modal analysis of HMSIW slot antenna

Hi,

I have a HMSIW linearly polarized U-slot antenna (see attachment #1 and #2) tuned at 10 GHz (see attachment #3) and I would like to calculate a modal analysis. I am interesting in first 10 modes.
The antenna should operates in fundamental mode which is TE 0.5;0. Based on the results calculated by FEKO (see attachment #4), the antenna operates in the 7th mode which is not correct, the 6th and the 8th modes are not calculated at all and the 9th mode is some kind of artefact. I think the modal analysis is not correctly calculated at all.

Quick info about settings:

start frequency: 3 GHz
end frequency: 18 GHz
frequency step: 50 MHz (301 frequency samples)

number of modes to calculate: 100
model has infinite dielectric substrate (Arlon CuClad 217 with er = 2.17 and tan(alfa) is set to zero) and infinite ground plane

mesh is finer than mesh size: Fine setting (length of the edge is 0.5)

data storage precision: double precision

 

What I am doing wrong?

 

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