Accurate Models of Time-Invariant Beampatterns for Frequency Diverse Arrays

Different from conventional-phased arrays providing only angle-dependent beampatterns, frequency diverse arrays (FDAs) produce angle-range-dependent and time-variant transmit beampatterns. Recently, time-invariant range focusing beampatterns have been reported in some works, which could not be achieved by traditional antenna arrays. However, this paper shows that these papers neglected the time-range or frequency-phase relationship and led to erroneous simulation results and conclusions. The formulas of time-invariant FDA are carefully reviewed, and the unnoticed misconceptions are analyzed. By reestablishing the correct signal models, a set of numerical examples are presented to demonstrate that the beampatterns of FDA arrays are actually time variant in free space.