Antenna simulation problems in HFSS..

Hello everyone,
I'm relatively new to HFSS and am trying to simulate an antenna that works perfectly fine in ADS Momentum. The list of problems I'm facing are:

1. The antenna gives me 40 dB of return loss in Momentum but only 10 dB in HFSS. I thought it could be because of the infinite ground in ADS. I verified that and thts not the problem. Anything else anybody can think of?

2. The CPW port definition is a mystery to me. If one has to fiddle with the port size for the port impedance to get to whatever value, one could have the right CPW line and still not have the correct simulation results. Is this correct or is there another way to define the ports to have a particular impedance for a Tline?

3. I can write an equation in Momentum to find the input impedance values. Can this be done in HFSS?

4. Is there a thumb rule for the size of a radiation box that confines the circuit?

Thanks,
Ananth.

gernally momentum is not good at far field simulation.
you can look at example from hfss to define the port

radiation box size is not problem, result is same whatever you choose

Hello Ananth, if you want to define a radiation box, you should use a thickness of lamda/4 at least, howewer lambda/2 is better. You could use a PML boundary. Check the Topic "Convert a project from Designer 1.1 to HFSS, you can find some interesting info.
Sincerely
S.

i) Finite ground plane of CPW geometry, it will shift your passband and change your impedance behavior

ii) Finite extent of your dielectric layer?

iii) HFSS should give you the better simulation based on items i) & ii)

Thanks for the info everyone. The radiation boundary suggestion hekped out and I'm able to make my cct work now..