Harmonic-Based Direction Finding via Time-Modulated Frequency-Diverse Array

This work proposes a Time Modulated Frequency Diverse Array (TM-FDA) architecture, innovatively configured for direction-finding purposes. The system is built by combining the standard frequency diverse array philosophy with a specific time modulation scheme of the radiated signals, thus enabling a full control of the generated harmonic patterns with high level of reconfigurability. In particular, the design of a two-element TM-FDA is addressed, being a valuable solution to develop a passive localization system based on the strategic correspondence between the beam pattern at the different harmonics and the observation direction. The localization procedure is effective by setting a closed-form relationship between the frequency offset among the array elements and the relative delay of the radiated signals. The theoretical analysis has been validated by measurements, carried out in an indoor environment, using a two-monopole array operating at 2.45 GHz. The proposed TM-FDA system ensures uniform detection accuracy across all directions, enables asymmetric positioning, and outperforms traditional time modulated arrays for harmonic-based direction-finding applications.