What is the problem with designing coils using EZNEC?
NEC-based softwares were originally develop for antenna simulation using linear segments in the Method of Moments (MoM) formulation. Recently I found AN-SOF, which is an MoM software that uses "curved segments" for modeling the antenna geometry, so its performance is better than NEC-based softwares in the case of helical, loop and spiral antennas. Also, I didn’t find a lower limit for segment length. As a matter of fact, the developers have provided a coil as an example of the software simulation capabilities, and there is a simulation of an RLC circuit 1 cm in size at only 50 Hz.
The pragmatists among us would probably like to employ EZNEC, an antenna modelling program, which allows you to define in a very user-friendly way helical coil structures. However, this valuable method is not without its pitfalls: EZNEC coil model • Coils in EZNEC are in fact defined as polyline structures. The projected polygon of the polyline should have the same area as the projected circle of the real helical coil. I will leave it up to the reader to do this trigonometric calculation. • The more segments in the polyline, the more accurate the model would respresent the real helical coil. However, EZNEC has a lower limit for the segment length which is proportional to the wavelength. • With respect to the two previous points, it is quite cumbersome to optimise a coil design using EZNEC. In practice, it is often much easier, quicker and more accurate to resort to the above calculator instead of creating a geometrical EZNEC coil model. Once the results are obtained from the calculator
