Not good means the s11 is -15 - -20dB at my operating frequency.
I want it to be at least -30dB - -35dB.
I simulated the picture that i uploaded in my first post, fr4 substrate(er = 4.6, tand=0.018) and PEC on the bottom side(same dimensions as the fr4).
I want to minimize the parasitic capacitance that appears because of the step.
After some simulations i saw the following:
If I increase the length of the wider microstrip it appears different resonance frequencies. Nevertheless , the max value of S11 is at -15 - -20 dB too(at these frequencies).
So I want something to fix the step.
However, i tried a taper with a length 0.5mm connecting the two microstrips and the S11 was -25dB. My problem here is the length 0.5mm. I dont want it so small and if I increase its length, S11 is getting worse.