hfss mode

If we dont' define the number of modes in HFSS, the result will include all of modes of our structures.
Ex. for Rectangular/Circular waveguide, if you dont' define number of modes => there are lots of mode can be seen TEmn, TEM, TMmn...

shalom hosseinali,

As a rule of thumb, to calculate the number of modes: count the number of metals in the port subtract one.

For example a microstrip waveport has two metals (trace+ground) which means you need only one mode.

Two close microstrip waveports has three metals (left trace+right trace+ground) which menas you need two modes (differential mode and common mode).

Regards,
Itai

dear all,

i have build a cavity and it is fed by a slotted waveguide.
(like a microwave oven)
th lowest resonant mode for cavity is TE564.
i wonder if i should tell HFSS to solve only for TE564 mode or will it solve automatically?
should i use the "modes" option of HFSS?

Regards

Hi,

all Eigenmode Solvers (HFSS, CST) sort the modes by Eigenfrequncy. The one with the lowest Eigenfrequncy will be calculated first. Your therefore should directly get the correct Eigenmode if the calculation is performed correctly.

F

dear thaihoa,

i dont agree with you.
If u dont define a mode HFSS will only solve for the dominant mode not for all modes.
Try to incerease the "mode" option in waveport wizard, you will see that the time will increase for the adaptive analysis.

dear hosseinali,

propogation inside a wg or cavity depends on the dimensions of the structures.
generally dominant mode is the one with 0's and 1's.(like TE10, TEM 010)
sometimes if you combine structures (like a wg and a cavity) dominant mode may be something like TE645 which is different from TE10 or TE01.
As a result dominant mode is the mode that is most closer to the cut off frequency.
Offcourse there may be more modes than dominant mode.

I suggest you to change the "mode" option in the excitation wizard in HFSS.and anlayze your system.
After then try to use "zoom region" and see the shapes of the modes depending on the number you have entered into "mode" option.

regards

Hi Itay !

I was wondering how the rule considering to a waveguide port ?
I think its very usefull for CPW ports (like microstrips, striplines etc...)

Best regards,

Itzik

Hi

the number of modes is équal to nuber of metal in your structure - 1

Thanks

I think it means resonace modes and It shows the resonance frequencies of your structure.
for example If your structure contains 3 resonator with the same dimensions...then first three modes have almost same resonance frequency and next 3 mods are same but in 3 higher frequency and so on.
be successful