How does HFSS differentiate between signal and ground conductors?

[cannibol_90]

Upon exciting a structure via wave-ports/lumped ports, how does HFSS differentiate between signal and ground conductors? How can one assign them separately? I thought, integration line was responsible for differentiating between these two. But, it is not!

For example, if one has a 2 plate concentric cylindrical conductor and excites them with a waveport, which one of them would carry the signal? Which would be the ground? How does HFSS decide this?

 

[moh.haroun]

It doesn't decide pal. The excitation integration line can even be inverted and still giving the same results. it is not even important to decide that. The structure is excited with a field and the solution which includes fields and s parameters are calculated depending on Maxwell equations and boundary conditions. So as i know it isn't important on EM problem solution to know where is the ground and where is the signal.

 

[PlanarMetamaterials]

The concepts of "ground" and "signal" lines are purely artificial. A TEM mode is supported by two or more conductors -- choosing to establish a reference conductor ("ground") is completely arbitrary, and only done out of convenience. In complex systems, we generally establish a global reference (think the conductor backing "ground" plane of a PCB with multiple microstrip traces), because then we only need to refer to each of the smaller traces when referring to a "signal". However, we could just as accurately choose one of the "signal" traces to be the reference and refer to the "signal" on the "ground" plane.

 

[cannibol_90]

Thank you PlanarMetamaterials and moh.haroun!

More doubts follows!

1. Why is only TE10 mode considered in a waveguide (dominant mode; I know! Any particular reason?)? Why not TE20 or TM11? Is it because more connectors/probes are need for exciting/detection?

2. How does one excite the structure with higher order modes like TE20 or TM11 using HFSS? Draw 2 integration lines for TE20?

 

[PlanarMetamaterials]

1. Why is only TE10 mode considered in a waveguide (dominant mode; I know! Any particular reason?)? Why not TE20 or TM11? Is it because more connectors/probes are need for exciting/detection?

Yes, ease of excitation/detection is a large part of it. The TE10 mode, being dominant, is supported at the lowest frequency. This means that the for a given frequency, the waveguide can be physically smaller when using this mode - and space savings is usually equated with money savings.

2. How does one excite the structure with higher order modes like TE20 or TM11 using HFSS? Draw 2 integration lines for TE20?

No -- you simply instruct the waveport to support more modes. Each mode will have its own integration line (the direction of the E-field). HFSS will generally find modes in order of increasing cutoff frequency.

 

[cannibol_90]

Is the dominant mode propagating and the other modes evanescent?

 

[PlanarMetamaterials]

Is the dominant mode propagating and the other modes evanescent?

In general? No. The dominant mode is just the mode with the lowest frequency cutoff.