Can anyone help me design an antenna for 0.5 GHz to 2 GHz ?

I have started with monopole disk antennas but I have very strict size constraints of maximum dimension to be 10 cm. I could get as low as 20 cm only. I use HFSS.

Do you know this tool?
http://www.antennamagus.com/

Ooops .... no HFSS support. Sorry!

Yes I know that but can you suggest me something by just quickly going through their antenna database, if you have access to magus ?

If the problem is still valid, I suggest a disk-cone antenna. You can find a lot of information on the internet, e.g.

https://www.youtube.com/watch?v=IaFSX7ycj0I
or different construction https://www.youtube.com/watch?v=xhW4QQruBTo
Some results of my calculation

Make it flat. Use this idea:
https://www.youtube.com/watch?v=KVvO6021VIc
Scale dimensions down - make it smaller.

can you make it work from 500MHz and fit into 100mm square? Not sure without trying or modeling. (Thanks to Hagster for pointing that.) If you are getting close try loading it: cut teeth (log periodic tooth antenna, again: idea courtesy of Hagster); sandwitch it between two blocks of plastic.

http://www.antenna-theory.com/antenn...g-periodic.php

This antenna.