Known as Prism 200, the ultra-wideband machine operates at 2GHz. “This frequency is a good balance between angular resolution and attenuation by the wall,” programme manager Alan Wiltshire told EW. “The transmitted wavelength is physically short enough to allow it to penetrate some reinforced structures which have steel grids embedded in the concrete.”
The radar sends out 100 narrow, band-limited, pulses per second from its single transmit antenna and picks up any reflections though three receive antennas – allowing unambiguous resolution in three dimensions.
Field of view is 120 degrees horizontally and 90 degrees vertically. See here for a video demonstration.
Undisclosed signal processing is used to de-clutter signal returns: identifying moving objects and reject all stationary objects including walls and furniture. “Prism 200 will monitor several subjects and track movement, even in difficult environments such as offices with their angular surfaces and metal objects which can act like a hall of mirrors to a normal radar,” said Cambridge Consultants.
According to Wiltshire, sitting very still does allow people to hide from his device. “The first step was the tracking of moving people,” he said.
Images displayed to the operator are entirely synthetic, consisting only a reference grid, and floating purple prisms, one for each moving object in the room (see picture), with Windows CE handling the display.
Several views are available including 2D plan, side and front views, or an isometric ‘3D’ image.
Four feet on the unit’s base stop it slipping on the wall and, as the unit will be tracking everything else until it is firmly on the wall, a button allows images to be refreshed once it is in place.
For longer term use, tripod mounting away from a wall is also possible.