how to plot three sectors antenna

hello
i design unidirectional antenna and draw its radiation pattern as circle (2d) in matlab now i want to sector this antenna in to three sectors (120 degree) how can i do that using matlab

You just design an antenna having a 120 degree azimuth beamwidth and plot its pattern the same way you plotted the unidirectional antenna. Typically these are v-pol colinear arrays with a reflector. You could use image theory to calculate point source phases and locations to obtain the azimuth array factor.