この方が、読みやすいでしょうか。
# Gnuplot script for AA-30.ZERO reset set terminal aqua enhanced title 'AA-30.ZERO' size 1200 900 set multiplot layout 2,2 title 'My Antenna' set grid unset key fname = 'mydata.txt' set datafile separator ',' z0 = 50.0 z(r,x) = r + x*{0,1} rho(z) = (z-z0)/(z+z0) retloss(z) = -20.0 * log( abs(rho(z)) ) / log( 10.0 ) vswr(z) = ( 1+abs(rho(z)) ) / ( 1-abs(rho(z)) ) set title 'Impedance (R, X, and Z)' plot fname using 1:( abs(z($2,$3)) ) with line linewidth 3, \ '' using 1:2 with line linewidth 3, \ '' using 1:3 with line linewidth 3, \ 0.0 with line linewidth 3 lc "#80000000" set title 'Return Loss' plot '' using 1:( retloss(z($2,$3)) ) with line linewidth 3 linetype 4 set title 'VSWR' plot '' using 1:( vswr (z($2,$3)) ) with line linewidth 3 linetype 7, \ 1.0 with line linewidth 3 lc "#80000000" set title 'Smith Chart' set polar set grid polar set size square set xrange [-1:+1] plot '' using ( arg(rho(z($2,$3))) ) : ( abs(rho(z($2,$3))) ) : (3*$1) with line linewidth 3 linetype 6 unset multiplot reset