<CST question> Port Impedance

Hello everyone,

I'm simulating a piece of 50 ohm microstrip line using CST MWS 4.3.
I've defined an input and an output port and simulated the line with no
special difficulty.

so far so good.

The problem :

The output port must connect to the antenna, which introduces a
complex impedance (something like 47+j*3 ohms).

My question :

How can I introduce to the output port this specific impedance
without building the actual antenna model on the output side ?

Thanks alot,

P.

Hello,

I think it's not possible to do that in CST MWS directly..
I suggest to export the calculated S-params of your microstrip line.
Then connect these S-parameters with S-parameters (or complex impedance) of your actual antenna in any linear simulator (like Microwave Office).
Also CST design studio can do this job.

Cheers,

e.

Pushhead said:

Hello everyone,

I'm simulating a piece of 50 ohm microstrip line using CST MWS 4.3.
I've defined an input and an output port and simulated the line with no
special difficulty.

so far so good.

The problem :

The output port must connect to the antenna, which introduces a
complex impedance (something like 47+j*3 ohms).

My question :

How can I introduce to the output port this specific impedance
without building the actual antenna model on the output side ?

Thanks alot,

P.

Click to expand...

You can add RLC elements in MWS, it will be your impedance only at one frequency, though.

Added after 26 minutes:

Actually, if your ms line is uniform you shouldn’t simulate that, just the antenna with an input port corresponding to the cross-section of the ms line. Then you can add the desired ms line length in the deembeding.
However, if the ms line is curved, or have other structures on/near it then you should simulate the antenna (I assume it is a planar antenna) and feeding together because of some level of extra coupling/interaction. In fact, sometimes even a simple ms line contributes to the radiation pattern, so again you should simulate together.
Give some details (frequency! type of antenna, length of ms, other geometry details including of the antenna).

I think the best way to get the formula from a book and compute it yourself. You don't need a field solver for this.

Had the word antenna never been mentioned, you would probably be right, but often the antenna-feeding parasitic coupling/interaction (plus the effect on the radiation pattern) cannot be neglected and one needs a field solver.

Well, the "antenna" is a complex impedance in his case.

Pushhead said:

The output port must connect to the antenna, which introduces a
complex impedance (something like 47+j*3 ohms).
P.

Click to expand...

I would put the quotation marks on the word impedance not on antenna, after all that’s what it is there in reality not some abstract “complex ohms”.
I am sure pushead knows that basic formula, otherwise he/she should not even talk about an “antenna” or “MWS”.
The effects mentioned by me (twice) can modify the results, that is why you need a field simulator.