Scattered field problems

Hi

I need to simulate the scattered field of a single-layer array rods plced in air. I used "solve for: scattered field" setting.
The background field setting Ex=Ey=0, Ez=exp(-i*(x*cos(theta)+y*sin(theta))*emw.k0).

Lastly, I plot expression :emw.relEz. I know that emw.relEz=emw.Ez-emw.Ebz, but the background field exist in the whole domain, and whether I need to define the the background field only in the incident domain? and how?

I have come here hoping someone can clarify for me. Thank you!