Smith charts from Touchstone files in gnuplot

Touchstone S1p files are already in gnuplot format,
which seems unlikely mere coincidence.

Necessary gnuplot files

thanks to Roman for improvements

smithgrid.p is loaded >>one time only<< to generate 3MB file "smithgrid.dat"
- smithloop.p is called by "smithgrid.p".
- Once "smithgrid.dat" is generated, neither are needed again.
smithlabel.p is called by "plotsmith.p" to format and label charts.
plotsmith.p calls "smithlabel.p", draws the grid using "smithgrid.dat"
and also plots S11 for any included S1p files.
- multiple copies of "plotsmith.p" may be wanted for various S1p file comparisons.
png.p load 'png.p' generates "gnuplot.png" from the currently displayed plot.

why bother?

gnuplot makes it pretty easy to plot multiple S1p files on a single Smith chart.
Gnuplot has a command line:

C:\Users\ormpoa>gnuplot

        G N U P L O T
        Version 5.1 patchlevel 0    last modified 2017-04-18

        Copyright (C) 1986-1993, 1998, 2004, 2007-2017
        Thomas Williams, Colin Kelley and many others

        gnuplot home:     http://www.gnuplot.info
        mailing list:     gnuplot-beta@...
        faq, bugs, etc:   type "help FAQ"
        immediate help:   type "help"  (plot window: hit 'h')

Terminal type is now 'windows'
Options are '0 color solid butt enhanced standalone'
Encoding set to 'cp1252'.
gnuplot> load 'smithchart.p'
gnuplot> replot "BNC.s1p" u 2:3 w l title "50 Ohm BNC S11"

Replacing "BNC.s1p" at that last prompt will plot S11 from whatever Touchstone files you have.
Replotting with more files draws them all on a single chart, facilitating comparisons.

To record that Smith chart for posterity, generate 'gnuplot.png' from within gnuplot:

gnuplot> load 'png.p'

S-Parameters and Smith Charts - Nick Gamroth, Oct 2004