simulating electrically very large problem (1D/2D)

I have access to some MoM based simulators, but I have a very large problem now. I can reduce the problem to a 1D/2D problem as shown in the image below:

It is too large to run with 2.5D MoM, as it will be around 500lambda large. The geometry is relatively simple and can be constructed out of straight lines (as in the example). The source can just be an infinite source where E goes into the paper. Is there any free, or very affordable softwave where you can draw such a problem and run a 2D EM solver, or approximate solver based on UTD (Unified Theory of Diffraction)? This will very likely save very much time and memory. Besides antenna related software, photonic/optical software may solve the problem also (I just need to scale my structure).

I am not looking for a semi-empirical propagation prediction tool, or a tool that used a simple Fresnel zone approximation.