You're in luck! I just happen to be working a six element collinear array right now. The procedure is to draw two rectangles from the ends of your feed microstrips perpendicular to said microstrips through the dielectric to the groundplane of your board. Do not assign any material to these rectangles. With one of the rectangles selected, right click on the Excitation icon in the project window. Click Assign/Lumped Port in the popup menu. Next assign the appropriate impedance to the port, default is 50 ohms. Next is the tricky part, assigning the integration line. You must draw a vector line from the center of the rectangle edge which touches the groundplane to the center of the rectangle edge which touches the feedline. I think there is another step, but for most cases, that completes a lumped port creation. Repeat this for the other rectangle you created and you have a pair of lumped ports.
Now comes the port weighting:
Click HFSS/Fields/Edit Sources. This will bring up a list of your ports with the default magnitude and phase of the inputs. If you have the optimetrics option, you can create variables for these inputs and set goals, etc etc. However, if you just want quick look data and have a pretty good idea what you need for element weighting, just put in some values and analyze your model and see how your radiation pattern comes out. Several iterations will probably get you a good enough pattern you can make up some copper test coupons and do some actual measurements.
Have fun,
Lighterup
