Solutions of Time-Invariant Spatial Focusing for Multi-Targets Using Time Modulated Frequency Diverse Antenna Arrays

This paper proposes two classes of time-modulated frequency diverse arrays for achieving time-invariant spatial focusing for multiple targets. Both are based on modified time-modulated optimized frequency offset (TMOFO) that depends only on the range, and they are termed TMOFO-based phase conjugating array (TMOFO-PCA) and TMOFO-based harmonic beam array (TMOFO-HBA). For the TMOFO-PCA, each phase conjugator in each channel is fed with a local oscillator signal at twice the RF frequency plus a small interelement frequency offset, resulting in the generated range-angle-dependent retrodirective beampatterns with single time-invariant maxima for each of the multiple interrogators. For the TMOFO-HBA, the multiple harmonic frequencies in a conventional time-modulated array are utilized with a common small interelement frequency offset, resulting in the simultaneous generation of range-angle-dependent harmonic beampatterns with single time-invariant maxima for each of the multiple targets. To validate the proposed two-array schemes, numerical examples of uniformly excited, equally spaced TMOFO-PCAs and TMOFO-HBAs dealing with two targets are reported and discussed.