Target Localization Using the Electromagnetic Frequency-Difference Autoproduct

This article introduces the electromagnetic frequency-difference autoproduct, the outer product of the harmonic electric field vector with itself at nearby frequencies, and describes its capacity to improve target localization in random scattering media. The electromagnetic frequency-difference autoproduct is a dyadic quantity that synthetically estimates electric field content at the difference frequency of two constituent electric fields. It is a generalization of the acoustic (scalar) frequency-difference autoproduct. Derivation of the autoproduct governing equation precedes numerical examination of plane wave propagation and scattering from perfectly conducting infinite cylinders. Using linearly-polarized antennas in the vv- (TM) configuration, 3-5 GHz target localization experiments were conducted in wooded areas where randomly-located tree trunks were the primary scatterers. Beamformed outputs demonstrate the advantages of autoproduct processing for active target localization of a metallic reflector at 12 m transmitter-to-target distance. While the lower effective frequency reduces resolution, robustness against scattering and other random media effects is increased.