US Patent 7852256 Through the-wall motion detector with improved antenna

A flat panel antenna used at a wall in a through-the-wall CW radar application is spaced from the wall by a half wavelength to eliminate the effects of energy reflected by the wall back to the antenna. In one embodiment, a ½-wavelength dielectric absorbing material insert is placed adjacent the flat panel antenna, which allows the flat panel antenna to be pressed against the wall for antenna stabilization, with the index of refraction of the material desirably being 3.