Mininec 3
(updated 11 Jan 2014)
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The original MININEC was written by John Rockway with a little prodding and support from Jim Logan. It is often stated that MININEC is just a little version of its big brother, NEC-2. There are actually significant differences between these two codes. Both codes use the Method of Moments to solve for currents on electrically thin wires. However, each code starts with a different version of the integral formulation for the currents and fields for wires. Then, each follows significantly different algorithms for implementation of the Method of Moments.
In 1980, when the first version of MININEC was written, PCs had not been on the market for very long. PCs were typically limited to 16K memory with a 8 bit word length. There was no FORTRAN. MININEC had to be written in BASIC. The first version of MININEC was written in 500 lines BASIC and required 32k of memory. Nonetheless, this version proved surprisingly accurate for dipoles and monopoles. The first public release of MININEC occurred in 1982. The code was 550 lines of BASIC and would run on an APPLE II computer with 64 kilobytes of memory. It could compute the current distribution, impedance, and far field pattern of an arbitrarily oriented set of wires in free space or over a perfectly conducting ground plane. In interpreter BASIC (there were no BASIC compilers then) the problem size was limited to 10 wires and 50 currents (or 70 segments with junctions).
In 1984, partly to meet the demand for MININEC as well as share other computer algorithms, the authors teamed up with two colleagues, Peter Li and Dan Tam. They published a book that contained an improved version of MININEC along with some other useful algorithms. MININEC2, as it became known, was not significantly different from its predecessor, but the limitation for wires intersecting the ground plane was removed.
In the mid-80's, computers were getting faster, had more memory, and utilized math coprocessors. BASIC compilers also became available. These factors opened up new vistas for MININEC. In 1986, the authors released MININEC3. This code featured a new user interface which automatically determined wire connections from the user inputs for wire end coordinates. It could also read and interpret a limited NEC input data set. However, there was no way to save and edit geometry data. MININEC3 included near fields, a Fresnel reflection coefficient correction to the patterns for real ground, and an expanded lumped parameter loading option. MININEC had grown to just over 1600 lines of BASIC. With a math coprocessor and a BASIC compiler, MININEC3 could solve antenna problems up to 50 wires and 50 current unknowns. The NOSC public domain version of MININEC 3.13 was distributed via ACES (Applied Computational Electromagnetics Society) as part of the NEEDS 2.0 package. It was interactive but had no built-in structure viewer nor output plotting.
The next MININEC effort by the authors produced the MININEC SYSTEM in 1988. The release of the MININEC SYSTEM happened to coincide with the introduction of Microsoft Windows that took the PC world by storm. However, the authors were too close to publication to backtrack and implement a Windows system. This was the first version of MININEC that required a compiler, a BASIC compiler for DOS. Up to 50 wires and 90 current samples or 190 segments were permitted without recompiling.
In 1991 and 1992, Roy Lewallen, W7EL, and Brian Beezley, K6STI, introduced advanced versions of MININEC (ELNEC, MN and AO) which included better user interfaces and graphics displays.
In 1995, the authors published the first of a series of MININEC for Windows codes. The first code was MININEC Professional for Windows. An improved solution of the potential-integral formulation for the currents resulted in a more accurate formulation in the solution for the currents on wires. In addition, FORTRAN was used for the computationally intensive portions of MININEC. This led to an increase in speed over previous versions of MININEC. Because it was a Windows application, text and graphical outputs were easily transferred to other Windows applications such as spreadsheets and word processors. Mouse support and printer drivers were also supplied by the Windows environment. Entries were made in tables through individualized window screens. On line, context sensitive help was provided along with diagnostic preprocessing diagnostics. MININEC Professional was dimensioned for 1000 wires and 2000 unknowns.
In 1996, the authors published MININEC Broadcast Professional for Windows which was similar to its predecessor, but more powerful. Additional features included an improved voltage source model, a plane wave source model, automated convergence testing, design analysis post processing, array synthesis, and ground wave calculations. MININEC Broadcast Professional was dimensioned for 2000 wires and 4000 unknowns. Also in 1996, the authors published MININEC for Windows, a simplified version of MININEC Professional which is more suitable to first time users and their pocketbooks. This code is dimensioned for 400 wires and 800 unknowns.
In 1999, the authors published another improved set of codes, the Expert MININEC Series. The new series featured "Expert" assistance in selecting appropriate input dialog boxes while constructing a model. Context sensitive help was still an important feature. Accuracy and speed were also improved.
Advantages
of Mininec
You
might ask - why care about MININEC when we have NEC-2 and NEC-4
available. MININEC does have certain advantages when compared to either
NEC2 or NEC-4. Some of them include close-spaced wires, close-spaced wires of
different diameters, tapered-diameter
elements, different
diameter wires joined at an angle,
and placing sources at a wire junction.
Comments are welcome!
contact Roger: email to WB0DGF @ ARRL.NET
or
rgcox2 (at) gmail.com
Roger Cox - Spring Lake, MI