S11 from MIMO antenna SImulation

Hi everyone,
I have a little confused when simulate MIMO antenna.
Firstly, i simulate two antennas that are symmetric each other with one port only for antenna 1.
Second, i simulate them in the same manner but with two port for both antenna 1 and antenna 2.
The results of S11 from the First and the Second are very different.
I am wondering that am i wrong? I worked with HFSS and assign the "Lump Port".
Thank you so much!!

gemmy94 said:

I am wondering that am i wrong?

Click to expand...

Probably the mesh is not adequate. Have your simulation converge to a higher precision.

you both cases are different and i would expect to get different results! are you simulating diversity antenna? if yes, you may need to optimize the antenna for your application.

PlanarMetamaterials said:

Probably the mesh is not adequate. Have your simulation converge to a higher precision.

Click to expand...

I expected S11 in two case is the same, because in HFSS the first port only excited, so in my view i thought S11 in both case will not change.

- - - Updated - - -

pragash said:

you both cases are different and i would expect to get different results! are you simulating diversity antenna? if yes, you may need to optimize the antenna for your application.

Click to expand...

I expected S11 in two case is the same, because in HFSS the first port only excited, so in my view i thought S11 in both case will not change.

gemmy94 said:

I expected S11 in two case is the same, because in HFSS the first port only excited, so in my view i thought S11 in both case will not change.

Click to expand...

im a CST user so im not sure about having a port 2 and not exciting it! is it possible in HFSS? from my understanding (in CST), having a port means exciting it/injecting input drive. maybe thats why you see different results.

pragash said:

im a CST user so im not sure about having a port 2 and not exciting it! is it possible in HFSS? from my understanding (in CST), having a port means exciting it/injecting input drive. maybe thats why you see different results.

Click to expand...

You can actually select which port you want to use as excitation in CST. ie. Have a port 2 and not excite it in simulation, instead only excite port 1.

hi gyz182,
based on my understanding, you want to simulate the performance of primary antenna in presence of diversity antenna. am i correct?

for that, you just need to put port1 to primary antenna and simulate. you dont need to care about secondary antenna since you are not exiting it. i really dont know why you get different results when you not exiting port2. im just suggesting simulation which close to your use case. maybe the problem you are facing is HFSS/CST problem which you dont want to deal with. just simulate as per your usecase.

Hi pragash,

No, I am just letting you know that in CST, you can define 2 ports but only use one as excitation.

i think both antennas are exited when you apply two ports.

Selecting a port excitation also determines which S-parameter will be calculated. If All ports is selected, the simulation is repeated such that each defined port will be stimulated once. With this setting, all N*N elements of the S-parameter matrix of your device will be calculated. In contrast to this, if one specific port is chosen to be stimulated, only N S-parameters of an N-port device are calculated. An exception of this rule is a loss-free two-port device, where all its S-parameters are computed in only one simulation run. In this situation, the fact that the matrix is symmetric for all loss free structures is taken advantage of. The corresponding modes can be selected below.

Finally, it is possible to define a specific selection of port modes by opening the Port mode list... dialog. Here, each port mode is listed separately and can be marked for calculation. The simulation runs are then performed one after another. However, it is also possible to choose a simultaneous excitation of the selected port modes with different excitation signals.