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FEKO Tutorial 1

FEKO is a Method of Moments (MoM) tool that can be used to calculate the

radiation pattern, impedance and gain of an antenna while mounted on some

defined geometry. In addition, it can calculate the isolation or mutual

coupling (S12) between pairs of antennas, the near fields around an antenna

and the electric currents that flow on an antenna or the surrounding

structure.

The basic flow of performing a FEKO analysis consists of:

1) Building a geometry, for the antenna (example – a wire to represent the

antenna) in CADFEKO or EDITFEKO.

2) Building a geometry to represent surrounding geometry (for instance, can

model an antenna on top of an airplane or an antenna on a supporting

structure which will affect the antenna’s performance) in CADFEKO,

EDITFEKO or an external tool.

3) Meshing the Created Antenna and Surrounding Geometries (CADFEKO

or EDITFEKO)

4) Requesting Solution Types and Setting Solution Parameters (CADFEKO

or EDITFEKO)

5) Running the FEKO solver (FEKO)

6) Read in and interpret results using PostFEKO.

These steps will be described in this FEKO tutorial. FEKO version 4.0 and

FEKO Suite 5.4 will be used.

For a more advanced tutorial, see Tutorial #2 - Blade Antenna on a

Cylinder.

First, let's click the CADFEKO button wherever we have FEKO installed. If

you have everything set up properly, you’ll see a screen similar to that

shown below. This is where we can build geometry using a fairly simple

graphical user interface.

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The easiest way to learn this stuff is to play around with it. We’ll walk

through a couple of examples. The first, we’ll look at a simple wire dipole

and calculate the impedance and radiation pattern.

The first step is to make our antenna. Note that the default settings for all

geometry lengths are meters. This can be altered by clicking

ModelModel Unit and selected a different unit, if say, you prefer inches.

Let's say we want a dipole antenna to operate at 600 MHz. The wavelength

at this frequency is 0.5 meters, so a half-wavelength dipole would be 0.25

meters. We’ll first declare a variable called “Length” to represent this.

Right-click on the “Variables” label in the Model Tree as shown below

and select “add variable”:

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The following window pops up, and we enter the length as 0.25 (the unit is

meters unless we specified otherwise). Then click create, and the variable is

saved in the Variables Tree.

For now, that is all the variables we'll make. You can add as many

expressions for variables as you want, and even define variables in terms of

other variables if you feel like it.

Now, we'll create the geometry of our antenna. Click the “create line”

button on the far left side of the CADFEKO screen:

A create line window pops up. We will place this dipole centered at the

origin (x,y,z)=(0,0,0), with the length given by our declared variable

“Length”. We will name it “dipole” in the label panel. Click create to

create the dipole, then close to close the create line window (see window

below).

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This is all the geometry we'll need to model a simple wire antenna.

In the next tutorial, we'll look at adding sources to the dipole, meshing, and

requesting output from FEKO.

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FEKO Tutorial 2

Sources and Meshing in FEKO

Continuing the FEKO tutorial from the previous one, we now have a line

that represents our dipole antenna. It is simply a wire (the default property

all objects created is to be made of metal with infinite conductivity – which

is usually what you want). To make it an antenna, we need to add a voltage

source to the center of the wire. This is simple. In the CADFEKO tree,

right click Ports and then select Create PortWire Port.

Once you select Wire Port, another window pops up. The Edge box is

initially highlighted – this is the place where the wire port should be applied.

We simply select the object we want the port applied to. In this case, just

click anywhere on the wire we just created. Then select the location as

“middle” to have the port at the center of the wire. Then click Create, then

Close as shown in the window below:

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We now have a port, but to calculate the radiation pattern we will need to

apply a source. This can be done by right clicking on Excitations in the

Solution list of the CADFEKO model tree, and then selecting Voltage

Source.

The add voltage source dialogue pops up. We want to apply the source to

Port1, and we’ll leave the magnitude and phase at the default values of 1

and 0, respectively. You can assign a name here if you want, but

VoltageSource1 (the default) is fine. Click Create, then Close.

We need to specify the solution frequency now. We would like to see

results at 600 MHz, so right click on Frequency under the Solution bar and

select “Set Frequency”:

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The frequency window pops up, and Enter 600e6 for 600 MHz, then click

ok:

Note that we could select a frequency range if we wanted instead of a single

frequency point.

Now we need to mesh our geometry (our geometry is just the wire). The

MoM technique works by reducing maxwell’s equations to an integral

equation, then approximating the integral via discrete chunks over space.

Hence, a mesh grids up our geometry (into triangles), that the solver uses to

obtain the solution.

At the top of the screen, there is a Mesh menu, click that and then click

Create Mesh. See window below.

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The mesh needs lengths specified which will determine how finely to grid

the geometry. The mesh should have triangles that are no longer than an

eighth of a wavelength, or wire segments not longer than one twelfth of a

wavelength. When the create mesh window pops up, click the “suggest“

button next to the edge length and segment length fields. This will

determine the required lengths for you based on the frequency we specified.

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For wire segment radius, this should be significantly smaller than the

segment length – we want the wire to be thin. If the wire is to be thicker,

consider using a cylinder instead to model the antenna. You can enter a

value 4e-3, which is about 10% of the segment size. Click create, then

close, and you have your mesh.

In the next section, we'll look at requesting outputs from FEKO, running the

FEKO solution kernel, and then viewing the output in PostFEKO.

Requesting Outputs, Running FEKO and Using

PostFEKO

At this point, we have our antenna geometry, port, source and mesh.

We've set the solution frequency to be 600 MHz. Now, we need to request

outputs. Right click on Solution in the CADFEKO tree, and click

“Request Far Fields”.

The Request Far Fields window pops up, and if you click the 3D Pattern at

the bottom (see window below), you will be requesting the far field pattern.

The default setting will be the entire sphere, with a grid sampling in 5

degree increments. You can change these parameters if you would like.

Then click create and then close, and you have told FEKO that you want to

see the far field patterns (including gain) once the analysis is complete.

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We can also request currents if we want, or S-parameters. For fun, lets

request the S-parameters. We need to specify a port impedance. The default

is 50 Ohms, and that’s a good value so we’ll use it. Right click on

Calculation under the Solution tree, and then click “Request S-

parameters”. The following window pops up, and simply click “create”

and then “close” and the solution will calculate the S-parameters for you.

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We’ve now made a model of a linear wire antenna (dipole), created a mesh,

added a source and a port, and requested our outputs. We now save our

CADFEKO file and we are ready to run the FEKO solution kernel.

Now, simply click RunFEKO (or ALT-4) and FEKO will analyze your

file (make sure you didn’t make any obvious mistakes), perform the

numerical simulation and process the results.

FEKO runs (this should be very quick because our model is so simple) and

the FEKO kernel shows the status on the screen.

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We've now set up our model in CADFEKO, run the FEKO solution kernel,

and we're ready to process our results using PostFEKO. Go to Run

PostFEKO (or ALT+3) and PostFEKO (FEKO’s utility to view the output

or solutions) will come up. Lets look at the 3D Radiation patterns first. On

the Far Left Column of buttons, click the “view radiation patterns”:

We immediately see a graph of the 3D Radiation pattern. You can change

the quantity to “gain” or “directivity” as desired, and the scale to dB. Then

change the Min and Max Limits so that they are to your liking. You can also

rotate the radiation pattern in 3D if you want by clicking on the graph and

moving it around.

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Note that the gain is 0.2 dB because it includes mismatch loss – reflection

due to impedance mismatch from our 50 Ohm port to our antenna. If you

click directivity, you will get 2.2 dB as the peak – the expected value for a

half-wave dipole antenna.

To view the S-parameters or Impedance of this antenna, simply click the

buttons on the top row, and then play around with the display settings. If

you want to know what a button does, you can hover the mouse over it and

it will display a brief description, or just click it and see what it does.

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This wraps up the brief tutorial on FEKO. You gain understanding of

PostFEKO simply by screwing around with it, click buttons, and see what

happens.

FEKO and PreFEKO are more complicated, so you may get to another

tutorial or see the manual that provides more details.

Good Luck

Dr. Zuhair M. Hejaz

Nov. 2009G