You have theta as an argument for the function Ks but I don't see it referenced in the function's definition.
If all you want to do is to plot the function for different values of th (theta) then something like this would work,
ListPlot[Table[f[th],{th,{0, 22.5, 45, 67.5, 90}}],Joined->True,PlotRange->{{a,b},{c,d}},Framed->True]
f[th] will be a function that produces a discrete set of points for each value of th.
