Frequency Selective Surface

We are going into a bit of a niche topic of antennas, but certainly cutting edge. I remember when the very words frequency selective surface and the initials FSS were classified. Of course, today there are textbooks on the topic, so I guess I’m free to cover at least what’s in those books.

Let’s take that chain link fence in . To keep the math simple, let’s just say those open squares are 10 centimeters by 10 centimeters. When an opening is less than 1/10 of a wave-length, very little of the radio wave gets though the opening. So at 1 meter, or about 300 MHz, and lower, a radio wave sees that fence as a sheet of metal. But as we approach a half wavelength, or 50 centimeters, the openings are pretty porous. The waves pass right though the fence. Above 600 MHz or so, the fence is pretty much not there. So that fence is a frequency selective surface with the characteristics of a 300-MHz high-pass filter.