rcs (radar cross section) hfss

i have to study the RCS of the following structure : ground , substrate (height 1.526mm) and a patch on top of the substrate (dimension of patch 58mm x 58mm). sweep frequency 0.8Ghz-2Ghz.

my questions are :

1) which are the dimensions of the airbox ( lamda/4 of the minimum frequency counter from patch , substrate or ground)?
2) should i use radiation boundary or PML ?
3) the ground should be infinite or not ?
4) should the substrate have the same dimension as the gound (expept the height )?
5) the airbox should be all around the structure (namely the structure should be in the middle of the airbox on every axis OR the ground should touch the down face of the airbox which i leave it without set it as boundary )?

i measure magnitude of RCS - frequency.

I don't know much about RCS, but I would assume if you had an infinite ground plane, the RCS would be infinity. As such, since you are intersted in the RCS of a patch antenna, I would have thought you need to simulate it with the ground plane size you will actually use - not an infinite one. Likewise for the substrate - it needs to be the size of whatever you are using. I'd be tempted to make the radiation box a quarter wave all around the antenna, but I don't know if that is sensible or not. Normally for patch antennas, they are simulated sitting in the bottom of the airbox, but I'm not so sure this would be good for your application.

I don't know enough to comment about the PML or radiation boundary. There are several HFSS experts here.

A quick Google found these - both refer to patch antennas, RCS and HFSS.

http://www.jpier.org/PIER/pier.php?paper=11100703
http://ieeexplore.ieee.org/xpl/login...mber%3D1220402

Deborah

ok after reading some papers and a lot of articles I end up to the conclusion that the structure should be sitting in the bottom of the air box (there is no reason to be in the middle as I have a structure with ground ). so I have new questions now.

1) the surround radiation boundary of the the air box should touch the structure or it should be lamba/4 away as the upper boundary?

2) in every example ground and patch are just rectangles (sheet 2dimensions ) and assigned as boundaries PEC. in my case where the structure supposed to be realistic ,it was asked these items to be objects namely 3d (the same dimensions as before but with height about 0.3mm). is that correct or i should follow the examples ?

I used radiation boundary and PML to get RCS of a particle respectively some time ago.I found the results of the two boundary are different with each other ,but the radiation boundary is better for getting RCS,PML will need more memory for calculating.