Abstract.
Generalized ambiguity function versus spatial coordinates is obtained for
orthogonal signals recirculated in the multistate radio holography system using
two-measure transmitter and receiver antenna arrays. Two kind of orthogonal
regular signal ensembles are considered: linear frequency modulation signals
with uncovered spectrum and monopulse multi frequency signals. Each element of
a transmission array can radiate a signal with a certain spectral width and its
own center frequency from a frequency grid. New target observation method is
based on the recirculation of orthogonal regular signals in a spatial feedback
loop formed by the radio holography system and the target. The recirculation
method is implemented by means of tapping, amplification, and feeding of a
portion of the received signal into the transmitting circuit, where this signal
is combined with the current signal generated by a transmitter source. The
obtained sum signal is again radiated toward the target. With the use of
transmitting array with orthogonal signals, the recirculation method can be
implemented in each antenna element.
Spatial resolution analysis of
radio holography systems
with antenna arrays is based on a construction of an averaged multidimensional
generalized ambiguity function (GAF). Detailed study of generalized ambiguity
function and the 2D its sections along spatial coordinates allows estimation of
the spatial and angular resolutions; GAF sidelobe level; and the possibility of
unambiguous measurements of the delay (range) and the angular coordinates for
different combinations of the aperture dimensions, the number of elements, and
the frequency spacing of the orthogonal regular signals radiated by the array
elements. The GAF functions are constructed and calculated in result of the
space–time signal processing with the use of the averaged complex correlation
integral of the reference and received vector signals.
Generalized ambiguity functions are compared in two cases - presence or absence
of a signal recirculation in a spatial feedback loop. Recirculation affect
causes significant narrowing (some times) of GAF main lobe that is equality to
enhance the spatial resolution of a point reflector when a transmission
coefficient of a spatial loop achieves 0.7-0.9 values. In that case,
GAF sidelobe levels are sharply decreased and it is appeared the possibility of
unambiguous measurements of the delay (range) and the angular coordinates.
Key words: multistate
radio holography system, generalized ambiguity function, signal recirculation,
antenna array.
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