# 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.

1. Set the model unit to millimetres.
2. Define the following variables:
• rInU = 21 (The inner radius of the elliptic arc in the U direction.)
• rOutU = 31 (The outer radius of the elliptic arc in the U direction.)
• rInV = 0.8*rInU (The inner radius of the elliptic arc in the V direction.)
• rOutV = 0.8*rOutU (The outer radius of the elliptic arc in the V direction.)
• freq = 2.49e9 (The operating frequency.)
3. Create a quarter of the ring.
1. Create the first elliptic arc.
• Centre point: (0, 0, 0)
• Start angle (A0): 0°
• End angle (A1): 90°
2. Create the second elliptic arc.
• Centre point: (0, 0, 0)
• Start angle (A0): 0°
• End angle (A1): 90°

Create a quarter of the ring antenna.

1. Create a surface from the two elliptic arcs using the Loft tool.
1. Rename the label to sector_1.
2. Create the full ring antenna.
1. Copy and mirror sector_1 around the UN plane.
2. Copy and mirror sector_1 and the copied part from Step 5.a around the VN plane.
3. Union the four sectors to create a single ring structure.
3. Create four edge ports.
1. port_North with its port edge on the positive Y axis.
2. port_East with its port edge on the positive X axis.
3. port_South with its port edge on the negative Y axis.
4. port_West with its port edge on the negative X axis.
Note: All four ports point in an anticlockwise direction.
4. Set the frequency to freq.
5. Specify the symmetry about 2 principal planes.
• X=0: Geometric symmetry.
• Y=0: Geometric symmetry.
Tip: Exploit model symmetries (if it exists) in a large or complex model to reduce computational costs.
Note: Electric or magnetic symmetry does not apply to characteristic mode analysis, since there are no active sources involved. The geometrical symmetry enforces a symmetrical mesh.