[EVO X]

Interesting article. It doesn’t say what frequency it works at. Here is an other interesting article about people radar. It would obviously have to operate a frequency such that the signal doesn’t get scattered or absorbed by the structure.

[GingisK]

The military one was a Doppler Effect device. The operator wore headphones and listened for swishy noises. People sounded like someone walking through Styrofoam peanuts with other odd noises in accompaniment.

It operated at a number of frequencies just to optimize reflections from watery objects such as people.