Offset paraboloid reflector design

I'm playing with the Antenna Toolbox, but I can't generate an offset reflector where the paraboloid is not symmetric (e.g., I would like only to have a section of the parabola, defining focal length, diameter, clearance...). Any attempt of using the propertires of the reflectorParabolic just moves the feed, reflector size, tilt...but always symmetric parabola.

ant = reflectorParabolic;
ant.Exciter = design(hornConical,18e9);
ant.Tilt = 40;
ant.Radius = 0.5;
ant.FocalLength = 1;
ant.FeedOffset = [0 0 0];
ant.Exciter.Tilt = 90;
show(ant)