The key visible feature of most embassy and diplomatic sites that give away their secret spying missions are large windowless areas on top floors, and also sheds or hangers on the roof which are designed to look as though they might contain lift or air conditioning apparatus.
At the US Embassy in Berlin, the lighter coloured panels on the south west, north west and northeast corners of the rooftop surveillance facility are dielectric "radio windows" which allow all types of radio signals to reach collection and analysis equipment on the roof and floor directly below.
The "radio window" panels are made of special material which does not conduct electricity. That is so weak radio signals coming in from all corners of the city are not diminished (attenuated) as they pass into the building and reach the sigint (signals intelligence) antennae.
Usually, dielectric window panels for signals intelligence work are made of plastic or fibreglass. They are often shaped and coloured to look as though they are a normal part of the building, or are special architectural features...
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