at ground level for a given input power. Go to Setup tab > Near Field panel and set the desired coordinate system (Cartesian or Cylindrical: Z = 0, Spherical: theta = 90°). Go to the Excitation panel to set the input power (it is customary to set 1,000 W). To increase the conductivity of the soil and therefore the radiation efficiency, we can use a radial wire ground screen.

Regarding the feeding point, we can put a source at the position of the base insulator if the feedline will be connected there in the real life antenna. In this way, we will obtain the input impedance of the antenna, which we can then post-process (e.g. tuning house + transmission line coming from the transmitter).

To speed up the simulation, we could use a simplified model, which consists of a single vertical wire with a triangular cross section. The radiation pattern will be the same as before, but we must be careful at the feeding point.

The base of the tower in the detailed model forms a short transmission line to the source position at the tower center. In the simplified model, we can offset the source from the center a distance equal to the half width of the tower to simulate the short transmission line effect.

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We see that most of the time we are interested in calculating only the E-field in antenna projects when we are talking about the near field. For this reason, we have added an option to enable or disable the automatic calculation of the H-field when we click on the “Run ALL” (F10) button. Go to Tools > Preferences > Options tab.

If we are only interested in the near field and we don’t want to waste time calculating the far field, we can click on the “Run Currents and Near-Field” (F12) button.

In the “Simulate” menu we also have the options: “Run Far-Field”, “Run Near E-Field” and “Run Near H-Field” to calculate each field separately.

There is always a trade-off between speed and accuracy. However, we often need to prioritize speed in the first simulations of an antenna model. Here are some tips to speed up the calculations.

1. Start with the minimum number of segments (10 segments per wavelength). AN-SOF sets the minimum number if you write “0” (zero) as the number of segments on any wire. In a wire grid, use one segment per cell side if the electrical size of each cell is < 10% of the wavelength.
2. Set the Quadrature Tolerance between 5% and 10% in Setup tab > Settings panel. This parameter only has an appreciable effect when there are parallel wires very close to each other (about two wire radii apart).
3. Go to Setup tab > Settings and set Interaction Distance = 0. It also only affects parallel wires that are very close to each other.
4. To calculate the gain, directivity and efficiency usually it is enough to set a spatial resolution of 5 or 10 deg in the far-field. Setup tab > Far-Field panel > Theta Step = 5 and Phi Step = 10 deg.
5. Last but not least, just calculate what you really need. The “Run ALL” option will calculate everything, currents, far and near fields. If you only need the currents and the far-field, click on “Run Currents and Far-Field (F11)”. If you are only interested in the input impedance, go to Run > Run Currents in the main menu.

The example in this figure shows that we can run a simulation more than 3 times faster, especially by setting the Interaction Distance to zero. You will find the “car.emm” project in the Examples folder which is installed together with AN-SOF.