  In this paper, a review of indirect microwave holography for through-wall
imaging is presented. Indirect microwave holography is an imaging technique,
enabling the complex object scattered fields (amplitude and phase) to be
mathematically recovered from intensity-only, scalar microwave measurements. By
removing the requirement to use vector measurement equipment to directly
measure the complex fields, indirect microwave holography significantly reduces
the cost of the imaging system and simplifies the hardware implementation. The
application of a back-propagation algorithm enables the reconstructed amplitude
and phase images to be obtained at the plane of the concealed object. In order
to demonstrate the validity of the reviewed approach, experimental work is
carried out on a metallic gun concealed under a 5 cm thick plywood wall and it
is demonstrated that the indirect microwave holographic TWI can produce good
resolution amplitude and phase images when back-propagation is applied. TWI of
a concealed dielectric box representing non-metallic ordnance is also performed
to demonstrate the ability of the technique to reconstruct through-wall images
of concealed dielectric objects. An investigation of the resolution
characteristics of the system suggests diffraction limited resolution can be
achieved.

Applied Physics;Signal Processing