The AN-SOF Calculation Engine

The AN-SOF engine is written in the C++ programming language using double-precision arithmetic and has been developed to improve the accuracy in the modeling of wire antennas and metallic structures in general.

The computer code is based on an Electric Field Integral Equation (EFIE) expressed in the frequency domain. The current distribution on wire structures is computed by solving the EFIE using a Method of Moments (MoM) formulation with curved basis and testing functions, called the Conformal Method of Moments (CMoM) >. In this method, curved wires are modeled by means of conformal segments, which exactly follow the contour of the structure, instead of the traditional approximation based on straight wire segments. The linear approximation to the geometry can be a very inefficient method in terms of unknowns or computer memory. By using curved segments, the number of unknown currents, simulation time and memory space can be greatly reduced, allowing for the solution of bigger problems.

Old MoM codes suffer from several drawbacks due to the linear approximation to geometry and the use of the so-called thin-wire Kernel, such as: divergent input impedance, poor convergence for curved antennas (helices, loops, spirals) and bent wires, and singularities that appear when two parallel wires are close to each other or close to a lossy ground plane. With the CMoM and an exact Kernel formulation we have removed these limitations and obtained the following advantages:

• Decreased number of calculations and increased accuracy of results.
• Decreased simulation time and computer memory usage, allowing us to model larger and more complex designs.
• Ability to simulate from extremely low frequencies (circuits at 60 Hz) to very high ones (microwave antennas).