Hi, bazookazuz:
You can try to use the GEMS-F iterative solver. Your structure has 8076 unknowns. It may require about 540 MB RAM for the SMSi solver. If you have 2 GB, you should be able to solve it using SMSi solver quite easily. It may take 10-20 minutes per frequency point. I noticed that you define coarse frequency points. For most structures, you may consider putting more points (100-500). Putting more points will not slow down the simulation because IE3D nromally can finish it using about 6-20 points. For this particular structure, I am afraid it may take more than 20 points because there are so many resonances from 1 to 20 GHz.
If you want to increase the size of the strucutre and SMSi matrix does not have enough RAM for it. You can use GEMS-F iterative solver. It can reduce the RAM or may speed up the simulation. I am running your structure with 8076 unknowns. It does not seem to me the GEMS-F can be faster than the SMSi significantly. However, I can see it reduces the RAM requirement from 540 MB to below 100 MB. GEMS-F solver should yield accurate results as long as the iteration can converge.
Best regards.
Added after 1 minutes:
By the way, your log array is a slotted log array because z = 0 is the ground plane. Your polygons are on z = 0 and IE3D is using m-current modeling for the slot structure. Just want to make sure.
Added after 5 minutes:
Sorry. It was my mistake. The polygons are on z = 1.6 and z = 1.6 is a ground plane. The array is a slotted log array. Regards.