EBG ground (mushroom structure) in HFSS

Hi Guys,

I've been struggling with this for some time and decided to come here for help.

Attached is my EBG (mushroom-like structure) design which is composed of:

1) 4x4 elements
S11= -28dB
which is a good result and what I would expect from this design

2) 8x8 elements - the one I need help with
When I expand the 4x4 into 8x8 (keeping the same dimensions) I get -->
S11= -17dB
which is not acceptable, I don't know why the S11 parameter has gotten worse for my 8x8 design:?:
I don't know whether my problem is with the boundaries, excitation, solution setup...:?::?:

In both cases I'm using:
h=1mm
air box with radiation boundary
waveport excitation
dielectric const. = 2.2

I'd really appreciate your support on this, I'm sure a quick look at my 8x8 element hfss files will do the trick ;-)

I'm really in desperate need of any ones help with this post. This is for my Thesis and unless I master this EBG design I'm at a stand still :-(

Hi Khaled,

I'm not sure about your specific design, but in general with periodic structures I've found that if adding more cells results in a degradation of desired results, then there is an inappropriate phase condition inside your unit-cells.

For example, in EBG structures you typically want to ensure that the unit-cells are half a guided wavelength in size (depending on your setup) at the desired operational frequency. Have you run an eigenmode simulation on your unit-cell to determine the wavelength across the cell?

Good Luck

khaled.ayman said:

Hi Guys,

I've been struggling with this for some time and decided to come here for help.

Attached is my EBG (mushroom-like structure) design which is composed of:

1) 4x4 elements
S11= -28dB
which is a good result and what I would expect from this design

2) 8x8 elements - the one I need help with
When I expand the 4x4 into 8x8 (keeping the same dimensions) I get -->
S11= -17dB
which is not acceptable, I don't know why the S11 parameter has gotten worse for my 8x8 design:?:
I don't know whether my problem is with the boundaries, excitation, solution setup...:?::?:

In both cases I'm using:
h=1mm
air box with radiation boundary
waveport excitation
dielectric const. = 2.2

I'd really appreciate your support on this, I'm sure a quick look at my 8x8 element hfss files will do the trick ;-)

Click to expand...

yet not used HFSS........................But Probably u have changed distance b/w the unit cells .............just wondering rather resonent frequency changed or not ?

PlanarMetamaterials said:

For example, in EBG structures you typically want to ensure that the unit-cells are half a guided wavelength in size (depending on your setup) at the desired operational frequency. Have you run an eigenmode simulation on your unit-cell to determine the wavelength across the cell?

Click to expand...

Hi,

How do I do this? the eigenmode simulation on my unit cells?

polarizadmax said:

yet not used HFSS........................But Probably u have changed distance b/w the unit cells .............just wondering rather resonent frequency changed or not ?

Click to expand...

Knowing that the mushroom-like structure is basically acting like an LC circuit, then I would say Yes, changing the unit cell does impact the resonant frequency as well as changing the gap size (all of these affecting the effective capacitance of the structure). Moreover, changing the connecting via radius has some unpredictable effect on the S11 and reflection phase (due to the change in inductance.

I've successfully been able to simulate the Patch antenna (probe fed) and the mushroom structure, but each on it's own. When combining both together into one structure (please check the attached structure) the results just don't come out as I would expect, S11 is not very good (in the range of -15) and reflection phase is not aligned with S11 having a 0 degree reflection at the resonant frequency.

I've done a great deal on parametric analysis, trying to play around with the cell size, gap width, via radius, as well as the mushroom structure distance from the patch. But so far all in vein.

khaled.ayman said:

Hi,

How do I do this? the eigenmode simulation on my unit cells?

Click to expand...

https://www.edaboard.com/threads/265560/#post1140645