# Creating the Model

Create the model in CADFEKO. Define any ports and sources required for the model. Specify the operating frequency or frequency range for the model.

Note: Assume the focal point of the lens is located at the global origin.
1. Define the following variables.
• freq = 30e9 (The operating frequency.)
• epsr = 6 (relative permittivity.)
• tand = 0.005 (dielectric loss tangent.)
• lambda_0 = c0/freq (The wavelength in free space.)
• D = lambda_0*10 (lens diameter.)
• F = 1.5*D (focal length.)
2. Define the following derived variables for the model construction.
• alpha = arcsin(D/(2*F)) (The included angle to the edge of the lens.)
• arclength = alpha* F (The arc length to the edge of the lens.)
• n = sqrt(epsr) (The refraction index of the lens.)
• T = (2*F - sqrt(4*F^2 - D^2))/(2*(n-1)) (The thickness of the length.)
• v0 = (F + T) / (n + 1) (The ellipse offset distance.)
• u0 = sqrt(n^2 - 1) * v0 (The diameter of the lens.)
• w0 = n*v0 (The major axis length of the ellipse.)
3. Define a dielectric medium, glass.
• Relative permittivity: epsr
• Dielectric Loss tangent: tand
• Label: Glass

Construct the lens by subtracting a sphere from an elliptical spheroid.

1. Create a sphere.
• Definition method: Centre, radius
• Centre: (0, 0, 0)
2. Create the elliptical spheroid.
1. Create a sphere.
• Definition method: Centre, radius U, radius V, radius N
• Centre: (0, 0, v0)
• Radius (Ru): u0
• Radius (Rv): u0
• Radius (Rn): w0
3. Subtract the sphere from the elliptical spheroid.
1. Rename Subtract1 to Lens.

A closed region is by default set to perfect electric conductor (PEC).

1. Set the region of Lens to Glass.
2. Set the solver method for the dielectric lens antenna to use RL-GO.
Tip: Open the Face properties dialog and click the Solution tab. From the Solve with special solution method list, select Ray launching - geometrical optics (RL-GO).
Tip: Use the View by solution tool to verify the applied solution methods.
3. Set the frequency to freq.

The dielectric lens is illuminated by a far field pattern source. The E-field pattern is described by the following equation.

(1)

1. Define the far field data definition.
• Load field data from a Feko Solver (*.ffe) file
• File name: Ideal_CosineQ4_Xpol.ffe
• Number of theta points: 91
• Number of phi points: 181
• Label: FarFieldData1
2. Create a far field point source utilising the far field definition, FarFieldData1.
• Magnitude scale factor: 1
• Phase offset (degrees): 0
• Field data: FarFieldData1.
Note: The far field source is positioned at the origin which coincide with the focal point of the lens.