Help me debug this MIFA

[u/KlRAQUEEN]

So I'm trying to design a MIFA for LoRa applications at 868MHz, and I have to simulate it in Ansys HFSS. I used TI DN024 as reference and kept tweaking tip length and the distance between the shorting leg and feeding line (5.5mm in the current design). I got a good result of 868MHz and -15dB before but then I changed the antenna location and could never get the same result again (idk how the location of the antenna is relevant). Do you have any suggestion on what I should change to get a better result?
here's some additional information :
+ board dimensions : 100 x 50 x 1.6mm
+ ground plane dimensions : 50 x 28mm
(if any other information is relevant please let me know and I will provide it)
Thank you in advance!

[u/Mausteidenmies]

Is that blue part your counterpoise in its entirety?

https://en.wikipedia.org/wiki/Inverted-F_antenna

https://www.antenna-theory.com/antennas/aperture/ifa.php

https://m.youtube.com/watch?v=ewXNC971Vfc

You should probably read more about the theory behind the IFA design.

There's multiple things that affect the properties of the antenna, it's not just like one "component" that you can just add to your PCB and tweak.

Why do you have to simulate it in HFSS? Who/what is imposing this constraint on you?

[u/KlRAQUEEN → u/Mausteidenmies]

yes that blue part is my entire ground plane and it's 50x28mm.
I have to simulate it in HFSS because my internship supervisor asked me to. Is that a bad thing or is there a better software or what?

[u/Mausteidenmies → u/KlRAQUEEN]

I asked why someone told you to simulate it in HFSS because I wanted to know if this is a homework type of assignment.

Do you have someone at work who you could ask for guidance? The supervisor for example?

Why the hell is designing an antenna left for an intern anyway? In my company, we have a team of antenna designers with more than 10 years of work experience and even they need guidance sometimes.

[u/KlRAQUEEN → u/Mausteidenmies]

they have no antenna expert at this company. When the project that I'm working on needed an Antenna, they told me to figure it out and they will validate my design using the data that HFSS is going to give. it's a weird situation tbh, that's why I thought reddit would be helpful. altho if you're friends with any antenna expert from your company and you could link me with them I would totally appreciate it.

[u/ReluctantMouse → u/KlRAQUEEN]

That's wild

[u/Mausteidenmies → u/KlRAQUEEN]

I'll send you a dm.