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.
Download ISM 433MHz Helical Antenna model: