Adding inductance to a slot

Hi

I'm trying to hit the resonance of a slot on rectangular waveguide antenna. Its always capacitive, I want to add inductance to get resonating at the right frequency. I tried almost every thing ( width and length of slot, distance from the edge, displacement from the center line ) all don't shown any inductance added? Any one can help thank you in advance

if any body can help please. My center frequency is 9.6 GHz but my antenna resonating at 9.2 GHz. I tried almost everything to get it up to 9.6. But does not
I know the resonance is mainly driven by the slot length based on WG dimensions. it looks like the resonance is stuck at 9.2