Small helical antennas for the 433 MHz ISM band are a good example where we need advanced software that has the ability to model:
- Curved wires with exact description of the helix contour.
- Very close wires, spaced a fraction of the wire radius.
- Horizontal wires almost touching the ground plane.
- Bent wires at right angles or less.
- Short segments, below 0.001 wavelength.
- Thick wires by means of Exact Kernel instead of thin-wire approximation.
AN-SOF includes all these features.
In this example, a perfect ground plane is used to get the input impedance: 48 Ohm, very close to the 50 Ohm of the antenna datasheet. We must subtract 3 dBi from the gain to obtain the gain in free space. It is a simple model, but it coincides very well with reality.