Circular polarized cantenna feed for dish for 1500-2000mhz

[rwgast_lowlevellogicdesin]

I am not sure if I have this down right but... If I wanted to build cantenna dish feed, for l-band sat and not wifi would I do this...

First off can diameter, I used this calculator. I entered 1700 for the freq and 120mm for diameter and it seems this is pretty ideal.
http://www.changpuak.ch/electronics/cantenna.php

Now as far as length im not sure if this is a calculated factor I read the longer the better?

Second doing the Left Hand Circulation I would install one probe at the bottom and one on the left hand side of the tube. Next I would use something like the coax phasing system used in a cross yagi in order to get the proper phasing?

What about ditching the probes and just using something like a cloverleaf in the can? From what I understand you dont want a crazy hi gain antenna feeding a dish though if I am correct this will just cause a ton of side lobes?

I also thought about feeding with a "cross fire" antenna the FPV people are using, should I use a wave guide for any feed antenna I choose? Im not going helical. This is a small 18 inch dish and is only going to give me 15-20db max at 21cm /L Band. Also Ive seen dual feeds but I dont see many details on how there made... If I wanted a wide band 1500-2000(1900mhz really) and a 290-1320 feed of the same dish how could I achieve that?

This is my first work with a dish so im sorry if these are stupid questions, almost everything I have done has been vertically polarized except a patch.