Radio holography using MIMO retrodirective antenna array

Retrodirective antenna array (RDA) technology can be used for the development of cover broadband radar systems, wireless communications and wireless power transmissions with spatial recirculation of orthogonal signals. Retrodirective multiple antennas of radio-electronic systems receive sounding signals reflected from the object and automatically retransmit them in the direction of the irradiated object. In this case, a well-known self-focusing effect occurs along the target coordinates due to the recirculation of radiated signals in a spatial feedback ring containing a reflecting source. A distinctive feature of RDA broadband systems is automatic control (selfsteering) of the antenna pattern in search and tracking mode. Radio holographic system based on MIMO retrodirective antenna array with re-emission and recirculation of orthogonal signals in spatial feedback rings is considered. Generalized ambiguity functions (GAF) are determined in result of the space–time signal processing and calculating the complex correlation integrals for the reference and received vector signals. GAF function for MIMO radio holographic system is constructed with respect to spatial coordinates for an ensemble of orthogonal signals, taking into account the partial transmission coefficients of feedback rings. The spatial resolution characteristics are studied for a short-range radio holographic system using MIMO retrodirective antenna array in the microwave range. In this paper, we perform comparative analysis of GAF two-dimensional cross-sections along spherical spatial coordinates for MIMO holographic system in the presence and absence of spatial recirculation of regular orthogonal signals with spectrum separation. Detailed study of the generalized ambiguity function and 2D its sections along spatial coordinates allows to examine the range and angular resolutions as well as to estimate GAF side lobe levels for different combinations of the aperture dimensions, the number of antenna elements, and the frequency spacing of the orthogonal regular signals radiated by the array elements. We compare GAF sections in two cases – presence or absence of a signal recirculation in a spatial feedback loop. Recirculation affect causes significant narrowing (in some times) of GAF main lobe width 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 side lobe levels are sharply decreased and it is appeared the possibility of unambiguous measurements of the delay (range) and the angular coordinates of a point reflector. The super spatial resolution effect was uncovered in a radio holography system based on MIMO antenna arrays with spatial recirculation of orthogonal signals.