Discussion Forum

If you want to simulate the true (or nearly true) field distribution at the feed, then instead of using the lumped-port approximation, you need to first solve for the field distribution there, to use in exciting the antenna. There are at least a couple of ways to do this. Look at the examples involving boundary-mode calculations. Also, for TEM-line excitations, you can often solve for the fields with the electrostatic model, then use them to drive your RF model.

Thankyou so much for your reply sir,

Could you please guide me in where i can see these (boundary mode calculations) examples? I have looked around application library of comsol multiphysics but all the examples there are using either lumped port or port boundary condition for exciting the antenna.

I have attached the microstrip patch antenna model made in comsol and CST below.

Just to highlight again:- My problem is, i am using the same parameters to model an antenna in comsol and CST, the results (S11 = -20dB, directivity in particular direction) obtained in CST are good. However, in comsol its very different (S11= -15dB, directivity spread all side).

The only difference that i can see in both the models is this wave port used in CST, shown in the attached file. As you can see in the diagrams, the wave port is somewhat floating in the air. I don't know where is wave port in comsol.

So, in comsol, I am using lumped port as shown in attached file. The volatge used is 1[V] and input impedence is 50 ohm.

Please help.

I've attached an example (my own) of a parallel-plate TL with two numeric TEM RF ports, where the fields on the ports are first solved using the boundary-mode method. You can also compute the S parameters and impedance, which I included in the Results section.

I hope this simple model helps you enough so that you can figure out the rest of what you need to do. Good luck.

Enjoy.

Thankyou sir,

But, i'm not able to open your file in my comsol version. The comsol version which you are using is 5.4 and mine is 5.2.

Can you suggest some other way?

The Comsol1 picture seems to show that the ground plane is only under the feed line and not under the patch. A patch antenna needs a proper ground plane.

Well, if you have an active license, I suggest upgrading to the latest Comsol version. It is always best to have the latest version, if you can. But if not, perhaps another person reading this forum can help you by providing some other example in v5.2 or earlier. Good luck.

Hello sir edigar,

I make the ground plane partial to have the wideband. If i make the groud plane size of substrate then the anteena becomes narrow band.

Thankyou for you help sir robert.