You'll probably want to model the antenna as a 50 ohm resistor (that's a fairly standard resistance for antennas and long wire runs) with a voltage source on the end away from the circuit. Drive the voltage source with a small 60 Hz sine wave (the most common EMF anywhere near power lines) to get a rough idea of how the circuit will behave.
Your goal is to make the right kind of signal appear at the node where the antenna connects to the rest of the circuit, and a Thevenin equivalent to the antenna is the simplest way to do it.
The results of a SPICE simulation are always artificial. It's practically impossible to model a circuit completely, so you're really just trying to get a feel for the first-order effects. You set up a simulation for a specific set of conditions and see how certain nodes behave. Then you build a real version of the circuit, drive it the same way in a controlled environment, measure the same nodes, and see whether the real behavior is anything like your model's prediction.
If the real circuit behaves roughly the same way as the simulation, it means your model is accurate enough to be useful. If the real circuit's behavior doesn't match the simulation, it means something is happening in the real circuit that didn't get into your model.
You generally don't model just for the sake of modeling though. The point of having a usable model is to test a range of variations in something.. input signals, noise levels, component tolerances, etc. The first step in setting up a simulation is deciding what you want to learn from it.
When you void a product warrany, you give up your right to sue the manufacturer if something goes wrong and accept full responsibility for whatever happens next. And then you truly own the product.