You've stumbled into the mysterious world of Microwave Engineering, where a physical volume of space is modeled as a circuit. (I mean Microwave energy, not microwave ovens.) Really, the only way to figure out what your signal problems are is to draw a 3D model of your "space" and run it through a tool similar to Ansoft's High Frequency Structure Simulator - this is the same tool that professionals use to verify that a trasmitter or source (satelittes, radar, etc.) is going to function properly. And, I can attest to the fact that designing microwave enclosures is a fine art bordering on divination. A tool like HFSS is like cheating, it solves Maxwell's equations over a mesh inside a volume, and it can spit out some amazing animations that show you an approximation of how waves travel through space.

The previous responses about a "Faraday Cage" are not necessarily correct. While a Faraday Cage can create a noiseless volume of space, from your description, there is simply a rectangle of metal mesh between you and your wireless whatchamacallit. If your house/apartment/teepee was made of steel, or metal - then you might be having problems. Or, if there is paint on the wall that contains a metallic component, you might be creating a faraday cage unwittingly. Any picture frames on the wall?

A so-called "Faraday Cage" can shield a volume of space from energy of any frequency, and there is a great resource at BOLT Lightning Protection that gives you a good equation for calculating the attenuation of a signal depending on the specifications of your metal mesh doorway.

I think most wireless routers operate near the 2.4 GHz or 5 GHz, and you shouldn't have to worry about being line-of-sight to your router. I've had wireless ethernet work through various materials - (my floors are made of wood, and I frequently find myself on my neighbor's wireless router).

T. O'Brien