HFSS - Results validation problem: only 2 (of 3) resonances obtained in Fork Monopole

Simulation not validating desired resonances - monopole antenna

I am trying to validate the S-parameters of a fork-monopole antenna given in the paper:
**broken link removed**

Antenna resonances required at: 2.4 GHz, 3.7 GHz, 5.25 GHz
However, I get only 2. I have used HFSS v12 for the simulation.

When I simulate without the L-shaped parasitic structure on the rear side [here only 2 resonances are expected]: the last (~5 Ghz) resonance is weak, and the first (2.4 GHz) resonance dominates.


However, on adding the L-shaped parasitic structures to the rear side [full structure], the ~5 GHz resonance vanishes & I only get the middle (~3.5 GHz) and the initial (~2.4 GHz) one:


Both solution frequencies of 7 GHz and 10 GHz give nearly same S-11 plots.
I have used a rectangular T-structure instead of the slightly smoother one, as suggested in the paper.


Kindly help...I have been trying this over a month now and am unsuccessful.
Thanks in advance.

Attachment: my 2 simulation files and plots.

After spending a month on it, I'd be tempted to fabricate one and see if you actually observe the same same as the authors got, or what your simulations software shows.

You could also ask Ansys to comment. They might see something wrong with your model. I've not looked at the paper, but did the authors experimentally verify the 3 resonances, or were they found by simulation.

You could try another solve that's not based on FEM, but based on FDTD.

Let us know how you get on - the frequency coverage sounds a useful one.

Dave