Modelling with NEC
What is NEC?
Here is an extract from the NEC-2 Manual, Part III: User’s Guide
The Numerical Electromagnetics code (NEC-2) is a computer code for analysing the electromagnetic response of an arbitrary structure consisting of wires and surfaces in free space or over a ground plane. The analysis is accomplished by the numerical solution of integral equations for induced currents. The excitation may be an incident plane wave or a voltage source on a wire, while the output may include current and charge density, electric or magnetic field in the vicinity of the structure, and radiated fields. NEC-2 includes several features not contained in NEC-1, including an accurate method for modelling grounds, based on the Sommerfeld integrals, and an option to modify a structure without repeating the complete solution.
Well, basically you can now build an antenna in your living room or shack and see how it performs without having the antenna in the air. Cool, that will save quite some time.
Currently I am using the free modelling program 4Nec2 from Arie Voors. I've also used mmana from Makoto (Mako) Mori JE3HHT. Here is a nice little tutorial by Al Couper NH7O on antenna modelling using mmana.
If you are going to use 4Nec2, I would strongly recommend you read "Getting Started with 4NEC2 tutorial" which you'll find attached to the application.