Learning Forum

[Amarveer]

Hello,

I am struggling to understand the difference between driven modal and driven terminal solution types. I studied online help and ANSYS HFSS user guide and understood that in a Modal solution, the S-parameters are determined by employing the concept of the incident, reflected and transmitted power whereas in Terminal solution the voltages and currents are used to examine the S-parameters. 

Just with this understanding, I am nowhere because I couldn't implement this knowledge to build something. I don't know when should I use modal and terminal solution types.

Also, it is not making sense to me because ultimately the powers are computed using voltages. I might not convey my understanding appropriately in this post and the reason is I am skeptical about my understanding.

If possible, kindly assist.

Thank you and Regards!

[VivekKamble]

Hi,
HFSS has three solution types. Traditionally, the Driven Modal solution type is used for most HFSS simulations, especially those that include passive, high-frequency structures such as microstrips, waveguides, and transmission lines.

For simulations that deal with Signal Integrity, the newest solution type, DrivenTerminal Mode, is used. These simulations generally include models that have multi-conductor transmission lines. The driven modal and driven terminal solution types are similar and rely on the same mathematical calculations when solving a given problem. The difference in the two solution types is in the types of results that are available to a user. Simulations that use the driven modal solution type yield S-matrix solutions that will be expressed in terms of the incident and reflected powers of waveguide modes.

The S-matrix that is given by the driven terminal type, however, is expressed in terms of terminal voltages and currents. As a practical example, if HFSS is used to model a pair of coplanar, parallel microstrip transmission lines, then the driven modal solution will yield results in terms of the even and odd modes that propagate on the structure. By contrast, the driven terminal mode solution will give the common and differential mode results. The eigenmode solver will provide results in terms of eigenmodes or resonances of a given structure. This solver will provide the frequency of the resonances as well as the fields at a particular resonance

[rakibulraju08]

Hi Vivek. Thanks for the great writing. Which solution type is better for simulating an antenna using differential feeding? I have been using modal soultion but my E plane scan result for port 1 and port 2 are different. How do I look for differential matching in this case. I am including the resutls of my simulation. Thanks.

[VivekKamble]

Hi, You can use the Driven Terminal Solution type.

[Meghjit Majumder]

Hello, I am trying to simulate a dual orthogonal fed patch antenna. So which type of Solution Type should I use?

[Nazanin]

Can anyone explain what migh cause different results in driven terminal and driven modal for a similar structure?

I have a 2x2 antenna array which works fine when exciting with four 50 ohm wave ports on 4 edges of the board (simulation is done in driven modal). Also, when I simulate two connectors connected to the same 50 ohm CPW transmission line separately, the results are good and similar in both driven modal and driven terminal.
Also the result is good when I simulate my antenna connected to 4 connectors in driven terminal. However, the problem is that when I simulate the same design in driven modal the results are not good and different from the results I got with driven terminal.

can anyone tell me what can cause these huge difference between driven modal and driven terminal when I connect the connectors to my antenna?