set polar
unset tics
set rtics 0.2 font "Times,8"
set border 0 lt 0        # raxis の線種を破線にする
set grid polar pi/12
set term pngcairo enh font "Arial,10" size 480,480
set out "polar_rtics.png"
set size ratio -1
set rrange [0:1]
set samp 200
plot cos(2.5*t)**2 lw 2 lc rgb "#009933"