Revisit Time-Variant Beampatterns for Frequency Diverse Arrays

Recently, an argument on the possibility of achieving the time-invariant beampatterns of frequency diverse arrays (FDAs) was discussed. The conclusion that time-invariant FDA beampatterns are impossible in free space applications is indisputable. However, the analyses are not convincing as they tangle two issues, namely the time-range relationship and the pattern propagation as time elapses. In this paper, the time-variant FDA beampatterns with a single maximum at the specific spatial position have been revisited and carefully examined. Following rigorous illustrative simulations and analysis, the authors argue that at a fixed time instant, the previously reported time-variant FDA beampatterns with a single maximum at the target locations are possible when the time references are carefully selected.