Stepped Impedance Resonators and H(B-fields)

I have designed a capacitively loaded 3 section microstrip stepped impedance resonator. The SIR has a low-high-low impedance configuration. I have placed capacitors at the input and outputs to tune the resonator down to around 400 MHz (first fundamental fr). The current is localized in the center thin section. I don't quite understand the phenomena. Is it because of reflected waves, constructive interference? How do I solve this problem or explain the phenomenon?

Which simulation software tool are you using (ADS, HFSS, Ansoft Designer etc)?

I have access to ADS and HFSS.