Radar imaging consists of data pre-processing, calibration
and imaging procedures. The pre-processing removes antenna
coupling along with unwanted reflections by background
subtraction and suppresses noise by a 10-18 GHz band-pass
finite impulse response filter. It also includes deconvolution of
the system impulse response out of the pre-processed data in
order to compress the received pulse that improves down-range
resolution and, finally, the sharpness of the focused image. The
calibration makes the time scale of the acquired radar signal
corresponding to its actual travel time to target and back. A
small metal sphere placed at a given distance is used to
calibrate the system. The estimated time shift between the
actual and measured travel times is applied to all the data
measured afterwards.
The imaging technique is based on Kirchhoff migration that
has been widely used in seismology and recently applied to
UWB radar imaging [7, 8]. It accounts for the wave front of the
scattered electromagnetic field, which results in a more
accurate target reconstruction than ray approximation. For
multi-static radar configuration Kirchhoff migration can be
expressed as follows